Autocross: Dry/Wet Perfomance and Tire Pressure

[A4_Mike]

For those of you that autocross in your Audi's, what tire pressures are you all running?

I just got back from an autocross event today that featured dry pavement in the morning and then wet pavement in the afternoon. With the stock 17 in. sport wheels running Pirelli P6 Four Seasons, I normally run about 40 psi (cold tire) on all four corners. Today I decided to see how the handling dynamics would change if I bumped the tire pressure so I put all four tires at 45 psi (cold tire). How did it go? I had a really hard time figuring the car out today. It normally has a lot of understeer, but today it would go from understeer to a slight oversteer. With conditions worsening in the afternoon, the A4's handling just became even more difficult to figure out. With the water on the pavement and high tire pressure, the tire's clearly had a hard time maintaining grip. In the end, I did not put down any really competitive times, but it sure was a lot fun!

A serious lesson was learned though. 45 psi was far too high and really modified the A4's handling characteristics in a negative manner by loosing too much grip. Based on my 6+ months of autocross experience and messing around with tire pressures, it seems like ~40 psi (cold tire) works best. I have not messed around with putting more pressure in the back and reduced pressure in the front - I'm thinking that will be my next step. Perhaps 40 psi in the front will maintain grip and a ~43 psi in the rear will help neutralize the front end bias by allowing the rear tires to loose some grip.

[absolutegtr]

I have yet to autocross, but have read, that for the A4 lower pressure in the front tires will reduce understeer somewhat...

[NyteEscape]

yea, next time i go out, im gonna try that as well. i have a rs4 sway in the back to help things, so lets see...

[EBG 18T]

i have been running 39psi cold f&r on khumo MX's 245-40-18 w/ my current suspension setup.

[SportSter]

I usually run about 35-40 with my yokahama s-drives.

[BlueHand_Q]

I normally set my pressures at 42-F and 40-R in the morning......as the day and conditions get hotter the car set up needs to be adjusted, when understeering you need to either raise the pressure in the front or lower the rear widening the gap to get the car to rotate better. So far it's been working out great for me....my semi-mod 3.0 has been pretty competitive against stock S4 and R32!

[mxrz]

You auto-x on the all season P6 tires? Damn...

[[email protected]]

Pretty sure those are OEM on that model, aren't they?

[A4_Mike]

Yes, the Pirelli's are OEM. I got the A4 a year ago, with brand new Pirelli's installed so that is what I have to work with.

[3ohAvant]

get some new tires. even st tires are ok, but get something better than those : )

as for pressures. starting with cold temps is fine, but after each run, you'll most likely want to bleed some off. over the course of your run, your temps go up, as do your PSIs. then you will want to bleed some air out, to bring it back to where you want them to be.

a tire temp gauge works, if you're that hardcore, or a laser IR temp gun, if you are less so. and even less than that, a temp probe for your thanksgiving turkey.

you want as even of tire temps from the outside, middle to the inside of the tire. if the average of the out and in are more than the middle, then you are under inflated, if you middle is higher than the average of the outter and inner, then you are overinflated. what you want to do is check this RIGHT after your run, and not your tire pressure at that time. then just before you go out for your next run, adjust accordingly. other things tire temps will tell you, if you need more camber, if you need more front bar, less bar, more rear bar, a compression change, etc, etc.

there are two trains of thought, much lower or much higher pressures in the rear to get rotation. we used to run with the much higher in the rear in our gti. and we recently went to much lower in the rear. we had to do a major alignment change, but the rear is now about as tail happy as it was before, when we had the really high PSis in the back. high PSIs out back give you less of a contact patch, and you can get the tail around.

for you, i would stick with PSIs around 40. the 46 cold was way too high, esp for the wet conditions. as it gets colder out, and there is less grip, or water, you want to lower your PSIs.

for now, you can use your hand to feel how hot the tire is. also, since you've been doing it for a while now, you might consider left foot braking and left foot tapping of the brake to get rotation from the back end. if you are really new, i would not suggest trying this. NOTE, if you LFB for too long, you will get fuel cut, I think its 3 secs or more.

[A4_Mike]

Thank you everyone for the input.

So after an entire weekend of autocross (Intermediate School on Saturday and a event on Sunday) it is time for me switch out the current Pirelli's.

