Z3 Tire Options?

Just joined and just purchased a 2001 Z3 3.0 auto with HT. I'm interested in tire size options for normal year round driving, but also good looks.

Stock is 245/40 17 rear and 235/45 17 front. That's a side wall height of 98 mm and 106 mm. I was considering 255/40 17 rear and the 225/45 17 front. That's 102 and 101. Any other suggestions? Can I go any wider on the rear? Should I go narrower on the front?

Tire will probably be Michelin Pilot Sport A/S Plus.

The car has summer tires now Dunlop 245/40 17 all around . Think I'll keep these for track? With different rims.

Thanks.

Actually, the stock sizes are 225/45R 17 front, 245/40R 17 rear. I'm currently using this setup with BFG g-Force sports. They are reasonably priced, fairly quiet and ride well.

I ran the car briefly with 255/40R 17 rear tires but it felt a bit sluggish to me. However, my car is a 2.8 stick so it might be different on your car.

Your car looks like it has the Sport Package, so KevinR is correct about the stock tire sizes. The stock wheel sizes are 7.5x17 F and 8.5x17 R, so rotating tires will not be possible with a Pilot Sport A/S Plus even if you go with the same size tires F and R. If you go wider at the rear or narrower at the front from the stock sizes, the car will just understeer more than it does with the stock staggered tire sizes, so that does not seem to be the way to go, unless the "look" is more important than the balance. Putting the same size tires F and R will make the car handling more neutral.

7.5" rim size is smaller than Michelin specs for a 245 (range is 8 - 9.5"), but it's close. You need to be sure you are not rubbing the 245's on the front. If you want to vary from the stock staggered sizes and go with the same size F and R for balance, the two choices would seem to be 235/40 (which would be 2.3% shorter F and 1.3% shorter R than stock), or 235/45 (which would be 1.4% taller F and 2.5% taller R than stock). Rim size range for a 235 is 7.5 - 9", so OK for both F and R. The taller /45 would partially offset the optimistic BMW speedometer, but would make your effective gearing slighly taller. The shorter /40 would have the opposite effect. For street driving a 3.0i, I'd probably go with 235/45 if you do not stay with the stock tires sizes, especially if running A/S Plus in Maryland.

FYI - My 2001 has the Sport Package and I have run Michelin Pilot Sport (not A/S, I live in Houston) 225/45 and 245/40 since the original Dunlops wore out.

Thank you very much. So the previous owner put the larger tires on front to help correct the understeer of the stock set up. But he left the narrower rim size. The tires do not rub. But the front tires do look noticeable different in their side wall. I suppose for any normal driving on the street, the stock narrower tire would fit better and I won't notice the understeer unless I was driving outside legal limits anyway. But the correct solution is to keep the same size front and rear, and buy wider rims for the front.

I was thinking of buying another set of rims for the summer tires, all same size. I wasn't thinking of buying 6 rims. Not sure anyone would want the narrower front rims. The suggestion to buy 235/40 might be the best since it would give a little more acceleration. Maybe I'll just buy another set of staggered rims????

Can't really speculate on why the PO put 245/40 on the front, but unless the PO has told you the reason I would not just assume it was done for balance.

Without knowing more specifics about your intended use for the car, and your budget, it is difficult to discuss wheel and tire sizes much more. An automatic Z3 does not seem to be a good track car. Wider tires will work against you if you plan to drive the car in the winter snow (I assume this is why you are considering Pilot A/S Plus). Wider rear wheels and tires may be fine for the track, where you can turn the DSC off and steer the car with the throttle to overcome the inherent understeer. I don't know if the 8.5x17 rear wheel will fit the front of a Z3.

As for your "narrow" front wheels, the two-piece Z3 Sport Package wheels were the most expensive stock wheels BMW put on a Z3. More expensive than the one-piece M Roadster wheels. If your front wheels are in good/excellent condition, I'm sure there will be buyers out there who don't think 7.5 is narrow.

Sure glad I joined this site. These are excellent comments. As to which tires I plan to buy - I doubt I will actually ever drive in snow, but my main concern is rain. I want a tire that is excellent in rain. I also like the tread design with slanted grooves, it just seems like the right design to clear water. Thinking about track usage is probably just that - thinking. It may never happen, and if it did, it would just be for learning the car better.

