K75 suspension question?

[hipfink]

Just bought a low milage K75c 1988. My only complaint so far seems to be the suspension. The bike seems to have a sort of "gyroscopic effect" when riding it. It has a precision instrument rear shock that was set on the lowest preload. I increased it to the higher range. Anything else I need to be thinking of..front fork, etc. It's a hard sensation to describe, almost a circular feel, front end always moving... any thoughts except I may be nuts? Love the bike otherwise...

[rkasal]

Just bought a low milage K75c 1988. My only complaint so far seems to be the suspension. The bike seems to have a sort of "gyroscopic effect" when riding it. It has a precision instrument rear shock that was set on the lowest preload. I increased it to the higher range. Anything else I need to be thinking of..front fork, etc. It's a hard sensation to describe, almost a circular feel, front end always moving... any thoughts except I may be nuts? Love the bike otherwise...


All motorcycles have a gyroscopic effect when riding above ten or fifteen miles an hour. This explains counter-steering. I bought a '95 K75 with 4,815 miles two weeks ago (and have added 1,200 plus my F650's mileage) and it does handle diffferently than the F650. Much differently.

Last week, I added new front and rear tires even though the old ones by appearance were good. The new tires although making the bike now feel as new as the mileage do track on pavement that is grooved. Whithin the first mile of riding on the new pavement I thought my tire was low so perhaps it's a tire issue as my front end as I wrote, tracked?

Do you have this sensation on all types of pavement at varied speeds? Is the pressure in your tires correct? How about the forks? Any leaking? Please describe the sensation you have.

Nice bikes, though, arent't they?

Regards,


Randy Kasal

[hipfink]

hey Randy,,,thanks for the reply.....it happens over 20 MPH or so and seems to happen on all pavement. it's hard to describe but feels as if there is an almost circular motion to the front end. I have an 85 K100 and it doesn't do this. the tires look new but are old, so maybe that would help help to change those out. No leaks by the front fork...thanks again....gary and yes I really like the bike otherwise...

[rkasal]

hey Randy,,,thanks for the reply.....it happens over 20 MPH or so and seems to happen on all pavement. it's hard to describe but feels as if there is an almost circular motion to the front end. I have an 85 K100 and it doesn't do this. the tires look new but are old, so maybe that would help help to change those out. No leaks by the front fork...thanks again....gary and yes I really like the bike otherwise...

Hi Gary,

If those are original tires and even if they look good and even if they don't feel hard anywhere, I'd change them out. My tires looked and felt good with only 4,815 miles but they were 12 years old. I personally would suggest you start with the tires for safety's sake to track down what you're feeling while riding. Good luck!

Regards,


Randy Kasal

[motoedde]

...any thoughts except I may be nuts? Love the bike otherwise...

Try changing the fork oil...
Choose a brand of oil first and then weight...vary the weight higher or lower within that brand. Weights between brands vary...that is a 10 weight in one brand won't feel as firm as a 10 weight in another brand...

Either way...changing th front fork oil would be a good thing....10 weight would be a good start...

edde

[PGlaves]

The K75 and K100 bikes have a characteristic that I can only describe as a vague undulation that feels like your butt is moving in a slow circle underneath you. This is characteristic of a shock which is providing insufficient damping. When you feel that leaned over in a moderate sweeper, you know it is time to rebuild or replace the rear shock.

BMW specs 7.5wt fork oil. If the springs have been replaced with anything even slightly stiffer than the stock springs, then the forks too are under damped. I prefer 10wt fork oil which provides better damping.

[Kayseventyfive]

I prefer 10wt fork oil which provides better damping.

Any particular brand?

[PGlaves]

Any particular brand?

I have often used PJ1 - simply because it was easy to find. Silkolene also makes an oil I have used fairly often. Both are good. Try a Honda shop - or any shop that sells a lot of different dirt, enduro, or motocross bikes.

