XC70: Wheels/Brakes temp spare tyre

[yostumpy]

My current tyres are std 235/55 17 m+s rated jobbies, and fronts are 4mm and rear 5mm. Now when i come to replace I was going to go up to 235/60 17 in Michelin Cross climate 2 flavour, that will lift it by about an inch. Then I thought, 'what about the spare and the difference in height' Well , the spare is only a T125/80 17, this means the spare is 2" shorter that a std 55 section 17" tyre. (3" shorter than a 60 section). being AWD I'm surprised the system copes with this, without damage. My old landrover would have probably ended up with transmission wind up, but with the haldex, it must sense one tyre is moving much faster than the other 3,think it's slipping, and 'do something?' Confused!

[Tatsfield]

Your other option is to investigate what modifications would need to be made to the rear load area floor to accommodative the extra width of a standard sized spare wheel in the wheel bay There is a thread describing a modification of the floor carried out by an owner but it means losing the "stand up shopping bag flap". This assumes that your chosen wheel/tyre combination diameter will sit in the well. As usual on this topic, I close with my angry disbelief that Volvo could actually design a 4 wheel drive, go-anywhere vehicle without the provision for a go-anywhere spare wheel!

[yostumpy]

Yes but my point is the fact that the AWD drive train is capable of being able to run tyres of such a different size , on the same axle, without issue, or damage.

[Tatsfield]

So it is but only for limited periods of time. I suspect that the limitation on the skinny spare not only reflects the limitations of the wheel itself but also the ability of the transmission to cope with it for other than very short journeys at low speeds. That's where a permanent full size spare wheel would make life easier for everyone if Volvo had taken the time to consider providing adequate storage for it.

[ferg55]

5% of 235mm is only 11.75mm ( 1/2" )

[ferg55]

And, your total difference between the space saver and your 235/60 proposal is just 41mm ( 1.6" )

[yostumpy]

Originally Posted by ferg55

5% of 235mm is only 11.75mm ( 1/2" )

235/55. 17 diameter 27.2” …..742 revs per mile
125/80. 17 diameter 24.9”….. 811 revs per mile.

[ferg55]

So, using those dia's to calc the height difference between your current tyre and space saver:

27.2 - 24.9 = 2.3

then divide by 2

= 1.15" height difference

Plus another 1/2" if you want to increase to the 60 profile:

= 1.65"

[ferg55]

But I think we're talking cross-purposes, I am calculating the height difference of the tyre sidewall (tarmac to rim), only because you mentioned a 1" lift in your first post and then went on to talk about the height of the space saver. But I realise now you are actually interested in diameter. Sorry for the confusion.

[Tannaton]

The AWD system on all post 2003 Volvo model doesn’t care about differences in wheel diameters. Whatever’s the combination of tyres and temporary spares - it will be fine.

The only land rovers that you had to worry about was the Mk1 freelander with its thermo viscous coupling.

The larger mich’s will be a nice upgrade.