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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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      11-11-2012, 10:02 PM   #23
idrift4wd
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This makes no sense. Its recommended to have all tires matching, but not mandatory.

The car will drive fine under normal driving conditions. Of course the possibility of getting a flat on the two non-rft, but it really wont make a huge difference. RFT are heavier then non-rft. If that is your situation then go for it. if you have the money then of course match them. You're not going to die or mess up any mechanical like these people make it seem.
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      11-12-2012, 05:41 PM   #24
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Quote:
Originally Posted by idrift4wd View Post
This makes no sense. Its recommended to have all tires matching, but not mandatory.

The car will drive fine under normal driving conditions. Of course the possibility of getting a flat on the two non-rft, but it really wont make a huge difference. RFT are heavier then non-rft. If that is your situation then go for it. if you have the money then of course match them. You're not going to die or mess up any mechanical like these people make it seem.


i mixed my tires (non run flats in rear) and at a gas station a cute chick noticed my bad ass ET streets in the rear and started asking about my car We ended up going for a drink and i went home with her. In the morning i left her place and got in a wreck bcuz the front tires felt like they were floating when i raced a street bike from a red light. It was a little wet out. Anyway the cars in the shop, i got a ticket for reckless driving and my wife found out about the girl bcuz she wrote "call me" in lipstick on my dash board. I must have been pretty drunk.

So yea, OP i wouldnt do it
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      11-12-2012, 06:53 PM   #25
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Runflat tires aren't made out of some magical, technologically advanced material that controls every aspect of your handling. If it was, every tire would be made out of it, because they are virtually the same. A runflat tire is designed to be driven approximately 50 miles at 50mph or less with little or no air pressure "safely". Driving any tire without air in it will cause the tire liner to breakdown and shred from rubbing against itself leaving a lovely smelling ground rubber.

Runflat tires are not designed to support the weight of the vehicle, the air inside them is, runflat tires are designed to have thicker material so that when you drive on them flat they don't immediately shred away and could make it down the road a ways. Several if they are punctured at all are completely ruined because they can no longer fulfill that purpose.

Mixing run flat tires and non runflat tires is not dangerous in the least, mixing performance rated tires or models of tires across the same axle can be dangerous, but no more than having a wheel out of alignment. The weird feeling that people may be experiencing by mixing tires could possibly be related to the difference people feel in running nitrogen in their tires, completely in their heads.
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      11-12-2012, 11:12 PM   #26
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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...
Quote:
Originally Posted by CombatNinja View Post
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...
Quote:
Originally Posted by driverman View Post
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.
Quote:
Originally Posted by Tom K. View Post
No problems yet - but your car is an accident waiting to happen...

Tom
Quote:
Originally Posted by 335dM View Post
So stupid!
You guys are all f^%&*#$ retarded... Seriously. Just stop. It's annoying the living sh*t out of me reading all of these responses. Go for it OP. Adding a non-RFT to the rear would most likely make every single numnuts above me safer. Your car will understeer more, that's all. If you tracked your car it wouldn't be a good idea, but only b/c the boat would understeer even more.
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Last edited by Sauce; 11-15-2012 at 11:47 PM.
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      11-13-2012, 06:23 PM   #27
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Quote:
Originally Posted by Sauce View Post
You guys are all f^%&*#$ retarded... Seriously. Just stop. It's annoying the living sh*t out of me reading all of these responses. Go for it OP. Adding a non-RFT to the rear would most likely make every single numnuts above me safer. Your car will understeer more, that's all. If you tracked your car it wouldn't be a good idea, but only b/c the boat would understeer even more. However, if you tracked your car you wouldn't be asking this question so your good!!!
http://www.tirerack.com/tires/tirete...jsp?techid=136

http://www.conti-online.com/generato...nd-mixing.html

http://us.coopertire.com/Tire-Safety...re-Mixing.aspx

And this one from the official TüV side:

