Waves77

So what'd you think about the article? Is it really necessary for us tall guys to have a different design than "regular" frames?

BarracksSi

The interesting thing is, these properly-designed tall frames just make the wheels look small and the head tube look skinny. On the other hand, other tall bikes that come to mind (like NBA stars Bill Walton's roadie and Yao Ming's Gunnar) look crazy, with the saddle almost directly above the rear axle.

Thylacine

Absolutely. One of the key motivators to me starting a custom bike company was just how bad bikes are for almost anyone over 6ft.

The bigger you are, the 'wrong-er' they get. Mainstream companies try to squeeze as many people as they can on 5 sizes, and even for me at 6ft 3ins, there's not really any stock bike whose geometry I like. The majors just don't care about you.

The biggest issues from my perspective are -

a) Chainstays are too short - your seat goes up and back, and the stays don't. How dumb is that?
b) Steering speed and weighting should be the same, but they're not. You can't just steepen the HTA and expect roses!
c) Fit is fit - the majors as I said don't care about you, but they're also scared of what the big boys really need in terms of top tube lengths - don't have the tubes, or don't want to spend on the tooling for carbon.
d) Tube diameters need to go up if the tubes get longer, or the bike will handle bad and feel bad.

Everything in proportion.....and......don't be scared to throw out the book if the book is wrong!



ps: I really, REALLY want someone to do 31" wheels. Hello Kirk Pacenti?

Thylacine

Neither of those are properly designed. In fact, they're exactly what not to do.

BarracksSi

By "these", I was referring to Thylacine's frames, which I quoted.

Shimagnolo

What?
Putting 90% of the weight on the rear wheel isn't the right thing to do?

I like the way you think.
I have very long legs out of proportion to my height.
I've found I need to always buy the biggest frame I can find, and then use a zero-setback seatpost just to compensate for the lousy design of the large frames.
My current roadbike is a secondhand custom Litespeed, for which I had to have a custom CF fork made with less rake than standard in order to get rid of the highspeed shimmy.

Sassonian

Beautiful looking bikes Thylacine!

You can see that my bike shares some design philosophies...

https://www.dropbox.com/photos/Zinn/#/

jfmckenna

All my bikes except for my Moots compact have hi-speed shimmy. I attribute the fact that the moots is compact frame and therefor a bit tighter to why it doesn't shimmy. But I don't really know.

BTW to those of you who experience it, simply clench your knees to the top tube and the shimmy will stop. When I descend now I always have a knee on the TT just from experience.

Shimagnolo

There is no excuse for high-speed shimmy in a properly-designed frame.
The problem is the dumb practice of putting steeper head tubes on tall frames, which reduces trail, thereby reducing stability.
A fork with less rake restores the trail.
Google "Dave Moulton" to find his articles on steering geometry.

Thylacine

It's more than just trail. Trail was figured out decades ago - there's only really a handful of acceptable HTA/Rake/Trail combos that work in the real world.

The factors that other companies don't factor in, is front end weight distribution, and the amount of effort required to initiate a turn. You need to take into account bar design and width, and stem length because it all adds up to steering geometry that at the end of the day will either work or it won't.

No bike of any size should shimmy. I've never, ever made nor had myself a bike that shimmies. In fact, the faster you go, the better they handle. At 80kph it should feel like you're standing still.

Waves77

So at what point would you say that a bike needs to let go of the trying to imitate the regular geometry of a smaller sized bike? (eg once you reach a 20cm head tube, or 60cm top tube)

Thylacine

I have no idea. We design bikes to fit people, so I have almost no idea what constitutes 'normal' or what 'regular geometry' really is.....short of the historical mean 405mm chainstays, 73º/73 angles, 43mm rake fork.