Thursday, April 20, 2006

Going Custom Part 5: Final Design

After some more email and phone discussion with Jim Kish we finalized the design:

ST length c-c 49cm
TT length (effective, c-c) 51.5cm
TT slope ~7.5 degrees
HT length 14cm
ST angle 73
HT angle 73
BB drop 7cm

Recommended stem length 11cm (anywhere from 0 degree to -10 degree, depending on desired bar position and spacers)

2 water bottles, ST bottle above front der clamp
TT brake routing, cable stops under TT
STI HT mounted shifter cable adjusters
Salsa dropouts
Alpha Q 44mm rake fork 1.125" steerer
27.2 seat post
68mm English BB shell
1.125" front derailleur clamp.

I plugged in exact HS stack heights, fork heights, and tube diameters into BikeCad

Jim never once said the bar is going to be exactly here... I think he has built enough bikes to know that you just can't know for sure until you build the bike up, given small differences in tire diameters, HS stack heights, fork rakes, fork heights, etc.....

So with this CAD drawing even though it is showing mm dimensions it might not be reality. But it will be close which is what stem spacers and different stem rises are for. The bike will look good with a stem between -10 degrees or -5 or even 0. That is a lot of variation for changing bar position.

The above drawing shows a -10 degree stem with 10cm of spacers. The Free version of Bike CAD does not give you the dimiension from the saddle to the top of the bar. But you can extrapolate it. Because it does give the Handlebar height above the BB (621mm). Add 13mm to get from the center of the bar to the top of the bar=634mm

And I know my saddle will be at 700mm and the seat tube angle is 73 degrees. So I can calculate how high above the BB the saddle will be in the vertical plane (sin73*700=669.4). My desired drop from the top of the saddle to the top of the Handle Bar is 35mm which we found in the bike fit.



What about reach?

I am going to use a Rocket V saddle just like on my two mountain bikes

the setback behind the BB is 50mm.

My road bike Serotta fit shows a reach from tip of saddle to center of bar of 470mm. This was measured with a Selle San Marco that had a set back of 28mm
So with the Rocket V it would be around 470+(50-28)=492.

The diagram shows BB to Bar of 439. Add the 50 for the saddle setback and you're at 489. Close enough for government work.

See what you can do with your time when you don't watch TV.

I am really really pleased with the final design. It has accomplished several of my original goals.
-The stem length is proportional to the top tube. Not too long or too short. 90-100 is too short, 120-130 is too long
-The bars are getting high enough w/o resorting to a)lots of spacers, b) a high rise stem
-The slope of the top tube is gradual and not super slopey like those Giant compact geometry
-It looks balanced, and also has a sleek-racer look with the negative rise on the stem.

So the design is finalized, and it is in his que. He needs to know color by 5/5/06. And if I want a fork painted he needs that too.

Oh man. Choosing a color!! Maybe it would have been better to go with a builder who's leadtime was 4 months as it probably takes that long to chose a color.

Stay tuned for choosing a color!!!


At 1:00 PM, Anonymous Anonymous said...

Jim likes to use longer than 'normal' chainstay length (at least he did on mine)...make sure you know this going it. Works great for me. Tell him to set up the rear brake bridge as high as practical with a normal-reach brake, so that you can run a 28c tire, if you want...extra clearance is always handy. Your front center is skinpy, but that's the way the Serotta 'classic' fit kit works. Your steering will be fast, but unsettled on rough pave'.


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