http://reifentest.popgom.de/reifenwe...e-vorschriften

I'm not making this up guys... Sure your car will not break out the first corner but would you drive a car that has a 1% chance that the breaks stop working...
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      11-14-2012, 01:13 PM   #28
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Quote:
Originally Posted by BMW_Belgier View Post
http://www.tirerack.com/tires/tirete...jsp?techid=136

http://www.conti-online.com/generato...nd-mixing.html

http://us.coopertire.com/Tire-Safety...re-Mixing.aspx

And this one from the official TüV side:

http://reifentest.popgom.de/reifenwe...e-vorschriften

I'm not making this up guys... Sure your car will not break out the first corner but would you drive a car that has a 1% chance that the breaks stop working...
The brakes are going to stop working if you put non rft's on the rear? Wow, just wow..
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      11-14-2012, 01:48 PM   #29
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Quote:
Originally Posted by BMW_Belgier View Post
Sure your car will not break out the first corner but would you drive a car that has a 1% chance that the [brakes] stop working...
Quote:
Originally Posted by Sauce View Post
The brakes are going to stop working if you put non rft's on the rear? Wow, just wow..
I think he's using an "analogy" here. i.e. since we wouldn't choose to drive a car that we knew had iffy brakes, why would we drive a car with iffy tires?

I don't know enough to offer my opinion on mixing RFT with go-flats, but I hope this at least clarifies BMW_Belgier's post before everyone goes down the wrong road.
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      11-14-2012, 02:05 PM   #30
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Quote:
Originally Posted by gpb View Post
I think he's using an "analogy" here. i.e. since we wouldn't choose to drive a car that we knew had iffy brakes, why would we drive a car with iffy tires?

I don't know enough to offer my opinion on mixing RFT with go-flats, but I hope this at least clarifies BMW_Belgier's post before everyone goes down the wrong road.
THX

That is correct, my english just isn't my mother language...
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      11-14-2012, 02:45 PM   #31
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Quote:
Originally Posted by BMW_Belgier View Post
That is correct, my english just isn't my mother language...
You're doing better than a lot of native English speakers.

For what it's worth, brakes are different from breaks although both are nouns. Just to be even more confusing, break is also a verb that means something different from the noun of the same spelling. At least the word brake is a little more sane in that your brakes are what allow you to brake, hopefully allowing you to stop your car.

Confused yet?
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      11-14-2012, 04:10 PM   #32
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i tried to warn you guys

lost the car, bunch of money and the wife over it.
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      11-15-2012, 07:46 PM   #33
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Quote:
Originally Posted by gpb View Post
You're doing better than a lot of native English speakers.

For what it's worth, brakes are different from breaks although both are nouns. Just to be even more confusing, break is also a verb that means something different from the noun of the same spelling. At least the word brake is a little more sane in that your brakes are what allow you to brake, hopefully allowing you to stop your car.

Confused yet?
THX I really try but it isn't always easy...

So guys (and ladies), all those sites of tire testers, manufacturers and official safety testers are all making this up? Convince me with facts that mixing RFT and non-RFT is completly safe!

I gave you enough info saying it's not safe...
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      11-15-2012, 08:30 PM   #34
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Quote:
Originally Posted by Sauce View Post
You guys are all f^%&*#$ retarded... Seriously. Just stop. It's annoying the living sh*t out of me reading all of these responses. Go for it OP. Adding a non-RFT to the rear would most likely make every single numnuts above me safer. Your car will understeer more, that's all. If you tracked your car it wouldn't be a good idea, but only b/c the boat would understeer even more. However, if you tracked your car you wouldn't be asking this question so your good!!!
Know how I can tell you don't know what you're talking about?
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      11-15-2012, 11:43 PM   #35
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Quote:
Originally Posted by CombatNinja View Post
Know how I can tell you don't know what you're talking about?
Tell me!
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      11-16-2012, 04:51 PM   #36
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Just make sure you're not mixing on the same axle
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      11-17-2012, 08:16 AM   #37
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Quote:
Originally Posted by Sauce View Post
Tell me!
Fitting runflats vs. regular tires on the front of a car has absolutely no relationship to how much understeer the car will end up with. Every tire, properly inflated, will have its own performance envelope based on compound, tread design, tread depth and load. Knowing simply that the front tires are runflats and the rears are not is not sufficient information to determine that the car will have increased understeer.
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      11-17-2012, 02:38 PM   #38
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Quote:
Originally Posted by CombatNinja View Post
Fitting runflats vs. regular tires on the front of a car has absolutely no relationship to how much understeer the car will end up with. Every tire, properly inflated, will have its own performance envelope based on compound, tread design, tread depth and load. Knowing simply that the front tires are runflats and the rears are not is not sufficient information to determine that the car will have increased understeer.
Wow you got me there...

