rch427

I am building up a 45 year-old handmade British frame, and am trying to figure out what my (clincher) rim options are. The frame may have originally had 27" rims fitted to it. Also, the tires I want to mount are actually more readily available for 27" rims than for 700Cs.
I measured from the (theoretical) center of the front hub spindle to the point inside the fork legs where the tire would be likely to hit, and it's 13.5". Likewise, I measured from the (theoretical) center of the rear spindle at the forwardmost point (they're track dropouts), and again, 13.5".
I've read quite a few guides to wheel-fitting, but have never managed to get a solid sense of what is what (thanks, rim manufacturers, with your illogical sizing!) It's my understanding that 700c rims are 8mm larger in diameter than 27" rims. Is that correct? Am I correct in thinking that 700Cs might not even fit the frame?
Thanks in advance!

HillRider

700c rims are actually 8mm smaller in diameter than 27". Their ISO diameter sizes are respectively 700c = ISO 622 mm and 27" = ISO 630 mm. Switching from 27" rims to 700c requires lowering the brake shoes by 4mm and conversely, going from 700c to 27" requires raising the brake blocks by 4mm

masi61

+1 to this. rch427 could you comment on what type of brakes you will be using. Whether you can easily fit 700c wheels or not is dependent on your answer.

ThermionicScott 

Got any spare wheels? That’d be a faster way to find out what’ll fit.

mpetry912 

remember it's not only a matter of what rims will fit but what brakes you'll use and will they reach

on an older bike that was built for 27" rims, if you run 700s you may not have enough brake reach

/markp

SurferRosa

99.99567 percent of the time, it's the other way around.

Bill Kapaun

You'd expect somebody "building a bike up" would have some spare wheels laying around. Even if installed on their other bikes.
"On paper", a 27x1-1/4" tire is 27.3" diameter. it might be a 26" bike?

Iride01 

Maybe if you measure from the fork ends to the mount hole in the head tube for the brakes or the dropout about where the wheel will sit to the brake bridge, you can figure out what wheel it is intended for. This might help you figure it out...


Shimano Framebuilder Info - Pvdwiki

The measurement might not match exactly as there aren't any strict rules for where one puts them. It's a bicycle. And for most purposes close enough was all that counts. A few frame builders might actually acknowledge that.

Even if it measured for a 27" wheel, I'd put a 700C on it and just find some long reach brakes if normal reach brakes don't have enough adjust for pad position or are too weak to give sufficient stopping power because the pads are furthest out in their mounts.

700C wheels and tires are more plentiful and still widely used. 27" wheels and tires have long since been gone and what is marketed today is old tech just to supply the demand for replacement parts of old bikes. Little new technology gets implemented into them. And for the most part, only the more cost effective for manufacturing versions still survive for marketing today. In other words, the cheap stuff.

rch427

My front hub will be a Sturmey-Archer drum brake hub, and my rear hub will be a 3-speed with backpedal drum brake hub. No calipers for me!

rch427

For normal people, perhaps, but all of my bikes have white or cream tires. And for whatever reason, they are more readily available in 27" sizes.

rch427

Sorry, I should've mentioned that I don't use caliper brakes. Drum brakes in the front, back-pedal brakes in the rear. Sounds "low performance", but on SF's streets, and Eroicas, they work fine for me.

rch427

All of my bikes are set-up with drum brakes in the front and geared hubs (with backpedal brakes) in the rear, so alas, it's not like I can just throw a QR lever and swap wheels to test for fitting. That would be too easy!

rch427

"Little new technology gets implemented into them"
Thank the gods of Valhalla! (or wherever)
The last thing I want near my bikes is new technology!
I'm old and my frames are old, so my components are suitably old. Hell, my Gnome et Rhone (c. 1947) has wooden rims. So...

rch427

gah -- you're right. Despite looking at a multitude of sites that explained the differences in sizes, I still managed to get them reversed. (≧︿≦)
Thanks for pointing that out.

grumpus

The only common(ish) size larger than 27" at 630 mm is British 28" x 1-1/2" at 635 mm, as used on big old roadsters, still made in India I think. Regular European "28 x 1-5/8 x 1-3/8" and mountain bike "29 x 2.2" etc. are alternative terms for 700C at 622 mm, so 4 mm smaller on the radius than 27", needs an extra 4 mm reach on the brakes. The recent use of 27-1/2 inch or 27.5 to refer to 650B mountain bike tyres is perhaps confusing, they are 584 mm so smaller than 27". However 27" x 1-1/4" overall diameter is 694 mm (630 + 2 * 1.25 * 25.4) and 650B with a 2.35" tyre is 703 mm (584 + 2 * 2.35 x 25.4) so it kind of makes sense, although those are both larger than 27 actual inches which is 686 mm. When in doubt always use the ISO (formerly ETRTO) size definition which is the actual dimension in millimetres.

grumpus

Stick with 27 inch wheels and you'll be getting mostly tyres like we had in the 1970s, while 700C tyres are likely lighter and/or grippier and/or more puncture resistant, certainly available in much greater variety. There are a few 27" touring tyres available of reasonable quality, if you can find them in stock - Schwalbe Marathon is one that is often recommended (if you want robust and don't mind heavy).

ThermionicScott 

You can get Panaracer Ribmos in white and 700x28C, if that helps: https://www.amazon.com/Panaracer-8W7...dp/B0056CB3PI/

JohnDThompson 

Going from 700C (622mm diameter) to 27" (630mm diameter) brings concerns with frame clearance and rim brake reach. But your proposed change, from 27" to 700C and hub brakes, does not carry those concerns. I anticipate no problems fitting the wheels if you build them using your current hubs, but tire clearance could still be an issue if you mount significantly wider tires than you currently use.

grumpus

I meant to say: fit the brakes you want to use, measure from axle centre to brake block centre in millimetres and double it to get the rim diameter. Compare with available rim sizes (the centre of the braking surface is about the same place as the bead seat).

ThermionicScott 

What's the issue? It's not like you need to attach the reaction arm (or tighten axle nuts) in order to put a wheel in the frame for checking tire clearance.

rch427

I have had to remove wheels for various reasons (changing tubes, etc.) and dismounting the reaction arm, then having to re-mount it, make sure the rim runs straight in the frame, adjusting the shifting cable, and so on, is a PitA, and to be avoided if possible. You kids with your QR hubs don't know how easy you've got it.
Also, since tires have different profiles, I'd be dealing with the vagaries of those when swapping from another bike, rather than having an understanding of the underlying principles (which is to say, the actual diameters), which I have never understood. For most of my bikes, I have been able to re-used the rims that I got them with, and for some of the others (like the G&R), rim size selection was easy (650B) because there was no alternative that would fit. Live and/or learn.

rch427

Thank you!
Yes, I have the white Panaracers on my DeRosa, and am pretty happy with them. They're a bit soft, which is good for grip, although they wear kind of quickly. But at <$20 a pop, that's not a big deal.
Thanks

rch427

Yes, I have those 28" wheels on my Raleigh DL-1 Tourist. Each of the steel rims on it weighs about 3 lbs., but AFAIK there's no alternative alloy rim possible (especially since the braking system is integral to the frame). And that's why I almost never ride the DL-1 here in SF; it weighs close to 60 lbs! (We did take my late wife's matching DL-1 to London one year for the Tweed Run. It was no fun wrestling the box I had it in, through 2 airports, the Underground, and a hotel's narrow staircases, lemme tell you...)