Replacing Vintage 27" wheels with 700c

Many older vintage road bike frames (made up until around the late 1980's) were built to use  27" x 1 1/4" sized wheels. Plenty of them are still going strong today. However, to keep these vintage bikes in regular use, owners often need to change to the more modern 700c size. This seems mainly due to the far wider choice of readily available wheels and tyres.

Hub spacing can be an issue, 700c wheels tend to be built for a frame rear dropout spacing of anything from 126mm to 135mm. The older frames built for use with 27" x 1 1/4" wheels may well have a narrower space between the rear dropouts. Sizes can vary massively on older frames 120-124mm is not unusual.

There are solutions, but keep in mind it's always preferable to adapt a wheel to fit a frame rather than the other way round. A vintage 700c wheel of similar age is more likely to have a suitable hub spacing and should be a good candidate for replacement for a 27".

Or if your replacement wheel is using a screw on freewheel with 5 6 or 7 gears, the wheel is likely to have a spacer on the drive side of the axle like this one does.

vintage 700c threaded screw on freewheel hub

If your wheel is too wide then you can look to replace this spacer for a shorter one to reduce the hub width by a few mm. Occasionally you find there are more washers than required on an axle and you can remove two to help give you the right OLD (Over locknut-dimension). Sometimes you can replace the locknuts with narrower ones. If necessary a wheel builder can easily adjust the dishing of the wheel to compensate if the hub ends up a long way off centre. A wheel running a freehub is less flexible as the OLD is pretty much dictated on the drive side by the length of the freehub body.

If your wheel is still too wide to fit your frame and all options are exhausted. Then cold setting a steel frame is a possibility. This should be done professionally. It's easy to bend a frame too far and cause structural damage to the stays, this generally results in an expensive trip to a frame builder anyway, so you may as well get the job done right first time.

Once you have got your hub spacing sorted out, it's time to think about the actual wheel rim size. Wheel sizes are confusing at best. The wheel size 700c is also known as a 28". However it is actually slightly smaller than the vintage size found on many older road bikes which is 27" x 1 1/4". This is due to differences in measuring convention. The BSD (Bead seat diameter) rim size is 622mm on a 700c and a 630mm on a 27" x 1 1/4".

Whilst this size difference is only minor (the inner tubes are interchangeable but the tyres are not) a change to a smaller wheel means the brakes will sit at a higher point on the wheel. This can often be significant enough to cause your brake blocks to hit your tyres, quickly leading to catastrophic brake and tyre failure.

The answer is to have longer reaching brakes. If you can move the blocks far enough down the slots on your calipers then you are ok. But if your brake blocks can't move any lower then you probably need to replace your calipers with longer reaching ones.

Changing brake calipers can bring about another compatibility issue with your frame bolt holes. Most modern brake calipers available on the market use recessed allen fittings. Newer frames have a wider caliper bolt hole entry on the rear to allow a recessed allen bolt to fit in. On older frames the hole is narrower and the caliper is held in place with a standard nut tightened onto the caliper bolt. 

One option is to drill wider holes into the frame and fork, but in all honesty who wants to do that? A less destructive option is to source vintage long reach calipers. Or find a modern equivalent that is compatible. There only seems to be a couple of modern branded options out there these days. (We have a few vintage calipers in stock here).

One modern option is Acor, they are dual pivot and long reach. These are actually very good brakes, they have great stopping power but are not too special to look at. They generally cost about £30 a pair. They are easy enough to find online if you search for 'Acor dual pivot 53-73mm'.

Raleigh have a lesser known option which is the modern version of their 730A forged alloy brake calipers. They have a long reach of approx. 52-72mm. They do cost a little more than the Acor at £38.95 but they look more traditional. We stock them here.

That should be plenty for now to get you started with the switch to 700c wheels. If you have questions, or anything to add, please comment below or on social media. As always, likes, shares and retweets are appreciated.

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  • craig ferguson on

    I’d need a good reason to change from 27" to 700c.If you need to swap brakes it’s not a proposition.New 27" wheels are readily available for not much money and there’s a reasonable but limited selection of tyres on the net.If it ain’t broke,don’t fix it!

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