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I'm trying to work out if my current brakes are long enough to work with 700C wheels (ie 622mm rim), rather than 630 (27"). The question I have is, will the wheel sit at the same point in the dropout? Do I need to factor in a different diameter quick release bolt? Or do they have the same diamater?

Will the frame spread make a difference?

Thanks

Tom

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1 Answer 1

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I will use 27" to describe ISO 630 in the remainder.

You need to be able to move your brake pads down by about 4mm. If you can do this, you should be OK. Velo-Orange has a nice page describing the process (if you don't have the sufficient brake adjustment, put in a 700c wheel which has appropriate hub spacing (probably 126 mm - Velo Orange (among others) are also willing to sell you a prebuilt wheel for this purpose), and measure from the center of the caliper bolt hole to the center of the rim, and that is the reach required for a replacement caliper (then, you can buy a cheap replacement caliper) ). If you're spreading the frame to take a 130 mm hub (you shouldn't need to do cold setting for this with a cup-and-cone hub), the angle change is tiny (you can work out the trigonometry for it), so you will need a little less range of adjustment. The QR is irrelevant. The wheel can sit slightly further back in the drop out (maybe about 2-4 mm) to match the angle exactly of the brakes hitting the wheel, but I don't think this is necessary (once again, you can measure the angle from the dropout center line and the brakes with the vertex being center of the axle, and use a little math or adjustment to match it for the brakes with the new wheel, but it should be tiny). In other words, you'll figure it out when you put in the new wheel and adjust the brakes.

For completeness, people using Canti's often have to swap to something else, like PlanetX's Frog Bollox for the additional adjustment range. Velo-Orange does point out that most original brakes for 27" bicycles are not very good even compared to cheap brakes today, so you may want to get new brakes anyway.

Also, note that you can still buy 27" wheels (see here) and tires from brands like continental or whatever, though there is certainly more expense and less selection.

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Thanks Batman - great answer. I'm upgrading my shifters to brifters, from downbar friction shifters, so unfortunatly I'm having to go to 700c, as you can't get modern freehub wheels in 27" - otherwise I'd be happy to stick with 27". –  7thGalaxy Feb 25 at 14:21
    
One alternative in that case is to get Retroshift levers (retroshift.com) - They're essentially Tektro brake levers with a mounting point for your old downtube shifters on them. If you just want shifters near your hands, you can always get bar ends. These may save you some money over the brifter switch. –  Batman Feb 25 at 15:20
    
Hi - I looked into them. In the end I can get a sora set cheap enough that it works out (especially as I want to get my two bikes using the same standard kit, to make maintenance easier). –  7thGalaxy Feb 25 at 16:34

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