Track tires and setup questions

[TexasZed4MC]

Ok I have a set of 18x9.5 et355 track wheels. TC Kline has suggested 255/35 and 275/35 tires setup. I know others of you have 265/35 square. Let me know your thoughts of good and bad both sets. ALSO is using a 10mm spacer on the rears a good idea to get the rear offset better? Help me out track experts!

[Finnegan]

Rear offset of 22-25 (10-12mm spacer rear) for a 9.5 ET35 would be good.

Tires are another question. The 255/35 size has a 3.66% difference in diameter to stock front tire sizes whereas the 265/35 is under 3% difference. Rule of thumb I've always heard is to stay within 3% for ABS/DSC. But assuming you're running with those off on the track, I doubt it's a variable.

It may come down to driving style and preference. The largest plus of the square 265 set up is that with the same front/rear wheel sizes you can rotate front to rear to level out wear.

A 265 front is going to have almost .5" more section width than the 255 tire, which probably means better heat dissappation (if driving close to the limit with higher slip angles). A bit less grip rear, a bit more front as well (hence style).

The 255/275 sticks more to the stock stagger (but 20mm, not 30mm stagger). 275 has a bit more section width as well. This does affect driving dynamics a bit.

I think others with experience with the different sizes and more track experience than me will need to kick in more to this discussion.

[seank]

Originally Posted by TexasZed4MC

Ok I have a set of 18x9.5 et355 track wheels. TC Kline has suggested 255/35 and 275/35 tires setup. I know others of you have 265/35 square. Let me know your thoughts of good and bad both sets. ALSO is using a 10mm spacer on the rears a good idea to get the rear offset better? Help me out track experts!

So, just so I understand this, you have a square set-up of 18x9.5 et 35 wheels? And Tc Kline said to run a 255/35 and 275/35 rear tire set-up?

If so, I think there was a misunderstanding.

TC Kline has probably raced these cars more than anyone. That being said, everyone has opinions on car set-ups. TC prefers a soft suspension set-up.

There is no need, for tracking the car, to add a spacer in the rear unless you just want it to look good.

Regarding running a square set-up, I chose this set-up but I am not positive that it is the best set-up for the m coupe. Most BMW's race cars run a square set-up, but the m3 turner car ran a slightly narrower front by 5mm. I think it was due to the car having issue with power over-steer, but that is just a guess. That being said, it was nearly a square set-up. The z4m is much more balanced from the factory than other bmw's, so maybe a staggered set-up will work best.

I would personally search the nation for who is setting track records (nasa, scaa, BMWCCA) in the z4m and pick there brain a little. I think it would be the best place to find the truth.

Otherwise, just drive the car, make changes to the car set-up gradually. This will even happen as you get faster. The set-up that works now will probably not work as you get faster.

[jmillet]

My track setup is 245/40-18 up front and 255/35-18 rear Toyo R-888 tires mounted on E46 M3 wheels. I have 10mm spacers up front to clear the stock calipers and TC Kline DA coil over struts. With this setup I experience virtually no under steer and very manageable over steer.

[seank]

Originally Posted by jmillet

My track setup is 245/40-18 up front and 255/35-18 rear Toyo R-888 tires mounted on E46 M3 wheels. I have 10mm spacers up front to clear the stock calipers and TC Kline DA coil over struts. With this setup I experience virtually no under steer and very manageable over steer.

Spring rates would be helpful for him to use this information, as well as sway bar sizes if they are not stock.

[Kgolf31]

Originally Posted by seank

Spring rates would be helpful for him to use this information, as well as sway bar sizes if they are not stock.

500#front 600#rear, it's in his sig.

OP - TCK was probably talking about a staggered set-up for wheels. I've talked to them and they recommended going a 10.5 rear wheel.

10-12mm spacer will be perfect. APEX I know recommends 12mm.

Personally, it all depends what you want to achieve. Do you need more tire to power down (although you can achieve this by more toe-in as well) or do you want rotate tires? and eliminate understeer?