[Beemer01]

After I replaced the old shock on my K100, the handling nuances, which I couldn't quite get a handle on, vanished. I knew it was different that my old Honda. A new front tire probably helped as well.

Ride on.:bolt

[hipfink]

broad question but which rear shock has anyone had to most luck with...

gary:

[PGlaves]

broad question but which rear shock has anyone had to most luck with...

gary:

Since we (Voni and I) have had 7 K75s and ridden them about 500,000 miles I have had a lot of different shocks. OEM, Works, Progressive, Hagon, and an OEM K100 take-off self-leveling Nivomat.

Right now my K75 standard has an OEM shock, my K75RTP has an OEM shock (they were on them when I bought them), and Voni's K75S has the Nivomat on it.

I actually like the OEM shop for the K75S a lot. That's what I settled into on Old Smokey after I redid the forks with S components. Downside is that they are not easily rebuildable. I like the Progressive 420 shock which has a nitrogen charged reservoir (bladder) internal to the shock body. The last new one I bought was a Hagon. It worked fine, but was a little harsh - probably my fault in setup though.

Theen there is Wilburs and Ohlins - many more $$$ but truly good premium shocks. A K75 is not high performance enough to need that expensive a shock in my opinion but lots of folks just have to have the best.

[deilenberger]

Since we (Voni and I) have had 7 K75s and ridden them about 500,000 miles I have had a lot of different shocks. OEM, Works, Progressive, Hagon, and an OEM K100 take-off self-leveling Nivomat.
Snippage..
Theen there is Wilburs and Ohlins - many more $$$ but truly good premium shocks. A K75 is not high performance enough to need that expensive a shock in my opinion but lots of folks just have to have the best.
It's actually Wilbers (lots of people make the mistake..) and the new guy on the block - Hyperpro..

I'll have to disagree with Paul - I had most of the shocks he had (never a Hagon or Nivomat) and a few others, including Ohlins and Wilbers on my K bikes.. and the top of the line shocks provide a top of the line handling experience - especially if you take the time to really dial them in correctly. On a K bike I found the rear suspension to be over-sprung and under-damped, and there are no provisions for changing that.

If it's a case of having the "best" suspension - then $$$ comes into play. To me - it's worth it - a really good suspension can make the bike more confidence inspiring, and safer. To me those two things make the money well spent. First major change I made on my R1200R - was at around 2,000 miles - a set of Hyperpro suspenders front and back. The stock suspension on the Roadster is good - the Hyperpro is great.

[Montana]

The best thing I did for a 1990 K75RT was have Progressive springs put in the front forks. It was a whole new animal.

[mrich12000]

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Motorcycle Shock Absorber Good shocks :german

With thanks to, www Webike.com





Progressive Suspension 420 Series

wBW Reviews Home

Motorcycle suspensions take a beating, and motorcycle shock absorbers and springs don't seem to last long at all. Automobiles can sometimes go 70k miles or so before the shocks need replacing, but a 600-pound motorcycle's suspension can be gone in as little as 12,000 miles.

Our 1986 BMW R65 test mule came to us with a '70's style BMW suspension: soft and cushy. According to Roland Slabon's book "BMW Motorcycle Buyer's Guide" (see the wBW review), only 364 of these rare monoshock BMW's were imported into the U.S.A. in 1986.

It was comfortable to ride in an old-fashioned sort of way, and it handled well enough for the vintage, so it didn't occur to anyone that the rear shock was knackered.

Until the handling got very weird. The bike felt like it was on ball bearings - as soon as the handlebars were moved in any direction, the rear end of the bike felt like it would swing out as if on a hinge. This was way more play than the "normal" BMW Airhead frame flex should allow, and it got too scary to ride.

At first, we thought something was wrong with the steering head bearing adjustment. Many attempts at changing this didn't do a thing for the handling problem though. A quick note to the BMW Airheads email list came back with recommendations to check the frame for cracking. But the bike only has about 25k miles on it, and the frame and engine mounting bolts seemed fine.

