Roadster vs interstate pillion room

I have a 1974 Roadster and when I'm sitting normally there is very little room for a pillion. Is the Interstate any better in this respect and if so would changing just be a matter of simply swapping tank, seat and sidepanels? I am 6'3" tall but there is twice as much pillion room on my T140 Bonneville.

There isn't much difference in the actual seat length, but, to accommodate the longer Interstate tank, the Interstate seat is positioned roughly 3-4 inches further back on the frame so if the rider sits in the same position as before, the pillion will have more seat space, and yes it is basically just a matter of swapping, tank seat and side panels.

It seems to me that the 'natural' sitting position on a Roadster leaves insufficient room for a comfortable pillion. I have to sit uncomfortably far forwards to generate adequate pillion room (I am 6 foot tall).

With an Interstate tank fitted, the seat is 3-4 inches further back as LAB says, but I sit in the same position as on the Roadster, so that 3-4 inches is pure pillion space.

Like you seem to be contemplating, I've also bought an Interstate tank and seat so I can swap over easily, I'll keep it in Roadster trim for normal use and convert to Interstate for longer trips.

Note: changing the side panels is not actually necessary, but you may prefer to. IMHO Roadster side panels look perfectly Ok with an Interstate tank, but not vice-versa.

The Interstate seat is wider. Im 5'8" and 120 pounds so room isnt a big deal solo on the
roadster but no matter the pillion is cramped.
The Interstate AN seat I have, new, is about an inch and half longer and wider than the
Roadster. The top view of the Interstate seat is more rectangular.

If you are going to ride two up, either the Interstate or Fastback seats are more comfortable.

you should also consider reinforcing/strengthening the rear loop, particularly with the interstate setup,

plenty of info here on that

When changing to an Interstate configuration you may also need to change the grab rail. The early Mark II and IIA's had a specific grab rail for the Roadster and another for the Interstate. Later in that production year they changed to using one grab rail (p/n 06-4978) for both the Roadster and the Interstate.

So if you need to change the grab rail I would recommend getting the later one. That way you can reconfigure your bike from Roadster to Interstate by just repositioning the grab rail.

Peter Joe

Thanks for all the helpful replies - I'm guessing I need at least an extra 6-8" rather than 3 to 4" but I think the best way forward is to find an Interstate and try it for size with my lady. Good points re side panels and grab rail.

Interbacks are rather comfortable two up. Interstate tank with long range fastback seat and tail section.

the weight of your pillion could be a frame issue

the only thing supporting is the tubular frame loop section rear of the shock as stated above

I have seen that loop severely bent downwards by a heavier pillion rider

many consider it a weak point.........