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Re: The bike that slowtwitch built [LostNTransition] [ In reply to ]
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LostNTransition wrote:
This is the first time I've seen brakes out on the aero bars (you don't have anywhere else to put them though).

It seems like it might be a bit hard to stop, not that you would want to when riding that beauty anyway.
Natascha Badmann's bike had no base bar and a twist brake on the aerobars I believe?

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https://twitter.com/smaryka
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Re: The bike that slowtwitch built [23] [ In reply to ]
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Lovely! But replace the fork with a Blackwell Time Bandit.
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Re: The bike that slowtwitch built [23] [ In reply to ]
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Very cool. Would love to see some numbers on this thing :P

My Blog - http://leegoocrap.blogspot.com
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Re: The bike that slowtwitch built [leegoocrap] [ In reply to ]
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Good grief, what an utterly awesome machine.
Beauty & danger in equal measure.

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´Get the most aero and light bike you can get. With the aero advantage you can be saving minutes and with the weight advantage you can be saving seconds. In a race against the clock both matter.´

BMANX
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Re: The bike that slowtwitch built [Herbert] [ In reply to ]
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Herbert wrote:
Oh my. Holy batman.



Not quite the same, but to some degree the middle part of the bike reminds me of the old Trimble frames. I couldn't find any images around google that are that great, but here is one:


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Re: The bike that slowtwitch built [23] [ In reply to ]
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It's missing lights:

First frame with a negative CdA? Awesome work. -J

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Life is tough. But it's tougher when you're stupid. -John Wayne
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Re: The bike that slowtwitch built [Herbert] [ In reply to ]
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I love the fact that the door in the background needs to be painted and the lawn has been completely neglected. Makes me feel a little less guilty for blowing off similar household duties to train.

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Dale Stephanos (Formerly PappaD)

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Re: The bike that slowtwitch built [PappaD] [ In reply to ]
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No need for a water bottle,,

BECAUSE IT'S SO FAST!

I would love to see this thing moving.
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Re: The bike that slowtwitch built [23] [ In reply to ]
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The only thing that bike needs is a giant ST logo on the rear disk.

And a front disk, just for kicks =).

Well done. Seriously, that thing looks like a beast and would turn a lot of heads at a TT or tri.

Long Chile was a silly place.
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Re: The bike that slowtwitch built [23] [ In reply to ]
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very cool!

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Official Polar Ambassador
http://www.google.com/...P7RiWyEVwpunlsc2JtQQ
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Re: The bike that slowtwitch built [23] [ In reply to ]
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Impressive. What's it weigh?
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Re: The bike that slowtwitch built [23] [ In reply to ]
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wow. apologies in advance, but there is virtually nothing aero about this bike. the wheels and the fork perhaps, but the frame is an unmitigated disaster from the top tube on down. the top tube should be ovoid anywhere rear of the head tube airfoil - full stop. and if the attempt here is to develop negative drag, airfoils of no more than 15%-20% should be considered - e.g. NACA 0015 or 632-015 - or even better, truncated Kammtail airfoils (e.g. a truncated NACA 0020 with a 3:1 aspect ratio) which will be much more forgiving in crosswinds, yet just as slippery and still generate forward thrust. furthermore, the rounded front on the head tube and elsewhere on the bike likely experiences complete flow separation well before its apex (at about 82 degrees) creating pressure drag and turbulent airflow. moreover, the undulating sides of the frame are simply creating skin friction and/or flow separation and pressure drag - you'd be better with nothing at all. and that tail? sorry.

the best thing you might be able to do to repair some of this is install 'trip wires' -- around 0.5mm-1mm thick should do it - the entire vertical length of the head tube and anywhere there's a forward facing tube surface. place the 'trip wires' on either side roughly 30-45 degrees away from center axis -- this may at least re-attach the airflow to the sides of the frame.

the other option is to rip it all out and order truncated NACA 0020 foam cores from someone like Flying Foam (http://www.flyingfoam.com) and then cover them with a fiber composite layer.

then of course there's the reduced trail in the fork by going 'funny' with the 650c on the front. no issue going to a 650c, but important to go with a 650c wheel in the rear as well. that'll drop the bottom bracket to just above the UCI/USAT minimum of 240mm (hey, you're already about half-way there...), and by re-introducing the correct amount of trail in the front fork, you'll also get some control back (all the more so since the bull bars have been cut off...)
Last edited by: chadman_98126: May 14, 13 0:18
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Re: The bike that slowtwitch built [chadman_98126] [ In reply to ]
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and just realized that's probably a 650 fork with that 650 wheel, correct? if so, the front of the frame has already been dropped around 51mm and the trail on the front fork will be just about shot.
Last edited by: chadman_98126: May 14, 13 6:20
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Re: The bike that slowtwitch built [23] [ In reply to ]
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Holy shit I love it.
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Re: The bike that slowtwitch built [chadman_98126] [ In reply to ]
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Going from a 368mm 700C fork to a 340mm 650C fork I get a change in BB drop from 70mm to 84mm for the Felt Geo. HTA from 73 to 75.1. Trail from 60 to 48.

I agree with all your points, I'm just pointing out that the geo change isn't quite as bad as you think.
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Re: The bike that slowtwitch built [cyclenutnz] [ In reply to ]
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cool
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Re: The bike that slowtwitch built [cyclenutnz] [ In reply to ]
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plus another 25.5mm drop in the fork for the smaller 650c wheel... (so a quick SWAG puts the trial in the 36mm range or less. twitchy.)
Last edited by: chadman_98126: May 14, 13 6:27
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Re: The bike that slowtwitch built [chadman_98126] [ In reply to ]
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So maybe the Trimble comparison is appropriate?
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Re: The bike that slowtwitch built [chadman_98126] [ In reply to ]
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First off I would like to say thank you. Although the compliments make me feel warm and fuzzy, the reason I posted it here is because slowtwitch is notorious for being brutally honest and over analyzing every aspect. There are alot of smart people here with constructive criticism.So thank you for being first.

