Anyone else use Bridgestone RE-11's?

[Silver Ignition]

Just wondering who else uses Potenza RE-11's and how you like to tailor your tire pressures for Autocross.

I've been told to run higher pressures (in the 35-40psi range) but I've found better luck with the RE-11 around the 25-30psi range. The lowest I've run them so far was 22psi and even then I still wasnt rolling the sidewalls according to the chalk marks.

[Thorpedo]

I always had horribly mushy feel when I ran them that low. I was usually within a couple pounds of 35 on asphalt, 38 on concrete. I've run them in 255/40 two full years in a row. (Around 14 events a year)

[Silver Ignition]

Originally Posted by Thorpedo

I always had horribly mushy feel when I ran them that low. I was usually within a couple pounds of 35 on asphalt, 38 on concrete. I've run them in 255/40 two full years in a row. (Around 14 events a year)

My last few events I was dropping pressures each run; started around 35psi and worked my way down to about 25psi over the course of the day and was continuing to get faster. I did notice once I got below 28psi or so the car got a little less predictable, but my times were still getting faster. May have just been me getting more familiar with the course.
I have my first event [of the year] coming up on the 15th so I'll try to maintain 35psi and see how it goes.

[renfield90]

No experience with this particular tire, but running any street tire at 22psi sounds unsafe. If it's not rolling over at that pressure you may not be driving to the full potential of the car. If you stay at that pressure, there's the potential for the sidewall to roll over so much it catches and flips the car.

[Silver Ignition]

Originally Posted by renfield90

No experience with this particular tire, but running any street tire at 22psi sounds unsafe. If it's not rolling over at that pressure you may not be driving to the full potential of the car. If you stay at that pressure, there's the potential for the sidewall to roll over so much it catches and flips the car.

It was only one run and more of a "lets see how stiff these sidewalls are" kinda thing...

[wparsons]

Originally Posted by Silver Ignition

My last few events I was dropping pressures each run; started around 35psi and worked my way down to about 25psi over the course of the day and was continuing to get faster. I did notice once I got below 28psi or so the car got a little less predictable, but my times were still getting faster. May have just been me getting more familiar with the course.
I have my first event coming up on the 15th so I'll try to maintain 35psi and see how it goes.

Try the reverse to validate your data... start low and work your way higher. If you still get faster through the day then you know that pressure wasn't the factor, familiarity with the course was.

[justint5387]

Originally Posted by renfield90

No experience with this particular tire, but running any street tire at 22psi sounds unsafe. If it's not rolling over at that pressure you may not be driving to the full potential of the car. If you stay at that pressure, there's the potential for the sidewall to roll over so much it catches and flips the car.

Quite over-dramatic there

[renfield90]

Originally Posted by justint5387

Quite over-dramatic there

There is a reason we tell noobs to put 40psi in their tires for their first autocross. Some people in my region have seen it happen first hand.

It's all fun and games until you have to crawl out of your own car and get help flipping it back over.

Also, I notice a lot of noobs (myself included, when I was in my noob stage) and even some more experienced people like to drop pressures and say that the car feels faster/better/insert improvement here/etc. What is actually happening is they are lowering the effective damping rate (yes, your tire sidewall acts as a damper in a way and is part of the overall suspension picture) of the tire, which makes it feel easier to drive. In general, lowering tire pressure actually reduces total grip available unless your starting pressure was so high that the tire was becoming a torus. See here: http://farnorthracing.com/autocross_secrets12.html

[vroom4]

Would be epic if that's what actually happened

[vroom4]

Please post a video of someone discussing how low tire pressure could result in flipping the car. Please please please.

[renfield90]

It's more likely with a higher profile tire like a 195/60/15. If the pressure is too low and you're driving too aggressive you get an insane amount of rollover onto the sidewall, and then if you hit a bump or dip in the pavement just right that sidewall starts acting like tread and applies a force to the car, which (due to the insane sidewall rollover) is already in a pretty compromised position.

At low pressures on street tires you're also at risk of the tire bead separating itself from the wheel, and this I have witnessed first hand on a Subaru STi. Best case scenario you chew the hell out of the wheel lip. Worst case scenario is your wheel lip finds a bump, expansion joint, etc. Either the wheel breaks or the pavement breaks...if the inertia of the car does not provide enough force for either of those, you flip.

No, it's not super likely, but it isn't far fetched - if someone handed me the keys to autocross their street car on 22psi, I would refuse.

Originally Posted by vroom4

Please post a video of someone discussing how low tire pressure could result in flipping the car. Please please please.

Come on dude...so it's not real unless there's a video on the internet saying it's true? The nice part about the laws of physics is they don't care if you believe it or not.

It is easier to flip a car than you think. That's why we wear helmets.

[vroom4]

Sorry, this is a big fat bullshit sandwich you are feeding us.

[Thorpedo]

Originally Posted by renfield90

No, it's not super likely, but it isn't far fetched - if someone handed me the keys to autocross their street car on 22psi, I would refuse.

Yes, yes it is far fetched. If your autocross tracks run on embankments it may be another story, but that would certainly be a special circumstance.

If you've been telling your newbies to run 40lbs of air in their tires to prevent them from tipping then you shouldn't be letting Rav4s and Smart cars into your autocrosses. Your average autocross car doesn't run any amount of measurable risk for what you're saying "isn't far fetched". Give it up.

[ViperASR]

Originally Posted by renfield90

It's more likely with a higher profile tire like a 195/60/15. If the pressure is too low and you're driving too aggressive you get an insane amount of rollover onto the sidewall, and then if you hit a bump or dip in the pavement just right that sidewall starts acting like tread and applies a force to the car, which (due to the insane sidewall rollover) is already in a pretty compromised position.

At low pressures on street tires you're also at risk of the tire bead separating itself from the wheel, and this I have witnessed first hand on a Subaru STi. Best case scenario you chew the hell out of the wheel lip. Worst case scenario is your wheel lip finds a bump, expansion joint, etc. Either the wheel breaks or the pavement breaks...if the inertia of the car does not provide enough force for either of those, you flip.

No, it's not super likely, but it isn't far fetched - if someone handed me the keys to autocross their street car on 22psi, I would refuse.

It is easier to flip a car than you think. That's why we wear helmets.

So you're saying that everyone driving around in their street cars with ~32psi in their tires are constantly on the edge of rolling over?
The absolute worst that will happen is the tire will pop off the bead, and you will destroy a rim and a tire. Saw it happen to an s2000 locally. Can confirm the car did not roll over.

I autocross my Z2s at 28-29psi. Center of gravity and roll centers be damned, she's going over