New tyres and TC issue? Suggestions?

[Alonso92]

Hey Guys, new poster but lonnnng term reader

I've had my 08 120d coupe for a couple of years now with pretty much no problems! However the other week as I was on a motorway and the tc light kept on flashing on and of everytime i would press on the throttle a little bit, thopught it was strage but kept on driving.
I eventually got a blow out so I assumed I had a small puncture on the rear and the car was detecting a difference in wheel speed.

I then mail ordered a pair of non-run flat tyres (205/50/17) to get rid of that awful thudding you get on every bump but stupiddddly assuming the rear and the front sizes were the same. Got them fitted on the rear but the car felt horrible, the only way i could explain it is as if you was steering a ship. the TC light sometimes appeared but assumed it was due to the rears not being runflat and the fronts being runflat.

After a lot of thinking of why the steering felt so bad, I look at the sticker on the B pillar and it says that the rears should be 225/45/17 :telloff: so i got a second hand set (non-runflat) on the back. When driving on the motorway as you go round slight bends the TC light still flashes and bogs the car down and eventually does it on straights getting so bad that I have to take of the traction control off. Whats am I missing? :roll:

[C70R]

Sounds like a dicky wheel speed sensor to me. Are you able to pull the error codes off somehow?

[stevieturbo]

So are front and rear tyres as per spec ?

Differing diameters can cause problems. No warning lights staying on ?

All tyre pressure monitors etc working as normal ?

[wild rover]

Check for slight play on the wheel bearings?

[McVities]

You've fitted second hand tyres to the rear of the car.......

You haven't specified what brand they are.
You haven't told us how old they are - the date code will be printed on the sidewall.

[FordPrefect56]

Alonso92 said:

Hey Guys, new poster but lonnnng term reader

I've had my 08 120d coupe for a couple of years now with pretty much no problems! However the other week as I was on a motorway and the tc light kept on flashing on and of everytime i would press on the throttle a little bit, thopught it was strage but kept on driving.
I eventually got a blow out so I assumed I had a small puncture on the rear and the car was detecting a difference in wheel speed.

I then mail ordered a pair of non-run flat tyres (205/50/17) to get rid of that awful thudding you get on every bump but stupiddddly assuming the rear and the front sizes were the same. Got them fitted on the rear but the car felt horrible, the only way i could explain it is as if you was steering a ship. the TC light sometimes appeared but assumed it was due to the rears not being runflat and the fronts being runflat.

After a lot of thinking of why the steering felt so bad, I look at the sticker on the B pillar and it says that the rears should be 225/45/17 :telloff: so i got a second hand set (non-runflat) on the back. When driving on the motorway as you go round slight bends the TC light still flashes and bogs the car down and eventually does it on straights getting so bad that I have to take of the traction control off. Whats am I missing? :roll:

Let's go back to basics. I assume you can understand that if a TC system was so sensitive it got triggered by having worn tyres on one end and new ones at the other this would be a bad and silly thing n'kay? The average tread depth of a new tyre is 8mm and 1.6mm is the legal limit so anything less than about 7mm difference on radius front to rear can't possibly trigger the TC system.

The sidewall depth on a 205/50 is 102.5mm (205 x 0.50) and on a 225/45 is 101.25mm (225 x 0.45). Near as dammit the same radius so this could never trigger a TC system. It means you have a problem in the TC system that is nothing to do with the tyre sizes. Maybe a wheel speed sensor.