Cycling and bicycle discussion forums. 
   Click here to join our community Log in to access your Control Panel  


Go Back   > >

Fifty Plus (50+) Share the victories, challenges, successes and special concerns of bicyclists 50 and older. Especially useful for those entering or reentering bicycling.

User Tag List

Reply
 
Thread Tools Search this Thread
Old 04-06-07, 09:28 PM   #1
Yen
Surly Girly
Thread Starter
 
Yen's Avatar
 
Join Date: Mar 2007
Location: SoCal
Bikes:
Posts: 4,113
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Tire size for new cyclocomputer

Another newbie question....

I bought a cyclocomputer today to keep track of my distance and time on my new bike.

The instructions explain how to change the tire size in the odometer function. The default setting on the computer was 820. I have 700x40c tires on my bike. The side of the tire says "42 - 622 (700 x 40c)". How does all that correlate with the default setting on the computer? I can raise or lower that number..... but to what?

Jen
__________________
Specialized Roubaix Expert
Surly Long Haul Trucker
Yen is offline   Reply With Quote
Old 04-06-07, 09:34 PM   #2
Jet Travis
Ride Daddy Ride
 
Jet Travis's Avatar
 
Join Date: Feb 2007
Location: Villa Incognito
Bikes: 1983 Trek 720; 1983 Trek 620; 1989 Gi Cannondale Bad Boy Ultra; LeMond Victoire; Bike Friday Pocket Rocket Pro
Posts: 2,648
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Do the instructions show settings for different tire sizes? If so is there one for 700 x 40? That would be the one to use. They may also have instructions for rolling the tire (on the bike) and marking the distance of one full revolution, then setting up your computer based on the distance. Worst case, you can do what I do in times of mechanical stress--go to the lbs when its not too busy and ask for help.
__________________
"Light it up, Popo." --Levi Leipheimer
Jet Travis is offline   Reply With Quote
Old 04-06-07, 10:14 PM   #3
Yen
Surly Girly
Thread Starter
 
Yen's Avatar
 
Join Date: Mar 2007
Location: SoCal
Bikes:
Posts: 4,113
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
No, the instructions just say how to set the tire size on the computer, nothing about how to determine tire size. I may try rolling the bike one revolution.

Thanks,
Jen
__________________
Specialized Roubaix Expert
Surly Long Haul Trucker
Yen is offline   Reply With Quote
Old 04-06-07, 10:16 PM   #4
Digital Gee
I need more cowbell.
 
Digital Gee's Avatar
 
Join Date: Jun 2005
Location: Reno, Nevada
Bikes: 2015 Specialized Sirrus Elite, 2012 Masi Evoluzione
Posts: 8,111
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by Yen
No, the instructions just say how to set the tire size on the computer, nothing about how to determine tire size. I may try rolling the bike one revolution.

Thanks,
Jen
I can't answer your question, but I am impressed you can read the "manual" that came with the gadget. I'm guessing it's one large sheet of paper that's folded in half six times, and has the instructions printed in half a dozen languages, in 6 pt. font.
__________________
2015 Sirrus Elite
2012 Masi Evoluzione

Proud member of the original Club Tombay
Digital Gee is offline   Reply With Quote
Old 04-06-07, 10:18 PM   #5
Bill Kapaun
Senior Member
 
Bill Kapaun's Avatar
 
Join Date: Feb 2007
Location: Mid Willamette Valley, Orygun
Bikes: 86 RockHopper,2008 Specialized Globe. Both upgraded to 9 speeds.
Posts: 9,371
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 77 Post(s)
Go to this link-
http://sheldonbrown.com/cyclecomp_a.html

Multiply by 10 should get you close. It appears the computer default is a 26X 2.125 tire.

When you have a chance to actually ride a precisely mesured distance, you can "tweek" the numbers then.

PS- Tires tend to run a bit smaller than their "listed" size, so you might want to use a slightly smaller number, like about 3% smaller.

Edit- I forgot which forum this was. Are you old enough
Bill Kapaun is offline   Reply With Quote
Old 04-06-07, 10:27 PM   #6
Yen
Surly Girly
Thread Starter
 
Yen's Avatar
 
Join Date: Mar 2007
Location: SoCal
Bikes:
Posts: 4,113
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by Digital Gee
I can't answer your question, but I am impressed you can read the "manual" that came with the gadget. I'm guessing it's one large sheet of paper that's folded in half six times, and has the instructions printed in half a dozen languages, in 6 pt. font.
Actually, it's printed in ONE DOZEN languages. It was fun hunting for the English section. Thank God for bifocals!!

