Tyre sizes and traction warning light

[Jordie172]

Hello all,

I have bought a 182 on a 05 plate, the traction control light comes on not long after driving/startup.

I have noticed a mismatched tyre size front to back.

Fronts are 215 40 16
Rears are 205 45 16

I make that a 13mm different in radius. Will this be causing the issue or be a possible cause? It could do with 2 new tyres to be honest so hoping to kill 2 birds with one stone.

When your driving and the traction + serv warning lights appear, its like the abs is kicking in and then the warning comes up and it drives fine.

Jordie

 

[Canary172]

I think 205 was the original width of tyre fitted to all corners on 182 models. Whether the difference is tyre diameter is causing the warning lights to appear, I'm not sure. Hopefully one of the experts will be able to clear this up!

 

[Jordie172]

its the 40 and 45 % aspect ratio which is causing the difference. Dunno how much difference is allowed before the traction sees the wheels are slipping?

 

[MicKPM]

It doesn't see them as slipping, more likely it will see the front wheels rotational speed as 'X' and the rear wheel speed as 'Y' and so is flagging the wheel speed data as inconsistent to allow the ESP/ABS program to work.

 

[Jordie172]

Hopefully this is the reason, i will get some tyres on it asap

 

[MicKPM]

The easiest way to prove it IMO would be to scope the wheel speed sensor outputs as a picture can speak a thousand words.

Normally the ABS/ESP program will not allow for a 2% difference in speeds as it has to interrupt and react to smaller percentages in extremely small timescales so this will be your problem.

 

[ripp]

just don't throw away the 205/45 ones cause that's the standard size! (if you didn't know that already)

 

[Jordie172]

Thanks Rip, i googled that before ordering.

So now ive got 205/45R16 all round.

Not taxed so cant go road test, but noticed something when in garage before. If i start the engine, the traction/esp light and serv light is off. If i turn the wheel to the right and back its fine. Turn it left and about 1/2 turn before full lock both warning lights come on.

I think when the wheels are straight (by eye) the steering wheel is slightly off.

As anyone had issues with wheel alignment causing traction/serv warnings? I assume the steering is out of line, which means the steering angle sensor is out also.

 

[MicKPM]

The steering angle sensor has a 5% tolerance but this could be an issue yes... This is also why we'd normally advise a proper diagnostic session

 

[Jordie172]

Aye, thanks.

I cant get the car to any diagnostics as its not taxed until 1st Jan, but will get in touch with DTM or someone close by for a better indepeth diagnosis.

 

[MicKPM]

Aye that would be a good plan but if it does turn out the SAS isn't showing 0° at true center get the steering alignment corrected rather than recalibrate the SAS itself.

 

[Jordie172]

thanks for the advice, ive dropped DTM an email to see if they can have a look. Id rather go somewhere that knows the system than any old ATS etc for alignment alone.

 

[ed55j]

I used 185 60 15 front and 195 50 15 rear once and didnt have any dash lights come on, was comically high at the front lol

 

[Jordie172]

Tyres changed, still got the issue.

However this morning, the ABS light started flickering, then stayed on along with red STOP and the handbrake warning light.

DTM are closed until at least 13th, so ill just continue to use it. Noticed the pads are very low so will replace at weekend as the rear seems to be binding/dragging a little too.