It is sad to say but I really think we’re seeing the last days of the 650c wheel tri bike as we know it. Consumer sentiment usually moves with great momentum and I’d estimate in a few years time Dan’s IMH bike survey will have less than 25% of the field on 650s. Just judging by my weekend riding group - 5 years ago almost every one road 650s save a few new to the sport on road bikes. This year - I know two guys on KM40s everyone else is on 700s. Sad but true…
monty, I couldn’t help but notice that you did not actually provide any proof, contrary to your subject line.
What gives?
this whole thread makes me feel better about being 6’ and riding a 56 frame with 650 wheels. some people tell me i’m on the wrong bike but it’s the only tri bike i’ve ever had so i don’t know any different. rides good to me!
650’s are 1. Lighter
Difference in weight is very small and is compensated by a longer headtube (or stem) to achieve same position. It is a draw, And a few grams will not make you any faster.
2. more aerodynamic
This is false. While true when considering the wheel only (smaller frontal area), it is compensated by the drag from the longer head tube.
3. have a lighter tire and rim which is much closer to the hub. Rotating weight away from the hub is the most important weight when considering a wheel, not the hub.
The famous “rotating weight” myth. Rotating weight is important only when accelerating. Accelerations and deccelarations are small on a time-trial. The force needed to accelerate the wheels are very very small compared to the rest of the rider and bike. Any difference results in fractions of a second. This can be demonstrated assuming that excess weight is at the rim (worst case scenario).
*4. The smaller tires can hold more tire pressure, and thus reduce the the increased rolling resistance caused by spinning faster. *
??? It is easy to run clinchers at 170 psi on both 650 and 700 and tubulars in excess of 200 on both. The increased rolling resistance of 650 wheels is not due to the wheel spinning faster (tangential velocity is the same for both) but due to the higher curvature of the smaller wheel which results theoretically in a more deformed tire at the contact patch (I say theoretically, but I am not sure if this has ever been measured). In any event, differences are again extremely small.
5. They accelerate quicker.
See point number 3 about rotating weight.
Francois in Montreal
I agree, I have many new extra tires and tubes stored inside the house with the bikes, but at times it gets hard to fight the urge of a 700 road bike when you are out riding with friends, or on a century. Maybe I will just make my own 650 carbon road bike in my garage.
Hokay…you should just go wid’ whaddevah makes you feel faster, no? If 700c is yer t’ing then go wid’ it. If you like ‘da 650c kine, ‘den go wid’ dat. I know, in me bones, that 650c is beddah fo’ me. If you t’ink you beddah on da kine 700c, 'den do it.
Most ‘dis stuff all up in yo’ coconut, anyhow.
Kahuna
Symantics…
Thank you!
Most of this thread is pure conjecture with no scientific proof provided.
Right on, my hoale braddah!
its like dis and like dat and like dat and like dis…I bet you dropped out of 2nd grade to pursue a triathlon career…
I practice my pidgin on this forum, sir. I live out here in HI, and if you don’t know how to speak it, you definitely aren’t going to know what’s going on. For instance, I could’ve taken offense at your gibe and replied back with “baddah you!”, which is pidgin for “you irritate me”.
I however, choose to take the high road (sniff) and have chosen to elucidate all of you poor miscreants who are not as fortunate as I to live in paradise 
Kahuna
Good lawd…“chosen to elucidate”? I type too fast (and don’t think fast enough :-). “chose to elucidate TO all of you”.
Spank you veddy much.
Kahuna
Most of your post agrees with me, even though you may not see it that way.
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You agree there is a difference in weight, and aren’t most of the bike and it’s components weights very small in comparison. If we didn’t knock a few grams here and there, we would still be riding 35 lb. Schwinn Varsitys. And the difference in wheels isn’t that small when comparing other parts…
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As you say, the wheel is more aerodynamic. That’s what I said. You can go on about the head tube and all that, but blowing on a stationary bike, in a wind tunnell without the wheels turning, fighting friction on a road surface, with a rider aboard, dosen’t convince me that an extra inch or so of head tube evens out the wheel spinning, aero advantage.
