The new Adjustable Carbon Fiber (ACF) seat has been a game-changer on the V20/V20c models. It also fits very nicely on the S40, as it was designed to do. However, due to the more upright backrest angle, many riders feel like they need additional support at the front of the seat-pan. We make an adjustable seat-pan extension for the S40's stock seat exactly for this reason. However, we failed to anticipate this need in time for the release of the ACF seat. We are working on designing and building an adjustable extension specific for the ACF seat. In the meantime, we have a temporary solution making use of our supply of existing carbon fiber seat extensions from our stock S40 seats.
This blog explains the temporary solution for any S40 owners who wants to upgrade to the ACF seat. Once we have the new seat extensions specific to the ACF seat in stock, we will send those out, but given lingering supply chain issues, it may be a year or more before they are in stock. This blog also has useful information for the general installation of the ACF seat on the S40.
Photo: S40 ready to add Adjustable CF seat.
Position the lower section on the frame.
Attach the extension and lower section using two 30 mm M5 bolts and two nyloc nuts. Washers are optional. Do not overtighten these bolts. After you have ridden some, there will probably be some compression on the foam which will make the bolts feel loose again. Simply retighten to snug the extension to the seat.
Note the foam insert that has been glued underneath the extension.
This is a view from underneath, showing the added length of the extension (blue arrow).
Closeup of the front of the extension with the foam underneath.
Next, we will use this yoke to attach the upper edge of the lower section to the frame. Note the barrel nuts that slide into the yoke ends.
Yoke attached, side view.
Yoke attached, top view.
Note: the yoke allows the use of long frame struts for mounting accessories on the back. End of strut at green arrow, well past the yoke.
Some may prefer to cut off excess strut length, as on the right, below. This allows the use of the internal bracket, which is slightly lighter than the yoke and intended for use on the V20. However, it can be used on the S40. "Weight weanies" may want to do this to save some grams. To recap, the S40 can use either the yoke or the internal bracket to attached the lower section. The V20/V20c must only use the internal bracket.
This photo shows the internal bracket installed, and that the struts will not pass below this point.
Next, attach the upper section using four M6 bolts and nuts (green arrows, washer optional). The blue arrows show where the headrest attaches. The red arrows show access holes for adjusting the Perez clamp so that you can adjust the struts without having to completely remove the upper section of the ACF seat.
With Velcro in place for the Ventisit pad. You may also use the more cushy stock pad, just put Velcro where you need it, without covering up any access holes.
Final photo: Looks great. But more importantly, it feels great to ride on.
Installing the ACF seat headrest is easy. Many people do not need or use a headrest on the S40, but many people do. The video below shows general information for installing the ACF seat on a V20, which is almost exactly the same as we discussed here. The instructions for adding the headrest begin at approximately 7:57.