Front End Dive on a K75

I have, as some of you know, a kind of hybrid K75(s). I was originally a 1986 K75 Standard, but had been modified to an "S" version by the addition of a complete factory new fairing, low bars, Progressive front springs, Works Racer rear shock and assorted other goodies including stainless brake lines.

My problem is that under even moderate braking the front end dives pretty hard. I had a 91 K75 that didn't do this hardly at all.

It is possible that the fluid in the forks is older, I have had the bike 2 months. It is also possible that the previous owner blew smoke about the front Progressive spring upgrade.

The dive is very severe any time I hit the brake hard. It stops well, but feels like it might do a stoppie at any time and the forks move about 4"? A lot more than my old bike.

Any suggestions?

Jim

JimVonBaden said:

I have, as some of you know, a kind of hybrid K75(s). I was originally a 1986 K75 Standard, but had been modified to an "S" version by the addition of a complete factory new fairing, low bars, Progressive front springs, Works Racer rear shock and assorted other goodies including stainless brake lines.

My problem is that under even moderate braking the front end dives pretty hard. I had a 91 K75 that didn't do this hardly at all.

It is possible that the fluid in the forks is older, I have had the bike 2 months. It is also possible that the previous owner blew smoke about the front Progressive spring upgrade.

The dive is very severe any time I hit the brake hard. It stops well, but feels like it might do a stoppie at any time and the forks move about 4"? A lot more than my old bike.

Any suggestions?

Jim

Click to expand...

So aside from the springs, you've got the front forks of an '86 K75?

If "yes", there's your answer. By '91, BMW had put the 'S' type forks, as found on K75s's, to the full line of K75's. So though you've got relatively fancy springs up front, you've got the damping of the older forks which were known for their bouncy old-school BMW feel.

Also, when the PO installed the springs, they may not have taken the time to increase the preload. Since you're a ...um... bigger person, the stock preload is probably insufficient.

The best bet, if you want to match or do better than what you had with the old bike without the expense of installing 'S' forks, would be to install some racetech cartridge emulators. They can be, from what I understand, tricky to get set up properly but you probably can't do much better - especially at $150.
race tech cartridge emulators

Re: Re: Front End Dive on a K75

knary said:

So aside from the springs, you've got the front forks of an '86 K75?

If "yes", there's your answer. By '91, BMW had put the 'S' type forks, as found on K75s's, to the full line of K75's. So though you've got relatively fancy springs up front, you've got the damping of the older forks which were known for their bouncy old-school BMW feel.

Also, when the PO installed the springs, they may not have taken the time to increase the preload. Since you're a ...um... bigger person, the stock preload is probably insufficient.

The best bet, if you want to match or do better than what you had with the old bike without the expense of installing 'S' forks, would be to install some racetech cartridge emulators. They can be, from what I understand, tricky to get set up properly but you probably can't do much better - especially at $150.
race tech cartridge emulators

Click to expand...

That was very PC of you Knary!

Thanks for the info on the springs, it makes very good sense. Do you think that a heavier weight fork oil would do any good at all?

Does this also explain the slightly twitchy steering? The bike tends to have VERY lite steering and almost falls into turns. It also tends to wallow a little on high speed sweepers.

Or maybe it's just my...um size...

Jim

Re: Re: Re: Front End Dive on a K75

JimVonBaden said:

That was very PC of you Knary!

Thanks for the info on the springs, it makes very good sense. Do you think that a heavier weight fork oil would do any good at all?

Does this also explain the slightly twitchy steering? The bike tends to have VERY lite steering and almost falls into turns. It also tends to wallow a little on high speed sweepers.

Or maybe it's just my...um size...

Jim

Click to expand...

I'd bet it has much to do with the handling. With a stiff rear end, squishy front end and your mass, the front is heavily compressed making it want to go nose first.

Heavier oil will help some. I'd recommend setting the preload (it's done with some PVC spacers on top of the springs) AND fiddling with the oil. Lots of riders only change the oil to something heavier. But slowing the damping mostly helps with how the front end deals with rapid bumps and doesn't completely address the wallow and dive.

Re: Re: Re: Re: Front End Dive on a K75

knary said:

I'd bet it has much to do with the handling. With a stiff rear end, squishy front end and your mass, the front is heavily compressed making it want to go nose first.

Heavier oil will help some. I'd recommend setting the preload (it's done with some PVC spacers on top of the springs) AND fiddling with the oil. Lots of riders only change the oil to something heavier. But slowing the damping mostly helps with how the front end deals with rapid bumps and doesn't completely address the wallow and dive.

Click to expand...

That makes perfect sense since I now lean further forward than I did on my old K75. Combined with the lesser shocks it would be that way. Funny though, I always felt my old K75 was a bit sluggish.

