Login required to started new threads

Login required to post replies

Prev Next
Re: The bike that slowtwitch built [23] [ In reply to ]
Quote | Reply
Sweet!
Quote Reply
Re: The bike that slowtwitch built [23] [ In reply to ]
Quote | Reply
23 wrote:


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.


This is not always the case - carefully designed, truncated airfoils can result in lower drag, even at zero yaw. on a properly designed Kammtail, the geometry forms smaller vortices on the blunt trailing edge that are shed quickly, which in turn can result in a lower Cd than the original airfoil. with yaw greater than zero, the delta between the truncated Kammtail and the original airfoil is even more pronounced.
Last edited by: chadman_98126: May 14, 13 17:57
Quote Reply
Re: The bike that slowtwitch built [chadman_98126] [ In reply to ]
Quote | Reply
You need to realize when something is so damn awesome that it transcends criticism. This is the Meatloaf of tribikes.



"Are you sure we're going fast enough?" - Emil Zatopek
Quote Reply
Re: The bike that slowtwitch built [23] [ In reply to ]
Quote | Reply
coolest bike I've seen in a long time

---------------------------------------------------------------
http://www.onelesshiker.com
http://www.twitch.tv/1horsepower
Quote Reply
Re: The bike that slowtwitch built [cyclenutnz] [ In reply to ]
Quote | Reply
cyclenutnz wrote:

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.


on a 98cm wheel base the 52mm drop with the smaller 650c wheel and fork results in a 3 degree increase in the HTA and with a 41 cm chain stay the BB drops about 22mm. so with a typical BB ground clearance of 268mm you end up with a BB clearance around 242-246mm - just on the edge of the 240mm UCI/UASC/USAT minimum. running instead two 650c wheels on a 700c frame you end up with the about the same frame drop (25.5m vs. 22mm) that "23" is trying to achieve, but with a bike that still handles properly and is actually aero. install a pair of Tektro R725 brakes (or a set with a similar 24-26mm drop) and you're pretty much set.

QED.
Last edited by: chadman_98126: May 14, 13 18:24
Quote Reply
Re: The bike that slowtwitch built [chadman_98126] [ In reply to ]
Quote | Reply
You need to use x,y of bottom of the HT for the radius (assuming your swag was based on s=r*theta) rather than the WB. The frame pivots on the rear axle as it loses elevation from the fork/wheel assembly.

Which is 782mm on a 54 Felt B2. That with a 59 shortening (31mm on wheel, 28mm on fork) gives the figures above.

But I still fail to see the advantage of bringing 650c into the picture at all - fewer wheel choices (and more importantly - tyres).
Quote Reply
Re: The bike that slowtwitch built [cyclenutnz] [ In reply to ]
Quote | Reply
Certainly. In the absence of the head tube to rear axle radius, the wheelbase is a pretty reasonable approximation. given that the drop from the smaller wheel size is 25.5mm (622-571)/2, and all things being equal, the fork being roughly 25.5mm shorter, the rotation of the bike is roughly 3 degrees or ATAN (51/980), in the case of a 98cm wheelbase.

As for the 650c, certainly the 700c might be preferable - there are advantages to both, I was simply suggesting that "23" needs to look into keeping the wheel sizes the same, either 700 or 650, but not both and not with a shorter front fork - a 32-34mm trail on a TT bike with the bull bars cutoff seems a bit, um, imprudent.

btw: I believe the new P5 drops the bottom bracket 12-15mm. I believe it's still in the 250mm range, but they're definitely making the move to lower the overall profile of the frame. :-)

best.
Last edited by: chadman_98126: May 14, 13 20:48
Quote Reply
Re: The bike that slowtwitch built [chadman_98126] [ In reply to ]
Quote | Reply
btw: "23" you should give some serious consideration to 'roughing up' the outer perimeter of those tires to prevent flow separation - think dimples on a zipp wheel.

seeing as this is DIY, something to consider would be perforated vinyl film (similar to what they use for one-way printed window signs on stores and buses) with either 30/70 or 50/50 light permissibility. in the case of the disk wheel, a concentric ring covering the outer bulb portion would do nicely (but keep the center circle inside the bulb perimeter smooth and flat). and the case of the HED tri-spoke, basically the entire surface (outer rim, spokes, etc.). the vinyl is pliable and flexible enough that you might be able to overlay the entire side of the tri-spoke with one piece. and the diameter of the perforated holes is around 1.6-2.0mm so just about the right size (and depth) for a dimple.
Last edited by: chadman_98126: May 14, 13 20:39
Quote Reply
Re: The bike that slowtwitch built [chadman_98126] [ In reply to ]
Quote | Reply
Hi chadman,

In theory, covering a tri spoke with dimple film could be interesting.
In practice, it's been in the wind tunnel.
Unfortunately I'm not allowed to quote results.
But the tri spokes in our house are clean and smooth.

