Bike Computer/Wheel Roll ut

rottenhat

Just got a computer, entered the wheel measurement listed in the manual (2136mm for 700 x 28c) and headed down to the shops as a kind of shake-out ride. The distance registered seemed a bit on the high side so when I got home I figured I'd actually measure the roll out. The actual roll out proved to be 2190mm which would mean that the distance reading I'd got previously would have been on the low side. I checked the roll out on the other bikes that are sitting around the flat and in every case the actual roll out was 50 - 60mm more than the estimates in the manual, which seems like a sizeable difference. Have the rest of you found that the manuals tend to underestimate? Is it something specific to Cateye? Or am I measuring incorrectly somehow?

72hundred

How'd you work out the roll yourself?

rottenhat

Mark a point with the valve stem vertical at the bottom of the wheel, roll forward until the stem is in the same position again, mark that point and measure.

72hundred

rottenhat wrote: »

Mark a point with the valve stem vertical at the bottom of the wheel, roll forward until the stem is in the same position again, mark that point and measure.

Is that on a good grip surface? Carpet might slip a good bit. Also are you sure you're rolling perfectly perpendicularly forward. These things could throw off the measurements a lot.

jautukas87

72hundred wrote: »

Is that on a good grip surface...

Also when riding, tires will be squished a bit more.

rottenhat

jautukas87 wrote: »

Also when riding, tires will be squished a bit more.

And the prize goes to Jautukas...I was measuring it without anyone sitting on the bike. Revised measurement is 2127mm which is indeed a little less than in the manual. Thanks for the input, chaps.

72hundred

rottenhat wrote: »

hanks for the input, chaps.

Shame your not right! It would mean we're all going 3-4kph faster than we think!