Tire size for my Timeattack bmw 135i

[Hellracers]

Hello my first post here. I'm coming from Sweden and have just bought my BMW 135i coupe 2008 that I'm going to drive in a Timeattack series here in Sweden.

I need some help to get a good setup of tires for my car. My rims are BBS ch-r 18" 8.5" in front and 9.5" in back. Could be a size down because rims and tires are on the car so not that easy to measure. I have KW V3 coilovers, my tyres now are 215 in front and 245 in back pilot sport 4. I having a hard time to get the power down as is.

I have some rules that I need to follow for my series.
-Maximum 960mm of tire width
-no R tires

What would be the best option for me? (it's going to be for me me a track car that I'm driving on the streets on weekends when the weather is fine not a DD)

I have no idea what tire size I can get on before its a problem, so help me please 😁
Stagger setup and go for 235 in front and 245 in back or 225 f 255 b

Or a square setup and go for 235 or 225?

So please help me out what size I should go for and a great tire for tracking

[machine4321]

I switched from a 225/40-18 f 255/35-18 r

To square 255. I haven’t got the track yet but can feel the car has much more front end grip and seems to be much better balanced. But again I haven’t driven it hard yet

[iminhell1]

Corner balance the car first.
I would say setting that suspension up correctly should really aid in traction.

It doesn't look like you have much of any room to go wider in the back without rubbing. Unless there's a spacer and you can move the wheel in a little I think you're really limited here.



Hancook RS-4
Bridgestone RE71R
Yokohama Advan A052

[ShocknAwe]

Would caution wider than 255. Hard to fit and every car is different.

[Driven5]

Since I have some theories about how computer and physics might interact to either slightly increase or decrease outright performance with a 235/245 setup, I can't say that I'd recommend that without back-to-back testing against 235 square.

So if starting from scratch, my personal philosophies on car setup and tuning might be inclined toward initially developing the car around a 235 square setup. However, that wouldn't be a very cost effective approach with your current car.

Starting with your current setup, I'd focus on tightening the nut behind the wheel. First get consistent results with the current setup, then use that to clearly identify the effect of any changes you make. In the meantime, the easy button would be to start with bumping up to 225/255 once these tires are worn out, provided you have sufficient fender clearances at your desired alignment settings. You may find you like the staggered setup, or you might find you would rather square it up more.

I would caution that 'trouble getting the power down' on corner exit may not actually be highlighting a shortcoming of the car.

[Hellracers]

Thank you everyone for the answers, it's very helpful to get others perspective on this 😁

[PcarDefector]

Originally Posted by Hellracers

Hello my first post here. I'm coming from Sweden and have just bought my BMW 135i coupe 2008 that I'm going to drive in a Timeattack series here in Sweden.

I need some help to get a good setup of tires for my car. My rims are BBS ch-r 18" 8.5" in front and 9.5" in back. Could be a size down because rims and tires are on the car so not that easy to measure. I have KW V3 coilovers, my tyres now are 215 in front and 245 in back pilot sport 4. I having a hard time to get the power down as is.

I have some rules that I need to follow for my series.
-Maximum 960mm of tire width
-no R tires

What would be the best option for me? (it's going to be for me me a track car that I'm driving on the streets on weekends when the weather is fine not a DD)

I have no idea what tire size I can get on before its a problem, so help me please ��
Stagger setup and go for 235 in front and 245 in back or 225 f 255 b

Or a square setup and go for 235 or 225?

So please help me out what size I should go for and a great tire for tracking

I have a lot of comments, questions and recommendation about building your 135 for time attack and track use.

1. getting traction down
This might be due to overdriving or too much speed or throttle in a slow corner. The 135 naturally understeers due to suspension limitations. The following will make your 135 more balanced.

2. Reducing understeer
There are several modifications needed to make the 135 handle more neutrally including:
A. Upgrading rear subframe bushing - the 135 squats in corners or acceleration due to voids in the subframe leading to understeer and a nervous feeling. Upgrade to Whiteline KDT-917 2 pcs or the M3 RSFB bushings.
B. Increase front camber - upgrade your control arms to the M3 variant. Also you will need camber plates as the KW V3 doesn't come with them.
C. Run square tire/wheel setup - staggered setup will enhance the understeer while square makes the 135 more neutral and handles better. Also for track use, you can rotate the tires and carry less spares in a square setup..

3. What tires and size to use:
A. I'll be using a 235 (235x40/18) square setup. Others have used up to 255 square with more camber and rolling front fender lips. There are clearance issues with the front springs and fender lips depending on your wheel offset and tire size.
B. don't get too hung up on tire size as some 235 are as wide as 245. More front grip means you will get more rear grip if you won't overpower the rears.
C. There are plenty of tire choice in the sticky 200 treadwear. See this link from tire rack. https://www.tirerack.com/tires/TireS...earDiameter=17. Tirerack doesn't carry Nexus which is an excellent choice for their SURG tire.
D. There are new variants coming for 2021 including the RE71RS and Kumho V730.

4. lastly, the 135 has a lot of weaknesses as a track toy. You will need to address these shortcomings or face expensive repairs. They include:
A. Oil starvation - this is more of a problem on N55 than the N54. The quick fix is to overfill by 1/2-3/4 litre and check your oil after every session. Spun main bearings are fatal and if your car starts to seize, pull over when it's safe to do so.
B. Melting brake pistons - the 6 piston brembos use ceramic backings which will fail under sustained track use. Fixes include titanium backings for the brake pad and adding brake ducts.

This forum is a godsend to preparing your 1 series for track use. Read the post by fe1rx, gingerextract, andyw, dean mccaron, mightymousetech and others who post in the track forum. The 135 needs a lot of enhancements and you will benefit from other people's experiences

EDIT: ignore my brake piston comments. I saw that you have upgraded to aftermarket brakes.

[gixracer]

just finished a weekend at Grattan with 255 square on 17's. Definitely is better in front tire turn in response. Mid corner is vague so i'm going to up grade to a whiteline sway up front to level out the car. Currently on stx coil overs with camber maxed out.
this is comes from a previous setup of 245/35-18 with b8's and swifts. Certain tracks with 255's plan on rolling fenders depending on offsets. The rear fenders suck to roll. you my have to grind down some. The main contact point for me was in the rear metal to bumper connection.
hope that helps
why the 960 max treadwidth?

[tsk94]

I'm assuming he meant 9.6" max tread width? 960mm is a 3 foot wide tire haha.

I've tracked a 135i and a 128i, both with 255 square. On a 135i, especially if you're making more then stock power, I can see running a stagger like 245/265. 255 square is still nice for being able to rotate tires. I think 255/275 fits 'fairly' easily as well (fairly being a very relative term).

Don't know your offsets, but wheel wise with an 8.5" in the front you can run 235-255 and with 9.5" in the back you can run 255-275s. 235/255 or 245/265 shouldn't be too hard to fit with your suspension.

[spidertri]

Pretty sure it's 960mm of total tire width, divided amongst the 4 wheels with whatever configuration works best. 235F/245R, 225F/255R, 235 square, etc.

[tsk94]

Originally Posted by spidertri

Pretty sure it's 960mm of total tire width, divided amongst the 4 wheels with whatever configuration works best. 235F/245R, 225F/255R, 235 square, etc.

Makes sense. Didn't cross my mind it could be for all 4. For NASA they give measurements per tire in mm so it never occurred to me it could be for a set haha.