If my B110 1171cm3 A12 it

It's not hard to calculate. Put a chalk mark on the tyre at the bottom, and on the ground beside it. Push the car along untill the chalk mark is at the bottom again. draw a line on the ground, and measure how far between the two marks. Do you have a 4, or 5spd gear box? If it's 4, then top gear is 1:1. If it's five, then check wiki for the ratio's. Then take your revs, (5500 or what ever it is if you have 5th gear) and divide by the diff ratio. Then multiply this by the distance travelled in one revolution of the rear wheels. This will give you metres per minute. Multiply by 60, to get metres per hour. Divide by 1000, to get kilometeres per hour.

HOWEVER THIS WILL NOT ACCOUNT FOR,
losses from clutch slippages,
Losses from the tyres not having 100% driving friction against the road,
or any growth of the tyre size from centrifugal forces.