Bill - thanks, I'll try that. (Old enough for what?)
__________________
Specialized Roubaix Expert
Surly Long Haul Trucker
Yen is offline   Reply With Quote
Old 04-06-07, 10:34 PM   #7
Louis
Senior Member
 
Join Date: Dec 2001
Bikes:
Posts: 4,866
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by Yen
No, the instructions just say how to set the tire size on the computer, nothing about how to determine tire size. I may try rolling the bike one revolution.

Thanks,
Jen
If you do a rollout, be sure your tires are inflated to the pressure you normally ride. Do the rollout while you are on the bike with someone holding you up but not pushing down on the bike. If you measure this distance in cm, I'm guessing there will be a way to enter that number.
Louis is offline   Reply With Quote
Old 04-06-07, 10:57 PM   #8
Bill Kapaun
Senior Member
 
Bill Kapaun's Avatar
 
Join Date: Feb 2007
Location: Mid Willamette Valley, Orygun
Bikes: 86 RockHopper,2008 Specialized Globe. Both upgraded to 9 speeds.
Posts: 9,371
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 77 Post(s)
I figured out the "code".
Tire diameter in inches * PI (3.1416)

Your tire- 40mm
622MM (rim)
622+40+40
=702mm (Diameter of the tire)
1mm = .03937"
702*.03937= 27.638"
27.638" * Pi (3.1416) =86.8"
*10 = 868

868 is the "magic number for you!

It appears since your tires are listed as 42 AND 40 MM, 40 would probably be the number to use in your initial calculations. (to allow for the slightly smaller actual size)

Since this is the 50+ forumn, I had to make sure you're "old enough"

I've BEEN wearing bifocals for 49 years!!!
Bill Kapaun is offline   Reply With Quote
Old 04-07-07, 08:50 AM   #9
Old School
Senior Member
 
Old School's Avatar
 
Join Date: Jan 2006
Location: Marin County, CA
Bikes: Trek 5500 OCLV, Trek Fuel EX 9
Posts: 1,179
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by Louis
If you do a rollout, be sure your tires are inflated to the pressure you normally ride. Do the rollout while you are on the bike with someone holding you up but not pushing down on the bike. If you measure this distance in cm, I'm guessing there will be a way to enter that number.
Use this method only if you are truly committed to "Fred" level accuracy!
Old School is offline   Reply With Quote
Old 04-07-07, 08:53 AM   #10
Old School
Senior Member
 
Old School's Avatar
 
Join Date: Jan 2006
Location: Marin County, CA
Bikes: Trek 5500 OCLV, Trek Fuel EX 9
Posts: 1,179
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by Bill Kapaun
I figured out the "code".
Tire diameter in inches * PI (3.1416)

Your tire- 40mm
622MM (rim)
622+40+40
=702mm (Diameter of the tire)
1mm = .03937"
702*.03937= 27.638"
27.638" * Pi (3.1416) =86.8"
*10 = 868

868 is the "magic number for you!

It appears since your tires are listed as 42 AND 40 MM, 40 would probably be the number to use in your initial calculations. (to allow for the slightly smaller actual size)

Since this is the 50+ forumn, I had to make sure you're "old enough"

I've BEEN wearing bifocals for 49 years!!!
I knew one of our 50+ forum members would have a 128-key calculator, horn-rimmed glasses, and a pocket protector!
Old School is offline   Reply With Quote
Old 04-07-07, 09:42 AM   #11
Yen
Surly Girly
Thread Starter
 
Yen's Avatar
 
Join Date: Mar 2007
Location: SoCal
Bikes:
Posts: 4,113
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
LOL!! I'm beginning to look forward to the hilarious responses in this forum.

Thanks everyone!

I'm off to a little league game so I will take another look at this later.... my head is spinning with numbers right now. It's drizzling this morning so no riding today unless it clears up later then I'll test the accuracy of the computer.

Thanks again everyone.

