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[Grale]

So i have purchased some 19" cls rep alloys, i have just started getting around to putting my tires on.

I went to my local garage ATS and the guy started looking at my current wheels/tyres... No mate you can't put these on here.. your braking distance/ suspension will be all to cock!! the suspension is set up softer for runflats he said.

What he has been told from BMW is that you cannot put non runflats on a car that has them fitted as standard. he told me in a rather smug tone i'm just telling you but obviously we know nothing, and disapeared shaking his head into the back.

What the hell was that all about, is there any truth to this?

[Express]

hes full of it

[ceb]

Originally Posted by Grale

So i have purchased some 19" cls rep alloys, i have just started getting around to putting my tires on.

I went to my local garage ATS and the guy started looking at my current wheels/tyres... No mate you can't put these on here.. your braking distance/ suspension will be all to cock!! the suspension is set up softer for runflats he said.

What he has been told from BMW is that you cannot put non runflats on a car that has them fitted as standard. he told me in a rather smug tone i'm just telling you but obviously we know nothing, and disapeared shaking his head into the back.

What the hell was that all about, is there any truth to this?

Technically he is correct. The BMW suspension design takes the RFTs into consideration.

That said, many people have swapped to non-RFT without too many issues.

What can happen?

You might have warranty issues. Not very common but a dealer could refuse warranty service on the suspension because of the tires and/or aftermarket wheels.

You'll have to figure out what to do about a spare.

BMW roadside assist may give you grief

[HighlandPete]

BMW will always advise staying with RFTs, that is their policy. But you can pick it to pieces, as they also offer a range of wheel options on some cars. Which is the car designed for? Or is it about compromises? Even some vehicles can be specced for the UK without RFTs and you can tick a box for RFTs, without suspension changes. So which tyres are the car designed for?

In reality, even some BMW dealers will fit non run-flats and have no issues with customers choosing alternative high performance tyres to the correct load/speed ratings. Often flag up the negatives, like the lack of spare, etc.

There is a cautionary thought, later model cars typically have softer suspensions, partly to sort the harsh ride issues with RFTs, so a softer tyre will possibly change the dynamic characteristics a bit more on these models than the earlier examples, which almost to a driver, improved the ride and control characteristics in a beneficial way. So we do need to know why we are changing tyre types and/or what compromises we can expect.

There was a BMW/Bridgestone demo (well documented) where they ran different tyres on standard 5-series cars. The test including a standard non run-flat, current and 3rd generation RFTs. The goal, to prove the 3rd generation RFT is as good as a standard 'non run-flat'. If the conventional tyre is a "no no", what were they doing trying to get the car to run like on a normal tyre? To me, as an engineer, that was the "final home goal", "shot themselves in the foot" that RFTs are the ONLY tyre to have on a BMW, as even BMW are trying to get back to the real characteristics of a normal tyre on their production setup.

I've questioned the "designed for RFTs" from their introduction, as they made many BMW examples, half the BMW they are without them, more "compromised for RFTs" has proven to be the case.

HighlandPete

[Grale]

Interesting reading Pete. I was thinking about the suspension setups on e90's, my car is an e90 Msport so it has different suspension than a standard e90, i don't know the differences tbh I'm guessing harder setup and msport sits lower than standard!
So how does that relate to the runflats that are on two different setups but on basically the same car except for the Msport package?

Sorry if typed incorrectly from my iPhone

[driverman]

I have an E90 328i with ZSP. It came with Bridgestone RFT's. I wore them out, went through a set of PS2's and now have DW's.

BMW designed, built, tested and tuned the suspension, wheels and tires to work together under a wide range of conditions. As soon as we change any of those components, we change the balance. The question is how and by how much?

My car felt the most planted and responsive on smooth roads with the RFT's, but the ride was terrible on rough roads, the car hopped around during turns on rough roads, the RFT's were hard to repair, they didn't last long, they were expensive and they were heavy. Look at these weight differences:

RFT's front:28 lbs/rear:30 lbs = 116 lbs
PS2's front:23 lbs/rear:24 lbs = 94 lbs
DW's: front:20 lbs/rear:23 lbs = 86 lbs

Changing from RFT's to DW's means softer sidewalls and 7-8 pounds less per tire. I can definitely feel the difference in terms of ride (better), noise (better) and steering response (worse). But the overall handling is still excellent and the car feels quicker. But I'm now using a suspension that was designed, built, tested and tuned for RFT's with tires that have very different characteristics. Every time I go over a bump, the suspension has to respond to a wheel/tire combination that's 7-8 pounds lighter than it was designed to work with. Every time I go into a turn, the suspension has to work with sidewalls that are much softer than it was designed to work with. And what are the differences "at that limit" and under emergency braking? I don't know.

