If you get two identical computers and put them on two identical bikes with identical settings can you still get a variation in the reading?
P.S. Happy New Year to all.

Yes. Depends on tire size, air pressure. weight of the rider.

And do you ride exactly in the same place. Some people veer more side to side on their "straight path".

I've also noticed that a change from 60 to 70 PSI on my 26x1.50" tire makes nearly a 4% difference. Maybe that's telling me something, since it's 65 MAX?

Forgot to add-
Computers are basically just a clock that runs and counts pulses vs time. The clocks probably vary somewhat. Temperature MIGHT have a major effect, if it's a cheap timer. That shouldn't affect distance traveled, but could alter the indicated speed.

Mostly related to weight, air pressure in the tires, and ambient temperature.
I have noticed that computers with the sensor on the rear wheel are more prone to inacuracies then front wheel ones, mainly due to higher percentage of the rider's weight being on the rear tire.

Another X factor is interference. Even with a wired computer, you can get erratic readings around high voltage transmission wires.

Don't forget to factor in the ammount of time you spend seated vs standing on each bike.
Mt bikes ridden offroad might see slight tire slip in some conditions.

Yes.




All measuring instruments have some tollerance limits. We're not talking about National Standards Lab accuracies here.

I used to commute on my bike. It was 11 miles one way. The reproduceability of the distance readings came down to a very low figure something less than 100 yards. The precision (how close their repeat measurments agree) of bicycle computers is very good.

I rather doubt that anyone on these forums or anywhere else has taken 2 identical computers and identical bikes and tried to compare measurements. I think my experience is as close as you are going to get. You can even try it yourself. Do an out and back ride. Check the reading at the halfway point and record it. Then take a reading at the end.

You can get your computer to a pretty high degree of accuracy, more accurate than your car, if you use the roll out method to measure your tire's circumference. Your distance traveled will be within 1% of a ride companion who has also calibrated his bike/computer using the rollout method.