Monday, March 31, 2008

Making a new seat

So I've decided that I need to replace my seat. The shape just isn't in agreement with my anatomy. I think I need a somewhat more laid back chest position with a more gradual transition into the shoulder area. This will mean more work holding my head up, but I prefer that.

I decided to build the seat from fiberglass. I carefully weighed the options between carbon fiber, glass, and wood, and decided on glass for the simple reason that I already have about 3 yards of the stuff in the basement and thus won't need to order anything.

My general approach is to make a simple wooden frame and stretch fabric over it, then make a plaster mold of me sitting in the fabric seat. This should recreate a comfortable shape for me while allowing a lot of control over the position.

I started by using an adjustable seat mock up I made some time ago to decide on an approximate shape. I then pulled this shape off it by scribing a piece of plywood, and made a simple form from plywood to hold tensioned fabric. I added more lumbar curve to the form from what I had on the mock up because I expected that to collapse under weight more than other places on the seat. I also scribed a line about an inch smaller than the line I took from the hard seat to account for fabric stretch.

I covered the seat with several layers of scrap fabric until I got the right amount of strength and stiffness. Most of the fabric is either muslin or some other lightweight non-stretchy cotton fabric. A heavier fabric like canvas would be preferable and would require fewer layers, but this is all stuff I had around the house so it didn't cost me anything.

I had originally intended to saturate this fabric directly with plaster, but a test showed this wouldn't work well. So instead I covered it with plastic and saturated a few layers of burlap. Much furious mixing and spreading ensued, but with the help of my lovely wife, I was able to get everything in place, another layer of plastic over the plaster, and sit in it before the plaster set up too much. I hung out and watched some TV for an hour while sitting in my seat. And then carefully pulled myself up by using a sling I had pre-rigged from the ceiling (to avoid cracking the plaster) .

Tonight I'll add some stiffening ribs to the plaster and then tomorrow pull it from the "seat". After that I'll add some more layers of burlap to build up the thickness to account for a seat pad, and also give it more stability. Then pull the glass mold from it.

Friday, March 28, 2008

Adjustable Seat Concept

So based on a thread at BROL as well as my own observations on climbing performance, I started thinking what it would take to make a seat that is adjustable on the fly. The idea here is that there was a study that showed that the optimal hip angle for power production is about 105 degrees. (I'll try to hunt down that study again... I should have bookmarked). But that relatively "closed" position is less than optimal for aerodynamics. Also torso angle has some impact as well. Plain and simple we are designed to do aerobic things upright not lying on our backs.

The drawback to that position is that (sans fairing) it's aerodynamically crap. So what would be great would be to have a bike/seat that you could adjust over a wide range on the fly to suit the conditions. A more upright seat for climbing, more laid back for flats/downhills/headwinds. Somewhere in between for traffic. etc. This gives the added benefit of allowing you to vary the muscles involved which should improve long term endurance similarly to an upright bike.

The requirements that I can see for this seat are as follows:
  • The hip joint to pedal distance must remain constant.
  • The shape of the seat must be comfortable and efficient in all positions
  • The adjustment range must be at least 30 degrees with multiple intermediate positions. (continuous adjustability is desirable though not required)
  • The seat must be able to be adjusted safely while riding.
  • The weight must not be significantly more than a nonadjustable seat (total seat weight should be in the 4lbs range or less)
To this end I am thinking of a hardshell carbon seat in 3 sections. The seatpan will be attached to the frame, the back rest will be supported by the frame by ratcheted stays, and the shoulder rest will be supported by connecting members that make a parallelogram with the seat back so that the angle to the ground remains constant. The following images show the general idea. They are not to scale and the lower pivot would probably need to move to keep the hip-pedal distance constant, but it shows the concept.

Thursday, March 27, 2008

First 100 miles, some observations

So I'm right around 100 miles on the bike now. Not sure of the exact distance since I didn't have a computer on the bike for the first few rides but it's around there somewhere.

No pics to show right now. I made a few mods to the seat to improve comfort. I made a cutout in the upper back area first. That only partially solved the battered vertebrae problem. It basically just moved it up to the vertebrae at the base of my neck. So I made a sort of u-shaped channel there by cutting out part of the seat and gluing on some of the previous cut out material to reinforce it. Looks decent and is a lot more comfortable.

I'm still not 100% happy with the seat. I think fundamentally the shoulder rest is just too steep for my anatomy. I may make my own seat from wood or carbon in the near future as a replacement. I'm still pleased that I went with this seat, and I'd recommend Ed's seats to anyone, but as with any hardshell it may or may not fit you ideally.

