650C vs 700C wheels for triathlon bike

[WKB]

I am looking to buy a dedicated triathlon bike this spring and am trying to research the options before I make the purchase. I can ride a 52-54cm size bike, some of which are made with 650C wheels. Others are the 700C. What are the relative advantages/disadvantages to each wheel? I weigh 152 pounds, if that makes any difference.

Thanks in advance, Keefe.

 

[capwater]

I am looking to buy a dedicated triathlon bike this spring and am trying to research the options before I make the purchase. I can ride a 52-54cm size bike, some of which are made with 650C wheels. Others are the 700C. What are the relative advantages/disadvantages to each wheel? I weigh 152 pounds, if that makes any difference.

Thanks in advance, Keefe.

I had a 650 and dumped it in favor of a 700. Other than certain small frame bikes and some women's specific stuff, everything is going towards 700. I like the wheel interchangeability between my TT bike and my road bikes. Do the math, smaller wheels need to turn more times to achieve the same distance. And how do you turn a wheel more times, you pedal more!

 

[badkarma]

As long as a 700c wheel will fit in your frame (and it should with a 54cm frame), go with that.

 

[daveornee]

I am looking to buy a dedicated triathlon bike this spring and am trying to research the options before I make the purchase. I can ride a 52-54cm size bike, some of which are made with 650C wheels. Others are the 700C. What are the relative advantages/disadvantages to each wheel? I weigh 152 pounds, if that makes any difference.

Thanks in advance, Keefe.

Advantages to 700C: more choices of rims, tires, tubes, hubs, lower rolling resistance, and more interchageability. Disadvantage 700C: weight, relative stiffness, and aerodynamics.
You need to compare the wheels on their own merits for your application and budget.

 

[Eden]

I had a 650 and dumped it in favor of a 700. Other than certain small frame bikes and some women's specific stuff, everything is going towards 700. I like the wheel interchangeability between my TT bike and my road bikes. Do the math, smaller wheels need to turn more times to achieve the same distance. And how do you turn a wheel more times, you pedal more!

Not quite true - if you adjust your gearing appropriately for the smaller wheels you can get the same overall gear ratios and therefore the same speed for the same cadence so that isn't exactly a disadvantage unless you are not smart about the gearing you put on the bike or you are sooooo powerful that you can't find a big enough gear to compensate for the smaller wheels.

That said I'd have 700c wheels on all of my bikes if I could for the convenience factor. 650 tubes with long stems are harder to find, tires are harder to find (I have Velocity deep V's on my bike). You generally either have to frequent triathalon shops or special order stuff or both. I'm very small so a 700c wheel would never let me get aero- the headtube just has to be too long. My road racing bike on the other hand is a 700c wheel bike.

so pros
lighter wheels than comperable 700's so theoretically faster acceleration
possiblility of finding cheap used equipment from those selling off 650 stuff (btw anyone want to sell me a used 650c rear disc cheap )
shorter people can get a small enough frame to have at least some drop and therefore get aero, bigger people I guess can get really aero??

cons
harder to find supplies - if you don't have a tri specific shop in your area you'll probably have to special order a lot of supplies.
(on a road bike, generally doesn't matter for tt's or tris) forget neutral service! It's much less likely you'll ever get a wheel unless you bring it youself.

 

[gclark8]

I have 700 on my road bike and 650 on my Try bike.

* The 650 do spin up faster than 700.
Velocity Deep-V and Sparticus (650) wheels on the Try bike,
Conti GP4000 tyres on the Sunday best wheels,
Conti Ultra Gator Skins on the training wheels,
Tubes, all Conti Race 650 with 60mm valves.

* Ask "little jackie" about 24" (507) wheels and 152mm cranks.

 

[alienator]

I have 700 on my road bike and 650 on my Try bike.

* 650 do spin up faster than 700.
Also Velocity Deep-V (650) on the Try bike,
Conti GP4000 on the Sunday best wheels,
Conti Ultra Gator Skins on the training wheels,
Tubes, all Conti Race 650 with 60mm valves.

* Ask "little jackie" about 24" (507) wheels.

Here we go again, perpetuating the lovely ol' myth about how low moment of inertia wheels "spin up fast." Again, the fact is that the differences in acceleration are sooooooooooo small because humans accelerate sooooooooo slowly.

The "650 wheels accelerate faster" myth was played out so long ago and shown to be a farce.

