Consider the following photo: OK ST’ers, let’s look at what we are working with here to gain an understanding of one application for a 650c wheel frame. Our customer is a short torso, long leg triathlete who will be using aerobars most of the time on flat to rolling courses. They are an experienced and well trained runner, but relatively new to road cycling. They do own a road bike and have experience with clipless pedals. The customer has completed three triathlons up to Olympic distance. Their goals are to continue in the sport for recreational and fitness purposes and potentially go up to 1/2 IM within 24 months (note to self, I wager this customer is registering for '07 IMMoo- they are enthusiastic, fit, motivated and seem to love the sport, it is the next logical extrapolation even though they didn’t come out and say it.) We measure the customer, their bike and evaluate their position on their current road bike with Profile aerobars. This is a synopsis of what we learn: Their road frame is too large in the top tube and too large in the seat tube even for effective road cycling. My guess is someone in an LBS saw their log legs and just handed them a 56cm road frame. As a result, they are on the nose of the saddle and report significant discomfort. Additionally, their back is bothering them after 45 minutes in the aerobars in the lumbar region and they report saddle tenderness in the crotch, especially the upper/forward region of the crotch. They own good cycling shorts that fit and use chamois cream. The reach measurement in the aero position is way too long. The aerobars themselves are angled incorrectly and are also too long for thier body dimensions. Their measurements indicate a short torso, long leg configuration. The distribution of femur length to tibia length is relatively normal (i.e, does not have abnormally long femur- thankfully…). Limb length is longish compared to height and torso.
Now, here is our challenge ST’ers: We need to facilitate a short torso fit on aerobars and accomodate an effective transition from bike to run. The reach needs to be short, but the saddle height needs to be jacked up there for a long inseam. Bonus: The customer is highly adaptive to a lot of saddle to handlebar drop and trends toward higher cadences. They move very little on the saddle, have a relatively strong core and pedal effectively for their experience level.
So, we do the following:
Sell them a frame with a relatively high seat tube and a zero setback post but with a very short top tube, moderate stem length (90mm) and custom sized aerobars (Visiontech 250mm’s with 1.5cm cut off each end) and 40 cm base bars.
But here is the catch: The top tube needs to be so short to match their torso length that 700c wheels won’t fit anymore- or if they fit, the wheelbase would be too long for reasonable steering and weight distribution. So, we select an appropriately sized seat-tube dimension frame built around reduced diameter 650c wheels (such as the Guru Cron-Alu pictured) that are more in scale with the rider’s torso length and reach and voila! Perfect fit! Perfect Reach! Perfect weight distribution! Perfect handling! (not too responsive in the aerobars, not too stable in the aerobars…).
Wheel size selection can be tied to reach and torso length, and this is one example of that. Now, the downside: The darn saddle height has to be so high that the center of gravity is pretty high. Maybe a lower bottom bracket frame? (custom…).
But here is the catch: The top tube needs to be so short to match their torso length that 700c wheels won’t fit anymore- or if they fit, the wheelbase would be too long for reasonable steering and weight distribution. So, we plug in some reduced diameter 650c wheels that are more in scale with the rider’s torso length and reach and voila! Perfect fit! Perfect Reach! Perfect weight distribution! Perfect handling! (not too responsive in the aerobars, not too stable in the aerobars…).
Tom… when you say “we plug in some reduced diameter 650c wheels” it sounds like you put 650c wheels on a 700c frame, which I’m sure is not what you did… I’m guessing you mean “plug” into your formula for finding a bike…
I just got my side mount pedals. They might be just the thing for her. You will be able to use a 3-4 cm lower seat tube, and lower the stem/bars by the same amount.
The incrased Q factor might bother her, but I think she could get used to it. And, getting out of them is VERY weird and VERY different. The lowered saddle height should make the ‘Hi!Yo! Silver!’ mount easier.
Thanks for the lesson. For a new triathlete who is learning by the trial and error method, it is cool to see that there is a science behind it all. I could be this customer-5’4 with longer legs and shorter torso and I do have 650’s and I am starting to love my bike. It feels weird to say that!
