Author Archive

Rebuild Reprise

June 11th, 2011 Comments off

So it’s all back together…

…and as expected the chain line clears the swingarm just fine. I had to remove about 4″ of chain but I left the slightly long rear cables intact for now. It was fun to ride around on it again… feels like it’s been a while. One or two more test rides then I’ll strip it down and start the finish. Here’s another gratuitous picture…


June 8th, 2011 Comments off

After some pondering I settled on fixing the chain rub by moving the rear pivot. So I dismantled the bike, cut out the pivot tube and cut a new ‘fishmouth‘ in the main boom. I clamped the back-end in place to check the fit. All seemed well so I welded it back together.

It seems to have worked. I assembled the back end and the chain line clears the swingarm completely, even when the suspension is bottomed out. I say ‘seems’ because I’ve yet to build the complete bike and test ride it. I’m reasonably confident it’ll be OK, because the suspension will never be fully compressed: the worst that could happen is occasional chain slap.

So next steps are (1) rebuild the bike and test ride it, (2) break it down again and finally (3) prep and paint.

This is dragging a bit… I’d hoped to be done by now.


May 23rd, 2011 Comments off

It looks like the reason for the insidious chain rub is the swingarm attitude. It’s flatter than in its original setup. Compare these pictures, starting with a detail of the donor bike.

A horizontal line from the pivot intersects the swingarm about 2/3 of the way down. On the Longshot the intersection is lower, passing almost through the dropout:

The effect is to raise the rear axle, lifting the chain line to the point where it hits the frame. So the question is how to push the axle back down? I could move the seat post back, but that would be an offensive amount of work and disruption. I could make new upper shock mounts, increasing the standoff to rotate the swingarm around the existing pivot. It would work but doesn’t feel right – that junction takes a lot of stress and with the increased length any alignment error would make it prone to bending.  I could move the main swingarm pivot closer to the seat post. The angle of the shock would be slightly steeper but I don’t think that’s a big deal.

There’s more thinking to do, but moving the main pivot seems like the best alternative.


May 21st, 2011 Comments off

That chain is turning out to be problematic.

Adding the second idler took up the slack and stopped the chain falling off. As a side effect it eliminated all the pedal bob. So far, so good. I set the suspension to compress about 25% under static load – the sag – and that pushes the pivot down a little. This brings the frame closer to the chain line, and when the chain is pulled tight it touches the frame:

Notice the small groove the chain has worn in the swingarm. On the smaller cogs there’s no problem, but riding in 1-3 causes some nasty rubbing.

Tightening the suspension so there’s no sag is a non-starter. That defeats the purpose of having suspension in the first place, and it won’t work: the shock isn’t long enough to prevent the rubbing. Pushing the idler and chain horizontally away from the frame won’t work either: the deviation needed to avoid that hefty swingarm is too great. I have a nasty feeling that some cutting and welding is going to be necessary, but first I have get my head around the geometry…


May 9th, 2011 Comments off

The bike is back in one piece. The recent modifications are not hugely obvious but constitute a fair amount of change.

  • Transmission: the addition of the second idler has made the chain much more manageable (i.e. it doesn’t fall off now). Shifting is not exactly crisp but it gets there. The rear derailleur needs realignment which will help it run quieter.
  • Cabling: the zap straps are gone. Housing runs are routed through guides and stops and all straight runs are exposed cable. Hooking up that front derailleur was interesting, requiring a recycled noodle and link arm to make the 90° bend. The brakes have lost that spongy feel and it all looks a lot neater.
  • Cranks: it’s hard to tell the cranks are shorter, though the effect may be more evident next time I head for that hill. I use clipless pedals on my regular bike but have been holding off fitting some on the recumbent. I’m riding fairly confidently now…might be time to try them.

There’s room for improvement. The seat doesn’t quite match the angle of the seatpost and flexes slightly under load. Firmer attachment would make the seat conform, but the current 4 woodscrews would strip out. I think I’ll just bolt it down. The suspension unit is barely adequate and jerks rather than smoothing out the ride. I’ll service and adjust it, and maybe keep my eye open for a better quality replacement.

