I just blew a tire yesterday a hole the size of a quarter - the tire is shot. Luckily my spare was 8/32 and very close to the other tires as well - Maybe 1 or 2 32 off. Is this ok? Tire shop says I may be close and would need to replace all 4 tires. I figure this kind of wear would be normal - no? I also need to get a replacement spare - used preffereably - anyone have some laying around?

Thanks...

 

Christo, if you are that close on your spare, that will be close enough. I don't see any problems coming in the future because of this. Yes it is off, but that little of a difference is very minimal. It wouldn't be any worse than making a turn in your car (probably less severe than making a turn). I would not worry about it. As for getting another tire for a spare, all you can do is look around at used tire places and see what they have in their stock. But, it is advisable that when you get new tires, you replace all 4 at the same time.

 

Thanks Chris! I did find some on eBay believe it or not, so I just may get one to replace my spare. My tires are still good maybe close to 3/4 of their life left - so I will hang on.

 

Just quick calculation based on 17inch wheel. If the one spare is 1/16 down, it will turn 0.5% slower than others. This difference will be split between the differential on that axle and the center unit so that the viscous coupling will only see 0.125% speed differential. In other words, you will be ok with the spare with 2/32 tread down.

 

When would the tread throw off the diff?

 

Christo, as long as you have an open differential, the tire speeds can be as different as you want them to be side to side. Where the issue comes is that the transfer case needs the front and rear diveshafts to be spinning at the same speed (ie, the fastest tire in the front being the same speed as the fastest tire in the rear). If you get the driveshafts spinning at different speeds, then you have to have something giving in. Under normal situations, the tires will hopefully be the thing giving in and making the driveshafts spin at the same difference. If something else gives, that is where you run into breaking axles, driveshafts, U-joints, etc. There is some forgiveness in the system to account for turning and stuff like that. But, it can only do just so much making up. This is where having the viscous coupling (02-03 X-types), it will be more forgiving than a hard coupled transfer case (04+). Unless you have modified your car, you have open differentials on the front and rear of your car.

 

Gotcha, I need to replace the spare and I was considering buying a used tire with 6-7/32 of tread wear so I would have something in case of an emergency. But I guess as long I am not way off between front and rear I should be fine.

 

There is no "hard coupled" transfer case....
all cars have a center planetary differential in the transfer case that is set up to send 60% torque to the rear. Early cars have a the VC between the front and rear outputs of the centre differential
Later cars have an open differential, but still 60/40 split in the middle. All cars have open 50:50 front and rear diffs.

THe issue with tire diameter is if there is too much relative speed difference in any of the 3 differentials, the small spider gears end up spinning as you drive instead of being stationary. The little bearings for these small gears are not up to being worked continuously. Something will let go.

Probably the worst problem would be in an early car, with the front and rear tranfer case outputs running at different speeds... that will kill the VC eventually.

 

Well I am still shopping to get a new tire on there. I just came across a tire shop that swares I can put a new tire on as long as I stay within the same brand of tire. Being that some manufacturers may have more rubber than others (circumfrance wise) - what do you guys think? 2 tires are 7/32 and 1 is 6/32...

 

You could find a tire shop that will shave the replacement tire down to match the tread depth of the others. I believe Tire Rack offers that as a service, buried somewhere within their web pages.

Jag has a spec for minimum tread differential between tires, I can't recall exactly what it is right now. I would think that there are so many variables for weight distribution and tire rolling radius (e.g. # of passengers, steering angle, tire pressure, full or empty gas tank, full trunk) that it's hard to believe there is ever uniform rolling speed among all 4 tires. I drove on my brand new spare from Iowa to Eastern Ontario 5 years ago and never experienced any long term problems as a result when compared to the other tires which had 1+ year of wear on them.

*update* here's the link from Tire Rack on shaved tires/AWD:
http://www.tirerack.com/tires/tirete...jsp?techid=18&

--Geoff
03 X-Type 2.5 Sport 147k km
06 S-Type R 46k miles