The bike was designed for zero degrees of yaw. I have a feeling it will stall dramatically at a certain increasing yaw angle. In my original post I said sub 10 yaw assuming that it would be such a bullet at angles approaching zero that it would be faster avg out to ten still. Pure speculation. From a yaw perspective the oviod top tube makes perfect sense and is going into my mental data base.

As far as far as the airfoils go the reason they are so deep is so that the diminishing angle is minimal, should be deeper more effective head on airfoils than any bike. You cant make a bike that is best at everything, this one uses super deep airfoils at the expense of catching more crosswind. You are correct saying Kamm tails would help this, but you are wrong on saying it is just as slippery. A Kamm tail is merely a compromise on a longer more optimized full airfoil and is NOT faster at discussed yaw. Its a specialized bike and not for an ag going 17 mph in brutal crosswinds.

How else would you make a leading edge of a nosecone ( practically the only vertical tube)? all bikes i know of have a rounded leading edge. This is more effective at yaw. A pointy nose would be terrible at anything other than zero yaw, but awesome at zero. I compromised creating a reduced rounded one inch nose tapering up to the peak with of the headtube. creates a nice long oval shaped nose.

the tailbox and bottom bracket box only smooths airflow by reducing frame gaps secondarily. They theoretically use the splitter effect along with the disc wheel to reduce clashing turbulent wind from the body. Yes the containers do undulate VERY slightly as you look down the bike. ie the bottom bracket box is slightly narrower at the center of it than the peak of the tube diameters. yes, perfectly flush would be optimized (future upragde?) but to say that it hurts aerodynamics is similar to saying the much greater undulation of the bulge on a disk wheel makes it worthless because of all the skin friction and pressure drag it created.

im excited to get it in the tunnle to get a more worthwhile view of the bike than speculation.

The steering geometry is something I did quite alot of research before hand. Yes, it makes the steering more sensitive to reduce trail. Put on a 150 stem it smooths it out. Im not a roadie so cant compare it to a 13 lb super agile crit bike, but doesnt seem like anything different than before for steering. I took it over dips around curves and 180 turn arounds. Is steering optimized, probably not, but it works perfectly fine for tt and tris. btw putting the only way to have a 650 wheel is with the 650 fork. putting a 650 on the back would be impossible if u want brakes, and would defeat the purpose of a front 650 at all.

This was built with some hand tools and a box of junk on my gf back porch. This is my first 'prototype' and would love to continue refining it. Especially increasing its effectiveness over wider yaw. I appreciate the criticism! please keep it coming.

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Re: The bike that slowtwitch built [Rambler] [ In reply to ]
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maybe so haha, however I did study the Trimble alot before I built. The Trimble was a bullet without rider in the tunnel. The opposite with the rider. similar to catching more water with very slightly spread fingers in swim pulling, the proximity of the leg to the frame mass created additional drag. In proper tt form the knees are in at the top tube. This leaves the largest leg frame gap at the crank and the legs approach the frame closer as you move up. I specifically avoided the problems of the Trimble by placing the bottom bracket box low for appropriate leg spacing for air to flow proper (like the p4) and placed it angled further back to reduce crosswind pressure on front and increase splitter plate effect toward back. so theoretically I eliminated the Trimble problem.
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Re: The bike that slowtwitch built [23] [ In reply to ]
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assuming the airfoils are symmetric and laminar - they appear to have about a 8:1-10:1 aspect ratio, they will likely never stall. they will generate lift. lots of it.
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Re: The bike that slowtwitch built [23] [ In reply to ]
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Nice looking rig. Crosswinds might be pretty frustrating though.
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Re: The bike that slowtwitch built [23] [ In reply to ]
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and rather than just throw pot shots at this, here's a quick listing of max angle of attack for different lambda, where lambda is the ratio of rider speed to windspeed.

lambda = 2, max angle of attack = ~27 degrees
lambda = 3, max angle of attack = ~16 degrees
lambda = 4, max angle of attack = ~11 degrees

so for a rider traveling along a TT course at 40kmh with a windspeed of 10kmh, the absolute maximum angle of attack they will ever see is about eleven degrees and the frame airfoils will never stall. not even close. conversely, the rider will be constantly being pushed to the side except for that short moment that they are facing directly upwind and downwind. everything else is pure lift (i.e. a near constant side force, never stall)

along those lines, NACA 0015 or 0018 series airfoils (with an aspect ratio between 5.55-6.67) are pound for pound the best airfoils for upwind, downwind and crosswind performance. period.

(and yes, I develop wind turbines...)
Last edited by: chadman_98126: May 14, 13 13:24
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Re: The bike that slowtwitch built [23] [ In reply to ]
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23 wrote:
From a yaw perspective the oviod top tube makes perfect sense and is going into my mental data base.

Ha ha love that line: Translation -"I hear you, but I'm going to do fuck all about it!"

i have a feeling I'll be using that myself
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Re: The bike that slowtwitch built [chadman_98126] [ In reply to ]
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chadman_98126 wrote:
plus another 25.5mm drop in the fork for the smaller 650c wheel... (so a quick SWAG puts the trial in the 36mm range or less. twitchy.)

Funnily enough I never included the ability to change wheel size in the fork length change effect calculator - I was just thinking of swapping different length forks with the same wheel size.

Adding in the effect that you've noted gives:
HTA: 73 becomes 77.3
Trail becomes 34
BB drop 100

That could be a bit exciting.
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