Hello,
Got a right/rear flat on my 2017 XC60, but it's only got 8K miles on it. Lots of life left on the treads. Am I good to just replace the single tire, or is it imperative that I swap out both tires on the rear so I don't screw up any AWD or other system? Thank you for your thoughts.

Dan

 

Nope, just put a new tire on, your car is not full time all wheel drive. Certainly on some AWD systems it is best if all tires are the same exact diameter. And yes the tires on each axle should turn at the exact same speed due to their diameter. (except they never do in any turn, sharp or slow, you are in) If not the differential will actually move - and sure after xxx miles maybe the diff will be worn more than normal. IMHO - worry about something else.

 

Thank you hoonk! Exactly what I needed to know. I assume it makes no difference that it's a T6 R-Design with regards to the AWD system? I'll have my guy just do the one wheel then.

Best,
Dan

 

Read first: https://www.cars.com/articles/do-i-n...1420684865769/

https://www.consumerreports.org/tire...s-a1061792056/

And read this:


Val Smith, Former Master Mechanic and auto craftsmen (1967–2014)If you have to replace one tire and the other three are in good condition and less than one year old, should you purchase a new set or just replace the single damaged tire?

It seems I answered a question like this a few months ago. Many here have told you “yes” it is OK, and others have said you “must replace in pairs”, and they mention tread depth as an indicator. However you have left out a couple crucial bits of information in your question. 1) Is the car front or rear wheel drive? 2) Is the car All Wheel Drive? 3) Is the car a ‘part time’ 4 wheel drive? 4) How badly worn are the other tyres? (Time on the car is irrelevant as I wore out a set of new tyres in 200 miles driving Autocross)

OK let me go technical here. Tyres have size indications on them ie: 225/65 R 16 etc., but this is only a generalization of size, as different brands and styles within the brands will have variations in the tyre circumference within this standard size. Matched circumference is crucial to survival of the differential!! If each tyre on a drive axle spins at slightly different speeds due to circumference differences of the tyres, the small gears within the differential will be spinning/walking. These gears do not have any bearings and are not designed to spin in continuous use, only when turning and each drive tire is driving in a different arc. As this happens the differential will build heat, loosen up from excessive wear and have play/looseness in these “side gears”, and in some cases the cross pin that they spin upon may also loosen up within the differential housing/cage. If it is a press fit and not bolted in place, should this pin come loose it is catastrophic for the differential. This is true for all standard differentials (unless planetary gear sets) and in AWD and 4WD they also have a 3rd differential within the transfer case requiring that ALL tires have the same circumference, thus the need to replace all 4 tyres in that case.

So my answer to the question is “maybe”. If you can match the tyre construction type and circumference of the other tyre on that drive axle then you can replace just one. Or if you want you can replace just one if you mount it to the non-drive axle, and never move them around unless you match circumference for drive tyres. However if the circumference is too different then you may see a wheel speed ‘trouble code’ for the ABS system. The choice is yours, but I always recommend to replace tyres on 2WD in axle sets. Just put the best 2 of the other 3 on the other axle and put the 3rd into the boot as a spare.

Also; I read here and have had others recommend to put the best two tyres on the rear of a FWD. However I do not agree with this suggestion as the front tyres perform all the turning and driving traction as well as 70+% of the braking. “Nuff said”

 

As a general rule is good to replace tires in tandem like brake rotors and pad for example. However, at only 8K miles, it should be fine to replace the one rear tire. I did it last year when my wife destroyed a relatively new Michelin by running off the road. We replaced the one rear tire and never notice a single problem with the drive and balance of the SUV. Cheers!

 

Thank you Comet. Good info here and in those articles.

 

It would be even more brilliant to put the new one on the front. Or bigger ones on the front if we don't want to assume they're all perfectly sized. Measure them if you like. If the car thinks the rear tires are going faster than the front tires, you're not going to see any awd coming on from that.

Let me just add here, recommending that you replace pairs on an AWD car is extreme nonsense. Whatever AWD-specific risk there is, this would clearly double it, and everybody should easily figure that out.