Tire Pressure & Handling

PeerBlock

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Has anyone bothered to experiment with different tire pressures for their Gen 5? I started out with the stock 29 PSI front & rear recommendation, but I don't think that's optimal for street driving, nor is it good for track. The rear tires should definitely have lower pressure than the fronts, in my opinion, because the rear end is light and because the tires are quite wide.

I tried 32 front and 26 rear, which I think is better on the street. Inflating the fronts to 32 psi seemed to make the steering more responsive, although I don't know if it's going to cause uneven wear on the tires. Dropping the rears to 26 definitely helps with traction during acceleration.

I think that going 32 front and keeping rear at 26 or even lowering it to 24 would make for a pretty good feel in most driving situations. The potential issue with 24-26 psi are that if you hit a pothole you might damage the rim, and you might roll the sidewall if you take a turn too hard.
 

05Commemorative

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Car's weight is 50/50, so wondering why you say light in back?

On the track, I do typically run the fronts 1lb more than rear, but that suits my driving style.

On street, I always just leave at 29 all around. assume you want more rear traction for straights and thus the lower pressure. Not sure why the front change though. on the street for turns, the car has more grip than could ever used for street situations.
 
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PeerBlock

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Car's weight is 50/50, so wondering why you say light in back?

On the track, I do typically run the fronts 1lb more than rear, but that suits my driving style.

On street, I always just leave at 29 all around. assume you want more rear traction for straights and thus the lower pressure. Not sure why the front change though. on the street for turns, the car has more grip than could ever used for street situations.

Because the majority of the vehicle's mass is in the front of the car. The engine is not symmetrically located between the front and rear as well as side to side. Also, because wider tires require less pressure to support a given weight. Think snowshoes - they work because they spread your weight across a larger area. The rear tires do not need the same amount of air pressure as the fronts to support the same weight and so should have at least slightly lower pressure than the front.

Weight distribution only refers to the weight on the car's axles, it does not tell you whether the weight is biased toward a particular section of the axles. Drive a mid-engine car with 50-50 weight distribution and compare to a Viper - you'll note that the mid-engine vehicle is a lot more tail-happy even if it has a lot less power.

Anyway, my working theory is that more pressure in the front results in slight oversteer while also improving traction during hard acceleration. I did not lower the rear tire pressure solely because I wanted better traction for acceleration; I wanted to see if it made any noticeable difference on the car's handling characteristics.

Are the numbers cold?

Yes.
 

vancouver-gts

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PB, you're comparing mid engined [ my friend's Noble M400 for example ] cars to the Viper, forgetting to mention most mid engined cars are cabover designs with the driver sitting forward while the driver sitting far back to compensate for the forward mass you're talking about in the Viper.With tire pressures set at 29 driving switchback roads I hang pretty dang good with the Noble that is an awesome handling car. He's advantage against the Viper is the weight [ 2350lbs ] of his car, allowing him to brake before corners much later [ less mass weight to slow down] pulling out sooner gaining distance from after turns. But I make up this shortcoming in the straight!50/50 weight distribution is great on the Viper with its wheel base as well.

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05Commemorative

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This is confusing to me. if weight on axles is same per corner, how do you conclude the majority of the mass is in the front? The engine and driver sit between the wheels.

Yes, more pressure in front or less in rear will create less oversteer (ie, it will push). Yes, get the wider tires have an effect, but the car is already extremely balanced and that is what you are looking for, correct?

Because the majority of the vehicle's mass is in the front of the car. The engine is not symmetrically located between the front and rear as well as side to side. Also, because wider tires require less pressure to support a given weight. Think snowshoes - they work because they spread your weight across a larger area. The rear tires do not need the same amount of air pressure as the fronts to support the same weight and so should have at least slightly lower pressure than the front.

Weight distribution only refers to the weight on the car's axles, it does not tell you whether the weight is biased toward a particular section of the axles. Drive a mid-engine car with 50-50 weight distribution and compare to a Viper - you'll note that the mid-engine vehicle is a lot more tail-happy even if it has a lot less power.

Anyway, my working theory is that more pressure in the front results in slight oversteer while also improving traction during hard acceleration. I did not lower the rear tire pressure solely because I wanted better traction for acceleration; I wanted to see if it made any noticeable difference on the car's handling characteristics.



Yes.
 

Dom426h

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Peer, take your "theory's" to an NARRA ViperDays trackday and see what the guys who set up the comp coupes & ACR-X's think of them...


