Cruise control inop above 40mph

[coneybiller]

Hi all, just wondered if anyone can shine some light on my above issue. I have no lights on the dash and the ABS/BAS system self tests on startup without issues. The cruise control works between 20 and 40mph and the limited works fine at any speed.
I've read that tyre sizes can be an issue? I've got genuine merc alloys (as printed on the back of the spokes with P/Ns). They are 17 X 7.5" 5 spokes (Alhena ?).

Current tyre sizes are:

Front - 225/45R17
Rear - 245/45R17

Could this be a cause of my cruise control issues? Or should I look elsewhere?

Hopefully someone can help here?

Cheers

Ben

 

[whitenemesis]

Are you sure the rims are 7.5" all round then the tyres should be 225/45 all round.

If they are staggered, then rears will be wider and tyres should be 245/40.

 

[coneybiller]

Thanks for the reply. Yep, checked all 4 corners and they all say 17" X 7.5" on the back side of 1 of the spokes.
According to Mercedes-Benz Fitting Chart and Wheel Fitment Guide | Alloy Wheels Direct under then W210 section, it lists that size as 235/45R17, does that seem right?

 

[BTB 500]

I've got genuine merc alloys (as printed on the back of the spokes with P/Ns). They are 17 X 7.5" 5 spokes (Alhena ?).

Current tyre sizes are:

Front - 225/45R17
Rear - 245/45R17

You've got a 3% difference in rolling radius between front and rear ... not much, but might be enough to make it drop out of CC:

Car Bibles : The Wheel and Tyre Bible

 

[coneybiller]

That's where my line of thought is. Didn't realise it would be quite so tight on the tolerance side of things. But once the tyres on one of the axles are low enough, I shall replace for 235/45R17 and see what happens!

That is the correct size I'm presuming? I'm only going by the website I listed before. Black circles lists 225 and 235 for my registration. Not sure which 1s to go for now =\

 

[BTB 500]

Check your handbook for tyre sizes, failing that the data on the Alloy Wheels Direct fitting chart (linked to earlier) should be correct.

 

[coneybiller]

You know what, it never even crossed my mind to check the handbook
I'll do that tomorrow and see what it says. Hopefully it has my wheel type in there!
Thanks for your help. It is very much sounding like wrong tyre size! When the ditch finders are a bit more worn and I've replaced a few of my other troublesome items, I'll get decent, proper fitment tyres for her. L

Oh and any recommendations on tyres?
I've got my eye on Pirelli Cinturato P7 Blue XL. Due to a AA rating for wet weather and fuel economy performance.
Any others? I do a lot of motorway miles (600miles per week) whatever the weather. Fuel economy is important as it comes out of my pocket!

 

[stevesey]

I seem to remember getting the the ABS light on my W202 C240 when cursing on the motorway with a virtually new spare and a down to the tread makers tyre on the same axle.

 

[coneybiller]

Hmm so it's very sensitive then. Did the light go out when you had replaced your tyre(s)?