Tyres- tread depth

Post by **Chilla** » 11 Mar 2008, 22:11

Anyone know the acceptable wear limits between tyres so as not to have an effect on the VC ? .....ie is it ok to run say 7mm on the front and 6mm on the rear.
thanks in advance

Post by **..lee..** » 11 Mar 2008, 22:15

belive its 2mm but thats for same tyres, same make/size.

Post by **Chilla** » 11 Mar 2008, 22:27

Thanks lee

any idea why tyres from same manufacturer?

Post by **toomanytoys** » 11 Mar 2008, 22:38

Becuase each manufactuer makes there tyres slightly different, the compound/slip angle, the way its constructed etc etc... if the rears are lower tread depth then they will spin faster than the fronts.. the VC will "think" the rear is slipping so engages.. not good.. this is made worse as most of the drive is going through the rears, so they naturally have a slip (slip angle) this makes it worse still.. better to have the slightly deeper tread on the back as the slip will kind of cancel out the fronts fast rotation...
thats the theory in any case...

or fit the deeper treads to one side of the vehicle... (same can be applied if using 2 makes of tyre...

if you have a mixed bad of makes and depths, then you ought to drop the prop... or get a new set of tyres.. or perhaps the vc is shot in anycase...

Post by **HarryMann** » 11 Mar 2008, 22:56

any idea why tyres from same manufacturer?

I suppose makes common sense and so that their rolling circumferences are the same (as simple size, AR spec. doesn't guarantee that at all, at all)

Post by **Chilla** » 11 Mar 2008, 23:02

cheers tmt
wanted to get the vehicle through mot and current rubber is v low and have spare 2 same make with 7mm and 2 different makes with 6mm.
Will put the theory to practice and bung the 7mm to rears and see how it goes....ta!

Post by **Chilla** » 11 Mar 2008, 23:08

HarryMann wrote:
any idea why tyres from same manufacturer?

I suppose makes common sense and so that their rolling circumferences are the same (as simple size, AR spec. doesn't guarantee that at all, at all)

cheers HM...yes was going to check on rolling circ' tomorrow.....do you know of any percentage difference before the vc is activated?

I should add this is a short term fix before I get me 15" boots!
thanks

Post by **HarryMann** » 11 Mar 2008, 23:17

[img:640:480]http://vw-tristar.web.surftown.se/178%20(45).JPG[/img]Credit vw-tristar.web (Syncro Tristar For sale in Vehciles for Sale section)

2mm, what VW always said, though have to admit I've run with more, but they didn't say the world would come to an end, just that that was their recommended limit from testing etc. (based on VC heat/action)

so 2mm wear = 4mm on diameter (0.16"), calculate the percentage from the charts here, on Syncro website...

http://www.club80-90syncro.co.uk/Syncro ... %20rpm.htm

14" Typ. is std on Syncro Tristar from factory: 2 metres TRC(from charts) is 78.74"; assume truly circular (but isn't really) equiv. diameter = 25.06"
This now becomes 25.22 so that's 0.6% difference, Mmm

Did I go wrong, nope, don't think so, that's how much they allow 0.6%

Post by **CycloneMike** » 12 Mar 2008, 06:54

I remember some years ago a bloke I knew had an Audi 80 V6 Quattro.
He had 2 new tyres on the back, but they fitted the wrong aspect ratio.
The drive traiin gubbins (I don't pretend to understand AWD) were knackered in 6weeks.
Ratio was only out by 5%. Fortunately the tyre people were good and admitted their mistake and covered the costs of repair.
Not an answer to your question but I expect there could be a lot of people who wouldn't realise how much damage tyre difference can do.
Mike.

Post by **toomanytoys** » 12 Mar 2008, 08:01

Same happened on Calibra's.. apparently they were very sensetive to tyres.. they have a VC just like ours....

Post by **HarryMann** » 12 Mar 2008, 08:39

Calibra VC very similar to ours but quite a bit 'tighter' (non-technical term there

)

Post by **toomanytoys** » 12 Mar 2008, 09:07

Bloomin heck.. no wonder they break stuff and are more sensitive then!!!

Post by **andysimpson** » 12 Mar 2008, 20:41

Lots of car makers have used a VC (cheap 4wd), vw's guide is tyre make and type, size and speed rating must all match up and tread wear should be SIMILAR.

The bigger you go with tyres the bigger your tolerance will be.