V70 AWD and matching tyres....
Discussion
Recently acquired a V70 D5 AWD. Came on 4 matching Michelin Primacy 3 tyres with about 5mm of tread.
As is the way within a week of ownership I’ve picked up a puncture on the RNS. The puncture is very close to the edge and thus not repairable.
I note from the handbook it says about matching tyres MUST be used so as to not cause damage to the AWD system.
Obvs a new matching Primacy will have about 7mm of tread which is 2mm over the over 3. I also don’t want to go down the route of a part worn.
Will I be ok to just put two new ones on the rear, or is the AWD system so sensitive it will in theory want 4 new tyres??? Seems a bit bonkers if the latter.
As is the way within a week of ownership I’ve picked up a puncture on the RNS. The puncture is very close to the edge and thus not repairable.
I note from the handbook it says about matching tyres MUST be used so as to not cause damage to the AWD system.
Obvs a new matching Primacy will have about 7mm of tread which is 2mm over the over 3. I also don’t want to go down the route of a part worn.
Will I be ok to just put two new ones on the rear, or is the AWD system so sensitive it will in theory want 4 new tyres??? Seems a bit bonkers if the latter.
In short, no. Not even close.
You can do some maths to prove it.
A 215/60/R17 tyre has a diameter of about 690mm.
So, the circumference can be calculated as Pi x radius squared.
For a 690mm tyre, this is 2167mm. This means it will rotate 461 times every kilometer.
For a tyre with 2mm of wear, this drops to 2155mm. This means it will rotate 464 times per kilometer.
You can see, an extra 3 times per kilometer is not significant.
You can do some maths to prove it.
A 215/60/R17 tyre has a diameter of about 690mm.
So, the circumference can be calculated as Pi x radius squared.
For a 690mm tyre, this is 2167mm. This means it will rotate 461 times every kilometer.
For a tyre with 2mm of wear, this drops to 2155mm. This means it will rotate 464 times per kilometer.
You can see, an extra 3 times per kilometer is not significant.
I resolved this with two new rear tyres. Seems to be fine.
But on what you’ve said, I would say it could be significant? 3 extra rotations per km.
My commute is 35 miles, or 56km. So each journey to work there would be nearly 170 more rotations. Which is over 3000 extra rotations a month. Is that not enough to ‘wind up’ the transmission?
But on what you’ve said, I would say it could be significant? 3 extra rotations per km.
My commute is 35 miles, or 56km. So each journey to work there would be nearly 170 more rotations. Which is over 3000 extra rotations a month. Is that not enough to ‘wind up’ the transmission?
No mate. Not really.
Think of it like this: it will slowly rotate one wheel slightly more than the other. On a perfectly straight, flat road.
What do you think happens when you go around a roundabout? I bet you just go around it. You probably don't immediately go around a roundabout the other way to unwind it!
You can 'wind up' transmissions if you have differential locks applied, on a grippy surface.
For an AWD system designed to operate on roads, it's not a problem.
Different sized wheels and/or tyres (as in a 17" and 19" wheel on the same axle) can, and will cause problems. The ABS ECU won't expect such differences in wheel speeds, and you may very well hurt transmission or driveline components.
But, with such a tiny difference in wheel sizes between one worn tyre and one brand new one, there's no need to worry at all.
Think of it like this: it will slowly rotate one wheel slightly more than the other. On a perfectly straight, flat road.
What do you think happens when you go around a roundabout? I bet you just go around it. You probably don't immediately go around a roundabout the other way to unwind it!
You can 'wind up' transmissions if you have differential locks applied, on a grippy surface.
For an AWD system designed to operate on roads, it's not a problem.
Different sized wheels and/or tyres (as in a 17" and 19" wheel on the same axle) can, and will cause problems. The ABS ECU won't expect such differences in wheel speeds, and you may very well hurt transmission or driveline components.
But, with such a tiny difference in wheel sizes between one worn tyre and one brand new one, there's no need to worry at all.
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