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[Stock4Evr]

Can someone provide me with an explanation as to why the 2012 135i has different size tires on the front and rear? What do they do for the ride and performance of the vehicle?

Also can I replace them with regular tires all of the same size? As somewhat once said, what difference does it make. Seriously folks what difference does it make?

Your responses are appreciated.

[Stock4Evr]

No tire specialist?

[Solo_M_Tech]

there are alot of reasons. Asthetics, safety, fitment, traction, etc etc etc. yes you can run the same size tire all the way around. alot of people have done it. You will need new wheels that are all the same widths in order to run a square tire set up.

This is a very complex question. No simple answer either. To OVER GENERALIZE THIS... the engineers who designed the car, determined it needed a staggered wheel and tire set up to both meet the needs of the car, and to meet safety requirements.

[Gary@TireRack]

Apex, well stated.

[Solo_M_Tech]

Originally Posted by Gary@TireRack

Apex, well stated.

Thank you.

[Stock4Evr]

Apex
Thank you for your response. I guess it all has to do with all of your response.

[fe1rx]

Originally Posted by ApexResistance

To OVER GENERALIZE THIS... the engineers who designed the car, determined it needed a staggered wheel and tire set up to both meet the needs of the car, and to meet safety requirements.

And because their marketing bosses said so ...

[ShocknAwe]

Nothing wrong with a square setup. All depends on the purpose of the car or how much under/oversteer you are going for. Personally, I'm not sure I can say if it's possible to overtire the rear of this car. I'd love to get a 305+ back there and see.

[Solo_M_Tech]

Originally Posted by ShocknAwe

Nothing wrong with a square setup. All depends on the purpose of the car or how much under/oversteer you are going for. Personally, I'm not sure I can say if it's possible to overtire the rear of this car. I'd love to get a 305+ back there and see.

I know a 1M that's rocking 295's on the back... don't know about 305+. That's ALOT of tire.

[MightyMouseTech]

Because it's RWD.

[lowbudgethero]

Originally Posted by ApexResistance

I know a 1M that's rocking 295's on the back... don't know about 305+. That's ALOT of tire.

and while it's partially due to the suspension it's very easy to get the 1M rear end to slide out even with the 295s

[JimD]

A point of clarification. I have a e88 with sport and I originally had 205/50s on front, I think with 7 inch wheels, and 225/45 with 7.5 inch wide wheels. I wanted to go square when I bought PSS replacements and I think it helped me get them - I'm not sure they make 205/50s. Tire Rack said I would be OK with the 225/45 on my 7 inch wide front wheels as did the tire shop that installed them. I've been running that way a year or so and I see no downside. I've rotated tires from front to back. I wouldn't run an autocross that way but for daily driving it is fine. I think the slightly wider wheel may affect the tire contact area slightly but I am closer to the same front to back than I was originally.

BMW had a design plan when they picked the size tires for my car but it included understeer. I haven't pushed mine to the limit but I think going square has made the handling more neutral. I need to find the time to autocross to be sure.

So I would check before concluding you can't go square without changing wheels. It may or may not be true. There is almost certainly a tire size that will work with both wheel widths.

[135Pats]

Originally Posted by ApexResistance

I know a 1M that's rocking 295's on the back... don't know about 305+. That's ALOT of tire.

Originally Posted by ShocknAwe

Nothing wrong with a square setup. All depends on the purpose of the car or how much under/oversteer you are going for. Personally, I'm not sure I can say if it's possible to overtire the rear of this car. I'd love to get a 305+ back there and see.

I can tell you from experience that you are physically not fitting anything north of 285 in that wheel well. 265 is fine, 275 (what i'm currently running) is tight, 285 wouldn't have been street-able unless I raised the car to at least stock height.

Can't even imagine trying to fit a 305 out back. Sure would look nice though...

[Solo_M_Tech]

Originally Posted by JimD

A point of clarification. I have a e88 with sport and I originally had 205/50s on front, I think with 7 inch wheels, and 225/45 with 7.5 inch wide wheels. I wanted to go square when I bought PSS replacements and I think it helped me get them - I'm not sure they make 205/50s. Tire Rack said I would be OK with the 225/45 on my 7 inch wide front wheels as did the tire shop that installed them. I've been running that way a year or so and I see no downside. I've rotated tires from front to back. I wouldn't run an autocross that way but for daily driving it is fine. I think the slightly wider wheel may affect the tire contact area slightly but I am closer to the same front to back than I was originally.

