Replacing a tyre/s?? Worries over centre diff etc

[cliffdunedin]

Hey guys, i've bought a nice set of OEM 18's off TM but 1 of the tyres has a bubble in the side wall so needs to be replaced.

My Q is: Can i replace the one by itself or the 2 on the same axle OR do i need to replace all 4 like i've read online which sounds totally ridiculous and scaremongering to me.

Cheers

[GC8E2DD]

Depends entirely on the tread depth. The greater the difference between the old and the new, the harder work it will be for your diffs. Also, different makes of tyre have differing rolling circumference even within the nominal sizes. If three of the old tyres are in good condition, I'd be selling them to fund four new ones.

[cliffdunedin]

 GC8E2DD said:

Depends entirely on the tread depth. The greater the difference between the old and the new, the harder work it will be for your diffs. Also, different makes of tyre have differing rolling circumference even within the nominal sizes. If three of the old tyres are in good condition, I'd be selling them to fund four new ones.

Sell 3 good tyres and then buy 4 new!

Is this actually what Subaru drivers have to do every time they get a puncture or get uneven wear? I thought all the info i was reading was taking the piss... but if this is actually case i'm starting to regret buying one!

[Joker]

10+ of only ever buying 2x new at a time on the same car 1998 BG5C JDM GTB LTD, no ragrets

the motor died before anything else (split heater hose = BHG

[Marky]

No, just replace the one, or if in doubt the pair

Ideal world you'd do all four at once, realistically most people don't with next to no ill effects

Subarus aren't the only 4wd car in existence

[DRFVDR]

Obviously you have never had a centre diff seize because of running new tyres on one axle with worn on the other,

I have and it cost my $5k to fix

upto you though

its your car

do as you want

[GC8E2DD]

 cliffdunedin said:

Sell 3 good tyres and then buy 4 new!

Is this actually what Subaru drivers have to do every time they get a puncture or get uneven wear?

No. This is what I'd do; dependent on tread depth and the availability of the tyres you're matching. I'm not all Subaru drivers. I tend to keep my cars a long time. I also couldn't be bothered having one tyre perpetually out of sync with the others. It's your car, do what suits =]

[cliffdunedin]

Cheers for the replies guys... Sorry I was just a bit pissed off, I bought this car as a replacement to an Audi Quattro that served me well for 5 years but just getting tired, with many naysayers saying "Ohhh stay away from Subarus" blah blah blah, bought a clean example with a PPI from Crowesport (all good) bought it back to Dunners and then within a week I had to replace Trans and now being told that it could F up from replacing one tyre...FML!!

Surely that's a design flaw! My old BF5 rolled around on 3 19's and one 15 for about 3 months when I was a young fella SMH

[DRFVDR]

Any AWD vehicle that runs a Viscous Centre Diff, comes with this warning, I have seen it in the user manual for Subaru also A 100 series landcruiser, an AWD Hiace and just recently in the use manual of our AWD Mitsi Rosa.

So not a "Subaru" thing just a Viscous thing

[ADIKT]

Why not buy a second hand tyre with similar tread depth?!

[McDoof]

 

Surely that's a design flaw!

Not really a flaw, it just comes with the territory on an AWD car. I made the mistake on my old MK2 Golf Syncro which also has a viscous centre diff. Blew the diff within about 2 weeks. Some of the later Automatic Subarus may be able to handle it better due to having a trickery electronic centre diff. Personally I would only ever do all 4 ,but that is because I have some amount of OCD and really hate having tyres that are different.

If money really is tight then you can probably get away with just doing 2, but I think over time you may have issues.

If it comes down to it, then pick up a set of ATR Sports for next to no money for new tyres (go with a 225 45 18 rather than the stock 215 45 18 they fit the stock rim, are heaps cheaper and also make your speedo almost accurate) and sell the 3 good ones you have on TM if they are worth selling.

