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Old 04-14-11, 10:34 PM   #1
jchabalk 
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Mixte 650b Build Question

Hi there, I'm putting together a Soma Buena Vista (size 50cm in graphite) for my wife.

She test rode a few sizes last weekend and the 50cm is the right fit for her. The bike she rode was built up with a 700c wheelset and there was a lot of opportunity for toe overlap at the front wheel. I was thinking of building it up for her with a 650b wheelset to get a little extra space and wanted to see if there was anything special i should look out for if i do that. (the frame is spec'd for 700c wheels.)

Outside of using a long reach brake i can't think of much off the top of my head, but I've always built using the "recommended" wheel size. I've found a couple of Buena Vista frames built up with 650b here:

This one's super-nice

And another; also very nice


The test ride(s) were "to kill some time," while we happened to be near the shop. It's for her birthday which is in a couple of months, (and I'm doing it on the down-low, so don't tell her)
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Old 04-15-11, 12:38 AM   #2
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From 622 to 584 there's still a 19 mm drop to deal with, but apparently that's doable with the right brakes on that frame.
It'll drop the bottom bracket closer to the ground which will increase the risk of pedal strike. Whether that's relevant or not in your case I don't know.
Some people would find the biggish gap between fenders(if you decide to use them) and the tires unsightly, unless you scrounge up some fender drop bolts or spacers.
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Old 04-15-11, 06:17 AM   #3
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Toe overlap is not a problem at normal speed.
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Old 04-15-11, 06:29 AM   #4
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Toe overlap is not a problem at normal speed
Even mid-size frames often have toe overlap too. My 55cm Litespeed has some even with my size 9 (Euro 43) shoes and the cleat set over the ball of my foot.

Last edited by HillRider; 04-15-11 at 07:48 AM.
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Old 04-15-11, 08:04 AM   #5
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To the OP: I am just nearing completion of a 58cm Soma Buena Vista 650B for my wife. I was inspired by yet another Soma BV 650B build that another forum member did (I'd have to find the link). 650B wheels do in fact work on this frame, but you need to have extra-long reach brakes (73mm). I went with Tektro R589 dual-pivot brakes. The only catch is that for the rear brake to reach adequately, the wheel must be positioned at the very front of the dropout. I was a little concerned about this since I'm running an 8-speed IGH on this bike, and IGHs place a huge amount of torque on the axle, something that derailleur gearing doesn't do. However, I've been told that it's simply not a problem, as long as the wheel is securely in the dropout.

Here are some pics (click to enlarge, and sorry for the crappy iPhone pics):







I also chose to go with really fat 650B tires (42mm Grand Bois Hetres) for their supreme comfort, versatility for riding on pavement, gravel, trails, etc, and amazingly low rolling resistance. These tires end up having the same overall diameter as 23mm 700c tires, so the reduction in toe overlap is minimal, especially with fenders. You might get an idea of this from my photos. However, since your wife's from would be significantly smaller, the toe overlap may be mmuch more pronounced than with the 58cm frame. If you go with narrower 650B tires, for example 35-38mm, you can then also go with narrower fenders and then you'll have a more significant reduction in toe overlap. But as mentioned above, toe overlap is usually not a big concern.

I'm a big fan of 650B conversions, as it allows you to have a much wider tire on a frame that otherwise doesn't allow it, while not affecting the bike's geometry.
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Old 04-15-11, 10:46 AM   #6
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I'm always sceptical of the need to convert bikes that already have good clearance to a new tire size. However, looking at the Soma Website, the BV can only clear a 28mm with fenders, and they actually recommend doing a 650B conversion if you want more rubber.
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Old 04-15-11, 11:20 AM   #7
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I'm always sceptical of the need to convert bikes that already have good clearance to a new tire size. However, looking at the Soma Website, the BV can only clear a 28mm with fenders, and they actually recommend doing a 650B conversion if you want more rubber.
Some people have squeezed 32mm 700c tires with fenders on a Soma BV, but yes, the main reason for 650B conversion is to lay down more rubber without changing the geometry of the bike. I'm getting 42mm tires on there with fenders.
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Old 04-16-11, 04:51 PM   #8
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thanks for all the replies! southpaw, that build looks great!

i'm probably going to go with a 32 (or maybe bigger tire). i'm concerned with the drop too. the bike we rode had a 165mm crank on it and didn't have a whole heck of a lot of clearance either. i've got to check the geometries and see if maybe the 52 looks a little different..
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Old 05-11-11, 12:57 PM   #9
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Here's a pic of the bike completed. With the 58cm frame and 42mm 650B tires, the BB drop isn't bad-- BB height is 265mm:

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