I personally think you are uninformed about tire pressures & weight distribution from your above comments.
 
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PeerBlock

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PB, you're comparing mid engined [ my friend's Noble M400 for example ] cars to the Viper, forgetting to mention most mid engined cars are cabover designs with the driver sitting forward while the driver sitting far back to compensate for the forward mass you're talking about in the Viper.With tire pressures set at 29 driving switchback roads I hang pretty dang good with the Noble that is an awesome handling car. He's advantage against the Viper is the weight [ 2350lbs ] of his car, allowing him to brake before corners much later [ less mass weight to slow down] pulling out sooner gaining distance from after turns. But I make up this shortcoming in the straight!50/50 weight distribution is great on the Viper with its wheel base as well.

I never said that mid engine cars don't handle well - they do - but many of them are tail-happy. Most engines weigh more than the driver and the driver is not sitting in the middle of the car, he or she will be on the driver's side. Most cars, even "standard" sedans, are close to 50/50 weight distribution between front and rear, and while passenger placement is considered a factor in balancing the vehicle, it would be silly to make vehicle balance dependent on the driver - how do the designers know how much a particular driver will weigh?

This is confusing to me. if weight on axles is same per corner, how do you conclude the majority of the mass is in the front? The engine and driver sit between the wheels.

Yes, more pressure in front or less in rear will create less oversteer (ie, it will push). Yes, get the wider tires have an effect, but the car is already extremely balanced and that is what you are looking for, correct?

Because weight being equally split across the axles does not explain the vehicle's moment of inertia, i.e. the force required to turn. In the case of handling, it would be the amount of traction required for the car to go left or right. The weight of the driver relative to the axis on which the car turns is going to be to the left or right - only specialized cars have the driver seat in the middle, putting the driver's weight right on the axis. The same is true for the mass of the engine; it's either in front of or behind that axis, not directly on it.

Peer, take your "theory's" to an NARRA ViperDays trackday and see what the guys who set up the comp coupes & ACR-X's think of them...

I personally think you are uninformed about tire pressures & weight distribution from your above comments.

Might want to read the original post before embarrassing yourself there, ace.
 

05Commemorative

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Very few sedans have 50/50 weight balances.

2nd, if you want to express a concern about the weight and position of the driver, then do you want to also allocated tire pressure differently right to left to compensate. are you really thinking this has a dramatic effect on a 3300lb car with 50/50 weight distribution and the grip of a viper on the street? My point being, don't bring in the driver weight to the equation and if you do, realize that weight to closer to the rear axles than the front which then goes counter to your original point that viper has all its mass in the front.

I think it is really as simple as this. 29lbs was chosen by the factory as the best compromise for ride, tire wear, safety and handling. If you increase front tire pressure and push the car to the limit, it will "push" more relative to OEM setting. If you lower the rear pressure, it will also "push" more relative to OEM setting. If you do the reverse (lower front or increase the rear), with will be more "loose" relative to OEM. both of these will be noticed at the limit.

My point to you on cornering, if driving on the street, either will be so minor, it won't matter unless driving at the limit which would be incredibly high for the viper. I will also say, when driving these cars at the limit (on a track), the rear pressures go up faster than the rears, thus why I typically have the fronts a bit higher to balance. don't think street driving gets you anywhere close to this concern.

So, I will stand by if you want a bit better bite for straight acceleration o the street, I get lowering rear a bit. if you want smoother ride, you can lower all a bit. cornering on the street, I think you are wasting your time.
 
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PeerBlock

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Very few sedans have 50/50 weight balances.

Did I say that they DID have 50/50 weight distribution (not balance) or did I say they had CLOSE TO...reading comprehension: give it a try.

2nd, if you want to express a concern about the weight and position of the driver, then do you want to also allocated tire pressure differently right to left to compensate. are you really thinking this has a dramatic effect on a 3300lb car with 50/50 weight distribution and the grip of a viper on the street? My point being, don't bring in the driver weight to the equation and if you do, realize that weight to closer to the rear axles than the front which then goes counter to your original point that viper has all its mass in the front.

For a vehicle that uses the front wheels to turn, the optimal weight distribution is going to have a bias to the rear.

If you want to see this "in action", go to your local walmart and get a shopping cart. Put a heavy item (20-40 lbs) in the MIDDLE of the cart and then push it through the isles zig-zagging left to right. Move the item as far back as you can, and repeat. Let me know which position results in the cart being easier to turn left to right...and note that accelerating and stopping the cart does not change "feel" regardless of whether the item is in the frontmost part, the middle, or all the way in the rear.

