650c vs. 700c ?

[kneejerk]

I've been wondering and wondering why TT bikes and Triathlon bikes used to use 650c wheels? It seems to me that there may be an aero advantage with the smaller wheels? I guess it comes down to the amount of speed that the rider can attain. With a 700c wheel, it should perform better with higher speeds because it rolls over stuff better at a higher speed..... possibly reducing some frictional losses with the road/tire. Also, I see that the 700c being larger spins slower at "higher" (I'm thinking 30+mph or so) which may reduce some spinning resistance the wheel may have encountering air. But, if speed is momentum.... wouldn't the 650c spinning faster hold speed better?

My suspicions stem from my own experiments with having a wide tire 700c commuter bike, then switching to a similarly wide tire 26" commuter bike (similar spec. bikes otherwise) and finding that I averaged a bit higher speeds with the smaller wheels on the road. I seem to also notice better acceleration on the smaller wheel bike. I have since ditched the 700c commuter bike and will likely not go there again. The added weight of the 700c wheel seemed to be it's handicap.

I do ride a lightweight road bike aswell. I now wonder if I may be faster with a 650c wheel size. Especially since I cannot average the 30mph I imagine it takes to reap the full benefit of the larger wheels.

Some disadvantages I forsee with the 650c wheels are a rougher ride, faster tire wear and less stability.

Anyone have further insight?....... I guess I could Google it.

Too bad I don't have room for two TT bikes, one 650c and one 700c to compare!

 

[ihavenolimbs]

Wheel size

From what I've read:

700c wheels have lower rolling resistance but greater rim mass (therefore inertia) and are less aero.

At high-speed though aero dominates, low-speed favours low rolling-resistance. Less inertia means faster accelerations as well.

Bearing losses are usually very small so the 650c spinning faster is not a big problem here. Also, with both the 700c and 650c, the top of the wheel is doing twice road-speed.

I doubt the difference you're feeling is just due to the differences between 650c and 700c wheels though. The difference should be negligible.

I have two sets of Aluminium 700c wheels and one set is like 2 km/h faster on the flat because the older wheels have poked bearings, are out of true, and have slower tyres.

But you're not even using the same bike for both wheelsets so the differences you're feeling could be due to many, many things. (Geometry, wear, tyres, ...)

 

[mercycle]

Smaller frontal area using 650s. The delta is probably only significant for those in the top 5% of the sport (cycling or triathlon), but for everyone else, it gives you a boost because they're cooler. With carbon rims, the delta in static weight is probably not all that much. Rotating weight is probably still a potential factor, the smaller diameter on the 650s means you aren't trying to accelerate as much mass, but once you reach steady state, it's a moot point.

650s spinning faster may give you a bit better gyroscopic stability.
Overall stability on the bike is driven more by the geometry of the front end: head tube angle, fork rake, resultant trail measurement.
Bigger wheels sustain their rotation better than smaller wheels (assuming all else is equal).

Crit racing at an elite level may be one application that intelligent use of 650s would be an advantage: tweak the frame geometry to get a smaller, more compact bike, plus the advantage of accelerating 650s vs 700s.
The major disadvantage of 650s is Neutral wheel support. They have 700s, you run 650s, you're hosed if you flat.


One advantage that I believe 650s have over 700s: strength. If you're an old fat guy, the smaller diameter builds up into a stronger wheel even if it has fewer spokes.

 

[avanti]

650 and even smaller dia wheels were attractive for team TT events because the riders are closer together (better drafting) and the third rider hits the line sooner (If my memory is correct the 1984 Olympic team pursuit gold medal was won by 1/1000 second (= 0.5 inches at 30 mph).

Since then rider position and equipment aerodynamic efficiencies have erased the need for smaller wheels.

A couple of women in my club ride 650s and a problen is finding tires & tubes -sometimes they have to be ordered, and not all tires are available in 650.

 

[Bustedknuckle]

I've been wondering and wondering why TT bikes and Triathlon bikes used to use 650c wheels? It seems to me that there may be an aero advantage with the smaller wheels? I guess it comes down to the amount of speed that the rider can attain. With a 700c wheel, it should perform better with higher speeds because it rolls over stuff better at a higher speed..... possibly reducing some frictional losses with the road/tire. Also, I see that the 700c being larger spins slower at "higher" (I'm thinking 30+mph or so) which may reduce some spinning resistance the wheel may have encountering air. But, if speed is momentum.... wouldn't the 650c spinning faster hold speed better?

