1 Computer, 2 tire sizes
01-09-17 | 09:25 AM
#1
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Joined: Jan 2015
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From: Madison, IN
Bikes: 2015 Jamis Quest Comp
1 Computer, 2 tire sizes
I'll be switching wheel-sets, with included tires, on my bike between Cyclocross tires (700x30) and Road tires (700x25mm)
If I just set my bike computer for a "700x28mm" tire circumference, how far off will the speed/mileage be?
(I have a magnet for each front wheel)
If I just set my bike computer for a "700x28mm" tire circumference, how far off will the speed/mileage be?
(I have a magnet for each front wheel)
01-09-17 | 09:28 AM
#2
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From: Pittsburgh, PA
Bikes: '96 Litespeed Catalyst, '05 Litespeed Firenze, '06 Litespeed Tuscany, '20 Surly Midnight Special, All are 3x10. It is hilly around here!
Most Cat-Eye computers have setting for two wheel sizes and it's easy to toggle between "A" and "B" when you switch bikes.
Assuming your tires are true to their marked size (the 30 is really 30 mm and the 25 is really 25) setting the circumference for a 28 mm tire (213 cm) your mileage will read 0.4% low with the 30 mm tires and about 1% high with the 25 mm tires
Assuming your tires are true to their marked size (the 30 is really 30 mm and the 25 is really 25) setting the circumference for a 28 mm tire (213 cm) your mileage will read 0.4% low with the 30 mm tires and about 1% high with the 25 mm tires
Last edited by HillRider; 01-09-17 at 09:33 AM.
01-09-17 | 09:42 AM
#3
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From: Roswell, GA
Bikes: '93 Trek 750, '92 Schwinn Crisscross, '93 Mongoose Alta
Well, 700x25mm is about 2105mm circumference, 700x28 is 2136 and 700x30 is 2145. Doing the math, the difference between 2105 and 2136 is 1.47% and between 2136 and 2145 is 0.42%.
01-09-17 | 10:55 AM
#5
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From: St Peters, Missouri
Bikes: Catrike 559 I own some others but they don't get ridden very much.
Two things:
1. How accurate do you really need for it to be? "Measure with a micrometer, mark it with chalk and cut it with an ax."
2. Garmin, never have to worry about wheel size again.
1. How accurate do you really need for it to be? "Measure with a micrometer, mark it with chalk and cut it with an ax."
2. Garmin, never have to worry about wheel size again.
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01-09-17 | 06:55 PM
#6
Senior Member
Joined: Aug 2005
Posts: 33,657
Likes: 1,119
From: Pittsburgh, PA
Bikes: '96 Litespeed Catalyst, '05 Litespeed Firenze, '06 Litespeed Tuscany, '20 Surly Midnight Special, All are 3x10. It is hilly around here!
01-09-17 | 09:18 PM
#7
rebmeM roineS
Joined: Jan 2006
Posts: 16,231
Likes: 366
From: Metro Indy, IN
Bikes: Bacchetta Giro A20, RANS V-Rex, RANS Screamer
Agree that using same setting for both wheels will get you in the ballpark. Not a large ballpark.
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Bacchetta Giro A20, RANS V-Rex, RANS Screamer
Bacchetta Giro A20, RANS V-Rex, RANS Screamer
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