# Thread: 21 inch diamondback insight 1. need help with bike computer

1. ## 21 inch diamondback insight 1. need help with bike computer

I recently got a new bike, a diamondback 21 inch Insight 1, and also got a Bell f20 bike computer. Im confused about the tire calibration on the bike compute. It tell me to enter a 4 digit number, which I understand, but when I went to my tires to get the numbers needed, i was confused. this is exactly what it says-
Weinman
700Cx28C/38C
ETRO 622x 19
Aluminum Alloy
-
im running off this sizing chart- http://sheldonbrown.com/cyclecompute...ation.html#ccc
and the part im confused about is " 28C/38C" according to that chart, where should only be one #C. I need to know the right input number for the bike computer to work correctly. Any help is welcome, thanks.

2. Use the 4-digit number in Group F on Sheldon's workpage.

For instance, a 700 X 28C tire will be 2136.

3. Yeah, I understand that. The part Im confused about is my wheels say "28C/38C" . I mean, which one is it?

4. oh, and also, if anybody knows what kind of valve these tires need, that would be helpfull too.

5. Measure the inflated tire across it. 28C is a hair more than 1 inch. 38C is closer to 1-1/2 inches. I'd be inclined that you'd want tubes with Presta-valves, but it's up to you and the diameter of the valve-hole in the rims.

That 28-38 business is utterly confusing. Please keep us posted.

6. thank you, it is the 28c i believe, but what do you mean by measuring across? i measured from the wheel rim, and that looked to be 1 inch, maybe a bit more. and then i measured from side to side, i got about 1 1/8 to 1 1/4. And i should have been more clear, i meant what kind of nozzle do i need to inflate the tires. i have bigger size plug in air compressor that i have used for my cars, lawn mower, and my old mountain bike. this tires valve is much smaller, so i got a multi-use hand pump, but either this pump does not have the correct attachment, or i am simple not using it correctly. any ideas?

7. You have Presta-Valves from your description - and 2136 tires - and you need to learn how to do this. So:

To use the compressor (which shouldn't be used unless you can set the pressure-output), you need an adapter:

http://www.niagaracycle.com/product_...ducts_id=20312

This will allow you to use a compressor, or a hose from the local gas-station. Better still - buy a floor-pump. Use the Search here to find good ones.

Now to use a Presta, first unscrew the top of the brass-valve on the top. It should unscrew a few turns. Now give it a quick press to blow it clear - if it is inflated, if not don't worry - and fit the pump-chuck (the part of the pump that goes on the valve) over the unscrewed valve. Or fit the adapter on it and screw that down. Then attach the chuck. Now pump it up to the proper pressure. Look at the sides of the tire to find out how much pressure it takes. For a 28C - around 90psi.

8. my frame pump came with one of these adapters
http://www.niagaracycle.com/product_...oducts_id=2475
is that the right thing to use? and how would i go about using it? i tried screwing it on to the presta valve, and the putting the pump head over it. it fit, but when i pumped, the air would not go anywhere.

9. I found out the Roll Out method to be very accurate for my bike computer.it's from Sheldon Brown's web site as well.

10. And,,,,,,,,, I use a compressor to check tires every day - and the output is regulated at 150 PSI....just be gentle. My tires take 85 PSI.

Why is everyone so afraid of a compressor? That's one of their functions......

11. Unscrew the top of the brass Presta-valve. Then push it in for a half a second so you hear air whooshing out - if it already has air in the tube - and screw the valve-adapter onto the Presta-valve. Now try it.

Those are the correct adapters you linked to.

12. Ok, thanks for the help, i got it working, it just takes forever to inflate the tires with my frame pump.I guess thats what i get for getting it from Target.

13. Originally Posted by Wanderer
And,,,,,,,,, I use a compressor to check tires every day - and the output is regulated at 150 PSI....just be gentle. My tires take 85 PSI.

Why is everyone so afraid of a compressor? That's one of their functions......
i would actually prefer to use a compressor, but the nozzle dosent fit on my new bike tires.

14. A compressor is a risky thing to use on bicycle-tires/tubes. You could blow the tube & tire clean off the wheel. I suggest getting a decent floor-pump with a gauge. This way you can simply top-off your tires before going off on a ride. The search-function here will unearth a plethora of recommendations - as well as cautions - for a good floor-pump.

15. how much would a good floor pump cost? and would anyplace besides the lbs have them?

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