My suspicions stem from my own experiments with having a wide tire 700c commuter bike, then switching to a similarly wide tire 26" commuter bike (similar spec. bikes otherwise) and finding that I averaged a bit higher speeds with the smaller wheels on the road. I seem to also notice better acceleration on the smaller wheel bike. I have since ditched the 700c commuter bike and will likely not go there again. The added weight of the 700c wheel seemed to be it's handicap.

I do ride a lightweight road bike aswell. I now wonder if I may be faster with a 650c wheel size. Especially since I cannot average the 30mph I imagine it takes to reap the full benefit of the larger wheels.

Some disadvantages I forsee with the 650c wheels are a rougher ride, faster tire wear and less stability.

Anyone have further insight?....... I guess I could Google it.

Too bad I don't have room for two TT bikes, one 650c and one 700c to compare!

Interesting hash of wheel inertia and it's contribution to energy requirements of riding.

http://www.biketechreview.com/archive/wheel_theory.htm

 

[kneejerk]

I found a good discussion on another Triathlete board which pointed out some insightful stuff.

I am sure I noticed a difference in both of my commuter bikes. At my commute speeds the smaller 26" wheels perform better. I can see how the faster you go the more the wheel weight doesn't matter and the aero aspects play big.

The Triathlete forum I found pointed out that the 650c's are surely better for climbing events and that some top racers have switched to them in the Pro ranks for mountain days. That is where wheel mass would play big.

I'm left to wonder if me the average Joe that cannot average more than 20mph on a long solo ride would benefit from the 650c wheels. I'm thinking I may.

Ah forget it. I want some aero wheels now!

 

[mercycle]

anything that you think makes you faster does. At least in your own mind.

 

[L29205]

anything that you think makes you faster does. At least in your own mind.

+1
what works for you is more important than what anyone's opinion matters.

I have both 650c and 700c bikes, my triathlon parents were on the leading edge of the 650c wheels and the 78% plus seat tube angles.

650c lower inertia, compact geometry as pluses. The down side is availability of equipment, most aero wheel manufactures do not support 650c in their high end product do to lack of demand. Next the compact geometry impacts the drive train harder than most people take into account. The chain is shortened significantly and when you combine that with have to go to a 56/45 x 23/11 in order to keep your gear ratios correct it makes a shifting nightmare for whatever drive train you are running. Tires are available if you want to wait for them don't expect to find them off the shelf. A personal opinion here but I feel the attack angle on the tires compared to the road make a smaller wheel bike more squirrelly. Great for crits but not a comfortable feeling for long solo's. (As a note I have done a 112 miles on 650c wheels multiple times without issue so take that opinion with a grain of salt)

The lower inertia combined with a forward geometry is great when you get off the bike and want to run.

The 700c bikes easy to find parts and supplies. Slower off the line and coming out of the corners. Slower up the hills but the rotational mass going down the hill can make up for half of the next hills energy.

I am just building up a Cervelo P3c with the same group as my Kestrel KM40 and both will have Hed 3's one is 650c and the other is 700c both have the same geometry. Ask me again in a year.

Hope this helps. I would personally recommend whatever bike you are comfortable with combined with the best aero wheels you can afford.

 

[TheDude]

Funny,
we are talking going 650c, and all the Mt. bikers are talking 29'ers.

 

[mercycle]

Funny,
we are talking going 650c, and all the Mt. bikers are talking 29'ers.

But the larger diameter wheels roll over things easier, and last time I checked there are normally a few more things to ride over on a trail than there are on the road...

 

[RDV4ROUBAIX]

Funny,
we are talking going 650c, and all the Mt. bikers are talking 29'ers.

I'm missing something here too. Haven't seen a 650c road bike out and about in over ten years, and back then it was usually a Tri-geek showing up at a crit. But the 650c didn't help them at all since Tri-dorks have the worst bike handling skills out of anybody. That size was an anomaly at best in the road scene. As for MTB, 29'ers are more popular than ever, but the new wheel size making some headway in the US is the old Euro standard 650b. Kirk Pacenti is the mastermind behind that, and seems that a lot of the QBP and other industry folks around here are really hyped on it.

 

[egtalbot]

There are loads of 650 wheels at tris (though very few of the top overall riders at local tris), I see 'em all the time. Even saw a few shorter masters riders riding them at TT's.

All things being equal, it seems like the 650's would handle worse around turns. On most courses I don't think that would make up for their advantages stated elsewhere in the thread.

I ride in my aerobars most of the time (except in recent months tryingt o improve my mass start race performances) and I've always had 700cm. I wouldn't be opposed to trying a bike smaller wheels if the opportunity arose. But it's hard to find a bike in a shop with 650cm wheels that's the size of say a P3 54cm, which fits me perfectly.