Minimum tread depth

[eliot-ness]

New WOF regulations specify that the minimum tread depth is now 100% of the tyre width. How is that going to work when on many bike tyres the tread tapers off towards the edges when new? A quick blat up H16 would make many new tyres illegal in the first 100ks and most of the bikes, (and cars) I've seen on dealer's forecourts wouldn't get a warrant.

[onearmedbandit]

Where did you hear this from?

[eliot-ness]

Where did you hear this from?

The local garage when I took the bike for a wof. (not bike dealers)

[Ixion]

It's been out for a while. Doesn't really work with bikes, and the rule has sufficient exceptions.

Info sheet here

Excerpts (my emphasis)

The rule now states that a tyre must have a tread pattern depth of at least 1.5 mm (excluding any tie-bar or tread depth indicator strip) within all principal grooves that contain moulded tread depth indicators and around the whole circumference of the tyre.
Virtually all tyres have moulded tread depth indicators. However, a small number of tyres, such as some retreaded or vintage tyres, may not have moulded tread depth indicators. For these, we have retained the old requirement of at least 1.5 mm tread depth across 3/4 of the tread width and around the whole circumference of the tyre.



Vehicle inspectors may disregard the outer end of a lateral groove where it normally tapers off over the shoulder. Note that the tread is only that part of the tyre that is in contact with the ground.



I have no idea if bike tyres have moulded tread depth indicators. I suspect not. The "in contact with the ground thing would be interesting, since bike tyres are curved. In contact when stationery ? Are chicken strips disregarded, they've never been in contact with the ground.

[Motu]

Out of his arse I think - here is the new rule....it's been the new reg for over 6 months,some people are just a bit slow.

''A single tyre must have a tread pattern depth of
at least 1.5 mm (excluding any tie-bar or tread
depth indicator strip) within all principal grooves
containing moulded tread depth indicators and
around the whole circumference of the tyre.''

We were talking about it at my last update course,and no one is happy about it.So we are only allowed to take tread depth readings from principal grooves with a TWI.As far as car tyres go - if there are only 2 centre grooves with TWI's,then the rest of the tyre can be bald (but not through to cords).I was showing one customer this week that I was failing two tyres that would of passed with the old rules,and passing one that would of failed....and he was concerned about the tyre I was passing.Same rules for bikes.

It's not about safety - customers were complaining to LTNZ that perfectly good tyres were being failed.So now we fail good tyres,and pass dangerous ones....good move LTNZ.

[sinned]

I think you will find most/all bike tyres have moulded tread depth indicators. Many bike riders tend to run the tyres to zero tread at the centre and the last bit goes in one ride of 100 - 200 kms.

I don't see a problem with this regulation. My tyres still wear out too quickly.

[Ixion]

Hm. Out of curiosity, I just went and looked at my tyres. Out of 9 that I could check, only one appeared to have any form of wear bars. Admittedly I didn't check all round the fronts, cos it's too hard to get at and turn the wheel. (I do know what they look like on car tyres)

[Bonez]

New WOF regulations specify that the minimum tread depth is now 100% of the tyre width. How is that going to work when on many bike tyres the tread tapers off towards the edges when new? A quick blat up H16 would make many new tyres illegal in the first 100ks and most of the bikes, (and cars) I've seen on dealer's forecourts wouldn't get a warrant.

I would imagine if a tire wears that quick in 100kms it would be stuffed after 6 months anyway. Time tire changes around WOFs.

Motu points out it's "circumference" of the tyre not "width" btw.

[Motu]

Bikes ''normally'' wear in the middle...so a moot point really.The principal groove will be the centre groove,if there is none then the 3/4 rule applies.

Car tyres are a nightmare - normally there are 3 or 4 principal grooves,that's easy,but only 2 grooves means a lot of tyre can be worn before it can be failed.A consolation is some of the more radical directional tyres with long grooves going from the centre to the edge,that's a principal groove and has a TWI....just a little wear on one edge and she's a fail.

[Ixion]

Hm. makes mental note to buy tyres with only two grooves for the cage.

What about block tread types, on 4WDs etc. ?

I suspect that bikes at any rate, 90% of places will use the good old "have a squizz, hm, y' tyres a bit hungry mate, that's a fail sorry", and only resort to measuring if there's an argument.

[Bonez]

Bikes ''normally'' wear in the middle...so a moot point really.The principal groove will be the centre groove,if there is none then the 3/4 rule applies.

Car tyres are a nightmare - normally there are 3 or 4 principal grooves,that's easy,but only 2 grooves means a lot of tyre can be worn before it can be failed.A consolation is some of the more radical directional tyres with long grooves going from the centre to the edge,that's a principal groove and has a TWI....just a little wear on one edge and she's a fail.

Yeah, some bike tires don't have a centre principle groove at all. The Shinko on the CX for example has about a 1 inch ungrooved centre and the rain grooves go from there out to the edges.

[Bonez]

Hm. makes mental note to buy tyres with only two grooves for the cage.

What about block tread types, on 4WDs etc. ?

I suspect that bikes at any rate, 90% of places will use the good old "have a squizz, hm, y' tyres a bit hungry mate, that's a fail sorry", and only resort to measuring if there's an argument.

Maybe in your area. Here most inspectors I've come across seem to use a common sence approach.

[Ixion]

Maybe in your area. Here most inspectors I've come across seem to use a common sence approach.

That's what I meant. They have a look and if it's obviously at the end of its life , fail, otherwise OK. Most of the time they don't bother to actually measure it, just write down a number. And when they do that gadget out its always an afterthought.

[Bonez]

That's what I meant. They have a look and if it's obviously at the end of its life , fail, otherwise OK. Most of the time they don't bother to actually measure it, just write down a number. And when they do that gadget out its always an afterthought.

Here inspectors deffinately measure them.

[Ixion]

Southern pedantry