Are 650c wheels relevant today?
8.10.04 by Dan Empfield
(www.slowtwitch.com)

This question is asked with accelerating frequency. Once 650c wheels were the toast of triathlon, and half of all the bikes in the Hawaiian Ironman were of the smaller-wheel variety (see tables below showing wheel size in the Hawiian Ironman). The late 90s saw their peak. Since then 650c wheels have ebbed, and now two-thirds of Kona’s bike have dual 700c wheels, with the balance primarily 650c font and rear. Why did 650c wheels gain their popularity in the first place, and are the reasons for their rise still in force?

To answer this one needs to understand the basis for the bikes most good triathletes ride in no-draft races (like the Ironman). Most good riders position their saddles farther forward while riding with aero bars—on road bikes without aero bars their saddles would be further back. This isn’t to say that all those who ride without aero bars would prefer to ride further back. While road riders without aero bars do ride further back, track riders don’t. In fact, UCI rules of competition speak to this. Under UCI rules a road rider’s bike must have its saddle nose 5cm arrears of the bottom bracket. It’s long been traditional, however, for track riders to place their saddles further forward, and if you’re a trackie your saddle’s nose can be right over the bottom bracket.

Track riders compete in shorter events and pedal with much faster cadences. A roadie would find it hard to ride with his saddle that far forward, because he’d have to hold up his torso’s weight with his upper arms—very tiring over the long haul. Triathletes, however, have this problem licked. Aero bars allow one’s upper body to rest skeletally on the armrests, and therefore anyone on a bike with aero bars can ride reasonably far forward and do so comfortably.

The fact that a triathlete can ride comfortably with his saddle further forward is not the same as saying he should. of course, I do think he should, if he’s typical, however that’s a separate argument and not one I’m prepared to make today. Half or more of experienced triathletes do ride forward—notably the clear majority of those at the top of the sport—and this truism creates the basis for the 650c argument.

Just because a triathlete can find for himself a forward position that is both comfortable and powerful does not mean he’s solved all his problems. He must also be aerodynamic and his bike must handle well. Fortunately, the aerodynamic problem is largely academic. Yes, the reason the rider moved forward was to gain comfort and power, but as he did so he also lowered his handlebars to preserve a favorable hip angle while pedaling. Happily, lowering his bars also serves to shrink his front profile and improve his aerodynamics (usually). But, there is still the issue of handling.

The problem is weight distribution. You move your saddle forward. That throws your weight forward. Also, you’re riding with a flatter back, which also places more weight on the front wheel. Finally, you’re laying yourself down on the front of your bike instead of supporting your back in part by your spinal erectors—easier on the back, but at the cost of bad weight distribution. As a result, doing all this on a standard road bike might cause you to have as much as two-thirds of your weight on your front wheel, instead of, say, 60% on the rear wheel, which might be the case if you were riding seated on your road bike with your hands just behind the hoods.

All this weight on the front of your bike might not be all that problematic if you’re riding down a reasonably straight, flat road. The problems come when you’re descending, cornering, braking, or any combintion of the three. This would be the case whether you're in or out of the aero position, that is, your tri bike might be a bad handler even when you’ve got your hands around the pursuit or road bars. What is the solution?

Enter 650c wheels. The idea was this. You’ve repositioned your weight forward relative to the bottom bracket. Why not reposition your wheels back under your body to compensate? The way you do this is easy. You shorten the chainstay (distance from bottom bracket back to rear wheel axle) and you lengthen the front/center (distance from bottom bracket forward to front wheel axle). The reason 650c wheels work for this is because you can get a shorter chain stay distance if the front of the rear tire doesn’t hit the back of the seat tube, or the front derailleur cable.

No, the front wheel diameter doesn’t matter when it comes to fixing this weight displacement issue. However, remember one thing you’re doing on a tri bike. You’re lowering the front end. There is a practical limit to how low the front end can go with a 700c wheel underneath you. Placing a 650c wheel in your fork ends allows you to get the front of the bike lower. The smaller the bike is, the more you need that 650c wheel in front, so as to get the bars low enough.

And it worked well. The first time anyone saw a bike like this in a triathlon was when Ray Browning rode the first ever Quintana Roo Superform in the New Zealand Ironman. He shattered the bike course record and creamed the field, and though his competitors ridiculed the bike pre-race they didn’t think it looked nearly as funny afterward, when the organizers handed Ray the prize money check.

But that was then. What about now? What has changed? Several things.

First, getting the wheels back underneath the bike is not going to be as urgent a chore as it once was. One doesn’t need to shorter the chain stays quite as much, because you can fix the weight displacement issue by creating a longer front/center than has historically been the case. This was not possible before, because of stricter rules. Without going into specifics, the rules are less strict now, and the trend is to go less strict yet. Therefore, long front/centers on tri bikes, and very long wheelbases, will be more in evidence as time goes on.

But, there’s still the issue of front-end handlebar positioning. Can you get the bars low enough on a 53cm bike with 700c wheels? It’s easier than it used to be, for two reasons. First, integrated headsets mean today’s 13cm head tube is now the functional equivalent of what was an 11cm head tube,. The head parts are sucked up inside of the head tube instead of being placed above and below it. Second, many aero bars today feature armrests that do not elevate that high above the centerline of the pursuit bar. Therefore, a “lower profile” armrest allows you to get considerably lower on a bike with the same head tube.

In the old days, a 5’10” guy would have a difficult time achieving an aggressive position on a tri bike built with 700c wheels. Nowadays this same guy riding a bike with an integrated headset and low profile armrests will have no problem at all.

However, there are three issues to be tackled. One is what we used to call “toe clip overlap” in the old days, before clipless pedals. I still call it that and upon reflection I’ll bet there’s a generation of riders that has no idea what I’m talking about. It’s the clearance between the back end of the front wheel and the toe of the rider when the crank is in its forward-most position. Tri bikes have short “cockpits,” that is, the top tubes are shorter than top tubes on road bikes (if the bike builder knows his job). Even with shallower head angles and a bit more fork rake, on shorter bikes (smaller than 50cm) you’re going to perhaps run into a problem with front wheel clearance. This still begs for a 650c solution.

Second, there’s just the issue of spryness. Bikes below 50cm with 650c wheels handle like bikes taller than 55cm with 700c wheels. Anybody who denies this just isn’t applying the test of reasonableness. There is no way a 60cm bike is going to handle the way a 48cm bike handles if they have the same size wheels. You can get it pretty close, but still no cigar. I’m 6’2” and I ride about 60cm worth of bike. If you’re 10% shorter than me you’ll ride a 49cm bike, roughly, and if you do so with 650c wheels you’ll have wheels that are 7.7% smaller in overall diameter than my bike. In this case our two bikes would handle roughly similarly.

Finally, there’s the question of the speed value of 700c versus 650c. There will always be exponents of one wheel size versus the other. My training partner slays everyone on straight-line descents, even those who weigh considerably more than him, and he swears it’s his 650c wheels. Others claim differently. One cannot deny, however, than many of the very fastest bike rides in the history of timed triathlon racing occurred on 650c wheels, both in the men’s and women’s fields. All this is anecdotal, however rides in Zofingen, IM Canada, IM New Zealand, IM Hawaii, IM Germany—most of the big courses in the big races of yesteryear, when 650c wheels were popular—still stand up today, as much as 12 and 15 years after they were accomplished. So…

The answer to the question, “Are 650c wheels still relevant?” depends on what you value. As a speed weapon, the jury is not only still out, but probably is long dead, 15 years after the debut of dual 650c wheels in triathlon. However, there is no doubt the geometric argument for 650c is less compelling than it once was for bikes over 50cm.