SAM-UK300

iTrader: (8)

Hi,

Im sure I remember reading on here before that if you run different wheel sizes front and back I.E 18x9.75 on rear and 18x8.75 front then it will make your diff go bang, is that correct or have I made it up?

Anybody doing it succesfully?

Cheers in advance

SAM-UK300

iTrader: (8)

Anybody ?

forgedmarco

iTrader: (10)

I think it has to be same size with equal tread all round or could cause diff problems

paul98typer

As above Pretty sure they have to be same size.
Had problems with a calibre 4x4 many years ago which had different tyres, replaced all the tyres with same brand/size and sorted.

legacy_gtb

iTrader: (3)

Has to be the same! The smallest difference in rotational speed front to back will continuously wind up the centre diff, which when sitting at motorway speeds for a length of time will overheat the silicone oil in the viscous coupling in the centre diff and either lock it up completely or turn it into an open diff.

swaynie

iTrader: (6)

As long as you use the same profile such as a 245/45/18 and a 225/45/18 the rolling radius is the same it's just that you will be running a slightly wider rear.

Turbotits

iTrader: (2)

Yep width isnt a problem providing all tyres have the same rolling radius

scoobyricht

iTrader: (4)

The rolling radius on 245/45/18 isnt the same as 225/45/18, there is nearly 2 inches difference in the circumference. 245/40/18 is closer to 225/45/18 though at just under 1 inch difference but still not gonna be diff friendly.

BillyBrown

Yeah I would agree, as long as the are all the same overall diameter (rim and tyre profile) you'll be ok, a different width shouldn't be a problem.

JonMc

iTrader: (51)

If you stretch a tyre over a wider rim will it not also have a different rolling radius because of the stretch affecting how vertical the sidewalls are

legacy_gtb

iTrader: (3)

Theres some bad advice here, be careful!

All 4 tyres should be the same make, size and condition.

SAM-UK300

iTrader: (8)

Thanks everyone for your replies... So justo clarify , it's the overall diameter that matters and not the width... So I can have a 9.75j wheel on the back and a 8.75j wheel on the front and as long as they both have the same profile tyre and the correct width tyre on both wheels I.e no stretch that should be ok?

banny sti

iTrader: (68)

Some proper retards in here, stick with the same size tyres front and rear as the educated folk have said

scoobyricht

iTrader: (4)

I dont think some people realise that the "45" is a percentage of the width.

alcazar

iTrader: (2)

NO!

Any difference in rolling radius between front and rear will knacker the centre diff.

It is almost impossible to get the rolling radius spot on unless using the SAME width wheel, same diameter and same size tyres.

You have been warned.

richie001

iTrader: (3)

I wouldn't risk it,but it's your car.So do what ever you want

SAM-UK300

iTrader: (8)

Top Man, Thanks, I'll stick to same all round!

legacy_gtb

iTrader: (3)

Id go a bit further than that. Make is fairly important too!

Run a tape round a brand new toyo 2254517 and a yoko of the same numbers and theres a significant difference.

Only way to go with a subaru viscous centre diff is to buy tyres in sets of 4 and rotate them occasionally so they wear out at the same time.

alcazar

iTrader: (2)

I would agree, and it's what I do. Makes tyre changes a PITA to pay for.... like most stuff on a Scoob.

ScoobP1

iTrader: (1)

With the price of decent rubber these days you might as well just change the centre diff IF it did let go.

Could work out cheaper.

legacy_gtb

iTrader: (3)

Dont understand??????

It doesnt make it more expensive, it just means you pay twice as much half as often!

Trolley jack under the rear diff and scissor jack under the front sill means a rotate takes 5 minutes.

And the 'IF' is more of a 'WHEN' by the way. Theres probably more high mileage open diffed imprezas about than youd realise as the symptoms dont show themselves until things get slippy. If the diff is so buggered its locked up then youll get massive mid corner understeer.

Guest

iTrader: (2)

Has anyone got any more info on what happens if the centre diff fails? Is there any way of telling other than getting the car on a set of rollers?

swaynie

iTrader: (6)

Just to clarify measurements on tyres

jura11

iTrader: (7)

Hi there

You can't run different sizes wheels and tyres on the car,you will kill diff very soon,simply is not worth it


Jura

alcazar

iTrader: (2)

good grief.......

ScoobP1

iTrader: (1)

How many Subaru owners are going to swap all 4 wheels every 1k or so and then buy all 4 new tyres in 1 go? About 1% or less I would think.

How many centre diffs fail on Subaru's? Not the 99% that don't swap their wheels around I'm sure.

Getting rid of good rubber just because it isn't the same depth as all the others just does not make financial sense and so I'd take my chances with the diff.

My Audi Quattro is the same and had no ill effects. Not sure if it has a centre diff but I wouldn't swap the wheels about all the time or buy 4 new tyres just to keep them all the same depth.

richie001

iTrader: (3)

I paid £500 for a set of 18" Goodyear Eagle F1 and took about 30mins to fit.I think I new diff would cost a lot more and that not including cost of labour etc to fit the new diff.

ScoobP1

iTrader: (1)

Diff failure is probably not going to happen over the life of 1 set of tyres though.

Not saying this route is the best option but it is the probably the most common option by the masses consciously or not.

legacy_gtb

iTrader: (3)

7

You only need to rotate the tyres once half way through the life of the tyres, not every 1k as you suggest. And I dont know any subaru owners personally who dont do this.

How many centre diffs pop ..... thats probably a question for someone like dave at api who does alot of box rebuilds, but I can say for sure its more than you realise now these cars have become cheap enough for people to run on a shoestring.

Worst bit is, if the viscous coupling is buggered, you might not notice till your stuck in the snow spinning one wheel. This is because the centre diff will still work as a diff with or withoutthe viscous coupling.

And audis centre diffs arent viscous in the same way, so theyre alot less fussy!

legacy_gtb

iTrader: (3)

Wrong bud. One long motorway journey could do it.

Do you know how they work?