CatEye Astrale 8 & 650 Tires

[Aggie_Ama]

Thanks Renee, we keep tinkering with it. Maybe we will get the magic number soon!

It is the tire circumference that is off on mine. We have tried to get them lined up and are off by about .50 for a 20 mile ride. My average speed is slightly lower. Overall, it gives me a pretty close measurement. I just want it perfect. My poor husband has tried to figure out the math at least 3 times.

[DebW]

The way to get it perfectly tuned to your bike is to roll the bike N tire rotations and measure the length L. Then L/N is the length of one tire rotation and goes into the computer expressed as millimeters. Maybe use your driveway and mark the valve-down tire position with chalk, then roll the bike forward with your weight on it, and mark the valve-down position again after 5 tire rotations. Do this with your husbands's bike too, and you should be in sync.

[MomOnBike]

You will never get the distances you ride up to line up exactly, you know. There will be small variations, such as the differing lines each of you take around corners, the odd wobble that one person has, the fact that one of you slaloms (can't spell it, you understand, right?) down a hill for fun, etc. This can add up to a lot of variation over a long ride.

OTOH, your rolling speed should be really, really close.

What I'm saying is, it will never be perfect, but you can probably get it "close enough for jazz."

[natheless]

If it's going to nag you, why not call/email Cateye and ask them what the setting would be? Or if it's possible, enter the tire size manually?

(Otherwise, I agree, little variations can add up over a long ride - though I'd think to less than 1/2 a mile in 20.)