How do I know if I can replace the 27 inch wheels with 700c wheels on my bike?

Question

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.

Answer 1

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.

Answer 2

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.

Answer 3

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:

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.

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

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.

Answer 4

I am working on a similar project. Take a look at this on YouTube:

Answer 5

I would be switching to 700c with disc brakes so obviously would not need to be concerned with O/D. And my Motobecane has plenty of clearance to make the switch.

Answer 6

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.

Answer 7

Don’t listen to anyone that claims it’s not possible to convert because of rim brake compatibility. If you don’t have enough reach with the current brakes installed… all you have to do is source new brakes!

I can’t say that about all bicycles though, some conversions will require some mechanical know-how and tinkering capabilities, or the drive to learn which is something I wish more people were open to try. It’s sad to hear that people will give up on the first set back like “my brake arms don’t reach.” Have they not noticed that bike parts/components are 99% non-proprietary to the frame?