Framebuilders - Long Crank Frame Question
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04-19-12, 06:22 AM
I'm having a custom frame built. Like pretty much everyone else I've been riding 170 mm cranks, but with my 34 3/4" inseam, I'm considering asking to have the frame optimized for the 190's that the various online formulae agree would be proportionate for me.
My question is this. Given that this is a once in a lifetime sort of investment, should I decide that I'd really rather be on shorter cranks, how much compromise would it be to be riding, say, 170's on a frame designed for the longer ones?
04-19-12, 01:06 PM
Jumping from 170 to 190 cranks is a huge change. Longer cranks do slow your cadence a bit, if you are a spinner from 30 years of using 170mm cranks then jumping to 190 cranks might not agree with your pedaling style without re-training your physiology and technique. At minimum, you should try riding 190 cranks on an existing bike, make sure that you really want to use them before commisioning a frame desiged around them. For most anything except touring/commuting, 190 cranks will require a higher bottom bracket so that you can still pedal through corners on a road bike and/or avoid off-road pedal strikes if this is a MTB or CX bike.
I have very close to your same inseam. I have tried 170, 175 and 180mm cranks for road, MTB and CX over the years. I think that 175 are a good compromize length for my physiology and technique. I could probably go longer for MTB (typically slower cadence) but I like the idea of having all my bikes with same crank length so there is not to much of a physiology change needed when switching between bikes.
04-19-12, 06:14 PM
"Given that this is a once in a lifetime sort of investment" I feel the same as Gary Jay, absolutely try'em before you commit. KHS makes a Lenord Zinn designed bike for tall people that comes with 190s, maybe see if you can ride one of these even if its only on rollers in their store. Even then the short time you ride them would'nt give you the full story. Were talking 20mm(.8") difference, so the bb would be that much higher for the same clearance on a bike made for 190s. I think the dialog for very long cranks(over 180s) is open for discussion as far as benefits go, Zinn's advertising talks about them like the best thing since sliced bread, other folks not so much(i'm in the latter category). I have a 39" inseam(yep, pretty tall guy) and I have ridden 175s or 180s for over 40yrs. At this stage I wouldn't consider going for a set over 180s but that's just me. If you could borrow some 29er(700c mtb) wheels with a taller, fatter profile to fit your current frame it would raise your bb about that 20mm so you could see what a shorter drop would do to the bikes handling. Another thought; you probably know someone who rides 180s, see if you could put them on your bike and give it a try. Maybe have the frame designed for 180s(which is how my frames are designed) which is a compromise, but it would be a shame to discover 190s are not for you after the fact and end up with a bike that's not right for you.
04-19-12, 06:17 PM
Thanks, that was really useful feedback. Of course, test riding a set of 190's is easier said than done. I've never been much of a spinner, and nowa days mostly mosey along rural roads, so that's why I was thinking the extra leverage might come in handy. Plus, the proportional idea seems to make sense. In most everything else, tailored to fit normally ends up working out better than one size fits all.
04-19-12, 06:31 PM
35.5" inseam and ride everything from 170mm to 180mm.
get a frame that fits, put some 175's on it and don't worry about online formulas.
04-19-12, 10:03 PM
There are certain things that have to be customized to the body for fit reasons. There are other things that are lever arms, and if you are already on the large side you probably don't need more leverage.
Think handle bars. Maybe they need to be wider for a guy who is 6'6" to fit or be comfortable, but does a guy that size need wider bars to muscle the bike, compared to a person 5'6"? He is already stronger.
Think golf clubs, a big guy needs them fit to him, but he already has a bigger motion, and more power, would he necessarily want longer clubs?
04-20-12, 01:57 AM
Just got my custom Gunnar Sport done - with custom 210's... I'm 6'8" with a 38" inseam. Given the info you've provided, 180's might suit you. Nice thing is those are out there by major mfgs. I have a Cannondale sporting Dura Ace 180's, for example.
My impression us far is that the cranks definitely feel different and I feel like I have better power/torque application. More of my leg feels like it's part of the conversation now.
Keep in mind that opinions vary on the long crank topic. It made sense to me, so I went for it. We raised the BB up on the frame geometry, but also kept it more or less sport touring-longer chainstays etc.
Let me know if you have any questions. The KHS Flite 747 seems like a cool way to get in the game if the rest of the frame fits and 105 fits the bill...
04-20-12, 03:12 AM
if i was tall enough to consider this, i would look at what extraordinarily tall pro cycling athletes use. track, road and MTB. i figure they are willing to do just about anything to gain an advantage, so they and their professional trainers and coaches have probably already explored this, in detail.
OTOH, raising the BB 20mm ain't much... i wouldn't be surprised if the BB's on most cyclocross frames are not 20mm higher than those on road frames.
05-08-12, 12:34 PM
I just took delivery of a Flite 747 last week...beautiful bike. Switching from a Soma ES with Campy 175 Cranks to this was a definite change. I teach spin classes and coming back to a spin bike after the 200mm cranks felt like siting on a trike!
The only mod I am making to this bike is the seatpost. The one that comes with it is 300mm and I am getting a Thomson 410 mm so I have a little more leverage with the cranks. Hoping to take it out for a longer ride this week.
05-08-12, 01:33 PM
Zinns shorter formula indicates 184. So 185, or 180, I would probably go for the latter on a touring bike. They have tons of gears, and I don't really feel like walking further to get the same distance. It's like lengthening your stride, but not going any further.
Neither of those is going to affect your frame fitting for a touring bike, pedal strike should never be an issue.
"OTOH, raising the BB 20mm ain't much... i wouldn't be surprised if the BB's on most cyclocross frames are not 20mm higher than those on road frames."
You are certainly correct that raising the BB height 20mm from the low end is not all that much. That is in the current range which is about 10.2-12", but anything in the upper 11s is rare.
On the other hand, Sachs who is a master XC frame builder specifies 85mm drop, and that works out to the lower end of the touring spectrum, contrary to what you might think. But might also set your mind at rest as to the need for heroic amounts of pedal clearance. In other words even with a little raise, you could probably still stay under 11" if you wanted to. And you could probably do no raise at all for most loaded touring.
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