Custom Bike - 650 vs. 700 wheels

[sarahkonamojo]

Reading between the lines. You WANT the 650 bike. So maybe you should just get it. And see what the fuss is about.

Seems the only negative to the 700 is the toe overlap. And aesthetics, PLLLEASE, nothing beats a new ride. Besides you will be on it, not looking at it ride by.

sarah

[Triskeliongirl]

It a little more complicated than that. Cervelo has some good info. on this at their website, as they offer 48cm riders a choice of the RS w 650c or the R3 with 700c, which they think are the two most accptable solutions, which I agree with: http://www.cervelo.com/bikes.aspx?bike=RS2009#G.

To build a small framed bike with 700c wheels, one of three things have to happen to fit the 700c wheel. One is severe toe clip overlap, which some people think isn't a problem, especially at high speeds on a racing bike, but clearly there are mixed opinions on this, especially for a more multi-use bike (and I have friends that have taken bad falls, or just got sick of always having to think about it, and some of us do need to navigate moving in and out of parking lots a couple times a day or traffic at slow speeds where it is a problem, but this is clearly an issue we will all have to agree to disagree on, it is very personal). There are many good racing bikes built this way, including the R3, blue, etc., so its clearly an option, especially for women who race and want access to a wider variety of high end wheels as blue tree mentioned.

The second option is changes to frame angles to accomodate the larger wheel in an attempt to reduce tco. Usually this means increasing the fork rake to push the front wheel further away from the rider, but this results in a bike that is too stable and handles poorly (I test rode a 50cm trek madonne that had this problem, it was very hard to get it to turn, felt like I was driving a mach truck).

The third option is to build the bike with too long a top tube, and expect the rider to accomdote with a very short stem. This also results in a bike that handles poorly, because it is too twitchy since the steering arc is dramatically reduced. (Or in this situation a rider could also push the saddle too far forward which effects their effeciency and balance on the bike).

SO, pros of 650c wheels are no toe clip overlap and good handling, with a reduced but adequate (at least for most of us) supply of high end wheels.

THe pros of 700s are a wider supply of high end wheels, but either severe toe clip overlap or compromises to the frame geometry that will effect the handling.

From what Susan says she wants this bike to do, I would recommend 650.

To understand better why its hard to fit a 700c wheel in a small framed bike, view the videos here: http://www.terrybicycles.com/videos
especially frame design 1 and 2.

[Triskeliongirl]

FYI, I pasted this nice explanation from the link I gave above from the cervelo website which I think gives a pretty balanced explanation of the issues (and they do sell 48cm bikes with both wheel sizes):

You will notice three geometric changes on the RS.

Longer headtube, to match the higher handlebar position.
Longer chainstay length. Because a higher handlebar position rotates the rider’s torso and therefore his center of gravity backwards. Longer chainstays ensure the weight distribution between the two wheels remains balanced for optimal handling characteristics.
Eliminated toe-overlap by using 650c wheels for the XS size. Toe overlap is not a problem for experienced riders, but can be intimidating for some. Using 650c wheels in the XS size is the only way to solve this problem without compromising the weight distribution and thus handling. Every solution that eliminates toe-overlap but keeps 700c wheels suffers in handling.
Explanation for the 650c wheel solution on the XS size: A smaller frame means the front wheel moves closer to the rider’s feet, causing toe-overlap. While inconvenient at walking pace, this issue disappears at normal riding speeds as the actual steering angles become very small. There are four ways to deal with this:

1) Accept toe overlap, after all it is not a problem if the rider is aware of it at low speeds, and it does not occur at higher speeds.
2) Use 650c wheels, which allow us to move the wheel closer but thanks to its smaller diameter it will never touch the rider’s toes.
3) Leave the front wheel far out front, but then the weight distribution will not be balanced.
4) Mess up the rider position by moving the rider forward instead of the wheel and handlebar rearward. But a changed position will not be comfortable, and the weight distribution will again be compromised.

Compromised weight distribution and therefore handling make options 3 and 4 unacceptable, leaving options 1 & 2. If you are a racer and neutral support is important, or you want commonality of parts with other 700c bikes, then option 1 is the best solution. We offer this on most of our road bikes. Option 2 is a great solution if you are concerned about toe overlap, never need neutral support and carry a spare for yourself (since your riding partners will likely have only 700c spare tubes, although even those work in a pinch, just fold them in – no problem).

