Wheel sizes--650cc vs. 700cc-- x23, 25?

Question

I've been wondering about the 650cc wheel sizes. The 700cc look to be the normal size, but there are also 650cc performance wheels--are these wheels for smaller kid's bikes? or for say Triathalons?

Also, how much faster would I expect to go from changing my tires from the x25 width to x23 or x21? Thanks in advance!

Answer 1

The 650 size is used on some Tri bikes. And yes, smaller riders, can benefit from the smaller wheel. It allows a smaller frame size, something kids and short women or even men may need. Also, several kids race bikes use 24" road wheels like the Felt f24. The Trek KDS uses 24" or 650 also as do the others.



As far as tires, width matters only to a point. 1st I will mention widths aren't always precise. One brand's 25 may be almost the same size as another brands 23 for example. Next, the total weight on the tires is important. A 200+ pound rider on 21s will actually be slower than on a wider tire. The reason is that the narrow tire will deflect and squirm too much under the weight. Simply put: not enough tire for the weight. I, and most performance/racer types use 23 and 25 to a less extent. If you have similar weight and pressure tires there isn't a big difference at all in this small range of tire width. 23 is popular because it supports most racer weight people in the 150 to 190 lb range and can be lighter than a 25. Few people use the 18-21 width because of what I mentioned above, plus greater chance of pinch flats, harsh ride (not enough air volume to absorb road shock) and less stability. This is why 23 to 25 are favored by riders and why manufacturers spec bikes with them.



EDIT: To add to this simple rolling resistence numbers do not reflect real road conditions. Here's a blurb on the subject of PSI: http://www.velonews.com/article/7508



It indicates, and is corrborated by many others that very high pressures may SEEM faster but in reality are not. The harshness felt in very narrow, high pressure tires actually indicates a lot of upward motion expending energy in the bounce and not forward motion. With this information in hand, it seems a fine balance between tire size and pressure is best. It's a debate that has been going on for sometime now.



In addition, rider comfort is an important issue as well as control (read about the car/jeep example in the link). A harsh ride will fatigue even the the best rider. So much attention is given to the bike frame regarding compliance vs stiffness, while wheels and tires can affect the ride as much or more than the frame, yet are not considered with the weight they deserve on this issue.



Rolling resistence and tire width are only part of the equation. Mountian bikers seem far more in tune to these real life condtions because the effects are more pronounced.



EDIT: Mr G I remember. But "pump to the max" is relative. If the max is 110psi (23 cm) then it's not really wrong. What it wrong is using the term. I have tires with a max of 145 - I pump them to 105-110.

Answer 2

Others have given you info on 650 vs 700 tire sizes.



Tires in the range from 700 x 25 down to 700 x 18 will all fit pretty much the same size rim. The question is how important is performance to you versus ride quality. A 18 width tire at 150PSI is not going to have much shock absorbing capability. A bad paving joint or a bad pothole that catches you by surprise may be fatal for the wheel and tire. A 25 tire might have been able to absorb the shock (or not) and damage may have been lessened.



Now this is not to say the narrow tires are excessively fragile. My partner and I raced the shop's racing tandem on 18 width tires at 150 PSI and never destoyed a rim on the 50-100 mile events we did.



Narrow high pressure tires have very low rolling drag. It you compared them to a 26 X 2 mtn bike tire it is probably an easy 20% difference.



The differences in a 21 versus a 25 are more subtle but are there. If you ride long distances at high speed or compete in tri's then I think you would see a difference. On your next tire change get some 18's or 20's and new narrow tubes. You will see the difference.

Answer 3

In case there is some confusion, 650 and 700 wheels are not interchangable. A bike is made for one or the other. As others have pointed out, due to the different diameters of wheels, your brakes would be in the wrong place if you attempted to swap wheels. Also, given the different diameters, the gearing would be completely different.



