1 Different size tire on rear of RWD car - Ok, or not?

[KDKPSJ]

Hello ATG!

My brother's car needs a replacement tire for passenger rear. The car is RWD with 225/45/17 on the rest. We have an extra tire of 245/45/17, a brand new one, and I am wondering if it would be ok to use it along with 225/45/17's.

Thanks in advance!

 

[exdeath]

No. Diff width AND diff height (slightly)

Least that will happen is a ABS light (and ABS being disabled), worst is burning up the clutches in the differential due to wheels spinning at slightly different speeds or losing control due to asymmetric handling.

A 225/45/17 tire and RWD tells me it's something sporty so you definately don't want to screw around with the tires like that.

It's ok to use to get it rolling to the tire store to get two identical tires, however don't drive it that way.

There isn't a severe difference in the two sizes, so YMMV.

 

[KDKPSJ]

I see! Yes, it's 06 E90 325i, so qualified as sporty It does, though, let me reset TPMS and ABS should work with reseted rotation speed AFAIK. But also, yes, I was kinda worrying about possible rear axle wear due to constant different rotation speed.

So, now I guess I gotta sell that 245 45 17 and buy 225 45 17 to replace the old one that keeps losing air

 

[exdeath]

Just get another new matching 245/45/17, or just take it in to Discount Tire or some place they can plug it up for like $12. You don't really want to match new and old tires on the drive wheels either unless the old one is still relatively new and of the same tread pattern and compound.

And you don't want to be ghetto with mismatched tires on a BMW anyway

 

[KDKPSJ]

Well, it's time for replacing that leaking one anyway (about 2/32 tread left), so patch it is not a good option

And looks like my brother doesn't care much about mismatching or performance, anyway The other 3's were used with about 7/32 from local tire shop! lol

 

[DivideBYZero]

That car doesn't have an LSD, but I still wouldn't do it. The dynamics are going to be messed up with a different sized tyre, and you don't want that on the driven wheels, especially when they're at the back, DSC or not.

 

[KDKPSJ]

That car doesn't have an LSD, but I still wouldn't do it. The dynamics are going to be messed up with a different sized tyre, and you don't want that on the driven wheels, especially when they're at the back, DSC or not.

So, it really is dynamic and performance issue, but not wear? Probably my brother may say ok since he's just using it for 'move me from A to B'. We share my G37 for fun driving

 

[DivideBYZero]

Checked it on a tyre size calculator and the difference in those tyres is:

- 6.78%

As I understand it 2.5% is considered the wiggle room, and you're way outside that.

 

[KDKPSJ]

Checked it on a tyre size calculator and the difference in those tyres is:

- 6.78%

As I understand it 2.5% is considered the wiggle room, and you're way outside that.

Hmm! I thought it would be about 2.8% (Still slight higher than your 2.5% margin, though ) according to http://www.miata.net/garage/tirecalc.html. I guess I looked at wrong number?

 

[DivideBYZero]

Hmm, yeah, I used that one and it came out at 3%. Odd.

 

[DivideBYZero]

I used this one:

http://www.etyres.co.uk/tyre-size-calculator.htm

OOPS!!!!11, it was my mistake. Running the sizes again yields 3.04%. Still, I'd just get a matching size rather than run mis-matched sizes.

 

[KDKPSJ]

I used this one:

http://www.etyres.co.uk/tyre-size-calculator.htm

OOPS!!!!11, it was my mistake. Running the sizes again yields 3.04%. Still, I'd just get a matching size rather than run mis-matched sizes.

Yay, I won!! JK

I ordered 225 45 17 RFT (I hate RFT!!! @#!%&) anyway, but since it will take about a week or two for it to be mounted (delivery time + me-have-no-time excuse) and the leaking one need replacement asap, I will mount 245 45 17 today to see if my brother can feel the difference.

 

[DivideBYZero]

Yeah, I have RFT on one of my BMWs and they do indeed suck.

 

[kevman]

don't do it duh vaal

 

[KIAman]

Switch to non RFT and buy a spare. I did and the ride and handling increased while the noise decreased.

 

[Throckmorton]

Bad idea solely because of the wear on the differential. With equal sized tires, the differential spider gears are only spinning while steering. With different sized tires they'll constantly be spinning.