I have some relatively old wheels which have 700C x 1.25 tires mounted on them. Can I replace those 1.25 tires with 700 x 25C tires? Or are there more specs that I need to consider?
slothead
Joined
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3,886 Posts
if making a 700c conversion, make sure your brake pads will reach the smaller wheel diameter or plan on making further changes.
i've made three 700c conversions: on two of my 1970s road bikes and another from 1980. the '70s bikes got new dual pivot calipers. for the 1980 bike, i was able to file the caliper arm down a bit to gain another millimeter of necessary pad reach.
it's not always necessary to make the conversion to gain the tire choice you want. i like 23mm tires which aren't available in the 27" size. but 25mm tires are readily available (called 1"). and the tire model i usually ride is available in 27".
and if "period-correct" components are important to you, long-reach brakes for a 700c conversion are sometimes difficult to find.
certainly do the upfront planning before making the conversion.
here's one of mine, a '76 motobécane grand record with 700c polished sun m13ii rims, sapim race spokes, vintage campy hubs, and panaracer pasela 23mm tires:
![Image]()
the tektro dual pivots look a little out of place, but not too bad. and, with kool-stops, not many vintage calipers can stop as well.
i've made three 700c conversions: on two of my 1970s road bikes and another from 1980. the '70s bikes got new dual pivot calipers. for the 1980 bike, i was able to file the caliper arm down a bit to gain another millimeter of necessary pad reach.
it's not always necessary to make the conversion to gain the tire choice you want. i like 23mm tires which aren't available in the 27" size. but 25mm tires are readily available (called 1"). and the tire model i usually ride is available in 27".
and if "period-correct" components are important to you, long-reach brakes for a 700c conversion are sometimes difficult to find.
certainly do the upfront planning before making the conversion.
here's one of mine, a '76 motobécane grand record with 700c polished sun m13ii rims, sapim race spokes, vintage campy hubs, and panaracer pasela 23mm tires:
the tektro dual pivots look a little out of place, but not too bad. and, with kool-stops, not many vintage calipers can stop as well.
Joined
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3,886 Posts
while most prefer 700c to 27", moving from one to the other doesn't necessarily represent an "upgraded" bike. you can still buy new 27" rims and build wheels yourself as i did recently for this 1970 gitane:
i used sun cr18 rims, sapim spokes and the original normandy high-flange hubs.
and on the new rear wheel, i used the original 5-speed freewheel.
you can also buy new 27" wheels with new hubs, but the hubs are usually gross and look out of place on vintage bikes.
Joined
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3,886 Posts
love it!
never ridden them for any length of time. i do like their weight savings.
i'm doing some work for a friend -- major wheel true on three tubular rims and a wheel build on another tub rim. i overshot the spoke length by a couple mm on the build. it's a mavic gp4 rim whose e.r.d. wasn't well documented online. but, being a tubular, i guess i don't have to worry about the protruding spoke puncturing rim tape and a tube like this problem might for a clincher. it was my first build on a tubular.
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