Message sent 7/14/12 for replacement of the pics.A number of people have asked lately how I did my seat modification. Instead of answering each one separately, I will post the process here. This thread will just show the basic idea behind the modification. Since each backside is different, your seat probably won't look like mine when it is done. But it will be oh-so-comfortable for YOU to ride. So, here we go...
First, remove the seat from the bike. There is a bolt on each side of the seat, toward the rear. I have two similar bikes, and three different types of bolt, so your guess is as good as mine what yours will look like. I think they are 10mm hex head when stock. Just take them out and lift the back of the seat, then pull back slightly and it's off.
Flip the seat over, and using a screwdriver, pry all the little staples loose. Then pull them out with a pair of pliers.
Once they are all out, the cover comes right off. Underneath is a plastic bag that I think is intended to keep water out. In my case, it was keeping water in, so I pitched it. What is left is the foam from the factory and a plastic seat pan.
From now on, you will want to make many trips to your bike for fitting purposes, so clear a path and put on some sneakers. I just set the seat on the bike and tried to visualize the new lines that I wanted, then I marked them out with a Sharpie right on the foam. You don't have to be exactly sure, because the original foam is all getting covered soon.
Next, I used a very sharp filet knife to cut along those lines I drew, all the way across the seat, being careful to keep the top of the seat flat. Remove the foam you've cut off and throw it away. After I did that, someone suggested using an electric knife. On the next one, I'll be trying that idea. It sounds like a good one.
Once I had the basic shape I wanted, I got a backpacker's sleeping bag pad. It's just a roll of blue foam about two feet wide and six feet long. You can buy them anywhere that sells camping supplies, including Walmart, for about six bucks...
I knew that the seat curved up in the back too much and hurt my tailbone, it was too narrow and didn't support my legs, and it was too round on top, causing my weight to sit on my midline, instead of my side parts that God intended for sitting on. So I tried to flatten and widen the seat. I cut six identical pieces of the blue foam to make the sides of the seat. These were 1/2 inch thick, for a total of three inches in increased width. I determined how wide I wanted the seat by sitting in a chair and measuring how much of it I covered.
I placed the pieces of foam on the sides of the old foam and pinned them there. I "stair stepped" them upward to give a slightly dished shape to the top of the seat. Then I cut some smaller pieces to fit along the edges of the top of the seat, leaving the center lower than the outside edges. I cut one final top piece to smooth things out a little. Here, you can see all the individual pieces attached loosely with tape prior to gluing...
Using DAP contact cement (nasty stuff, be sure to heed the ventilation warnings), I glued the layers together and affixed them to the factory foam...
Then I went outside and placed the seat back on the bike. I sat on it while I had an assistant mark areas that felt too bulky under my legs. I took the seat off and used the knife to shave away the foam in those areas until the seat was nicely contoured to my body. After that, I glued the top layer on, which got rid of all the sharp steps between layers...
Remember, you are working with foam. It's easy to cut, so I made everything a little large as I went along and then fine tuned it with the knife. In the picture above, you can see that the top layer has yet to be trimmed down to the exact shape I ended up with.
Once everything is glued and set up, I did a little carving here and there to make it fairly symmetrical. I tried a sander (I had heard this would smooth things nicely) but didn't have much luck with it. So I just used a sharp utility knife and got things as tidy as possible.
Now, on to the cover...
I bought a yard of marine vinyl at the fabric store for something like ten dollars. This was more than enough. I talked to several upholsterers and seamstresses, and then did it my way anyhow. I'm sure there are more efficient methods than mine, but I'll tell you how I did it anyway.
I just turned the seat upside down and traced it onto the back of the vinyl, scribing about two inches larger than the seat all the way around. Then I divided the seat into two halves and traced two front/side/rear pieces. Those two pieces I sewed together at the front and rear, making a skirt that ran all the way around the seat. Just lay them back to back and sew each end.
Put the skirt on the seat inside-out. This is where symmetry in your foam is pretty important. The right side of your cover is on the left side of your seat, so you want them to be the same shape. You can still carve on the seat a little at this point, but it's getting late in the game because you put on the "smoothing" layer already. Lay the top of the cover on the seat upside-down and pin it and the sides together, back to back. Sew all the way around, just outside the pins. Pull the pins as you come to them with the sewing machine. Turn the cover right-side-out and try it on the seat. Most likely, you will need to oversew the first seam in order to tighten the cover up. Look for any bags or gaps and mark them. Then turn it out again and sew inside the original seam. This is not my field of expertise, and any sewing questions you have will probably be better answered by the butcher at your grocery store than by me. Here's a picture of the whole mess inside out and unfinished...
Once you have the cover fitting nicely, you will need to attach it to the seat. I had a couple of heavy duty hand staplers that would not reliably penetrate the tough plastic of the pan. I'm told that you can buy an electric upholsterer's stapler for around $100. I ended up using a pneumatic soffit stapler. I just cut the staples to the right length and then loaded them into the gun one at a time.
Start at the front and pull the cover as tight as you can. Staple through the vinyl into the plastic. Move around the pan in BOTH directions, adding a staple first on the right, then the left, and so on until you meet at the back. As you are going around, continue to pull the vinyl tight. Any slack that developes can be pulled down under the pan and stapled in a "dart" (a nifty word I learned from the lady at the fabric store. It means "A little wedge-shaped fold"). Once you have the cover all nailed down, you are pretty much done. Just put the seat back on the bike and ride off into the sunset.
Here are shots of the stock seat and the new seat to demonstrate the difference in my posture.
And the final result without my butt in the way...
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