I know it is possible to reduce understeer with sway bars, spring rates, shock adjustments and camber (front and back) among other things.

Has anyone also tried to reduce understeer with different tire pressures in the front and back of the car? How effective do you think this would be? What pressure differences would you recommend for daily driving and for track?

 

it will help. i use to do that when i autoxed. usually ran 3-4psi higher in the front than rear but you have to play around with the pressure to get it right. it will also depend on the type of tire you're using as well as ambient temperature (to a much smaller degree)

 

Altering the tire pressures to adjust over-steer/under-steer seems to be a common practice for AutoXing. I've seen it being done on RWD cars as well.

On FWD cars, you can also use the throttle to change the balance. Acceleration shifts weight to the back wheel, increasing under-steer. Deceleration shifts weight to the front wheels, increasing oversteer. Stomp on the brakes in a turn and a MINI the tail can swing out.

 

I have read contradicting info about this subject. Some people say more pressure in the front tires will help reduce understeer, while others say the exact opposite, i.e. more pressure in the rear tires will reduce understeer. I am confused. Which way should it be? Seeking some input from the experienced track rats on this subject!

 

I would think that whatever you do to give the front tires more grip than the rears would decrease under-steer. So, the pressure that gives best grip on fronts would be a good place to start. Then reduce grip on the rears until it balances the way you want.

After a certain point, increasing pressure in a tire will narrow the contact patch and reduce grip. That's why over-inflated tires will wear out in the middle before they do at the edges. It may be that lowering pressure below the optimum may reduce grip as well. An under-inflated tire will wear out on the edges before the center.

With hard cornering, I would think that an over-inflated tire would be safer, as long as it doesn't exceed the max pressure recommended for the tire.

 

Let me go get my slide ruler and i will figure out the co-efficient of the drags square root of pie minus the modulous of elasticity and the sign of x to the nth degree.

 

to a point increased pressure in the front will reduce understeer by gaining grip. the ones that says more pressure in the rear will reduce understeer is also correct but you do it by reducing grip.

even on my rwd bmw with -2.2 front camber I put in 4psi more to start. then I adjust it from there until I find the balance I like and just try to keep it there by checking the pressure after each run. for track you'd need to be a lot more careful since you'll be on the track for 20mins session (or more). this means if you inflated the front to 39psi (cold), your hot temp can be 45psi (ie, dangerously high).

 

Robin got it about right. If you elect to use higher pressures in the rear to decrease understeer, or increase rotation, loosen the car, the transition from understeer to oversteer can be quite sudden. With lower pressure in the rear the transition is smoother and more progressive.

For auto-x I will run 8 psi lower pressure in the rear and have a nice predictable release. On the track I might only run 5-6psi lower in the rear. At that setting I seem to be able slide the car sideways as I approach the limits.

On the street I will run about 4 psi difference and seem to get uniform tread wear across the tires.

 

For the track, what psi do you run for the front and the back? Do you use r-comps? or street tires?

 

What actual pressures are you running? No problems with losing the seal between tire and wheel with these pressures?

Interesting. I wonder if that would work out the same for a 2nd Gen. MCS, and if there is much difference in balance between 1st & 2nd Gen.? Do you have any suspension mods?

 

Wait....did someone say 'pie'?

Mini Pie.... mmmmmmmmmmmmmm

 

while this is true, its best to try and get the understeer tuned out as much as possible. lifting even alittle is slowing you down

 

Justintime,

Do you have any recommendations for front and back tire pressures to reduce understeer?

When are you going to be in the NE?

 

pressure are going to be VERY tire and track dependent. Not something that is going to be universal. Go out to an empty lot and set up a short slalom course and play with the pressures.

 

Yes this is generally true. I am looking to get some information on what people do run and have found to help me ball park it before I fine tune. Should the front be higher than the rear or vice versa.

 

fronts higher most of the time. but is dependent on tires too. sometimes higher rear helps more than lower. and personal feel is important.

