Tire shaving / buffing - how to avoid replacing ALL your tires when one goes on an AWD?

Random Twitch

Forum Member
Joined
Apr 16, 2021
Messages
16
Location
Australia
Car Year
2007
Car Model
Forester X
Transmission
Manual
Hi all

I've been reading about avoiding the need to replace all 4 tires when only one needs replacing on an AWD like a Subi.

If this is new to you (like it was to me a little while ago), the basics are these: AWD systems like the Subi need all four tires to be pretty equal in diameter, i.e. they should have the same degree of wear. This avoids mechanical damage to the drive train. So, when you need to replace one tire, you should be replacing all of them so all four tires are the same size.

This is expensive, and therefore sux.

One alternative solution I read about on this forum is 'tire shaving' (I can't find the post now). Its a.k.a. 'tire buffing'. You buy a single replacement tire. A specialist can then shave down (or buff) the tire to take a few millimeters off - your brand new tire would then have the same diameter as your worn ones.

It sounds simple. But does anyone have actual experience doing this with their Subi?

How far does the shaving go - how does the technician know when enough has been taken off the new tire to match the wear of the existing ones? How many millimeters are we talking about, anyway?

It seems this service is more common in North America than here in Australia (something about the snow)? It *seems* only specialist services do it here, shops that service motorsports. I've found two in Melbourne that advertise it, and none in Adelaide.

I read on a motorsport site that shaving improves traction on a dry track, but it rules out the tyre for use in the wet. Clearly this is not what you'd want on a road vehicle! Is it just because they shave off so much material for motorsports?

In which case, is it even possible for Subis here in Australia?
 
@Random Twitch I seem to remember reading the tyre shaving was not an option for road tyres in Australia?
 
Oh. "not an option"? As in legally prohibited?
 
That would, by necessary implication, rule out the use of any spare tyre that wasn't equally worn.

IME, that's plain rubbish.

My three Subarus dating back to 1994 have all been AWD. I have played mix-n-match with spares that were all but brand new, with tyres that were quite worn. They have never caused any kind of problem.
 
One partial solution is 6 rims and tyres. I rotate all 6 about every 6-12 months thus evening out the wear. They still eventually wear out but the chances of being without at least one spare is minimal. If there is a need for one new tyre then it can be the "more or less" permanent spare and get little use and then become part of the next new set.
In the past I have had 2 new ones on and 2 partly worn ones with no great problems. I guess the wear on them was not significantly different, too far back to remember.
IMHO if all tyres are more or less the same wear then all should be ok.
 
hmm.

My problem is I have a different brand (but same size) spare than my 4 Geolandar ATS 012s. 26 000km on them, so about halfway through. In hindsight it was a really poor decision to not get the fifth AT as a spare back then, and I was kind of hoping I could buy one now and have it shaved down to the same level of wear.

Of course, I've since read that different brands can actually measure different diameters even if its the same size stamped on the side. I have absolutely no idea by how much (2mm? 10mm?). So there's a size difference due to brand and wear. I feel doubly screwed right now.

Have a couple of long road trips planned. Nightmare scenario of being a 1000km from a tire shop isn't comforting, unless what Ratbag says is true - in which case it would be probably just fine to limp back to a shop.

ateday offers an interesting (if expensive) approach - maybe one day when I am a bit richer and have somewhere to store the 6th wheel!

What would you do in my situation? Bite the bullet and get a whole new set early, or just trust the setup I have got until its time to replace the ones on the wheels anyway?
 
ateday said:
One partial solution is 6 rims and tyres. I rotate all 6 about every 6-12 months
Click to expand...
Also been doing that for 20 years
Random Twitch said:
I've since read that different brands can actually measure different diameters even if its the same size
Click to expand...
That's correct - my newer Yoko GO15s are about 3mm larger in diameter than the BFG/AT they replaced
 
Just use the spare on the front (open diff), if it's bothering you as much as that.

Differentials work all the time, regardless of tyres being slightly different in diameter.

The one thing that will kill a Subaru's differential/s is doing donuts. I've seen the result of that - f'ugly! Took the idiot who owned the car less than a week to destroy it after a rebuild. I've got a photo somewhere.
 
.. right, but even if both front and rear are open, you've only halved the magnitude of the issue for the center diff.
 
Still trying to reconcile the money that has to be spent versus the millimeters involved in the problem. Headache.

@Kevin, how did you make that measurement of your old tyres? If I tried it, I'd probably introduce 3mm of error just by slightly misapplying the measuring tape.
 
  • Inflate all tyres to correct pressure (36 psi).
  • Park on flat ground (concrete pan).
  • Take off hub caps, or hub nut covers if alloy wheels.
  • Use steel tape measure to measure vertically from centre of hub nut to ground (by placing tape measure end on ground, not the other way around!).
 
Actually, if you think about it, it's probably the actual circumference that matters more. Even if the tyre pressures are different and the height of the wheel centre is a different, the tyre still has to roll over the ground, and so it's the circumference that matters. The tyre pressure probably does not matter. Maybe I'm just being pedantic here.
 
I saw a post somewhere that described rolling the tyre along a floor next to a measuring tape to get the circumference. I thought that was pretty keen, so to speak. And liable to introduce error into the measurement.

So I tried to see if any stores here have Yokohama Geolandar AT GO15s, but they're all out for at least a week.
Anyone have a good alternative to this they can recommend, one that comes in 215/60R16?
 
Random Twitch said:
I saw a post somewhere that described rolling the tyre along a floor next to a measuring tape to get the circumference. I thought that was pretty keen, so to speak. And liable to introduce error into the measurement.
Click to expand...
That will only tell you the unloaded circumference. A valuable figure for some purposes, but not accurate for others. A tyre is always partially "flat" when it's carrying a load.
Random Twitch said:
So I tried to see if any stores here have Yokohama Geolandar AT GO15s, but they're all out for at least a week.
Anyone have a good alternative to this they can recommend, one that comes in 215/60R16?
Click to expand...
Bridgestone are having a "four for the price of three" here in Victoria ATM.
I've just put 4x Bridgestone Turanza Serenity Plus 215/60 16 on Roo2 for $606, fitted and balanced.

IME normal standard size road tyres are perfectly adequate for all but the most extreme rocky conditions, and better for everything else.

Our SG Forester already has wider, lower profile tyres than my 1968 Landcruiser had, with the same rim diameter and about an inch wider.

The above tyres handle superbly, are very comfortable, almost silent, and will last a long time.

Even hard core off-roaders spend about 95% of their time driving on sealed roads ... ;) .
 
Thats a good deal, @Ratbag, thanks, I had missed that. Have booked myself in. Better (I think) than the Dunlop SP Sport FM800 alternatives I was looking at.

That will only tell you the unloaded circumference. A valuable figure for some purposes, but not accurate for others. A tyre is always partially "flat" when it's carrying a load.
Click to expand...
Yes, that's what I was thinking - its not the effective circumference of the tyre given load, pressure and wear. How these are supposed to be equal across all 4 tyres to within 1/4" i.e. 6mm is straining my imagination a bit.

As is, measuring it accurately enough. If you measure with a tape from the centre of the hub to the floor (i.e. radius), but you're out by just 1mm, then your calculation of the diameter (2 x Pi x radius) is going to produce more than 6mm of error - pretty useless for these purposes.
 
I am having a good run out of my (6) 215X65X16 Bridgestone 697 Duellers . About 50k kms so far and estimate another 30-40k left. All wearing evenly but a tad noisy on bitumen, not excessively so though.
 
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