Cheers,

Damon Rinard
Engineering Manager,
CSG Road Engineering Department
Cannondale & GT Bicycles
(ex-Cervelo, ex-Trek, ex-Velomax, ex-Kestrel)
Quote Reply
Re: The bike that slowtwitch built [cyclenutnz] [ In reply to ]
Quote | Reply
In my mind the 650c front and 700c rear has nothing at all to do with bike aerodynamics, but body aerodynamics. Sure it dropped the bb to near the usat minimum and that is nice. Its about changing your body position. It drops your aerobars near 5cm for 'free' without any hip angle closure. its much more important to reduce the profile of the rider than drop the whole system a bit with no frontal profile change.
Quote Reply
Re: The bike that slowtwitch built [23] [ In reply to ]
Quote | Reply
Hi 23,

That was my thinking when I made the Kestrel track bike Sean Wallace rode to the silver medal in the 1992 pursuit world championships. We did what you did: dropped in a 650C front wheel and fork. At the time I did the math, and like cyclenutz and others, found about 3 degrees of rotation everywhere: seat angle, head angle, top tube, everything. In this case I also jacked up the back (packaging the conversion dropouts made that automatic) and ended up with ~4 degrees.

Yes, trail was greatly reduced, but Sean said he liked it, and in practice it was never a problem for him. Not that I would design a bike that way on purpose, but it wasn't dangerous under the right rider.

Cheers,

Damon Rinard
Engineering Manager,
CSG Road Engineering Department
Cannondale & GT Bicycles
(ex-Cervelo, ex-Trek, ex-Velomax, ex-Kestrel)
Quote Reply
Re: The bike that slowtwitch built [damon_rinard] [ In reply to ]
Quote | Reply
damon_rinard wrote:
Hi chadman,

In theory, covering a tri spoke with dimple film could be interesting.
In practice, it's been in the wind tunnel.
Unfortunately I'm not allowed to quote results.
But the tri spokes in our house are clean and smooth.

Cheers,


nice! I'm on a total 'turbulence tripping' tear of late and have been looking at some innovative ways to handle bluff bodies, so my inclination is to 'rough it up' when I see a smooth bluff body. [note: dimples seem like more of a last resort for turbulence tripping and probably only make sense in the case of a golf ball, and maybe on the outer rim of a wheel, maybe. case in point, I kind of chuckle when I see the dimples on the front of the new Garneau helmets...]


btw Damon: what do you take of this frame design? when I first clicked on the thread I was excited to see something 'crowd-sourced' by the slow-twitch community. not exactly what I expected to see.
Last edited by: chadman_98126: May 15, 13 6:39
Quote Reply
Re: The bike that slowtwitch built [damon_rinard] [ In reply to ]
Quote | Reply
damon_rinard wrote:
Hi 23,

That was my thinking when I made the Kestrel track bike Sean Wallace rode to the silver medal in the 1992 pursuit world championships. We did what you did: dropped in a 650C front wheel and fork. At the time I did the math, and like cyclenutz and others, found about 3 degrees of rotation everywhere: seat angle, head angle, top tube, everything. In this case I also jacked up the back (packaging the conversion dropouts made that automatic) and ended up with ~4 degrees.

Yes, trail was greatly reduced, but Sean said he liked it, and in practice it was never a problem for him. Not that I would design a bike that way on purpose, but it wasn't dangerous under the right rider.

Cheers,

34-36mm trail for a track bike is a quite a bit different than an open air TT on public pavement, no? and without bull bars??
Quote Reply
Re: The bike that slowtwitch built [chadman_98126] [ In reply to ]
Quote | Reply
Hi chad,

Tripping is nice, but you have to be careful. On a cylinder, there are a lot of places you can position a trip strip that add drag, and only a very narrow range of places you can put one that decrease drag. This is also sensitive to speed and yaw, so in general tripping isn't very robust for bikes. And none of the tripped surfaces is as low drag as a good old fashioned airfoil.

In my experience, surface treatments (trip strips, dimples, rough paint, etc.) can *sometimes* reduce drag on *non-aero* shapes. But 99.99 percent of the time it's faster to just choose a good aero shape to begin with.

Cheers,

Damon Rinard
Engineering Manager,
CSG Road Engineering Department
Cannondale & GT Bicycles
(ex-Cervelo, ex-Trek, ex-Velomax, ex-Kestrel)
Quote Reply
Re: The bike that slowtwitch built [chadman_98126] [ In reply to ]
Quote | Reply
Hi chad,

I keep recommending this to folks: build a fork with horizontal drop outs. Ride. Use the front skewer, choose a different rake/trail. Ride again. Compare.

