speed

[Tazzy]

just a quick question

i have 15' vectra alloys on my car, with 195,60,15 tyres, i know they are too big as theyve majorly damaged my arches, i will soon be putting 45's on them!

anyway, was just wondering, at 30mph, will i actually be doing more or less than 30mph on this size tyres? as i understand the rolling radius will be more as they are bigger?

cheerz!

[Nova_Tek]

I went from a 145/75 R13 standard nova wheels to a 195/45R15 wheel tyre package.

From what I have gathered by these electronic speed boards that tell you when you have krept over 30mph in a 30 zone and flash 'SLOW DOWN 30mph'

when i do around 31 / 32 mph they will flash 30 at me. So taking that into consideration id say when doing 30 on your speedo you maybe doing about 28ish in real terms

The circumference of the tyre is only very sliightly bigger then a standard 1.2 tyre and shouldnt cause too much issue.

*PS. This is only a rough idea and I am going by what my car did and does now*

[dannyb]

I would have thought the speedo would read 30 when in fact you are going faster with bigger wheels as 1 revolution of the wheel is now covering more distance. I'm not entirely clear on that one though. The old wheels and tyres (145 70 13) have a diameter of 533, the new ones (195 45 15) will have a diameter of 558 so not much difference to worry about though.

[Stuart]

*cough* speed in gear in sig link *cough*

[Nova_Tek]

I would have thought the speedo would read 30 when in fact you are going faster with bigger wheels as 1 revolution of the wheel is now covering more distance.

Thats true only if your speedo was completely accurate with the original wheels. Usually speedos read more optimisticly then what your actually going so in a way these bigger tyres are making the speedo a bit more true.

Best thing is to stick to the speed limit lol

[Tazzy]

youre not getting what im saying, my corsa is sitting on 15' alloys with 60/195 tyres, these i know are too big, hence the reason why i ask if i travel at the speed my speedo tels me, 30mph, if that is reading 30mph, what speed am i actually driving at?

would it be 32mph? or 28mph? for example!

cheerz!

[Iain]

Borrow a GPS system and find out for yourself (Tom Tom?). :)

I'm doing less than 30 when my speedo reads 30 with 195/50 tyres (15" wheels)