Current Projects chat and miscellany

Odd things happen in that gap, which is why Look designed the new 596 Triathlon bike to have a gap of about 12mm, a counter-intuitive decision in the light of a decade of ultra close wheel cutouts. The reason for the frame to follow the line of the tyre as closely as possible is to make the seat tube act as the leading edge of an aerodynamically integrated body including the rear disc wheel - this works really well as long as the wheel isn't turning, which is why the likes of Cervelo etc. provide horizontal dropouts and adjusters to allow you to optimise the gap. Even with the disc spinning, the bulk flow over the whole system stays nice and smooth, and you get low drag, as long as you only measure the drag force pushing backwards on the bike. Traditional wind tunnel tests don't measure how much power is used to actually keep the wheel spinning, and this is where it gets interesting, and where Look made a discovery which has influenced some track teams to start running bigger gaps between the rear wheel and the curved seat tube.

Essentially, what happens is that the rear tyre boundary layer gets pulled into the tight gap and is then acting as a thin shear layer; the bit by the tyre wants to keep up with the tyre, the bit by the tube wants to stay still, and as any fule kno, the friction in a layer a fluid being sheared between two surfaces goes up as the thickness decreases.

As a result, increasing the gap a little bit makes the drag pushing on the whole system a tiny bit bigger, but the relatively large increase in the thickness of the shear layer (about a 4 or 5 fold increase in thickness compared with typical "tight" clearance) makes the power required to spin the wheel a tiny bit smaller. One of those tiny bits turns out to be a little bit bigger than the other if you judge the increased gap just right, and the design becomes an act of balancing one set of drag against another. The same effect also explains why some of the latest time trial frames have more clearance around the tyre as it go through the fork crown than was fashionable as recently as a few years ago.

Yeah I was going to say that.

:)

Interesting, thanks.

Not so much a current project, more "soon to be current" but i am having talks with Ricky @ Feather Cycles about a Lo-Pro build..

Exciting times ahead.!!

nuknow, that panasonic is lovely!

Not so much a current project, more "soon to be current" but i am having talks with Ricky @ Feather Cycles about a Lo-Pro build..

Exciting times ahead.!!

Shweeet.

Awful pictures but here's my latest WIP.
Cannondale Capo (58cm) - Dura Ace/Mavic Wheels (rear not shown in pictures). Carbon front end. Will be used for fast summer commuting and with a seperate set of forks a little track racing later in the summer. Still needs bar tape, rear wheel fitted, time atac pedals (for road use), post and spesh toupe saddle.

saddle angle, desticker wheels, remove valve caps, align tyre logos, tape bars. Job done. ;)

Nuno - that Panasonic is bonkers. Love it!

that panasonic is amazing!

hey Chris - might see you tomorrow. Look forward to seeing this bike.

I'm probably selling the Panasonic very very soon, can't justify owning 5 track frames.
Will keep everyone up to date. (it needs DT repair though).

picked this up from soperRiva last week and it's going to be a labour of love

http://img691.imageshack.us/i/dscf1695u.jpg/
http://img260.imageshack.us/i/dscf1699m.jpg/
http://img691.imageshack.us/i/dscf1700h.jpg/

frame's a bit of an oddity as Air tubing and those pencil seat stays make for a whippy rear end, inefficient power transfer for track sprints, yet it has track ends that look OEM. Time trial use, early aero bars?

anyway:

frame to be stripped and painted (thinking 80's pearlescent yellow)
new Columbus Air fork with possibly chromed crown, frame coloured legs, chrome ends
Basso decals
refinish notched seatpost
polish tange levin headset, reseat lower cup
store/move on concor seat and 979 dural fork

as to the chainset I'm weighing up 600AX over Campagnolo or Mavic

optional front brake to match

undecided on stem and bars

timespan:, hmm, a year to eighteen months :)

Farckin sweeeeeeet

Columbus seatpost too

I think it'll look good raw, but that's just me.

Air tubing and those pencil seat stays make for a whippy rear end, inefficient power transfer for track sprints, yet it has track ends that look OEM. Time trial use, early aero bars?

What year is it? Possibly a pursuit bike from the days before lo-pro became ubiquitous, or maybe people just accepted much less stiffness in the olden days. A Look 496 is probably 5 times stiffer than the old 531 Track tubeset, but people didn't used to wobble round the corners even so.

year? who knows, between 1980 and 1990? no numbers except for size on underside of BB shell.

when i disassemble i'll see if there's a circular stiffening tube inside the down tube as i believe this was used later to reinforce.

probably spot on with the pursuit intent, aggresive stem and pursuit bars?

raw steel finish, oh no!

Just picked this frame up

Bought this wheel and was going to make it into a fixed but it may look ok on the Jackson nice Ultegra hub and Ultegra cassette

or i could use a set of those Giant 12 blade things.

Finally got my cranks off to reveal a 7400 Dura Ace BB which I'm quite happy with. Problem is I have no idea what cranks to use to get a decent chainline, transmission database doesn't seem to be much help.

What hub and BB spindle length you got, S?

Dibs on the Bob Jackson.

probably spot on with the pursuit intent, aggresive stem and pursuit bars?

No, drop bars for an early 1980s pursuit bike with full sized front wheel, see first pic in this thread http://www.lfgss.com/thread16620.html

What hub and BB spindle length you got, S?

Unbranded formula hub, BB axle length appears to be 110 but my measuring methods are shit.

Most track chainsets should be fine then. Just get DA to match your BB.

Formula give 42mm chainline, and as far as I know 111mm does too.

Most track chainsets should be fine then. Just get DA to match your BB.

Formula give 42mm chainline, and as far as I know 111mm does too.

Sweet. I'd love a DA track chainset. However wallet contents < DA Track chainset :(

Save up!!

sell stuff and save up, time is your friend after all.

Ed, speaking of time, you been using it to look for that strap?