[TexasZed4MC]

Understeer is my biggest dislike on the car. There is plenty power. I can correct body roll with swaybars and springs

[dorifto88]

Originally Posted by TexasZed4MC

Understeer is my biggest dislike on the car. There is plenty power. I can correct body roll with swaybars and springs

could also play with tire pressure. i increased pressure in the rear and it helped me.

[inTgr8r]

Originally Posted by TexasZed4MC

Understeer is my biggest dislike on the car. There is plenty power. I can correct body roll with swaybars and springs

I used to feel the same way.
More aggressive alignment (zero toe) and add some neg. camber and understeer be gone!

[Kgolf31]

Originally Posted by dorifto88

could also play with tire pressure. i increased pressure in the rear and it helped me.

Increase of pressure, usually, will make you lose grip.

Lowering pressure will increase tire grip.

Typically, I run 4-5 pounds less in the rear than the front.

[dorifto88]

Originally Posted by Kgolf31

Increase of pressure, usually, will make you lose grip.

Lowering pressure will increase tire grip.

Typically, I run 4-5 pounds less in the rear than the front.

ya, I wanted to increase grip in the front by lowering grip in the rear.

[Kgolf31]

Originally Posted by dorifto88

ya, I wanted to increase grip in the front by lowering grip in the rear.

Yea, I read your initial post completely wrong.

Whoops

[TSM330i]

We are going to run BFG R1 in 265/35-18 square on our e86 3.0si race car. If I were you, I'd put the widest tire I can fit on the car. Running a square setup will allow you to swap tires to even out wear as well and help with longevity.

[JasonH]

Originally Posted by TSM330i

We are going to run BFG R1 in 265/35-18 square on our e86 3.0si race car. If I were you, I'd put the widest tire I can fit on the car. Running a square setup will allow you to swap tires to even out wear as well and help with longevity.

What width wheels and offset? How much negative camber up front? I assume you'd need camber plates to fit the 265s up front.

[a_riddler]

I believe you can get by with as little as -2.7 up front for 265s. You can do -2.5 with just camber bolts, but past that you are talking camber plates.

[David70]

Originally Posted by dorifto88

ya, I wanted to increase grip in the front by lowering grip in the rear.

I don't know if you are right or wrong but just asking to learn something.

In my mind if I go around a corner at 50 mph and the front wheels start to slip but the rears don't, then I increase tire pressure of the rears to reduce their grip, I would expect that now I might have all four tires losing grip around the 50 mph turn. I wouldn't expect the front to now have increased grip.

Seems to me that if I don't do anything to the front's tire pressure, the point that they slip shouldn't change. The overall balance of the car will with the rear tire pressure change.

[seank]

Originally Posted by David70

I don't know if you are right or wrong but just asking to learn something.

In my mind if I go around a corner at 50 mph and the front wheels start to slip but the rears don't, then I increase tire pressure of the rears to reduce their grip, I would expect that now I might have all four tires losing grip around the 50 mph turn. I wouldn't expect the front to now have increased grip.

Seems to me that if I don't do anything to the front's tire pressure, the point that they slip shouldn't change. The overall balance of the car will with the rear tire pressure change.

Not increase rear pressure, but decrease rear pressure by 1 psi. This assumes you are running the correct pressures to begin with.

You can also do these to the car:
-Increase rear sway bar/ or decrease front stiffness
-Increase front tire width
-add a splitter to increase front grip at higher speeds

You can also drive the car differently depending on when it happens in the corners (which depends on the corner, as well as skill and ability)
-trail brake more, sometimes all the way to the apex
-left foot brake through the corner with the gas on the pedal to load the front (really good for very long corners but not easy to master)

Hope this helps.

[sadar]

Originally Posted by inTgr8r

More aggressive alignment (zero toe) and add some neg. camber and understeer be gone!

+200%
Toe is probably the biggest reason this car understeers.
Zero Toe is the way to go.