Now you're ready to tuck everything back together, and get back to riding. The changes made to the shape of the seat will inevitably affect how challenging it will be to stretch and staple the stock cover back in place. Those areas where you've built up foam and added height to the seat will pose the bigger challenges. In most cases, if the stock cover does not have any seams in it, you should be able to stretch the cover enough so to give you sufficient area for stapling. Even if you have to muscle the cover back in places, the staples all around the edge will share the tensile (pulling) forces acting on the cover, helping to make sure that the cover doesn't rip at any one of the staple points. Over time, vinyl covers will stretch a bit, therefore making subsequent stretches easier. And chances have it that you will have to take the cover off at least a couple of times to tweak things a bit.
This may seem like a topic that doesn't need any explanation. However, if you've ever tried to fire staples into the bottom of a plastic seat pan with a manual staple gun, or even a cheap powered one, you'll realize that getting the staples securely, completely back into the seat pan is not like stapling a piece of plywood. The plastic is relatively hard, which is why you should at least use a decent consumer-a commercial-grade electric staple (see the Tools page for more info).
If you're using a regular, heavy-duty staple gun like the Arrow ETFX50 shown on the Tools page, hold the seat in your lap or some way so that you can press the vinyl against the seat pan firmly with the staple gun (see picture below). Don't put the seat on a rough floor or chipped up workbench. They may give you a stable, firm base, but they're likely to scuff or rip the vinyl cover.
If the seat pan doesn't have a firm support against which you can push firmly, the staple will probably only drive half-way into the plastic. If this happens, carefully remove the staple so as not to rip the vinyl (as described in the Removing the Seat Cover section) and give it another shot. Try not to avoid ripping or getting holes in this strip of vinyl that you're using to re-attach the cover.
As you test ride your seat, you'll likely make adjustments to your modifications—shaping, adding, or removing a bit of foam here and there. Assuming this will be the case, you may want to use fewer staples to re-attach the seat cover for the first versions. Once you get your seat to a place where you think it will stay for a while, you can then drive in staples so they are about one inch apart. Taking off and putting the cover back on will naturally create little staple holes in the plastic. Don't sweat this. Nobody sees this minor imperfection and, as long as your staples are driven in completely, the seat cover is not going anywhere.
Getting a Firm, Even Tension on the Cover
The re-installed cover should be relatively tight to avoid having it move or wrinkle as your body shifts around on the seat while riding. This is one aspect of sportbike seats that makes them different from ,say, cruiser seats. If you've increased the overall amount of foam on your seat, and you decide to re-use the stock seat cover, this should be easy since you'll be forced to use the same size cover over comparatively more foam.
To make sure that the seat cover's tension is applied evenly across the seat, work from side-to-side. First, staple a small section of vinyl in the middle of the front and back parts of the seat, making sure the vinyl is pulled tight enough. Use a couple of staples for both the front and back parts. This will hold the vinyl in place as you work from side to side. Work from side to side by pulling a bit of cover around one side of the seat pan and inserting a staple. Remember not to pull and staple so much of the seat cover to one side that you'll end up with too little to work with on the other side. If this does happen, don't worry—simply remove the staple and give it another try. Continue to pull and staple the seat cover incrementally from side to side until the sides are completed.
Now evenly stretch and staple the back and front parts of the seat cover. You'll find it easier to get an even tension on these areas since most of the seat cover is now firmly in place with the sides stapled. If you seem to be pulling the vinyl to one side more than the other, remember to work from side to side to evenly distribute the seat cover tension. Check for loose areas and wrinkles. As you find these spots, remove a few staples as necessary, and restretch and staple the vinyl.
Check out the picture to the right that shows a basic stapling pattern described above.
Getting a Firm, Even Tension on the Cover
Note: You'll probably end up going back and forth between stapling, unstapling and adjusting, re-stapling, and so on. A lot of times you won't know how to make the vinyl fit well until you've secured some of it down. Just be patient, make sure you stretch your vinyl firmly over the seat, and make the process as iterative as you need to. Almost always, you can find a way to get your seat cover smooth. It may not look like a Russell Day-Long, Sargent, Corbin, Rick Mayer custom, stitched cover; but you can make it good enough.
Dealing with Corners
Some stock seat pan shapes have some corners with relatively sharp corner radii. These corners are usually found on the front part of the seat that fits around and under the tank, along the bottom as the pan rises to the back, and at the rear of the seat. The picture below shows an example of a seat shape—the same one used throughout this site—that has a couple of corners that may be tricky.
If you're re-using your stock seat cover, it may already be be cut and stitched to fit around these corners nicely without creating wrinkles (see the picture below for an example). If not, or if you're using a new piece of vinyl, incrementally pull, tuck, and staple small sections of the vinyl. These overlapping sections around a corner are sometimes referred to as "gathers." The pictures below show some examples of how these gathers or pleats look around the corners.
If the gathers result in excess folds of vinyl will be visible when the seat is installed, you can trim this excess vinyl with scissors by pulling up the vinyl by its "ears" at the fold and cut it along the fold line to within about 1/2 inch from the edge (see the picture to the right). Eventually, you should end up with the seat cover that's smooth on the top, and pleated and smooth enough underneath to fit snuggly against the rear seat cowl.
When the Stock Cover No Longer Fits
A trickier situation is when you have substantially changed the shape of the underlying foam on a stock seat that is a more unusual shape that necessitated a cover with seams. Sometimes in these situations the original cover will not quite fit over the new foam.
The pictures to the right show a stock and modified Kawasaki Concours seat that. The underlying shape of the seat was modified too much to re-use the stock cover. As a result, I simply used one piece of marine-grade vinyl to cover the modified seat; and also made a small saddle strap so that it wouldn't be too plain looking. Is it as slick looking as a $450 aftermarket seat? No. But it cost me about $75 for the materials, and I was able to tweak it as much as I wanted to until it fit just right. My comfortable driving time went from about 30 minutes to about 10 hours. I'll take it.
Occasionally a modification might result in the stock seat cover fitting in all areas except where the seat meats the tank. If this is the case, just don't staple that area. There will be plenty of staples to keep the seat very secure, and this gap will be invisible once the seat is installed. The pictures below show an example of this situation, both with the seat off and installed.
One Other Option
If you'd like a new stitched, seamed cover to fit over your self-modified seat, you can always take your seat to an auto upholstery or custom motorcycle seat shop. This certainly will cost you some extra money, but less than if you had a shop do the entire modification job for you. And while you may be able to the modify the shape of your seat, the skill and experience required to cut and stitch a nice looking seat cover is beyond what most do-it-yourself riders are willing to develop.
Sometimes watching someone else do this job can be a big help, even if the project details are different from yours. If you don't know someone who's good at this, the next best thing is a video. Here are a a couple of videos that simply let you watch others work with a cover. Notice how they take their time and pay attention to the details to get things just right.
... If that got you hungry for more, here you go!