[Triskeliongirl]

One more point Susan, in your original post you commented the the FIT would be identical with either design, but ask about the *handling* and TCO. Fit just describes your contact points on the bike, basically the points where your bottom, feet and hands contact the bike. You can keep that constant on bikes with many diff geometries (using diff. stems, etc), but the bikes will not always handle or perform the same. On some, you may even have pain if your body is not well balanced. I assune with a custom build both designs that are being proposed will have you balanced, but you need to understand if the only difference will be TCO w the 700c, or there will also be compromises that effect handling.

[MartianDestiny]

I certainly agree that choices in geometry affect handling and thus the geometry considerations when considering 700c vs. 650b should also be looked at from a handling perspective.

However, I've gotten the impression from this thread that if you want a 700c wheel on a small bike then you are going to have to live with either a) a horribly sluggish slow steering bike with the wheel way out in front of you b) a horribly twitchy bike or c) some weird compromise in your seat vs. pedals position.

As a 5' tall rider with two 700c road bikes (one an XS Giant and one a 47cm Wilier) I disagree. Yes, the geometry on both bikes is slightly different than the medium versions. However both of them have different handling characteristics that fall well within normal and are in fact adjusted to the purpose of the bike, just like the bigger frame sizes. The Giant is more stable, but it's also an entry level, relaxed geo bike. The Wilier is a race machine and acts every bit of the part, including the quick handling (but not twitchy). I rode quite a few bikes before I bought the Wilier, all of them 700c. I could feel different handling characteristics in most. None of them had horrible handling IMO (I didn't like the Trek for other reasons).

Anyway my point is that yes there are compromises for both wheel sizes. Handling is not necessarily one, especially not to the extremes in some of the other posts. A good builder is able to get the bike to handle the way they (you) want it to, at least in my size (46, 47cm) with either wheel size.

Me, I ride 700c and have no desire to change that.

[Triskeliongirl]

I certainly agree that choices in geometry affect handling and thus the geometry considerations when considering 700c vs. 650b should also be looked at from a handling perspective.

However, I've gotten the impression from this thread that if you want a 700c wheel on a small bike then you are going to have to live with either a) a horribly sluggish slow steering bike with the wheel way out in front of you b) a horribly twitchy bike or c) some weird compromise in your seat vs. pedals position.

As a 5' tall rider with two 700c road bikes (one an XS Giant and one a 47cm Wilier) I disagree.

No, that is not what I said. But, to have it handle normally, you will have either toe clip overlap, or a longer reach. You may have one of these options, but find its not a problem for you.



SUSAN, ONE MORE CONSIDERATION: Are you planning to have this built w s/s couplers (which I highly recommend). I thought you might since it is replacing your friday for travel. If that is the case, 650C/26" wheels fit more easily into the packing case than 700c. The terry tullus is a good 28mm 650c tire, and the schwalbe stevlio (recently replaced by ultremo) is a great 23mm 650c tire. Any wider, you'll want to consider 26".

[madscot13]

how easy/ difficult is it to switch between 26" and 650c wheels? do any certain types of brakes facilitate this?

In terms of proportions and aesthetics I like how 650c wheels look in proportion to 700 and small frames. I am always dreaming of my next bike. It seemed logical to get a 26" frame in the future for stand over issues. I know there is more to fit than that but on my current bike I don't have toe overlap and any reach issues are taken care of- anything more than that gets too complicated for me. I thought that with 26" tires with different wheelsets I could go as racy as I want or ride on gravel paths with wider tires, which 26" tires are more known for. yes the available tubes for 26" are limited (and 650c even more so) and I would probably get a custom wheelset for fast days, but there are a lot of options. You just have to be ready to sort of steer away from what the rest of the pack is doing.

schwalbe tires runs pretty narrow. check out there website and search ETRO at 559:http://www.schwalbetires.com/product...op0=OR&filter0[]=559-20

congrats on the sweetpea

ps 650 and 26" (well some) tubes are smaller than 700, so you can bring two

[Susan Otcenas]

SUSAN, ONE MORE CONSIDERATION: Are you planning to have this built w s/s couplers (which I highly recommend). I thought you might since it is replacing your friday for travel.

That's the plan!