So you really need to get off your whole incorrect and ignorant assertion that because a car has a 50/50 weight distribution over the axles, it is perfectly balanced - because weight distribution is not balance, and I've already explained why, twice.

I think it is really as simple as this. 29lbs was chosen by the factory as the best compromise for ride, tire wear, safety and handling. If you increase front tire pressure and push the car to the limit, it will "push" more relative to OEM setting. If you lower the rear pressure, it will also "push" more relative to OEM setting. If you do the reverse (lower front or increase the rear), with will be more "loose" relative to OEM. both of these will be noticed at the limit.

So you're going with the "factory recommendations are always optimal for every condition" bit? I consider them more of a guideline for a staring point. I can tell that you HAVE NOT experimented with different pressures and therefore it makes me wonder why you are still posting in a thread that asked for feedback from other Gen 5 owners that have experimented with tire pressures OTHER THAN the stock recommendations.

By adding 3 PSI to the front and subtracting 3 PSI from the rear I have noticed differences in the way the car feels and handles at all speeds, not only "at the limit". It does turn better with the additional pressure in the front, and it accelerates better with the pressure in the rear reduced. The rear tires are 10% wider than the front, so going to 26 PSI in the rear would be a pretty good starting point for anyone that wants to tweak their car's feel.

My point to you on cornering, if driving on the street, either will be so minor, it won't matter unless driving at the limit which would be incredibly high for the viper. I will also say, when driving these cars at the limit (on a track), the rear pressures go up faster than the rears, thus why I typically have the fronts a bit higher to balance. don't think street driving gets you anywhere close to this concern.

Hot tire will pressures eventually level off once all tires are at their operating temps. If your front tires have more pressure cold, the hot pressure will increase proportionally...so it seems that you are inadvertently confirming what I said in that the car does handle better with more pressure in the front tires than the rear.

Some people spend thousands on car parts for relatively minor gains...and considering that you haven't even tried deviating from the stock recommendation on tire pressure it doesn't make much sense to participate in this thread.

So, I will stand by if you want a bit better bite for straight acceleration o the street, I get lowering rear a bit. if you want smoother ride, you can lower all a bit. cornering on the street, I think you are wasting your time.

You think wrong. Try 32 front and 26 rear, on the street and/or track, and do it on the same day so that you can compare it to 29 all around.

Also, am I really the only one who thought to tweak tire pressures on the Gen 5 so far? Surprised to see that this is the first thread regarding the topic in the Gen 5 section.
 

05Commemorative

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I must say, you might top the list of biggest asses to be on this forum. You raise a stupid question that you think you already apparently know the answer too. You make some crazy assumptions, insult folks along the way. I must say, just a BS poster to begin with. If you want to see yourself in print, ok. If you want some real guidance, ask for it and look for it, but don't make stupid assumptions and comments along the way.

Shopping cart? seriously? semantics about the precision use of your language? seriously? If you like the feel of a 6lb difference front to rear, go with it. But don't say things like "all the mass is in front", where the driver sits and the other BS you were throwing out.

Have I tried this stuff, absolutely but you did not ask that. Have I tried it where the performance actually matters, of course, but you did not ask, you just assumed and then insulted. At no place other than a drag strip have I ever seen a 6lbs diff front to rear on a 50/50 weight dist car make sense.

So, please, re-read you own silly post and then your rude comments along the way and ask what are you actually looking for. Is there a problem you are trying to solve. Some guidance you seek or you trying to share some magic insights for all of us. Street performance driving, give me a break...

I tell ya, you make stupid assumptions when speaking with folks that actually do see through the BS you are throwing out. Yes, please set it to 32 fronts and 26 rears, and then go to a track for a track day. You will be pushing like a dump truck, but go ahead and convince yourself it feels better and the reason is all of the mass is in the front. Remind me who is not qualified to be on this thread?

Did I say that they DID have 50/50 weight distribution (not balance) or did I say they had CLOSE TO...reading comprehension: give it a try.



For a vehicle that uses the front wheels to turn, the optimal weight distribution is going to have a bias to the rear.

