You are reading a single comment by @BareNecessities and its replies.
Click here to read the full conversation.
London Fixed Gear and Single-Speed is a community of predominantly fixed gear and single-speed cyclists in and around London, UK.
This site is supported almost exclusively by donations. Please consider donating a small amount regularly.
BareNecessities
Having done almost all of my riding on rollers for the last year, I feel that my group riding capabilities should have diminished enough to take up triathlonism.
This is obviously a good excuse for a new bike, and in the spirit of my bikes, I am setting a time limit for it to be done, which will be Bespoked.
Having chatted with @scherrit (the Bike Whisperer, best fitter in the business) quite a bit, I have come up with the below drawing. This is only optimum as far as fit goes (assume stack and reach are fine), everything else is up in the air.
I do not and will not have access to a wind tunnel, so the plan is to stick to some overall rules of aerodynamix, and see where we get. These rules will be:
As small a frontal area as possible. Slightly problematic, as I am wider than I am tall, but anyway...
Ensure I fit on the bike in as slippery way as possible. It's no use having a bike thats as slippery as an eel on its own, if it makes me sit like a big sale when I'm on it.
Within reason be unconcerned with weight, up to a point. If you're weighing it, you're doing it wrong.
My scientific knowledge is very limited, and amounts to C/C in joint sciences GCSE, and a distrust of things I can't see, but others tell me are there. I am however willing to put these prejudices aside for this project. @mdcc_tester has been very generous with his knowledge, and I am blessed to have the walking brain that is @moth now working with me, so should be able to overcome my luddite ways.
As far as the design is concerned:
Tubing will be aerofoil, T45 aerofoil to be precise. T45 is like cool 4130, it's made in Britain, and is better than 4130 because of this. It is plain gauge, which is fine as we don't care about weight, and because as a working rule of thumb (@mdcc_tester steps in to itemize why I'm wrong) the tube is only going to be marginally stiffer than an equivalent tube with the diameter of the aerofoils thinnest axis, so in the case of the DT 24.8mm. Wall thickness is 1.2mm.
Full profiles of tubes are:
DT 53 x 24.8/ 1.2mm T45
ST 37.2 x 24.8/ 0.9mm T45
TT to be confirmed
Chainstays TBC
Seatstays 10mm /1mm 4130
BB PF30
As can be seen in the CAD drawing, I have got a slope on the TT. From an aero point of view, as far as I can tell, the best thing would be the TT to be parallel, the more slope on the TT, the more TT has to cut through the air. However, sloping the TT allows me to stiffen up the front triangle, which I fear is going to be an issue with the size of tubes I will be using, my weight (73kg) and prodigious power. Stiffness is also the reason I have specced a PF30 BB.
Headtube. What is slipperier, a smaller headtube with cups sticking out the top and bottom, or a bigger headtube with integrated cups? Again, undecided.
Componentry.
Groupset will be the infamous Talbot 7970 Di2 groupset, mainly because it is here, 10 speed means cheaper wheels, it's wires are all cut up, and I want to turn some custom shit pods for the extensions, which is only really possible with the doorbell esque first generation of Di2.
Wheels, don't know, deep.
Bars, don't know, possibly custom
Forks custom
Brakes EE direct mounts, hidden.
Also, will be building this almost exclusively in the evening, so will probably make many mistakes.