Runflats front Non Runflats rear?

[NickBMWZ4]

Hello.

I’m sure this has come up before and I’ve had a hunt but unable to find the correct answer.

I’m currently on 19” 235/35 front 255/30 rear. Bridgestone Potenza RFT’s
My rear tyres need replacing (squeaking at low speeds) and I want to move over the non runflats because of the horrendous ride quality.
Anyone had any experience of having the mix?
I’ve ruled out changing to 35 profile on the rear even though I’d love to fill the arches a little more.

Nick

 

[road warrior]

you are dicing with danger mixing the two, get your wallet out and do it properly

 

[Jembo]

you are dicing with danger mixing the two, get your wallet out and do it properly

+1 & fresh rubber all round really does make a huge difference

 

[mr wilks]

Interested to hear why have you ruled out 255 35 19 rear ? If you are on oe rims the fronts are technically "wrong" as they should be 225 35 so adding 255 35 rears would be no concern
As for the mixing , if the fronts are way off replacing that suggests plenty of tread , if so they are worth decent money so sell those & help fund a replacement set of 4 matching non runflats which are considerably cheaper than rftS .
As for the answer to your original question , ive done it a few times when trading wheelsets , mainly to explode myths & see for myself :wink: nothing happened no lights flashed , no strange steering occurred & i never felt like i was riding a rodeo blindfold obviously i wasn't doing trackdays or maxxing out on the autobahn

 

[john-e89]

you are dicing with danger mixing the two, get your wallet out and do it properly

Hmmm...can’t see it tbh RW, it’s not like mixing crossply and radials. You’ve the same quality tyre with, say, an OEM Bridgestone runflat, same tread, they’re just reinforced. If the pressures are correct I don’t see any particular problem, although both axles running all the same tyres is ultimately preferable.

 

[Smartbear]

I’ve run this concoction on my e89, still stable & handled well over a broad range of driving conditions
Rob

 

[NickBMWZ4]

Interested to hear why have you ruled out 255 35 19 rear ? If you are on oe rims the fronts are technically "wrong" as they should be 225 35 so adding 255 35 rears would be no concern
As for the mixing , if the fronts are way off replacing that suggests plenty of tread , if so they are worth decent money so sell those & help fund a replacement set of 4 matching non runflats which are considerably cheaper than rftS .
As for the answer to your original question , ive done it a few times when trading wheelsets , mainly to explode myths & see for myself :wink: nothing happened no lights flashed , no strange steering occurred & i never felt like i was riding a rodeo blindfold obviously i wasn't doing trackdays or maxxing out on the autobahn

Interested to hear why have you ruled out 255 35 19 rear ? If you are on oe rims the fronts are technically "wrong" as they should be 225 35 so adding 255 35 rears would be no concern
As for the mixing , if the fronts are way off replacing that suggests plenty of tread , if so they are worth decent money so sell those & help fund a replacement set of 4 matching non runflats which are considerably cheaper than rftS .
As for the answer to your original question , ive done it a few times when trading wheelsets , mainly to explode myths & see for myself :wink: nothing happened no lights flashed , no strange steering occurred & i never felt like i was riding a rodeo blindfold obviously i wasn't doing trackdays or maxxing out on the autobahn

Yes you’re right, they’re 225 at the front and yes selling them on eBay is a good idea.

 

[NickBMWZ4]

Thanks all. I’m a newbie to this forum and great to get such a quick reply.

I’m not sure what difference it makes but I read that increasing the profile on the rear makes them quite a bit larger then the front due to their tyre width.

 

[Smartbear]

Thanks all. I’m a newbie to this forum and great to get such a quick reply.

I’m not sure what difference it makes but I read that increasing the profile on the rear makes them quite a bit larger then the front due to their tyre width.

