Trackday Brake Questions

Fuzzystig

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Hey folks,

I'm still learning a lot about brakes, so posting to see if I can learn anything from the brain trust here about my last trackday experience.

For some context, I've had about ~6 or so trackways with this car on the stock brake setup but with fancy pads. I've used Ferodo DS2500 and Pagid RSL19 compounds in the past, both with pretty good success. The Ferodo compound isn't as ********, but they worked fine.

Since then I've stepped up to the SRT calipers + larger rotors up front, mostly looking to extend pad life for track days. This last weekend I went out to Thunderhill in NorCal with this new setup using the DS2500 pad compound - my goal was to do a back to back comparison with the new calipers but the same pad compound I've used before.

Pretty dissapointing! I didn't have the brake power I was expecting, and after just 3 sessions this is what my brand new pads looked like. My first thought is that the pad seriously overheating. I have Gen5 ACR brake ducts on the car, it was a cool day (~70's) and I've ran this same setup but with smaller pads and calipers in the past, so I don't think any overheating issues are coming from just driving the car.

So I ask: does anyone know why somethign like this might happen? I've used smaller variants of this same brake pad in the past and gotten ~2 full days out of them + a bunch of street miles, and now I step up to a larger pad and rotor setup and I only get 1 hour of track time, putting down similar lap times. Can a bad bed-in cause something like this? Can running mismatched pad compounds front/rear shift too much of the work up front if the rear's haven't heated up into their operating window? Any tips/discussion appreciated :)
 

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GTS Dean

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Ideally, you want to bed your discs with the pad you plan to use. I do not run race pads/rotors on the street unless it's just to the convenience store between track days. They wear better at optimum temps for the rotor/pad and that takes experimentation. The only time I run street pads/rotors on the track is if I'm on street tires in very cool, or wet conditions because they have lower torque rise, lower friction and are less prone to initial lockup at modest temps.

A common side effect of better brakes is people tend to use them MORE, not less than before - 'because they feel so good' and they wear out faster. Running different pads F/R is not uncommon, especially if you have a big piston area split like the Viper, or if you have a lot of weight transfer to the front. I run rear pads with high initial bite, lower ultimate torque and good release for trailing into the corner if I want. I run a medium torque pad on the front with good modulation. How much torque you run up front is proportional to how much tire grip and cooling you have.

I currently run Hawk DTC 50 Front, HT10 in back (40mm calipers) with 13" 1-piece slotted rotors. On 315/335 Hoosiers, I got 6 track days at Road America and COTA with the front pads. 8 days with the rear pads and front rotors. That's between 500 and 600 miles of intense track duty on this setup. The tires went the full 600 (25 heat cycles) and I did not flat spot or cord a single one. I have 27 years of track time in this car.

YMMV.
 

MoparMap

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Bedding or incompatible compounds between whatever was on the rotor and your new pad would be my first guess, but that's just based off of what I've read about brakes. Aggressive pads are supposed to wear faster, but I'd agree that just an hour of track time is way faster than what seems reasonable. That or maybe there is something wrong with the caliper setup and the pad is dragging? I would think you would have noticed that while driving though as I'd expect it would have been generating a lot of heat and causing other issues.
 
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Fuzzystig

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Thanks for the replies folks - I was hoping you'd reply Dean! Lot's of good info in your reply, so thank you.

I suspect the main culprit here for my super-short pad life was a poor bed-in procedure. My understanding is that without a properly bedded pad, the won't be as effective and actually run far too hot. These DS2500 pads aren't rated to work very hot, so poor bedding + high speed track + low speed rating all sets the setup up for failure!

For the next track day, I'll try either the Hawk DTC 80's (their highest temp pad - my priority right now is to get my brake's set up to take heat), Ferodo DS4.12, or back too Pagid's RSL19 compound. I just need to dial in my bedding process to make sure these are all used to their max!

BTW here's a pic from the day - besides the pad issue, the car did great. Dean, in the past you've recommended some alignment specs for me and with some of that advice I feel I really have the car set up how I like it - super neutral, and allows for a lot of steering adjustment by varying throttle!
 

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GTS Dean

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This is a handy chart. A track Viper likes a 295-315 front tire a lot. If you don't have ABS, then you are likely going to flat spot your 275 fronts with an 80 compound on 14" rotors. Judging from the torque rise, you'll have to be very careful to avoid that. I just don't know what kind of release they'll have.

I appreciate the kind words. A Gen 2 Viper should never be a car you can't throttle steer pretty well without fear of snap oversteer. You won't get that with a stock alignment and you need to possess some reasonable driving skills.
 
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MoparMap

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Wow, that's a pretty awesome chart. Seems like the kind of thing you almost never see because of "company secrecy" kind of stuff.
 

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