BHPC Forum Homepage
Forum Home Forum Home > Public: Open to anyone > Building
  New Posts New Posts RSS Feed - Reverse K-drive
  FAQ FAQ  Forum Search   Register Register  Login Login

Starting a new topic? Please try and put it in a relevant forum (Riding, Building, etc) but if you're not sure it's better to post in any forum than not to post at all.


Reverse K-drive

 Post Reply Post Reply Page  <12
Author
Message
Balor View Drop Down
Visitor (new)
Visitor (new)


Joined: 25 January 2017
Status: Offline
Points: 46
Post Options Post Options   Thanks (0) Thanks(0)   Quote Balor Quote  Post ReplyReply Direct Link To This Post Posted: 18 January 2019 at 8:25pm
Originally posted by RoyMacdonald RoyMacdonald wrote:

Miles says the loss over the traditional rotary drive due to the K-drive is 10%. But the aerodynamic gain being able to keep your feet within the Kingcycle fairing is considerabley more. 

I found the K-drive is hard on your legs though and harder to spin at a higher cadences. The Beano just uses short cranks. I do have short legs though. Short cranks do feel nice and comfortable to me.

Roy 

Yea, that is exactly what I've meant by the way. Reversed rotation K-drive should be like an 'oval ring on steroids' and oval rings shine at higher cadences.
Gears also a bit more efficient than chains - provided you keep them adequately lubricated (somehow)... preferably made from self-lubricating material.
Maybe in a few years I might have a prototype 3D printed from some allow to test my theory :) Progress marches on...

Short cranks do feel nice and comfortable to me.

How short are they? It took me a while to adapt to 140mm ones (I am nearly 6' tall though).

Anyone tried adapting to even shorter ones? 12? 10? 6? :)
Back to Top
Balor View Drop Down
Visitor (new)
Visitor (new)


Joined: 25 January 2017
Status: Offline
Points: 46
Post Options Post Options   Thanks (0) Thanks(0)   Quote Balor Quote  Post ReplyReply Direct Link To This Post Posted: 18 January 2019 at 8:42pm
Btw... a thought regarding short cranks.
The less your legs are bent during POWER phase the the more glutes are emphasized and less - quads. 

The gluteus maximus moment arm for hip extension indicates that it is a key hip extensor in the sagittal plane, and decreases with increasing hip flexion angle. The gluteus maximus is therefore most effective when the hip is near full extension, implying that exercises that produce peak contractions at this point will be most beneficial for its development.

Ok, google, what variables shift your 'leg angle' to more open during power stroke?

BB height, seat recline and CRANK LENGTH. Hm hm hm.
It also explains why bridging works, btw!
Back to Top
RoyMacdonald View Drop Down
BHPC Member
BHPC Member
Avatar

Joined: 09 March 2007
Location: Rye East Sussex
Status: Offline
Points: 402
Post Options Post Options   Thanks (0) Thanks(0)   Quote RoyMacdonald Quote  Post ReplyReply Direct Link To This Post Posted: 18 January 2019 at 11:52pm
Originally posted by Balor Balor wrote:

Originally posted by RoyMacdonald RoyMacdonald wrote:

Miles says the loss over the traditional rotary drive due to the K-drive is 10%. But the aerodynamic gain being able to keep your feet within the Kingcycle fairing is considerabley more. 

I found the K-drive is hard on your legs though and harder to spin at a higher cadences. The Beano just uses short cranks. I do have short legs though. Short cranks do feel nice and comfortable to me.

Roy 

Yea, that is exactly what I've meant by the way. Reversed rotation K-drive should be like an 'oval ring on steroids' and oval rings shine at higher cadences.
Gears also a bit more efficient than chains - provided you keep them adequately lubricated (somehow)... preferably made from self-lubricating material.
Maybe in a few years I might have a prototype 3D printed from some allow to test my theory :) Progress marches on...

Short cranks do feel nice and comfortable to me.

How short are they? It took me a while to adapt to 140mm ones (I am nearly 6' tall though).

Anyone tried adapting to even shorter ones? 12? 10? 6? :)

Ian Sims of Greenspeed tested a range found that at shorter than 110 mm power loss started to occur.

I used to be 5' 8" but now I'm 5' 5" however my legs are the same length they were 25 years ago because I've never had to adjust my seat position. Makes me more aero though. So it's leg length thats the determing factor for comfort I think. I have bikes with lengths of 140 and 150 and 190. The K-drive has a 185 mm effective length crank.

Miles designed the K-drive to be as flat as possible to get it to fit inside the fairing. Aerodynamics is everything. I just wish it felt more comfortable to use for me. (That's why I only did 50k on itBig smile) I never had any mechanical issues with the K-drive in that time. I replaced the chains on it occasionally. Start of every race season I think. I did have to fit new bearings in the Sturmey Archer hub as they started to fail. Maybe they did not design them to do 70mph.LOL

Roy


Edited by RoyMacdonald - 19 January 2019 at 12:04am
Back to Top
Balor View Drop Down
Visitor (new)
Visitor (new)


Joined: 25 January 2017
Status: Offline
Points: 46
Post Options Post Options   Thanks (0) Thanks(0)   Quote Balor Quote  Post ReplyReply Direct Link To This Post Posted: 20 January 2019 at 1:40pm
Found Kingsbury homepage... things are even more interesting!

http://www.kingcycle.co.uk/page11.htm

As for 'reverse K-drive', it seems that I was wrong and simply reversing rotation of secondary cranks will result in complex 'looping' motions, not merely reversed oval. :( Oh well.
Back to Top
 Post Reply Post Reply Page  <12
  Share Topic   

Forum Jump Forum Permissions View Drop Down

Forum Software by Web Wiz Forums® version 11.02
Copyright ©2001-2015 Web Wiz Ltd.