How Flush should the seat be with the tank on a K75RT?

[atarifan2600]

I've got a '97 K75RT, with what appears to be the Corbin/BMW Factory seat.  (Regular with a hinge, not low sliding!)
The seat is based on the Dual Canyon, but covered in a basketweave Vinyl, which isn't an option Corbin usually offers.

The seat is firm, but it works for me- I've done a saddlesore on it, and survived-  so I'm not necessarily getting rid of it because of comfort, but because the vinyl is getting torn worse by the day, and recovering it is awfully close to the price of a whole new seat.

Conventional wisdom seems to tell me that I can order any seat for a K75 or K100, from 86+ and everything should "just fit".


I purchased a seat off Ebay which purports to have come off a '93 K75.  It's a Russell Day Long built on a BMW plastic pan.  The problem is that when this seat is mounted, it's nearly 1" shorter than my current seat.  It barely touches the bumpers on the tank, and leaves a huge gnarly gap that can't be right.

I've got a friend that has a Corbin Rumbler that's not currently on his bike.  This pan looks and feels better than the pan on the ebay seat- it certainly looks "closer" to the pan on my seat, but it's still a shorter measurement from nose to tail.  It MAY fit a little bit better than the Day Long, but it's still a pretty generous space. 

Both the Russell And the Rumbler came with hinges that are different than the ones on my bike.  My seat has the shock-mount hinges, rather than the flat metal ones.  I can't transfer my shock-mount hinge onto the Day Long seat, because Tab A won't fit into Slot B.  (Even laying the seats on the bike with the ONLY fitment being the latch pin, the only one of the three seats that looks even close is the Corbin Dual Canyon.)

According to the Seat Fitting Guidelines, the Rubber mounts are for a "slightly later" K1100RS bike.
What's confusing me is that the Corbin diagram that Johnny's listed on that same page says "K bikes 93+ need 96-92 hinges... Except for RTs."

So did RTs originally come with non-rubber mount hinges?  Is there something about the tank fitment that the rubber-mount hinge is the right seat? 
Why the hell does nothing fit?

Why can't I find the P/N for the BMW Pan that the ebay'd Russell is covered on?
Is it possible to somehow adjust these things to take up an inch of slop that I'm not able to figure out?

I'm going crazy here, hopefully somebody has some ideas.


(The Russell seatpan is 52 53 453 497 0, which I can't find anywhere.  it looks like I can't read a P/N, but I'll let you look at it.  The Corbin Rumble is a K86R pan, and the factory Corbin is KCDS86-2.   I can't  find any information on the interwebs for a K86R other than my buddy's post about the K86R not fitting his K75S, and somebody in france selling one.)

Pictures of the P/N on the BMW/Russel Pan, and then the nose of the Corbin and the Russel, showing the ridiculous gap.

[Laitch]

Is the front of the seat under tension with the two cylindrical stops stuck on the tank that I see in the first photo? My experience indicates there should be a pad on the tank and no stops on the seat there or on the tank.

[Laitch]

Conventional wisdom seems to tell me that I can order any seat for a K75 or K100, from 86+ and everything should "just fit".

Presuming that there may not be unrecorded production variances in this case is probably not a good strategy.

I sold a Corbin that was mounted on my bike when I purchased it after I was given a stock seat from a '92 K75S. The front of the stocker had a gap from the tank pad that the Corbin didn't have and that other bikes I've seen didn't have. What I had to do was repress my gap-envy and sublimate my desire for closure by appreciating the local scenery instead of staring into the void.

As an unintended consequence, the gap between my tank and seat accommodates the width of the seat bag's rear strap buckle without crushing it or impeding the locking of the seat.

[atarifan2600]

My K75RT has two bumpers that are affixed to the tank.  They look well mounted, but it's impossible to say what the previous owner may or may not have done to it. I have no reason to believe that there's been any butchery that's related to this frame/seat-  the bike is otherwise fantastically clean.