Jen
__________________
Specialized Roubaix Expert
Surly Long Haul Trucker
Yen is offline   Reply With Quote
Old 04-07-07, 10:01 AM   #12
CrossChain
Senior Member
 
CrossChain's Avatar
 
Join Date: Jun 2006
Bikes:
Posts: 2,023
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Strange, often the directions will offer a handy, generic chart of tire sizes that allows you to eyeball a good approximation. Jen, unless you are a compulsive, pocket protector type....a close guess is good enough. Speed is relative to your own performance and soon you'll discover what is fast for you, easy for you, typical for you...and you won't be checking the computer so much. As for distance, unless you ride huge mileage, the difference between a "good guess" and "precise accuracy" isn't so significant.

Besides, wouldn't want your new-found joy in riding to descend into bean-counting compulsion (i.e. "If I sprint thru that red light I can keep my avg. speed up.")
CrossChain is offline   Reply With Quote
Old 04-07-07, 10:53 AM   #13
stapfam
Time for a change.
 
stapfam's Avatar
 
Join Date: Jan 2004
Location: 6 miles inland from the coast of Sussex, in the South East of England
Bikes: Dale MT2000. Bianchi FS920 Kona Explosif. Giant TCR C. Boreas Ignis. Pinarello Fp Uno.
Posts: 19,915
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
The mechanical side of biking is bad enough- but electronics get me every time. Now just a tip- Get yourself another magnet for the wheel- Then when you decide that you only want a quick 30 miler this morning- fit 2 magnets to the wheel. The 30 miles will fly past.
__________________
How long was I in the army? Five foot seven.


Spike Milligan
stapfam is offline   Reply With Quote
Old 04-07-07, 11:50 AM   #14
freeranger
Senior Member
 
freeranger's Avatar
 
Join Date: Jun 2005
Location: Kentucky
Bikes: 06 Lemond Reno, 98 GT Timberline mtn.bike
Posts: 1,014
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Use the roll out method and multiply the inches traveled by 25.4. That's your number.
freeranger is offline   Reply With Quote
Old 04-07-07, 03:23 PM   #15
Louis
Senior Member
 
Join Date: Dec 2001
Bikes:
Posts: 4,866
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by Old School
Use this method only if you are truly committed to "Fred" level accuracy!
Fred level accuracy? Hrumph! I'll put my roll out calibrated bike computers up against any other method. Any day.

Last edited by Louis; 04-07-07 at 03:32 PM.
Louis is offline   Reply With Quote
Old 04-07-07, 03:38 PM   #16
Monoborracho
Senior Member
 
Monoborracho's Avatar
 
Join Date: Dec 2005
Location: Deep In The Heart
Bikes: Seven Ti Tandem, Blue T12 tri bike, 92 Paramount, 93 Schwinn Mesa MTB, Soma Saga
Posts: 2,614
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 4 Post(s)
Quote:
Originally Posted by freeranger
Use the roll out method and multiply the inches traveled by 25.4 That's your number.
+1 to the above EXCEPT, this would be off by a factor of 10 on my Cateye computers, and much more if your computer is in inches (83 x 25.4= 2108). I have Cateye Enduro 8's on three of my bikes so I am always resetting something. These three bike computers use a setting equivalent to the rolling circumference measured in centimeters.

I think Yen's computer is set in units equal to 1/10th of an inch. Then again, maybe it is set to use inches with mph and centimeters with km/hour. (1 inch = 2.54 centimeters)

You guys are working this too hard. You can calculate circumference with diamters and pie, or pigh, or pi, but Bill Kaupan above has it right.

Yen, your tire is a 700 x 40. The instructions should list a setting for this tire. If they do not, go to a smooth floor, set the inflation valve on the bottom, and mark the spot. Roll it one revolution in a smooth straight line. Measure the distance on the floor in inches and convert to centimeters (cm) by multiplying time 2.54. That is the most accurate way to set the computer, using the actual rolling cirucmferenc. A 700 tire is about 83 0r 84 inches around, which would make a setting of 210 cm to 213 cm. Cateye lists a circumference of 220 CM for a "standard" 700x40 bike tire, so your circumference should be about 86.6 inches.

But you have a default setting of 820? It might mean 82.0 inches. Maybe your computer uses 1/10th of an inch as the calibration, in which case 820 = 82 inches = 209.92 centimeters (go ahead and call it 210) which is also "standard" circumference listed by Cateye for a 26" x 1.5" tire, a mountain bike size.

