The seat frames are the same throughout the original fortwo and the Roadster.
Swapping The Runners
If you really want to fit the LHD seats to your RHD fortwo (or vice versa) you will have
to swap the runners over as they are different for each side. This isn't the case on the
Roadster as both seats have the same runner set up. Have a look here for more seat info.
The other reason you may want to swap seats is that you prefer the colour of the back of the seats as these are available in matt black (which marks easily), hammered silver and hammered black.
The hammered finish is the same you get with Hammerite paint available at hardware stores.
To gain access to the seat runner fixings you have to remove the seat foam, see here.
Under the seat foam at the front you will find a 13mm nut on each side, remove them.
Either side at the back you will find a Torx45 bolt, remove both of these too.
You will now be able to lift the base off of the runners.
Look where the back joins the base, you will see another Torx 45 bolt on each side. Remove.
The runners will now be able to slide forward and down to seperate from the back.
The back is now a seperate part from the base and the runners.
Remember that the backs have the seatbelt guide attached so you cannot swap left for right.
You can now move the appropriate runner to whichever seat you wish to use on that side.
You could leave the original runners in place and bolt the new base to it.
There are few combinations depending on what you want to achieve, have a think about it.
When you swap the seat bases over, don't forget to swap the seatbelt clip over too.
This is held in place with a 17mm bolt. Remember to do it up tight.
Roadster Seats In A Fortwo
If you want to fit Roadster seats to a fortwo and don't want to just change the upholstery
you have two options. Firstly you can change the passenger side runners for the ones already
in your car, secondly you can weld a new bracket to the Roadster runner to make it fit.
To change the runners over, look at the info above. If you fancy welding, keep reading.
The fix involves drilling out the two hucks that hold the two brackets
on the original passenger side sliders. Once you have the brackets off,
you then have to weld the bracket on the new sliders. There is a knack.
Put the new seat in and bolt it up at the two points at the back of the sliders.
Take the brackets you removed from the old seat and slide them into their correct position.
Mark the position on the sliders so when the seat is removed they can be
repositioned and held in place. I found the easiest thing to use was sellotape.
Take a blade and strip back a bit of the paint just in front and behind the bracket,
line the bracket up and run two short seam welds front and back.
Use and angle grinder to level the weld at the back down level with the bracket.
Paint the weld and any other bare metal to inhibit corrosion.
The seat will now bolt in place in all 4 corners, plus it will slide further forwards.