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You agree that rotating weight is important when acellerating. So do I. Every time you touch the brakes in a race, you are accelarating afterwards. In some races that will be quite a bit. You compare the rider and the bike and positioning, I’m not talking about those factors. Remember it’s the wheel size I’m talking about. That’s like saying ,“Why spend hundreds lightening the bike, when you can just lose 4 lbs. of body weight”. I’m sure you can see the absuridity of that arguement. Take it to it’s logical conclusion, and you have a perfect body weight, and can still get the advantage out of superior wheels, and a lighter bike…
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Once again you fall into your trap of " I can put 170lbs. in my 700c tire". Of course you can, but what I’m saying that you can safely put a little more pressure in a smaller tire. Think how much goes into a car tire, now how much goes into a mountain bike tire, and now take it to it’s logical conclusion. Smaller tires and volume, higher pressure…
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See point number 3 above.
You see. we really do agree, thanks for the support…Monty
What about rotational aerodynamics? Since the 650 wheel has to spin faster to maintain a given speed isn’t there an increase in drag on the spokes as the wheel rotates? Depending on the math the extra rotational drag could offset the benefit of a smaller wheel.
This is an interesting discussion. I personally am not interested in 650’s at this time because at 6’4" with a 34" inseam I would look like I am riding down the street on a roller skate. I also only have the budget for a single bike and that bike is a road bike with clip-on aero bars, so not much need for 650’s in a geometry sense. My wife rides a much smaller bike than I do, so I would see some benefit to her riding 650’s just to keep things proportional and balanced.
Todd Pilger
Albuquerque, NM
As for my proof, do you not see that a lighter, more aerodynamic wheel, will be faster. Try an old cross 3, twice as heavy, set of training wheels, and then put on your race wheels. There’s your proof. Ride them of course, and let me know how it comes out…Second thought, I already know…
You might be right if you were using very un-aero training wheels. I’m talking about state of the art race wheels, which are discs, carbon 3 and 4 spokes, deep dish radial laced, etc… There is a lot less surface area inches when you downsize your wheel to 650. I don’t know the exact math, not sure anyone does yet, but I’m betting that the extra rotational force on the smaller surface area, leans an advantage to the smaller surface area…
(Devil’s Advocate Discussion)
If you are using a disk do you get extra benefit from the larger (700c) wheel because of the longer surface - similar to a longer boat (or body for that matter) being faster in the water?
Another reason that 650c wheels are not for me - my brother and I grew up riding mountain bikes and road bikes, and typically ridiculing the guys that exclusively rode for triathlons (as indicated by never wearing socks on the bike.) We are now much more mature since we are in our thirties - I love to race tri’s and my brother is happy for me - but he still threatens bodily harm if I don’t wear socks on the bike. I shudder to think what he would do to me if I showed up on a big bike with little 650c wheels.
Monty - if 650c is faster than 700c, why not go to 600c? Where do you suppose is the limit to “smaller is faster”?
I made the switch from a 700 to 650 about 4 years ago,and I’m am very happy that I did.
The only downside I’ve experienced with 650’s is I tend to spin out in the big ring on any downhills. Right now I’m riding with a 55 up front,and I’m thinking about getting something like a 60,(If they make chainrings that big).
I have a 56 up front on my tri bikes (650C) and find that by the time that I run out of gear I’m faster just coasting.
Your brother sounds like a real cyclist. I remember in the early 80’s when I started bike racing, and they had this dress code as bad as any catholic school. I got my team to wear leopard spotted skinsuits( black bottoms of course), and we shocked the cycling community. Of course over the years small things changed in cycling, but it wasn’t until triathlon that all hell broke loose. Something about a free spirit that leads to innovation, not just in sport, but art and science as well. Just think, without triathlon, we would still be riding colonago’s with campy super record on them. And remember those straps on the pedals, what a flashback.
Tell your brother to loosen up his coat and tie, and watch Beavis and Butthead sometime.
As for the 600c wheels, where are they? I would try them if there was such a thing, and remember what I said about Paula Newby-Frasier and her 24 inch wheels… I was her training partner and whipping boy during her 8 Ironman wins, and there seemed to be no disadvantage in her bmx wheels. It just never caught fire, so it died with the dinasours…