DIY bike fitting

(maybe not "bike maintenance" as such, but still "tinkering around with bike")

I was doodling around at home thinking how to dial in the fit on my road bike and wanted to measure the basic angles and lengths on my two quite different mtbs as well, to compare and see how much variation I can ride comfortably.

But you only connect with the bike at 3 points; hands, butt, feet. And if you use the knee-over-pedal-spindle and heel-on-pedal method to place your saddle, can't you assume that your saddle has the same relationship (height/setback) to your pedals, no matter bike? Assuming here too that the bikes are somewhat comparable, not completely upright bike vs. drops.

And if that is a given, you only have to look at the relationship between hands and feet. Since I have the same pedals and the same crank lengths on all 3, I used the crank center rather than the pedal as a stable starting point.

So I just measured the vertical distance between the crank center and the handlebars (actually I measured from the floor to both, then took the difference), measured the direct angular distance between the two and calculated the horisontal distance, the reach.

I have to doodle some more with the numbers I came up with (which won't be til next time I'm home with a cold, I suspect ;), but anyone have any comments on my reckoning? I'm hoping to come up with a kind of a comfortable range that suits me.

At the clinic I went to on sunday, they said the heel-on-pedal thing should make your leg almost straight on the road bike, and a little more bent on the mtb. Or the orther way round. :D:D:D

Hm. ;)

Oh, I forgot to say - I use the same mtb shoes on all 3 bikes too.

Heel on pedal is a very outdated methodology. With a huge variety of pedals and shoes available these days (with different stack heights), it's not a particularly accurate method to use.

Because of varying fork and seat post rake/angles, the most accurate way to set up multiple bikes would be to match the angle at the knee and hip at the DBC and 9:00 positions. This would be done with a goniometer.

Lorri

Quote:

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Originally Posted by velogirl

Because of varying fork and seat post rake/angles, the most accurate way to set up multiple bikes would be to match the angle at the knee and hip at the DBC and 9:00 positions. This would be done with a goniometer.

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My guess is that someone doing a DIY bike fit doesn't have a goniometer sitting around.:p:p

Quote:

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Originally Posted by divingbiker

My guess is that someone doing a DIY bike fit doesn't have a goniometer sitting around.:p:p

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Isn't yours in the drawer in the kitchen with the spatulas?

What the hell is a goniometer?

It's what you use to measure your gonies :D

Sorry. Joint angles. Like, how far are you bending at the hip, what is the range of motion of your knee, etc.

It's been 18 years since I first heard that word - I knew what one was but I never bothered to look up what the word actually meant - and it just clicked. "goni-" as in poly-gon. Duh.

heh-heh. I can see myself approaching my dh saying "Hi, honeeeeyyyy - would you like to measure my gonies tonight?" :D I've been waving measuring tape around all week as it is.

But my problem was really this: I'd like to compare the distance from where I sit to the bars (both vertical drop and horisontal reach) on all my 3 bikes, to see how different they are (or aren't). But measuring from the saddle is a bit tricky, as the saddles are different lengths, and I don't sit on them the same way. But can't I assume that if each saddle is fitted in the same way*, each saddle, or more precisely, my actual sitting point, will have the same vertical and horisontal distance from the pedal on each bike?

In that case I can use the pedal, or bottom bracket axle since all my cranks are the same length, as a starting point instead of the actual saddle.

(*in my case knee-over-pedal-spindle and heel-on-pedal-plus-a-little)

The measurements I've been using for transferring the setup from the professionally fit bike to the others:
1. center of crank to seat top
2. setback of seat measured as the distance the nose is behind the crank center, measured using a plumb line down from the seat
3. distance from the seat nose to the bars and to the hoods

I've tried to make them as close as possible and it's worked out pretty well.

If you have had a bike fit and you are just trying to replicate that on different bikes that have similar geometry, the way that MD suggests will work well because it will minimize the effect of seat tube angle which changes the knee over pedal and reach significantly.

If you have a willing participant, the best way to measure your joint angle is to do a brief film of you spinning on a trainer and freeze it with your pedal at dead bottom center (DBC), on a mountain bike or a road bike, that is when the crank is in line (at the bottom of the stroke) with the seat tube. It is not the same as true bottom center, that is the 6 O'clock position. Then you can use a compass to measure the knee angle. The knee angle should be 35 to 40 deg off of straight. Note that this is a different measurement than if you do the measurement statically. If you take the measurement by freeze framing while the person is actually pedaling the ankle movement changes the knee angle and makes it a larger degree of flexion. I like this movement better because is maximizes the fit while taking into account habitual ankle movements.