If you want to see this "in action", go to your local walmart and get a shopping cart. Put a heavy item (20-40 lbs) in the MIDDLE of the cart and then push it through the isles zig-zagging left to right. Move the item as far back as you can, and repeat. Let me know which position results in the cart being easier to turn left to right...and note that accelerating and stopping the cart does not change "feel" regardless of whether the item is in the frontmost part, the middle, or all the way in the rear.

So you really need to get off your whole incorrect and ignorant assertion that because a car has a 50/50 weight distribution over the axles, it is perfectly balanced - because weight distribution is not balance, and I've already explained why, twice.



So you're going with the "factory recommendations are always optimal for every condition" bit? I consider them more of a guideline for a staring point. I can tell that you HAVE NOT experimented with different pressures and therefore it makes me wonder why you are still posting in a thread that asked for feedback from other Gen 5 owners that have experimented with tire pressures OTHER THAN the stock recommendations.

By adding 3 PSI to the front and subtracting 3 PSI from the rear I have noticed differences in the way the car feels and handles at all speeds, not only "at the limit". It does turn better with the additional pressure in the front, and it accelerates better with the pressure in the rear reduced. The rear tires are 10% wider than the front, so going to 26 PSI in the rear would be a pretty good starting point for anyone that wants to tweak their car's feel.



Hot tire will pressures eventually level off once all tires are at their operating temps. If your front tires have more pressure cold, the hot pressure will increase proportionally...so it seems that you are inadvertently confirming what I said in that the car does handle better with more pressure in the front tires than the rear.

Some people spend thousands on car parts for relatively minor gains...and considering that you haven't even tried deviating from the stock recommendation on tire pressure it doesn't make much sense to participate in this thread.



You think wrong. Try 32 front and 26 rear, on the street and/or track, and do it on the same day so that you can compare it to 29 all around.

Also, am I really the only one who thought to tweak tire pressures on the Gen 5 so far? Surprised to see that this is the first thread regarding the topic in the Gen 5 section.
 

05Commemorative

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Lastly, I had to re-read you shopping car example because just blown away by it. such much so, have a difficult time where even to begin. Couple things to think about?
1) what is driving that cart? rear wheels? NOT
2) tire sizes and pressures? NOT
3) suspension spring rate? NOT

Dude, please understand the dynamics of a rear wheel driven car and how weight distribution shifts front to rear and side to size and how spring rates of the suspension and tires all make significant differences. Again, blown away.

Feel free to insult, but my only ask is you think before you do.

reminds me of a Jack Nicholson quote from the movie "as good as it gets" in the elevator seen when women asks him how he knows women so well. He says "I take a man and remove all logic and accountability" Just felt like I was speaking with the person he described.
 

Jack B

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He was temporarily banned at the VOA for the same crap. He also posted that you should dyno a car in 3rd gear. One more, it is a classic, "the S2000 is a legend".
Lastly, I had to re-read you shopping car example because just blown away by it. such much so, have a difficult time where even to begin. Couple things to think about?1) what is driving that cart? rear wheels? NOT2) tire sizes and pressures? NOT3) suspension spring rate? NOTDude, please understand the dynamics of a rear wheel driven car and how weight distribution shifts front to rear and side to size and how spring rates of the suspension and tires all make significant differences. Again, blown away.Feel free to insult, but my only ask is you think before you do.reminds me of a Jack Nicholson quote from the movie "as good as it gets" in the elevator seen when women asks him how he knows women so well. He says "I take a man and remove all logic and accountability" Just felt like I was speaking with the person he described.
 
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PeerBlock

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I must say, you might top the list of biggest asses to be on this forum. You raise a stupid question that you think you already apparently know the answer too. You make some crazy assumptions, insult folks along the way. I must say, just a BS poster to begin with. If you want to see yourself in print, ok. If you want some real guidance, ask for it and look for it, but don't make stupid assumptions and comments along the way.

So basically, you made a stupid statement, were proven wrong, and now you're too much of a ********** to simply admit it and you're trying to save face.

Shopping cart? seriously? semantics about the precision use of your language? seriously? If you like the feel of a 6lb difference front to rear, go with it. But don't say things like "all the mass is in front", where the driver sits and the other BS you were throwing out.

Wouldn't expect anything less from someone who fails to grasp high-school level physics.

Have I tried this stuff, absolutely but you did not ask that. Have I tried it where the performance actually matters, of course, but you did not ask, you just assumed and then insulted. At no place other than a drag strip have I ever seen a 6lbs diff front to rear on a 50/50 weight dist car make sense.

