Spare wheel size... odd?

[JJKM]

My 1991 torslanda has 14'' wheels on it. The spare wheel is knackered. A local scrap yard have a 15" hanging round; would it be safe to use this as a spare, hence running odd wheels?...

[Antz]

As long as the rolling radius of the tyre is the same youll be fine.

Get the size of your tyres, and the scrapyard tyre, stick it into a tyre size calculator (google for one) and itll tell you how far out of are. Anything below 4% deifferecne is usually considered fine.

[leftfootleashed]

Originally Posted by Antz

As long as the rolling radius of the tyre is the same youll be fine.

Get the size of your tyres, and the scrapyard tyre, stick it into a tyre size calculator (google for one) and itll tell you how far out of are. Anything below 4% deifferecne is usually considered fine.

That's true of changing all the wheels for a different size, but I don't know about running one different, that's a different matter.

It'll get you home though.

(Side story: I once had a VW Polo. The guy I bought it off told me about a cheap local tyre place. After a few months I noticed one of the front tyres was massively more worn on one side, more than a tracking issue would account for. My usual tyre place said it was the rack. I took it to my usual garage and told them this. They spent all day taking the rack apart and scratching their heads, and eventually realised one of the front tyres was a different size to the others. Needless to say, I haven't been to the cheap tyre place the guy recommended.)

[tannachyallen]

As Antz says, if you get the rolling radius to be near it is effectively the same size. Most space saver spares are nowhere near the same as the vehicles fitted tyres and they are supposed to get you home. So a 15" wheel with a tyre fitted to make the radius the same as your 14/tyre combination will work out just fine.

Regards,

Dave A.

[Yaxley]

Originally Posted by leftfootleashed

That's true of changing all the wheels for a different size, but I don't know about running one different, that's a different matter.

It'll get you home though.

I agree, in my opinion to use a different sized rim/tyre combination on the same axle, (even if the overall diameters of the wheels are the same), risks a potential difference in sidewall flex when cornering (particularly with the ‘balloon like’ aspect ratio of the Volvo 240 14 inch rim tyre).

Such a combination driven in a straight line would probably not significantly affect handling, but it is not something I would want to risk other than in an emergency.

Isn’t this why ‘special spare’ tyres have yellow markings and speed restrictions?

[tannachyallen]

Originally Posted by Yaxley

Isn’t this why ‘special spare’ tyres have yellow markings and speed restrictions?

Yes, exactly. It's just for emergency use. (I don't even carry a spare anymore).

Dave A.

[Volvorama]

I run a Torslanda on either 940 15" steels or 240 GLT Virgo Alloys, both with 195x65x15 tyres. Very slightly smaller rolling radius but vastly better to drive.
A 205x65x15 would probably get the radius back if you wanted to.