I think I will try the cheap route you just mentioned first. Maybe with those changes I can find a happy medium. I can live with the dive, if it's a little less pronounced.

Thanks, and I guess I will keep the Knary Yellow paint afterall.

Jim

JimVonBaden said:

I have, as some of you know, a kind of hybrid K75(s). I was originally a 1986 K75 Standard, but had been modified to an "S" version by the addition of a complete factory new fairing, low bars, Progressive front springs, Works Racer rear shock and assorted other goodies including stainless brake lines.

My problem is that under even moderate braking the front end dives pretty hard. I had a 91 K75 that didn't do this hardly at all.

It is possible that the fluid in the forks is older, I have had the bike 2 months. It is also possible that the previous owner blew smoke about the front Progressive spring upgrade.

The dive is very severe any time I hit the brake hard. It stops well, but feels like it might do a stoppie at any time and the forks move about 4"? A lot more than my old bike.

Any suggestions?

Jim

Click to expand...

I see Scott answered you to some extent.. a bit more info..

The K75S was the first K that came with the "S" forks, which have the damping concentrated in the left leg with the right one pretty much along for the ride (according to BMW) or - it might be compression damping is done in one leg and rebound in the other. Whatever..

There is a BIG difference between the "S" forks and the standard K forks (which your '86 K75 standard would have come with).

Aside from springs - the innards of the forks are different, and the forks have the integral fork brace (that the fender bits mount to).

I had the original K forks on a K100RT - and changing weights of fork oil, springs (three different types) never really made it satisfactory for me. My final step was going to be adding Race-Tech Cartridge Emulators to the forks - and I setup my spare set of forks for exactly that, and installed the emulators in them.

The spares are still sitting in my garage loft. Before I ever got around to installing them and doing the tuning - I got "S" fever, sold the K100RT and got THE K75S.

I heard good things about the BMW "S" forks - which IMHO are true. They are a great improvement over the stock front end.

Problem was finding them used (new was WAY too much $$$) - undamaged forks in a wrecked bike are quite rare. I never found any.

I also heard good things about the Race-Tech emulators (which are adjustable for damping..) - but I never got to try them out and I'm happy enough with the "S" forks on the K75S that I'm not gonna screw with'm.

If anyone is interested in the Race-Tech's - complete with forks and sliders (I'd recommend using aftermarket springs) - make me a reasonable offer off-line and they're yours.. I'm thinking on Helibars for THE K75S, and have to come up with a funding source

Best,

Hi Don,

You might want to reconsider the Race Tech emulators. Ute's '95 airhead has the K forks and, as you know, I had Race Tech emulators installed. Greatly improved the front end.

Even the BMW S forks use a damper rod - same damping for compression as for rebound. The cartridge emulators allow a reasonably compliant compression (soft) while retaining good rebound control.

Re: Re: Front End Dive on a K75

deilenberger said:

I see Scott answered you to some extent.. a bit more info..


Aside from springs - the innards of the forks are different, and the forks have the integral fork brace (that the fender bits mount to).

If anyone is interested in the Race-Tech's - complete with forks and sliders (I'd recommend using aftermarket springs) - make me a reasonable offer off-line and they're yours.. I'm thinking on Helibars for THE K75S, and have to come up with a funding source

Best,

Click to expand...

Hi Don,

I have wondered about several people's comments about the built in brace with the "S" forks. Some have also said that the standard forks had a one piece front fender. My bike has a two piece front fender just like my 91 had. Does that mean I may have an "S" fork set up? Is there a way I can check for sure? I also have the brake line that runs through the steering head.

If so, how would that effect the advice in this column about what to do about my dive problem?

I might be interested in your RaceTechs, depending on the dificulty in swapping them out, and setting them up. I am sure I could swap them out, but not sure if I could handle setting them up.

Jim

Don or Jon will remember better than I, but I seem to recall that the S forks had an "S" stamped into cap (the stout metal piece, not the plastic cover).

Re: Re: Re: Front End Dive on a K75

JimVonBaden said:

Hi Don,

I have wondered about several people's comments about the built in brace with the "S" forks. Some have also said that the standard forks had a one piece front fender. My bike has a two piece front fender just like my 91 had. Does that mean I may have an "S" fork set up? Is there a way I can check for sure? I also have the brake line that runs through the steering head.

If so, how would that effect the advice in this column about what to do about my dive problem?

I might be interested in your RaceTechs, depending on the dificulty in swapping them out, and setting them up. I am sure I could swap them out, but not sure if I could handle setting them up.

Jim

Click to expand...

Jim - the S forks have an S stamped in the metal cap on the top (under the plastic caps) - usually. Apparently the early ones installed on the K75S (like 1987) didn't have the S stamped in them. If it isn't on a K75S - I'd expect to see the "S" stamping on the top.