Speedometer---> is it accurate

[Kanulondon]

Since I now have bigger tyres a quick calculation reveals the actually height of my tyres to be around 0.8cm or 8mm higher than the standard wheels

What effect would this have on my speedo? Would I actually be going slower than it says or faster than it says?

KL

 

[Neil]

If you have bigger wheels then your speedo will under read, that is you will be going faster than your speedo says. The maths to work out the difference is quite simple (GCSE at the most).

 

[Kanulondon]

cheers

I thought it would under read but just wanted to be sure...I know about the maths but couldnt be arsed to do em!

I have more imp stats work to do...for my project hehe

Anyways I will do calcs later but I am think that something so minor wouldnt effect speedo that much esp @ lower speeds

KL

 

[ditchcrawler]

Re: cheers

Picked this one up from an old post but it seems relevant to some recent threads. According to my reckoning, if your wheels and tyres are about 8mm higher than they were, ie overall wheel diameter is 8mm bigger, then your speedo will under-read by something under 3 percent. In other words, if the speedo says 70mph you are really doing 72mph.

If the speedo is designed to read 5 percent optimistic (most cars do) then the effect of the big wheels actually cancels out some of the error. In other words, you can assume it's reasonably accurate now!

Word of caution, though: in general on a Bravo (or anything with 14" standard rims) the speedo under-reads by about 3.5 percent for every 10mm increase in overall wheel diameter. So if you have 17" wheels then even with low profile tyres you could be doing 70 when the speedo says 60 - outside your margin of error allowed by the plod.

Sorry if I'm trespassing on your patch Nige.

 

[Anonymous]

Re: Re: cheers

Trespassers welcome - your math is better than mine!
Nige

 

[Wimmy]

Speed/tyre calculation

Try the calculator on this page. Very useful:
http://www.chris-longhurst.com/carbibles/tyre_bible.html