Recumbent Trike – New Seat & Improvements

I have had the recumbent trike for a few years now. Returning from a ride and cranking up our steep driveway I heard a cracking noise and with each pedal stroke the seat raised up! Pulling over and checking the welds between the rear fork and longitudinal body tube had cracked. So it was time for some rework of the frame and I also had some other shortcomings that need to be addressed while I was tearing into the trike:

  • Seat – It is too narrow and the small amount of padding becomes uncomfortable after 15 miles or so
  • Rear deraileur – chain skips under load when climbing hills and down shifting under load is poor
  • Handlebars – can they be a bit higher or further forward? Shoulders get sore on longer rides.

So the bike was brought into the shop and the seat removed and frame inspected.

The cracks were along the weld joints but the rear fork had not broken completely free. The welds were ground down and it appears that in the original welding and grinding I may have been a bit overzealous in striving for smooth looking joints. The metal at the joint was thin. So I added a gusset appropx 1/4×3/8″ across the joint and re-welded everything. The weld fillets were much larger this time.

Now it was time to tackle the seat. I recalled seeing plans for a sling style seat at Recycled Recumbents. https://sites.google.com/site/recycledrecumbents/seat-frame-construction . I downloaded the instructions and reviewed them. They are very complete. So it was time to go to Home depot for 1/2″ and 3/4″ conduit and over to my neighbor Tom to borrow his conduit bender.

Bending the side rails went fairly well. I did end up making 4 pieces to keep 2 due to mistakes along the way. The bender was clamped in my workbench and I used a Wixey digital angle gauge to measure the angles as I bent them. Place it on top, zero it out and then proceed carefully with the bend while watching the gauge. When approaching the final bend angle, go slowly as it is easy to overshoot. The conduit does not like to be bent back very much to correct a bend. At this point, I was taking it on faith that the seat would be fairly comfortable. Later I would need to make some adjustments after riding.

I did deviate from the plans on the cross bars. I do not have access to a 3/4″ conduit bender, so the cross braces were cut and folded at approximately 45 degree angles and then the joints welded. The fishmouth ends were cut on the milling machine with a 5/8″ roughing end mill. I did have to enlarge the cut vs just a straight plunge. The pieces were clamped to the frame and the joints tacked in place.

Seat frame being tacked together while being temporarily clamped to the trike frame
Side view of the seat frame being tacked together. Note the marks on the rail showing where to make the bends as per the plans
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Close -up showing the already welded stretcher angle joint and a view of the birds mouth of the cross tubes

The seat welds were completed, ground down to look nice and the frame painted. Holes were drilled to match the brackets of the original seat.

The fabric for the seat is what is recommended in the plans, Phifertex Plus. I was able to find it in a matching bright yellow color on Amazon: https://amzn.to/37bmx5R. I also ordered some matching UV resistant polyester thread https://amzn.to/3C7kn5K which will be enough for dozens of seats. It took about 5-6 hours to cut, pin and hand stitch the seat fabric to the frame. I can thank my Grandma Ann for showing me as a child, how to make the overlapping running stitch that was used for the sides and the hem type stitch for the top and bottom edges.

Once the seat was completed, it was time to mount it and try it out. When mounted directly to the frame it was leaning too far back for comfort and the lumbar support curve dug into my back. I added a 1.25″ wood spacer behind the top cross bar to tilt the seat further forward. I also reduced the curve at the top of the lumbar region in half, straightening the top of the seat somewhat. This was done by taking the finished seat in my hands and pulling the frame straighter against my knee. It was about a 10 degree change. When re-mounted on the bike frame it was much more comfortable.

Seat mounted on the trike. Note the wood spacer block behind the upper seat spreader.
Another view
Front view with the new handlebars

After a few test rides it became evident that new handlebars were needed. The goal being to raise the grips a couple of inches for a more comfortable arm / hand position. The new handlebars are shown above.

To solve the chain skipping problem, I purchased a new rear deraileur hanger, a used but nearly new SRAM X0 9 speed deraileur and a used PARK DAG-2.2 deraileur alignment tool. With the parts and new tool in hand the “new” parts were installed and properly aligned per the Park Tool Youtube videos: Derailleur Hanger Alignment and Rear Derailleur Adjustment. This provided a huge improvement in performance both in almost completely eliminating the chain skipping and improving the ease of shifting under load on uphill downshifts.

I have since put on over a hundred miles with 20-30 mile rides and expect to do many more! The trike is now much more comfortable and fun to ride.

To see the original build process for the trike, see: https://bronkalla.com/blog/2017/07/15/recumbent-trike-project/ Note there are a series of food / cooking posts interspersed between the various trike build posts.