I'm unable to find any 'gap cover' that'd suilt the bill for this, other than the rubber tank pad that comes with the Low Seat-  but the low seat includes the plastic clips on the side to hold it-  and this isn't a low to high conversion or vice-versa.

I feel like there's some variance in what fits what bike, but I can't find any information at all that helps to put all the pieces together.

[Laitch]

To ask again, is the front of the seat in contact with the bumpers?

[atarifan2600]

Yes, I think it contacts the bumpers.

Disclaimer: I haven't sat on it to see how it responds under weight-  not just the front two bumpers, but the frame contact points.  The


I get the comments about just moving on and appreciating the comfort of the seat- but it really looks incredibly poorly put together, even from a distance.  A hell of a lot better than the tatty corbin, but that's a terrible choice to have to make.  I'd like to get the 'right combination' of seat/accessories/fitment for the bike, but it's hard to come by.

[Laitch]

A pad should be there instead of those bumpers regardless of whether it's a low or regular seat. On a bike with the regular seat, the pad is stuck onto the tank with adhesive. I'm not familiar the bumpers and haven't seen them on a BMW microfiche. Take them off and replace them with an aftermarket pad if you can't find a stock one. Cut yourself some out of the Snakeskin sheets here or find an attractive mudflap, worn tire or other such material then make yourself one and stick it on with adhesive.

Post a picture of the whole bike from one side taken from eye-level with the seat.

A hell of a lot better than the tatty corbin, but that's a terrible choice to have to make..

Compared with choosing between watching your child starve to death or running to get food and risk being shot by a sniper, it doesn't seem so terrible really.

[johnny]

greetings...

can slide the tank back off the steering yoke  for a flush seat tank fittment..

can velcroe the tank to the frame rails so it dosent slide around when hammering the twistys....

j o

[Laitch]

can velcroe the tank to the frame rails so it dosent slide around when hammering the twistys....

Although velcro is unquestionably more attractive and comes in a rainbow of colors, ratchet straps have a pleasing industrial look and can be used to hoist your bike up a cliffside and back over the guardrails, if you've used enough of them on the tank.

[atarifan2600]

sliding the seat back would involve lifting the rear pins on the tank out of the frame grommets, and having the tank sitting loose on the frame, except for the addition of that velcro? 

So now it seems like I'm into even worse decisions.
As long as we're making comparisons as to just how trivial and non-terrible poor bike fitment is, now we're not chopping off a limb and serving it to my starving family.


I understand that we can't find a fiche number for the bumpers- those have been driving me nuts. But I can't find a fiche indicating any gap cover, either.  I don't see any mention of that gap cover on anything other than a low seat, but if somebody can point me in the right direction.

How come I can't even find a part number that lines up with that seat pan ?  There's just enough mystery here that'll snap into place once the missing component is realized, I had just hoped it was a bit more obvious.

[Laitch]

How come I can't even find a part number that lines up with that seat pan ?  T

Speaking from wizened experience, it's because life is unfair, humans are flawed and the whole system is rife with imperfections right down to birth control pills and Ural hacks.

There are no gap covers so stuff something useful in there like sandwiches, moist towelettes, or tortillas.

[atarifan2600]

If I use Google Image Search on K75RT, I see a ton of pictures of bikes, and the only ones with any sort of fitment on the tank are the low seats, wherin the lack of battery covers is a dead giveaway.

Most of them don't even have the kneepads, but even that woudln't help.

Can you point me in the direction of a single 'gap cover' for how a k75 seat is fixed to cover a 1" gap between the tank and the seat?

I just want to make sure we're not under the assumption that I'm trying to get the seat FULLY FLUSH with zero air gap.  We're not talking storing tortillas and moist towlettes, it's closer to club sandwiches and neatly folded bath towels.

[Laitch]

Can you point me in the direction of a single 'gap cover' for how a k75 seat is fixed to cover a 1" gap between the tank and the seat?

No, I can't.

