what is the REAL size difference between 700c and 27"
07-19-07 | 01:44 PM
#1
Thread Starter
Fat man on a little bike.
Joined: Aug 2006
Posts: 102
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From: Castle, OK
what is the REAL size difference between 700c and 27"
ok, I have searched, I read Sheldon's page...I still dont know the answer.
27" tire is (roughly) 27" Diameter.
700c tire is what? I have been told that it is 29" roughly.
and on Sheldons sight he says 29"...BUT...if that were true, then why is it that brakes on older bikes have to be changed or adjusted down? seems to me that means they are smaller....
I am sorry, and it really does not matter I guess....just bugging me that I dont know.
27" tire is (roughly) 27" Diameter.
700c tire is what? I have been told that it is 29" roughly.
and on Sheldons sight he says 29"...BUT...if that were true, then why is it that brakes on older bikes have to be changed or adjusted down? seems to me that means they are smaller....
I am sorry, and it really does not matter I guess....just bugging me that I dont know.
07-19-07 | 01:52 PM
#2
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Joined: Dec 2006
Posts: 1,221
Likes: 24
From: Toronto/Montréal
Bikes: Eight homemade, three very dusty
Wheels' denominations are truly misleading.
An objective measure is that of the bead seat diameter.
27" wheels have BSD=630mm (24.8")
700c wheels have BSD=622mm (24.5"), so the former is 8mm larger in diameter.
The reason wheels are called 27", 26" or 29" is because they have approximately those diameters when some tire is seated. Of course it really depends on the tire, hence the confusion. A 700c rim with a big tire (29er) can end up bigger than a 27" rim with a small tire.
An objective measure is that of the bead seat diameter.
27" wheels have BSD=630mm (24.8")
700c wheels have BSD=622mm (24.5"), so the former is 8mm larger in diameter.
The reason wheels are called 27", 26" or 29" is because they have approximately those diameters when some tire is seated. Of course it really depends on the tire, hence the confusion. A 700c rim with a big tire (29er) can end up bigger than a 27" rim with a small tire.
Last edited by tuz; 07-19-07 at 02:01 PM.
07-19-07 | 02:09 PM
#3
07-19-07 | 02:10 PM
#4
The Improbable Bulk
Joined: Jul 2005
Posts: 8,379
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From: Wilkes-Barre, PA
Bikes: Many
If you look at this table for setting type D cyclocomputers, it tells of the radius of certain wheel/tire combinations... since type D cyclocomputers use radius to set wheel size.
https://sheldonbrown.com/cyclecomp_d.html
You will notice that the typical 27 inch tires (27 x 1 1/4) are between 700X32 and 700X35 in their over-all radius...
So any 700c tire that is 35 mm or wider will be taller than a 27" and anything 32 mm or narrower will be shorter...
By the way, 29" is the term for a massive 700c... which is why it is bigger than a 27"
https://sheldonbrown.com/cyclecomp_d.html
You will notice that the typical 27 inch tires (27 x 1 1/4) are between 700X32 and 700X35 in their over-all radius...
So any 700c tire that is 35 mm or wider will be taller than a 27" and anything 32 mm or narrower will be shorter...
By the way, 29" is the term for a massive 700c... which is why it is bigger than a 27"
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People do not seem to realize that their opinion of the world is also a confession of character.
- Ralph Waldo Emerson
07-19-07 | 02:14 PM
#5
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From: Ann Arbor, MI
Bikes: 1980 Masi, 1984 Mondonico, 1984 Trek 610, 1980 Woodrup Giro, 2005 Mondonico Futura Leggera ELOS, 1967 PX10E, 1971 Peugeot UO-8
ok, I have searched, I read Sheldon's page...I still dont know the answer.
27" tire is (roughly) 27" Diameter.
700c tire is what? I have been told that it is 29" roughly.
and on Sheldons sight he says 29"...BUT...if that were true, then why is it that brakes on older bikes have to be changed or adjusted down? seems to me that means they are smaller....
I am sorry, and it really does not matter I guess....just bugging me that I dont know.
27" tire is (roughly) 27" Diameter.
700c tire is what? I have been told that it is 29" roughly.
and on Sheldons sight he says 29"...BUT...if that were true, then why is it that brakes on older bikes have to be changed or adjusted down? seems to me that means they are smaller....
I am sorry, and it really does not matter I guess....just bugging me that I dont know.
Tony Oliver, in his great book "Touring Bicycles," gives a table of diameters v. ISO/ERTRO specs. My number is not far from his. He also gives a diameter of around 700 mm for 27 x 1 1/4.
So the real difference is a a larger diameter by about 20 mm, more if you compare 19 mm track sew-ups (660mm) to the 27x1 1/4's. This is enough to significantly affect whether you can use fenders or not, or even if you can upsize rims and tires on some frames, such as (lol!) converting that Colnago into a tourer.
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