Sponsored by The Tire Rack

[murphyrg]

OK, in searching the posts, it seems that this change works with the taller suspension setup on an xi, but what about my regular '09 335i with stock sport suspension? I want to improve the ride by increasing the sidewall height while keeping the width the same as the originals. Specifically, I want to go from 225/40-18 and 255/35-18 to 225/45-18 and 255/40-18 on my staggered 189 wheels with 34 and 37 offsets. I gain almost exactly 1/2 inch in radius (correcting the speedo!). And the difference in diameters between front and back is the same as stock, so the car shouldn't get confused. As long as nothing rubs, I think I should be OK - someone out there must have done this already, no?

Thanks

[techwhiz]

To get better ride, just dump the run flats.

[Dan Villa]

^ ditching run flats does help quite a bit but Xdrives do ride pretty hard. One of the things that bother me about this car.

[murphyrg]

Ditching the run flats was always part of the plan - I imagine that that will give the best improvement in ride by itself. I was just thinking that I could gain even a bit more improvement with the taller tires. I also wouldn't mind filling in the wheelwells a bit more without lowering the car - I already scrape the air dam on too many things around here.

[murphyrg]

Really? Only the X-drive guys put on these taller tires? Come on - I've got to order tires and I'm a bit nervous that no one has jumped in to say that there are no rubbing issues with a stock '09 with sport suspension.

[Aashenfox]

BMW designed your car to run on a certain diameter tire, I wouldn't go messing with that if I was you, it is tantamount to making a gearing change and may put long term stress on just about everything.

If you want a better ride, use a soft sidewall tire (such as Pirelli P Zero Silver) and a smaller diameter rim. Remember that with soft sidewalls you will have to avoid as many potholes as the 19" guys to prevent 'tumours' (bubbles) forming on the sidewall from pothole impacts. Its all a trade off.

Originally Posted by Aashenfox

BMW designed your car to run on a certain diameter tire, I wouldn't go messing with that if I was you, it is tantamount to making a gearing change and may put long term stress on just about everything.

lol says the guy with far from stock offsets, tire sizing, suspension setup, etc. What a pointless reply.

[floydarogers]

Originally Posted by murphyrg

OK, in searching the posts, it seems that this change works with the taller suspension setup on an xi, but what about my regular '09 335i with stock sport suspension? I want to improve the ride by increasing the sidewall height while keeping the width the same as the originals. Specifically, I want to go from 225/40-18 and 255/35-18 to 225/45-18 and 255/40-18 on my staggered 189 wheels with 34 and 37 offsets. I gain almost exactly 1/2 inch in radius (correcting the speedo!). And the difference in diameters between front and back is the same as stock, so the car shouldn't get confused. As long as nothing rubs, I think I should be OK - someone out there must have done this already, no?

My winter set is a square 225/45R18. No problems, "corrects" the speedo to almost dead on, be sure to calibrate with a GPS or whatever to know what the speedo is really reading.

[murphyrg]

I think that I'm talking about a pretty small deviation from stock here. I'm not changing offsets or unsprung weight. The front to rear wheel speed difference is actually better than stock. The change to the effective final gearing is less than 4% (and in the direction I want). This tire size combination is actually what is now coming on the F30 335 with sport suspension.

I'm completely comfortable with this change from a mechanical standpoint - I just want to know if there is a chance that the taller tires will rub on this car. No matter how much you look at the static tire to body clearances, it's always hard to determine clearances at all conditions such as full steering lock and max suspension deflection. And while the E90xi and F30 get away with this combination, I was hoping to hear from someone with an E90 sport suspension who had experience with the taller tires I'm considering.

[Aashenfox]

Originally Posted by FCobra94

lol says the guy with far from stock offsets, tire sizing, suspension setup, etc. What a pointless reply.

My tires are the recommended diameter. I'm not stressing my car, what do you mean? My offsets aren't even aggressive. But even if they were, what's that got to do with changing the diameter of a tire, thereby subtlely changing the gearing, that's not something I would want to do. Watch the Top Gear special where they climb a volcano if you want a relatively extreme example of what happens when you increase overall tire diameter, and these were torquey (if a bit fucked) cars. The particularly important thing in my mind is the effectiveness of the brakes. They will work much harder to stop a car on a tire with a 4% extra diameter.

Anyway, you may say I'm exaggerating, its only 4%, I'm just saying I wouldn't do it.