Tire pressure and understeer?

[jonathan12uiz]

Hey guys I thought maybe I could get help from some of you veterans. My nissan seemed to do great with the suspension dampening setup that I had @ this past event (4/10). I was running 32psi in my tires all around on the first 4 runs... My times consistently went down by about @ least a sec each run.

but after lunch, I figured with the heat and such I decided to go to 40psi up front and 32 in the rear.

Problem is that my times were consistent but @ least 1 sec slower than the first half of the day. I was running a consistent 65 i think. It seemed like I was understeering a lot more. is there a relationship between tire pressure and understeer into a corner?

Maybe it was just that I was stressing myself to beat my fastest time of 64.1 that I wan't on my game as much in the 2nd half.

[DAN]

Less pressure is more grip to a point. that point is different for every

car/setup. the best advice I can give if you are consistent with your

times is to test and try different pressures to get the car to do what

you want. just make sure you make changes that will be noticeable

then bracket your results to fine tune. So if you drop to 36 psi and

are faster by .5 seconds drop another few till you don't see

improvements, then bracket for the proper pressure you need.

example 40 psi / 36 psi faster / 32 psi faster / 28 psi slower than 32/

30 psi better but still slower/ 31 psi same as 32 / 33 faster than 32.

the point is test your configuration at the event and keep good

notes. our advice can get you in the ball park, but only your testing

can get the greatest results for you.

[DAN]

Oh and just my opinion but if you cant keep your times within at least a second you are not consistent enough to do real testing. My personal rule is 1/2 a second. I don't change anything unless most of my runs are within a 1/2 second raw times. I don't count cones or spins or anything those are anomalies to me and i don't count those results. Hope this helps. and I am by no means am I the shit. Ask Brian he is really consistent and knows how to set up a car, or ask Jeff who is very consistent, and he has far more experience than i do. He also has worked with many different cars and setups over the years.

[jonathan12uiz]

Thanks dan, really good info. I think i'm going to keep my 32psi for now since it seemed to feel right @ that moment. I'm looking to get better @ making consistent times. I'm still not too good @ reading cones as this is only my 2nd time out, but This past event I felt really confident at reading them.

[bronxbomber252]

Thanks for the complements Dan,

OK on to business... Tire pressures are a bell curve... meaning there will be a sweet spot where both more AND less will be slower. Also, every car, alignment, tire, driving style combo has a different sweet spot. In general, once you find that sweet spot you should stick close to it with only small adjustments (im talking no more than +-2 PSI) with conditions. But you probably are not consistent enough (heck, for me to say I am barely consistent enough, would be a stretch) to have to do much if any adjusting for conditions except when comparing a mid summer event to a mid winter event.

What happened to you, is you overshot the bell curve up front going into the afternoon and caused a loss of front end grip.

Personally I set the cold pressure and let the temps come up as I run since generally a cold tire likes less pressure than a warm one. so as the temps come up the pressure go with it. (you are inadvertently doing the same thing if you are not checking and adjusting your pressures between every run). When I ran FWD I basically optimized the front pressures then purposely over-pressured the rears to get the car to rotate better while keeping good responsiveness. That worked best for Me, with my style (which has changed a bit since then), driving my old RSX-S.

Bottom line. You need to experiment with pressures to figure out what method and pressures work best for your situation.

[josephkelley77]

Jon Everybody has answered you, I just wanted to give some advice. our cars have very similar chasis, I have a good bit of suspension work but I run 36F 245/40/18 - 32R 265/35/18. I bought cheap ebay tires($400 for the set) to get me by untill I could afford the 17" rims and tires I wanted. My RS-3's will be here thursday ( rims little later hope for RPF1) different profile/compound diff pressure, but 36 front 32 rear will be where I start at

[jonathan12uiz]

Apr 19, 2011 10:09:04 GMT -6 josephkelley77 said:

Jon Everybody has answered you, I just wanted to give some advice. our cars have very similar chasis, I have a good bit of suspension work but I run 36F 245/40/18 - 32R 265/35/18. I bought cheap ebay tires($400 for the set) to get me by untill I could afford the 17" rims and tires I wanted. My RS-3's will be here thursday ( rims little later hope for RPF1) different profile/compound diff pressure, but 36 front 32 rear will be where I start at

Thanks for that man. I was thinking of doing my first 2 runs at 32/32 but trying 34/32 the last 2 runs of the morning.

[jessew]

if you are understeering into turns, try lowering the fronts and/or raising the rear tire pressure (too a point, watch for sidewall rollover when lowering)

if you are oversteering try lowering the rear and/or raising the front.

my car likes 2 psi more in the front than the rear (yes yours may vary). anymore than this and my car understeers a good bit more. changing the tire pressure is the quickest way to play with the handling characteristics during a heat.

also, try not to adjust by more than 2 psi at a time. as brian said, you won't know if you overshot your best pressure for your car.

[jonathan12uiz]

Apr 19, 2011 13:47:32 GMT -6 jessew said:

if you are understeering into turns, try lowering the fronts and/or raising the rear tire pressure (too a point, watch for sidewall rollover when lowering)

if you are oversteering try lowering the rear and/or raising the front.

my car likes 2 psi more in the front than the rear (yes yours may vary). anymore than this and my car understeers a good bit more. changing the tire pressure is the quickest way to play with the handling characteristics during a heat.

also, try not to adjust by more than 2 psi at a time. as brian said, you won't know if you overshot your best pressure for your car.

Thanks man. I did notice some rollover on my sidewalls on my 1st afternoon run, hence the reason I decided to adjust my pressure, I guess I just shot it up too high. I should have just went to 35 first.

[bronxbomber252]

WARNING: Everyone please note that even if cars are similar, that specific tire model, size, suspension setting, and alignment have HUGE effects on proper tire pressure (cheap gauges do to). It is rarely if ever helpful to look at other's pressures unless they have nearly identical set-ups on the same size wheel/tires, and similar alignment.

Case in point, When I switched from Dunlop Star specs, to hankook RS3 I went from running 35 front 31 rear, to 38 all around. (no other changes were made)

[DAN]

So nest time out bring a good pressure gauge some white shoe polish ( we usually have some at the event to do tech) and a good notebook you can keep with the car so you can make notes. seriously even making a note seems stupid just make it and later you will be glad you did.

[jonathan12uiz]

Apr 19, 2011 17:54:18 GMT -6 DAN said:

So nest time out bring a good pressure gauge some white shoe polish ( we usually have some at the event to do tech) and a good notebook you can keep with the car so you can make notes. seriously even making a note seems stupid just make it and later you will be glad you did.

I will definetly be taking notes on the changes I make on the car. I see how it will help me log and improve.

[josephkelley77]

Apr 19, 2011 16:52:34 GMT -6 bronxbomber252 said:

WARNING: Everyone please note that even if cars are similar, that specific tire model, size, suspension setting, and alignment have HUGE effects on proper tire pressure (cheap gauges do to). It is rarely if ever helpful to look at other's pressures unless they have nearly identical set-ups on the same size wheel/tires, and similar alignment.

This is why I mentioned tire size front and rear, and that I have cheap tires ( Nankang NSII's), and that I have a good bit of suspension work.

[DAN]

I think I will get a tire log book for myself after i buy my next set. So then i can practice what I preach.

[jessew]

i need to start one too. i rely on memory too much and get it wrong sometimes