Running car on 2 different wheel sizes

B0bbyEwing

Normal (alloy) wheels: 225/40/18

I've had to take one of the rear wheels off (puncture). I was about to put the space saver wheel on when story short I was able to acquire a 'proper' wheel that came off a slightly lesser powered diesel estate version of my car

Acquired (steel) wheel: 205/55/16

The space saver said limited to 50mph & an inflate to 60psi notice was on it. That would've ruled out motorway driving.

I wont have my wheel repaired & back until Friday. 

Question is really, with the wheel I've been able to put on, should I be good for motorway driving?


NOTE: I said good. Different from ideal, obviously.

Jonboy_1984

ABS, traction control and some tyre pressure sensors work by comparing the rotation speeds of the wheels. Having two different size wheels on the same axle will potentially screw with them all.

Also likely to count as a modification in terms of insurance, so will possibly void everything except the third party liability in the event of an accident.

Krakkkers

There is less than 1% difference between the 2 wheels when you account for the profile (55% of 205 plus 16 rim) 
and (40% of 225 plus 18 rim) That said i would not do it.

BikingBud

https://tiresize.com/comparison/

Seem to be the same effective size but I would be concerned about the difference in width ie the contact area and the sidewall.

Is there a web support group for your vehicle they may give you a more informed perspective.

Krakkkers

Have you ever wondered why tyres are imperial diameter and metric width?

daveyjp

It really isn't a good idea to put on a totally mismatched wheel and tyre on a car and then use the car as normal.  Any serious accident (which may not even be your fault) and the car will be inspected.

I once put a space saver on the wrong axle for a 5 mile trip to have a puncture repaired.  Braking was scary.

ontheroad1970

Why does a space saver rule out a motorway trip that is urgent or needed to get to a tyre fitter?  I had a puncture in a relatively remote part of the Lake District and had to use a small section of motorway.  Driving 50mph on a motorway is not a safety issue, HGVs do it all the time - space savers aren't designed for prolonged use, but for getting to where you can change the tyre it is perfectly serviceable.

B0bbyEwing

6 posts in & we're still not sure whether it's fine or not. 

Though granted, I see you wouldn't do it Krakkers so thanks. 

At least I know there could be issues with insurance & such. 

Oh well, I'll see how it goes in a bit. 

B0bbyEwing

Well that answers that one then. 

No problems & also noticed absolutely no difference in the way the car drove. 

All good. 

prowla

I would not put different wheels on the same axle unless it was on an oval speedway car!

marlot

B0bbyEwing said:

Normal (alloy) wheels: 225/40/18

I've had to take one of the rear wheels off (puncture). I was about to put the space saver wheel on when story short I was able to acquire a 'proper' wheel that came off a slightly lesser powered diesel estate version of my car

Acquired (steel) wheel: 205/55/16

The space saver said limited to 50mph & an inflate to 60psi notice was on it. That would've ruled out motorway driving.

I wont have my wheel repaired & back until Friday. 

Question is really, with the wheel I've been able to put on, should I be good for motorway driving?


NOTE: I said good. Different from ideal, obviously.

I had a mondeo from new, which had similar - a smaller wheel, but bigger sidewall.  It had stickers on it saying 'emergency use only'.  NOT a space saver, but a steel wheel with a normal type tyre.

I'd be tempted to do similar in your case until you can get the original repaired.

Note that the car would be an MOT fail due to mismatched wheels.  That doesn't necessarily make it unroadworthy - it would also fail with the spacesaver on.