Advantages of 650c over 700c bike?

Triathlon Forum
1

I had a friend ask me about the benefits of getting a 650c or 700c bike. She is right on the edge and can get a size 50 frame from various manufacturers in either wheel size. I wasn’t able to explain what the benefits are with the smaller bike, if any .

Is there any truth that 650c size bikes are easier to pedal and climb better than a larger 700c bike? I had once heard that 650 bikes corner better, and this seems to make sense. I understand that there is less wind resistance at the lower 650c level, however, I would think that rolling on a 700c size bike would just be faster and easier.

I would think that getting 650c bike parts (wheels, tires, etc) is a lot harder since it’s not a “standard size”.

2

650 over 700 is good only from a standing start for a short distance, that’s where it ends.

3

I find my 50cm road bike with 700c wheels to be awkward handling. My 48cm 650 rides like a dream and corners really well. No toe overlap. I realize that toe overlap doesn’t really matter in normal situations, but when you are messing around you can end up on the ground fast when your wheel hits your foot.

Jodi

4

I ride a 51cm frame. I’ve time trialed for two years on a 650c bike and this past year I started using a 700c bike. On the new bike, I’ve yet to match performances I had on the 650 machine, but there could be many reasons for that (not the least of which would be that I’m no spring chicken and another year older is another year older).

I studied this question a lot before I made the change. Here’s a synthesis of my findings/conclusions:

Because 650c wheels have a lower moment of inertia, they accelerate more quickly and somehow this translates into them being better for climbing. (I would say I have observed this to be true.)

For whatever reason (perhaps a sort of flywheel effect), 700c wheels tend to hold high-end speed better with less effort. (I would NOT say that I’ve observed this to be true to any meaningful degree.)

Until recently, head tubes on most frames were too large/tall for a smaller rider to achieve a good aero position without going to a 650c bike. That’s changing now. But if you need smaller than a 51cm, you probably still need to be on a 650 machine.

Small frames with 700c wheels can be rather dangerous in sharp turns and turnarounds because the larger front wheel can come into contact with the foot causing loss of control. The 650c wheel size doesn’t present this problem to the small rider.

A disk wheel in 650c doesn’t seem to weigh that much more than a regular wheel in 650c. A disk wheel in 700c is a FREAKING ANCHOR!!! You’ll fly on the flats with it, but you’ll feel it back there when you go up a hill way more than you do when you’re rolling a 650c disk up a hill.

I looked at all of the information above and decided it was pretty much a toss up. Here’s the tie breaker:

Equipment choices … everything from frames and wheels to tires and tubes … are significantly more limited in 650c. Try finding a 650c latex tube. You can’t. Want dimpled wheels? Sorry. Want a Zipp Tangente tire? Out of luck. (For me, part of the fun of this sport is new toys!)

I said earlier that I haven’t matched my 650c times with my 700c times. That wasn’t entirely true. Someone else on this thread posted that 650c is best suited for shorter efforts. I do a lot of 10 mile TTs and I haven’t been able to top my 650c times on the new bike. But in a few long Tri relays where I basically did TTs up to 56 miles, I did have new personal best times on the new 700c bike.

This is subjective, so take it with a grain of salt. I should be chastised for even attempting to invoke a physics term like “moment of inertia.” A little knowledge is a dangerous thing when wielded by someone like me!

.

5

I agree with what you said as well. 50 and under 650 is probably better and 51 plus, 700 is better. 650 is faster accerating, but 700s once up to speed will travel faster, so which is more important in a tri? Most are not very technical, therefore 700s.

Pscyholist, I am also thinking about moving to 51 700c bike from years of 50-51 with 650s. Just curious, what is your height?

6

As psycholist eluded to, the main geometry differences are less chance (if any) for toe overlap and, most importantly, you can get a lower front end and hence a more aero/ST/FIST approved position.

The detractors are equipment choices and resale. Many bikes have very short headtubes now (like 10cm or under) with a lot of aerobar choices, so only the toe overlap (which I have even on a size M or 53-54 frame) is of concern, and this is only for slow speed, tight turns that one gets used to quickly.

7

Pscyholist, I am also thinking about moving to 51 700c bike from years of 50-51 with 650s. Just curious, what is your height?

I fluctuate between 5’6" and 5’7" depending on whether or not I need a haircut. Seein’ as how I’m bald, I don’t often need a haircut.

.

8

I ride 650’s because I like how they feel on the road better than 700’s. Never had a problem keeping them up to speed. Yes, they accelerate better (which is why I first used them on the track). THat also makes them a little easier to climb with (in my experience). But the cornering manners have more to do with the overall geometry and balance of the bike than the wheel size.