More test riding to do, but construction is basically finished. Soon I’ll have to strip it all down, break out the wire brush and prepare for painting.


April 25th, 2011 Comments off

My part of the world is quite hilly, and recumbents are famous for not being able to climb hills. A recent test ride on the Seymour Valley Trailway reinforced this in no uncertain terms.

picture by cvarles

I found the longer climbs quite challenging: it’s very hard to balance when you’re going so slowly. It’s possible that my general level of fitness may increase and that I may lose a few pounds but lets not count on either of those. A better hope might be to increase cadence, i.e. drop to a lower gear and spin the pedals faster.

On my regular bike I can maintain 80-90 rpm on the flat. It’s easier to spin if you reduce the circumference of the circle your feet turn, so for my recumbent I’ll shorten the cranks.

It was trivial to drill them out, and the best bike shop on the North Shore John Henry Bikes tapped the holes for me. All I have to do is trim and round off the ends and I should be back in business.

Progress Note: The second idler and the cable guides are all attached. Once the bike is assembled again I’ll be spinning back up that hill.


April 18th, 2011 Comments off

After some test rides I modified the steering linkage to make it more sensitive. Now I can comfortably do a U-turn in my street with room to spare. I think that’s decent for a bike with a wheelbase of nearly 8′, and though not exactly nimble, it’s sufficient to make it practical for street riding.

I fitted that front derailleur and have been zipping around getting a better feel for handling at speed. Sitting low down makes it feel like you’re steeply banking the turns, but I suspect that’s an illusion. Riding one-handed is easy – I haven’t quite summoned up the nerve for full hands-off. Looking back over your shoulder is practically impossible, so add a mirror to the shopping list.

The second idler is ready to weld in place to help manage the long chain. I cut all the cable guides and stops off my donor bikes, so I’ll be able to replace the temporary zip ties and miles of housing with long straight runs of naked cable. It’ll be much cleaner looking, and the reduced  friction will make my shifters and brakes more responsive.

First Ride

March 29th, 2011 Comments off

I resisted the urge to head to the top of the nearest hill for a Flintstone-style rolling test. Instead I fitted brakes and a rear derailleur and a very long chain:

Turns out I was quite wrong back in November when I speculated that a single idler would be sufficient. Of course, the reluctance of the chain to stay attached wasn’t enough to prevent a test ride.

It took a short while to get used to the low-down-feet-up position, but the steering felt quite natural. The bike is very smooth and stable and handles well even at low speed. I have to adjust the pedal position and I need a second idler then I’ll give it another try. Further and faster.

In the meantime, provisionally titled “Some Fat Bloke Stole My Bike” and with stellar accompaniment is the first ride in all its glory:


March 21st, 2011 Comments off

All the structural work is done, and I have a rolling bike:

That ‘T’ at the front is where the headlights will go. Here’s another view:

It came together very well. My only initial concern is the spectacularly large turning circle – perhaps not surprising given the near 8′ wheelbase. Tweaking those outrageous handlebars will help.

Next comes chain (around 14 feet!), brakes, derailleurs and shifters. Then, finally, a test ride.


March 14th, 2011 Comments off

This project would not have got beyond the theoretical without serious help from an extremely able friend of mine. It’s his workshop where much of the construction will take place, and it’s his welding expertise, gear and patience that’s making it all possible.

So, that fork came together nicely:

Then on to the frame. Though oxy-acetylene welding is slower than the electric arc approach I really like the relative quiet and ‘calm':

You get totally absorbed in the small puddle of molten steel 12″ from your face. Making it do what you want takes lots of practice, and I haven’t done this stuff since college. It’s challenging and fun and I’m learning a lot – here’s a sample of my work:

A vast amount of heat gets dumped into the workpiece and things cool down slowly. Because I did lots of prep there was usually another thing to work on while the previous piece was cooling. After some trial and adjustment, we had a mostly complete back end:

Add the seat tabs, then the seat and a wheel:

The front end should come together quite easily now. Here’s a clamped-together good approximation:

It should have been obvious all along but it’s only just sinking in. This is going to be a long ride.