Vehicle Weight vs. Lap Times

[NCVCA]

Does anyone have a process or formula for determining what affect the addition or reduction of weight in a race car will have on lap time over the same course?

I am wondering if there is a way to calculate fairly accurately how for example a 25 pound reduction in sprung weight would affect the track time of a 3200 pound car around the same circuit with all other variables held constant.

If you want to get real fancy I'd also like to know how an additional 10 HP would affect the same test conditions.

And if you want to really blow me away how 5 pounds of unsprung weight would affect the same test conditions.

Obviously this would be a platform to make weight reducing and horsepower improving decisions based on cost as it correlates to expected real world benefit.

Any ideas?

 

[joe117]

I believe one could come up with theoretical numbers for the result of hp increase or weight reduction for drag racing.

Road racing? Man, that is going to be hard to do.

If you had a certain track in mind, and you had baseline data for your speed coming out of turns,
you might be able to estimate the time reduction to the next braking point due to increased acceleration.

Decreasing the weight would have an effect on braking, that could be measured and cranked in.

You might also assign some better G number for cornering.

So,
I'm thinking that reasonable ballpark expectations could be developed but not a direct formula for increased performance on a road course.

 

[Rich Wesorick]

I don't know about formulas, etc., but I know of one pro racer whose rule of thumb is that 100 pounds SHOULD affect a car at the limit by 1 second on a 2 mile race track (key words- at the limit). For us mere mortals, this may not be the case though...

 

[joe117]

And I have often heard the drag race rule of thumb for street type cars in a quarter mile,

100lb = 10hp = 1/10 second

 

[Tom F&L GoR]

The real weight reduction benefit will depend on whether you remove it from the front or the back, unsprung weight or sprung, left or right side, and CG height... Also the average speed may matter, and since it's affected by aerodynamics, weight may matter less? Although I'm the bulldog engineer mentality and sympathize with you, this one might be way over the top for us. F1 teams do this, but then again, they have sponsors like HP or Intel to help with measurements and processing.

Joe is correct, there are online calculations for 1/4 mile times based on HP and weight. There are also basic physics equations to calculate g-force (speed in a circle vs. vehicle mass.) That might give you a clue, but it assumes that the driver applies maximum power/g-force/braking 100% of the time. Even the best drivers aren't exactly on the friction circle boundary.

Perhaps a clue would be to see what the weight penalties in certain race series do to lap times. Some circuits add weight to the winners to slow them down, and if you dig, you might find their reasoning for how much weight they add. You may have to find driver interviews where they complain that the 100 lbs costs them 2 seconds...

PS: Let me know if you do find anything! Some of you have been beaten by Miatas and VWs in autocross, and it's not because they have more tire or power. I think it's a real hidden benefit; I put on the Gen 2 exhaust manifolds on and will soon put the Gen 2 aluminum front suspension on my Gen 1. I took out the factory seats for lighter aluminum ones, removed the seat belt mechanisms in the door, and have a smaller battery. And ummm... other parts may not be what they seem either.

 

[joe117]

Fill the tires with helium.