brianbaylis@juno.com view: flat | tree
Subject: Re: [Frame] 650c track geometry
Date: 4/4/2011 9:12:22 AM
List: Framebuilders


Suzy,

I have built and raced just such a track bike. I raced it during my last=
 season of track racing in 1994; and it was in my opinion the best track=
 bike for all around racing that I have ever built for myself. I normall=
y ride a 700c 49 or 50 cm c-t track bike and have made at least a dozen =
for myself in the past 40 years. I opted for a 650c track bike after abs=
olutely loving the 650c road bike I built. =


I will have to look up the plans to give you all of the numbers, as I do=
n't recall everything off hand. But the seat tube is 47.5cm c-t, the top=
 tube slopes down 2 degrees, and the main tubes are all .5mm Columbus 1 =
1/8 record tubes. The chainstays are also Columbus Record and I built tw=
o forks for it. One with Columbus "AIR" fork blades and crown, and one s=
et with a traditional 22.2mm round track blade and old English form crow=
n of some sort. The other dimensions I will have to look up.

This frame was tested by Damon Rynard back when he was doing research fo=
r Bill Holland as to the relative stiffness of all sorts of bike frames.=
 He did a TON of tests and gathered some really interesting and useful i=
nformation. This frame was rated astonishingly high in stiffness in bot=
h the main triangle and the rear triangle. Even Damon was amazed!

Regardless of all that, this bike was not only a TOOL on the track, it w=
as for all intents and purposes, a WEAPON! There was not a rider small e=
nough to get a good draft on me, even a person my size and a 700c wheel =
bike would struggle, and BETTER yet, complain! The down side is, and I h=
ave not revealed this until now since I don't race anymore, is that you =
can not draft really tall riders that well. So I was careful where I pos=
itioned myself in the lineup and I didn't chase solo tall riders very of=
ten. The combo didn't work well and no one benefited from that situation=
. For small people a 650c wheel bike is a gift from heaven in my opinion=
. But many refuse to do the logical thing for fear of tire limitations. =
Silly, but true. the advantages FAR outweigh that small limitation, and =
the selection is getting better and has bee pretty good for quite some t=
ime. Especially true if you run tubulars, which is especially great for =
a track bike. That's another advantage, the wheel itself. I used 24 hole=
 high flange hubs on Sun tubular rims, cross 2 pattern, tied with dental=
 floss and glue. Amazing wheels!

If you want to know the rest of the numbers for my frame, let me know. I=
'll sort through the plans.

Obviously you are on the right track, no pun intended. 650c wheel track =
bikes are the BOMB for racing.

Brian Baylis



---------- Original Message ----------
From: Suzy <suzyfromoz@gmail.com>
To: framebuilders <framebuilders@googlegroups.com>
Subject: [Frame] 650c track geometry
Date: Sat, 2 Apr 2011 20:56:20 +1100

Hi guys,

I'm designing a track frame for a shorter person (5'1" or
thereabouts). I just did her a roadie, with 51cm tt-eff and 49cm ST
eff (key to the design was Dazza's 6 degree slope top tube, which
makes the actual seat tube 46cm c-c). I used 74 degree seat tube and
71.5 degree head tube, which when combined with 45mm rake forks makes
for 63mm trail, which is a tad on the slow side of neutral.

The main issue with the 700c wheels is not being able to get the bars
down as low as we'd like - the rider is an athletic 18 year old, and
she's quite keen on a decent amount of drop from saddle to bars.

So I'm thinking of building her a track bike, and the obvious solution
is to base it on 650c wheels. That makes for a whole bunch of
different compromises. I set the top tube length to 49cm, seat tube
length to 46cm, and went for 37cm chainstays. With 74 degree seat
tube and 73 degree head tube, most of the lug angles (with the
exception of the chainstay to seat tube, which is 68 degrees) work
quite well. The best bit is that with a 90mm deda newton track stem
(67 degrees) I calculate the bar drop to be a healthy 90mm.

So anyway, some questions. Firstly 650c wheels change the trail, for
the same set of angles and rake. What would be considered "neutral"
trail for 650c? Is 73 degrees a reasonable head angle for a 650c
track bike (it's supposed to be an all-rounder, so I'm going more for
a mass-start geometry than a sprint geometry). Does anyone have any
working examples they'd be willing to share?

Cheers,

Suzy

-- =

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


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