MOT Failure for worn tyres - have I been duped??

[tvr_nut]

Just had wifey's car fail MOT, allegedly having 3 of 4 tyres less than 1.6mm.

What confuses me is that the central bit of the tyres has tread depth indicators, and none of these were flush with the tyre surface (thus tread >1.6mm I thought).

The outer regions of the tread area (about 30mm width at inner & outer edges) do not have the full tread depth - i.e. even when new, the grooves here are 2-3mm less deep, I believe to avoid excessive movement of these outer tread blocks under hard cornering.

These outer parts of the tyre obviously do not have the full 2mm of depth left, but still have visible tread pattern. Thus I assumed the tyres were still legal, as the middle bit (with the depth indicator strips) would be the "central 75%" of the tyre.

Does anyone have knowledge of how this 75% is defined - I cannot believe Dunlop are making tyres with deliberately reduced tread depth on a portion of the tyre that is covered by the 1.6mm minimum requirement?

Are there any useful links that might help me get my facts straight before I take on the MOT man?

Any help gratefully received.

[bilton_d]

i don't think you have been robbed but why would you want to leave the tread to go below 2mm anyway? there are only 4 small contact patches that keep you on the road and with the wet weather why risk it for a few £££££££££££.
Unless your trying to kill her off?

[tvr_nut]

bilton_d said:

i don't think you have been robbed but why would you want to leave the tread to go below 2mm anyway? there are only 4 small contact patches that keep you on the road and with the wet weather why risk it for a few £££££££££££. Unless your trying to kill her off?

Nah - its better to tamper with the brake lines to do this!

It was more a case of not needing to shell out for the tyres until next months salary - and the query is because my own car is doe for MOT and has better tyres, but could fall foul of the same interpretation.

I have actually managed to answer my own question (as well as get a new set of boots for the car) this afternoon, courtesy of a rather useful website called www.motuk.co.uk - it contains the MOT Manual in full.

It also refers to the fact that as far as the "1.6mm across 75%" rule goes:

>> The tread pattern excludes any tie-bars, tread wear indicators, or features designed to wear out substantially before the remainder of the pattern, and other minor features. Grooves that had not been cut as deep as those containing the wear indicators when new, are not to be considered as part of the tread pattern. <<

Thus the shallow grooves between the shoulder blocks should not have been taken into account, and the tyres were (albeit just) OK, in my opinion.

That said, as they were close, I should not have been such a cheapskate either.........

What is interesting though, is the statement in the MOT Manual that:

>> Note: Each side of the central band of the tyre can be devoid of tread (ie. ‘bald’) and still meet the pass standard although in practice such tyre wear is unlikely to occur. <<

This is good news when you've ragged the outer edge to baldness on a trackday, but do not want to replace the whole tyre as the remaining 230mm is OK!