Ok, got the Schwinn 12 from WM. Installation went okay and the only confusion was which direction to mount the spoke sensor. The pic indicated the magnet to face inwards, but common sense said to make it face the fork mounted receptor. And I tied it as close to the hub as practical as it was said here to maintain balance.

Anyway, I have one question. Should I follow Sheldon Brown's calibration chart or the one in the manual. SB says a 23c should be 2097, but wheel diameter is 26.5" X 25.4 X 3.1416 = 2114. I put in 2117 as it was slightly larger and I did some math computing the difference between a 28c and 32c (19) and between a 25c and 28c (12) and that led me around the same number as a 26.5" tubular in the manual to 2117.

Is that close enough? Maybe, but it is very far from SB's 2097.

That is all.

If you want it to be accurate, you need to do a roll out measurement. Mark a spot on the tire in paint/whiteout and sit on the bike letting it roll at least one complete revolution. Measure the distance between paint marks and convert to mm. (25.4 mm = 1 inch).

That should do it. I have to input the tire measurement according to the manual's table. Also to be certain, you can do an alternate method of measurement using the roll out method as suggested by speedlever. I always use the method of measurement according to the manual's table of tire dimension.

what I find disconcerting is that even when i follow the instruction sheet for 2 different bikes I have significantly different avrg and max speeds. could the 2 bikes actually be that different? one is 27 1 1/4 wheel and tire, the other has 700 x 28c wheel and tire. I totally have to do the rollout again this year, but I remember it being confusign to measure in metric and make a 4 digit factor out of a 3 digit measurement ...

I did the roll out and got like 82.25 which equalled 2084 which is way off base. I put a piece of tape near the valve stem, then rolled until the stem was at the bottom again.

Good thing I have a backup. The block around my house has been measured at 1.1 miles with my car and my last bicycle with a speedometer cable. Just make a trip and note the difference!

thanks again

but you have to follow the rollout cuz that is the most accurate

I know, but maybe I didn't have the stem perfectly at a right angle to the ground. The best way I see is to mark the tire with chalk, white out or paint and that would be perfect, but quite the hassle. I don't see how it could improve on taking the diameter of the tire X3.1416.

Not sure about your calculator. 82.25 x 25.4 = 2089 (fwiw)

Tire pressure should be normal before doing the rollout check.

ok, nobody mentioned the tire flattening when you're on the bike. Surely that decreases the circumference. Got 82" with a 700x23c which is 2083.

What degree of accuracy do you have in measuring the diameter of the tire? If you just take the mfg word for the tire diameter, I suspect you will not even be close.

It's quite simple and very little hassle to do this right. Make sure your tire pressure is up. Put a healthy dot of paint or whiteout on the tire. Get on the bike and roll (in a straight line) at least one complete revolution so that you have at least two points to measure. Take the measurement in inches and multiply by 25.4 and you have the number to plug into your unit. Using 26 x 3.14159 is only close in the horseshoe/hand grenade department. But if that's close enough for you, so be it.

btw, the locking mechanism on this computer is garbage. Just pushing a button can cause it to come loose and hit the ground. It has a release lever that is supposed to let it slide out, but there is no need for this lever because it slides out so easily on its own.

You need to slide it all the way until you hear a click, then it should be firmly locked. I never had a problem with mine at all. I have my wireless come off its mount multiple times when I hit a bump. Whenever it hit the pavement, it loses all data and you have to reprogram again. So much for wireless for me. JMO.

also you can improve the tension of the clip by gently bending it upward without the computer in it. then the plastic arm will have a little more tension. and yes, push the unit back until you hear a click. it may not be bullet proof but it stays on.

back to the Schwinn. I cleared the DST and MAX on my last ride no problem, but when I cleared it for this morniong's commute it didn't stick ... weird. so now I have to subtract my last STATs to get the morning's STATs

On the same topic of cheap and simple computers, has anyone seen one that also offers cadence, as well as basic speed and distance?

Also, if you are going to use the roll-out method for wheel circumference, repeat the measurement 3-5 times and then take an average of all the measurements. This will be more accurate. You'll be surprised at how different each measurement is.

I have 2 of the $10 Schwinn and they work fine. I have one on my commuter & the other on my touring bike

it helps if you remember to attach the computer! I was 2 miles into my ride home when I looked down for an update and realized it was still in my pocket DOI!

Genius! I bent the tab upward and now its solid as a rock (well, better at least).