That puts you in a very exclusive club...of one.

So, please, re-read you own silly post and then your rude comments along the way and ask what are you actually looking for. Is there a problem you are trying to solve. Some guidance you seek or you trying to share some magic insights for all of us. Street performance driving, give me a break...

Right, because the majority of the driving done on a viper is on a track. Dude your occasional jaunt to a track to play with your car doesn't make you a pro racer, and your obvious lack of basic vehicle dynamics means you should have just said what pressures you run and left it at that.

I tell ya, you make stupid assumptions when speaking with folks that actually do see through the BS you are throwing out. Yes, please set it to 32 fronts and 26 rears, and then go to a track for a track day. You will be pushing like a dump truck, but go ahead and convince yourself it feels better and the reason is all of the mass is in the front. Remind me who is not qualified to be on this thread?

Uhh, I did try it and I do like it. Does that mean everyone will? No, but that's the nice thing about stuff like this. You can adjust it as per your preference. You attempted to derail the thread with your initial response but have only succeeded in making yourself look pretty dumb, and provided me with something to laugh at.

Lastly, I had to re-read you shopping car example because just blown away by it. such much so, have a difficult time where even to begin. Couple things to think about?
1) what is driving that cart? rear wheels? NOT
2) tire sizes and pressures? NOT
3) suspension spring rate? NOT

Dude, please understand the dynamics of a rear wheel driven car and how weight distribution shifts front to rear and side to size and how spring rates of the suspension and tires all make significant differences. Again, blown away.

Funny how when I try to dumb down a concept you should already be familiar with, you still cannot get it. The point of the shopping cart example was to illustrate "moment of inertia", which has very little to do with the weight distribution of the vehicle and more to do with the weight in relation to the axis.

Both the car and the cart turn by their FRONT wheels, therefore the axis is near the rear, and moving the majority of the mass as close to that axis as possible makes the cart easier to turn. I know, being stupid is something they have yet to cure. Have you looked into liberalism? Maybe you can blame your intellectual deficit on climate change and declare yourself a victim.

He was temporarily banned at the VOA for the same crap. He also posted that you should dyno a car in 3rd gear. One more, it is a classic, "the S2000 is a legend".

Jacky B still butthurt about being proven wrong by me (multiple times), and still a loser. Why he is still trolling these forums remains a mystery. Better go put more reflectix on your $100K car to stop the heat. Pure "tech modding" there...freakin *****. :D
 

05Commemorative

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My last attempt to help you out here and trying my hardest to be respectful so you hopefully you won't get yourself killed with your setup. I will refer to your exact quote from the beginning where you give YOUR "working theory" so we have no misunderstanding.

" Anyway, my working theory is that more pressure in the front results in slight oversteer while also improving traction during hard acceleration. I did not lower the rear tire pressure solely because I wanted better traction for acceleration; I wanted to see if it made any noticeable difference on the car's handling characteristics."

What I am telling you is that if you increase the pressure in the fronts, you will NOT get oversteer, but the exact opposite in that you will get understeer and what others call a push. Why, because you increase the spring rate of the front. btw, you get the same effect if you lower the pressure in the rear because you are lowering the spring rate of rear. You must know this very simple detail with all of your amazing physics insights, right?

So, your combo of increasing the front and lowering the rear will give you a car with a significant change for sure from stock, it will now push or understeer like mad. Now for you on the street at your speeds, you will likely think it is better. Please take it to a track and try it. Maybe ask someone there first, or atleast tell someone what you are doing and your theory, that way they will know what turn to send the wrecker to get you with you sitting there in the car off track because you could not figure out whey the front did not turn, even though you had this amazing working theory.
 

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Wow. :omg:

I'm in 05's camp on this one. :smirk:


I am still rolling in my old gen III, so I plead unfamiliar with the 'advanced driving dynamics' of the gen V. :rolleyes:

I do run a little more pressure in the fronts at the track. 32f / 30r cold, Hoosier R6.
With street tires / street driving, I run the recommended 29 all the way around.

On the track, I have become one of the faster guys..............not because I'm thinking about my tire pressures, but by concentrating on the other aspects of high performance driving and making a goal of improvement.

On the street, I don't give any thought to tire pressure because you can't push the car to any point that it will even matter.

My car is red.
I like red cars.
;)
 

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Most important sentence in this whole tread:

"On the street, I don't give any thought to tire pressure because you can't push the car to any point that it will even matter."

