Go Back  Bike Forums > Bike Forums > Folding Bikes
Reload this Page >

20" wheels "factor" for bike computer

Notices
Folding Bikes Discuss the unique features and issues of folding bikes. Also a great place to learn what folding bike will work best for your needs.

20" wheels "factor" for bike computer

Old 04-01-21, 04:04 PM
  #1  
Elbeinlaw
Senior Member
Thread Starter
 
Join Date: Jun 2020
Posts: 271
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 149 Post(s)
Liked 95 Times in 64 Posts
20" wheels "factor" for bike computer

In setting up my new Bike Friday I found an old but perfect condition wired bike computer in my parts box that I put on the BF. BF Mothership suggested a 20" wheel factor that resulted in a problem. Cadence works great, but speed and odometer are way overestimating . They also gave me a reference resource that is too damn complicated. I just don't want to do the calculations and measurements when riding time is so limited. So what I'm looking for is the number those of yall with 20"x1.75x wheels have used that produces close-enough results: OK is OK.
Elbeinlaw is offline  
Old 04-01-21, 04:48 PM
  #2  
alo
Senior Member
 
Join Date: Feb 2020
Posts: 1,059
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 529 Post(s)
Likes: 0
Liked 254 Times in 185 Posts
Explain yourself more clearly. Does your bike have 20 inch wheels? Is the computer set up for 26 inch wheels? Do you just want to know the difference in circumference? Or is it something else?
alo is offline  
Old 04-01-21, 05:48 PM
  #3  
Juan el Boricua
Senior Member
 
Join Date: Sep 2011
Location: San Juan, PR
Posts: 142

Bikes: 1980's Royce Union "fixed wheel", 1995 Trek 370, 406 -wheeled " shopper/minivelo"for running errands, SS Raleigh M60

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 37 Post(s)
Liked 42 Times in 34 Posts
Here you go; can be helpful if you ever change tire size and/or diameter:

https://www.cateyeamerica.com/tire-size-calculator/
Juan el Boricua is offline  
Old 04-01-21, 05:59 PM
  #4  
Moe Zhoost
Half way there
 
Moe Zhoost's Avatar
 
Join Date: Sep 2015
Location: Durham, NC
Posts: 2,533

Bikes: Many, and the list changes frequently

Mentioned: 5 Post(s)
Tagged: 0 Thread(s)
Quoted: 830 Post(s)
Liked 626 Times in 373 Posts
I always measure my circumference directly and use that number instead of what some chart says. Also, you need to keep in mind that there are 3 different sizes for 20" tires: ISO 406, 419, and 451 bead seat diameters.

Good luck.
Moe Zhoost is offline  
Old 04-02-21, 11:29 AM
  #5  
Elbeinlaw
Senior Member
Thread Starter
 
Join Date: Jun 2020
Posts: 271
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 149 Post(s)
Liked 95 Times in 64 Posts
Alo:

Does your bike have 20" wheels?: BF Mothership suggestd a 20" wheel factor--because I have 20" wheels.
Is the computer set up for 26" wheels? Since it was old but pefect condition It wasn't set up at all, but of course I could program it for various sizes ... but not down to 20".
Do [I} want to know the difference in circumference?: No, I want to know "the wheel factor ... number" that gets programmed into the computer that translates wheel revolutions into speed/distance, that's appropriate for 20" wheels. Maybe that's just the circumference, I don't know.
Or is it something else? YES. I want to try to avoid the measuring and math. Surely someone with 20" wheels can tell me what number they programmed into their computer ... and that should get me close.

But if not, I'll dig through Juan's and Moe's resources and get out my tape measure.
Elbeinlaw is offline  
Old 04-03-21, 05:17 AM
  #6  
Tourist in MSN
Senior Member
 
Join Date: Aug 2010
Location: Madison, WI
Posts: 8,671

Bikes: 1961 Ideor, 1966 Perfekt 3 Speed AB Hub, 1994 Bridgestone MB-6, 2006 Airnimal Joey, 2009 Thorn Sherpa, 2013 Thorn Nomad MkII, 2015 VO Pass Hunter, 2017 Lynskey Backroad, 2017 Raleigh Gran Prix, 1980s Bianchi Mixte on a trainer. Others are now gone.

