Wheel/tyre speed difference

My 90, as standard was fitted with standard steel rims and road tyres.
Since, they have been replaced with Disco steels and road tyres. They are about half to three quarters of an inch bigger. What is the speed difference according to the speedo? mine is in KM/h

Ashcroft transmission website calculator will help you

lynall said:

Ashcroft transmission website calculator will help you

Click to expand...

Okay, i'll have a look. Thanks

You might be better off downloading an app that will give you a GPS speed. I run 265's and GPS speed matches the speedo

Marmaduke said:

You might be better off downloading an app that will give you a GPS speed. I run 265's and GPS speed matches the speedo

Click to expand...

Yea, i have tried, but it displays less than the speedo, which does not make any sense... running bigger tyres should make it go faster? i will look for some others, maybe i'll find one what do werks.

Try a sat nav, most will display a speed

Surely bigger tyres would show lower speed as the distance travelled per revolution on the tyre would be further.

Fitted with bigger than standard tyres the speedo will show a speed which is slower than actual speed travelled.
An external device such as a sat-nav or app will not be influenced by the tyre sizes but only show actual speed.
Not making any allowance for either speed indicating device error, the external device will be showing a faster speed than the vehicle speedometer.
Due as XRIZLAX said with larger tyres distance travelled per revolution of the tyre would be further.
NOTE:- placing the two different wheels together off the vehicle may show that the new wheel tyre combination is half to three-quarter of an inch larger in diameter but if the side walls of the new tyre is more supple or under inflated then it may squash to a smaller diameter than the original tyres. This could also work in reverse and the smaller diameter tyres have the softer sidewall be underinflated thus having a greater effect on the vehicle speed comparisons. (just to confuse things).

All tyres are at 2.5bar atm, and i have checked when the tyre was on the ground, with a car attached to it, compared it to the old steels and they were as i say half to three quarters on an inch taller. I got confused before, i meant the speedo would display a slower speed. I just want to know what the speed would actually be, i will try with sat nav tomorrow. Cheers for the replies!