Got a track related question? I'll try to answer.

[funwheeldrive]

I'm going to the track for the first time this weekend. I'm still on the stock tires. What PSI should I have at the track? I think I run about 35psi for daily driving.

[7thgear]

@CSG Mike,


I've been hibernating this winter, but can you confirm if there has been any new updates to the Solo DL that are FRS/BRZ related? Or have they uncovered all the sensors they could?

[Apex_BRZ]

Rotors are looking sad and Road America is coming up in May. Curious what you fellas are running for rotors and why. I'm using Carbotech XP12 pads.

[dp1]

Originally Posted by funwheeldrive

I'm going to the track for the first time this weekend. I'm still on the stock tires. What PSI should I have at the track? I think I run about 35psi for daily driving.

I think around 38psi hot. You can start at about 33-34psi and measure after first session. Depending on ambient temps and driving style, you could add 5+ psi during the session and make them feel greasy after a few laps. I never drove stock tires on track so others can chime in.

[GotMunchies?]

Originally Posted by Apex_BRZ

Rotors are looking sad and Road America is coming up in May. Curious what you fellas are running for rotors and why. I'm using Carbotech XP12 pads.

I was recommended the Centric rotors by another racer on this forum. Ordered them from Amazon for less than $50/corner.

[ame="http://www.amazon.com/Centric-Parts-120-47021-Premium-E-Coating/dp/B000IY4A0Y/ref=sr_1_1?s=automotive&ie=UTF8&qid=1426700497&veh icle=2014-13-21598-13--7-6-7-19612-3236-1-1---1-0&sr=1-1&ymm=2014%3Asubaru%3Abrz&keywords=centric+rotor s"]http://www.amazon.com/Centric-Parts-120-47021-Premium-E-Coating/dp/B000IY4A0Y/ref=sr_1_1?s=automotive&ie=UTF8&qid=1426700497&veh icle=2014-13-21598-13--7-6-7-19612-3236-1-1---1-0&sr=1-1&ymm=2014%3Asubaru%3Abrz&keywords=centric+rotor s[/ame]

[brn12345]

I have now reached a stage in developing my BRZ where I can drive it at the limit on autocross and road race tracks. The suspension is dialed in and I am able to translate small adjustments into meaningful response from the car. I currently run KW clubsports, adjustable end links and Dunlop Direzza IIs. This setup took me a long time to dial in terms of ride height, compression and rebound adjustments, tire pressure and alignment.


In terms of feel, the car handles really well with the only concern being during high load turns on the road race track, I can feel the car shift weight to the front outer wheel with the rear being somewhat looser.. I have been contemplating a larger front sway bar to reduce this front transfer and make the rear more planted. On a setup like mine, what front bar would be recommended if any?

[CSG Mike]

Originally Posted by brn12345

I have now reached a stage in developing my BRZ where I can drive it at the limit on autocross and road race tracks. The suspension is dialed in and I am able to translate small adjustments into meaningful response from the car. I currently run KW clubsports, adjustable end links and Dunlop Direzza IIs. This setup took me a long time to dial in terms of ride height, compression and rebound adjustments, tire pressure and alignment.


In terms of feel, the car handles really well with the only concern being during high load turns on the road race track, I can feel the car shift weight to the front outer wheel with the rear being somewhat looser.. I have been contemplating a larger front sway bar to reduce this front transfer and make the rear more planted. On a setup like mine, what front bar would be recommended if any?

Can you post me a datalog?

[brn12345]

Originally Posted by CSG Mike

Can you post me a datalog?

Unfortunately I don't have a data logger. The time was via track supplied transponder. I do have a video though here is the link.
[ame="https://www.youtube.com/watch?v=w5PFNXFaF9E"]Subaru BRZ on Bahrain International Circuit (Inner Layout) 2015 - YouTube[/ame]

[ddeflyer]

Originally Posted by brn12345

Unfortunately I don't have a data logger. The time was via track supplied transponder. I do have a video though here is the link.

It is really hard to tell from your video, but I get the distinct impression that you are over braking several corner entries and then turning in too sharply. I also suspect that you are overlapping your braking and initial turn in slightly. I half way expect that you are doing the overlap on purpose in order to get more initial rotation into the turn, but I suspect from the video that that is not really what you want to be doing yet.

A slightly smoother start to your turn in will help to keep the maximum impulse against your front outside wheel from being as high. Essentially I suspect that you are not really using the full traction of your rear wheels and the squirminess you are feeling is some classic understeer on entry, oversteer on exit.

That all said, the video is really, really hard to judge from so I could be totally off base on this.

[travisb]

This is not necessarily a track question, but more for autocross. I did a few searches but did not find anything.

My question is about launches at the start of an autocross. How much wheel spin is desired to get the fastest launch?

I just purchased an openflash tablet and it has the ability to set a rev limit for launch. At 3400 I am still spinning a little bit with 215 ZII SS on fresh pavement at 70 degrees.

I realize the answer may be zero wheel spin is fastest, but sometimes what is fastest is also counter intuitive.

[CSG Mike]

Originally Posted by travisb

This is not necessarily a track question, but more for autocross. I did a few searches but did not find anything.

My question is about launches at the start of an autocross. How much wheel spin is desired to get the fastest launch?

I just purchased an openflash tablet and it has the ability to set a rev limit for launch. At 3400 I am still spinning a little bit with 215 ZII SS on fresh pavement at 70 degrees.

I realize the answer may be zero wheel spin is fastest, but sometimes what is fastest is also counter intuitive.

That's gonna change at every event dependent on conditions... which is part of the game when you're autoxing

[juliog]

^ Not much info on this forum but plenty of Google hits if you search for "tire slip ratio" or "wheel slip ratio". Most articles say 5-20% slip is fastest.

Ideal slip ratio will depend on your setup —tire compound, tire width, how much load/weight on the rear of the car, etc..— and the racing surface.

For any given surface, you could get close by using a data logger capable of measuring individual wheel speed (e.g. Aim Solo DL)... doing multiple launches at different RPMs where you floor the gas* immediately (assuming tire pressure is a fixed variable optimized for the other 99% of the run, not the launch), then looking at the data, readjusting, and so on.

Because you're measuring wheel speed individually, and the fronts won't be spinning (unless AWD), you can easily calculate the slip ratio for the rear wheels. However again remember that every surface will be different... and even if surface was a fixed variable, weather conditions will also affect available grip.

*I figure besides the initial RPM, how you ramp up your throttle input will also make a big difference. This is harder to A/B test unless you have a programmable launch control solution.

Edit: Mike beat me to it while I was writing this

[EAGLE5]

Too much wheel spin and I get no traction. Too little and i bog. My best acceleration is definitely with some spin. Time to distance might matter more for your autocross course. You should experiment.

[Doozer]

Hey folks,

Experiencing understeer on entry in long sweepers and can't break the rear free throughout the rest or the corner. Really, really frustrating.

Considering an upgrade to a 1.5 diff to try and get a little more free on entry and solve this dilemma.

Curious to hear some racers thoughts on if a diff *could* solve this issue (may very well be a driver issue, not sure).

There seem to be some different thoughts on diff preload as well. Some say lower is better, others more. Anyone play around with this and feel like commenting?

Thanks in advance