Mentioned: 38 Post(s)
Tagged: 0 Thread(s)
Quoted: 2438 Post(s)
Likes: 0
Liked 655 Times in 535 Posts
I roll the bike for one wheel revolution, measure that distance, enter into computer. I do not find it to be that difficult. Start with the valve stem at the lowest point, then roll for one revolution to get the valve to teh lowest point, not that difficult. It took me more time to write this post than to actually do it.
Tourist in MSN is offline  
Old 04-03-21, 03:44 PM
  #7  
GeezyRider 
Another Bozo on the Bus
 
GeezyRider's Avatar
 
Join Date: Aug 2015
Location: Delaware Sea Shore
Posts: 270

Bikes: Panasonic DX-3000, Trek Multitrack 720, Mercier Galaxy SC1, Raleigh Pursuit, Giant ATX 760, Retrospec Judd, Catrike Trail, EZ-1 SC, BikeE E2

Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 78 Post(s)
Liked 121 Times in 80 Posts
The Cateye Tire Size Calculator is a great tool. If you are looking for Wheel Size Diameter in mm and do not want to be bothered with entering data into the Cateye tool, I have used these successfully:

20 x 1.50 = 1490
20 x 1.75 = 1502
20 x 1.95 = 1575

These are approximations. Tires from different manufacturers will vary slightly and you may have to adjust accordingly.
__________________
Don

Last edited by GeezyRider; 04-03-21 at 03:52 PM.
GeezyRider is offline  
Old 04-04-21, 05:57 AM
  #8  
Elbeinlaw
Senior Member
Thread Starter
 
Join Date: Jun 2020
Posts: 271
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 149 Post(s)
Liked 95 Times in 64 Posts
Geezy Rider: THANKS!!!

Originally Posted by GeezyRider View Post
I have used these successfully:
20 x 1.50 = 1490
20 x 1.75 = 1502
20 x 1.95 = 1575
Do you know how rare it is for people to actually answer the question asked? I'll try these. Then later when I have more time actually do the calculations.
Elbeinlaw is offline  
Old 04-12-21, 05:47 PM
  #9  
tomtomtom123
Senior Member
 
Join Date: Jan 2017
Posts: 1,014
Mentioned: 6 Post(s)
Tagged: 0 Thread(s)
Quoted: 332 Post(s)
Likes: 0
Liked 110 Times in 78 Posts
You're not going to get accurate speed readings unless you actually roll the bike and measure the travel distance. And "factor" doesn't mean anything unless you know exactly what it is. It's not complicated math. It just wants to know your wheel diameter. It uses the magnet on your spoke to count each revolution. The measured travel distance formula is revolution x diameter x 3.14. the speed just takes the distance traveled and divides it by time.

Also the effective diameter decreases when you sit on the bike because the tire sinks under load and decreases the radius. So I sit on the bike and roll it 3 revolutions, take the distance traveled and divide by 3. My 2.1" wide tire is measured at an effective circumference of 1580mm at 3 bar pressure. If I don't sit on it, it's somewhere around 1590mm. Also if I decrease the pressure to 2.6 bar, I get something around 1550mm. This changes the speed and distance reading by up to 2%.
tomtomtom123 is offline  
Old 04-14-21, 02:24 AM
  #10  
Geepig
Senior Member
 
Geepig's Avatar
 
Join Date: Sep 2020
Location: Eastern Poland
Posts: 736

Bikes: Romet Jubilat x 4, Wigry x 1, Turing x 1

Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 194 Post(s)
Liked 188 Times in 144 Posts
Originally Posted by Elbeinlaw View Post
Do you know how rare it is for people to actually answer the question asked?
Probably not quite as rare as to be asked a question not so full of un-mentioned assumptions that it can be reliably answered. Since I live in Poland it helps to mention that I live in Poland otherwise I get answer that presumably work in Montana or Scotland.
Geepig 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


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information -

Copyright 2021 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.