In the picture below you'll see a couple of pads—14,15— and something that looks like a foam earplug—13. My bike has a 14. Both 13—I neither know nor care what that is because that's the way I am—and 14 may not be available as OEM. You could investigate 15 but it's designed for a different seat.

I think you're on the right track with the bath towels, especially if you find comfort in folding laundry.

[Laitch]

Wait! I think I hear a flock of goldfinches. I'd better go out and watch them for a while.

[TimTyler]

I've had Corbin low and Corbin high dual seats on my K75 and both have fit flush against the tank. No gaps.

[atarifan2600]

the Corbin Dual High has no gap at all.
The Corbin Rumble and the BMW/Russell both measure 1" shorter nose to tail, and have an appropriately sized gap.

I don't _FEEL_ that it's the bumpers causing the gap, because the front hinge and latch pin are going  a pretty good indicator of where fore/aft positioning is going to pull the seat, and those are currently bigger factors than deformation due to the bumpers on the tank.

I'll set up a photo shoot tonight with better lighting and the differences between the seats.  That'll help clarify, I understand the lack of info isn't helping.

[Inge K.]

About the mystery rubber pads on the tank.....these is used on the K11 models....could be that your tank
has been changed earlier.
Beside that, the late K11's and the late K75RT have identical fuel tanks............

Did put a Corbin Dual Tour on my K11LT, the same problem with the opening between the tank and seat.

[Martin]

I bought a spare seat and had it recovered and shaved. When I picked it up I fitted out the front of his place, on putting the seat down I had a large gap. He came out and had a look, we removed the seat and he took it back inside and heated the pan with a hot air gun. He then got me to hold the pan on the bench ,while he put his weight on the nose of the pan. He did this procedure a couple of times checking the fit on the bike, until it fitted. From observation I think the new upholstery was pulling the pan out of shape.
Regards Martin.

[atarifan2600]

Thanks for the K11-  that makes me feel good that it's actual BMW parts, but it doesn't help me know why one k75 seat seems to be able to cope with them, but the other two seats aren't necessarily shaped to wrap around them, or long enough to fit the frame.


So, for those waiting with bated breath-  Here's the first collection of pics.  I'm posting in groups of three, jsut to keep ti simple-  one eyelevel shot of where the seat meets the tank, one eyelevel shot of the rear of the seat to show that the seat is flush at the rear, and then a top shot.

The Factory Corbin-

[atarifan2600]

The Russell-

[atarifan2600]

The Corbin Rumble- interesting thing here is that the nose doesn't even touch the bumpers .

[atarifan2600]

And here's two tight shots from the opposite side of the bike.  These two are of the seat/frame bumpers and how they sit on the frame of the Russell-  they're approximately 3/4" back of the 'wear marks' from the factory seat, which is arguably about the length of the rubber on the tank-  but the tank rubber may just be brushing the nose of the pan, but it's not 'flexing' or shoving the seat backwards.  Even if the tank bumpers were responsible for the seat being shoved back far enough to create the gap, it seems like the rear seat would be just as bad.

The angle of the nose doesn't look like shoving it down would really correct the geometry of that pairing. 

And an obligatory sandwich shot.

[gazman]

The seat on my K11lt also sits away from the tank. I just cut a 1in strip of black memory foam that follows the contour of the seat an glued it to the tank. Works for me, looks ok.

[Laitch]

And an obligatory sandwich shot.

Thanks for the clear pix, atarifan. Clearly, club sandwiches aren't the way to go here, but innovation, acceptance or reupholstery are options.
Maybe gazman will share a photo. As for why there's variation in the pans—maybe we're just not meant to know that at this stage of human development.

[Laitch]

The Russell seatpan is 52 53 453 497 0, which I can't find anywhere.

Not that this site is particularly authoritative but this is what you get when you remove the spaces between all those numbers then do a search, atarifan. The front contour with the pronounced upsweep looks similar anyway. MAXBMW fiche indicates '87 K100 and K75 seats have different part numbers so they may be different parts with differing dimensions. That may explain fit discrepancies.