[Fozzy]

good info. here. To add my 2 cents, a suspension also changes over time, so riding on a suspension with 100K miles on it will respond differently than a new one. This could influence the ride as much other variables. There is variance when altering any set ups the question which is likely unquantifiable is how much? ie: what about aftermarket suspension + non RFT; many would argue this is better than stock.

[mycoupe]

Whether or not the changes from switching are good or bad are entirely up to the person driving the car. Some people like understeer, some like oversteer...who is right and which is better? Neither, per se. It all depends on what you want out of the car.

[MassBimmer]

I would venture to say that over 75% of people on this forum have already switched to non runflats...it's really not an issue at all

[ceb]

Originally Posted by driverman

I have an E90 328i with ZSP. It came with Bridgestone RFT's. I wore them out, went through a set of PS2's and now have DW's.

BMW designed, built, tested and tuned the suspension, wheels and tires to work together under a wide range of conditions. As soon as we change any of those components, we change the balance. The question is how and by how much?

My car felt the most planted and responsive on smooth roads with the RFT's, but the ride was terrible on rough roads, the car hopped around during turns on rough roads, the RFT's were hard to repair, they didn't last long, they were expensive and they were heavy. Look at these weight differences:

RFT's front:28 lbs/rear:30 lbs = 116 lbs
PS2's front:23 lbs/rear:24 lbs = 94 lbs
DW's: front:20 lbs/rear:23 lbs = 86 lbs

Changing from RFT's to DW's means softer sidewalls and 7-8 pounds less per tire. I can definitely feel the difference in terms of ride (better), noise (better) and steering response (worse). But the overall handling is still excellent and the car feels quicker. But I'm now using a suspension that was designed, built, tested and tuned for RFT's with tires that have very different characteristics. Every time I go over a bump, the suspension has to respond to a wheel/tire combination that's 7-8 pounds lighter than it was designed to work with. Every time I go into a turn, the suspension has to work with sidewalls that are much softer than it was designed to work with. And what are the differences "at that limit" and under emergency braking? I don't know.

HUH?????

Do you really think that psi = weight?

[HighlandPete]

If we go back to 3-series basics we can have, as an example, a sedan (ES saloon in the UK) on 16" wheels with non runflats or runflats, 17" runflats, 18" runflats, all setups with or without sport suspension.

Move on to the M-sport models and you can have 17" and 18" wheels fitted with run flats, plus you can delete the M-sport suspension on each wheel size, so again a set of variables.

We clearly know that the vehicles will have very different chassis characteristics with those variable and combinations. All approved by BMW, but certainly different to drive.

HighlandPete

[chromisdesigns]

Short answer, he's full of hot air. Many, if not most, BMW owners eventually ditch the runflats. Most who do are happy with the results. You will certainly have improved ride, and less jumping around on bumpy turns. You get a repairable tire. You may or may not like the softer turn-in -- I personally like it, but some miss the crisper turn-in with runflats. Overall, I think the handling improved when I ditched the runflats, mainly because the tires are now in contact with the road all the time, instead of jumping up in the air every time they hit a bump!

You defitinitely WON'T miss the slamming, hopping, and tooth-shattering ride of the runflats.

BMW assist doesn't care whether you have runflats or not.

You might want to consider a compact spare kit or fix-a-flat with a 12v compressor if you go conventional.

[ceb]

Originally Posted by chromisdesigns

Short answer, he's full of hot air. Many, if not most, BMW owners eventually ditch the runflats. Most who do are happy with the results. You will certainly have improved ride, and less jumping around on bumpy turns. You get a repairable tire. You may or may not like the softer turn-in -- I personally like it, but some miss the crisper turn-in with runflats. Overall, I think the handling improved when I ditched the runflats, mainly because the tires are now in contact with the road all the time, instead of jumping up in the air every time they hit a bump!

You defitinitely WON'T miss the slamming, hopping, and tooth-shattering ride of the runflats.

BMW assist doesn't care whether you have runflats or not.

You might want to consider a compact spare kit or fix-a-flat with a 12v compressor if you go conventional.

Incorrect. The tire person was technically correct. That is a fact, not opinion.

[CombatNinja]

Originally Posted by ceb

HUH?????

Do you really think that psi = weight?

That is not PSI he is quoting but the actual WEIGHT of the tyres. Runflats are always the heaviest in any given size. I'll bet you could increase fuel economy by over 1mpg just by dropping all of that unsrprung weight.

