Wheels for cycle tyres are logically sized according to the diameter where the tyre bead sits on a shoulder inside the rim. It's the only measurement that can be made on both tyre and rim and generally coincides with the middle of the brake block. The common 700C measures 622mm. Tyres are described by section and diameter accordingly: 32-622 and a good approximation to overall diameter is obtained by adding twice the tyre section to this figure, viz: twice 32 plus 622 equals 686mm - near enough 27in.
The next rim diameter down from 622mm (700C) that is worth any consideration is known as 26x1 3/8 the world over or 650A in France. It doesn't come with much of a diameter reduction and its only real advantage is that tyres in this size exist even in undeveloped countries: but often in scarce quantities and seldom of good quality. And you can't get any nice alloy rims. Forget it.
This size is known as 650B in France (26x1½ British), where a reasonable choice of tyres in various useful touring widths remains available. (I believe the Japanese like this size too, but apparently not for export.) Note the word 'remains'. I do not think many if any new bicycles are being mass-produced with 650Bs even in France, and so this has the appearance of a dying size (like our 27x1¼) for which tyres remain available only because Europeans expect a bicycle to last a lifetime - and why not! My guess is that choice will slowly dwindle to leave a few unexciting, basic tyres in the long term.
I get occasional letters from members who've been built a 'touring' bike with 571mm rims and are looking for a sturdier tyre than the 20mm ultra-high-pressure jobs it came with. Sadly I have to disappoint them. This is a wired-on (or flexible bead) equivalent to the 26in road-racing tubular. This size has its place - on a sports bike not a tourer - and good prospects of long-term availability, but don't expect anyone to manufacture tyres bigger than 25mm.
This, believe it or not, is the bead diameter of a 26in ATB tyre. The ATB has taken the world market by storm and enthusiasts' tendency to perch fat tyres on relatively narrow rims has led people such as Mavic and Campag produce lots of useful touring-width models. Compatible tyres of 30 to 37mm section also exist, which produce a wheel something less than 25 inches in diameter - a really useful reduction from 27in, but still not excessive.
The only snag is availability of these tyres, now and in the long term. Reliable European tyre manufacturers have only geared up to make the common widths of 47mm plus. There are presently only two narrower touring-type tyres on the market, and both are offered by relatively young marketing organisations with a reputation for conjuring products out of their far-eastern suppliers in immediate response to the whims of fashion, and for dropping them again the moment demand slackens! They offer these tyres because something a bit different may tickle the fancy of a zillion ATB owners, not because a few suckers have had a bike built that will accept nothing else. They only offer them to dealers who buy lots of their other stuff and if the zillions don't fancy them they'll surely disappear.
At present Orbit Cycles is the only volume user of narrow 559s, and they're a pretty small outfit. Rumours are, however, that some major manufacturers may be going over to 559 for hybrid bikes, which is the size they always should have come with and would be a step towards a long-term future for smaller touring wheels. Ultimately we could do with a full range of widths in each of a limited number of diameters. I'm backing 559 as the next one below 622.
[2000 update: many people nowadays buy MTBs for commuting and general use and are ditching the knobbly tires that came with them for slicks. In addition, touring bikes based on MTB wheels are growing in popularity. Thus there is a solid market for robust street tires, and manufacturers are providing an ever-increasing selection of them. However, there is still a lack of 'sensible' treaded tyres in 28 to 37mm sections. Practical and efficient European models such as Conti-Top-Touring, Schwalbe Marathon, Vredestein Spider etc. come in all sections down to 28-622 but only 47-559. Most of the several 32-559 that are now available are still semi-slicks, fine for people who bought a MTB for road use, but merely okay for touring since they don't offer much key on gravelly or muddy European bikepaths.]
A year or three ago, before all that teenagers wanted was a mountain-bike, there were junior sports bikes with 24in wheels. Peugeot's were 600A and Raleigh's were the slightly and annoyingly different 24x1 3/8: bead diameters 541 and 540 respectively. There's still a fair choice of 600A tyres, 28 to 37mm width, mostly from French manufacturers, and good prospects of a continuing if small demand for this size. A few kids will always want look-a-like road racers, and some lightweight folding bikes and HPVs also need a wheel under 24in.