File this under lessons learned, but attach your seat pad with velcro not double stick tape. Then when you carry it on a car rack, take the pad off. That nice looking original pad is still out there somewhere... wish I knew where. I replaced it with a much rougher looking section of camping pad. The looks are worse, but it's actually more comfortable so I'm not that upset. Still tho....

Chain clearance around the rear fork is something of a problem. I get a bit of rub in the highest gear on the side of the chain stay, and a bit on the bottom in the lowest gear. The side rub is just something I'll live with. It's minor and doesn't feel like it's really dragging at all, but it makes a bit of noise which annoys me. The rub on the low gear can be corrected with either a smaller rear cog or a larger idler. One or both of which I'll do eventually.

Hills... hills are interesting. My first few rides on steep stuff (10%+) worried me since I was really struggling. Until I realized I wasn't shifting to my lowest gear in the back. Once I got that sorted out it's a lot better. Last night I went out and did one section of my commute that is an average of 15% with a max of something over 20%. I didn't have any problem putting power to the pedals, but balancing is really hard at those speeds. I can only turn the bars so far without whacking my shins which is a bit of a problem under 4mph. The hill also involves a 180 deg switchback which I had to get off the bike to navigate. I just couldn't figure out how to make the turn that slow with the limited turning ability. Going down it's not a problem since I can just straighten my inside leg and coast and turn as sharp as I like, but no such luck uphill. I'm still not up to my df speeds, but I'm not too far off and I'm still getting my legs. On moderate grades I'm about 2mph slower on average. On flatter and steeper grades I'm actually about the same as on the df. Flatter because the aerodynamics come into play more, steeper because I can't ride any slower than about 3-4mph so I have no choice.

Traffic... I'm still a bit nervous in traffic though it's getting better. Riding uphill is nerve wracking in traffic since I don't feel as in control of the bike as I want to be, so I'm worried about swerving into a car. Riding on the flats is ok, but I'm still not as comfortable handling the bike as on my df, so there is still some acclimation that needs to happen there.

Road conditions... Potholes freaking suck. Rough roads at speed downhill are just unpleasant. everything feels like it gets transmitted directly into my lungs and it almost feels like an asthma attack. It's pretty bad. Fortunately most roads aren't that rough. I'm thinking about putting a wider tire on the rear wheel to help offset the effect somewhat. For the next bike I'm thinking either rear suspension or maybe just not as direct a coupling to the seat.

Speed... generally pretty good. Flatland speed is comparable to my old DF speeds. That will climb as I get more miles on my legs I expect. The speed profile is different, even on the flats. It's really easy to cruise along at about 19 mph, but then 21 feels hard. On the df 19 was working a little harder but 21 didn't feel like as sharp of a jump. Overall I'd say that the bent gives the same speed for less effort across the board, but the curve is just different. The thing accelerates downhill very fast as would be expected.

Comfort... apart from the aforementioned seat issues and the general battering from road surface, quite good. I've not done any rides over 20 miles yet, so time will tell, but I'm at least reasonably pleased so far.

What's next... So what about the next bike? I have a lot of ideas floating around, so I'm going to start drawing things in cad and mocking up ideas. Wait and see :)

Thursday, March 6, 2008

First (real) ride

So after days of lousy weather, a brief but unpleasant illness, etc... I finally got a free half hour to do a couple loops around the park. Total ride distance is about 5.4 miles, I don't have a computer mounted yet so avg speed etc are all unknown.

  • I was quite wobbly at first but that subsided after about a mile. After that I was just a little wobbly.
  • The bike climbs a lot better than I expected. I expect I'm still a bit slower than on my regular upright bike, but I am also expending a lot of energy just learning to ride the thing still, so that should go away. Riding uphill in the lowest gear (22.4 gear inches) is kind of tough to balance, though by no means impossible. Anything above that is gravy. I have no fears about doing the climbs on my commute.
  • My butt got cold
  • The only seat discomfort I had was from where my spine sticks out a bit more on my upper back. Seems to dig into the seat more than is comfortable and really gets jarred on hard bumps and rough surfaces. I'm thinking of making a small cutout in the seat to relieve this. Otherwise it was very comfortable.
  • I really notice the sounds from the rear of the bike more than I'm used to. I can hear the rear drivetrain and the rear brake a lot. Not a bad thing, just noticeable.
  • I feel my upper quads / hip flexors a lot more than I'm used to. Part of the recumbent adaptation I expect.
  • Even on a day with few people out and about, I got a lot of stares and comments.
  • GOOD mirrors are a wonderful thing.
Overall, I'm very happy about how the bike looks and handles. I'll do the small seat cutout, and I still need to make a bag to carry stuff, but otherwise I think I can call this thing done. Here are a few pics.