Factory Tire Size vs. Spare Size

[tigger73]

I recently bought a 2018 Tiguan Sportline and am looking at replacing the space saver spare with a full-size wheel as I do some country trips and think taking a full-size wheel is a good insurance policy from getting stranded.

A question for all you wheel/tyre experts out there. What should the difference in diameter of a (space saver) spare be from the stock wheel?

Reason I'm asking is that there's a reasonable size difference from the stock Kapstadt's on the Sportline and the factory supplied space saver and got me wondering if there's any recommended minimum size.

Kapstadt 20x8 ET41 running 235/45R20 - diameter = 719.5mm

Space saver 18x?? running 145/85R18 - diameter = 703.7mm

It's around 2.2% difference which I though was a bit much for something coming from the factory (155/85R18 tyre would be 720.7mm which is a lot closer size).

Also on a related point I was looking to run a 17" wheel as a spare until I also read the section in the manual on spares. Owners manual says that if the tyre on the spare is not the same as the other tyres on the car:

• Don't drive faster than 80km/hr,
• Avoid full acceleration, sudden braking or fast driving through bends,
• Don't use snow chains
• Check tyre pressures as soon as possible

So basically unless you get another matching rim/tyre you can't technically go over 80km/hr. I understand this as if there's different wheels/tyres fitted this can effect the operation of ABS/ESC/TCS.

So what do you do. Go and buy a matching spare, get a non-matching spare and drive carefully or just stick with the space-saver given that the non-matchng spare is going to be speed limited anyway?

[dylan8]

As long as the spare was close to the same width tyre and over all diameter I think you'd be OK.
For example lots of mk4s came standard with a 17x7 225/45 combo and the spare was a 15x6 195/65
Nothing in the manual about driving differently on that size.
Ive had 225/45/17s all round and thrown a single 205/45/17 on the back to get me out of trouble and it seemed OK even at 110km/h

However if your comparing a space saver to a full size wheel the large change in tread width wouldnt do wonders for handling and breaking in my mind.

[tigger73]

Yeah though mk4 has a lot less tech in terms of ABS, ESC, TCS, etc so changing Wheel size on these isn’t going to throw it out like it (possibly) will on a modern car.

I can’t find factory recommended min/max sizes anywhere. And VW Aus won’t comment other than quoting the owners manual.

Sent from my iPhone using Tapatalk

[dylan8]

For sure.

Anything closer than the stock space saver to the rolling diameter would have to be better and couldn't hurt

[Hillbilly]

Also it is usually recommended that you never use a spacesaver on the front wheels So if you get a front puncture change a rear onto it and put the spacey on the rear. Had this problem in NZ when the Jap imports all came with space savers.
Most people simply went to a wreckers and bought a wheel that matched. The spare wheel wells were large enough to take a full size.
We had to do this with Taxis as we werent allowed to have a spacesaver