Yes, some combinations ride like crap. No, most combinations aren't instant death. ;-)

Cheers,

Damon Rinard
Engineering Manager,
CSG Road Engineering Department
Cannondale & GT Bicycles
(ex-Cervelo, ex-Trek, ex-Velomax, ex-Kestrel)
Quote Reply
Re: The bike that slowtwitch built [damon_rinard] [ In reply to ]
Quote | Reply
totally agreed, not instant death, and more power to "23", and the idea of going a bit 'funny' with a 700/650 combo is a great idea for the reasons "23" cites. but as you said, I just wouldn't intentionally design something that way. :-)
Quote Reply
Re: The bike that slowtwitch built [damon_rinard] [ In reply to ]
Quote | Reply
damon_rinard wrote:
Hi chad,

Tripping is nice, but you have to be careful. On a cylinder, there are a lot of places you can position a trip strip that add drag, and only a very narrow range of places you can put one that decrease drag. This is also sensitive to speed and yaw, so in general tripping isn't very robust for bikes. And none of the tripped surfaces is as low drag as a good old fashioned airfoil.

In my experience, surface treatments (trip strips, dimples, rough paint, etc.) can *sometimes* reduce drag on *non-aero* shapes. But 99.99 percent of the time it's faster to just choose a good aero shape to begin with.

Cheers,

totally agreed, an airfoil is always better. the question becomes "what you do with the girl that brung ya?" there's definitely some good research out there on tripping cylinders and some innovative ways that I'm look at around placement and forgiveness on yaw.

best
Quote Reply
Re: The bike that slowtwitch built [damon_rinard] [ In reply to ]
Quote | Reply
damon_rinard wrote:
Hi chadman,

In theory, covering a tri spoke with dimple film could be interesting.
In practice, it's been in the wind tunnel.
Unfortunately I'm not allowed to quote results.
But the tri spokes in our house are clean and smooth.

Cheers,


Would that be dimple film, or the 3M riblet film that's impossible to find now?


--------------------------------------------------
Yeah, it's a great bike but the engine needs work.
Quote Reply
Re: The bike that slowtwitch built [bujayman] [ In reply to ]
Quote | Reply
sorry to put down all your hard work but that thing looks ugly!
Quote Reply
Re: The bike that slowtwitch built [desert dude] [ In reply to ]
Quote | Reply
yer just saying that because its black!

36 kona qualifiers 2006-'23 - 3 Kona Podiums - 4 OA IM AG wins - 5 IM AG wins - 18 70.3 AG wins
I ka nana no a 'ike -- by observing, one learns | Kulia i ka nu'u -- strive for excellence
Garmin Glycogen Use App | Garmin Fat Use App
Quote Reply
Re: The bike that slowtwitch built [cyclops] [ In reply to ]
Quote | Reply
well, i went with the ugly aerodynamic and black stealth look. if you want to look at pretty bikes with flowers, streamers, and a cute white basket I guess you'll have to look elsewhere :)
Quote Reply
Re: The bike that slowtwitch built [cyclops] [ In reply to ]
Quote | Reply
cyclops wrote:
sorry to put down all your hard work but that thing looks ugly!

+1
Quote Reply
Re: The bike that slowtwitch built [quellish] [ In reply to ]
Quote | Reply
quellish wrote:


Would that be dimple film, or the 3M riblet film that's impossible to find now?


In my case, I recently took some old Zipp 404's and breathed some new life into them by adding some dimples and new graphics using perforated window vinyl -- this is the same perforated vinyl film that they use on store windows and buses. the vinyl used here is "50/50" -- it let's 50% of the light through. the vinyl also comes in 30/70 (i.e. lower dimple density) and 70/30 (i.e. higher dimple density). this film creates dimples about 1.6mm diameter and approx. 0.125mm deep

cost: about $32
total project time: about 45 mins
project type: total DIY hack #cheapspeed

beats having to upgrade to a new set of Zipps when the existing wheels are still perfectly good.




Last edited by: chadman_98126: May 16, 13 0:04
Quote Reply
Re: The bike that slowtwitch built [23] [ In reply to ]
Quote | Reply
I go back and forth on liking this bike and not. I commend you for your hard work and vision to build one of the craziest looking bikes I have seen in a while.

I dig the hipster-ish hamster bars.

For the record, as I write this I am digging the bike

_________________________________________________
When all is said and done. More is usually said than done
Ba Ba Booey

Quote Reply
Re: The bike that slowtwitch built [23] [ In reply to ]
Quote | Reply
holy crap dude, take better care of your lawn. But seriously awesome job on the bike!
Quote Reply

Prev Next