Tyre sizes and ABS.

Honest John Back Room » Technical matters
View Threaded
Fri 13 Sep 2002 00:59
Tyre sizes and ABS. - Cyrill666 {P}
Hello,

I recently bought a Vectra Estate and noticed that the tyres on the back are 205/16/55 whilst the tyres on the front are 205/16/50. According to the handbook both front and rear should have a profile of 55.

I'm told that the differing profile will cause serious problems with the ABS system on the car.

Can anyone here comment on that? Is this true, if so, how serious?

Kind regards,
Cyrill666
Reply | Report as offensive | Link
Fri 13 Sep 2002 05:11
Tyre sizes and ABS. - RogerL
The difference in rolling radius between 205/50 and 205/55 is 10.25mm. Since the difference between new and worn tyres is 6mm and the ABS sensors work on deceleration, not speed, this mix of tyre shouldn't confuse the ABS computer.
Reply | Report as offensive | Link
Fri 13 Sep 2002 15:19
Tyre sizes and ABS. - Cyrill666 {P}
OK, thanks - you've put my mind at rest.

But, will differing tyre size have an effeect on ABS, if so, what would the likely outcome be? ABS activating unecessarily or failing to activate when needed? Just curious.

And another question if you don't mind :-)

Assuming the car is expecting to be driving on 55's and 50's are fitted - won't this affect the speedo reading?

Kind regards,
Cyrill666
Reply | Report as offensive | Link
Fri 13 Sep 2002 15:26
Tyre sizes and ABS. - Andy
It might affect your insurance, take it back to where you bought it from and demand the correct tyres are fitted.
Reply | Report as offensive | Link
Sat 14 Sep 2002 09:43
Tyre sizes and ABS. - TrevorP
With 50 tyres instead of 55, your speedo will over-read by about 3%.

(that is OF COURSE 3% MORE than it was before)
Reply | Report as offensive | Link
Fri 13 Sep 2002 17:29
Tyre sizes and ABS. - Cyd
Rest assured your ABS will NOT be confused by the differing aspect ratios.

However since your car has non standard tyre sizes it has been modified and your insurance will be void if you need to make a claim. If you bought from a garage take it back and ask for the correct size to be fitted. In the meantime inform your insurance of the issue and what you intend to do about it.
Reply | Report as offensive | Link

From choosing the right tyre to what to do when it goes wrong - we have the answers.

Tyre News And Advice