BMW had a design plan when they picked the size tires for my car but it included understeer. I haven't pushed mine to the limit but I think going square has made the handling more neutral. I need to find the time to autocross to be sure.

So I would check before concluding you can't go square without changing wheels. It may or may not be true. There is almost certainly a tire size that will work with both wheel widths.

You should try to fit a 245/35-18 on a 7.5" front wheel. Neither should you install a 215/35-18 on a 8.5 inch wheel. Even if you split the difference the 235/40 is too wide for a 7.5 inch wheel and too narrow for a 8.5 inch wheel. You need a square wheel set up to affectively use a square tire set up.

[fe1rx]

Originally Posted by ApexResistance

You should try to fit a 245/35-18 on a 7.5" front wheel. Neither should you install a 215/35-18 on a 8.5 inch wheel. Even if you split the difference the 235/40 is too wide for a 7.5 inch wheel and too narrow for a 8.5 inch wheel. You need a square wheel set up to affectively use a square tire set up.

Not really. 225/40R18 fits on both 7.5" and 8.5".

Specs for OE RE050A sizes:



Specs for ZII (for example) in 225/40R18. Nominally it looks like a downgrade at the rear but actually the tread width is negligibly different in width. If you really want square on OE wheels, this is the size to use.

[Solo_M_Tech]

I understand that yes you CAN. Fit a 225 on both wheel sizes but it would be far from ideal. The key word in my last post was affectively.

[fe1rx]

Originally Posted by ApexResistance

I understand that yes you CAN. Fit a 225 on both wheel sizes but it would be far from ideal. The key word in my last post was affectively.

The OP's question which was "can I replace them with regular tires all of the same size?"

The answer to that is clearly "yes", as according to the ZII spec sheet 225/40R18 fits on wheels from 7.5 to 9 inches. Given that the OE wheels are 7.5 and 8.5 inch, this tire size is completely satisfactory. Not only that the revs/mile match the OE tires. They are in fact the "ideal" size for the task of putting a square setup on OE wheels.

I have used several sets of tires in this size on OE wheels and they are completely effective in improving the handling balance, which is great if that is the effect you are looking for. Not everyone is.

[Solo_M_Tech]

Originally Posted by fe1rx

The OP's question which was "can I replace them with regular tires all of the same size?"

The answer to that is clearly "yes", as according to the ZII spec sheet 225/40R18 fits on wheels from 7.5 to 9 inches. Given that the OE wheels are 7.5 and 8.5 inch, this tire size is completely satisfactory. Not only that the revs/mile match the OE tires. They are in fact the "ideal" size for the task of putting a square setup on OE wheels.

I have used several sets of tires in this size on OE wheels and they are completely effective in improving the handling balance, which is great if that is the effect you are looking for. Not everyone is.

There you go OP. I guess you can fit square 225's on your stock wheels. Have fun with that!

[Indo Rider]

Originally Posted by ApexResistance

The key word in my last post was affectively.

Effectively. Sorry, would have let it slide, but twice in a row...

[BMW135pls]

Originally Posted by lowbudgethero

and while it's partially due to the suspension it's very easy to get the 1M rear end to slide out even with the 295s

Which aspect of the suspension makes it this way? Alignment? Something swappable for an upgrade part? Or just the general dimensions of the frame, something that can't be tuned out?

[lowbudgethero]

Stiff suspension + short wheelbase + 370ft/lbs of torque available at low rpm.

I have the same issue with TC off when I drive my own car

[BMW135pls]

Originally Posted by lowbudgethero

Stiff suspension + short wheelbase + 370ft/lbs of torque available at low rpm.

I have the same issue with TC off when I drive my own car

Interesting. The 1M has the same springs/shocks as the 135i right? Frankly with the mods I have installed I have some trouble breaking it loose. I'm running probably 400 or a little bit more torque straight to the rear tires, but it seems very stable, snakes on WOT straights though. Low speed traction loss seems to be harder to make happen. I mean I could probably do it if I go WOT with it around a turn, but that's not something I'm going to do in a 500 crank HP car in the middle of a turn on the streets.