A visitor to the wBW garage, after hearing the story, walked up to the back of the bike and pushed up and down. The suspension had about as much stiffness as a wet noodle. It became immediately obvious that the monoshock, a Koni (probably a replacement for the OEM BMW part) was completely gone. The spring was the only thing holding up the rear.

Why hadn't we noticed this? Like old age, motorcycle suspension failure starts the day the bike is built and is a subtle but continuous process. You get used to the way the bike rides and subconsciously compensate for it, until one day there's a sudden realization that something is seriously wrong.

Well, Koni is long since out of the business of manufacturing shock absorbers for motorcycles. Apparently, they sold the tooling to a manufacturer who makes the shocks under the "Ikon" (Koni spelled backwards!) name. Hagon also makes a replacement monoshock, but many owners of BMWs and other brands of bikes recommended Progressive Suspension's products.

Progressive Suspension has been around virtually forever, and they make shocks and springs for many different brands of street and off-road motorcycles; vintage and classic motorcycles; cruisers and even bicycles and radio controlled cars. Their piggyback reservoir shocks for R/C cars are a sight to behold!

Their products are commonly available at many motorcycle dealers and online retailers, and one of the nice things about the Progressive 420 is that it's rebuildable, making it virtually a lifetime shock. The prices are reasonable also, relatively speaking, that is. Motorcycle shocks are not cheap, and high-end racing shocks can cost several thousand dollars.

We found this 420 with bright red springs at Motorcycle Accessory Warehouse on sale, and purchased both the shock and a set of Progressive Suspension fork springs for a grand total of $444.00, including shipping. We haven't been able to figure out how to disassemble the forks on the R65 just yet, so that story will have to wait.

The Progressive 420 is a real beauty. The body of the shock is made from 14 mm chromoly steel, and it's hard chrome plated. It looks like it's custom-made; as an ex-machinist, I can appreciate from the way the shock is made. The taper up from the main body of the shock, and the upper and lower ball joint are especially nice looking.

Motorcycle Accessory Warehouse only had the 420 with red springs, but that was fine with us. The red complements the red pinstripe on the jet black R65's tank and battery covers, and gives the bike a custom look. There was a very small ding on the red finish on one of the windings of the spring, so we'll see how the finish holds up. It appears to be some type of plastic-like coating and not a paint or powder coat.






We weren't sure how hard or easy it would be to install the shock on the R65. This bike has a set of BMW saddlebag mounts installed, and the frame rails for the mounts covered the existing shock. It's a pain to remove the mounts, but as it turned out, that wasn't necessary.

We found that it was only necessary to remove a single bolt (yellow arrow, photo left) from the lower saddlebag mounting rail, which provide enough play for the old shock to be removed and to install the new one.

The monoshock attaches to the bike with upper and lower mounting bolts. After removing the two nuts that held the old shock in place, we found that it was possible to twist to top of the shock enough to slide it off the mount.

Sliding the shock off its lower mounting stud was slightly harder, but after some twisting and maneuvering, it came off without having to remove any other parts.

By the way, make sure the rear of the bike is propped up under the tire, because there's nothing holding up the rear of the bike once the monoshock is removed. As always, use caution.

Our Progressive 420 came with 4 washers. One washer goes on each side of the upper and lower mounts, and they help to ensure that the mounts don't bind on the bike's frame as the suspension travels up and down.

We didn't want to mar the beautiful surface of the new Progressive shock, so we were very careful when installing it. The round ball joint type ends in the upper and lower shock mounts are easy to rotate, and this helped to make the installation go smoothly. Once the shock is in place, torque the nuts to specifications and don't forget to tighten the saddlebag bolt if you have one.

The damping was at the third setting from the factory, and that's where we left it. We've toyed with the preload a little bit, but no particular setting seems to make much of a difference, probably because the bike's suspension is rather crude anyway and the small adjustments on the shock don't make it through all the rest of the chassis flex to make themselves noticed.