Yep, it’s a formula-the profile is a percentage of the tyres width giving the tyres height in mm.
So a 225/35/19 gives a profile (tyre height) of 78.75mm
Rob

 

[road warrior]

you are dicing with danger mixing the two, get your wallet out and do it properly

Hmmm...can’t see it tbh RW, it’s not like mixing crossply and radials. You’ve the same quality tyre with, say, an OEM Bridgestone runflat, same tread, they’re just reinforced. If the pressures are correct I don’t see any particular problem, although both axles running all the same tyres is ultimately preferable.

fair enough but the main reason folk bin runflats is the ride quality and if you still have 50% crap ride.....
I will bow to public opinion but it's not something I would do personally

 

[Jembo]

you are dicing with danger mixing the two, get your wallet out and do it properly

Hmmm...can’t see it tbh RW, it’s not like mixing crossply and radials. You’ve the same quality tyre with, say, an OEM Bridgestone runflat, same tread, they’re just reinforced. If the pressures are correct I don’t see any particular problem, although both axles running all the same tyres is ultimately preferable.

fair enough but the main reason folk bin runflats is the ride quality and if you still have 50% crap ride.....
I will bow to public opinion but it's not something I would do personally

For much of the time as many say won’t notice much difference - they’re both a round bit of rubber.

It’s the 5% when all hell breaks loose - Personally, I spend money on the same high quality tyres for the point RW mentions, they’re dynamically different & in an emergency won’t be consistent.

It’s a personal preference, where knowing you’re relying on only 4 small bits of rubber the size of your hand I want this area to perform as best as physically possible in those extreme emergency stress situations.

I suppose it also comes down to the view an insurer would take were you to be involved in an accident.

 

[Smartbear]

Hmmm...can’t see it tbh RW, it’s not like mixing crossply and radials. You’ve the same quality tyre with, say, an OEM Bridgestone runflat, same tread, they’re just reinforced. If the pressures are correct I don’t see any particular problem, although both axles running all the same tyres is ultimately preferable.

fair enough but the main reason folk bin runflats is the ride quality and if you still have 50% crap ride.....
I will bow to public opinion but it's not something I would do personally

For much of the time as many say won’t notice much difference - they’re both a round bit of rubber.

It’s the 5% when all hell breaks loose - Personally, I spend money on the same high quality tyres for the point RW mentions, they’re dynamically different & in an emergency won’t be consistent.

It’s a personal preference, where knowing you’re relying on only 4 small bits of rubber the size of your hand I want this area to perform as best as physically possible in those extreme emergency stress situations.

I suppose it also comes down to the view an insurer would take were you to be involved in an accident.

My car passed an MOT with that set up, so it was road legal
Rob

 

[Anonymous]

A few points..

A cars handling behaviour is created by many variables working in unison, the manufacturer takes a slice trough all these variables..so by now many Zs are not on the same datum points..wheel sizes changed, wheel offset, steering geometry, tyres sizes, tyre types, springs, shock absorbers etc etc ...so by that stage it’s almost impossible to attribute handling foibles to any one thing conclusively..you can only do it for sure by rebasing the car to original and just making one change at a time then seeing what happens...often it’s the compound effect of all the changes over the life of the car that then pushes it over the edge..

In the 1970s quite a lot of research went into motorcycle stability as policeman were being spat off their BMW bikes..it was found that the situation was created by compound variables and a relatively minor change in one could result in a previously stable bike going highly unstable..

On the other hand given that E89s can run highly asymmetric wheel sizes it seems strange how the size of a tyre changing in size could effect things so badly...more likely the tread pattern changing is an issue..

As an aside Continental have developed a tyre the Sports Contact 5P that is specifically orientated to assymettic set ups and claims a ‘15%’ improvement in dry handing as a result when compared to the Sports Contact 3 tyre..

 

[Nictrix]

In the 1970s quite a lot of research went into motorcycle stability as policeman were being spat off their BMW bikes..it was found that the situation was created by compound variables and a relatively minor change in one could result in a previously stable bike going highly unstable..

I thought the main issue was that the BMWs they used were not designed to carry the weight that the police strapped onto it and the bikes were unstable at speed. They were basically top heavy and the weight was in the wrong places. They were then limited to what speed they were allowed to do until they fixed the problem.