On the street I start at cold pressures of 27 psi front and rear (stock Michelin's) and I run my aggressive track alignment on the street....great grip and a better ride than a brand new Gen 5 with over inflated tires even though I'm running a full ACR KW suspension package.

On the track, the front pressures are always lower than the rear on my R6's....the exact pressure is constantly manipulated by looking at how much rollover I'm getting on the outside edge and temps across the tire surface. Your alignment settings, tire size and track temps all have an effect on tire pressures. Throw in a fat girlfriend to ride shotgun and you'll have to make further adjustments :D

Carry on.

Cheers,
George
 
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PeerBlock

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What I am telling you is that if you increase the pressure in the fronts, you will NOT get oversteer, but the exact opposite in that you will get understeer and what others call a push. Why, because you increase the spring rate of the front. btw, you get the same effect if you lower the pressure in the rear because you are lowering the spring rate of rear. You must know this very simple detail with all of your amazing physics insights, right?

The physics issues actually have nothing to do with this thread - you brought them up when you cited weight distribution as the primary deciding factor in how a car handles (which it is not).

If the car has a 50/50 weight distribution, as you've been asserting, then inflating the rear tires to the same pressure as the front tires would be equal to slightly over-inflating the rear tires if they were the same width as the fronts. Since the rears are wider, having about 10% more pressure in the fronts over the rear would be "neutral" inflation, or 32 front and 29 rear. Because the rear tires have fairly stiff sidewalls, you can lower them 3 PSI to gain extra straight-line traction without compromising their ability to perform while turning. You could also leave them at 29 PSI, as I did at first. 29 front / 26 rear would also be a "valid" setting that should have no ill effects on any of the car's capabilities.


So, your combo of increasing the front and lowering the rear will give you a car with a significant change for sure from stock, it will now push or understeer like mad. Now for you on the street at your speeds, you will likely think it is better. Please take it to a track and try it. Maybe ask someone there first, or atleast tell someone what you are doing and your theory, that way they will know what turn to send the wrecker to get you with you sitting there in the car off track because you could not figure out whey the front did not turn, even though you had this amazing working theory.

But just a few posts ago you were saying that the tire pressures wouldn't matter:

"My point to you on cornering, if driving on the street, either will be so minor, it won't matter"

And on the track, you claim that pressures only matter "at the car's limit", which I do not believe to be the case.

Critically over-inflating the fronts would cause the car to plow forward rather than turning, but bumping them up by 3 PSI over stock is not over-inflating them.

If I was going to track my car, I'd do a run at 29 all around and then adjust from there as needed. I would not run the same pressures for every track, because just like 29 all around may be a good starting point it is not set in stone - and that includes driving on the street, which is the type of driving the vipers will be doing most of the time.
 

05Commemorative

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You must re-read your own posts carefully. You brought up the physics point as well as the mid-engine car, etc. You also stated the car had all of its mass in the front. Once you come to grips with that not being the case, some if your assumptions will change.

Weight distribution is a factor. spring rates are factors, tire sizes/type, etc are factors. alignment is a factor. Aero is a factor. How much you weigh and where your weight is factors. many things, but you were only discussing tire pressures given everything else is the same.

What I led with is the car is a very balanced car by design based upon the above factors (it is not nose heavy), thus why you must factor in weight distribution. I also told you how the tire pressure changes will impact the car given all the other items listed are remain the same. Basic principle to follow, increasing pressures reduces grip/friction, lowering pressures increases grip/friction. Do tires have an optimal temp for highest grip? Yes. Will you get to that temp on the street? No

But again, on the street, these settings don't matter unless you want to do the following:
1) smoother ride - lower the pressures
2) better straight excel - lower the rears

But again, I still don't understand the problem you were trying to solve. You stated performance, so #2 above can apply. anything else, you not talking performance, you just talking a feel factor. Feel and performance are not always related

Lastly, to show you I am paying attention. Take your Gen5 for a drive on the street. Say you start with oem 29lbs all around. after a bit, they will all be in the 30-32lbs pending the air temp, how hard you are driving, etc.

Now, take it to the track with the same starting point. Do about 25min on the track going hard, you will come in and the fronts will be in the 35-36lbs range and the rears will be closer to 38-40lbs. Don't get caught up in the specific amounts as they will vary, but do recognize the rears will be higher. Then go back to my easy principle above on what that will result in? The car will have less grip in rear than when you started, which might be desirable. An ACR with its downforce can even change that more. My point being, on the street, total waste of time on these settings other than the specifics of the points above.