[chromisdesigns]

Originally Posted by ceb

Incorrect. The tire person was technically correct. That is a fact, not opinion.

Nope, the guy told the OP he "could not put conventional tires" on his car -- that's patently false. Plenty of people do and it works fine; better in many people's opinion!

Yes, BMW "designed" the suspension for runflats, whatever that means, but in the real world the design combination sucks on ride, tire life, tire maintenance, and cost.

And I still maintain (as do many others) that conventional tires handle BETTER in turns on bad roads, because they aren't hopping around like demented bunnies on meth -- which is exactly what the OEM runflats do.

When I got my 335, it scared the crap out of me the first time I took a fast sweeper over bad pavement -- the runflats were literally hopping sideways in the air. A good set of conventional Michelins cured THAT horror show real quick.

[ceb]

Originally Posted by chromisdesigns

Nope, the guy told the OP he "could not put conventional tires" on his car -- that's patently false. Plenty of people do and it works fine; better in many people's opinion!

Yes, BMW "designed" the suspension for runflats, whatever that means, but in the real world the design combination sucks on ride, tire life, tire maintenance, and cost.

And I still maintain (as do many others) that conventional tires handle BETTER in turns on bad roads, because they aren't hopping around like demented bunnies on meth -- which is exactly what the OEM runflats do.

When I got my 335, it scared the crap out of me the first time I took a fast sweeper over bad pavement -- the runflats were literally hopping sideways in the air. A good set of conventional Michelins cured THAT horror show real quick.

Re-read the OP's first message. The tire guy said "you can't use conventional tires...because the suspension is set up for RFTs."

That is technically correct.

I also don't see an option on the UK order guide for non-RFTs. BMW uses RFTs for all western countries and much of the developing world. I'm sure that there are some markets where nonRFTs are used but the UK doesn't seem to be amongst them.

Can you use conventional tires? Of course, and many people do, but the BMW suspension is designed for the stiffer sidewall.

[ceb]

Originally Posted by CombatNinja

That is not PSI he is quoting but the actual WEIGHT of the tyres. Runflats are always the heaviest in any given size. I'll bet you could increase fuel economy by over 1mpg just by dropping all of that unsrprung weight.

Ah. That makes more sense. How much of that unsprung weight saving is offset by the weight of a jack and spare?

[HighlandPete]

Originally Posted by ceb

Re-read the OP's first message. The tire guy said "you can't use conventional tires...because the suspension is set up for RFTs."

That is technically correct.

I also don't see an option on the UK order guide for non-RFTs. BMW uses RFTs for all western countries and much of the developing world. I'm sure that there are some markets where nonRFTs are used but the UK doesn't seem to be amongst them.

Can you use conventional tires? Of course, and many people do, but the BMW suspension is designed for the stiffer sidewall.

There are definitely models (not all) that can have have non run-flat and run-flat options in the UK. I use the 3-series example because this definitely exists and has caused some questioning in the UK on BMW's exact position on suspension vs. tire specification.

HighlandPete

[Fozzy]

None is offset. Who is carrying a spare? Is on the roof? Tire patch kit or BMW assist are the options. The reality is that unless you're in a major city you won't be able to drive to a tire shop that stocks run flats. So the ability to drive 30-80 miles on a blown runflat isn't always a saviour.

Originally Posted by ceb

Ah. That makes more sense. How much of that unsprung weight saving is offset by the weight of a jack and spare?

[therealm3]

Originally Posted by ceb

Ah. That makes more sense. How much of that unsprung weight saving is offset by the weight of a jack and spare?

none. Jack and spare are not part of the suspension.

FWIW - I switched to PS2's when my RFT's ran out and I have been very happy. The spare kit I got from bav auto actually doesn't take up that much space in the trunk at all.

[ceb]

Originally Posted by HighlandPete

There are definitely models (not all) that can have have non run-flat and run-flat options in the UK. I use the 3-series example because this definitely exists and has caused some questioning in the UK on BMW's exact position on suspension vs. tire specification.

HighlandPete

Could you point me to that on the BMW UK website because I can't find it. BMW Germany tells me that option does not exist in the UK.

[ceb]

Originally Posted by Fozzy

None is offset. Who is carrying a spare? Is on the roof? Tire patch kit or BMW assist are the options. The reality is that unless you're in a major city you won't be able to drive to a tire shop that stocks run flats. So the ability to drive 30-80 miles on a blown runflat isn't always a saviour.

If you are comparing apples to apples then you need to add the weight of a spare and jack.

I can lighten the weight of my car by removing lots of bits but most cars come with temporary spares if they don't have RFTs.