 

[road warrior]

fair enough but the main reason folk bin runflats is the ride quality and if you still have 50% crap ride.....
I will bow to public opinion but it's not something I would do personally

For much of the time as many say won’t notice much difference - they’re both a round bit of rubber.

It’s the 5% when all hell breaks loose - Personally, I spend money on the same high quality tyres for the point RW mentions, they’re dynamically different & in an emergency won’t be consistent.

It’s a personal preference, where knowing you’re relying on only 4 small bits of rubber the size of your hand I want this area to perform as best as physically possible in those extreme emergency stress situations.

I suppose it also comes down to the view an insurer would take were you to be involved in an accident.

My car passed an MOT with that set up, so it was road legal
Rob

im not sure tyre spec is part of an mot above tread depth and damaged sidewalls

 

[Smartbear]

For much of the time as many say won’t notice much difference - they’re both a round bit of rubber.

It’s the 5% when all hell breaks loose - Personally, I spend money on the same high quality tyres for the point RW mentions, they’re dynamically different & in an emergency won’t be consistent.

It’s a personal preference, where knowing you’re relying on only 4 small bits of rubber the size of your hand I want this area to perform as best as physically possible in those extreme emergency stress situations.

I suppose it also comes down to the view an insurer would take were you to be involved in an accident.

My car passed an MOT with that set up, so it was road legal
Rob

im not sure tyre spec is part of an mot above tread depth and damaged sidewalls

If you presented an illegal mix such as cross ply & radials on the same axle they would fail the car.
I don’t think it’s illegal to run runflats & non rf tyres front/rear :?
Rob

 

[Jembo]

Maybe a question for our resident Mr. Flux

 

[Busterboo]

... I don’t think it’s illegal to run runflats & non rf tyres front/rear :?
Rob

But not ideal, Rob. So why compromise?

 

[vld]

I don't change tires on an axle unless they are worn out. I currently run with RF on front and NRF on back. Still more comfort and no difference in handling. I drive fast (up to 200km/h where legal), I break short and corner aggressively. In my opinion, the only difference there is is about how they handle a puncture, nothing more.

 

[Anonymous]

Various statements from tyre suppliers...and manufacturers...I think I know which side the insurance companies would go with in a big fatal...your personal opinion or the suppliers ... :thumbsdown:

‘You’ll have safer handling and prevent damage to other parts of your car when all four tires on your vehicle match closely in type, tread depth and size. This is not the case when you mix and match run-flat tires with standard tires. Here’s why.

Run-flat tires (RFTs) are built with reinforced sidewalls, which make them a lot stiffer. This is why they can be driven between 50 and 100 miles (depending on the type) at about 50 mph with low or no air.

Difference between a run-flat and standard tire.

When there’s a big difference between your front and rear tires’ sidewall flex, your car’s handling will be imbalanced. You won’t have proper stability, especially when you need it most: around corners, at highway speeds and when swerving.

Due to the way they’re made, RFTs typically wear out long before standard tires. If you mix and match, you may end up with significant differences in tire tread depth between your front and rear axles. This could result in other problems if you replace only the two worn-out tires.’


‘Mixing Conventional Tyres with Run Flat Tyres

As a general rule of thumb, you should avoid mixing different tyre types on a vehicle. This is also true of combining conventional and run flat tyres on a car – as their handling characteristics may differ, they should not be mixed on a vehicle.’


‘Can I Mix Tires?

As a general rule, tires should not be mixed on any vehicle unless specified as acceptable by the tire or vehicle manufacturer. Drivers should avoid mixing tires with different tread patterns, internal constructions or sizes (unless front and rear staggered sizes are specified by the vehicle manufacture), and use identical tires on all of their vehicle's wheel positions in order to maintain the best control and stability. Additionally, drivers should never mix winter tires with all-season/summer tires, or mix run-flat tires with non-run-flat tires.’