Go Back  Bike Forums > Bike Forums > Electronics, Lighting, & Gadgets
Reload this Page >

how to convert my tire size for cyclocomputer?

Notices
Electronics, Lighting, & Gadgets HRM, GPS, MP3, HID. Whether it's got an acronym or not, here's where you'll find discussions on all sorts of tools, toys and gadgets.

how to convert my tire size for cyclocomputer?

Old 03-09-07, 07:32 PM
  #1  
Junior Member
Thread Starter
 
tamiann's Avatar
 
Join Date: Mar 2007
Location: Austin, Tx
Posts: 11

Bikes: '06 Giant OCR1

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
how to convert my tire size for cyclocomputer?

My tire size is 700x26c

That is not a default size on my Cateye computer. And I can't figure out how to convert it into mm. These are the closest default on the computer:

700x25c = 2105 L(mm)
100x28c = 2136 L(mm)

Can anyone help me out?

Thanks
tamiann is offline  
Old 03-09-07, 07:35 PM
  #2  
Body By Nintendo
 
Psydotek's Avatar
 
Join Date: Sep 2006
Location: Videogames ruined my life. Good thing i have 2 extra lives.
Posts: 3,187

Bikes: Giant TCR2, Giant TCX, IRO BFSSFG SE, Salsa Casseroll, IRO Rob Roy.

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
Can you manually enter the circumference? Most computers should have that option. Just lay out a tape measure and measure how far the tire rolls with 1 revolution. Convert to mm and enter into computer. I had to do that with my friends cyclometer.
__________________

Originally Posted by jsharr
A girl once asked me to give her twelve inches and make it hurt. I had to make love to her 3 times and then punch her in the nose.
Psydotek is offline  
Old 03-09-07, 08:37 PM
  #3  
Senior Member
 
Sir Lunch-a-lot's Avatar
 
Join Date: Jun 2005
Location: Calgary, AB
Posts: 410

Bikes: Montague Folding/E-Bike, Kuwahara

Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 31 Post(s)
Likes: 0
Liked 1 Time in 1 Post
Or Just take the diameter (in your case, 26 inches), and since the Circumference (C) is equivalent to the diameter (D) multiplied by Pie (pi) ( c= pi * d), you can figure out the circumference in inches by multiplying 26 inches by pi or 3.14159.

Apparently, there are 25.4 mm for every Inch (if my math and online unit converter is working right), so you can multiply the circumference in inches by the 25.4mm/inch, and that will give you inches.

So, if I have done my math and all else right, the total comes out to about 2075.
Sir Lunch-a-lot is offline  
Old 03-09-07, 08:53 PM
  #4  
*
 
vpiuva's Avatar
 
Join Date: Jan 2007
Posts: 3,458
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Likes: 0
Liked 2 Times in 2 Posts
700c*26 is not 26". It is 622mm+26mm+26mm=674mm*pi= 2117. But if you can't enter it manually, just go with the closest 700x25. You'll be off (2117-2105)/2117=<0.6% I think you can live with this.
vpiuva is offline  
Old 03-09-07, 09:08 PM
  #5  
Senior Member
 
Retro Grouch's Avatar
 
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
The "A" answer is to roll out your tire. Mark a line on the floor, line up your valve stem with the mark and roll your bike one tire circumference. Measure that distance in millimeters and use that value. That'll give you a real accurate answer.

The "B" answer is to interpolate between the factory numbers. In your example I'd use 2115.

The "C" answer is to use the closest suggested circumference in the computer set-up directions. Actually, to be honest, I always use the next bigger number because I want my customers to feel like they're riding a little farther and a little faster. It won't be as precise as rolling out the tire, but it'll be plenty accurate enough for any normal use.
Retro Grouch is offline  
Old 03-09-07, 09:08 PM
  #6  
Junior Member
Thread Starter
 
tamiann's Avatar
 
Join Date: Mar 2007
Location: Austin, Tx
Posts: 11

Bikes: '06 Giant OCR1

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
Yes I can enter it manually. I had input 2115, and that seems close enough.

