Trakhak

According to the tire sizing page on the Sheldon Brown website, 24" tires for Terry-style bikes are 520 mm and are not interchangeable with the 540-mm tires used for standard wheelchairs.

Johno59

I quote the ISO number. In a wheelchair shop a ISO in the 500s makes sense. In a normal bikeshop they look at you as if you're an alien and/or try to sell you a BMX or MTB tyre that is 2 inches wide. 24 inch can mean anything with the only exception being nothing is 24 inches.

tcs

Bill Boston (as noted above) designed these bikes in the 1970s because he was working with five speed freewheels with 14T small cogs. He needed the 27 inch (kids - ask your parents) rear wheel for gearing.

By the time Terry came along smaller small cogs were available and the larger rear wheel merely condemned shorter cyclists to carrying two different spare tubes - and on tour, two different spare tires.

A better design would have used two ISO32x559 wheels/tires. When this was suggested, the answer was, "No, because 559 is an off road bike size." ???

Johno59

My 24 inch funny bike used tubulars so it was wheelchairs or nothing. I eventually made a clincher set and that was less a hassle. The biggest pain was the 90mm hubs. But Brompton do 90mm hubs for an eye-watering amount but only broke one hub in 20K miles going flat out.
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dedhed

The St. Tropez Terry style I had come through recently had an ISO 547 front wheel.

T-Mar

The reason that most manufacturers selected the 420mm BSD version of 24" and 650C (571mm BSD) as the two standards for smaller frames, is simple. At the time, for their respective tyre/wheel categories of 24"/ 600mm and 26"/650mm, they had the smallest bead seat diameter for road rims. This allowed them to build frames with slightly shorter seat and top tubes than with other bead seat diameters in the category, given a common tyre width.

The only BSD standards that were smaller in each category were those used for ATBs. At the time, it would have been difficult convincing the tyre and rim manufacturers to invest money into creating road versions of what was considered an off-road standard.

Doug Fattic 

I've been a custom frame builder for over 40 years with roughly half my customers being fit recreational women riders. If their height is less than 5' 4", almost all had problems with an optimal fit on a 700C production frame with drop handlebars. The proportional "Terry" style of bicycle is a great answer at usually a very reasonable price as long as the shorter rider doesn't mind the look and has to carry 2 spare tubes. A small bicycle with two 650C wheels are harder to find.

The problem of fit for many women is that their handlebars have to be high enough to take pressure off of the sensitive areas of their crotch. Most often this means the handlebars are at least as high as the saddle (individuals vary so not always). If they are using drop handlebars with their saddle up there, then their butt needs to be further back. This saddle more rearward position is the opposite of the lawyer's solution for production bikes with a very forward seat position created by a steep seat angle (to get toes out of the way of the front wheel).

Georgena Terry (a short recreational rider herself) designed her bikes with a small 24" front wheel (and eventually with 650C wheels) that handles and fits shorter people well. She didn't do that because it made her bikes look cooler (although eventually the look became part of her brand identity), she did it out of necessity. I make a point of this because if you try and cram a shorter family or friend onto a bicycle with 700C wheels (even if it has a sloping top tube they can straddle), their position is unlikely to be optimum and as a result not enjoy bicycling particularly well. It is not impossible to ride a lawyer demanded design, it just isn't as good.

Johno59

That's a fantastic insight. I see lots of fit shortish women riding 700c bikes and it has always bugged me how strung out they looked. I have a question regards another thread regards an old Schwin - have you ever bent seatstays to center a lop-sided rear wheel?

Doug Fattic 

Bicycle manufacturers are heavily influenced (controlled) by their lawyers and accountants. They want to reduce inventory and eliminate versions that have low volumn so they begin the design of a road bicycle with 700C wheels end of discussion. It is understandable that choice requires a front center that puts the rotating front wheel beyond where the cyclist feet will smack into it. And if it was/is a steel frame they choose tubing strong enough that it isn't going to break if a really fat person rides it. And can withstand production brazing techniques. I hate the ride feel of a strong steel frame that can survive a 300 pound rider. So smaller people that probably don't weigh all that much get the worst bicycle because of those choices not related to proper bicycle position or ride quality.

Short and light Georgena Terry (both an engineer and custom frame builder) in the early 80's did what she could to bring an enjoyable cycling experience to people like her. She eventually sold Terry Bicycles but that company still makes available 24" and 650C X 28 tiresl.

To answer your off topic question, no I haven't bent a seat stay to make a rear wheel center (although it would work). If it is a frame with horizontal dropouts, I have sometimes bent the too short side dropout slot wider apart (more than 10 mm). If the wheel is resting on the bottom part of the dropout when the skewer is closed, then if bent the right amount, the wheel will center. Jack Briggs my teacher at Ellis-Briggs in Shipley West Yorkshire, showed me some other techniques to center wheels while the frame was being built (because one stay was too long). I was one of those Americans that went to Europe to learn frame building because our builders had retired or died by the time the bike boom started in 70/71.