I'm building up an old early 80s Terry Precision bicycle. Most of my time has been spent researching and sourcing the front wheel. It's a smaller frame which uses a smaller front wheel for shorter women. I learned that many small Terry frames use an ISO 520 24" front wheel so I went hunting around for that. None of my local LBS could source any 520 parts. I found a couple of online retailers that had the 24" road rims (i.e. not 24" BMX rims, typically ISO 507) and tires/tubes. I bought two rims, two tires, and three tubes for future spares.

I built the wheel recently and noticed that the brake reach on the front was about 20 mm more than on the rear wheel, which is a standard 700C (ISO 622). I realize now that the earliest Terry Precision bikes used the even-less-common 600A wheel size, or ISO 540.

Now I'm in a strange situation where I have invested quite a bit into a slightly wrong wheel size. At worst it will sit 20 mm lower in the front and I'll need to find a longer reach caliper brake for the front rim. Is that a problem?

Side question: does anyone know any companies that sell ISO 540 road rims (and tires/tubes)?

This whole front wheel situation kinda rags on my otherwise purist Terry restoration so I'm not sure what the best course of action is to proceed.

Turns out that ISO 540 is the size of some wheelchair rims today (along with 507). Has anyone ever used a wheelchair rim for their bike? Where can I find one?

P.S. I know these are many questions and that's against SE guidelines, but to be clear, the main question I have is whether or not using my ISO 520 wheel would be a big deal.


Interesting—Sheldon Brown's tire-sizing chart refers to the 540 size as "British juvenile or wheelchair"

In any case: The 520 wheel (which his chart lists as the Terry size—looking at the Terry website, I see they sell both sizes) will pitch you forward slightly and give you a slightly steeper effective head-tube angle. I don't think that would be a big difference. And you'll need to adjust your brake pads. In theory the size difference could be offset by using a fatter tire, but in practice, I think fatter tires are not made for the 520 size.

I've never heard of anyone using a wheelchair rim on a bike—the only possible downside I would imagine might be A) if they aren't available in the spoke count you want, or B) the braking surface.

You might contact Terry directly and see what they think.

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  • Thanks for your response. I actually have a running email thread with Terry and they suggested I contact VelocityUSA for info on 600A rims. They did not address whether I should go ahead and just use the 520. Argh, I really don't want a funny looking bike, haha. – fideli Aug 29 '11 at 20:07

There are plenty of 'long reach' sidepull brakes around, the problem is that none of them are any good. Department store mountain bikes come with them, they are a rare find sold as replacement/accessories. They flex/swing fore/aft quite a bit and tend to be made of poor quality materials with a spongy feel.

As for the parts you have bought, there are laws regarding distance selling and you can send them back hassle free. However, if you want to plough the 520 furrow, give the folks at Airnimal a call. They are very nice people and support their 520 rim bikes with spares at reasonable prices:


As for 600A (540/541), these were a common size on 'juvenile' 5 speed drop-handlebar road bikes by the likes of Raleigh up until ~1990 when 24" wheel MTB bikes came along, decimating any demand for anything else. Typically they were steel rims rather than alloy with Maillard bolt-on hubs. 650A made it to the high end, for time trial bikes, but 600A was 'juvenile' only in those days.

Another source you may want to investigate is Alex Rims. Drop them an email to see what they can do:


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  • I noticed that Alex rims sells two rims with ETRTO 540. One is the R390 road rim, 540x13 mm (which they also call 24 x 1 1/8). The other is the X404 MTB rim, 540x20 mm. I'll see if I can source the R390. I'm sure I can sell my 520 to someone with a more modern Terry bike. I'll check out Airnimal as well. Thanks! – fideli Aug 30 '11 at 0:30
  • Really? No such thing as good long-reach brakes? These look pretty nice: store.velo-orange.com/index.php/components/brakes/calipers/… – Adam Rice Aug 31 '11 at 16:07
  • @Adam Rice - these things are relative! You can get Shimano R450 'long reach' calipers from a bike shop by special order - Tektro and others do them OEM only. I was thinking XL-reach like those awful things you get on department store MTBs. – ʍǝɥʇɐɯ Aug 31 '11 at 17:57

The only ISO 540 narrow rims I have seen are Sun wheelchair rims. I think they make both tubular and clinchers. You can get narrow ISO 540 wheelchair tires from Sportaid.

I have been in the process of building a road bike for my 7 year old daughter. I decided to go with the ISO 520 rims. I purchase a set of Velocity Aerohead rims. However, the only tires available at this time are the Intense Micro Knobbies and the Terry tire. The Intese tires are available in 1", 1-1/8" and 1-3/8". The Terry tire is 24 x 1 (25-520) and I believe is made by Panaracer. All-in-all, 24" rims/tires are a pain since they have been made in 4 different ISO diameters including the Schwinn 'S'.

I hope this helps!

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  • It's unfortunate, given that the small-front-wheel bike is the ideal road bike for a small adult. Mfgrs aren't really interested in serving the broad public any more, it seems. – Daniel R Hicks Nov 15 '11 at 16:33
  • Thanks for the comment! I ended up getting an Alex R390 ISO 540 rim on eBay, which was an extremely rare find. I then picked up a Primo 25-540 wheelchair tire. Worked out great! For yourself, the Panaracer would work best. It was a pain, I agree, but as long as I can get tires and tubes easily going forward, I didn't mind having to source the rim. – fideli Nov 15 '11 at 17:31
  • fideli...... you made a wise choice especially if the brakes align well now. What spoke count is the Alex R390 rims? Just curious. – Duntov Nov 16 '11 at 22:39
  • @Duntov sorry I just saw your comment now. The count is 32H. – fideli Feb 17 '12 at 18:09

Beginning my search for a 540 rim for a Terry, and commenting: I went to the trouble of getting a Velocity 520 Aerohead rim built to a Shimano XT hub. It came from a trike and 'bent specialist,so it has the small compromise of assymetry, the hub including the integral mounting plate for a disc.

This early Terry, a Symmetry, in the largest frame size with a "24" front wheel, fits me, @5'6" and short arms, better than my usual 622 ride. What I don't like, though, is the unavailability of wider and more comfortable 25-32mm tires for the front. The Panaracer tires are standard 23mm nominal and maybe narrower in reality.

The Terry fork allows plenty of space for a fender in front,and the likely-Tektro front brake pads are at their lower limits, so there is room for a 540 - based wheel if the rim is 13-19mm between beads. Without that larger wheel, a larger and more comfortable rear tire, a 25-28mm, will make the handling more squirrely than it already is.

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