I recently purchased an 80's Japanese bike off craigslist called "Jupiter King." It has 27 inch tires but I want to switch to 700c for greater wheel/tire selection. I specifically want some nice yellow wheels with yellow rim. Help? I am quite a noob with bikes. Thanks for any help/advice.

  • Yeah, you'd have to get new wheels. That's $80-150, if you don't get anything fancy. And then you hope that the brakes will still work. – Daniel R Hicks Jul 3 '12 at 20:09

You may or may not be able to make that conversion with your existing brake/frame combination. Your brakes will have to reach farther because a 700c wheel is a smidge smaller than a 27 inch wheel. Depending on your setup, that may be possible. I'd recommend borrowing a 700c wheelset from someone to see if you can line it all up. If it all lines up, great. Purchase whatever 700c wheelset strikes your fancy. If not, you may be able to purchase brakes with a longer reach. Some older frames still won't work with 700c wheels even with the longest brakes available. If that's the case for your frame, you're stuck with 27's.

Personally, if it were me and I couldn't get it to work with the existing brakes, I'd stick with 27 inch wheels. If you start having to swap brakes out, it starts to get iffy and frankly, I think it's more hassle than it's worth. It's a lot easier (and maybe cheaper) to just start hunting for a frame that already has 700s on it.

  • A possibility that should always be considered, even in a "classic" bike, is to reposition the rear brake "bridge" on the frame via removal and re-brazing/re-welding, or to use some clever (!) adapter. THAT would be extra work... ;o) – heltonbiker Jul 3 '12 at 20:37
  • Believe it or not, that was something I considered with a past rebuild. But you can't reposition where the front brake attaches and I was hesitant to jimi-rig an adapter for something crucial like the brakes. – jimchristie Jul 4 '12 at 2:47

The difference between 700C and 27" is pretty small. The rims are 622mm and 630mm so the actual change in brake shoe position is 4mm (less than 1/4"). Look at your brakes and decide whether they will suit. You may be able to change the brakes to ones with longer arms (assuming caliper types).

Another issue may be the rear hub as these have got wider over the years. If it's only a couple of mm you can probably spring the rear forks enough to fit. If it's more than that I would advise you to find a frame builder who can reset the forks.

You will probably need to drop your brake calipers.

I did this on my 1981 Raleigh. Despite fitting long-reach Tektro R559 calipers, the back wheel looked like this:

Before caliper Before sidewall

There might have been another millimetre by fiddling, but not the difference I needed.

Please ignore the dodgy-looking cracked tyre sidewalls... they where only for testing.

Here's the drop-plate I made from 6mm of scrap aluminium bar.

enter image description here

Fitting that with lots of copper grease and some solid bolts gives this:

Caliper dropped OK After sidewall

Curiously, the same brake on the front reached the wheel rim perfectly without any crafting.

I should have lowered it even more, but this way there's clearance for a mudguard someday.

The outside diameter of a 700 wheel is obviously (?) 700 mm which equates to 27.5 inches. A 27 inch wheel has an O/D of 27 inches. If things are a bit tight you cannot replace a 27 inch with a 700C especially if using larger sized tyres i.e. 38-700 or even 35-700, I know as I have recently tried it. You could probably get away with a small tyre such as 25- or 28-700 but may have to use longer brake arms. Better going the other way but not a lot of point, really.

  • 1
    The rim diameter of a 700c wheel is actually slightly smaller than that of a '27inch'. 700c bead diameter is 622mm whereas 27" bead diameter is 630mm. – Argenti Apparatus Apr 2 at 14:21
  • Obvious... but wrong, sorry. 700mm is the nominal diameter of the tyre, not the wheel. These days, you only tend to find 700C but 700A, 700B and 700C all had different rim diameters so that different-sized tyres would take the total diameter to 700mm. – David Richerby Apr 2 at 16:14

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