Tyre size (circumference)

[pitscars]

Hi all - I have an Impreza - 2007 - automatic - recently discovered RHF tyre scrubbed out - (should have had that alignment done) - went to the local tyre guy - he did not have the exact same tyres - got two new ones on the front - 205/60/16s - same "size" as the rears - he assured me that the circumference would be the same - hmmmm - got home and measured them - the new front tyres are a good inch and a half bigger than the rears (in circumference) - I know this would be an issue with a manual car - but an auto ?? Cheers

[987687]

It's definitely a problem. The driveline in these cars is FWD with wet clutches that send power to the rear, difference in tire size will constantly slip these clutches and destroy them in short order.

Your best bet at this point is to get matching tires.

Earlier subarus had a fuse holder on the passenger side firewall under the hood that said FWD on it, you could put a 20a fuse in there to disable the awd to avoid transmission damage when using a spare tire. If your car has this fuse holder, go put a fuse in it immediately until you get the tire issue worked out.

 

Before you ask if you can run FWD mode indefinitely... It's a hotly debated topic, some people say it runs the solenoid at fully duty cycle to hold the clutches open, some people say it's fine and designed to work that way.... Bottom line is you have an awd car, fix the problem so it works correctly without damage.

Edited December 2, 2017 by 987687

[wtdash]

G'day,

+1 - DO NOT DRIVE w/the different tire sizes. 

 

 

 

go get 2 more that match.

 

Cheers

Edited December 3, 2017 by wtdash

[1 Lucky Texan]

^^^ what they said, tires should be IDENTICAL.

 

run FWD fuse (see your owners manual about use of emergency spare tire)

 

less desirable options; run new tire pair on opposite corners (only IF your rear diff is not limited slip), or, have new tires shaved down to match circumference of old tires (this may not work if the difference is as great as you say, plus, it wastes the utility of the new tires)