Frame not suitable for 70" fixed gear?

I was thinking about the stress on the frame being the same regardless of gearing. Obviously parts before the gearing (bad expression I know) like pedal spindles, or the guilty chainring bolts, would experiance more, the higher the gear. Looking at the situation simplistically that is (my favourite way).

(ED: good point about power peaking over the pedal cycle)

All my frames creek, I thought it was by design to warn peds I'm coming?

That's why spinning and fixed gears are good - it forces you to be smooth with your power delivery!

But, going full circle, that still leaves going up hills as a problem. I think most people have trouble spinning a 70" gear up 10%+ hills. I know I have to resort to 25rpm and wrenching on the bars for that full upper body workout. If you've got gears you can change down and spin. If there's any flex in the BB then fixed and hills will find it.

FWIW my BB occasionally creaks and groans, usually starts about every 2000km. If it doesn't go away within 100km or so then it's usually solved by removing and refitting the BB; no need to do anything with it, just removing it and fitting it is strangely enough. Note that just removing the cranks and refitting them (without removing and refitting the BB) isn't enough to fix the problem and the BB cups weren't loose either.

But, going full circle, that still leaves going up hills as a problem. I think most people have trouble spinning a 70" gear up 10%+ hills. I know I have to resort to 25rpm and wrenching on the bars for that full upper body workout. If you've got gears you can change down and spin. If there's any flex in the BB then fixed and hills will find it.

Using my terrible terminology. The BB area is 'before the gear' and therefore feels the silly amount of torque created by pulling on the bars, forcing cranks and generally giving it some body english.

I ride 78gi in Norway, up some serious hills, and fear that at some point something will give. I just hope its my cleats, as they are the cheapest part of the 'before the gear 'area.

I was thinking about the stress on the frame being the same regardless of gearing.

No. Think about where the loads of the frame are coming from. Ok, there's your weight and the vertical loading coming through the wheel/seatpost/handlebars. But there's also a twisting moment coming from your pedals which primarily acts on the bottom bracket. (you've also got your handlebars giving the same kind of moment). This bottom bracket load comes about because you're applying force to the pedals, and this force is at a distance sideways from the bottom bracket. This causes the bottom bracket to twist, and this resistance to twisting (bottom bracket stiffness) is provided by the down and seat-tubes, and also the chainstay.

More force/torque, more frame load. Big strong sprinters need frames with beefed up bottom brackets and it's not unheard of for frames to fail at the bottom bracket area.

But, going full circle, that still leaves going up hills as a problem. I think most people have trouble spinning a 70" gear up 10%+ hills. I know I have to resort to 25rpm and wrenching on the bars for that full upper body workout. If you've got gears you can change down and spin. If there's any flex in the BB then fixed and hills will find it.

Point 1: You can be pedaling at 50rpm and still be smooth with your power delivery.

Point 2: For a given gear ratio, power, cadence, and speed are linked. You can either produce the power to go up the hill at a certain speed or you can't - just because you're going slow doesn't mean you're pushing harder (in terms of torque) on the pedals. In fact it's the opposite, the person going faster (and necessarily at a higher cadence is pushing harder) because they've got to generate extra power to overcome speed-dependent losses (aero, rolling resistance, etc.).

Do the sums if you're feeling inclined! Essentially, because most of the power is dependent on rpm (the speed at which you go uphill) and torque is dependent on (1/rpm), rpm cancels out.

Courant

No. Think about where the loads of the frame are coming from. Ok, there's your weight and the vertical loading coming through the wheel/seatpost/handlebars. But there's also a twisting moment coming from your pedals which primarily acts on the bottom bracket. (you've also got your handlebars giving the same kind of moment). This bottom bracket load comes about because you're applying force to the pedals, and this force is at a distance sideways from the bottom bracket. This causes the bottom bracket to twist, and this resistance to twisting (bottom bracket stiffness) is provided by the down and seat-tubes, and also the chainstay.

More force/torque, more frame load. Big strong sprinters need frames with beefed up bottom brackets and it's not unheard of for frames to fail at the bottom bracket area.

I see what you mean.

TBH I was thinking about my last post, and realised that the frame is connected to the drive both before and after the gearing. Especially if, like you say, you consider handlebars etc.

Like I said its monday, and the brain is just starting up for the week.

I ride 78gi in Norway, up some serious hills, and fear that at some point something will give. I just hope its my cleats, as they are the cheapest part of the 'before the gear 'area.

Knees, they're the most expensive part! Look after those.

Knees, they're the most expensive part! Look after those.

Tis a good point.
I had planned on gearing down a bit, but cycle mostly out of town (ie dont need to stop much), and 78gi is a great gear for cruising at speed. Can't even cycle up my own driveway though.