I have a 73 plate 4WD Karoq fitted with 225/45R19 wheels and am looking to get a spare wheel instead of the ‘pump and goo’ in the boot.

According to Skoda it's ‘difficult’ to fit a full size spare because of the depth of the wheel well and a 125/70R18 space saver is identified even showing tyre pressures on the back of the fuel flap.

I've done a bit of digging and found out that the diameter of the 225/45R19 is approx 685mm where as the 125/70R18 is 632mm ie 7.73% smaller

How much of an affect would this be on all of the electronics that rely on having 4 wheels of the same diameter or as close to the same as possible?

I've also found that a 135/80R18 has a diameter of 673 mm so 1.75% smaller which would be a better match, but i dont see any info on this from Skoda

Which would be the best option the 125/70R18 or the 135/80R18?

Thanks

My 2023 4x4 Sportline was supplied from the factory with the 125/70 R18 space saver. See photo below - the 135/80 might be too big to fit in the polystyrene storage that goes around the spare wheel.

1 hour ago, thamestrader said:

My 2023 4x4 Sportline was supplied from the factory with the 125/70 R18 space saver. See photo below - the 135/80 might be too big to fit in the polystyrene storage that goes around the spare wheel.

The sidewall height of 135/80R18 is 20.5mm higher than 125/70R18, so there would need to be a gap of at least 20.5mm around the 125/70R18 for the 135/80R18 to fit.

The inflated 125/70R18 will be about 7mm wider than the inflated 135/80R18 when fitted to the same 3.5Jx18 ET25.5 5/112 57.1 space saver steel rim...not the nominal 10mm.

The width of an inflated tyre is measured from sidewall to sidewall, at the widest point.

Edited 7 October, 20257 Oct by Carlston

I bought a spare wheel, jack etc on line from the wheelshop close to Manchester. No problems with them giving me advice and delivery was quick. Although my car has 17" wheels and tyres, they advised me to go for their 18" spare. This fits nicely in the skinny wheel well but I don't have the foam inserts. I keep the tools in the bag supplied with the spare which sits in the right hand cubby hole in the boot.

On 07/10/2025 at 19:32, Carlston said:

The inflated 125/70R18 will be about 7mm wider than the inflated 135/80R18 when fitted to the same 3.5Jx18 ET25.5 5/112 57.1 space saver steel rim...not the nominal 10mm.

That should read, "The inflated 135/80R18 will be about 7mm wider than the inflated 125/70R18...".

Edited 8 October, 20258 Oct by Carlston

On 07/10/2025 at 16:13, mygreyskoda said:

Which would be the best option the 125/70R18 or the 135/80R18?

I would hope that Skoda have specified the wheel to be appropriate, rather than what just happened to fit the space. But like the "goo", where it falls down is when you get a puncture on a Sunday night, 200 miles from home. Being restricted to 50 MPH on a motorway with a procession of HGVs thundering up behind you doesn't sound like fun...

On 07/10/2025 at 19:32, Carlston said:

The sidewall height of 135/80R18 is 20.5mm higher than 125/70R18, so there would need to be a gap of at least 20.5mm around the 125/70R18 for the 135/80R18 to fit.

The inflated 125/70R18 will be about 7mm wider than the inflated 135/80R18 when fitted to the same 3.5Jx18 ET25.5 5/112 57.1 space saver steel rim...not the nominal 10mm.

The width of an inflated tyre is measured from sidewall to sidewall, at the widest point.

18 hours ago, Carlston said:

That should read, "The inflated 135/80R18 will be about 7mm wider than the inflated 125/70R18...".

Thanks Carlston

4 hours ago, Rbz5416 said:

I would hope that Skoda have specified the wheel to be appropriate, rather than what just happened to fit the space. But like the "goo", where it falls down is when you get a puncture on a Sunday night, 200 miles from home. Being restricted to 50 MPH on a motorway with a procession of HGVs thundering up behind you doesn't sound like fun...

I'm sure they have but I can't understand why they suggest the smaller diameter 125 instead of the 135 which has a much closer diameter to that of the 225's fitted to 16" 17" 18" or 19" rims

225/60R16" 676 mm diameter

225/55R17" 679 mm diameter

225/50R18" 682 mm diameter

225/45R19" 685 mm diameter

125/70R18" 632 mm diameter

135/80R18" 673 mm diameter

4 hours ago, Rbz5416 said:

I would hope that Skoda have specified the wheel to be appropriate, rather than what just happened to fit the space. But like the "goo", where it falls down is when you get a puncture on a Sunday night, 200 miles from home. Being restricted to 50 MPH on a motorway with a procession of HGVs thundering up behind you doesn't sound like fun...