I've hooked up a bike computer to my commuter. It reports my ride to work as 6.24 miles. My previous measurement was 6.1 miles using gmap-pedometer and a car odometer. The car odometer only has one decimal place, so conceivably it could be something like 6.15. My questions:

How much of the difference in the distances can be attributed to all those little extra turns etc. the bike makes compared to a car?

Is this close enough? If not, how can I get greater accuracy?

Assuming that the reading is off by .1 after six miles, how would this affect the speed reading? For example if the ride's top speed says 25mph, how much slower was I actually going assuming the car odometer is correct and the bike is off a bit?

Thanks in advance!