crandress 

When fitting a frame, what is most important, stand over height, frame size or geometry? I have always ridden a 51 or 52cm 700c frame. I was told I could go bigger with 650b wheels and the guy talked about the lower stand over height. Is this true? Or is the frame size/geometry more important? I never really thought about it. I was looking at a bike with 650b wheels that is 52 cm, so would that be too small for me? I don't think this too important when going from 27 inch to 700c, since they are pretty close right?
Sorry if this is a silly question, but thanks for your replies. Chris

plonz 

For me, it's both the seat tube and top tube lengths. I build my bikes to have the same saddle height, bar reach and bar height. The tube lengths pretty much tell me what seatpost and stem specifications I'll need to make it fit and I can determine whether or not it makes sense to do so. I really don't care about standover height.

All my bikes are sport or racing style so not big differences in geometry. I could see that being another consideration as it pertains to saddle fore/aft in relation to the crankset.

crandress 

Thanks, that is kind of the way I was thinking about it. Saddle height, seat tube and top tube lengths. Maybe those change if its a bike designed around 650b wheels versus a conversion. But I don't really think so.

Wildwood 

Sloping top tubes mostly eliminate the standover aspect. But for a horizontal top tube = if you cannot stand over it (dismounted from saddle) it is too big.

edit: not a silly question and examines the endless debate about what constitutes the perfect fit for a given ride.

Good fit first,
comfort at your 'touch points' second,
then tires then wheels.
The rest is just how much you want to spend on components, which may circle back to fit.
Get it?
Evolutionary undoubtedly.

McBTC

Interesting: a 650B wheelset apparently would enable the owner of a racing frame to run 28-30 tires that wouldn't otherwise fit under the brake bracket using 700C wheels (e.g., I can't run >25s on the rear). Nothing much to do with stand over height tho.

gugie 

For fit, all that's really important is the relationship between the saddle, handlebars, and cranks as far as positioning goes. What goes on in between those three points doesn't matter, for fit. What goes on in between matters for handling, load carrying, and aesthetics.
@Wildwood brings up a good point, but I've know of people who ride bikes that they need to stand on tip-toe to straddle over. You can do it, but uncomfortably.

Wildwood 

How much lower a horizonal top tube in 650B config greatly depends on tire size.

gugie 

Saddle to BB distance will not change. Top tube length, maybe, but not significantly. BB drop is the one thing to be concerned about, but in reality it's not very often an issue. I've had one conversion that didn't play well with 650b due to pedal strike concerns.

Salamandrine 

They are all important. The main thing is to get the relative positions of the seat, handlebars and cranks in the right spot. How you do it is secondary.

In the old days of level top tubes, both seatposts and stems had limited adjustment height. Sizing was generally done by standover height. You picked a bike you could straddle by 1-2" and called it a day. Bike shops would typically carry 2 or 3 brands with slightly different geometry. This way a longer torso person could find a bike with a longer top tube, and vice versa.

Realistically, bikes today have slanting top tube, BB heights vary, angles vary. Very long seatposts and long extension stems are readily available. There are lots of ways to make a bike fit. Many people now consider effective top tube length the first thing to consider when sizing a bike.

In theory a 650b bike would have the same standover height as a 700c bike of the same size - IF the bottom bracket is in the the same place, and all the angles are the same. Practically speaking there are so many variables you couldn't really say.

Generally, I think 650B is a good choice for a smaller frame, because it allows a little longer head tube. 52cm is only sort of small though. It is kind of transitional. I suggest you test ride whatever you are considering and see what feels best for you.

Wildwood 

Sorry if this sounds a silly answer.....

"When fitting a frame, what is most important......". My answer is: where will you be riding this bike and what is your riding style?
Road
Off-road
Track
Criterium racing
Camping
etc.

Or did I miss something?

edit: i get it that if you are considering 650B you're not looking at a track application?
Or anything competitive?

SJX426 

@gugie nailed it for me. I have found that 58-61 is my range with the extremes, marginal. I have been riding my SS Langster, which is at 61 and it touches me when I straddle it. Rides great and because the measurements are very close to what is on the Pinarello (60), it feels normal.

noglider 

Standover height is important for some but not everyone. Occasionally I will ride someone else's bike that is too big for me. I latch my knee over the top tube while tilting the bike to the side. Others won't trust themselves not to come down on it. If the bike that fit me the best didn't leave room under me, I wouldn't mind, but I'm just one person. To me, the 1" of standover height rule is more about fit than about safety. In other words, it used to be that if you had that gap, the bike was probably about the right size. But it's not always true.

crandress 

Thanks for all the responses! For reference, I mainly ride on roads and gravel for casual day rides. I have a Mercian Vincitore touring frame and a Bridgestone MB-3 mountain bike with road tires at present. I am looking for a couple vintage frames, or complete bikes for the right price. But in general level top tube bikes, one a racing bike that will likely get ridden less often and maybe even hang on the wall if it is pristine enough, and another as a touring/randonneuring type bike.

So when looking for a bike, I was in general looking for a 51-53cm or 20.5-21" road frame, since this is what I have always ridden. When asking a guy on Craigslist (or eBay) about the frame size (since he failed to mention), he responded and I said that the bike was not big enough for me. His response was something like, "remember, this bike has 650b wheels, so you would need a bigger frame size". I was skeptical, so I threw the question out here. The bike in question was designed for 650b wheels, not a conversion, so that made me think and I posed the question here. Not really sure I worded the question right, but I appreciate the responses.

