tyre sizes

[Davy Shearer]

Hi Folks


I've a V90cc 2019 running 235/50/19 and was wondering if anyone has tried 235/55/19 i've checked the sizes available and despite going up to 21" rims the 235/55/19 has the largest dia tyre it seems that the 55 profile has more choice and cheaper

Many thanks
Davy

[isleaiw]

Originally Posted by Davy Shearer

Hi Folks


I've a V90cc 2019 running 235/50/19 and was wondering if anyone has tried 235/55/19 i've checked the sizes available and despite going up to 21" rims the 235/55/19 has the largest dia tyre it seems that the 55 profile has more choice and cheaper

Many thanks
Davy

Because you are changing the depth (55) but not the width (235) that tyre will have a slightly higher circumference - meaning your speedo will be out, your gearing changed, and of course you will have to do all 4 at the same time so as not to mess up the 4x4 - unless things have moved on since my XC70...

[SuffolkBoy]

....and notify your Insurance company?

[Wizzpop]

Originally Posted by isleaiw

Because you are changing the depth (55) but not the width (235) that tyre will have a slightly higher circumference - meaning your speedo will be out, your gearing changed, and of course you will have to do all 4 at the same time so as not to mess up the 4x4 - unless things have moved on since my XC70...

A 3.3% change in speed. 70mph becomes 73.3mph.
It's normally recommended to keep within 2.5% change

[Philip Fisher]

Originally Posted by Wizzpop

A 3.3% change in speed. 70mph becomes 73.3mph.
It's normally recommended to keep within 2.5% change

Which way would it be out? I reckon at 70mph (on the dash) the genuine speed through GPS (on a level road) is about 67mph. So would this change improve this or make it worse?

[Wizzpop]

Originally Posted by Philip Fisher

Which way would it be out? I reckon at 70mph (on the dash) the genuine speed through GPS (on a level road) is about 67mph. So would this change improve this or make it worse?

Originally Posted by Wizzpop

A 3.3% change in speed. 70mph becomes 73.3mph.
It's normally recommended to keep within 2.5% change

70 on the original becomes 73.3. You are increasing the tyre diameter and therefore increasing the distance per wheel revolution

[isleaiw]

Originally Posted by Wizzpop

70 on the original becomes 73.3. You are increasing the tyre diameter and therefore increasing the distance per wheel revolution

so in theory if the speedo normally overreads and you are making it go faster than the speedo thinks, you could just be correcting the speedo error....

It would spoil my idea that 8% above the limit trough average speed cameras is OK as the speedo overreads though!