BMW F10 - New tyres & Warning lights

cw212010

Hi all,

Had a blow out on the back end last night, no damage to the car.

Decided to just grab some part worns this morning and put a pair on the back. These are non run flat and are 225/45/17 rather than 225/55/17 that was on before. A set of run flat 55's are still on the front.

As a result, I'm hit with faults on iDrive. Parking brake failure, pedestrian protection system, flat tyre monitor, brake system (all amber) and a red restraint system warning, loss of power, TC light when gently applying power, tight steering, loss of speedo.

I can only assume this is just the car noticing the difference between the front and rear size difference.

I can either take these tyres back and have 55's put back on, or I can (and would prefer to) put 45's on the front as they look better.

Can anyone see this being a problem and is this the likely error of the faults? If I deactivate the DSC traction control I suffer no errors.

daveyjp

The reason for the errors is due to rolling radius errors between front and back wheels. The car thinks the rears are going quicker than the fronts and will compensate by using the DSC.

Change the rears to brand new 55 profiles and all will be well. Don't change tyres because they look better, can you see the when in the car.

If you can't afford brand new OEM tyres for a BMW buy a Ford Focus with 205/55 16s. Cheap as chips!

cw212010

Would it hurt to put 45's on the front too though?

AdrianC

cw212010 wrote: »

Decided to just grab some part worns this morning and put a pair on the back. These are non run flat and are 225/45/17 rather than 225/55/17 that was on before.

The cheapest new tyres in the correct size are less than £50 each. The cheapest new tyres worth buying are £75 each.
http://www.camskill.co.uk/m54b0s466p0/

Exactly how much did you save by skimping on part-worns of the wrong size?

Even the very cheapest, earliest F10s on Autotrader are ten grand cars...

As a result, I'm hit with faults on iDrive. Parking brake failure, pedestrian protection system, flat tyre monitor, brake system (all amber) and a red restraint system warning, loss of power, TC light when gently applying power, tight steering, loss of speedo.

I can only assume this is just the car noticing the difference between the front and rear size difference.

Yep, absolutely. The car is expecting all four wheels to rotate at roughly the same speed. They aren't. You've put tyres 7% smaller in circumference on.

AdrianC

cw212010 wrote: »

Would it hurt to put 45's on the front too though?

Well, at least all four tyres would be equally wrong...

s_b

someone i knew did this with his 4x4 and broke the transfer box because the different rolling radiouses wound up the transfer box till it went bang
you really shouldn't be fitting different sizes to manufacturers recommendations because it would cause your insurance to be void and could cause an accident as slip angles would be changed from designed ones
i would go on to say who in their right mind would fit part worn in these sizes because you have to ask yourself where did the part worns come from/ a crashed car? a customer who felt all the grip had been lost on them or a european country where its deemed they are past their best
i havent even mentioned when were they made and what structural repairs have they undergone prior to being sold and do they indeed have the part worn stamp on them as requred by law

of course your on board computer is going haywire, its like having the speed flaps ice up on an aircraft but keeping the plane on auto pilot as everyone screams to their death

photome

Why would you put different size (different rolling radius) tyres on the rear and part worn to boot just to save a couple of quid?
doesnt make any sense to me

cw212010

Gotcha. What I'm considering though is if I replace the front tyres with 45's then the whole car is using them and this would not cause a mismatch.

BMW recommends the 225/45 on 18 inch wheels, where as I am using 17 inch.

In all honesty the guy at the garage said it would be fine to do so, the front tyres need replaced in the next few weeks anyway so I was happy to migrate to 45's if there was no differences as such.

In short, will I be safe replacing the front set to match?

AdrianC

s_b wrote: »

and do they indeed have the part worn stamp on them as requred by law

The what...?
<googles>
http://www.tyresafe.org/tyre-safety/part-worn-tyres/part-worn-tyres-and-the-law
Well, well, well. I never knew that. Interesting...

http://www.legislation.gov.uk/uksi/1994/3117/made
What's particularly interesting is that it appears to also apply to tyres sold part-worn on wheels. I've certainly bought - and sold - wheels with tyres on and not marked the tyres. I've also bought and sold tyres that fail the minimum tread depth requirements of that legislation miserably. I guess I'll remove and bin any tyres from rims I'm selling in the future...

photome

cw212010 wrote: »

Gotcha. What I'm considering though is if I replace the front tyres with 45's then the whole car is using them and this would not cause a mismatch.

BMW recommends the 225/45 on 18 inch wheels, where as I am using 17 inch.

In all honesty the guy at the garage said it would be fine to do so, the front tyres need replaced in the next few weeks anyway so I was happy to migrate to 45's if there was no differences as such.

In short, will I be safe replacing the front set to match?

why dont you just replace the rears with the correct size

cw212010

I don't have an issue doing this, however the 45's are much nicer with the low profile look. The 55's belong on a truck there's more rubber than there is alloy!