Once upon a time Madison marketed a small Romany tourer with 600As. It was a sound concept, worth repeating.
This, I believe, is the size used by Georgena Terry for the front wheel only of her smaller touring and sports bikes, designed specifically for women. You can only get these bikes in America, which is perhaps a good thing because that's the only place I know where you can get these tyres. It's equivalent, however, to a 24in tubular and could be useful if a few tyres of around 28 to 32mm section existed (the widest I've seen pretends to be 28 but measures nearer 25) and if only the marketplace wasn't already so cluttered with uneconomically small quantities of umpteen other nominally 24 and 22in sizes.
I've skipped a whole load of sizes (mentioned above) to arrive at the 24in ATB. A few nice adult mountain-bikes appeared with smaller wheels at the beginning of the craze, but now this size is strictly for the kids. That means unexciting performance and a limited range of widths - all fat and knobbly. Unless kids move onto hybrids (unlikely) that's the way it will stay, which seems a good place to halt this trip down the ETRTO tyre size tables.
Small people have small hands and many women can only reach standard issue brake levers with their fingertips. Modern drop handlebar levers are generally closer to the bar than old designs, but this is still not enough for some who must search for special short-reach levers. ATB levers often have reach adjustment screws which stop the lever springing back so far when released and an ingenious person can always find some way of similarly reducing the motion of any other design of lever. A wedge or screw etc can be glued rivetted or screwed to the top of the lever so as to come up against the lever hood at a point when the lever is still a little way from its intended return position - or you can simply bend it a bit. It's obvious, however, that if you reduce the amount of available lever motion then the blocks don't move as far either - so small handed people are forced to keep their brakes adjusted closer to the rim.
Hands that are weaker too compound the problem. By judicious choice of brake and lever it is possible to assemble a system which amplifies limited hand strength, but you can never get 'owt for nowt' and increased leverage is also paid for by reduced movement of the brake block. Systems that combine recent designs of low-profile cantilever brakes and dropped handlebar levers (designed instead for racing sidepull brakes) provide numerous examples of this, since mixing and matching such barely compatible bits from Shimano's off and on-road groupsets - the way most manufacturers assemble a touring bike these days - requires the user has to maintain impractically close brake adjustment or else the lever will come up against the handlebar before the block even touches the rim. Optimum performance from modern dropped bar levers is obtained instead with older designs of mid-profile cantilever or with Mafac-style wide-profile types. (These are generally cheaper so it's no hardship - but the bike won't look so pretty!) If the levers are short reach it is even more necessary to avoid low-profile brakes.
We have to hope that body weight also reduces with size and strength, so that weaker hands won't have to pull so hard. Unfortunately this is often not the case and so the rider must fit the grippyest brake blocks they can find and make every effort to remove the twin evils of friction and lost motion from their cables, so that as much as possible of what they put into one end comes out of the other.
Ultimately there are hydraulic brakes. Nothing can get around the force and motion trade-off, but hydraulics do virtually eliminate the losses associated with cables.
To paraphrase a truism: 'One man's seat is another's instrument of torture' and women seem to suffer even more from bicycle saddles than men - perhaps because men designed them. But despite coming from the US doyenne of women's bicycles, the saddle designed most especially for women was also one of the most intensely disliked of this test; see the Roberts' write-up.
A range of Georgena Terry saddles is now imported by NTI (but not her interesting bikes). All of them have a cutout or deliberately weakened area in the hard plastic base, underlying the nose area. Roberts had fitted the ATB racing model, and the kindest thing we can say is that it must be better to bounce up and down on than simply to sit upon all day! We also have a sample of the Terry touring saddle on test which seems to suit it's rider quite well - expect a report in a future issue.
Only one saddle seemed to be a clear winner with everyone who sat on it: this was the Avocet Gelflex W20 fitted by George Longstaff. Another popular model was Isobel's Brooks B17. The Selle Italia Lady Turbo on the Islabike was too narrow and hard for some, but one or two really liked it.
Other pages in the Petite Bike Test: