What do steering dampers really do? - BMW Luxury Touring Community
 
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post #1 of 16 Old Oct 10th, 2010, 12:48 pm Thread Starter
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What do steering dampers really do?

Thought I'd ask if anyone really knows what they do. It's that, or take mine off (LT) and find out for myself.
Reason I ask, is Harley related. I have a Softtail Deuce that's probably my favorite bike of all times - yeah, I know, there's no accounting for taste, right?. What I really dislike about the bike is the wallowing in high speed turns. It feels like a frame flex, but I can't get rid of it. I'm running all upgraded suspension, and done everything I can think of short of scrapping it.
I do find that if I enter the curve a bit slow, then accelerate through it, it does settle down, but I'm not sure what that's telling me. I'm almost certain it's rear end related, and I am aware that the softtail suspension is archaic at best. This usually happens above 75 MPH in long sweepers, and yes, I do know that this is way beyond Harleys design and intent. I got to thinking that maybe a steering damper might help, but I'm not sure that they're intended to be used on the longer rakes of the Deuce.
Any thoughts? I've asked Harley guys, and all they say is that I need more chrome, or that my full face helmet is the cause
Thanks,
Frank
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post #2 of 16 Old Oct 10th, 2010, 2:48 pm
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Re: What do steering dampers really do?

The steering damper is similar in operation to a shock absorber. You really wouldn't like the LT without one as those of us who have had one fail can tell you. It allows a smoother feel while turning and resists the front wheel woobling effect. As to whether it would help to add one on your bike is a little harder to say. I would expect some improvement but with that frame geometry it may never feel right to you. Have you compared it with another bike of that model? There is always the possibility of a bad tire or other correctly problem on your specific machine.
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post #3 of 16 Old Oct 10th, 2010, 2:53 pm
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Re: What do steering dampers really do?

Generally a steering damper’s job is to keep the front end from shaking , AKA Tank Slapper . I don’t think a steering damper would help your Harley… But , then … I don’t know much about Harleys . I understand the rake & trail on most Harleys make them handle real well at parking lot speeds , but with that steering geometry at speed they tend to want to wander a bit . It might just be the nature of the beast .

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post #4 of 16 Old Oct 10th, 2010, 3:07 pm
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Re: What do steering dampers really do?

That wallowing is more or less a function of the type of bike. I bet the wallowing is more pronounced in curves where the road is not smooth, and especially pronounced when there are 'waves' in the road.

What it is in most bikes is basically that by compressing the shocks and springs in curves since the rear wheel does not EXACTLY go up and down straight but in an arc (basicallys its rotating around the mounting point in the front where the swingarm is mounted to the frame) you are changing the geometry of the bike. It get shorter and longer as the rear goes up and down and in a curve that expresses itself as a wallow. "they all do that, and in this case its serious)

You can make it less pronounced by stiffer springs (front and rear) and by a steering dampener, but it will never go away completely.
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post #5 of 16 Old Nov 1st, 2010, 4:41 pm
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Re: What do steering dampers really do?

For what it's worth, H-D has been running basically the same chassis on all the Softails since about 1986. And that chassis was not designed to blow anybody's mind in the handling department. For that kind of duty, scrounge up an FXR. No, the Softails were just meant to look cool and kinda have a little suspension-type action in back. At my dealership, we occasionally get people in saying things like "When I take one or both hands off the bars at 80 mph, the bike wobbles." To this I say:

1) Don't do that. That's why handlebars have two grips on 'em. Harley put 'em there for a reason. Use both of 'em. Or at least use them if you're gonna ride fast.

2) Check your tire pressure. Should be like 36 front and 38 rear. Check your steering head bearings. Should be free of any "notchy-ness" and adjusted to the correct pre-load - both can be issues on raked-out bikes like the Deuce. Check wheel bearing condition front and rear, and rear wheel alignment. Check swing-arm bearings for condition and any play. Your Deuce probably has at least 1 disc wheel. Any wheels that have wire spokes, check tightness of said spokes. Consider a fork brace up front.
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post #6 of 16 Old Nov 1st, 2010, 5:02 pm
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Re: What do steering dampers really do?

I would definitely put my money on frame flex as the cause for the wobble in curves. In bike (or car for that matter) design, degree of frame flex is mostly a trade-off between smoother ride and better handling, with Harley's usually designed for the smoother ride. I've not ridden the new FL frame, but I understand Harley did a good job redesigning that bike a couple of years ago to improve the handling by eliminating much of the frame flex. I put a lot of miles on my '01 Ultra, but got real tired of the frame flexing in corners. I rode the bike fairly aggressively (anyway, for a Harley) and after grinding down the edges of the floorboards, I decided it was time for a return to BMW. I purchased an '07 LT new and will probably never return to Harley as the BMW just fits my riding style.

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post #7 of 16 Old Nov 1st, 2010, 7:04 pm
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Re: What do steering dampers really do?

