I’m going to embarrass myself here…. Are 18” wheels + tyres the same size as 20” wheels plus tyres? I.e. do they have the same overall diameter? I thought the 20" just has a thinner tyre and the rolling distance is the same otherwise the speedo would be different between the Vogue and the HSE for example with the different spec wheels?

I’m picking up some 20” wheels at the weekend, but only a set of 4, could I keep my spare 18” as a spare?

With odd sized tyres I imagine the suspension will have a “plausibility scenario” issue as well as the axle diff would overheat if used for more than a few miles.

I never carry a spare with me, due to the LPG tank anyway and I’m usually close to home. But it’s sods law if I don’t have one I’ll get a flat!

Dan 

You will have the same rolling radius, else your speedo would be out. Keeping the 18 as a spare would be fine. Java with Ivory 2006 4.2 Supercharged. 23.5k miles - NOW SOLD!

jayzee wrote:

You will have the same rolling radius, else your speedo would be out. Keeping the 18 as a spare would be fine.

Yay. 

About half of the way down is an overall circumferance calculator/comparison for current wheel/tyre vs new wheel/tyre:

http://www.carbibles.com/tyre_bible_pg4.html

I would presume as long as they're not too far out you're OK for a short period - otherwise your diff will work overtime!

Yep, all fine.

But, you wouldn't want to have the 18" tyre on for long as the sidewall depth and flexibility are so different, I've never tried it but it could potentially affect handling or safety.

But, these days, who uses a psare for long periods of time? Discovery 4 HSE
1998 110 TUM HS FFR Hard Top XD WOLF
1982 Series 3 Hard Top

*Gone:L462 D5 HSE LUX, L663 Defender 110 HSE, Discovery 3 HSE, 2014MY Range Rover Sport 5.0 Supercharged AB Dynamic; L405 Exec Vogue SE 4.4, 5.0 Supercharged Autobiography, Defender TDCi XS CSW, Defender TD5 HT, Vogue SE TDV8, Vogue TD6, RRSport SC 4.2V8, Classic 3.9 Vogue Auto, Land Rover Series 3 SWB

sleepezy wrote:

About half of the way down is an overall circumferance calculator/comparison for current wheel/tyre vs new wheel/tyre:

http://www.carbibles.com/tyre_bible_pg4.html

I would presume as long as they're not too far out you're OK for a short period - otherwise your diff will work overtime!

Thanks for that, all seems fine:

 

dan_uk_1984 wrote:

?

I’m picking up some 20” wheels at the weekend, but only a set of 4, could I keep my spare 18” as a spare?



Dan

As already stated as long as the wheel/tyre combinations are the stock sizes 18/19/20 can be mixed as far as rolling radius is concerned.