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Clydesdales/Athenas (200+ lb / 91+ kg) Looking to lose that spare tire? Ideal weight 200+? Frustrated being a large cyclist in a sport geared for the ultra-light? Learn about the bikes and parts that can take the abuse of a heavier cyclist, how to keep your body going while losing the weight, and get support from others who've been successful.

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Old 07-26-08, 10:55 PM   #1
Alathea
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programming Trek Incite

The instructions give standard stock measurements for various wheels. Mine is a 26x1.75-not on the chart. I looked around at some other sites for measurements and I got 2045mm for that wheel size. My instructions for the Trek say that number is for 26 x 1.90 which is what I took off of there.

Why the disparity? SB's site is even more confusing because none of the numbers he has listed for measurements seem to correspond with the guide in my Trek instructions.

*damn search function* The more I read about Trek Incite, the less I like....I already have it on the bike and im having second thoughts now.....*sigh* what to do what to do. Its sitting next to me and my laptop and apparently im traveling 35 MPH.....my Max speed has been 136.9 MPH, Ive ridden for 15.8 miles (which I havent), and I just jumped to 16.2.

This must be what Einstein felt like.....defying the laws of physics.
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Old 07-27-08, 06:11 AM   #2
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I haven't had that problem with my incite 9i...in fact, it's been relatively bullet proof.

Why not customize the wheel size instead of using the chart? On page 24 of the manual the procedure is explained. If you only have the "quick guide" you can get a PDF of the full manual here.
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Old 07-27-08, 07:53 AM   #3
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Ill try that....I only have the one sheet insert that came with mine. I was looking for the custom size on the one sheet on the internet, I just found conflicting measurements for a 26x1.75 wheel. It also registers motion and distance that Ive never traveled.....it's the weirdest thing.

***thats the same chart that is included with mine*** Sheldon B's site's measurements don't approximate anything on the table with the computer, and another site says my wheel is a '2045' when the Trek chart says that is 26x1.95. My bigger concern is the erratic data. Mine is the wireless one. My wireless is shut off on my computer, and the phone is in the other room, so where is it getting it's data? O/N Ive traveled another 200 miles at an average of 37 miles an hour....

Last edited by Alathea; 07-27-08 at 08:00 AM.
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Old 07-27-08, 08:15 AM   #4
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You should have a marking on the wheel to tell you the size somewhere. My need to take the tire off though. Also, if your traveling 35 next to your laptop, get out of your car man , but I would pull the battery and let it reset it self or maybe try a new battery. I had to replace the batteries in my brand new Garmin when I got it last year. If that does not work I would take it back the shop. I have a 8i on my wife's bike and it has been flawless, but you might have just gotten a dud.
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Old 07-27-08, 08:20 AM   #5
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The size on my wheel is only in inches and width, not in MM, which is what I think the Trek guide numbers are. How much does it matter if I just punch in the 1.95 number instead of the 1.75? Is there that much difference between the width of the wheel and distance traveled? Isn't that more of a function of circumference? 26 in is 26 in, at least in my plane of existence
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Old 07-27-08, 08:51 AM   #6
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Ill try that....I only have the one sheet insert that came with mine. I was looking for the custom size on the one sheet on the internet, I just found conflicting measurements for a 26x1.75 wheel. It also registers motion and distance that Ive never traveled.....it's the weirdest thing.

***thats the same chart that is included with mine*** Sheldon B's site's measurements don't approximate anything on the table with the computer, and another site says my wheel is a '2045' when the Trek chart says that is 26x1.95. My bigger concern is the erratic data. Mine is the wireless one. My wireless is shut off on my computer, and the phone is in the other room, so where is it getting it's data? O/N Ive traveled another 200 miles at an average of 37 miles an hour....
The best way to do it, is by measurement. To do this you need a tape measure marked in metres, and some sidewalk chalk, and an extra set of eyes. You go out to the street and make a mark with the chalk, measure out 10m and make another mark. Pump up your tires, put your wheel on the first mark, with the valve at the very bottom, now ride to the other mark, have your assistant count the number of times the value hits bottom. If the valve is at the bottom when you hit your mark, then fine, otherwise, move forward until you do, and measure the difference. This will give you a number, say 10m 45cm 2mm multiple meters by 1000, cm by 10 and add them together, so you get say 10452. Divide this my the number of times the valve hit bottom, including the last time if you had to go over the 10m mark. Take the distance in millimetres and divide by the count, in my example you would take 10452/5 to give 2090.4 round this to the nearest whole number. The longer the distance the better the accuracy, so if you have a known measured distance, you can use that. For example a track that is a known 1/4 mile could be used (402 336mm). Better is a track for 1K or 2K running races though, as the numbers will make more sense.

