....that there is somebody on this forum who can tell me the difference between a K1100RS petrol tank and a K1100LT petrol tank.

Because, I've asked Motorworks if they've got a decent 1100 tank in stock, and they've asked which sort I'm after? And I've no idea - it's for a K75k which, unsurprisingly, doesn't feature in their listing info.

Any help...much appreciated 

RS tank is wider than the LT tank.
Won't put a RS tank on a K75, unless you have the S fairing.

I have a Canadian-sourced K1100LT tank on Big Block and a tank from my '96 US K1100RS in the garage. Both appear to have close to identical measurements (using a metal tape measure, so not totally accurate) across the stern, the bow, over the top centre and side to side underneath. I don't have the inclination to try them on each bike, but they surely look a lot alike. It must be some smidgen the thickness of a red pubic hair that they're different as it's not obvious in my unscientific attempt.

Also, realoem shows the same part numbers (and supercessions) for a prime tank between RS & LT: 16 11 0 026 150 & 16 11 2 307 468. California models use a different part number that's likely due to extra drain/vacuum lines for emissions purposes, 16 11 1 455 101 for LTs only, up to prod date 1/93.

That.......could explain a lot.

This is for the K75k which has an aftermarket seat/tail unit. It always puzzled me that the seat/tail unit seemed to be too wide at the front where it was supposed to line up with the rear of the tank - I ended up cutting the front off and re-making it so's it lined up properly.

Maybe, the aftermarket seat/tail unit was designed for a RS tank and I was using an LT tank?

Bloody Motorworks have now completely shut their customer collection point so I can't even visit them even thought they are only a very pleasant 30 minute ride away. There's no likelihood of them ever reopening it either - costs too much to have staff on hand to deal with annoying customers!

Thanks Arlina.

C'mon Arlina - more info please!

K1100 LT up to about Sept 93 had an identical tank to the K100 then at the introduction of the K1100RS the tank changed so as to accommodate the dual tube spine on the newer frames of both LT and RS. From approximately the same time the K75RT tanks changed to the same tank as the K1100 LT and RS. The spigots that the mounting rubbers sit on are longer to accommodate the wider section of the tank.
I have found that K75RTs from 93 or 94 the tanks can be either but from Sept 94 to end of production the K75RT had the later type of tank
There is a small difference of capacity (a few hundred mls) between the tanks but external appearance is the same when on the bike.

Top quality info guys, I really appreciate your tape-measuring and research.

So let me get this right - and for my purposes an '1100' tank is one with the wider clearance on the underside for a dual tube frame:

A tank from an early K1100LT might not be a '1100' tank?

A tank from a later K75RT might in fact be a '1100' tank?

But if it is an '1100' tank, then there's no differences between models to worry about.

...And things'd be much easier if I stopped thinking of it as an '1100' tank, instead a 'dual tube' tank.

Enlightened/confused in equal amounts 

Let's use ETK and see how many different part numbers there are for prime coated petrol tanks for the various models, and what the official Katalogue says they fit.

K75, K75C
16 11 1 453 382 - to 1/93, all markets
16 11 1 455 165 - to 1/93, California
16 11 2 323 867 - 2/93 on, all markets

K75S
16 11 1 453 382 - to 1/93, all markets
16 11 2 323 867 - 2/93 on, all markets

K75RT
16 11 1 455 011 - to 1/93, non-US markets
16 11 2 307 468 - 2/93 on, all markets (also K1 2/93 on)
16 11 1 455 101 - US markets, to 1/93

K1, K100RS-16V, K100 Std, K100LT, K100RS & K100RT
16 11 1 450 631 - up to 5/85 (7l/4l low fuel warning & tabs at the back), US & all other markets
16 11 1 455 011 - 6/85 on, US & all other markets (K1 & K100RS-16V up to 1/93)
16 11 1 453 420 - up to 5/85, California
16 11 1 455 101 - 6/85 on, California

K1100LT
16 11 1 455 011 - to 1/93, all markets
16 11 2 307 468 - 2/93 on, all markets

K1100RS
16 11 2 307 468 - All markets, all years (superseded from 16 11 2 026 150)

These are the latest part numbers available and all supersede from one other part number or multiple part numbers. I have followed these supersession chains to their end or common supersession and am satisfied with my cross references and duplications.

Hi Chris

I have converted a 92 K1100LT into an RS (came with an LT tank and now has a 93 RS Tank)

I by change was given a 75 tank last week (not sure what model but it had ABS ! and a round headlight) he gave me the loom and headlight as well), he also offered me frame and wheels but I declined  !! - all for free.

I just happened to have the tank off the RS (that was an LT) and tried the 75 tank on it and it appeared to fit perfectly but to be honest did not check the width. 

I still have the original 1100LT (92) tank, a k1 tank, an 89 k100 8v tank and two others that I can't remember so happy to check a few measurements if you need - but I don't have a k75.

So maybe back to Arlina.

Guys this is superb and it's making some sense.

Looking at TWB's part list, I think it's possible to deduce that there's only actually one tank the fits a dual top tube frame: 16 11 2 307 468. That's after adding Rick G's info that some early K1100LTs had a single tube frame - these will be the 'up to 1/93' K1100LTs in the parts list with the '011' tank that also features on K100 variants and the K1 (all single top tube bikes).
And then (this is great) the same '468' tank appears on the K75RT from '93 - which again underscores Rick G's info, matches what Arlina was saying, and also explains why Ringfad managed to fit a K75 tank to his RS-that-was-an-LT. Arlina was also correct about 1100 RS tanks being wider (as in the frame clearance) than LT tanks - at least for the early LT tanks! Phew.

Team effort! Free Guinness for everyone. Complete faith indeed!

And I can now tell Motorworks to stop asking difficult questions and just send me their best dual top tube tank 'cause they're all the same!

There IS an 'early' K1100LT frame (to 7/93, then beyond, all markets), but there is only one ever K1100RS frame, all markets. Slurps multiple free Guinni.