different profile tyres front and rear

pd52

Had my MOT theis week all was fine apart from an advisory - different profile tyres front and rear

fronts are 205 17 40
rears are 205 17 45

bridgestones

All tyres have loads of tread on them and ive been driving around for 6 months since ive had the car with different profiles and its seemed fine.

The guy at the MOT place said its probably ok and he was just 'informing me'

Do you think I should get the front or rear tyres changed to match?

Its a fiesta 2009 reg

neilmcl

What is the correct tyre size for your car? What does it say in the handbook?

It wont make a great deal of difference so change them when you need to.

Iceweasel

So which is the correct size?

What does it say on the tyre pressure label on the driver's door-post or in the handbook?

The car will not handle as designed by the manufacturer.

Having non-standard tyres might well have insurance implications.

I wouldn't give them any 'wriggle room' to refuse a claim.

A 3rd party claim would be unaffected but they might refuse to pay out for your damage

pd52

205 40 17 according to the book.

forgotmyname

Rather than the handling i would be thinking more of the ABS issues. It wil be sensing the front/rear wheels going at different speeds. That could upset the ECU in an emergency braking situation.

How much tread left on the wrong tyres?

pd52

forgotmyname wrote: »

Rather than the handling i would be thinking more of the ABS issues. It wil be sensing the front/rear wheels going at different speeds. That could upset the ECU in an emergency braking situation.

How much tread left on the wrong tyres?

Around 6.5mm

marlot

As you have matched tyres on each axle, it's fully roadworthy.

You have a choice: Either replace the tyres (sell the old ones on ebay?) or run with them until they wear out.

The sizes are close enough that they won't particularly affect the handling of the car.

I guess the only potential issue is if you're ever unfortunate enough to have an accident and an insurance assessor takes the position that the wrong tyres are a serious issue. I don't know how likely that is.

One final thought - do you have a full size spare? If one of the wrong tyres gets a puncture you'd then have mis-matched tyres on that axle.

neilmcl

forgotmyname wrote: »

Rather than the handling i would be thinking more of the ABS issues. It wil be sensing the front/rear wheels going at different speeds. That could upset the ECU in an emergency braking situation.

How much tread left on the wrong tyres?

A lot of cars can accommodate multiple tyre sizes as options including different tyre ratios between front and back. A 5% difference in tyre ratio will have no ill affect.

pd52

marlot wrote: »

As you have matched tyres on each axle, it's fully roadworthy.

You have a choice: Either replace the tyres (sell the old ones on ebay?) or run with them until they wear out.

The sizes are close enough that they won't particularly affect the handling of the car.

I guess the only potential issue is if you're ever unfortunate enough to have an accident and an insurance assessor takes the position that the wrong tyres are a serious issue. I don't know how likely that is.

One final thought - do you have a full size spare? If one of the wrong tyres gets a puncture you'd then have mis-matched tyres on that axle.

no spare wheel just tyre foam/repair stuff:(

The insurance issue is my main concern

Spicy_McHaggis

I don't know the car or speed/load rating but for £150 is it worth the risk?

Joe_Horner

The nominal difference between the two on diameter is 20mm. Given that the difference between a new and worn tyre can be about 15mm, that means that the difference in your case is not going to upset the car's handling, ABS ecu etc.

Incidentally, the ecu will cope just fine with a "steady" difference in speed like this would create because it's far more interested in (very) sudden changes in speed.

From the insurance POV it's pretty well established that they can't refuse payout on even your "own car" cover following an incident for minor irregularities that didn't have a bearing on what happened. Good tyres, wit (presumably) suitable speed ratings, that are legally fitted (ie: same size across each axle) and only different by about the depth of the tread won't have a bearing on anything that might happen so you'll be fine.