Sponsored by The Tire Rack

[sblument]

Hi all:

I plan to buy a new set of rims/tires for driving schools/autox only. I want to eventually put r-comps on them but not yet as I'm only a novice.

2006 330i ZSP stock rims are 18x8 front / 18x8.5 rear.

I want to get a non-staggered setup to reduce understeer.

I'm thinking of getting 18x8.5 all around, but what are the advantages and disadvantages of getting 17 inch rims instead vs. 18, and of getting 8.5's all around vs. say 8 or 9

(simply put what are the advantages and disadvantages of smaller vs. larger wheel radius & width, and do you agree with my choice of 18x8.5's all around for a good non-staggered setup?)


Thanks for any opinions...

[sblument]

I'm thinking 17 vs. 18 diameter, and wider is better.

My stock setup is:

front: 18x8 +34 225/40/18
rear: 18x8.5 +37 255/35/18

I think I will go with:

front/rear: 17x8.5 +0 245/40R17
(Kosei K1's on sale at tirerack)

This setup would stick out 34mm vs. the stock rears so would be
wider. Diameter would be .37in less. Speedo difference would be -
1mph. Weight of the pkg with typical tires would save 40-45lbs.

Not bad at all--total cost about $1000 with a cheap set of high
performance street tires (non-RFT of course) that I can burn up on
the track. Street tires + non-staggered = good for learning.

My RFTs alone are more than the whole pkg. Want to stick with the
less grippy street tires for awhile then can upgrade to r-comps later.

[davig]

It seems like a good approach. 17s are less expensive and more choices for tires. Will the front tires clear OK?

[335iheLLraiseR]

what are r-comps?

[Corey]

Wheel sizing isn't exactly a simple subject.. but you have the right idea. To start simple generally wider is better. A wider wheel fits more tire which increases the tire's contact patch. When it comes down to it the tires are the only thing between your car and the road and as such increasing the amount of tire and/or quality of tire under your car will provide a bigger performance gain than any other suspension modifications you may make.
With that said keep in mind I am talking only of the wheel width. Ideally for autocrossing you would keep the track width to a minimum while maximizing the width of the wheels because a "smaller car" is a more maneuverable car ( to over simplify things).

When it comes to diameter things aren't so clean cut. Assuming the overall diameter will stay nearly the same moving down to a 17" diameter wheel introduces a host of changes:

1. Keeping the same overall diameter means that going down to a 17" wheel means the sidewall height increases. A taller sidewall has lower spring rate than a shorter one and the shocks don't absorb this motion. A tire with a stiffer spring rate means more of the suspension's movement can be dampened by the shocks. What this translates to is the tires will be less responsive, ie a less predictable and softer ride.

2. On the other hand, a larger diameter wheel pushes the weight of the wheel/tire further to the outside of the rotating diameter. Because of this it takes more energy to rotate the wheels resulting in slower acceleration.

3. A higher diameter wheel provides more clearance for suspension components and tie rods, and more importantly for bigger brakes.

There are other issues such as pinching low profile tires, tire rollover, etc. that should be considered. Generally in autocross you run higher than normal pressures in street tires to prevent things like this.

There is no cut and dry answer to what wheels are "the best" but the more you know the more informed choice you can make for your particular application.

I actually started this season on a car identical to yours and just recently the owner upgraded to a lighter 8.5" non-staggered setup and better street tires and the difference was exactly as you'd expect: more neutral handling with less understeer. As it sounds like you've experienced, in stock form the car likes to push. Going non-staggered helped quite a bit. The new non-runflat tires helped quite a bit too. Hope this helps!

[davig]

Originally Posted by 335iheLLraiseR

what are r-comps?

Very soft (treadwear 40-80) and sticky tires which, although street legal, are primarily used for autocross, track days etc.

[S4to335]

Originally Posted by 335iheLLraiseR

what are r-comps?

A bunch of info on R compounds can be found here:

http://www.europeancarweb.com/tech/0...nds/index.html

[sblument]

Corey,

Great response, thanks. I'll post pics of my new setup once I get 'em...

Seth

[sblument]

hi davig,

I think the fronts will clear fine, placing my trust in the tirerack website, which is supposed to show you only compatible fitments if you specify your car first

[davig]

I thought about these as they are great value for the $$. The zero offset concerned me-I hope you're right and please keep us informed.

[sblument]

Just placed order tonight from tirerack:

245/40ZR-17 Kumho Ecsta MX

17x8.5 Kosei K1 Racing Silver

[sblument]

Pkg came today...will put them on this weekend @ autox

[davig]

If you can, I would suggest that you put some miles on them to scrub and scruff them prior to evading cones. Good luck.

[sblument]

good advice--I'll go easy on them at first

[sblument]

from today...new rims

[Dascamel]

How do they feel on the road? Also, anyone ever try this size on a 335i sedan?

[sblument]

Road feel: didn't do a long test but aside from the autox course, drove them out a short distance away on moderately bumpy pavement in normal suburban traffic.

My impressions are, as compared to the stock Potenza RFTs:

street
-ride is about the same as the RFTs, although I had them at 38psi for autox--ride would have been better at a lower pressure vs. my RFTs which were at something like 32/36 front/rear. Plus these are extreme perf summers vs. max perf (anyone interested may check out the tirerack page on this topic for a great explanation of the difference between all these tire types)
- steering wheel effort is slightly reduced at parking lot speeds. on the street no difference

autox
- tires were brand new so didn't push them as hard as last time on my RFTS. non-staggered setup reduced understeer. feels more balanced. tires have terrific grip and give nice feedback when they're at their limit

fitment and impressions would be exactly the same on a 335i vs. 330

[sblument]

at Putnam Park road course in Mt. Meridian, IN. Windy City BMW HPDE

[UKRBMW]

Originally Posted by Dascamel

How do they feel on the road? Also, anyone ever try this size on a 335i sedan?

I'm also curious if these will work on a 335 sedan!!!

[sblument]

Yes this setup will work fine on a 335.

[Don Nguyen]

Get the D-force LTW5 wheels that we sell!

It is on our site, if you want to check out the specs.

They are very light wheels, and come in more sizes than what Koseis offer for their K1 wheels.

Let me know if you have any questions.

They cost a bit more than K1s, but it is very worth it, and it isn't very much more.

-Don

[getInline]

Originally Posted by Don************

Get the D-force LTW5 wheels that we sell!

It is on our site, if you want to check out the specs.

They are very light wheels, and come in more sizes than what Koseis offer for their K1 wheels.

Let me know if you have any questions.

They cost a bit more than K1s, but it is very worth it, and it isn't very much more.

-Don

Hi Don,

Does anyone have any pictures of these wheels on an e92? Preferably the Anthracite. They look not bad and I certainly like the weight.