Actually no, that's a huge backfire on yourself. To simplify what you just said, having different tires front to rear has no effect on handling balance. Even more retarded than any of the previous retarded retardedness. Even a sh*tty non rft like Hankook V12's are much grippier than stockers.
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      11-17-2012, 02:54 PM   #39
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Quote:
Originally Posted by Sauce View Post
Wow you got me there...

Actually no, that's a huge backfire on yourself. To simplify what you just said, having different tires front to rear has no effect on handling balance. Even more retarded than any of the previous retarded retardedness. Even a sh*tty non rft like Hankook V12's are much grippier than stockers.
as i do agree mixing rft and non doesnt make a difference.

there are performance RFT that also grip better then oems. Idk how understeer would work into how the car handles. the tire is heavier, but in terms of grip, i dont see how rft and non rft are that much different.
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      11-17-2012, 03:07 PM   #40
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Originally Posted by idrift4wd View Post
as i do agree mixing rft and non doesnt make a difference.

there are performance RFT that also grip better then oems. Idk how understeer would work into how the car handles. the tire is heavier, but in terms of grip, i dont see how rft and non rft are that much different.
I'm just assuming that rft means the stock tires. They are expensive, heavy and generally don't perform as well. I'm not sure which run flat tire you are referring to, but I agree that they can do their job just fine. But at the end of the day anyone interested in serious performance is going to have a non run flat tire on their car.
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      11-17-2012, 04:26 PM   #41
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So please explain to us then how fitting stock RFTs up front and regular tires out back will, by default, result in significantly more understeer. I'm all ears...
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      11-17-2012, 06:59 PM   #42
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Quote:
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So please explain to us then how fitting stock RFTs up front and regular tires out back will, by default, result in significantly more understeer. I'm all ears...
Do you understand the basics of car dynamics?

More grip in the rear means the front washes out first aka understeer. Or in your case you'll hit the wall going straight.

More grip in the front means the rear will give up first aka oversteer. Or again, in your case, you will hit the wall backwards in a big cloud of smoke.

And once more, it is a VERY safe assumption to assume the non rft tires are grippier.
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      11-17-2012, 08:02 PM   #43
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Quote:
Originally Posted by Sauce View Post

And once more, it is a VERY safe assumption to assume the non rft tires are grippier.

Ummmm, okay...

You are an idiot.

KTHXBYE
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      11-17-2012, 08:06 PM   #44
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Quote:
Originally Posted by Sauce View Post
Do you understand the basics of car dynamics?

More grip in the rear means the front washes out first aka understeer. Or in your case you'll hit the wall going straight.

More grip in the front means the rear will give up first aka oversteer. Or again, in your case, you will hit the wall backwards in a big cloud of smoke.

And once more, it is a VERY safe assumption to assume the non rft tires are grippier.
Thats totally understood, but all that matters is the how much thread the wheel has, how much thread is touching the road, stickness of the tire, and the tire compound. What if the car it self is prone to over steer?

RFT only change the structure of how the tire is made. RFT are much heavier so they might not perform as well, but not a difference anyone can tell daily driving on it. Track is a different story.

Oem tires on m3 are RFT michelin pilot sport 2 and it handles amazing.
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