I may need to replace a single tire on my '98 XC due to a cut in the sidewall. All existing tires on the car have only 3/32" wear from new. Is this enough wear to warrant replacing all four tires in order to prevent potential bevel problems? If I put a single new tire on, should it go on the rear or the front? I appreciate any advice from other XC owners who had a similiar situation.
Thanks!

im sitting here amazed. until i read this thread i didnt even think of this potential tire problem. i dont have the mechanical knowledge of almost every poster here but i do have more empirical experience than anyone here. ive used "used" tires since i bought the car and changed one at a time over and over, never once thinking about circumference or euclidian geometry. once in a while im able to get a good set of four. i drove 4000km once on the spare. ive had varying treads all the time. anyway, ive i just rolled over 668000km/415000miles and i havent touched any differentials or anything related to it. just whats happened to me is all. not recommending this m.o. to anyone but ive actually "done the tests."

The gods are smiling on your and you have good karma! Keep on rolling Breadboy...your stories always put a smile on my face. Ever had a sunroof leak? LOL....see my post further down.
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1998 S70 T5 Emarald Green Metallic, 2004 V70 2.5T Ruby Red, Previous Owner of Black '94 850 Turbo Wagon. My cars have been running so well lately they've got me worried.

wow 415k and not even changed the oil in the difs?? - whats the vehicle?

Breadboy has an 855T 1996. Laughs at awd owners as he passes them in the dealships :)

Klaus
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(V♂LV♂s 1975 164, 1995 854T, 1998 V70R)

ahh so the dif fluid has been changed then as im pretty sure the dif fluid is shared with the box in an fwd 850 ...would need to check though!

considerably more fluid to cool etc in that scenario...

still say it HAS to be casuing ware though, only question is if its noticable or not!

i too own an 850 and have to say it causes me (touch wood) little greif, went to a dealers once...they tried to kill it never went back!

i dont even know what the "dif fluid" is. btw its a 95 850 turbo wagon. japan ive got stories you wouldnt believe. 669000km and rolling.

Love to hear them...you should start a thread just for that purpose: Breadboy's 850 Adventures." LOL
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1998 S70 T5 Emarald Green Metallic, 2004 V70 2.5T Ruby Red, Previous Owner of Black '94 850 Turbo Wagon. My cars have been running so well lately they've got me worried.

Mike

Read this about shaving tread on a tire.

www.tirerack.com/tires/tiretech/techpage.jsp?techid=67


Miker

Mike

I understand the dilemma.

Did you think about getting a new tire and have it shaved to the same depth ?


Racers do this all the time to eliminate the squirm you get with brand new tires.

Your next question is where to get this done.

Hey, I'm just the idea man.

Are there any race shops around you? Do a google on speed shops, maybe.

Miker

the problem is whats known as wind up....and oh yes it can happen in non 4 wheel drive cars too!
essentially two tyres of slightly different diameters on one differential force the diff to always be compensation and 'wind it up'.. same sort of reason you shouldnt use locked diffs on road only on loose surfaces...
now to the maths...3/32 = about 2.4mm..

now thats difference in radius so its 5mm in diameter.... piD gives us circumference....so roughly 5*3 = 15mm for every turn of the wheel...

so no sir you should not replace only one...not if you like your diffs! (and i bet they are a LOT more money than the tyres!)

sorry guys i cant agree..

the diff (on the axel) is there to allow the wheels to turn at differnet velicitys when cornering ...not all the time.... so if you have differnt sized tyres on each wheel your essentially going to exceedthe duty cycle of the diff...and heat the fluids etc up.. at the very least you will get accelerated wear..at the worst....well lets say it might not be pretty! You may also stress the central diff too.....

I have no idea if these cars have locking diffs (aka propper 4wd) if they do even on the loose stuff mismatched tyres are a serious no no.....

of course its only my 2c and arguably worth that but i wouldnt risk my several thousand $ worth of over complicated over electroniced 4wd sytem for the sake of the cost of a couple of tyres....

oh and 1.5cm assuming a 22" diameter wheel represent just under 1% in difference in rotational speed....

I like your math and respect your judgement in wanting to replace all 4. But 15mm = 1.5cm = 3/4inch, and that shouldn't be enough to warrant the computer or sensors to engage slip control. Just having tire pressure off by 5lbs on one wheel would do that also.
If he were to put the new tire on the right front, it wears the quickest on my car btw, then he should be good to go.
It's not like putting on a space saver spare and driving 30 miles to the closest service station, that will cost $$$$. Which is why I now joined AAA.

Klaus
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(V♂LV♂s 1975 164, 1995 854T, 1998 V70R)

It's not going to do anything to a diff to always have one tire on one side bigger than another. Nor to a WWD center diff for the rear tires to turn less than the fronts (which they always do, in fact, because rears always follow a tighter turn than fronts) -- what you don't want to do is drive a 4WD with the center diff locked, or in some 4WDs (like my 460 Gelaendewagen) without any center diff, on dry pavement.

Rather than a strictly mechanical thing about the differential, it's a concern of the pumps and other controls that diverts torque to the differentials. The reason for mismatching concern is for there to be a continuous signal of different speed which is going to have the AWD system continually thinking that there is wheelspin (or slippage) and trying to divert power (as it compensates for this alleged slippage).

By the way, you're 100% about this sometimes being a problem with 2WD cars. About ten years ago, Mercedes sedans with a certain antiwheelspin software would, when faced with mismatched tires, put the engine in low power mode (to lessen torque output) and the car would suddenly just go slower, and slower, and eventually just barely crawl down the road regardless of how the driver stomped on the gas pedal!

I had the same issue on our '98 XC with only 2/32nd wear. Volvo NA said to buy all four new, and many others said pretty much the same, but some gamble a little more with the mismatched sizes. The consistent size of all 4 tires at all times seems to be the most common thread in discussions about AWD failures, so it is really a tough call. I found a great answer on Ebay - I located an exact match tire with same amount of remaining tread - about $45 delivered to the door from Texas. Sngle tires don'w sell at a premium. There are quite a number of used tire businesses around so you might try a search to see what you can find. As for where to put the thicker tire, I forget, but there are a number of threads in the archives that discuss this with a fairly consistent answer- just don't want to guess on your dime here.
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Mike Sullivan ('95 855T (88k), '98 V70XC (92k), '95 855 NA (135k). Past Volvo's: '85 744 (256k), '86 245 (165k), '86 245 (195k), '88 745 (208k), '91 745 (196k), '93 965 (147k) .

So long as it is the same make, pattern, etc. it should not pose a problem. That is not much of a difference in diameter.

Klaus
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(V♂LV♂s 1975 164, 1995 854T, 1998 V70R)