Thanks so much!!!
tamiann is offline  
Old 03-09-07, 09:52 PM
  #7  
Senior Member
 
Join Date: Feb 2005
Location: Oklahoma
Posts: 9,438

Bikes: Trek 5500, Colnago C-50

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 4 Post(s)
Likes: 0
Liked 7 Times in 6 Posts
Originally Posted by tamiann
Yes I can enter it manually. I had input 2115, and that seems close enough.

Thanks so much!!!
Good choice. Actually rollouts aren't as accurate as they sound.
Al1943 is offline  
Old 03-09-07, 10:05 PM
  #8  
Senior Member
 
Join Date: Oct 2005
Posts: 1,735
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 5 Times in 1 Post
Originally Posted by Al1943
Good choice. Actually rollouts aren't as accurate as they sound.
Why is that?
masiman is offline  
Old 03-09-07, 10:12 PM
  #9  
Senior Member
 
Join Date: Sep 2001
Location: Montreal
Posts: 6,521

Bikes: Peugeot Hybrid, Minelli Hybrid

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 2 Post(s)
Likes: 0
Liked 2 Times in 2 Posts
Rollouts are only accurate for a particular tire pressure and weight being carried on the wheel. the figure will also change as the rubber wears off the tire. Close is good enough.
AndrewP is offline  
Old 03-10-07, 12:00 AM
  #10  
Senior Member
 
Sir Lunch-a-lot's Avatar
 
Join Date: Jun 2005
Location: Calgary, AB
Posts: 410

Bikes: Montague Folding/E-Bike, Kuwahara

Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 31 Post(s)
Likes: 0
Liked 1 Time in 1 Post
Originally Posted by vpiuva
700c*26 is not 26". It is 622mm+26mm+26mm=674mm*pi= 2117. But if you can't enter it manually, just go with the closest 700x25. You'll be off (2117-2105)/2117=<0.6% I think you can live with this.
Oh. Okay. My bad. I thought the 26 was the measure of diameter. I usually don't see tire sizes measured in this fasion. So... if you don't mind my asking, what does the 700c*26 indicate then?
Sir Lunch-a-lot is offline  
Old 03-10-07, 12:31 AM
  #11  
Body By Nintendo
 
Psydotek's Avatar
 
Join Date: Sep 2006
Location: Videogames ruined my life. Good thing i have 2 extra lives.
Posts: 3,187

Bikes: Giant TCR2, Giant TCX, IRO BFSSFG SE, Salsa Casseroll, IRO Rob Roy.

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
700c is the wheel size, 26 is the tire width in mm i believe.
__________________

Originally Posted by jsharr
A girl once asked me to give her twelve inches and make it hurt. I had to make love to her 3 times and then punch her in the nose.
Psydotek is offline  
Old 03-10-07, 06:33 PM
  #12  
Senior Member
 
Join Date: Feb 2005
Location: Oklahoma
Posts: 9,438

Bikes: Trek 5500, Colnago C-50

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 4 Post(s)
Likes: 0
Liked 7 Times in 6 Posts
Originally Posted by AndrewP
Rollouts are only accurate for a particular tire pressure and weight being carried on the wheel. the figure will also change as the rubber wears off the tire. Close is good enough.
+1
And if the computer sensor works off of the rear wheel there will be a bigger difference between the loaded bike and the unloaded bike.
Al1943 is offline  
Old 03-10-07, 08:27 PM
  #13  
Senior Member
 
Join Date: Aug 2005
Location: Pittsburgh, PA
Posts: 33,656

Bikes: '96 Litespeed Catalyst, '05 Litespeed Firenze, '06 Litespeed Tuscany, '20 Surly Midnight Special, All are 3x10. It is hilly around here!

