I removed my side rails some time ago (mostly for aesthetic reasons).

I was doing some fiddling with the bike the other day and the side rails crossed my mind. They are hefty! And they bolt into some reinforced areas at the front and middle of the fender. It dawned on me they might be there to reinforce the strength of the frame under the pillion seat. I have carried a passenger many times without the side rails on (with no problem), but I just had one of those 'holy sh!t' moments when I realised it may not be safe!

Anyone know if this is the case, or have thoughts/experience to share?

You Know it's a lot stiffer with them on.
Is it strong enough
Without them?
Worst case scenario
Heavy passenger
Hit a big bump
Might not work out so great..

That is one beautiful Cafe Racer. Absolutely gorgeous.!!

I remember seeing some earlier posts about this. It was mentioned that without the rails, people have seen the tail of the fender "wag" side to side quite a bit under acceleration. I would consider them structural. If you don't like them chromed, maybe you could scuff them up and paint them the fender color. Or maybe chop the fender and move the tail light assembly elsewhere to get the weight off the tail of the fender.

My only experience was with removal of saddlebag supports, where you need to partially unbolt the rails. When reinstalling the bolts to them you could affect fender alignment slightly when you tightened things up. There was some play in the whole that stiffened when it was all tight.

There is re-inforcement in the weld up of the fender,  but in the end it's all just overlaid and tweeked sheet metal. I suspect that's pretty strong if you don't have a B-seat, if you do and have a load on the rear of the fender (i.e. passenger) they add a good mount of horizontal support along it's length. That's an awful large amount of steel for looks only.

If you have the sissybar and your pasenger leans back on it, that could be quite some leverage applied to the rear of fender below the high point of the arc of curve. That force could act to bow the sides of fender and cause a failure (collapse). So I suspect it adds strength not only lengthwise to down force but also to stiffen side walls laterally.

The fender bolts to the frame. 1/4" past that, the frame ends. The passenger seat is carried entirely by the fender. The side rails bolt to the fender and no part of the frame In fact the frame is atleast 3" away ending before the back end of the rider seat. If the tail was wagging side to side, rails or no rails its the fender and its thick as Druck inner bracing that has started to give. Rails wont slow it down, and may accelerate its demise.

The rails were presumably originally fitted to allow for a sissy bar which does need to be beefy to keep your passenger from taking an unscheduled dismount. Back in those days those big tall sissy bars were all the rage, with Yamaha even selling an extra tall one for those maxims from 82 to 87 IIRC. I had one and a bunch of maxim people were asking for it.

I've hacked many of these and almost the first thing I do is toss that. Only reason I haven't done it on my sons bike yet, he's learning and if he's not stopping I can use that to provide some "braking" Now however he's slamming on the brake I'll need to get him to feather it, as soo as he figures it out, off this thing goes.

Cool.
Srinath.

Give it a look when you change the tire.
You've proven it's strong enough for what you're doing.
You could have her follow you and accelerate away hard from a stop, run the gears, get on it, and ask her if the fender is going nuts.
Mine shook the license plate to ruin, even with the braces.

@Srinath .. haha ... I have to admit, as I've been working in slimming the bike down, the biggest stumbling block is ... what to do about that rear end!