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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > Wheels and Tires Forum Sponsored by The Tire Rack > run flat in the front but not the rear?



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      11-10-2012, 06:29 PM   #1
nixta325
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run flat in the front but not the rear?

Hey guys

so i have a e92 rear wheel drive
my rear tires are basically bald and my front tires are perfectly fine for a while longer.

my question is do i put non run flats in the rear while i still have run flats in the front. or do i just put run flats in the rear again? does it really matter if i have run flats in the front and regular in the rear?

My plan was to put a wider tire on my rear wheels but the run flats dont come wider than a 255 so i would have to do non run flats if i wanted to make them wider.

give me your feedback thank you

John
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      11-10-2012, 06:59 PM   #2
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personally I wouldn't do it. Either get RFTs for the rear and make the switch when they wear out, or buy four matching non-RFTs now.
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      11-10-2012, 07:39 PM   #3
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Don't do it...
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      11-10-2012, 08:01 PM   #4
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It is highly recommended not mix different kind of tires! This can lead to unsafe handling and to a possible collision!

DO NOT DO IT! Can't even imagine how the ride is with mixed RFT and non-RFT tires...
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      11-10-2012, 08:10 PM   #5
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I did it. I had non run flats in front and run flats in rear. It was fine, no problems at all. I did it because I didn't want to spent 800 on tires that keep getting nails in them. So I got 2 non run flats for the front for about 250.00 total.
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      11-10-2012, 08:20 PM   #6
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Quote:
Originally Posted by Deathkut View Post
I did it. I had non run flats in front and run flats in rear. It was fine, no problems at all. I did it because I didn't want to spent 800 on tires that keep getting nails in them. So I got 2 non run flats for the front for about 250.00 total.
This belongs in the "cheap" thread...

You, sir, are plain stupid endangering other people with that decision...
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      11-10-2012, 08:26 PM   #7
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im pretty sure its fine. go for it
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      11-10-2012, 08:59 PM   #8
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Quote:
Originally Posted by BMW_Belgier View Post
This belongs in the "cheap" thread...

You, sir, are plain stupid endangering other people with that decision...
How is he stupid? I hate it when people who don't know shit about anything comment and try to talk other people down.

A non rft/ rft mixture is safer than having bald tires.

The sidewall stiffness of an aux rft system is comparable to that of a regular tire. Self supporting tires such as bmw's system have the equivalent stiffness of a regular tire but just with some support patches built into the tires sidewall OUTSIDE of the inner wire and the beading is a bit more tough/stronger to hold the flat tire against the rim.

I'd say, go with a tire that is non rft with a stiffer sidewall than say a 'nexen' tire. i.e. nitto neo gens, etc. then when the fronts wear out replace those. Get a spare and toss it in your trunk.

I'm going with the above solution when my rft's are gone.
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      11-10-2012, 09:27 PM   #9
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I am pretty sure it is safe if done in pairs on the same axle. I personally am going to upgrade to a non run flat tire and a small 12V compressor along with AAA for a spare tire. I just dont like the ridgedness of the RFT.
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      11-10-2012, 09:30 PM   #10
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Quote:
Originally Posted by thatswhatsh3said
Quote:
Originally Posted by BMW_Belgier View Post
This belongs in the "cheap" thread...

You, sir, are plain stupid endangering other people with that decision...
How is he stupid? I hate it when people who don't know shit about anything comment and try to talk other people down.

A non rft/ rft mixture is safer than having bald tires.

The sidewall stiffness of an aux rft system is comparable to that of a regular tire. Self supporting tires such as bmw's system have the equivalent stiffness of a regular tire but just with some support patches built into the tires sidewall OUTSIDE of the inner wire and the beading is a bit more tough/stronger to hold the flat tire against the rim.

I'd say, go with a tire that is non rft with a stiffer sidewall than say a 'nexen' tire. i.e. nitto neo gens, etc. then when the fronts wear out replace those. Get a spare and toss it in your trunk.

I'm going with the above solution when my rft's are gone.
what he said.
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      11-10-2012, 10:07 PM   #11
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Quote:
Originally Posted by BMW_Belgier View Post
This belongs in the "cheap" thread...

You, sir, are plain stupid endangering other people with that decision...
Wow some people have no idea....


It is not "dangerous" to run rft in front and non-rft in rears. Its dangerous to run different sized tires on the same axle or tires with different amounts of tread remaining on the same axle. Or drive around with bald tires or have deflated tires or have a sidewall bubble or one of a million other things. The composition of the sidewall of a tire does not determine its ability to be mated with various tires on different axles.
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      11-10-2012, 10:35 PM   #12
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Search the forums, there are plenty of threads on these boards about people doing this an it introducing strange ocillations in transient maneuvers and overall "spooky" handling characteristics.

Generally, this is not a board for people that are so broke that they want to mess up their handling for a few dollars. Not worth it...
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      11-10-2012, 10:45 PM   #13
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running pirelli's RFT's in the front and continental extremecontact's in the back. No problems at all. Just make sure when they rotate the tires they don't mix them up.
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      11-11-2012, 08:24 AM   #14
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I've read threads on this topic in the Tires forum and the overwhelming response was don't do it.