Well, since there have been at least three threads about 650c wheels on bikes over the past month, none of which I took the time to respond to, I figured this would answer a lot of questions. So I’ll argue this is more “info” than “mercial”.
Also, I would suggest there is no subversive element to me posting product related commentary. I mean, I post under my own and my bike shop name with a disclaimer at the bottom.
But still, it is a topic worth revisiting ever week for the past two years ad nauseum.
It looks like a 90 deg stem with a couple of spacers. How about a negative -17 or -25 stem (one of those Profile H20s), loose the spacers, on a similar toptube length 700C frame? Maybe?
I enjoyed the commentary. Thanks for the info, Tom!
I enjoy the discussion about function and theory, but another reason that I prefer 650c tri-bikes is totally impractical: I don’t want my triathlon bike to be a road bike with aerobars. I want my tri geom bike to be as triathlon-y as possible. I want roadies to scratch their heads at my tri’s design and explain to me that it’s not about the bike, it’s the engine and not the chassy, and every other silly roadie cliche. Cycling is my hobby and I love collecting bikes almost as much as I love riding them. I love my road bikes. I love my offroad bikes. I love my triathlon bikes, but I prefer them to be as different from each other as possible.
To me, for a shorter person the main advantage of 650C is that the rear wheel can be moved forward a little bit, theirby giving the proper weight balance and handling. Second is that the front can be a bit lower although the person in the foto could get low enough with 700C.
That’s actually a workable solution but I think it may not feel as “in scale” to the rider in terms of handling. Realistically, the wheel base would prbably only be about 1-1.5 centimeters different so wouldn;t affect handling too much, but it may feel like a larger bike.
In any event, I like the shorter chainstays and more compact wheel base. There are a few too many spacers here for my taste and a higher head tube would have been nice. If the customer were up for custom, Guru actually could do that. One minor drawback to a higher head tube is that, as the head tube gets higher it does angle back toward the rider a trifle, effectively shortening the stem a little bit as it gets longer (taller).
You’re right though, and that would certainly provide the same three “points in space”.
I would suggest the *disadvantages *may include: Less availability for wheels in particular, and also in tires although to a lesser degree. The gearing may need to be adjusted upward from the common 53/39 in the front and 11-23 in the rear to a slightly larger 54 or 55 tooth chainring with a 42 tooth in the front and an 11-21 or 11-23 in the rear. Chain line on shorter chainstays may result in very poor crossover gear performance. For people who already own a 700c road bike, buying a 650c tri bike does not offer parts commonality with regard to wheel size, an inconvenience.
There is some misinformed lore out there that 650c’s are somehow “slower” than 700c wheels. That is not true. This usually sparks some debate about aerodynamics and rolling resistance ad nauseum, but the differences in rolling resistance and aerodynamics and weight between 650c and 700c are largely not worth the discussion.
Interestingly, there was about a one year fascination with using a minor weight and the lower gear advantage of 650c wheels for road riders in the Tour de France during mountain stages. Claudio Chiappucci, Maurizio Fondriest, Laurent Jalabert and Oscar Friere all expereimented with 650c road bikes during mountain stages to try to induce some type of climbing advantage. The experiment didn’t yeaild tangible enough results to stick, and team mechanics hated it since they then had to deal with two tire and wheel sizes for spares during the race, a maddening logisitcal challenge during a stage race.
One thing for sure, the use of 650c wheels on road and tri bikes is rife with misunderstanding and misinformation. I’ve heard things like “A tri bike has 650c wheels” and “650c wheels are dead”. This are not well informed statments and are technically inaccurate.
My take on 650c wheels is comparable to shoe sizes: You either are or aren’t a 650c wheel rider based on body dimensions. That said, there are a substantial number of “fence sitters” who could actually go either way- and I fit in that category. I like racing on 650c’s and some frames, such as the Litespeed Blade, fit me better by far in their 650c version.