And I’ve also never had problems with availability of rims, tires, or tubes.

9

Why would you think that a 700 would travel faster?

jaretj

10

I own a 700c road bike and a older 650c Tri bike. Of course there is a huge difference in the geometry of both bikes, but I don’t find that much difference in the ummm… roll factor? Oddly, I am much more comfortable climbing with the tri bike. I seem to be able to get over the front wheel better. I can also get up to speed quicker on it. However, once I’m rolling, I don’t notice much difference. At 6’2", I can get in a pretty aggressive aero position (ie lots of drop) due to the low front end.
Getting tubes hasn’t been an issue for me yet, but finding a deal on rubber is getting more challenging. I don’t see ever selling it because I like the looks and it fits me perfectly. (I have been on a 3 yr quest to find the right set of race wheels. Although readily available on eBay and ST’s classifieds and cheaper than a race set of 700’s, I still haven’t found the right set at the right price.)

Brad

11

That’s just not true …

I find that 650’s are better for shorter distances like you said, and that they accellerate quicker, especially on hills.

My aero profile is a hellava lot better too.
I like 700’s if I were doing bike races, but not tri’s,but hey that’s just me…

12

700 advantages: Rolling resistance, ubiquity
650 advantages: Aero, weight, handling.

13

The ONLY real advantage of 700’s over 650’s is if you do road races and need neutral wheel support.

14

I’m close to 6’0" and have never heard of a 650c tri bike built for someone my size or bigger. I have always thought of 650c frames being in the 51cm or less size. Are you using a standard 700cm frame with 650c wheels?

15

The only thing that surprises me more than how often this question comes up, is how much mis-information there is about it.

The message we give is simple: make sure the bike that fits you and don’t worry about wheelsize. I would suggest that in general tri bikes 51cm or smaller should use 650c and road bikes under 48cm should be 650c.

The rationale for this is a bit more involved, but first the bare facts:

  1. The work required to maintain a given speed is no different between 650c and 700c.
  2. You can’t go further for the same work just because your wheels are bigger. Making 650c wheels go around faster to make up for their smaller size is done with gearing, no additional effort is required.

After that, for every point for a wheelsize there is a counterpoint:

  • 650c wheels have a lower moment of inertia which means they will accelerate faster, buy also decelerate faster. This means little to triathletes provided you don’t plan on coasting. It is a benefit on technical courses that require more braking and accelerating.
  • 650c wheels are more aero, but 650c frames are less aero. Assuming you have to get your bars to the same height, less wheel means more frame. Which is better depends on the particular wheels and frame and is hard to say for sure.
  • 650c wheels are lighter, but 650c frames are heavier (see above).
  • 650c wheels are stiffer. This means they will climb and sprint better, but also may make them slightly less comfortable.
  • 650c wheels will have slightly more rolling resistance, but far less than difference in different tires.
  • 650c wheels and tires are less common, but any decent road/tri shop will have what you need and the bigger ones probably have deals on 650c stuff (I know we do!).

My bottom line… I like 650c, but not enough to let it influence my bike choice. The biggest issue I see is shorter riders who want to ride a 51cm P3C who should be on a 48cm. The worst part of that is, IMO, the 51cm P3C (already too big for them) should have been made with 650c wheels as well because with 700c it fits even bigger!

16

The biggest issue I see is shorter riders who want to ride a 51cm P3C who should be on a 48cm.

Ha! funny you should mention this. My friend was recommended a 48cm bike, but really wants the P3C (not sure what size but I suppose it’s 51cm). She is thinking that another bike in 50cm/700C might be the compromise (if she can’t have the P3C). Good marketing, I suppose.

17

The reality is that that may not help. Although a 50cm frame may have a shorter top tube (very questionable, check the geometry), it isn’t likely to be any shorter. In that size the limiting factor is the 700c wheels. You just can’t make the bike “smaller” unless you make the wheels smaller.

18

YaHey, my bike is a purpose built, tri-geometric, 58 cm frame using 650c’s. It was built in 2000, just at the end of the 650 “next big thing” craze. It’s a pretty cool bike. I used to get heckled for it, but as it ages it seems to be getting more attention as a conversation piece. It’s also pretty fast. I’d upload a pic for you, but I’m pretty sure everyone here hasn’t got the heckling out of their systems… :wink:

Brad

19

I posted mine on the “round tubed compact frame” thread last week. But here’s another shot at it:

http://i5.tinypic.com/89l418m.jpg

650’s on a frame that is probably about 1cm on the big side, and I’m 5’9" plus a little.

20

another small disadvantage, if you have a 650 tri and 700 road bike, is you need to keep two sets of extra tubes, tires, etc. using 700 on both, i never worry about what spare parts are laying around