I'm not an expert, but it seems like a bad idea because:
- RFT have stiffer sidewalls. That's why they provide great steering response and can support the weight of the car with no air pressure. Having RFT's in front and non-RFT in the rear will cause oversteer.
- There are usually significant differences in the ways different tires respond to various driving conditions, including dry traction, wet traction, turning, braking, etc.

If the front and rear tires respond differently to different conditions, you might not notice much in normal driving, but there might be a huge difference in emergency conditions or when you intentionally push your car. The traction and stability control systems were developed and tested assuming you have the same type of tires on both axles. I've noticed differences when I replaced the rear tires with the exact same type of tires on the front because the new tires have more tread (10/32 instead of 3/32).

But don't take my word for it. This thread will be moved to the Tires forum and you'll hear the same thing from the experts.

The OP states that he wants to put wider tires in the rear than stock. Going wider causes understeer. It's possible that the oversteer caused by the RFT/non-RFT combination will be cancelled out by the understeer of the wider tires, but it's more likely that making these changes will upset the handling balance and who knows what will happen in emergency and edge conditions.
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      11-11-2012, 10:26 AM   #15
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Quote:
Originally Posted by fenixxishot View Post
Wow some people have no idea...
Whatever...

http://www.e90post.com/forums/showthread.php?t=726185

http://www.e90post.com/forums/showth...Different+tire

http://www.e90post.com/forums/showth...Different+tire

And it goes on and on...

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      11-11-2012, 12:00 PM   #16
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Quote:
Originally Posted by nixta325 View Post
Hey guys

so i have a e92 rear wheel drive
my rear tires are basically bald and my front tires are perfectly fine for a while longer.

my question is do i put non run flats in the rear while i still have run flats in the front. or do i just put run flats in the rear again? does it really matter if i have run flats in the front and regular in the rear?

My plan was to put a wider tire on my rear wheels but the run flats dont come wider than a 255 so i would have to do non run flats if i wanted to make them wider.

give me your feedback thank you


John
All 3 series BMW's are rear wheel drive ( with the exception of optional 4WD or AWD ) with that said the rear tires can be any size you want as long as the front tires match or are smaller.

RFT do come larger than 255, I have 18" Wheels Staggered Front and Rear ( Factory option from BMW ) 245 REAR and 235 FRONT ,and yes they are RFT's.

IMO Run Flat Tires are not necessarly an ideal performace tire. I think the engineers at BMW were looking for a way to eliminate the spare tire in the trunk to make room for a battery thus providing a better weight distribution. Since the military adopted Run Flat technology the BMW egineers looked there. Just my opinion.

There are many benefits too not use the Run Flat tire There is only one benefit to running the RFT
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      11-11-2012, 01:53 PM   #17
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Quote:
Originally Posted by nixta325 View Post
does it really matter if i have run flats in the front and regular in the rear?
Not at all - UNLESS you plan to drive above 30 mph, or drive on wet roads, or encounter a situation requiring emergency maneuvers, etc., etc.

Years ago this same debate arose re mixing radials & bias ply tires and the folks who were to cheap to spring for 4 radials caused quite a few accidents.

Tom
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      11-11-2012, 02:15 PM   #18
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From Gary at Tirerack on one of threads posted by BMW_Belgier:

"Avoid mixing tires, especially run flats with non run flats. Search and find many members reporting problems when mixing the two."
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      11-11-2012, 02:31 PM   #19
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I mixed and I have not had any problems..

I'm not a fan of the RFT but 2 were brand new. Decided I'd replace the 2 worn out ones and see how I got on. Never had any issues.. so I left it. I would have just replaced them if I felt I had needed to.

I will ditch the other RFT's when they need replacing.
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      11-11-2012, 03:28 PM   #20
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Quote:
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I mixed and I have not had any problems..
No problems yet - but your car is an accident waiting to happen...

Tom
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      11-11-2012, 04:24 PM   #21
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I don't see how it would be an issue if you invested in a ultra high performance tire like a star spec, rs3, or RE-11 that are designed for autox and light track days. These have super stiff sidewalls for top handling under heavy point loads. These may not be as stiff as a RFT but they are certainly more stiff than most performance tires.

Personally I'm investing in Dunlop Star Specs once my RFTs are out. I've had track and autox experience with these and they perform like crazy and have great tread life.


With that being said; I do agree that running regular summer tires would be unsafe because they will roll over before the rears in a turn causing a violent oversteer

Last edited by GOTMH8N; 11-11-2012 at 04:29 PM.
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      11-11-2012, 07:22 PM   #22
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Quote:
Originally Posted by Deathkut
I did it. I had non run flats in front and run flats in rear. It was fine, no problems at all. I did it because I didn't want to spent 800 on tires that keep getting nails in them. So I got 2 non run flats for the front for about 250.00 total.
So stupid!
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