Let me add one last point for context. For those that take their Vipers to the track and know how to drive them, they will all tell you that what people describe as "performance" on the street is really a joke. The car will never get pushed anywhere close to what it is capable of unless you are just doing straight shots. I am not a drag racer, but guessing the guys like Jack that do that would also say street driving is nothing compared to what happens on the strip.

So, the reason I bristle a bit at your post is the overall premise is off when someone says performance for the street when the car is already in its stock form over qualified for the street. Take the car to the track, do these adjustments in real-time through the day and truly learn the impacts. Just note how in 25 min session, the characteristics change. You will learn a ton from the seat of your pants in an environment that does not lie. Then go driving on the street and understand street driving is the equivalent to a cool-down lap on the track.
 
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PeerBlock

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You must re-read your own posts carefully. You brought up the physics point as well as the mid-engine car, etc. You also stated the car had all of its mass in the front. Once you come to grips with that not being the case, some if your assumptions will change.

You brought up the physics elements in your initial responses and I attempted to explain why 50/50 weight distribution does not clearly portray what kind of handling characteristics to expect from a car. It's like saying "both cars have 4 wheels so they should both handle well compared to a motorcycle, which only has 2".

A FRONT ENGINE vehicle will have most of its mass in the front just like a mid-engine car will have most of its mass in the back in relation to its turning axis, and it is the proximity of mass in relation to this axis that determines how well the car is going to change direction.

Have you ever seen an F1 race car go around a turn? It almost seems to defy physics as to how fast it can be moving and yet still make relatively sharp turns. It's no surprise that the weight bias of an F1 car is toward the rear...if 50/50 were ideal, wouldn't F1 race cars seek out 50/50 weight distributions, considering how much money and reputation is on the line?

The reason a mid-engine car is tail-happy around turns is that it's a victim of its own success - i.e. it is so easy to turn that unless the driver has a feel for it, it is easy to swing the rear out.

I'll repeat, the only reason I mentioned these things is to explain that weight distribution over the axles does not dictate handling, and tire pressures can be adjusted to enhance traction based on the type of driving being done. Tire pressure DOES NOT alter the balance of the car and I never suggested that it did.

Weight distribution is a factor. spring rates are factors, tire sizes/type, etc are factors. alignment is a factor. Aero is a factor. How much you weigh and where your weight is factors. many things, but you were only discussing tire pressures given everything else is the same.

The other 'factors' are not part of this topic, this is exclusively tire pressures on a stock Gen 5 that has not had any modifications done to the suspension, engine, or had any weight reduction.

What I led with is the car is a very balanced car by design based upon the above factors (it is not nose heavy), thus why you must factor in weight distribution. I also told you how the tire pressure changes will impact the car given all the other items listed are remain the same. Basic principle to follow, increasing pressures reduces grip/friction, lowering pressures increases grip/friction. Do tires have an optimal temp for highest grip? Yes. Will you get to that temp on the street? No

I'm quite aware of the relationship between the traction provided by the tires based on their temperature, as well as the fact that increasing their temperature increases their internal pressure...but your blanket statement is not entirely accurate.

There is a pressure range that is "ideal" for a particular tire, and if you are above or below this range, you will not have full grip. On the street, you will not be reaching high speeds regularly. Increasing front tire pressure (over rear tire pressure) will INCREASE oversteer at low speeds, have neutral characteristics at highway speeds and understeer fast speeds that you should not be reaching on any public road.

I have only tested 32 front 26 rear on the street, and I would not run this on the track because I would prefer to have less understeer at track speeds, but on the street I suggest trying this out and seeing what you think. The car feels "better".

But again, on the street, these settings don't matter unless you want to do the following:
1) smoother ride - lower the pressures
2) better straight excel - lower the rears

Or if you want a "sportier" ride, follow my suggestion.

But again, I still don't understand the problem you were trying to solve. You stated performance, so #2 above can apply. anything else, you not talking performance, you just talking a feel factor. Feel and performance are not always related

Was not trying to 'solve a problem', was trying to start a constructive discussion about tire pressures. Vehicle handling is dynamic, that means it's subject to change, so the "right" answer lies within a range and is not one specific number.

