Pros/cons of 18" spacesaver wheel in the boot of a 20" wheeled car?

[gr1nch]

Hi folks,
A pothole (or two) killed two of my tyres and both rims in one go on Saturday. My car is now with Mercedes Grimsby getting a full check. But it got me thinking about punctures generally as I've only got a tyre inflation kit in the boot.

But on two wheel websites I looked at the only spacesaver wheel for my car is 18" and mine are 275/35R20 on the back and 246/40R20 on the fronts.

Is this normal then to carry a standard 18" around? Any pros cons? I guess the outer diameter of the tyre is really what counts, but am not certain.

 

[clk320x]

Yeah AFAIK it won’t be a problem

 

[Gbrowncls55]

Yes it's the outside circumference that matters so the 18 should have a higher profile. Also make sure it clears your calipers (not sure what car you have but if it's an amg it's worth checking). I used to have a 911 turbo 3.6 and if you got a puncture in a rear you had to move a front wheel to the rear and put the space saver on the front....real pain

 

[MikeInWimbledon]

Hi folks,
A pothole (or two) killed two of my tyres and both rims in one go on Saturday. My car is now with Mercedes Grimsby getting a full check. But it got me thinking about punctures generally as I've only got a tyre inflation kit in the boot.
But on two wheel websites I looked at the only spacesaver wheel for my car is 18" and mine are 275/35R20 on the back and 246/40R20 on the fronts.
Is this normal then to carry a standard 18" around? Any pros cons? I guess the outer diameter of the tyre is really what counts, but am not certain.

It's the external circumference that matters, as long as the wheel clears the callipers, which on an S350d won't be a problem because most S350's are running on 18's.

Personally I'd try to buy a used wheel similar to one of your "normal front" wheels. It's a little bit more weight, but then you've got something to swop to when (cough) "your wife" damages a rim by driving over a pothole. (while not forgetting that they're different sizes front / back)

Obviously, if you'd been on 18's, you almost certainly wouldn't have damaged either your tyres, or your rims on those potholes last week. ("Two extra inches make all the difference," I'm told) But you knew this, didn't you ?

.

.

 

[Petrol Pete]

Check the tyre pressure. chalk mark a vertical line on one of your tyres and the road surface, roll forward (or back if you really want to) until the chalk mark on your tyre has done a 360' revolution then mark the road surface again.

Measure between the two chalk marks and hey presto ! you will have the actual circumference of the tyre.

 

[BTB 500]

All 3 of our vehicles have a spare that doesn't match any of the road wheels. As mentioned it's fine so long as the rolling radius is correct and they clear the brake calipers.

 

[BTB 500]

Personally I'd try to buy a used wheel similar to one of your "normal front" wheels. It's a little bit more weight, but then you've got something to swop to when (cough) "your wife" damages a rim by driving over a pothole.

You need to make sure it will fit in the car - the wheel well in the boot of our C Class is too shallow for a standard front wheel.

 

[baxlin]

You need to make sure it will fit in the car - the wheel well in the boot of our C Class is too shallow for a standard front wheel.

Also, I think I read somewhere that there's a law exemption that allows different wheels/tyres on the same axle when using a 'temporary' wheel (ie spacesaver), which may not apply to an odd size full road wheel?

 

[BTB 500]

Also, I think I read somewhere that there's a law exemption that allows different wheels/tyres on the same axle when using a 'temporary' wheel (ie spacesaver), which may not apply to an odd size full road wheel?

You could be right ... the factory spare on our Vito is a standard 16" steel wheel (not a space saver), but it's painted red and has a large "50 mph" sticker on it. I guess purely because it's not the same size/width as the factory 17" alloys - presumably this speed restriction makes it legal.

 

[Petrol Pete]

Also, I think I read somewhere that there's a law exemption that allows different wheels/tyres on the same axle when using a 'temporary' wheel (ie spacesaver), which may not apply to an odd size full road wheel?

You are probably correct, as long as the rolling circumference is the same on the same axle , if mis matched the differential could suffer and all sorts of lights could flash on the dashboard , ABS, TC , etc

 

[renault12ts]

The spare is speed restricted. So, there should not be a problem.