Changing tire size - what fits?
02-01-13, 05:54 PM
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Changing tire size - what fits?
I have a 1995 Cannondale R300; and I am looking at getting some new tires for it.
Stock it came with 700x23 tires, and I am interested in putting 700x25 or even 700x28 tires on, but I am very concerned about the clearance I have. Seems like there should be enough clearance at the brake calipers but I am mostly concerned about the clearance of the clamp on the front deraileur. It is already relatively tight with the 23 tires.
My question is... How can I measure, to ensure that the tires I order are going to fit?
Stock it came with 700x23 tires, and I am interested in putting 700x25 or even 700x28 tires on, but I am very concerned about the clearance I have. Seems like there should be enough clearance at the brake calipers but I am mostly concerned about the clearance of the clamp on the front deraileur. It is already relatively tight with the 23 tires.
My question is... How can I measure, to ensure that the tires I order are going to fit?
Last edited by gt eunuch; 02-01-13 at 06:02 PM.
02-01-13, 06:14 PM
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The derailleur does not impact tire size. You need to worry about brakes, brake bridge and maybe the chain stays where they meet the BB shell. I have a Crape R800 from 2004 (CAAD7 frame) and run 25mm tires without issue.
02-01-13, 06:15 PM
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Maybe I should take a picture, but the mech on the front deraileur is currently less than a cm from the back tire...
edit: here is a pic, you can see there is about .5 cm between the tire and the silver protrusion on the front derailleur mech.
edit: here is a pic, you can see there is about .5 cm between the tire and the silver protrusion on the front derailleur mech.
Last edited by gt eunuch; 02-01-13 at 06:35 PM.
02-01-13, 06:27 PM
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Yes, in some cases part of the front derailleur and clamp can be the limiting factor in tire size since they are so close to the tire. Measure the clearance (in mm) you have currently with the 23mm tires. In theory you should be able to use tires with width = 23mm + 2 x current clearance. But tires frequently vary in their actual width and aren't exactly the size stated, so I wouldn't go right to the limit suggested by that formula.
02-01-13, 06:33 PM
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Watch your units: A cm is 10mm or almost 4 tenths of an inch. If you really have that much clearance you should be able to mount 25mm or 28mm tires, at least.
If you meant 1mm clearance you are stuck with what you've got.
DOS: I also have a bike where the derailleur lever is the tight spot as regards tire clearance.
If you meant 1mm clearance you are stuck with what you've got.
DOS: I also have a bike where the derailleur lever is the tight spot as regards tire clearance.
02-01-13, 07:05 PM
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Wow that is close. What kind of derailleur is that, it has much more mechanism directly behind the seat tube than my 105 and ultegra derailluers. That said on my c'dale with 25mm tires the rear tire comes within less than half a CM of my seat tube and about same clearance for chinstay. I doubt I could go to 28mm but I have used 25m. Michelins on the bike which measure more like 26.5mm.
02-01-13, 09:09 PM
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gt eunuch, The largest tire I could put on a Cannondale 2.8 road frame was a 25 mm Conti. It was darn close.
Brad
Brad
02-01-13, 09:22 PM
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Shimano's 8-speed front derailleurs had a relatively long actuating arm and, in the large chainring, could come very close to the rear tire on frames with short chainstays. Later 9-speed and 10-speed fd's had a shorter actuating arm and were less of a problem.
