[clark]

Has anyone here seen plans for an inexpensive fork stiffness meter?

I use a 2004-5 110mm Drop-off Comp with quick release drop outs a lot. To make it stiffer I use a Skraxle (or an XT-skewer so tight it is not quick to release). But even still, there are disconcerting instances during rocky descents where the relationship between the bars and the direction the wheel is pointing is not what it should be.

In the interest of quantifying the benefits of 20mm drop outs I am building a fork stiffness meter consisting of a laser level that mounts as a stem cap. The idea is 1) put the rim in a well, 2) pull on the bars with a fishscale, 3) use the laser scribe line to make sure the bike is verticle, 4) use the laser scribe line to determine the amount of twist.

Budget is $50.

Please reply if you have ever tried something like this and can make things a bit more effficient (by providing detailed plans?).

 

[El Caballo]

Good project!

The tough thing is going to be keeping the bike still enough while taking two different measurements (force and no force).

I would invest in a second laser pointer (cheap). You could clamp it to the headtube or other part of the frame and aim it so that it intersects the scribe line from the laser level when the bike is in the jig and the handlebars are unweighted. Then you apply the weight/force to the handlebars and measure the distance between the pointer and the scribe line...this gets you deflection in one step and you don't have to worry about whether the bike moved in the jig between measurements.

 

[clark]

Thanks for thinking down this road a bit.

Yes that is where I am headed.

Looking into it, here is where I am at:

There are several items that contribute to handlebar wind up. By mounting a laser vertical scribe line projector on each element and projecting the lines onto a distant garage door one should get a series of spaced lines that show each element's contribution to wind up. (There is some memory of looking at electron energy levels in some lab in school )

The least expensive ones have a bubble level on the top that one has to adjust to make the beam level. I hope to use this indicator on the top of the stem to make the bike level as I pull with the fish scale. Here are the reference points planned (all tires at 40 psi):

1) Rim (level attahed to 3 spoke reflector pushed all the way to the lower rim)
2) Hub (level attached to middle of hub and brought into alignment with all others at start)
3) Stem Cap

I have some Mavic 819 and 823 wheels that are very stiff, both on hi-lo flange stout disk hubs. This method will illustrate the wind-up contribution of both the wheel and the fork/hub interface. I hope to compare the same fork with two different lowers so that the "crown/stanchion" flex will cancel.

Depending on the outcome I might end up with an undrilled Stan's Flow rim on a Hadely 20mm hub - trying to mimic Fulcrum road wheels.

... Right now I have no clue about the wind up contribution of each part.