95 K100rs - Shocks Adjust

[Carguz]

Will the rear shock adjustment adjust my road height as well? (Sorry for the ignorance). Can I raise or lower the bike by compressing or expanding the shocks?

I wouldn't mind lowering it a bit.

Thank you!

[BeemerMike]

Do you mean 95 K1100RS?

I believe the only adjustment on your rear shock is spring preload (the ramp adjuster). Spring preload is NOT primarily intended to adjust ride height, but rather to compensate for different loads on the bike (one rider, two riders, luggage, etc.).

However, assuming you keep the bike load constant, IF you increase the preload it will raise the back a little (but the ride will be firmer/harsher), and IF you decrease the preload it will lower the back a little (but the ride will be softer).

Bottom line - Use the spring preload to adjust for the load on the bike, and not the ride height. If you want to adjust the ride height directly, you will need to get an aftermarket shock that includes this adjustment.

[PGlaves]

Will the rear shock adjustment adjust my road height as well? (Sorry for the ignorance). Can I raise or lower the bike by compressing or expanding the shocks?

I wouldn't mind lowering it a bit.

Thank you!

Yes - adjusting the spring preload tighter raises the ride height and looser lowers the ride height. That is in fact about all that adjustment does.

[bikerfish1100]

what Paul said.

the other adjustment on a stock K11 shock is the small dial at the base of the shock assembly that has a screwdriver slot through it. that adjusts the rebound damping- how fast/slow the shock extends back to it's "normal" position after being compressed.

you can get an aftermarket shock that either has ride height adjsutments, or one that is built to lower the back end of the bike (the front should also be lowered an equivalent amount). do a search on aftermarket shocks if you're interested in brands, options, etc.

[BeemerMike]

what Paul said.

OK, I need to look up some suspension references when I get home today. IF the ONLY effect of adjusting the spring preload is to adjust the rear ride height, then there would seem to be no reason for a rear shock to have BOTH an adjustment for spring preload AND and a separate adjustment for ride height. Some shocks do have both (e.g., the rear shock on my 916). :confused:

[PGlaves]

OK, I need to look up some suspension references when I get home today. IF the ONLY effect of adjusting the spring preload is to adjust the rear ride height, then there would seem to be no reason for a rear shock to have BOTH an adjustment for spring preload AND and a separate adjustment for ride height. Some shocks do have both (e.g., the rear shock on my 916). :confused:

Mike,

Here is the logic. When the weight of the bike is on the strut (spring/shock) the spring compresses somewhat. In that position what is compressing the spring is the weight of the bike. By screwing the "preload" collar to a position on the strut further from the top eye, all I have accomplished is raise the back of the bike when the weight is on the strut and the spring is pushing back.

There are some suspension systems that use a pivoting link system that is even more pronounced that the inch or so we can typically adjust a screw collar around the shock.

[BeemerMike]

Here is the logic. When the weight of the bike is on the strut (spring/shock) the spring compresses somewhat. In that position what is compressing the spring is the weight of the bike. By screwing the "preload" collar to a position on the strut further from the top eye, all I have accomplished is raise the back of the bike when the weight is on the strut and the spring is pushing back.

There are some suspension systems that use a pivoting link system that is even more pronounced that the inch or so we can typically adjust a screw collar around the shock.

Paul,

Yes, I understand the logic that increasing the spring preload will increase the ride height some, but what I am stuck on is whether increasing the ride height is the ONLY effect. It may be, but I just want to check some references.

[BeemerMike]

BTW - Carguz has started another thread about an 85 K100RS. Could you clarify which bike you have . . . a 1985 K100RS or a 1995 K1100RS? To my knowledge, there is no 1995 K100RS.

Thanks.

[PGlaves]

Paul,

Yes, I understand the logic that increasing the spring preload will increase the ride height some, but what I am stuck on is whether increasing the ride height is the ONLY effect. It may be, but I just want to check some references.

Let me know what you find - I'm more than happy to learn more, right, any time.

[Carguz]

My typo.

Sorry.

[deilenberger]

Let me know what you find - I'm more than happy to learn more, right, any time.

http://www.eilenberger.net/Suspension/suspension.htm

See section on preload and sag. That is the real purpose of the adjustment. A side effect is it will change ride height, but "ride height" is another way of saying "dynamic or loaded sag". IMHO it's more important to get the shock within it's normal working range with your butt and crap on the bike than it is to set the seat height (ride height.) I've made the mistake of trying to compensate for an overly tall bike by reducing preload, and ending up with an almost unrideable bike due to the shock bottoming out.

[BeemerMike]

OK, new day, new cup of coffee, and chance to check some references.

1. DECREASING the rear spring preload will LOWER the rear ride height, because it will INCREASE the "static sag" (i.e., with weight of bike + rider + other load) of the rear suspension. (The rear spring will start out less compressed, and therefore the rear suspension will have to compress more to generate enough spring FORCE to support the weight of the bike + rider + other load.) This will NOT change the spring RATE, assuming you have a "straight-rate" spring, and not a "progressive-rate" spring, so the ride quality will NOT be softer (this is the big mistake I made in my first post - oops!).

2. INCREASING the rear spring preload will have the exact opposite effect (i.e., will RAISE the rear ride height. It also will not change the spring rate, so the ride quality will NOT be firmer.

3. However, adjusting the rear spring preload will also change the "free sag" (i.e., with weight of only the bike) of the rear suspension, and in the same direction as the static sag. This is not too much of a concern when DECREASING the spring preload, because you just end up with some more free sag, but when you INCREASE the spring preload you have to be careful not to reduce the free sag to zero, or "beyond" zero, and therefore "top out" the rear suspension.

4. Rear suspensions that have BOTH spring preload adjustments AND ride height adjustments (like my 916) allow you to adjust the rear ride height without changing the static sag or the free sag adjustments. Therefore, once you get the correct/desired spring rate (assuming you are playing with this), and adjust the spring preload to give you the correct/desired static and free sag, you can separately adjust the rear ride height without changing the other adjustments. (This is where I got "confused" in my earlier posts.)

Carguz - Therefore, you CAN lower the rear of your 1985 K100RS by decreasing the preload on the rear shock (i.e., via the ramped collar). However, for a "rider only", I think the BMW factory recommendation is to set the preload collar on its lowest setting ("0" or "1"), so I'm not sure you would gain anything unless your rear shock is now set to a higher preload for some reason. Also, remember that if you set the spring preload on its lowest setting to lower the bike AND you then carry a load on the bike other than just you (passenger, luggage, etc.), the rear suspension will be compressed even further, and you will reduce the available suspension travel, and therefore risk "bottoming out" the rear suspension on a big bump or dip in the road.

Therefore, although you CAN adjust the ride height by adjusting the spring preload, I still think the principal reason to adjust the spring preload is to maintain the free sag and static sag within the desired ranges.

As someone else said, you also have to be sure that you raise and lower the front suspension the same amount as you change the rear suspension, if you make significant changes to "factory" rear ride height (at least if you want to maintain the BMW factory set up). This is fairly easy to do on your bike, but don't start playing with it until you really understand the effects.

If you go to the Ohlins website, they have a very good explanation on how to adjust motorcycle suspensions, including how to check the static sag and free sag (both front and rear), how to adjust the sag, and how to check that you have the right rate springs in the front and rear for your bike, for your weight and bike load, and for your riding style.

Good luck!