650 wheels are mostly put on time trial/triathlon bikes. 650 wheels have a slightly smaller aerodynamic profile than more standard 700C wheels. The difference is pretty slight, but since you can't draft in a time trial or triathlon any advantage is good. As well, being smaller, 650 wheels are somewhat lighter than 700C wheels. Of course, any reduction in rotating mass allows you to accelerate more quickly. As well, the smaller wheels allow a more upright geometry which will be more comfortable for riding in an aero position.



The downside of 650 wheels is you have fewer choices of tires and a poorer ride qualtiy. (A larger wheel meets obstuctions in the road at a lower angle than a smaller wheel. Thus, a larger wheel transmits less of a jolt to the rider.) Furthermore, few bike shops keep 650 wheels in stock. If you have problems, most shops will have to special order a wheel for you.



Most roadies ride 700X23 tires. A 23mm tire provides a good balance of grip, shock absorption and rolling resistance. I suggest you experiment with some other tires and see what feels best for you. I wouldn't expect to find much performance difference, though.



Hope this helps.

Answer 4

700c is the "normal" wheel size. It really isn't practical to switch from 700c to 650 because there are a lot of other things that need to change as well -- the brakes are just the start of it. I've had both 25 and 23 tires on my bikes, but you can't go just by the numbers. A Specialized Transition Armadillo 23 is bigger than 25s in most other brands. Right now my bike has Michelin Pro2 Race 25s because they came with the bike. Only 100 psi, they feel kind of tubby and squishy to me. When they wear out I'll replace them with Continentals. The local bike shop has the Force/Attack set on sale for $40 off. That's a 22 for the front and a 23 for the rear. Rear tires always wear out faster than the front. When the rear in that set goes, I'll probably replace it with the Conti GP 4000S "Black Chili" 23 tire.



I would expect speed gains from changing from a 25 to a 23 to be measurable but small. I've never made that change myself without changing several other things

Answer 5

Some bikes are made specific for 650cc, mostly woman's bike. I would go with the 700cc. On my old mountain bike I put some 23 city tires on it and felt a big difference. However it couldn't perform like a road bike, too heavy and tires being too small. But for commuting and city riding I recommend doing the thinner tires. Hope this helps

Answer 6

650's are used mostly on TRIATHLON and time trial bikes because:



1. More aerodynamic

2. Allows steeper seat tube angles (important for riders using aerobars, and trying to run after a hard bike effort)

3. Less rotating mass, thus better acceleration.



I suppose they might work better on a small womens' frame as well. Not being a small woman, I never looked into that.



700's with their associated tubes and tires are more widely available, so stick with that.



Speed difference from 25 to 21 to 23 would be small. Small enough that you might not notice if you don't race. FWIW, I use 19's on my 650c race wheels.

Answer 7

MR it wasn't all that long ago that you advised people to pump their tyres to the max!!!



When I put forward the argument of 'Bounce' and slower speed, - people here disagreed and gave me thumbs down!!!



That has happend on a number of occasions when I gave my often controversial opinion,_ LOW AND BEHOLD - a few weeks later people are giving the very advice that I was originally slated for - BIZARRE ISN'T IT ??????????



On this occasion answering the question late, I will echo the words of others, 650c wheels are best suited to TT and smaller bikes. Narrowing your tyre sizes are akin to higher pressures, - if you have super smooth roads or a velodrome then by all means do it!



.

Answer 8

Yes! I was just talking about that the other day when I tried to sit on my daughter's Sit N' Spin. I'd also love a Big Wheel, too.

Answer 9

700c (or 622mm) is standard road/cyclocross/hybrid/"29er" size WHEEL diameter (not including tire). 650c (or 571mm) is not something to be concerned with, unless you are into time trials, or are very small. Pretty much everything these days is either 700c or 26'' (559mm/Standard MTB size). As far as width goes, I really couldn't tell you how much faster you would be able to ride. Be aware that with ultra-skinny tires you will run a greater risk of damaging your wheels if road conditions are poor.

Answer 10

smaller bikes use the 650 sizing.



going from 25->23c wouldn't feel any different, except they might be higher pressure tires. some even say that wider tires offer less rolling resistance.



pro's use 23's for what it's worth.