The shock comes with a preload adjustment wrench that works with a 3/8" drive ratchet. The spring has a lot of compression against the preload adjustment collar, making the collar difficult to turn. I'm also afraid that turning the ring will wear away the red coating on the spring's coils. I'm hoping that once the nice red coating starts coming off that it won't begin to peel away from all of the entire spring. Only time will tell...

But the bottom line is that the Progressive 420 is a revelation. The bike now handles better than it ever did, and it's a nice feeling to think that a nearly twenty year old bike handles better than some new ones I've ridden. It's hard to describe, but the shock really smoothes out all the bumps with a very silky feel. There's no abruptness or harshness at all, and the best thing I can say about it is that I don't notice what's happening in the rear of the bike at all, other than it goes where I want it to with no fuss. And the rear end doesn't wallow at all (like it did with the old shock), so it's a very controlled but smooth feeling, both on compression and rebound. If we would have known that this was possible, we would have replaced the shock a long time ago with a Progressive unit, even before the original unit was worn.

We also wanted to perk up the R65's front end; see the wBW article on installing a set of Progressive fork springs for more information.

Meantime, the 420 has made a huge difference in the way the R65 handles and feels, so I'm very pleased. Progressive makes an extensive line of shocks and springs for many different motorcycle brands and models, so chances are they'll have one for your bike.

Note: webBikeWorld® has no affiliation or financial interest related to the products, retailers or manufacturers listed. For informational use only. All material and photographs are Copyright © webWorld International, LLC - 2001-2007. All rights reserved. Terms and Conditions.

Product Review: Progressive Suspension 420-Series Shock Absorber
Available From: Progressive Suspension
Made in: U.S.A. Suggested Retail Price: $418.70 (Street price is ~$380.00)
Product Comments: Very nicely made shock absorber; looks like custom made. Chromoly steel; rebuildable. Nitrogen gas charged. Comes with cool-looking progressive rate springs in black or red. Internal bladder eliminates need for external reservoir. Five position damping adjustment. Threaded collar adjusts preload but collar is a bit stiff and doesn't turn easily. Provides excellent ride characteristics and gives very smooth but controlled ride. Gives the bike's rear end a "silky buttery" feel without wallowing.
More wBW : Motorcycle Maintenance and Repair | Motorcycle Performance Parts



Suspension Tuning Guide-Suspension Troubleshooting Symptoms




Here are some basic symptoms of suspension damping problems that you might find affecting your bike. Remember these are extreme examples; your symptoms may be more subtle. You may also have to find an acceptable compromise on either end of the adjustment spectrum. It all depends on how the bike's handling "feels" to you.


LACK OF REBOUND DAMPING (FORK)

The fork offers a supremely plush ride, especially when riding straight up. When the pace picks up, however, the feeling of control is lost. The fork feels mushy, and traction "feel" is poor.
After hitting bumps at speed, the front tire tends to chatter or bounce.
When flicking the bike into a corner at speed, the front tire begins to chatter and lose traction. This translates into an unstable feel at the clip-ons.
As speed increases and steering inputs become more aggressive, a lack of control begins to appear. Chassis attitude and pitch become a real problem, with the front end refusing to stabilize after the bike is countersteered hard into a turn.


TOO MUCH REBOUND DAMPING (FORK)

The ride is quite harsh--just the opposite of the plush feel of too little rebound. Rough pavement makes the fork feel as if it's locking up with stiction and harshness.
Under hard acceleration exiting bumpy corners, the front end feels like it wants to "wiggle" or "tankslap." The tire feels as if it isn't staying in contact with the pavement when on the gas.
The harsh, unforgiving ride makes the bike hard to control when riding through dips and rolling bumps at speed. The suspension's reluctance to maintain tire traction through these sections erodes rider confidence.