The hardest part is finding your own language on the little folded up manual, and then finding it again when you need. Why do I buy the same computer? So I can have extra copies of the little folded up instructions.
__________________
Most economic fallacies derive from the tendency to assume that there is a fixed pie, that one party can gain only at the expense of another.....Milton Friedman
Monoborracho is offline   Reply With Quote
Old 04-07-07, 03:54 PM   #17
Louis
Senior Member
 
Join Date: Dec 2001
Bikes:
Posts: 4,866
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
All my computers will take a rollout reading in centimeters directly entered into the computer. No need for higher mathematics.

Rollout is the best method to calibrate any bicycle computer. Period.

Let's see now, Who are we going to listen to when it comes to bicycles? How 'bout Sheldon Brown? Yeah, that's the ticket. http://sheldonbrown.com/cyclecompute...n.html#rollout

Fred level accuracy...my ass!
Louis is offline   Reply With Quote
Old 04-07-07, 04:03 PM   #18
Monoborracho
Senior Member
 
Monoborracho's Avatar
 
Join Date: Dec 2005
Location: Deep In The Heart
Bikes: Seven Ti Tandem, Blue T12 tri bike, 92 Paramount, 93 Schwinn Mesa MTB, Soma Saga
Posts: 2,614
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 4 Post(s)
Quote:
Originally Posted by Louis
Fred level accuracy? Hrumph! I'll put my roll out calibrated bike computers up against any other method. Any day.
+1
__________________
Most economic fallacies derive from the tendency to assume that there is a fixed pie, that one party can gain only at the expense of another.....Milton Friedman
Monoborracho is offline   Reply With Quote
Old 04-07-07, 04:12 PM   #19
Bill Kapaun
Senior Member
 
Bill Kapaun's Avatar
 
Join Date: Feb 2007
Location: Mid Willamette Valley, Orygun
Bikes: 86 RockHopper,2008 Specialized Globe. Both upgraded to 9 speeds.
Posts: 9,371
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 77 Post(s)
I knew one of our 50+ forum members would have a 128-key calculator, horn-rimmed glasses, and a pocket protector!

None of the above!
Bill Kapaun is offline   Reply With Quote
Old 04-07-07, 04:38 PM   #20
Yen
Surly Girly
Thread Starter
 
Yen's Avatar
 
Join Date: Mar 2007
Location: SoCal
Bikes:
Posts: 4,113
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by Monoborracho
+1 to the above EXCEPT, this would be off by a factor of 10 on my Cateye computers, and much more if your computer is in inches (83 x 25.4= 2108). I have Cateye Enduro 8's on three of my bikes so I am always resetting something. These three bike computers use a setting equivalent to the rolling circumference measured in centimeters.

I think Yen's computer is set in units equal to 1/10th of an inch. Then again, maybe it is set to use inches with mph and centimeters with km/hour. (1 inch = 2.54 centimeters)

You guys are working this too hard. You can calculate circumference with diamters and pie, or pigh, or pi, but Bill Kaupan above has it right.

Yen, your tire is a 700 x 40. The instructions should list a setting for this tire. If they do not, go to a smooth floor, set the inflation valve on the bottom, and mark the spot. Roll it one revolution in a smooth straight line. Measure the distance on the floor in inches and convert to centimeters (cm) by multiplying time 2.54. That is the most accurate way to set the computer, using the actual rolling cirucmferenc. A 700 tire is about 83 0r 84 inches around, which would make a setting of 210 cm to 213 cm. Cateye lists a circumference of 220 CM for a "standard" 700x40 bike tire, so your circumference should be about 86.6 inches.

But you have a default setting of 820? It might mean 82.0 inches. Maybe your computer uses 1/10th of an inch as the calibration, in which case 820 = 82 inches = 209.92 centimeters (go ahead and call it 210) which is also "standard" circumference listed by Cateye for a 26" x 1.5" tire, a mountain bike size.

The hardest part is finding your own language on the little folded up manual, and then finding it again when you need. Why do I buy the same computer? So I can have extra copies of the little folded up instructions.
Monoborracho, I have the Cateye Enduro 8 (what an unbelievable coincidence... or is it a very popular calculator for the price point?). You offered the simplest method (why didn't I think of that??) to measure the distance traveled by one revolution of the tire. I will try it later.

Since you have 3 of this particular calculator, how do you like it? Anything I should know about it?