The reason the charts are different, is that tires are different, and you may run a higher pressure then the chart does, you may have a heavier load on the bike. So best is to measure it, if you change the tire used for the sensor, then redo the measurement. Get a little sticky or piece of tape, write the number on it, and attach it to your bicycle somewhere, the back of the computer maybe.......

Wireless computers work by a radio signal, a very small transmitter on the wheel sends a very weak radio signal to a receiver, in the computer unit. There are no frequencies reserved for this use, and as with any other radio transmitter, a stronger signal can walk over the transmission. This is what often happens, a portable phone, wireless networking, wireless microphones, they all use a similar radio band, and wireless bike computers in order to keep the power use low, seem to have the lowest power. This is one reason I prefer a wired computer.
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Old 07-27-08, 09:13 AM   #7
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Do the rollout test and be done with it man! You've spent more time here debating the issue than if you had just rolled it out and plug in the the numbers!

The numbers are accurate for YOUR personal wheel. Plus every instruction booklet provided with the speedo tells you how to do it. Even the cheapo $14 units.
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Old 07-27-08, 11:22 AM   #8
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*shrug* not being a butt, just wondering why the difference on a 26 in wheel based on width rather than just circumference.
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Old 07-27-08, 11:35 AM   #9
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*shrug* not being a butt, just wondering why the difference on a 26 in wheel based on width rather than just circumference.
Don't forget bicycle tires are round, not square like car tires, so the wider the tire, the larger the circle, which means a 2" tire is a bigger circle then a 1.75" tire, so it's actually taller as well. This is how some riders can put a 700C wheel on a bicycle designed for 26" wheels.
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Old 07-27-08, 01:39 PM   #10
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I just take a piece of string and put a small loop in one end.
I then "lasso" the tire and mark the string with a pen.
Then I simply measure the string length with a tape measure and convert to MM.
1" = 25.4MM

I think doing a roll out test is a waste of time. If you are doing just ONE revolution, measurement errors will negate any "perceived" accuracy.
Also keep in mind that if you are off by just a bit, it's still just a bit. 1 part in 2000+ is <.05%!

For 1.75, split the difference between 1.50 & 2.00. (or interpolate the difference)

BTW, according to the chart, my 26x1.50" tires are 2030MM. Actual size is 2038MM. (Serfas Drifters @ 70 PSI)
"Identical" sized tires vary between manufacturers!
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Old 07-27-08, 03:22 PM   #11
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Okay. 82.25 inches x 25.4 = 2092mm. Thats what ive got. Thats a bit more than the 2050 that was in there before.
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Old 07-28-08, 09:01 AM   #12
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Okay. I don't get it. If my circumference is as above, and I multiply it by 25.4 and get what I get in MM, and its equating to having a 2+ inch wide tire on there, but its a 1.75. Im either doing something wrong, or this chart is really off. I measured the outside (tread) circumference of my tire, both rollout (x3) and just once, as Bill suggested. Is is really that off? Wow...
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Old 07-28-08, 10:08 AM   #13
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Okay. I don't get it. If my circumference is as above, and I multiply it by 25.4 and get what I get in MM, and its equating to having a 2+ inch wide tire on there, but its a 1.75. Im either doing something wrong, or this chart is really off. I measured the outside (tread) circumference of my tire, both rollout (x3) and just once, as Bill suggested. Is is really that off? Wow...
Realise that any generic chart is going to be a rough guess, it may have a different air pressure, a lighter/heavier rider, a different tread pattern, different tread thickness, different base construction, different sidewall stiffness. Any combination of factors, could result in a 10mm difference from what you measure. A 10mm difference at 2m per revolution is, 500m over 100km, or .5% this means over a 5 000km riding season your off by 25km or over 3,000 miles your off by 15 miles. This is likely more accurate then your cars odometer, many of which are 5% accurate.

Another way of seeing if you are reasonably close, is to borrow or rent a hand held GPS, ride a nice route, say 10 flat miles according to the GPS and see how the odometer compares. If the odometer is within the range 9.950 and 10.050 miles, that's less then .5% probably close enough. If it's more, then adjust the odometer accordingly, and do the same route again. Much closer then .5% and your getting anal about it.
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Old 07-28-08, 10:50 AM   #14
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Okay. I really just use it to track my riding distance, I just like it to be relatively accurate as I start to add miles. I already notice a difference between the maps I plot and the Trp. but I understand why that is. Im also worried about speed in general, or average speed at least. An incorrect wheel measurement will result in faster or slower readings than what I am actually doing. Im not going to tackle the mountains anytime soon, I just want to be know that when I say I averaged 11 mph or a top speed of X that it's correct.

Thanks for all the input!
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Old 07-28-08, 06:11 PM   #15
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I've done he roll out on all my bikes, maybe the 13 that Iv'e had. Very close to mile markers on the trail with a little fine tune, right on.

I've tried the generic settings and they are wayyyyy off! Skip em'!:thumb"
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