That is what made HD buy back my 2005. wobble...especially induced in curves.

If you are SURE your engine/drive train is not loose, then a wheel brace AND damper might help.

If you have an "over" front end, you might also make sure you don't have too much slack in the front tubes or steering head.... if you can shake the front end at all, that's bad. You also need to make sure you aren't having a "runout" problem on the front axle...

Balance of tires will be very helpful...and, you need to know that the "upgraded" suspension is working (damping) properly.

If all that's been done, then you are having frame flex.. look for any "cracks" in the paint... it might be visible...

Frame flex can be seen if the fasteners aren't snug, too....

Suspension flex can occur at the "rubber" mounts.. upgrade them to Poly.

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post #8 of 16 Old Nov 2nd, 2010, 1:04 pm
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Re: What do steering dampers really do?

The structure of any motorcycle has two modes of oscillation. They are called weave (about 3 Hz) and wobble (about 15 Hz).

What is your frequency of oscillation? or poor disturbance rejection?

The way you describe it, I suspect it is weave mode. That is caused by low roll stiffness of the rear axle suspension mechanism. Roll is the rotational stiffness of the rear axle structure elements about a longitudinal (i. e. in the direction of travel) axis.

I doubt steer damping would help as that is usually provided to damp the wobble mode which is caused by the steering head & front fork deflection.

There is a lot published on weave and wobble modes & probably including what to do about them.
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post #9 of 16 Old Nov 2nd, 2010, 6:06 pm
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Re: What do steering dampers really do?

The damper on the LT does absolutely nothing for small moves, very little for slower long moves. It only becomes active after the bar tips have moved a couple inches, and then only if they move pretty fast.

The only reason for it is to damp rapid moves to prevent fast oscillation. Just about any bike will get into a rapid oscillation at some fixed speed if conditions are correct and the damper is not working right.

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post #10 of 16 Old Nov 2nd, 2010, 6:55 pm
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Re: What do steering dampers really do?

I don't know a whole lot about the newer Harley's,
That is anything that was assembled in the US from imported parts, in other words after 1969.

But I had a similar issue on my Shovelhead couldn't find it,
turned out to be the swingarm bearings,
didn't know that for sure until I replaced them.

Here's a little HD "trivia" for you.
The first "Jap part" put on an HD was a Hitachi starter on the 1964 Sportsters,
After 1969 just about all the electronics were imported,
after 71 they all had Showa front forks.
Harley guys don't like it much when you know more "trivia" about their bikes than they do.


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post #11 of 16 Old Nov 2nd, 2010, 7:36 pm
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Re: What do steering dampers really do?

Er ah I reckon they dampen the steering . Seriously sit on the bike with it on the center stand and have someone push down on the top case so the front wheel is off the ground. Then rotate the handle bars slow left to right. Now rotate them fast left to right & you can feel the damper work. Or you can do it right to left if you prefer.

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post #12 of 16 Old Nov 4th, 2010, 6:31 pm
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Re: What do steering dampers really do?

Quote:
Originally Posted by SilverBuffalo

Here's a little HD "trivia" for you.
The first "Jap part" put on an HD was a Hitachi starter on the 1964 Sportsters,
After 1969 just about all the electronics were imported,
after 71 they all had Showa front forks.
Harley guys don't like it much when you know more "trivia" about their bikes than they do.
Actually, the First Electric Start Sportster was 1967 and it used an American made Prestolite starter until 1974 when it went to the Jap Hitachi!


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post #13 of 16 Old Nov 4th, 2010, 8:00 pm
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Re: Thread hijack!

Quote:
Originally Posted by indianut
Actually, the First Electric Start Sportster was 1967 and it used an American made Prestolite starter until 1974 when it went to the Jap Hitachi!
Sorry but I don't agree the 65 Panhead and 66 and later Shovelheads used the Prestolite starter.
the 64 Sportster was a prototype and the first HD to have electric start, (Hitachi)
they made it look like a mini dresser, I saw it at the Rose Bowl swap meet in LA in 1973,
(for sale, nobody wanted it, think of what it be worth now)

but I think we might both be a little right and maybe a little wrong.
because Sportsters didn't go into production with an electric start until 67.
and you're right it was a Prestolite and they were junk.


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Last edited by SilverBuffalo; Nov 4th, 2010 at 8:13 pm.
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post #14 of 16 Old Nov 5th, 2010, 7:04 pm
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Re: What do steering dampers really do?

The First HD with Electric Start was the 1964 GE Servicar.


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post #15 of 16 Old Nov 5th, 2010, 8:05 pm
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Re: sorry about the thread hijack

There's plenty of HD forums were we could debate this for weeks,
if you want to debate this further here, start another thread
or take it private,
one or two off topic is cool anymore and it becomes a matter of etiquette,
I'm done here.


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post #16 of 16 Old Nov 6th, 2010, 7:54 am
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Re: What do steering dampers really do?

Sorry!


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