howdy.

are there some road or cyclocross frames that just shouldn't be ridden as fixed gears by some people?

there are obviously a lot of big, strong people who have converted frames of various materials and configurations into fixies without damaging themselves or their bikes.

but my salsa las cruces conversion, which i never noticed flexing while riding roads geared or single speed, is just all sorts of bendy since i went fixed a few days ago.

do physics and good judgment suggest limitations on using a frame for something different than its intended purpose? should a scandium cx bike be ridden fixed by someone who's 225 lbs. and maybe a bit stronger than average? or am i just needlessly nervous because i have zero fixed-gear experience?

any insight is appreciated.

'zero fixed-gear experience' is most likely the culprit, not the frame. As you get used to riding fixed, you will ride much smoother. Also, you may notice more existing flex in your frame when riding fixed (not because of) than when you are able to coast because you tend to have more weight on the saddle under more situations.

I'm not a clyde nor do I have a scandium frame, just ridden fixed for a couple decades, but the above may be complete BS

I will chime in as fellow clyde that rides fixed (2+ years now). I know I put more stress on a frame when riding fixed than geared just because of uphills. I am riding a normal gear (low 70's), but still need to get out of the saddle to make it up the hills with my extra padding (270lbs btw). I don't know if frame flex would be more noticable fixed than SS. I only SS offroad and that bike is steel and really doesn't flex much. All of my fixed gears except one fixed MTB are steel frames. Steel is real. Personally, I would swap parts over to a steel frame and see how you like that.

I rock my bike much more riding fixed than free. Mostly this happens because I use my gears to keep my cadence up and seldom, if ever, hammer the pedals as hard as I do climbing on my fixie. I suspect what your're feeling is more about rocking the bike than actually flexing it, especially if you're cx bike has a high bottom bracket. Pushing and pulling the bars on a tall frame like my SP Marinoni sends my top tube from thigh to thigh and it's not particularly flexy.

When I was riding my steel MTB frame as a fixed gear, I noticed tons of flex around the bottom bracket. Oddly enough it was most noticeable on downhills when I was close to spinning out. Didn't really hurt anything, just an interesting sensation.

That's the only bike I've noticed that with. The old Schwinn frame is hell for stout, and the Cross Check doesn't really flex much either.

Did you get a new wheelset to go fixed? If so then are you sure that it's not wheel flex you're feeling?

One difference between riding fixed and riding free is that it is harder to unweight your bike when you come across potholes, curbs and other obstacles. If you have trouble getting the hang of negotiating rough terrain on a fixed gear and end up just ploughing through everything, that is going to have an impact on your bike.

Also, you are going to be mashing more than you would on a geared bike and spinning faster than on a geared bike. Riding like that could flex the frame more.

Finally, you are going to pedal a ton more revolutions which will rack up stress on a Scandium frame faster than if you rode it geared.

those are all really good points.

i notice the flex most often in the bottom bracket while doing track stands at stop signs and lights.

potholes, hammering up hills, spinning out (or resisting) on downhills--all that stuff feels super stiff and solid.

but i can actually watch both the cranks (180 mm race face on a square-taper BB) and the frame's tubing flex while standing on them.

i'm not worried it will break, just curious.

it'll be gone soon anyway. i finally learned how to measure it properly, and its dimensions explain why its always felt far too small for me.

anyone interested in a slightly scuffed and scratched 56 cm las cruces frame with a new cross-check fork? $350 or bo.