Calibrating Computer - I Hate Math
#1
Sassbucket.
Thread Starter
Join Date: Oct 2007
Location: los angeles, ca
Posts: 113
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 4 Post(s)
Likes: 0
Liked 0 Times
in
0 Posts
Calibrating Computer - I Hate Math
I just picked up my first computer. I need to figure out the circumference of my wheel to calibrate it, and It's giving me a bit of trouble. My wheel is 700 x 25.
Here's the formula I followed, as per the manual:
distance from floor to hub: 13 3/8" (13.375)
multiply by 25.4 to convert to mm (339.725)
multiply that number by 6.28 (2 x pi) = 2133.473
I had entered 2105 based on Sheldon Brown's recommendation for a 700 x 25 wheel. But this is a pretty substantial difference. When I entered 2133, it seemed like the miles were racking up really quickly. I'll be the first to admit that I don't have the best sense of distance, so I could be wrong.
Any ideas?
Here's the formula I followed, as per the manual:
distance from floor to hub: 13 3/8" (13.375)
multiply by 25.4 to convert to mm (339.725)
multiply that number by 6.28 (2 x pi) = 2133.473
I had entered 2105 based on Sheldon Brown's recommendation for a 700 x 25 wheel. But this is a pretty substantial difference. When I entered 2133, it seemed like the miles were racking up really quickly. I'll be the first to admit that I don't have the best sense of distance, so I could be wrong.
Any ideas?
#2
Senior Member
Join Date: Oct 2002
Location: Southern Maine
Posts: 8,932
Mentioned: 129 Post(s)
Tagged: 0 Thread(s)
Quoted: 12161 Post(s)
Liked 1,475 Times
in
1,088 Posts
And now for something to really mess with your head.... tires companies
do no provide precise size measurements.
Try a number, use it for a while, it will seem high or low. So change it a bit and
see if you can get closer. You can also try to measure by seeing how far the tire actually rolls. I found that more trouble than it was worth. I just want to be close, and if the mileage reads a little on the generous side, I am not one to complain.
do no provide precise size measurements.
Try a number, use it for a while, it will seem high or low. So change it a bit and
see if you can get closer. You can also try to measure by seeing how far the tire actually rolls. I found that more trouble than it was worth. I just want to be close, and if the mileage reads a little on the generous side, I am not one to complain.
#3
Sassbucket.
Thread Starter
Join Date: Oct 2007
Location: los angeles, ca
Posts: 113
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 4 Post(s)
Likes: 0
Liked 0 Times
in
0 Posts
I actually measured my wheel with a tape measure. As you said, I know not to trust what the tire says!
The reason I'd like to get pretty accurate is because I'm so bad with distances. I really have nothing to base myself on to judge if I'm too high or too low.
The reason I'd like to get pretty accurate is because I'm so bad with distances. I really have nothing to base myself on to judge if I'm too high or too low.
#4
Senior Member
Join Date: Sep 2006
Posts: 1,195
Bikes: Kona Cinder Cone, Sun EZ-3 AX
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times
in
0 Posts
I had entered 2105 based on Sheldon Brown's recommendation for a 700 x 25 wheel. But this is a pretty substantial difference. When I entered 2133, it seemed like the miles were racking up really quickly. I'll be the first to admit that I don't have the best sense of distance, so I could be wrong. Any ideas?
f you require more accuracy, you can do a "roll-out" test. Since the effective tire size is affected by tread thickness, tire pressure, and rider weight, the rolling circumference should be measured by rolling the bike with the rider aboard for one wheel revolution.
You may use the valve stem as a reference, starting the roll with the valve right over a perpendicular line on the floor, and ending when the valve is back at its low point one revolution later.
Another approach is to put a small dot of paint on the tire and measure the distance between the marks that the paint prints on the road. With either approach, the rider must hold the handlebars absolutely straight while an assistant balances and pushes the bike. Otherwise, the wheel may not follow a straight path.
You may use the valve stem as a reference, starting the roll with the valve right over a perpendicular line on the floor, and ending when the valve is back at its low point one revolution later.
