MnHPVA Meeting
June 12th 2002
Show-N-Tell
Click thumbnails to read details and see more and larger images.
Meeting Report: Dave Polaschek & Mark Stonich
Photos: Mark Stonich
Sophie Breen's little bike Most of the meeting was held outside, as we only had a small room. Once it started raining, the room didn't seem so small.
Lance Oberg passed around an English SusTrans (Sustainable Transportation) Map for our inspection.

Dave Gray's electric ????
Ride Announcements;
26th Blind Lizard Picnic Sunday June 16th. Motorcycles and Bicycles, the older and/or stranger the better.
TCBC Recumbent ride - Sunday June 16th – Starting from Calhoun Cycle - 30 miles of hills? - about 50% bents last time.
Tour d'Amico July 4th - too late for prelim t-shirt?

"Tall Dave" Johnson's funky tube
Carl Gulbronson started a discussion of tire size oddities. The 2 most common "20 inch" sizes (there are at least six 20" sizes) have bead seat diameters almost 2" different. Same with the two most common "16 inch" sizes. There are also several different 26" sizes "The best thing about standards is that there are so many to choose from." 406 vs 451 - they're both nominal 20s. Theoretically, 451 should roll easier, but the best go-fast tires are only made in 406. 20" BMX tube/tires will fit 406 in a pinch. For more on tire sizes, see Mark Stonich's and Sheldon Brown's "Tire Sizing" Pages.

The Four Faces of Dawg
A discussion of power assisted bicycles . Any amount of gas power means you're legally a moped. With electric, as long as you're under 1kw, you're legally a bike in the US. In Europe the limit is only 250 watts, which is a problem for load carrying, commercial bikes.

Carl also had a handout about the Twike (twin-bike) 55mph, human-powered/electric hybrid mini-car with 5kw motor. Jeff Caswell commented about riding one in Europe.


Luke's Big Buck Boinger

Not HPV, But Cute
Someone asked if a person with reduced range of motion in one knee should use different length cranks, or short on both sides? Mark Stonich said he'd set someone up with different length cranks years ago, and it worked fine. (At the meeting, I forgot to mention that the one I did was for a person who's bad leg was also shorter. This worked out perfectly. If both legs are equal length, but one has a limited range then either use same length cranks or build up the pedal for the good leg. Mark)
Denis Diekoff talked about the Yellowbike Coalition

  - First year they lost all the bikes - They've still got two warehouses full of donated bikes needing work - Taken over by bicycle/pedestrian association - old Renaissance Box building (10th & Sibley, ) Open wed & thur night for shop night - would like to be open on weekends and are looking for people to help out. If interested, reply to Denis' posting on the mailing list. They wouldn't mind people cannibalizing bikes to build cool 'bents.

Tech Talk

Mark Stonich talked a bit about Steering Ergonomics, Steering Geometry and "SWB Pedal Steer".

  SWB recumbents with the cranks well ahead of the head tube tend to weave down the road, more so when pedalling hard. SWBs with the headtube close to the cranks usually don't have this problem. This is often misinterpreted as "Boom Flex", so many SWBs are being overbuilt. Frame flex on a monotube bike primarily occurs on the load path between the seat and the BB shell. If frame flex were the culprit, the further back the headtube is, the less it would be deflected, which would lead to less steering input.

   I looked at why some bikes have the headtube further back, and saw that these bikes usually have shallow head angles. Shallow head angles mean that you either have a lot of rake, or a lot of trail, and manufacturers are hesitant to build/supply forks with a lot of rake. Many people have the mistaken notion that trail provides some sort of self centering effect. The opposite is true. Trail is actually the same as caster, which is what causes a vehicles wheels to turn in response to side loading. When your feet get to the bottom of the pedalling stroke, inertia is fed into the frame. Since pedals are offset from the frame a fraction of this inertia ends up as a force that causes unwanted steering on SWBs.

  If your steering ergonomics are correct, 6" to 12" of tiller, and reach and handgrip orientation set up as in http://bikesmithdesign.com/EvoBars/EvoBarSetup.html, there will be a strong self-centering force. With an LWBs typically shallower head angles, large amounts of trail translate to wheel flop which counteracts the self centering force provided by tiller and good ergonomics. This leaves you with vague steering.


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