I am running in our club's TIR (Street Tire) class where street tires with a treadwear rating of 140 or higher are allowed. Any suggestions on which tires to buy and where to buy them?

I can get discounts from a wide variety of places through my club and SCCA membership, but I would like to hear you all's suggestions before I start digging deeper.

At the moment, I am looking at the Dunlop Direzza Sport Z1 Star Spec.

[3ohAvant]

There really are only 3 tires that you should be considering.

I have driven all 3. Well mainly two of them. I have quite a bit of experience with the advans ad07 and the bridgestone reo1-r. I've driven on the Dunlops, but only a few times.

The advans. I would get it money was no object. The bridgestone was THE tire to get, if the advans didn't come in your size, and for a while, bridgestone was the only game in town, because of the available sizes. Now, the bridgestones are way more money, almost as much as the over-priced advans.

I have read really good things about the dunlops, and for the money, I don't think you can lose.

The tires to watch out for, when its avail in your size, and in mass quantities, is the toyo (i think its called the) r1r. And then kumho will be coming out with an MX replacement, but thats been the rumor for a while now.

On advans, our gti took 2-3 last season, losing to a Turbo Porsche (an indexed Street tire class). This year, with more car prep, it has a lock on 1st, and I just recently squandered 2nd. I am in third, where I will probably wind up, unless the 2nd place guy, (last years 1st place porsche) sucks it up in the last two events of the year.

The advans probably wear a big better then the re01r. Bur the reo1r for what it is, still lasts a long time. Both are good in light rain.

[A4_Mike]

Thanks for the input 3ohAvant.

I was looking primarily at the Dunlop's due to their performance/price ratio. I have read and heard through word of mouth that they perform very well. The most difficult thing seems to be that they are not readily in stock.

[A4_Mike]

Any other tire recommendations? The Dunlop's seem to be on Back Order everywhere whereas the Advans and Bridgestone's are more than I am willing to pay.

There is a Tire Discount nearby that will be having a "Grand Opening" soon so I'll be able to get $100.00 off a set of four tires that are over $300.00 and some other benefits due to my local car club membership. Any recommendations from their Discount Tire inventory?

I was looking at the BF Goodrich g-Force Sport. Not as good as the Dunlop's, but they are atleast available and for a reasonable price.

[B6 Dude]

On my B5, I ran a good bit more pressure on the rear then the front, to help the back come around easier. I suspect the B6 will be more in the rear as well, though I haven't autocrossed it yet.

I've been hearing that Falken Azenis tires are very sticky and pretty good bang for the buck -- you should be able to find some reviews at tirerack or other places.

Cheers,
-Neil.

[3ohAvant]

dunlops, for the money. prob one of the best bang for buck tires (autox)

falkens about 2-3 years ago, the best hands down tire for the money for autox. great wear and great stick. but times and technology has changed.

as for what else... go to the toyo tires site. look at the new r1r. then find a local retailer. and then print out the rebate form. : ) i have only seen one car on them, and the tread pattern makes me a lil weary, but the guy on those tires, he was FLYING!

[A4_Mike]

I managed to get in line for an order for the Dunlop's so I am hoping they can get them in as early as possible. I am antsy to get a new set of proper street tires since I have a track and autocross event in early September. I need time to get them on and still have a few days to remove the mold release. We'll see how it goes...

[A4_Mike]

Today, I got the all season Pirelli P6's removed and they have been replaced by a proper street tire - the Dunlop Direzza Sport Z1 Star Spec.

With less that 30 miles on them already, I have noticed that there is a substantial difference between them and the Pirelli's in simple daily driving. I think it is safe to assume that there will be an even more significant difference when I take them out on the track and autocross in about four weeks. I can not wait!

One more photo for good measure...

[3ohAvant]

fyi, when at autox, try to not use any tire dressing at least a month prior.

i have since stopped using ANY tire dressing on tires that i ever plan on autoxing.

[A4_Mike]

fyi, when at autox, try to not use any tire dressing at least a month prior.

i have since stopped using ANY tire dressing on tires that i ever plan on autoxing.

Thanks for the advice. I will make sure to keep that in mind when I wash the car from here on out.

Thoughts on my new post regarding my alignment?