Mentioned: 39 Post(s)
Tagged: 0 Thread(s)
Quoted: 2026 Post(s)
Likes: 0
Liked 1,095 Times in 741 Posts
Originally Posted by Retro Grouch
The "C" answer is to use the closest suggested circumference in the computer set-up directions. Actually, to be honest, I always use the next bigger number because I want my customers to feel like they're riding a little farther and a little faster. It won't be as precise as rolling out the tire, but it'll be plenty accurate enough for any normal use.
That's funny. I use the next smaller number for my own bikes. A 700x23 is recommended by Cat-Eye at 210 cm and calculates at 209.8. I set my cyclometers at 209 because I want to be sure I've ridden at least the indicated distance.
HillRider is offline  
Old 03-10-07, 08:38 PM
  #14  
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
Who cares. Just use the number and re-verify with GPS or gmaps. It's not important to have millimeter accuracy only that it's consistent (within reason).
operator is offline  
Old 03-10-07, 09:12 PM
  #15  
*
 
vpiuva's Avatar
 
Join Date: Jan 2007
Posts: 3,458
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Likes: 0
Liked 2 Times in 2 Posts
Originally Posted by Sir Lunch-a-lot
Oh. Okay. My bad. I thought the 26 was the measure of diameter. I usually don't see tire sizes measured in this fasion. So... if you don't mind my asking, what does the 700c*26 indicate then?
700 is just an approximate tire diameter when they came up with this crazy system. The actual rim diameter for a 700c wheel is 622mm. The tire size notation is the tread height above the rim, in this case 26cm, which you have to add twice (ie. both sides of the wheel) to obtain the actual tire diameter.
a 700x20c tire would be 622+20+20=662cm in diameter.
a 700x39c tire would actually be 700cm diameter
vpiuva is offline  
Old 03-11-07, 05:11 AM
  #16  
Senior Member
 
Retro Grouch's Avatar
 
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
Originally Posted by Psydotek
700c is the wheel size, 26 is the tire width in mm i believe.
It is the width. If you think of a tire as being a round tube, as it gets wider it also gets a little taller. Consequently the circumference isn't the same for all 700c tires.
Retro Grouch is offline  
Old 03-11-07, 05:13 AM
  #17  
Senior Member
 
Retro Grouch's Avatar
 
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
Originally Posted by HillRider
That's funny. I use the next smaller number for my own bikes. A 700x23 is recommended by Cat-Eye at 210 cm and calculates at 209.8. I set my cyclometers at 209 because I want to be sure I've ridden at least the indicated distance.
So if we rode side-by-side all day, by the end of the day I would have ridden farther and faster than you. Wimp!
Retro Grouch is offline  
Old 06-10-07, 04:36 PM
  #18  
Senior Member
 
Join Date: Apr 2007
Location: Newark, Ohio
Posts: 758

Bikes: 2002 Dahon Boardwalk 1, 2003 Sun EZ-Sport Limited, 2011 TerraTrike Path 8, 2018 Gazelle Arroyo C8 HMB

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 2 Post(s)
Likes: 0
Liked 1 Time in 1 Post
Myself, I just used the cyclocomputer calibration chart that Sheldon Brown has. More accurate than certain owner's manuals. (My Schwinn cyclocomputer's manual listed 27 x 1 1/4 (32-630) as 2155 mm circumference, the same as 700x32C (32-622), when it was really 2161...)
bhtooefr is offline  
Old 06-10-07, 04:46 PM
  #19  
Trans-Urban Velocommando
 
ax0n's Avatar
 
Join Date: Nov 2006
Location: Lenexa, KS
Posts: 2,400

Bikes: 06 Trek 1200 - 98 DB Outlook - 99 DB Sorrento

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
When the only person you're trying to beat is yourself, consistancy trumps accuracy any day. Just hop on your bike and enjoy it. Give yourself some goals of riding further and faster than the month or week before if you want, and you don't need to worry too much about it.

If you want brutally honest accuracy, go get a Garmin Edge. Even GPS can be off by a bit but it'll probably be more accurate (although arguably less consistant) than a regular wheel-rotation-counting cyclometer.
ax0n is offline  
Old 06-10-07, 05:45 PM
  #20  
Senior Member
 
Winter76's Avatar
 
Join Date: Jun 2007
Location: The Peg
Posts: 663
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
Originally Posted by bhtooefr
Myself, I just used the cyclocomputer calibration chart that Sheldon Brown has. More accurate than certain owner's manuals. (My Schwinn cyclocomputer's manual listed 27 x 1 1/4 (32-630) as 2155 mm circumference, the same as 700x32C (32-622), when it was really 2161...)
+1 for this, I used his chart to calibrate my schwinn wireless computer, worked great!
Winter76 is offline  

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
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service -

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.