Wheels are the part of an old road bike most likely to have been swapped, and the part you're most likely to want to change. Before you buy a bike or a wheelset, it helps to know four things: the rim size, the rear spacing, how the gears attach, and whether the rims take tubular or clincher tires.
27 in and 700c are different sizes
A 27 in clincher rim has a bead seat diameter of 630 mm. A 700c rim is 622 mm. Tire sizes are standardized by that diameter, so a 27 in tire won't fit a 700c rim or the other way around.
Most French bikes imported to the US before the mid-1980s used 27 in wheels, even though the size was never used in France, where bikes came with 700c or 650B. Race bikes on tubular tires are a different case, covered below.
700c has the bigger choice of tires and rims today, so many owners move a 27 in bike to 700c. That can work well, with one catch.
Brake reach is the catch
A 700c rim has a radius 4 mm smaller than a 27 in rim, so the braking surface sits 4 mm closer to the hub. The brake pads have to reach 4 mm further down. If the old calipers already sit at the bottom of their slots, they won't reach.
Measure before you buy wheels. Reach is the distance from the brake mounting bolt to the middle of the pad. Go by the millimeters, since short and long reach mean different things to different makers. If the old brakes won't reach, you have two fixes.
- Longer-reach calipers. Calipers in the 47 to 57 mm range are sold for exactly this conversion.
- Drop bolts, which mount a caliper lower on the frame. They're a common fix for the same swap.
Watch the mounting style. Many older frames and forks were built for brakes held on with an exposed nut. Most modern calipers use a recessed nut that needs a larger hole in the back of the fork crown and brake bridge. Old frames won't take recessed brakes without drilling, so look for nutted calipers.
Longer reach also costs some braking power, because the pad sits further from the pivot. Good pads and cables make up most of that.
Rear spacing
Rear spacing is the width between the rear dropouts, and the rear hub has to match it. Road bikes went through three common widths.
- 120 mm for five-speed freewheels.
- 126 mm for six- and seven-speed.
- 130 mm for eight speeds and up.
A 1970s five-speed bike is likely 120 mm. A 1980s six- or seven-speed bike is likely 126 mm. Most road wheels sold today are 130 mm. Measure the gap between the dropouts with no wheel in, or ask the seller to.
A steel frame can take a hub one size wider by springing the stays apart as you fit the wheel. This is how many 126 mm frames end up with 130 mm hubs. For a bigger jump, such as 120 to 130 mm, the frame should be cold set, which means bending the rear triangle to the new width and then checking that both sides are equal and the dropouts are parallel. A framebuilder or experienced shop can do it. Done carelessly, it can damage a frame.
Don't cold set aluminium or carbon. That includes bonded aluminium frames like the Vitus 979.
You can check the result yourself with a string run from dropout to dropout around the head tube, as described in our frame inspection guide.
Freewheels and freehubs
Most vintage road bikes use a freewheel, where the sprockets and the ratchet are one unit that screws onto threads on the hub. Shimano's freehub, introduced in the late 1970s, puts the ratchet inside the hub and slides a cassette of sprockets onto it. Freehubs took over once bikes had more sprockets.
So you have two routes. Keep the bike's freewheel and buy a threaded hub, which keeps the period look and the original gearing. Or move to a freehub wheel and a cassette, which usually means 130 mm spacing and new shifters to match the number of sprockets.
French freewheel threading existed, but nearly all French bikes sold in the US used standard British freewheel threads, so an American-market French bike rarely needs a French hub. Old freewheels come off with a splined removal tool that matches the brand, so check you have the right one before you start.
Tubulars and clinchers
Many vintage race bikes came on tubular tires. A tubular has no bead. The casing is sewn closed around the inner tube, and the tire is glued onto a special rim. A clincher is the ordinary tire and tube that hooks into the rim.
The rims aren't interchangeable, but the size is. Full-size tubulars sit at the same diameter as 700c clinchers, and there's no true 27 in tubular. So a bike built for tubulars takes 700c clincher wheels with no change in brake reach. That makes a tubular bike one of the easiest to fit with modern clincher wheels.
If you keep tubulars, treat old ones as decoration. Old glue lets go, and a tire rolling off in a corner is a crash. Fit new tires with fresh glue, or keep the old wheels for display and ride on new ones.
What the bikes we cover tell you
A few catalog details show how much this varies. The Peugeot UO-8 came on 27 x 1 1/4 in clinchers, an export size that was never used in France. The Colnago Super was spaced 126 mm for a six-speed freewheel by 1981, and in 1991 Mercian built its frames, like the Vincitore Special, at 126 mm unless asked otherwise. A 1988 De Rosa Professional measures 126 mm too. The 1980s Peugeot PSV-10 used Maillard Helicomatic hubs, whose clusters only fit Helicomatic hubs. On anything older, measure before you buy.
Keeping it original or making it a rider
There's no wrong answer here. Original wheels matter on a collector bike, and they're worth keeping even if you ride on something else. For a bike you'll ride every week, a good 700c wheelset at the right spacing, with tires you can buy anywhere, is a fine upgrade that's easy to undo.
For period hubs, rims, freewheels and complete wheels, our sister store components.allbutnew.com covers vintage road bike components. For the bikes themselves, every model page in our catalog lists the wheel size and spacing where we could confirm it. The 1970s bike boom page shows which bikes are most likely to be on 27 in wheels, and the first bike guide covers what else to check before you buy.