KevinR has used 255/40 rear and that diameter is really close to the 225/45. So that is probably the combination I'll use. The other option is 245/40 and 235/40. But BeemerMike TX if you have comments I would appreciate them.

I will look into the rim width issue on the front. So that if I do use the old 245/40s for the track I'll have the correct rims. Any suggestion on which type rims to try to find used? Actually is my current rim a type 42?

I cannot think of any beneficial reason to put 255/40 tires on the back for a street car running DSC, other than appearance. They will only increase the understeer, and since they will be about 1.3% taller than the stock 245/40 rear tires, they will make your effective gearing slightly taller, which will decrease your acceleration a little. You want to compare the alternative rear tire size(s) to the stock REAR tires, and NOT the FRONT tires. Wider tires will increase the potential for hydroplaning.

Oops - forgot about hydroplanning - Thanks for mentioning. Seems 245/40 and 235/40 will keep ratios correct and keep rear tires bigger than front tires in height. Seems right?

Given what I've read, my suggestion is that you just stick with the stock 225/45 Front and 245/40 Rear tires sizes. Michelin Pilot Sport A/S Plus seems like a very good all-weather tire that provides extra wet-weather capability over a Pilot Sport.

Thanks, Mike. Even though I'm back to the original sizes, it was a good education!

Originally Posted by BeemerMikeTX

I cannot think of any beneficial reason to put 255/40 tires on the back for a street car running DSC, other than appearance.

I'm using a set of take-off 17" wheels from an E90 325i sport package car. 255/40 is the correct rear tire size for the E90, and the tires were already on the wheels. Once I determined that the wheels fit and I liked the way they looked, I switched to the correct 225/45 & 245/40 size tires.

KevinR - I think we are saying the same thing. For a Z3 for street driving, if you are running 225/45 on the front, there is no performance reason to go up a size to 255/40 on the rear. Stay with 245/40.

Originally Posted by BeemerMikeTX

KevinR - I think we are saying the same thing.

We are.

I was just trying to clarify why I had experience with the 255/40.

Originally Posted by KevinR

We are.

I was just trying to clarify why I had experience with the 255/40.

Before, when you said your Z3 felt sluggish with the 255/40 rear tires, did you mean handling or acceleration?

Originally Posted by BeemerMikeTX

Before, when you said your Z3 felt sluggish with the 255/40 rear tires, did you mean handling or acceleration?

Acceleration. The closest description I can give is that it felt like 2 people in the car with the trunk full of luggage - at all times. Switching to the 245s seemed to solve that perception.

I drive a 00 2.3 and LOVE the Michelin Pilot Exalto for summer. Good luck!

I have 255/40-17's all around on 8.5x17's and the car handles exceptionally well, neutral and none of the complaints which have been opined about.

Well, since you posted, I will confess. I did put 255s on the rear with 225s on the front. Now the diameters are the same. I cannot feel any difference from the 245s on the rear. The car does seem to turn a little easier with the 225s on the front vice the 245s, but that could just be my imagination.

My 540 has 255/40/17's on the back and there is a noticeable sidewall difference from the the 225/45/17 on the Z3 . You guys are not having any DSC issues running a larger tire on the back?

Originally Posted by ricrx7

I did put 255s on the rear with 225s on the front. Now the diameters are the same. I cannot feel any difference from the 245s on the rear. The car does seem to turn a little easier with the 225s on the front vice the 245s, but that could just be my imagination.

Having the tire diameters the same F and R is not really a technical/performance goal to target by itself . . . the issue is variation from the diameters the car was set up for by the factory. Yes, 225 on the front will probably feel like they turn easier than 245, especially in normal street driving, because they are narrower and have less resistance to turning. However, as you approach the limit of adhesion the 225/255 set up will have more understeer than the stock 225/245 set up or a 225/225 set up (or any other size same F and R).

255/40 front and rear will indeed have more "neutral" handling than staggered 225/245, which was opined about previously. The main issue is whether 255/40's fit the front without interference issues. Apparently they do.

I am learning quite a bit from reading thru this thread. Am I safe in assuming that I can upgrade my 2000 2.5liter Roadster from 225/50/16s all around...to 225/45/17s in front and 235/45/17s in back? I am looking for a SLIGHTLY wider/taller tire in back.

Thanks in advance. I appreciate all of this info.