Design Challenge Progress

[Matthew D. Ignacious Budd]

1. A frame designed to handle the tight spaces and full contact rigors
of tournament polo that can accommodate a proper fit along a broad
spectrum of proportions and supports multiple drive train and wheel
formats. (Playing on Prototype Tomorrow at Bostons Open Sunday Pick Up
next to Harvard Stadium. It handles like a BMX bike that is better at
carrying momentum-Awaits proper fork)

2. A tiny road frame for a little lady barely 5'2" insistent on 700c
and all the touches that'll make it look fast. (At the local bike shop
where the customer works-parts and paint may get the works but it's
out of my hands)

3. Customer with a 29.5" inseam wants to experience the full benefit
of large wheels off road (1st iteration on the drawing board awaiting
sign off of design and dimensioning, parts and tubing order next week)

4. Forks

5. Head Badges.(Just cut one Already)

Good enough, mental exercise can take a back seat for a moment, I am
going for a ride. Enjoy the weekend everyone.

[Suzy]

Hi Matthew,

I've just built a frame for a 5'1" (155cm) woman, based around 700c wheels.

The secret was Dazza's cool 6 degree sloped lugs, which allowed us to
get enough standover height. The frame is 51cm effective top tube.

One of the cool things about making such small frames is that they're
uber light. With Dazza's lugs and Zona tubing, it's just 1625g.

http://www.littlefishbicycles.com/kristyn_pics/index.html

We built it with 165mm cranks (SRAM rival) which allow for a little
more toe clearance and allow us to get the saddle up a tad higher. 3T
ergosum handlebars are also really useful, as they come in a 38cm
width. We used a 17 degree stem to drop the bars down lower as well.

More pics are at my flickr site - http://www.flickr.com/suzy_j

Good luck!

Suzy

--
Suzy Jackson
http://www.littlefishbicycles.com

[mman...@fuse.net]

---- Suzy <suzyf...@gmail.com> wrote:
> We built it with 165mm cranks (SRAM rival) which allow for a little
> more toe clearance and allow us to get the saddle up a tad higher.

The toe clearance I understand, but how does a shorter crank length raise the saddle higher?

Martin Manning

[mallard]

Foot's farther down at BDC with a longer crank, hence saddle lower to bb or vice-versa ...

tom mallard

[mman...@fuse.net]

...if the BB height is fixed.

---- mallard <mal...@mallard-design.com> wrote:
> Foot's farther down at BDC with a longer crank, hence saddle lower to bb or vice-versa ...
>

[mallard]

Saddle is to the foot, closer to the bb for a shorter crank thus the saddle is higher off the ground.

tom

[mman...@fuse.net]

Yes, but if you set the BB height to maintain pedal ground clearance the saddle height from the ground is also the same.

[mallard]

Sorry for all this confusion on reference point ... great semantics to straighten out, I believe the statement was referring to where the saddle ends up in reference to the wheel so st is the critical measurement here if I got it right.

[mman...@fuse.net]

But ST length doesn't set saddle height.

---- mallard <mal...@mallard-design.com> wrote:
> Sorry for all this confusion on reference point ... great semantics to straighten out, I believe the statement was referring to where the saddle ends up in reference to the wheel so st is the critical measurement here if I got it right.
>

[Mark Bulgier]

Suzy wrote:
> > We built it with 165mm cranks which allow for a little more

> > toe clearance and allow us to get the saddle up a tad higher.

Martin Manning replied:

> The toe clearance I understand, but how does a shorter crank
> length raise the saddle higher?

Most people set the saddle height a certain distance from the pedal at the bottom of its stroke (the point furthest from the saddle). If you use a shorter crank, the pedal is higher at that point, so you must raise the saddle to maintain the same saddle-to-pedal distance.

Martin is maybe the smartest guy on this list, so I think we may just be using the words differently.

Mark Bulgier
Seattle, WA
USA

[Mark Bulgier]

Ah I see. Some emails got filtered as junk, and I didn't see Martin's explanation before I wrote my last.

Martin Manning wrote:
>
> Yes, but if you set the BB height to maintain pedal ground
> clearance the saddle height from the ground is also the same.
>

I was assuming the frame was already chiseled in stone and only the cranks were changing, but I agree with Martin if you're still in the frame design process.

My bad.

[mallard]

Hmmm, if you drop the bb to the short crank for equal road clearance you move the saddle closer to the wheel, thought the idea was to get the saddle away from a 700c wheel & short rider so keeping bb static, just my take.

tom

[mman...@fuse.net]

<blush> There are a lot of degrees of freedom, and if one considers that BB height is one of them, then the saddle height would be lowest with minimum pedal ground clearance (independent of crank length), and that would also maximize toe clearance since the BB center is below the axle center. Being that this is a small frame with relatively large wheels, the upper headset bearing is probably higher than desired to get the handlebar drop right, so a BB at minimum height might not be the best for that. This is a lugged frame, and so the angles may be constrained... My original question was asked because I don't see a direct connection between crank length and saddle height, which I assumed meant height above ground. Suzy might fill in the rest of the thought process and what compromises were chosen in order to make it work.

MPM

[Suzy]

The main constraint is indeed bar height in this case. By keeping the BB at a more normal height but using shorter cranks, we were able to raise the saddle 10mm over usual, thus giving us extra bar drop. An advantage is better cornering clearance. The 6 degree top tube also helps, to keep standover okay.

[mman...@fuse.net]

Okay, thanks for the additional info.

So, if the handlebar height is at its lower limit (due to HT length and or TT/DT tube clearance), then the minimum saddle height (in space) is set by that constraint too (for saddle-HB drop), and the BB goes where it needs to go to get the needed saddle-to-pedal distance.

Given that, and that pedal ground clearance is not an issue, the shorter crank length is really just buying extra toe clearance, which could likely be used for more optimum steering geometry.

MPM

[Wade Patton]

Gotta know when to say "no," that it's outside of your "sound design"
parameters. Lose a sale, gain some respects. my input is that you
don't want to become known as the guy who'll build _anything_, but it's
your call. good luck with 'em.

mas specifically: 1. don't axe me. 2. and you don't get to make any on
parts? no thanks.(looking fast? bwah) 3. get silly, make it a 36".
4.&5. carry on as before yo.