[Joker]

reckon we need more info on failures Darf & Doof

like i said never any issue on the same car for 10 years here, & highly doubt anyone turns left equal amounts of right corners 'evening' out diff wear on the same axle

I say the centre diff should be able to cope with a new pear of tires up front (always put your new rubber there)

otherwise how do they cope with 70/30 & 90/10 power/torque splits like most SUBARU cars run

genuinely keen to learn & build up the resources here, I'm not just trying to stir for once

[McDoof]

My failure was not on a Subaru to be fair. It was a VW where it runs in FWD until it detects a speed differential and then engages the rears. I am guessing that this has something to do with why it started to make funny grinding noises. You can probably get away with some degree of different rolling circumference though without it going bang.

[Joker]

(& I have feeling DRVDR's failure was also NOT on a Subaru)

sorry to be nit picky but seems a little like scare mongering to me

[McDoof]

Not scaremongering, just sharing the experience that I have had. I did mention in my original post that it was on VW and that I have a pet hate for different tyres, so my bias goes towards having the same rubber on all 4 corners.

[loner]

I would say on a sloppy road diffs the heat generated would be very small and easily dissipated. Probably prolonged driving with uneven tyres on tight motorsport diffs on tarmac, you'd have problems.

edit: in fact viscous diffs are effectively open until they see a large speed differential for a period of time, then they start to lock.

plated diffs on a stock car need a lot of torque to lock up, so they are effectively open when cruising.

Edited November 8, 2015 by loner

[DRFVDR]

 Joker said:

(& I have feeling DRVDR's failure was also NOT on a Subaru)

sorry to be nit picky but seems a little like scare mongering to me

Mine was not a Subaru either BUT a Viscous diff is a viscous diff, a 10% variance seems to the rule of thumb, if you Understand how a Viscous diff works then you will be very cautious.

[Joker]

10 % would be hard to come by if you run the numbers on tread depth on the same 'size/brand' tires no? even in new vs bald circumferance / total wheel height (car calculator available in a link in General section)

Edit : here's the thread for Car Calculator V2.1 download HERE! Convert KW>HP / rolling diameters and MORE!

waiting for Newsuba to pop in : yes different brand tires with the same size rating CAN be quite different if you get a tape / piece of string out & measure, even in the same brand in different production runs

I still stand by the Pair at a time method & you should be fine in a Subaru (always run matching brands / sizes etc)

happy t osay I'm wrong if anyone ever pops up with a failed centre diff in a Suabru

Edited November 9, 2015 by Joker

[scratch]

I had it happen in a bh legacy. I worked out there was 20mm difference in circumference front to rear, was enough to lock the diff on even short drives.

[Marky]

How much difference would say 3psi difference in inflation across front and back axles make to rolling circumference?

Just curious now

Like for arguments' sake, there's a truck in my workshop now with 8 driven wheels (3 axles, twin wheels on both back axles and 2 diffs), do they change them all at once? Sets of 4? (Genuinely curious I'm gonna ask the driver when he gets back haha)

[Andy_Mac]

The larger diameter the less impact tread wear will have though ay, so a full size truck one could probably get away with it without any trouble

Have always had an odd whine to mine that has made a few clicks when turning in the last while, wonder if thats wear from it having different brands with different depth tyres when I first got it.

Edited November 9, 2015 by Andy_Mac

[Joker]

 scratch said:

I had it happen in a bh legacy. I worked out there was 20mm difference in circumference front to rear, was enough to lock the diff on even short drives.

WHOA 20MM GETTING SOME GOOD INFO NOW

WOW CAPS TOO BAD

Edited November 9, 2015 by Joker

[McDoof]

 

How much difference would say 3psi difference in inflation across front and back axles make to rolling circumference?

That's actually a very good question. Especially on those with a bigger tyre profile. I think the difference is less marked on a low profile tyre because the side walls are generally quite stiff.

[loner]

Does a lower or higher pressure change the circumference? I don't see how.

[McDoof]

A flat tyre reduces the diameter of the wheel so this means a smaller rolling circumference.