Thoughts part 2

Pass and advise. You can only measure where you are sure to find the deepest grooves and those are the ones where there are tread wear indicators.

I don't test the parts of the tread where TWI's aren't found. I was specifically told not to by the trainer on my 3 day course.

So with this tyre the worn section is not raised tread what would you do. I get why your wording the manual but as a lot of testers say it's not clear enough. To me the rules should apply only to where the wear indicators are black and white

Those outer grooves taper away towards the end of the groove, so can we really state that those grooves are cut to the same depth as the twi grooves?

If we do, how would a tester know what the original grove depth would have been when the tyre is presented with the groove worn as it is?

Pass and advise in my opinion.

You are going to come across primary grooves without TWI that need testing gaz

Excessive ;
Totally agree if the groove has totally worn off and the tester can't dertermine the depth originally,then ya pass and advise

This might help
mattersoftesting.blog.gov.uk/getting-into-the-groove/

The important wording is ;

We only examine primary grooves with TWI ......OR ..., .....
The grooves originally cut to the same depth.

Ok then
You've determined it's a primery groove without where indicators which are cut to the same depth as the primery grooves with wear indicators ,are in the central 3/4"s of the tyre,determined with your triangle,checked depth with tread gauge,its below 1.6mm therefore its a fail.

We only measure the central 3/4's of the breadth of the tread. Always look for the witness marks on the tread area which show exactly which part of the tyre is in contact with the road. They are usually a bit darker.

The Tread Breadth is the area inbetween these witness marks highlighted below in red....



Once the breadth is established you assess the grooves to which the legal minimum tread depth requirements apply, you must establish which grooves are the primary tread grooves.

Primary grooves

The primary grooves of any tyre are those grooves that contain the tread wear indicators (TWIs) or those that were originally moulded to the same depth as them.. Evidence of TWIs can usually be seen in those grooves designed to have them and their position is normally marked on the sidewall of the tyre at the shoulder of the tread. Generally, TWI’s are marked with a small arrow or ‘TWI’, however some manufacturers use their own specific markings.

Secondary Grooves

These grooves are not of equal depth to those with TWI’s and are designed to wear out before the primary grooves.



Making your assessment

Vehicles where 1.6mm tread depth applies

When you assess the central three-quarters of any tyre, remember that the breadth of tread includes plain surfaces and any grooves. When you assess the minimum tread depth requirements, you only need to measure the primary grooves, those grooves that contain the TWIs or those that were originally moulded to the same depth as them.

You might find secondary grooves within the central three-quarters, and they may be below the required minimum tread depth requirements. Even if this is the case, provided the primary grooves meet the minimum depth requirements, the tyre is acceptable for this part of the inspection.

The tread pattern outside of the central ¾ of the breadth of tread can be bald.

Valid point nitros44. Still, having the same tyre on the other side has changed the outcome of the MOT in this case.

Would you fail an offside steering arm ball joint for excessive play? What if the nearside gator was missing?

OK you are still misunderstanding i'm afraid. The tread width, you tell us is 205 mm. We must make sure that the whole of the tread pattern in the centre 75% of that tread width has a depth of 1.6mm or deeper. The 'primary grooves' making up the 53% are not just part of the 'tread pattern' being tested. They are the tread pattern. All of it.So as long as the whole tread pattern - ie the grooves with the tread wear indicators and others cut to same depth are 1.6mm or deeper, then the other grooves are to be ignored. You will have tested the 75% required to the standard required, and passed and advised.