They do have an aero advantage. That's it.

Oh, and they do help in the fitting of small frames and small people.

 

[badkarma]

Here we go again, perpetuating the lovely ol' myth about how low moment of inertia wheels "spin up fast." Again, the fact is that the differences in acceleration are sooooooooooo small because humans accelerate sooooooooo slowly.

The "650 wheels accelerate faster" myth was played out so long ago and shown to be a farce.

They do have an aero advantage. That's it.

Oh, and they do help in the fitting of small frames and small people.

+1, to elaborate
Theoretically, 650s will accelerate faster, but the actual acceleration delta will be practically negligible. If you're on rollers, you'll notice that wheels accelerating much more quickly than when you're on the road, this is b/c you're putting all your energy into the rotational kinetic energy for the wheels, whereas on the road, the energy you exert goes into the rotational KE of the wheels, plus the translational KE of the frame+rider (dominant term). So if you can accelerate 650s slightly faster, it won't make a noticeable difference. If 650s make such a big difference, why stop there? Why not use the smallest possible wheels that'll fit on a bike frame?

 

[vadiver]

+1, to elaborate
Theoretically, 650s will accelerate faster, but the actual acceleration delta will be practically negligible. If you're on rollers, you'll notice that wheels accelerating much more quickly than when you're on the road, this is b/c you're putting all your energy into the rotational kinetic energy for the wheels, whereas on the road, the energy you exert goes into the rotational KE of the wheels, plus the translational KE of the frame+rider (dominant term). So if you can accelerate 650s slightly faster, it won't make a noticeable difference. If 650s make such a big difference, why stop there? Why not use the smallest possible wheels that'll fit on a bike frame?

This could get into one of those interesting physics discustions real quick....

I could go and do the figures but thought about being lazy. I think all of this will fall into the category of, in practicallity, it does not matter but...

A 650 wheel will accelerate faster (albiet not signifcanly in real application), but it will also slow down faster too.
Does the size of the wheel matter in maintiaing speed. For instance, while riding (in a frictionless vaccum) does it take more or less energy to maintain current volocity of a 650 vs a 700 wheel? Or is it all a matter of the mass and areo of the wheel?

So if my goal it to get to my cruising speed fast, the 650 is the choice. If I want to coast farther the 700 is the choice.

If the above is correct, for me personally I can get to crusing speed on flat asfault in less than 10 seconds. On a closed course, with the exception of turns in excess of 90 degrees (or down hill) I loose almost no speed in turns, thus do not need to accelrate for very long to get back to speed. So at best I can shave 10 seconds off of my time in a 45 minute TT.

 

[Eden]

So at best I can shave 10 seconds off of my time in a 45 minute TT.

the last tt I did, I came in 1/10th of 1 second ahead of the next person......

OK OK I fess up it was an uphill tt so its not exactly the same thing, but 10 secs can be significant enough to make a difference

 

[alienator]

A 650 wheel will accelerate faster (albiet not signifcanly in real application), but it will also slow down faster too.
Does the size of the wheel matter in maintiaing speed. For instance, while riding (in a frictionless vaccum) does it take more or less energy to maintain current volocity of a 650 vs a 700 wheel? Or is it all a matter of the mass and areo of the wheel?

Does it matter? I mean, do you ride in a vacuum? If weight is held constant, the moment of inertia of a 700c wheel is only 19% greater than a 650c wheel. To get an idea of how little that matters, someone did an analysis at Analytic Cycling comparing the accelerations of a 1 lb wheelset and a 2 lb wheelset: the difference was negligible, and the heavier model wheel had a moment of inertia that was 100% greater.

So if my goal it to get to my cruising speed fast, the 650 is the choice. If I want to coast farther the 700 is the choice.

No, you won't be able to tell the difference. You have completely forgotten everything else that goes into the equation. Rolling resistance is higher for 650c tires because their casings have to deform more to form the contact patch. As for aero concerns....well a very rough estimate of areas presented to the wind are, for a 23mm tire, 155 cm^2 for a 700c tire and 143 cm^2 for a 650c tire. So, the 650c tire will present about 8% less area to the wind. Since, drag is linear with area (to first order), there will be at most an 8% difference in drag. At most. The actual difference in drag will be less.

 

[alienator]

the last tt I did, I came in 1/10th of 1 second ahead of the next person......

