Talbot Frameworks PRJCT SLVLSS

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.

1 Attachment

• mcdonoughTT2.2.15.pdf

Aerofoil tubing below.

1 Attachment

If you don't like it for any reason....
Sounds incredible.

This will be epic ..
The direct mount brakes excite me the most .. esp the cockpit/forks

Crystal Palace's own Rob English®

Have to dig out my Scherrit drawing. This look like it might fit me.

Looks cracking. Cut to the chase. Colour scheme. What you thinking?

this sounds awesome!

I want to turn some custom shit pods

will you mislabel this a veronica moser?

Rob English is annoyingly very good at making bikes. It is a bit like the south park episode about the simpsons already doing everything, with the same moral: Just make it the best that you can.

Colour scheme shall be kept underwraps until Bespoked, but will be being attacked by my friend with the 1K/2K skills @hoops.

@dancing james I told a customer next time they poo over here they should come and say hi. Workshop is colder than outside due to 2 tonnes of metal acting as ice cubes. Hands don't work very well.

random thoughts:
There were some anecdotes/basic tests/internet wisdom(disclaimer!) that at bike speeds your chosen tubes will be less draggy with the thin end forward.(mimicking the front end of a longer airfoil)

also if the headtube is airfoil-shaped then go for more tube / less spacers. If the headtube is round make it as short as possible and use a positive rise stem (which becomes a very long oval shape to the wind)?

subbed because of what the fuck did i just read

@svendsvin, my internet wisdom says that 'tear drop' tubing such as the reynolds 'aero' tube available are best turned around, but there's a fair amount of evidence that a true aerofoil works best as you would expect.

Head tube is round.

Due to an ordering error, I have many rotor cranksets, so may as well use one of them. I shall not be using q rings.

1 Attachment

They dont look like 'on trend' 165mm ..

170mm fit me fine, I have gears, and I not really very 'on trend' as a person therefore to keep life simple I maintain 170mm over all bikes.

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.

I wouldn't anticipate stiffness being a big problem with the tubes you've listed, I'm 25kg heavier than you and my 753 lo-pro is very ridable. However, it'd definitely look at losing 60mm of that huge headtube and putting it back between the base bar and the elbow cups.

Headtube. What is slipperier, a smaller headtube with cups sticking out the top and bottom, or a bigger headtube with integrated cups?

For a plain circular cylinder, I'd bet on the external cups being better as that drops about 10mm off the tube diameter for most of its length. If you're going to be clever with the shaping, you can make an integrated headtube which is circular at the ends and an ellipse narrower than an EC headtube in the middle (have a look at a classic Cervelo P3 for a rough guide), in which case integrated will probably have more aeros.

I'd also have a look at making the wishbone the same width as the seat tube, that buys some stiffness probably with little or no aero penalty as it just moves the wake back behind the wishbone rather than behind the seat tube.

Brakes EE direct mounts, hidden.

Even if you hide them in the shed, they're still going to be shit for aeros. If you want to show off with direct mounted brakes, get TriRig Omega SV

1 Attachment

They dont look like 'on trend' 155mm ..

ftfy

huge headtube

@coldharbour has recently lost perspective on what qualifies as a huge headtube.

subbed!
what a great project. very rob english, but I'm really looking forward to follow the thread with all that knowledge there's gonna be thrown around here. a hell of a start already in that respect.

Wheels, don't know, deep.
Bars, don't know, possibly custom
Forks custom
Brakes EE direct mounts, hidden.

Nick it all off @Dammit's bike, I'm sure he won't mind.

Reckon you should look at Rob English for inspiration.

So, has anyone mentioned Rob English yet?

I hear he makes nice bikes.

Any idea how he is now after the crash. Plus i hope your build goes well but only after my dogs blxx cross.

the tubes on robs bike are far too skinny for me, and the geometry far too short distance TT. I need to be able to sit on the bike for 6-7 hours, so saddle perching is out.

That is a fantastic bike though. Total war.

Ah comfort bike, I was surprised at STR 1.54.

rep

:)