 

I couldn't give you a correct answer for this without a pyrometer or driving your car at that specific time lol. it is also dependent on what kind of tire/where that tire is being used. to reduce understeer you will want your front tire to have the best footprint possible which probably means you should try increasing the front pressures as there is a good possibility your tire is rolling over a little.

 

I am having a couple of friends drive the car in a few weeks to see what they think. I thought you may be up in this neck of the woods for a test drive.

I keep track of the psi and sometimes the temps of the tire. I try to keep the front psi (hot) below 43 psi. I may be overusing the brakes a little so I will adjust for that as well.

Thanks for all your responses and help.

 

I think that increasing the presure in the rear will make the tires more ridged and stiff, making them more likelyto loose traction over a softer front end. That is wat you are trying to get with oversteer... kicking the back end out.

 

out of curiosity does it start understeering more or less the hotter your tires get?

 

OK everyone, this past weekend I did a track day at Road Atlanta on my 215/45/17 Dunlop Direzza Sport Z1 Star Specs and I can provide some feedback.

I started with 30 psi cold all around and my hot pressures on the front tires were around 38-39 psi after a 20-minute session. The rear hot pressures were about 2 psi lower. With this cold starting pressure, understeer was significantly eliminated and the car felt and handled very well. My car has all of the JCW kits installed on it. See my signature for the details.

Watch me take a lap of Road Atlanta here: http://www.youtube.com/watch?v=01gU-yWXDqI

 

A little more understeering hot. I usually run 30 min. sessions so the tires do heat up more.

For example. at wgi, short straight into right hand turn 1, top out at speedo 110 mph, hard brake straight at a little before the 300 marker, gentle preload steering and trailing brake on the start of the turn as I take my foot off the brake onto gas, then full steering at turn in point to get to the apex. It will understeer right away and the car slows down. With this condition, I cannot get on full gas until apex when I can straighten the steering. Perhaps, I am carrying too much speed into the corner or too much steering input (or both). I am trying to see if I can adjust the tire pressure a little to get the car to rotate slightly so I can straighten the wheel earlier and get on power...

 

hmm hard to tell if its a driving error without being there lol. trailing in should rotate the car to point it towards the apex where you shouldn't have any problem getting on throttle early expecially in a fwd car. it almost sounds like your arnt trailing off enough (maybe carrying to much brake in after turn in) also if its understeering the natural thing your going to want to do is to turn the wheel even more.. BUT DONT!

but aside from that...

try both, keep the front tire pressure the same and decrease the rear alittle. Do it vise versa and see if either helps. you might as well try it vs. speculation. I'm thinking the front definately might need some more pressure. pm onasled or snid as they both have played a lot with the mini on the track

 

I was always told to higher on the rears, lower on the fronts to reduce understeer. I used to do this, until my last track session.

After a couple of sessions, my instructor looked at the tires/wear, and recommended reducing the pressures on the rears 1 PSI lower than the fronts, and then 2 PSI (ended up 35 hot on the fronts, 33 on the rears, R-comps). I was slightly skeptical, but went ahead and did it, figuring what the hell, and promptly ran the best lap times I've ever run. But not only that, the car just felt better, the rear was more composed, and I could get it to rotate more consistently.

The funny thing is I started with the fronts and rears equal, at 35 hot. I was going to do my usual higher in the rears, lower in the fronts, but I had asked Mike at TSW what he used for pressures as he was running the same tires as me, and, he suggested 35 front/33 rear (hot). I started at 35/35 simply because I'd never run the rears lower than the fronts before, so I thought I'd start out conservatively with equal pressures. And I wound up best right where Mike runs his, and got there at an instructor's (who has a long history of racing) suggestion who had no idea that these were the exact same pressures someone else recommended, so I wound up with tire pressures that worked fantastically, and were recommended independently from two different sources.

So I now believe the best thing to do is experiment with them yourself--I suspect everyone's driving style is different, and what works best for one person might not work well for another, but I'll probably change the pressures around a bit more from track to track, to try and find that sweet spot--it really does make a difference.

 

lol I run my mini at 36 33 on azenis. Its a relative issue though. to many dependents just gotta try things out depending on how the car is reacting to the track