Corsa-B.uk - Vauxhall, Opel and Holden Corsa B Owners Club

hey is there any way to get your speedo to show your true speed? a mean i already knew what my speedo says is wrong, but i was goin past one of those signs that tells ya how fast your goin and on my speedo it said about 36-38 and the siggn said i was doin 30 can u like a dunno recalculate it or summat?

You need to get the correct wheel/tyre combination for the speedo to read correctly. You must have bigger alloys or something on.

http://www.tyretraders.com/Tyrecalculator/

LesterPiglet1 wrote:You need to get the correct wheel/tyre combination for the speedo to read correctly. You must have bigger alloys or something on.

http://www.tyretraders.com/Tyrecalculator/

haha alloys actually i think i have smaller width tyres :s they will be changed though haha

Bigger wheels, smaller wheels, wrong profile tyres, all will mess up your speedo reading.

those signs are a pile,
they always show you going slower than you actualy are.

btw if you have fitted bigger wheels or lower tyres it does affect your speedo. but only by about 1 mph, and only really becomes a problem at speeds over 75-80mph, you shouldnt notise it at 30

Octane2097 wrote:those signs are a pile,
they always show you going slower than you actualy are...

so basically even though the standard on a corsa b where what, 145/80/r13s or summat and i have 145/60/r13s i think it shouldnt be like 7/8 miles out?

since you have smaller tyres than standard you lower the circumfrance of your whole wheel by about 5inch
call the circumfrance of a 13inch wheel with 80mm profile tyres on will be about 60inch approx
and the circumfrance of a 13inch wheel with 60mm profile tryes will be about 55inch approx

on 80mm profile tyres your wheels will fully rotate aprox 1056 times over a mile
however on 60mm tyres your wheel will fully rotate 1152 times over a mile
it would work out that its about 1.5mph diffrence at 30mph
so when your speedo says your doing 30mph you will probably be doing about 28.5mph
since your wheels are slightly smaller they have to turn faster making it look like your going faster than you actualy are.

thats why police speed cameras actualy give you a margin because not eveyone has standard wheels fitted to their car, plus the fact that EVERY single speedo is diffrent

After using this new link http://www.tyresave.co.uk/tyresize.html I find that changing your tyres has caused your speedo to give you a 10.3% error.

LesterPiglet1 wrote:After using this new link http://www.tyresave.co.uk/tyresize.html I find that changing your tyres has caused your speedo to give you a 10.3% error.

cool, whats the standard ones on a corsa anyways?

Depends which model corsa you have. Ive got a 1.2 16 valve and my standard tyres were 165 70 r13. If you look in the manual that came with the car it shud tell u in there - probably at the back somewhere

Jimi137 wrote:Depends which model corsa you have. Ive got a 1.2 16 valve and my standard tyres were 165 70 r13. If you look in the manual that came with the car it shud tell u in there - probably at the back somewhere

i didnt get a manual with mine and its a 1.2 8v ls....as it says under my name

Lucasmax wrote:

Jimi137 wrote:Depends which model corsa you have. Ive got a 1.2 16 valve and my standard tyres were 165 70 r13. If you look in the manual that came with the car it shud tell u in there - probably at the back somewhere

i didnt get a manual with mine and its a 1.2 8v ls....as it says under my name

just pointing out that under your name it says corsa merit 3d

roperstun wrote:

Lucasmax wrote:

Jimi137 wrote:Depends which model corsa you have. Ive got a 1.2 16 valve and my standard tyres were 165 70 r13. If you look in the manual that came with the car it shud tell u in there - probably at the back somewhere

i didnt get a manual with mine and its a 1.2 8v ls....as it says under my name

just pointing out that under your name it says corsa merit 3d

i know realised that after i wrote it :/ got mixed up between this and allcorsa sorrryyyy