Road Cycling - 700c vs 650c?

Guys,

I am in the market for a new TT / Tri-bike. I have narrowed the choices to the cannondale MultiSport or the QR Tequilo.

Both bikes are available w/ 700c or 650c wheels.

I think it would be more convenient for the TT bike to have 700c wheels, since I could "share" wheels (especially race wheels), tires, tubes, etc with my road bike.

Now, I've heard the stuff about 650 being faster to accelerate, lower weigth ans inertia, more aero...

In the "real world", is there that much of a difference?

guess it depends on how serious of a racer you're going to be, if you want more practical then 700c, if you want more professional 650c.

I'm not sure what the exact advantages are but that's my take on it :)

Finding 650 tyres can be a real pain. Unless you are short (under 5' tall), there is no real advantage to using 650c wheels.

VegasCyclist,

I'm sorry, but that makes no sense at all! You didn't provide any info, but you implied that if I am considering 700c, I must not be a "serious cyclist".

That's like saying that one is required to shave one's legs to be a serious cyclist - even though it doesn't make you faster!

Guess what - I don't live and train in Europe, so I must not be a serious cyclist!

Come on! I appreciate any real info, or personal experiance you can offer, but don't waste time saying things that amount to "just because".

I have no real world experience about this matter but it is for sure that smaller wheels accelerate faster and have less aerodynamic drag. But as someone said, tires can be hard to find. So, if all that matters is finishing first in a race, then 650c, else 700c would probably be easier to deal with when it comes time to buy new tires or move the wheels to another bike. So, after all it is sort of about how "serious cyclist" you are.

There are pros and cons to both wheel sizes.
The aerodynamic advantages of 650 are miniscule. 90% of aero drag is due to the rider. There is a wider choice of aerodynamic wheels in 700c
The have less inertia, so are quicker to accelerate, and decelerate, and less stable on descents. Their lighter weight makes climing easier.
They have higher rolling resistance then 700c (at the same tyre pressure).
There is less choice of tyres and less support during a race.

The sensible reasons for chosing 660c are predominantly to do with bike geometry. If you are a regular sized guy who wants a very low position, then 650c will give you that. Mainly they are for people who need small wheels to fit into small frames for small riders.

If your frame is big enough to accept 700c, then there is no real reason to use a less common size.

Originally posted by BikeEngine
VegasCyclist,

I'm sorry, but that makes no sense at all! You didn't provide any info, but you implied that if I am considering 700c, I must not be a "serious cyclist".

That's like saying that one is required to shave one's legs to be a serious cyclist - even though it doesn't make you faster!

Guess what - I don't live and train in Europe, so I must not be a serious cyclist!

Come on! I appreciate any real info, or personal experiance you can offer, but don't waste time saying things that amount to "just because".

easy there, I didn't define serious cyclist maybe I should have. how many races are you going in? are you only going to do one a year?

if you are NOT going to do that many races then high performance gear is not going to make a difference, that is true in any sport. If you are someone who does a bunch of races a year then it's a different story.

Look at it this way, if you are someone who does very litte racing, is a $3000 (usd) bike that weighs 300g less then a $1000 bike going to make you any better? no.

so in short find out how many races you are going to do, and maybe that will help you decide. That's my advice take it or leave it, but don't blast me because I didn't give you the answer you were looking for.

MichealW,

Thanks, that's the type of info I am looking for! Your points reflect what I was thinking to myself. Not that I was specifically looking for someone to agree with me...

The frame size I ride is 54-56cm, so the height of the 700c wheels doesn't compromise the geometry, or the lowness of my position.

If anyone else has additional points I should be aware of, I would appreciate the input.

Since the 650C wheel's faster rotational speed would offset its lower moment of intertia, the only advantages I can see are a slightly (50/700 = 7 percent) lower tyre and rim mass and the reduced wind drag noted by an earlier poster. These in turn would be offset somewhat by increased rolling resistance. For an average or larger-size rider, I would vote for 700C for practicality and replacement tyre and rim selection.

Does anyone have rough statistics on the relative popularities of 650C and 700C wheels in triathlons and in road racing? When I looked at new Nishikis in 1991, after breaking my frame, all of the company's road bikes had 650C tyres.

VegasCyclist,

Maybe I was a little harsh in my response. Sorry.

You have a point regarding racing background and intent.

FWIW, I've been racing for 6-7 years, I do 3-4 duathlons a year, 3-4 time trials a year, 2-3 road races a year. I've won a few state championships, and placed in others.

I have TT'd with 650 tri-bikes, funny bikes w/ 24" front and 700 rear, and converted (forward seatpost) 700 RR bikes.

My 700C racing wheels are lighter than any of the hi-perf 650C wheels that I have seen or read about. Aero dynamics seem good, but aren't as easily compared.

Although I do consider myself a serious cyclist, I am not a pro, nor am I sponsored - so, my finances are not unlimited.

So, there is a very real concern regarding the cost-effectiveness of going with 650C.

Also, though your point comparing a $1000 bike that weighs 300g more than a $3000 bike is valid, consider this - for most of us, it is more cost-effective to cut a few pounds off our bodies! Of course, I know there are more things to consider than just the weight difference (responsiveness, rigidity, geometry, etc).

agreed. I think someone once posted about areo helmets, and another poster pointed out the aero gain from those helmets is very small, and most of the drag is from the rider, knowing how to get low and small when riding will help reduce the drag.

no harm done btw:beer:

Thought I'd resurrect this old thread rather than start a new one; sorry for the redundancies....

I realize the good sense in most replies to this endless debate (650c vs. 700c).

I am not looking to squeeze extra performance out of a magically lighter, smaller diameter rim. I am looking for a good fit and comfy geometery for long rides.

I understand how 650s make sense in maintaining good geometery and a lower center of gravity for smaller people - women, teens, shorter men, say, 5'0", 5' 1" and under......

Here's my question: I am 5' 7" (actually halfway to 5'8"), but have a short inseam (about 29"). Also just turned 40 so my body is not liking the very aero position it used to. I have been avoiding the old bikes I favored in the past (49cm or less with LONG top tubes), and I am now using a higher bar position and swapping in shorter stems.

So, although I am not short per se, I do have short legs and do not need the same top tube extension I used to (I think about 50cm TT works for me these days). To get a comfy standover height of 750cm or less, would I be better off with a 700c compact (Giant OCR, Cervelo) or a larger 650c bike (49cm or so frame)?

I was considering the Cervelo because with the flip around seat tube, I was hoping to get a seat tube angle of no steeper than 73 degrees. The only other off the rack frame I've seen with my standover height and a 73 degree ST angle is the Rivendell. Would my options for slacker ST improve with 650c bikes?