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Shock Length & Steering Effects


Paul De

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I am looking for input on futzing with my rear shock length. I am installing a set of Ohlins on my '99 R1100RT and was wondering if anyone has messed with the shock length adjustment on the rear unit and can share the results of said tuning exercise. With the stock shocks I have felt the rear sat a bit low based on these two suspension settings I typically run. When I have the stock suspension dialed to the plush side (the way my co-rider insists it be set based on the accelerometer in her butt) as expected handling gets a bit vague. However, when setting up the suspension for solo spirited riding it also seems that to get the bike to handle crisply I have to set the stock rear shock spring preload (with matching rebound damping to stop any pogo effect) higher than required for good compliance chassis stability for my weight. So, last night at 2 AM as I began to torque down the mounting bolts I started pondering adding a milimeter or three to the rear shock length to quicken up the steering and maybe even clean up the fall in tendency I feel in the handlebars at slow speeds that this iteration of RT displays.

 

Being totally geekish, I realize some of this could be addressed through selecting tires with different aspect ratios and tread profiles. Right now I am running Metzler ME-Z6s front and rear. But since my Z6s have a good bit of life in them let's put that part of the discussion aside for now.

 

Fellow suspension tuning geeks, give me your two cents grin.gif

 

Thanks

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Wunderlich sell an adjustable paralever bar, which allows the rear ride height to be adjusted independantly of the shock settings.

 

Andy

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Too much to type here for an in depth reply, but here goes.

 

Your on the right track (lengthen shock) for trying to quicken up the steering input. Be carefull for what you wish for though. You mention trying 1-3mm which is fine and I wouldn't go much more than that. Given the rake and trail of these pigs, you could end up pushing the front when you initiate abrupt steering inputs. If your used to sliding the front for scrubbing speed, then you may be use to the feeling. For the faint of heart and the lack of experience using that technique, I don't recommend trying it.

 

Changing the bike ride height is common practice when setting up a track bike/aggressive sport riding. This is why most manufactures offer bike ride height adjusting as an option. I would use the adjustable paralever bar offered by Wunderlich and leave the shock alone.

 

If I where you I would install your new Ohlins and set them up properly. Once you get the static sag and rider height set up, do some riding and keep very aware of what's going on beneath you. Pull over and make small changes to the damping and write it down so you know where you are.

 

I would bet once you get the Ohlins dialed in, you'll forget all about changing the bike ride height. thumbsup.gif but it's still an option for after you get the shock set up.

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Andy,

I looked at the Wunderlich adjustable torque arm. Excellent quality product, but a bit pricey for what will be a set once and forget it item for me. Besides, I needed to address aging shocks before they puked their guts out and the ride height adjustment was a bonus feature to the primary need. Now If I had an S model stable mate to the RT that doo-dad would have been purchased a while back.

 

Mikey,

I did decide last night to dial in the shocks first with the rear shock set to OEM length even if I was getting a bit punchy by that time of the morning......but I feel a big futz coming on after that. Looking at how the shock length will multiply to ride height I am guessing that only a few millimeters will make a big difference. I was hoping that somebody in the community here had been down the path and could comment on the setting they arrived at for rear shock length. Looks like I may have to post a follow-up for later searches to find.

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What air pressure are you running in your Z-6? I normally run 39 psi front and 42 psi rear (cold). I was last week in the N.GA and TN mountains and tried to lower the front air pressure to factory recommended 36 psi. It caused the bike to feel like it did not want to turn. I had to work much harder to get it to turn, besides it caused several anxious moments. I believe the sidewalls on the Z-6 are softer then on other tires and require the higher airpressures for spirted riding.

My dealer has always recommended 42 psi front and rear for the RT.

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There are a number of after market torque arms. The less expensive ones are a fixed length that are shortened or lengthened from stock. The one I was looking at was actually a Verholen unit that can be adjusted, but is expensive. I can't seem to find the site I originally saw it but you can look at it here http://shop.verholen.de/, or if your German is good, you can read about it as well.

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I've tried all sorts of pressures, but that was an exercise is for controlling side wall squirm, which is diffrent than what I am adressing with rear wheel ride height. The ME Z2 were the worst and have gotten better with each generation. Now I find the ME Z6s have a sufficiently stiff side wall that I run 33 or 34 psi front (haven't stettled yet) and 36 psi rear when I go solo sport riding. I don't want to shrink the contact patch too much so I work up 1 psi steps from OEM specs until the squirminess just goes away.

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I just lengthened my rear ohlins for ride height. I took it to the maximum allowable and it may be a bit high. There is a gap in the threads on the bottom mounting pintle and the book says maximum adjustment should only show one "missing" thread, so that is where I put it.

 

I haven't noticed any steering effects in corners or otherwise, though the change in height was almost half an inch. I do feel myself tipping forward in the seat a bit more in spite of my seat jacks. The ride height is much more comfortable for me, allowing me to ride the seat in the second position instead of the top one. I will, however, probably adjust it down a bit.

 

a) I don't like leaning forward as much

b) when on the center stand I now have four points of contact; both tires and the centerstand. I figured this would make airing up the tires a bit cumbersome.

 

That's my .02

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