Another approach is to put a small dot of paint on the tire and measure the distance between the marks that the paint prints on the road. With either approach, the rider must hold the handlebars absolutely straight while an assistant balances and pushes the bike. Otherwise, the wheel may not follow a straight path.
#5
cab horn
Join Date: Jun 2004
Location: Toronto
Posts: 28,353
Bikes: 1987 Bianchi Campione
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 42 Post(s)
Likes: 0
Liked 25 Times
in
18 Posts
I just picked up my first computer. I need to figure out the circumference of my wheel to calibrate it, and It's giving me a bit of trouble. My wheel is 700 x 25.
Here's the formula I followed, as per the manual:
distance from floor to hub: 13 3/8" (13.375)
multiply by 25.4 to convert to mm (339.725)
multiply that number by 6.28 (2 x pi) = 2133.473
I had entered 2105 based on Sheldon Brown's recommendation for a 700 x 25 wheel. But this is a pretty substantial difference. When I entered 2133, it seemed like the miles were racking up really quickly. I'll be the first to admit that I don't have the best sense of distance, so I could be wrong.
Any ideas?
Here's the formula I followed, as per the manual:
distance from floor to hub: 13 3/8" (13.375)
multiply by 25.4 to convert to mm (339.725)
multiply that number by 6.28 (2 x pi) = 2133.473
I had entered 2105 based on Sheldon Brown's recommendation for a 700 x 25 wheel. But this is a pretty substantial difference. When I entered 2133, it seemed like the miles were racking up really quickly. I'll be the first to admit that I don't have the best sense of distance, so I could be wrong.
Any ideas?
Real joy is riding.
#6
Really Old Senior Member
I take a piece of string, tie a small loop in the end and then basically "lasso" the tire.
Mark the string where it overlaps and then hook the loop on a nail or something and stretch the string (approx same tension as when in "lasso mode") and measure it with the tape. Repeat until you feel you have a consistent measurement.
Divide that # by .03937.
As mentioned, a difference of 20+ out 2000+ is pretty small.
Or you could just enter 2111.
Mark the string where it overlaps and then hook the loop on a nail or something and stretch the string (approx same tension as when in "lasso mode") and measure it with the tape. Repeat until you feel you have a consistent measurement.
Divide that # by .03937.
As mentioned, a difference of 20+ out 2000+ is pretty small.
Or you could just enter 2111.
#7
Senior Member
Join Date: Feb 2004
Location: St Peters, Missouri
Posts: 30,225
Bikes: Catrike 559 I own some others but they don't get ridden very much.
Mentioned: 16 Post(s)
Tagged: 0 Thread(s)
Quoted: 1572 Post(s)
Liked 642 Times
in
363 Posts
Try riding the exact same route 3 or 4 times and see how closely your computer milages compare. Trying to program your computer to be more accurate than the variation among the repeated laps is fooling yourself.
#8
Uber Goober
Put a piece of masking tape on a tire at the bottom, matching piece on the floor. Sit on the bike, roll it forward one full revolution, measure from there back to the first tape. Removes the uncertainties about what the actual rolling diameter is, avoids using pi at all, etc.
#9
don't try this at home.
Join Date: Jan 2006
Location: N. KY
Posts: 5,900
Mentioned: 10 Post(s)
Tagged: 0 Thread(s)
Quoted: 959 Post(s)
Liked 477 Times
in
334 Posts
The rollout method works. If you don't have a metric tape measure, you can use google to convert it.
For instance, entering 83 1/8 inches in mm in google search, you get this answer:
(83 1/8) inches = 2 111.375 millimeters
google will convert a lot of units. 4 lbs in grams returns: 4 pounds = 1 814.36948 grams
For instance, entering 83 1/8 inches in mm in google search, you get this answer:
(83 1/8) inches = 2 111.375 millimeters
google will convert a lot of units. 4 lbs in grams returns: 4 pounds = 1 814.36948 grams
#10
Senior Member
Join Date: Oct 2004
Location: Iowa
Posts: 335
Bikes: Actual 10-speed Olmo road, Bianchi BUSS, Kona A-Ha, Schwinn Moab 2 rain bike
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Likes: 0
Liked 0 Times
in
0 Posts
I use the 5th thru 7th mile of the Quad City Marathon Course. I just ride back and forth, and adjust until the computer clicks off on the mile marks. I hear they measure those things pretty accurately for the runners.
