# What circumference did you enter into your Coker cycle computer?

On Mon, 8 Sep 2003 02:01:58 -0500, tomblackwood
<tomblackwood.tfe23@timelimit.unicyclist.com> wrote:

>Prior to getting the
>computer, I measued a number of my 4-8 mile local neighborhood rides in
>my car, and my post-computer rides of these loops measured out pretty
>much the same. Although since I used my car initially, that goes back to
>my debate with Klass, and I still don’t know how the “yell the speed out
>the car window” speed compares to the loaded with/without wobble
>speed.

Caution! As someone else remarked as well, the typical car distance
meter (name?) is notorious for bad calibration. Mine is off about 4%,
compared to roadside kilometre signs. That deviation is included in
the ‘yell out the car window’ assessment.

## Klaas Bil - Newsgroup Addict

If the crank is moving then it really sounds as if it’s loose. - onewheeldave trying to pinpoint the cause of a clicking crank

On Mon, 8 Sep 2003 09:49:50 -0500, schroder
<schroder.tfzt7@timelimit.unicyclist.com> wrote:

>You might expect that the
>radius of the flattened tire when you are sitting on it correlates to
>the circumference, but I think it is somewhere in between that and the

I haven’t given the physics involved much thought but it occurs to me
that the above is caused by the fact that the tyre contact patch does
not have a single ‘radius’ (quotes because then it isn’t really a
tyre radius while in the middle the ‘radius’ is the distance from the
wheel axis to the ground (loosely known as loaded radius). At the
sides of the tyre contact patch the situation is even more complicated
(3D).

## Klaas Bil - Newsgroup Addict

If the crank is moving then it really sounds as if it’s loose. - onewheeldave trying to pinpoint the cause of a clicking crank

Re: Re: What circumference did you enter into your Coker cycle computer?

Actually, I was thinking of the occasional signs that say, “MEASURED MILE BEGINS HERE”, as most of the highways that have mile marker signs don’t permit anything except motorized vehicles. I think it’s something about unicycles can’t go 45-Miles Per Hour, humph, blatant discrimination!

As for the accuracy of the mile marker signs, any road with measured distances that contain curves will be inaccurate. Does anyone know where the line of the mile marker posts is? That’s why I used the

[/b] because there were 50 foot intervals marked with a dot to locate the surveyors transit.

I suppose that you could borrow one of the rolling measurement things that the cops use at accident sites and mark your own line. Or, this would be cute, find a drag strip with a measured section. Drag racing uni’s! Brummm, brummm, screeeeech!

bump old but very useful thread

I just remembered that I have an old cycle computer on one of my old bikes, so today I installed it on the Nimbus 36 with the Wheel TA tire, (on the steel rim not the airfoil). I just want to describe my method to see if anyone here sees a problem with what I did.

(I did this before finding this thread)

I put a white tape on the wheel, with a black line on the tape where it touches the ground. I stood beside the uni and pushed it one revolution. Made one mark for the beginning of the rollout, and a second mark where the tape came to ground again. This is the unloaded rollout.

Next I let most of the air out of the tire so it looks similar to what it looked like when I last rode it. (figured this would be easier than trying to get a loaded rollout with no one to help me take the measurement). This simulated loaded rollout came about 38mm shorter than the unloaded rollout.

Here are numbers:

I’m not sure about the wobble effect I’ve been reading about, so as a first attempt to calibrate the computer I picked a number in the middle of this range, about 2806 mm, to use in the computer.

I have yet to try some distance riding to check for accuracy, (will maybe do a ride this evening), but at this point just from what I’ve said does anyone see any flaw in my methods?

Almost forgot to ask! All these old threads seem to deal with the Coker tire , I wonder if any others have calculated rollouts for the Wheel TA tire yet?

wobble would make the circumference lower, not higher. wobble means exactly that, wobbling left to righ when riding forward. so some of the wheels circumference is ‘eaten up’ by corrections left and right.

My results with 2778 mm. as my rollout distance on my cyclometer almost exactly match distances of known measured routes I get almost identical numbers. Of course, since I wobble, the 2778 is probably a bit low and my cyclometer should be showing longer distances than the map distances.

In the end, I’d rather know the A-to-B distance travelled rather the distance of the exact wobbly line I’ve traced out on the road.

Steveyo, is that on a Coker tire or the Wheel TA? (I’m assuming there’s some difference in tire diameter, some small difference anyway).

Since I feel the same way regarding wobble factor I think I’ll revise my computer’s number down to the 2781 I measured for simulated loaded rollout, since that’s pretty close to your “wobbly” number. As soon as I can log a ride along a precisely measured route I’ll know if that’s close enough.

Btw I also wonder if anyone has used Google’s gmap pedometer. With the satellite imagery you can trace your exact route and it measures your distance. I just don’t know if it has any bugs or inaccuracies in it. The best part about using it is that it’s cheaper than getting a portable GPS unit.

That’s a Radial TA. But I didn’t measure it at all, just took a number from reading these threads. I went on the low side to be closer to actual A-to-B distance and I’d hate to OVER-estimate my training, I’d rather under-estimate it. Then, when I do a race (like a measured hillclimb) I’ll be sure I trained at least as much as I think I have. Sort of a “Weep in the dojo, laugh on the battlefield” thing like in Dave Stockton’s sig line.

I lost my cyclometer on a night 36er ride last week, however. Instead of replacing it, I’m getting a Garmin Forerunner 205. We’ll see how it does with distances, though I doubt the top-speed measurement will be nearly as accurate. On the good side, now I can measure all my rides, not just on my 36er, and get elevation data and google earth overlays and all that cool stuff.

I use http://mapmyride.com which is like that but with more features, nice things for sharing routes, training logs etc.

It also supports import from gps for those that do have one.

Joe

Well, I measured 2743 with the “X” airfoil and TA tire, with 35 psi. I’m going to remeasure later this evening.

Steve, you will love the Garmin. I have the 305, and it works great. The only problem I’ve had is hitting the start/stop button by mistake with my KH gloves. I’ve done this on a few occasions, and lost some travel data until I realized it wasn’t recording.

Garmin includes upload access to motionedbased.com, so you can track all your trips and various data. You can then share the link with friends (and us, of course).

Thanks, good to hear.

Nice tip, I’ll give that one a go, thanks Joe! I didn’t notice yet if mapmyride offers a satellite view. I like gmaps satellite views because sometimes I ride along paths or alleyways that don’t show on the maps.

Just redid my calculations:

“x” Airfoil, TA tire, 30 psi: 2756

same, with 40 psi: 2768

Here’s a good place to get a measured mile

Not very good for measuring rollout though; nothing to hold onto!

Actually I think the track is only set up during certain times of the year; the rest of the time it’s raw salt with possibly no markers on it.