Different size of spare wheel

[kave]

At the moment we have four wheels with the tyre size 235/55 18". Our spare tire is 235/55 17". It's a 3,5% size difference.
Is it ok to use for a short while or do we need to replace the spare with same size?

 

[kave]

 

[WelshGas]

At the moment we have four wheels with the tyre size 235/55 18". Our spare tire is 235/55 17". It's a 3,5% size difference.
Is it ok to use for a short while or do we need to replace the spare with same size?

No. It is the overall Diameter/Circumference that is important.
Your mix of tyres would preclude this as you appear to be using non-VW approved sized tyres on the 18" wheels.
Approved VW Wheel/Tyre combination


You would need a 235/60 R17 103H tyre to give compatibility to use as a spare.

 

[Drpps]

Do you have all terrain tyres on at the moment?
The usual 18" tyre size is 255/45 R18 not 235/55
The usual 17" is 235/55 as per your spare.
A 255/45 18" won't fit in the carrier because of the width. I don't think the extra diameter of 235/55 18 would fit either but you might have to try one of the existing ones under there to find out. If the van came with 18" wheels from new then it would have had a spare supplied in the UK, only tyre sealant, so either the spare or the wheels have been added afterwards. If the rolling diameter is the same then using a 17" as a temporary spare in a similar way to a space saver would be fine but the rolling diameter of your current set up is at least 3.5% different. The van would be a few cm down on that corner. As a get out of the wilderness option it would be fine but very much a temporary solution until original is repaired/replaced and I am not sure I would be comfortable with the mismatch.

 

[Wesel]

At the moment we have four wheels with the tyre size 235/55 18". Our spare tire is 235/55 17". It's a 3,5% size difference.
Is it ok to use for a short while or do we need to replace the spare with same size?

Your avatar indicates that you have a 4motion. In this case it is not recommended to ride with wheels of different diameters!

 

[B J G]

A 235/60/17 tyre will be very close. There are a few 106 load rated tyres such as Michelin CrossClimate SUV but 102 load rated ones are more common and cheaper -- the load is sufficient for any Cali. + 850kgs.
I actually have a 235/60/17 102 as a spare.

Calculation shows a 0.16MPH difference between the 2 tyres + 60MPH but tread depths could vary that.