So, the reason I bristle a bit at your post is the overall premise is off when someone says performance for the street when the car is already in its stock form over qualified for the street. Take the car to the track, do these adjustments in real-time through the day and truly learn the impacts. Just note how in 25 min session, the characteristics change. You will learn a ton from the seat of your pants in an environment that does not lie. Then go driving on the street and understand street driving is the equivalent to a cool-down lap on the track.

By your logic, nobody should be talking about tweaking or modding the car from stock simply because it is "qualified" for the street. You're coming at this from the wrong angle entirely and are mixing track and street configurations as if they are both interchangeable. They are two different things that would require their own setups. Stock settings are generally conservative and "general purpose". That may 'qualify' the car but that doesn't preclude anyone from changing.

And if you want along with the intent of the original post, we could have had people post what pressures they run on the street and track to see if 29 all around really is the best, or if a trend emerges. Not going to happen if I have to keep debating off-topic points with you, is it?
 

Stuntman

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Tires have an optimum pressure. Severely over or under that optimal pressure will result in less grip. Too little pressure will cause the tire to roll over on its sidewall more, feel softer and 'vague', as well as having uneven load across the width of the tire (typically more load on the outside and inside, while the center of the tire is not being used as much. Likewise, an over inflated tire will be more responsive, give the sidewall some support, but overloads the center of the tire while the outer shoulders are not as evenly loaded.

At the end of the day, having the rear pressures optimal and a front that's too high could result in a responsive understeer, while too low of front pressure could result in a vague front feeling and understeer. Likewise a front tire at optimum pressure with a rear that's over-inflated would feel better on-center but hurts power-down and rear grip (oversteer) and an under-inflated rear could feel vague and sloppy and still cause understeer.

You want to find your target HOT pressures and bleed the front and rear pressures down accordingly. Once they cool down check them again and this number would be a good 'cold' pressure to start out with. To find your optimum pressure it will vary on your cars weight, alignment, spring rates, aero, tire size and compound. A probe-type tire pyrometer is a key tool in checking the tire temp spread to see how evenly your tires are being worked to adjust your setup and pressures accordingly.

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Allan

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Mr. 05,
Would you agree that even a cool down lap is more intense than aggressive street driving? (cornering grip wise of course)
Even throttle-off coasting around the corners on cool down is way faster than any 'street terrorist drivers' would imagine as a controllable feat.
 

05Commemorative

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Mr. 05,
Would you agree that even a cool down lap is more intense than aggressive street driving? (cornering grip wise of course)
Even throttle-off coasting around the corners on cool down is way faster than any 'street terrorist drivers' would imagine as a controllable feat.

completely agree. In fact, it tends to be the only lap you look down at the speedo and it is stunning some of the speeds you are doing during this lap.
 

Tom and Vipers

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I've wrestled with tire pressure and alignment for decades with regard to wear - nothing worse that burning the centers or insides and then not knowing how far off you are and how far you need to go to achieve the correct setting. You can do alignments, but there is no analytical method to establish even wear tire pressures.

Recently, I set tire pressure and toe-in in a small import solely by tire temperatures. The results were literally spectacular and I will never set toe-in and pressure by any other method.

I made corrections in 3 iterations and with each step, grip increased an amazing amount resulting in more grip than I ever thought the car was capable of.

Method used: drove the car like I did the most and then balanced inner -v- outer by toe-in and then pressure to make the centers the average of the inner and outer.

While there are many ways to set toe-in and I can only wonder about the effect of extremely wide tires, I would not care to claim temp is the best way to set toe-in on a Viper. However I will say, that if there is uniform temp across the tire, then the "grip" is being handled evenly over the entire surface of the tire. If one area is hot, then the other areas are not working as hard which means less grip on average.

I will say that temps are the absolutely best way to set pressure so you wear your tires evenly.

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RE: AutoX: This is another matter entirely, with the above, unless you have lots of caster and camber, you will need to run higher pressures to keep contact during severly tire roll on the tread and not on the sidewall - you put shoe polish on the sides to see where you are wearing. Of course, when you see you above setup has insufficient pressure, then you know you need more caster/camber. Suppose you have everything totally tweaked for AutoX at high G loadings, then when you drive on putlic roads and worse yet, trips, your settings will be all wrong! AutoX guys know just how much to turn their tie-rod sleeves to tweak their toe-in for the event and also how much pressure.

QUESTION: There is a lot of discussion how rear toe-in really affects handling "feel" and so I wonder how the preferred settings compare with uniform tire temps? or could it be that the "good" settings result in even temps?
 
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