Thanks so much to EVERYONE. This has been a very enlightening -- and entertaining -- thread.

Jen
__________________
Specialized Roubaix Expert
Surly Long Haul Trucker
Yen is offline   Reply With Quote
Old 04-07-07, 05:43 PM   #21
Terrierman
Senior Member
 
Terrierman's Avatar
 
Join Date: Oct 2006
Location: SWMO
Bikes:
Posts: 3,179
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 164 Post(s)
I just reset my Cateye Micro Wireless last night to the Coda. 700x28's. I have the instructions, and the figure I had to enter for that tire size for that computer was 2136. The scale is in millimeters. The table lists 2200 mm for a 700x40. At least that's what the paperwork says. I have no idea what the scale might be for Cateye Enduro 8.
__________________
It's all downhill from here. Except the parts that are uphill.
Terrierman is offline   Reply With Quote
Old 04-07-07, 05:49 PM   #22
Velo Dog
Senior Member
 
Join Date: Jun 2004
Location: Northern Nevada
Bikes:
Posts: 3,802
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
The 820, I'm guessing, is the circumference of the tire in inches multiplied by 10: 82 inches would be 6.83 feet or 2117mm, which is about the size of a 26-inch (diameter, as in a mountain bike) tire (most computers, at least all of mine, are set in millimeters, but it doesn't really matter). Just roll the thing out as somebody else has described, measure it in inches, multiply by 10 and use that as the setting.
Velo Dog is offline   Reply With Quote
Old 04-07-07, 07:04 PM   #23
Monoborracho
Senior Member
 
Monoborracho's Avatar
 
Join Date: Dec 2005
Location: Deep In The Heart
Bikes: Seven Ti Tandem, Blue T12 tri bike, 92 Paramount, 93 Schwinn Mesa MTB, Soma Saga
Posts: 2,614
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 4 Post(s)
Quote:
Originally Posted by Yen
Monoborracho, I have the Cateye Enduro 8 (what an unbelievable coincidence... or is it a very popular calculator for the price point?). You offered the simplest method (why didn't I think of that??) to measure the distance traveled by one revolution of the tire. I will try it later.

Since you have 3 of this particular calculator, how do you like it? Anything I should know about it?

Thanks so much to EVERYONE. This has been a very enlightening -- and entertaining -- thread.

Jen
#1 - set it to AT (where it runs when you go) and leave it.

#2 - forget about using it on more than one set of wheels.

Its cheap, easy to use, and easy to reset.
__________________
Most economic fallacies derive from the tendency to assume that there is a fixed pie, that one party can gain only at the expense of another.....Milton Friedman
Monoborracho is offline   Reply With Quote
Old 04-07-07, 07:07 PM   #24
Monoborracho
Senior Member
 
Monoborracho's Avatar
 
Join Date: Dec 2005
Location: Deep In The Heart
Bikes: Seven Ti Tandem, Blue T12 tri bike, 92 Paramount, 93 Schwinn Mesa MTB, Soma Saga
Posts: 2,614
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 4 Post(s)
[QUOTE=Bill Kapaun]I knew one of our 50+ forum members would have a 128-key calculator, horn-rimmed glasses, and a pocket protector!QUOTE]


Are you talking to me?

You talking to me?

You talking to me?

Well, no pocket protector or horned rim glasses, but I have several calculators with a lot of buttons...one for scientific and one for financials. [ My slide rule is in a framed display box over my desk at home, but yeah, I know what all the numbers are for]
__________________
Most economic fallacies derive from the tendency to assume that there is a fixed pie, that one party can gain only at the expense of another.....Milton Friedman
Monoborracho is offline   Reply With Quote
Old 04-07-07, 07:07 PM   #25
Dchiefransom
Senior Member
 
Dchiefransom's Avatar
 
Join Date: Jan 2003
Location: Newark, CA. San Francisco Bay Area
Bikes:
Posts: 6,205
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 7 Post(s)
I put a piece of tape on the side of the tire for a rollout. I put the bike next to the garage or other long area next to a support where I can hold myself up, with the tape down. I mark the pavement, sit on the bike and move forward until the tape is down again, and mark that. Measure with a tape measure, use an online conversion site to get my units, and set my computer. My Enduro 8 used millimeters.
__________________
Silver Eagle Pilot
Dchiefransom is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off



All times are GMT -6. The time now is 11:55 AM.