LACK OF COMPRESSION DAMPING (FORK)

Front end dive while on the brakes becomes excessive.
The rear end of the motorcycle wants to "come around" when using the front brakes aggressively.
The front suspension "bottoms out" with a solid hit under heavy braking and after hitting bumps.
The front end has a mushy and semi-vague feeling--similar to lack of rebound damping.


TOO MUCH COMPRESSION DAMPING (FORK)

The ride is overly harsh, especially at the point when bumps and ripples are contacted by the front wheel.
Bumps and ripples are felt directly; the initial "hit" is routed through the chassis instantly, with big bumps bouncing the tire off the pavement.
The bike's ride height is effected negatively--the front end winds up riding too high in the corners.
Brake dive is reduced drastically, though the chassis is upset significantly by bumps encountered during braking.


LACK OF REBOUND DAMPING (REAR SHOCK)

The ride is plush at cruising speeds, but as the pace increases, the chassis begins to wallow and weave through bumpy corners.
This causes poor traction over bumps under hard acceleration; the rear tire starts to chatter due to a lack of wheel control.
There is excessive chassis pitch through large bumps and dips at speed and the rear end rebounds too quickly, upsetting the chassis with a pogo-stick action.


TOO MUCH REBOUND DAMPING (REAR SHOCK)

This creates an uneven ride. The rear suspension compliance is poor and the "feel" is vague.
Traction is poor over bumps during hard acceleration (due to lack of suspension compliance).
The bike wants to run wide in corners since the rear end is "packing down"; this forces a nose-high chassis attitude, which slows down steering.
The rear end wants to hop and skip when the throttle is chopped during aggressive corner entries.


LACK OF COMPRESSION DAMPING (REAR SHOCK)

There is too much rear end "squat" under acceleration; the bike wants to steer wide exiting corners (since the chassis is riding rear low/nose high).
Hitting bumps at speed causes the rear to bottom out, which upsets the chassis.
The chassis attitude is affected too much by large dips and G-outs.
Steering and control become difficult due to excessive suspension movement.

TOO MUCH COMPRESSION DAMPING (REAR SHOCK)

The ride is harsh, though not quite as bad as too much rebound; the faster you go, the worse it gets, however.
Harshness hurts rear tire traction over bumps, especially during deceleration. There's little rear end "squat" under acceleration.
Medium to large bumps are felt directly through the chassis; when hit at speed, the rear end kicks up.


Thank you Sport Rider http://www.sportrider.com/tech/146_0006_susp_trouble/index.html
:bolt

[BeemerMike]

In 1994 I installed an Ohlins rear shock/spring on my 1988 K75S, right before I went to one of the Reg Pridmore track weekends. I've installed a lot of "go fast" upgrades on bikes and cars over the years, many of which my amateur butt could never tell the difference. The Ohlins was NOT one of these upgrades. The back of the K75S immediately felt more stable and planted.

I agree with many of the posts that you first need to check the entire suspension and steering to make sure there is not some fault or misadjustment that needs to be corrected before you drop a wad of cash on a premium shock/spring, but if everything checks out and it still "wanders" . . .

[motoedde]

broad question but which rear shock has anyone had to most luck with...

Its hard to dis the OEM without knowing the conditions surrounding its application...that is, the size and weight of the rider(and baggage), the use of the bike(twisties, highway, city, off-road), etc.

Shocks on our bike are mislabeled...the OEM unit has a shock and a spring coupled as a singular unit, with basically three options for pre-load and no options for damping.

Many aftermarket shocks/spring unit have more options for pre-load, damping, spring rate, etc. than the stock. And setting them up properly as well as dialing them in properly for the type of riding you's doing is KEY!!!!

I bought a YSS shock coupled with a Wilbers spring from EPM Performance (http://www.wilbersusa.com/)...set-up properly, it is a noticeable difference and costs JUST as much as buying an OEM unit.

HTH