Wildwood 

We're all talking 'pubic bone height' for standover? Right?

I want to be able to standover any bike I ride regularly. Can I ride a bike that's too big? Sure, but let's not guide the thread starter into believing this is a good thing, just to achieve a top tube length (or some other measurement) they think they need.

Andy_K 

I generally don't worry much about standover height. I have a few bikes on which my nether region solidly touches the top tube when I stand over it. There seems to be a pervasive fear that this could lead to a painful experience in the event of an unplanned dismount, but how often do you keep the bike completely vertical when you crash? It's not uncomfortable standing at a stop sign, so I'm OK with it.

Regarding geometry, top tube length and seat tube angle are tightly coupled with regard to fit. You generally will want to keep your saddle in the same position relative to the pedals regardless of geometry, so you'll move the saddle back more (relative to the seatpost) on a bike with a steeper seat tube angle than you would on a bike with a slacker seat tube angle. The rule of thumb is that one degree change in seat tube angle makes about a one centimeter difference in "reach" (the horizontal distance from the bottom bracket to the top of the head tube). For instance, my Sequoia has a 550mm top tube and a 74 degree seat tube angle while my Trek 614 has a 560mm top tube and a 73 degree seat tube angle, but these two bikes have almost exactly the same reach.

If you buy a frame that is designed for 650B wheels, as opposed to putting 650B wheels on a bike that was designed for 700C wheels, you may encounter another effect. The bike designed for 650B wheels is likely to have less bottom bracket drop. If it has a level top tube, this may mean that the "stack" (the vertical distance from the bottom bracket to the top of the head tube) is shorter on the 650 bike, though you'd probably see that reflected in the proportions of the seat tube and top tube lengths. In any event, this can be compensated for with more seat post extension and a taller stem.

I actually have a spreadsheet that I use to calculate stack and reach. For bikes with a completely horizontal top tube it's a pretty simple formula. I use that to figure out whether or not a given frame will fit me. I've had pretty good success even selecting a stem length and positioning the saddle based on this spreadsheet.

Ballenxj

For me, stand over height is not nearly as important as seat to fully extended pedal is. I learned long ago that with your butt firmly planted on the seat, your leg should be fully extended when your foot is on the pedal in it's furthest downward part of the stroke. Your knee should not be hyper extended at the point, and have just a very slight bit of bend for proper fit. Of course a properly sized top tube to fit your upper torso should also be taken into consideration too. And yes, you should have a wee bit of clearance between the top tube and your crotch when standing flat footed while straddling the bike.

escii_35

1++ Top tube length.

Standover only gets me when I ride a non-slopeing top tube bike with fatter tires.

plonz 

This is some great information. I currently do my reach measurement from the seat/top tube intersect to the center of the stem's bar clamp. I just sort of "feel" any difference in saddle fore/aft due to seat tube angle and either change stems accordingly or accept the bike having a different feel.

What does the logic look like to calculate reach by factoring seat tube angle/down tube length/stack? I build a lot of these "calculators" as well and I'd like to give this one a try.

Bikerider007

For me it takes multiple rides. And will the bike be agressive or just casual group. Almost like moods. Standover is just the beginning. Saddle forward or back, saddle height, crank length, pedal, shoe, bar width, top tube, geometry. That's a lot to calc and variables are almost endless between bikes. I sometimes slide forward in the saddle for a change as one does between gears to relax a muscle. Does that mean bike does not fit? Maybe bike should be set up forward and I'll slide back? Hard to tell someone what their fit is.

crandress 

All great info, thank you! Not sure I have figure out whether I can get a larger frame in 650b or not, but great info. I was looking at a Peugeot PX-50 (650b) that was a bit bigger than I normally ride for a 700c bike, 21" or a little over 53cm versus my normal 51-52cm. I suspect it would be just fine.

palincss

My 700x32C randonneur is a 59cm, my 650Bx42 randonneur is a 60cm. Both are level or nearly level top tube bikes and both have the same stand-over height.

Bikerider007

Oh yea I forgot tire size. Most 650b guys run wider and larger tires. This would be one of gugies areas of expertise.

philbob57

So bike fit is complicated. Experienced riders differ on bike fit. Who knew?

My best c-t size is 52-54, C-T. I can ride a 60 cm bike with the seat slammed; I owned a 58 for a couple of years and came down hard once. That was enough. Standover is the most important measurement for me. YMMV.

The Golden Boy 

I ride 21"/ 53/54 Bikes. 22 1/2 and 56 are just a smidge out of my comfort zone when stopping. And any smaller I feel cramped.

bradtx

Chris, Maybe I'm dense, but all seat tubes are measured from the center of the BB shell to wherever the manufacturer deems correct. If I rode a 52 cm 700C roadie and wanted a 650B roadie, I'd look for one that measures the same as the 700C bike. Because manufacturer's specs are different, you have to measure the two bikes to the same place on the top tube from the BB. C-C measurments would have been a nice standard of measurement.

I'm short legged so standover height isn't a concern, I can cope. I usually go for the TT length, which is often measured C-C.

Brad