OK OK I fess up it was an uphill tt so its not exactly the same thing, but 10 secs can be significant enough to make a difference

If you were in better shape or better motivated, you also would have beat out that person ahead of you.

 

[vadiver]

the last tt I did, I came in 1/10th of 1 second ahead of the next person......

OK OK I fess up it was an uphill tt so its not exactly the same thing, but 10 secs can be significant enough to make a difference

I do not care how close the person was behind me, that is their problem. I care about how much time I needed to make up to beat the person who won.

I agree 10 seconds would be a factor. But that would be assuming I spun the 650s up to speed instantly and took 10 seconds to spin the 700s. Since I do not know my exact acceleration I suspect the difference to be less than 2 seconds on start.

Although that would still imply you finished 1.9 seconds behind the above mentioned person. My point was more of, are there other ways to shave the 10 seconds. Granted I have not competed in many TTs but there has only been one that I finished and thought that there was nothing more I could have done to go faster. Every other finish I knew where I lost time on my goal, and it would be much more than 10 seconds.

 

[Eden]

If you were in better shape or better motivated, you also would have beat out that person ahead of you.

read it better I did beat the person - by 1/10th of 1 second

all things considered I only ride 650's on my TT bike (which by the way I was not using for the uphill tt - I was using my regular 700c road bike) because I am short enough to absolutely need to. I would probably use a normal 700c tt bike if I could. Its just easier to use standard equipment.

In all the flat tt's that I've done none have been quite so close as that, but the uphill ones have been. The year before I came in 6 seconds ahead of the next person down.

 

[vadiver]

Does it matter? I mean, do you ride in a vacuum? <snip>


No, you won't be able to tell the difference. You have completely forgotten everything else that goes into the equation. Rolling resistance is higher for 650c tires because their casings have to deform more to form the contact patch. As for aero concerns....well a very rough estimate of areas presented to the wind are, for a 23mm tire, 155 cm^2 for a 700c tire and 143 cm^2 for a 650c tire. So, the 650c tire will present about 8% less area to the wind. Since, drag is linear with area (to first order), there will be at most an 8% difference in drag. At most. The actual difference in drag will be less.

No I do not ride in a vacuum, I was doing that to assist with what you said I forgot in your next paragraph.

My gut feeling is for me, riding a 60 cm frame, the 650s would cost me time over all if there was a difference at all.

With the quick calculations you did, that 8% is only on the wheel correct? So I cannot say my time would be better by 8% since I am sure my body affects the areo on the bike much more than the wheels/tire.

 

[alienator]

read it better I did beat the person - by 1/10th of 1 second

Mea culpa. However, the point still stands, for such insignificant differences, rider condition and motivation are much bigger factors.

 

[Eden]

Mea culpa. However, the point still stands, for such insignificant differences, rider condition and motivation are much bigger factors.

my motivation was that I could not let myself be beaten by a person wearing a flourescent pink full body skin suit....... Ms. Cippolini maybe?

 

[alienator]

No I do not ride in a vacuum, I was doing that to assist with what you said I forgot in your next paragraph.

My gut feeling is for me, riding a 60 cm frame, the 650s would cost me time over all if there was a difference at all.

With the quick calculations you did, that 8% is only on the wheel correct? So I cannot say my time would be better by 8% since I am sure my body affects the areo on the bike much more than the wheels/tire.

Yeah, and that was a real dirty approximation, using total wheel/tire height and tire cross-sectional diameter (approximate) to get an area. And yup, it's important to remember that 8% was only with respect to the differing wheels. Keeping in mind that the best aero wheels will gain you roughly 0.4-0.5mph at 25mph over good ol' box section rims, then it's pretty easy to make the assumption that the aero difference between 700c and 650c wheels is going to provide a comparitively small benefit.

 

[alienator]

my motivation was that I could not let myself be beaten by a person wearing a flourescent pink full body skin suit....... Ms. Cippolini maybe?

See, that in itself is prolly worth 1 sec.

 

[gclark8]

OK, some best times for my old cross town commute:

Merida MTB with flat bars and Conti Sport Contact 26x1.3 Slicks: 42min,
Giant Upland Ladies MTB, Purple, with my 650c training wheels/Conti Ultra Gator Skins: 47min,
Felt SR81 with 700c Conti 23mm GP4000 tyres: 50min
Felt SR81 with 700c, the original 25mm Felt Kevlar tyres: 55min.

Yes, in the real world, tyres and wheels and gearing, all make a big difference.