#11
Sassbucket.
Thread Starter
Join Date: Oct 2007
Location: los angeles, ca
Posts: 113
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 4 Post(s)
Likes: 0
Liked 0 Times
in
0 Posts
I guess I don't really want to get into splitting hairs. I'll just split the difference and call it a day. Thanks for all the help!
#12
No Rocket Surgeon
Join Date: Jan 2005
Location: Corona and S. El Monte, CA
Posts: 1,648
Bikes: Cannondale D600, Dahon Speed T7
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 6 Times
in
1 Post
I agree with rm-rf, the rollout method is the only way to go.
Pump up your tires. Put a tape measure on the ground. Get on the bike. You may need a "spotter" for that step. Ride your bike so the front wheel goes one full revolution (I'm assuming your pickup is on the front fork). Your valve stem is a good indicator. Just measure how far your bike travels in one wheel revolution. Convert to mm (25.4 mm/inch), and enter this value into your computer.
If you are really anal (as I am) you will do this a few times and average the results.
I use this converter a lot:
https://www.convertit.com/Go/ConvertI.../Converter.ASP
Simple!
Have fun.
Pump up your tires. Put a tape measure on the ground. Get on the bike. You may need a "spotter" for that step. Ride your bike so the front wheel goes one full revolution (I'm assuming your pickup is on the front fork). Your valve stem is a good indicator. Just measure how far your bike travels in one wheel revolution. Convert to mm (25.4 mm/inch), and enter this value into your computer.
If you are really anal (as I am) you will do this a few times and average the results.
I use this converter a lot:
https://www.convertit.com/Go/ConvertI.../Converter.ASP
Simple!
Have fun.
__________________
Fewer Cars, more handlebars!
Fewer Cars, more handlebars!
Last edited by eubi; 11-19-07 at 08:13 AM.
#13
Life is good
Join Date: Jan 2001
Location: Not far from the Withlacoochee Trail. 🚴🏻
Posts: 18,209
Bikes: 2018 Lynskey Helix Pro
Mentioned: 13 Post(s)
Tagged: 0 Thread(s)
Quoted: 522 Post(s)
Likes: 0
Liked 10 Times
in
10 Posts
Originally Posted by jc808
I just picked up my first computer. I need to figure out the circumference of my wheel to calibrate it, and It's giving me a bit of trouble. My wheel is 700 x 25.
__________________
The Lord is merciful and gracious, slow to anger and abounding in steadfast love. - Psalm 103:8
I am a cyclist. I am not the fastest or the fittest. But I will get to where I'm going with a smile on my face.
The Lord is merciful and gracious, slow to anger and abounding in steadfast love. - Psalm 103:8
I am a cyclist. I am not the fastest or the fittest. But I will get to where I'm going with a smile on my face.
#14
Senior Member
Join Date: Jun 2007
Location: Pittsburgh, PA
Posts: 352
Bikes: BiknBrian brand custom 26 inch commuter trekker, Cannondale F600 Single Speeded MTB, Nashbar Cro-Mo CX, some other bikes and parts that could be made into bikes.
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times
in
0 Posts
You can't just measure the circumfrence or diameter, you have to weight the tire. Your effective circumfrence will be significantly smaller with weight on it. Then you can just drive a couple mile route and make sure it closely mathches what the computer says.
#15
Senior Member
Join Date: Sep 2006
Posts: 1,195
Bikes: Kona Cinder Cone, Sun EZ-3 AX
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times
in
0 Posts
But first, you should ask yourself if you really care if the figures are off by 70 feet in a mile, and if you do care, why?
#16
Dirt Bomb
Join Date: Aug 2006
Location: Illinois
Posts: 2,855
Mentioned: 64 Post(s)
Tagged: 0 Thread(s)
Quoted: 5366 Post(s)
Liked 272 Times
in
226 Posts
If you put a dab of paint on a smooth road, then rode over it, then measued the distance between the spots you could get an accurate measurement.