Wobble

[Jetblast]

Hi all,

First post here so please be empathic...

After thinking of a sidecar for over 10 years and after 6 months of voyeurism on sidecar forums, 6 weeks ago I got a a new-to-me 1984 R100RS that I got attached to a Bimmer M-103 sidecar by a shop near Montreal. It was delivered to my door. It had a terrible wobble, the frame slapper type (after the tank has been destroyed by the initial tank slapper). I installed a prototype vertical, frame to fork, VW damper that eliminated the wobble enough to get the bike to the shop for safety inspection and take my daughters for their first ride.

Since then I went through the usual manuals and the Design formula thread to learn more about the rigging.

Found out my rig was toeing out and leaning in with almost no lead. I did what someone wrote: puttered with my rig to learn about it.

It's a tandem two seater that looks like a CJ tub. The cargo compartment is modified to add a seat.

I took the lead to a bit over 8", the best I can do with the hardware I got. Considering a wheel base of 58", it's not far from the 15-20% lead (with the conversion rate to Canadian units, it must be for us between 13-18% anyway)

I toed in at 3/4 inch as measured from the back wheel (since it's a BMW). On that, Snowbum, I have 2 questions: why are the wheels offset and how?

The lean-out is minimal.

I took it out and the handling was easier and lighter.

I disconnected the temporary damper (or is it dampener?) and there was no more wobble. I was quite proud of myself. I even put the BMW damper to 0.

Then I went for a longer ride to do errands at city speeds (30-80 kph or 20-45 mph). I was riding loosely and then the tub wheel hit a manhole. The wobble was back. It had been hiding it that manhole waiting for me. I finished the ride with the BMW damper set to 2 and it was ok all the way home. The only pain was from the tension in my you-know-what-muscle-tense-hard-when-you're-scared muscle.

Was the BMW damper sufficient enough or is it because I did not hit other major bumps?

Is that normal to wobble so much?

I need all the help I can get.

Thanks

(I'll try to figure how to post an image of the rig)

[Leaf]

Disclaimer: I may not know what I am talking about.

Is there any side-to-side play in any of your wheel or steering stem bearings?

The tank-slapper on a 2-wheeler is usually a sign of the steering stem bearings being shot, I think, though I've never had it happen on any of mine (yet).

[claude]

Checking Tires, wheels, mounting systems, steering head bearings, swingarm bushings or things as simple as playing with tire pressures can alleviate a low speed headshake. Not always though as sometimes a damper is required.
Jack up the sidecar wheel and see if you have any runout when you spin it. Also check for loose spokes.
I think the 'Bimmer' is marketed by Tran Moto and is based on a Chang Jaing chassis. I would suggest you contact Trans Moto. I do not know what they do as far as mounts go nor if they utilize a different than stock sidecar wheel.
click here:
http://www.trans-moto.com/m_103a.html

[GreatWhiteNorth]

I've got a full season riding on both a Goldwing GL1500 sidecar rig, and a KLR enduro rig. Both rigs will develop head shake under certain conditions. With everything I've read so far on the various forums, and experienced personally, I believe this to be normal. On my Goldwing, I rode it first without modified steering, and then with trail reduction accomplished by installing "Steerite" modified triple clamps - what a difference! It's like adding power steering - the head shake, when it does occur, is less pronounced and easier to deal with. On my KLR rig, if I ease up or let go of the handlebars completely, under certain conditions/speeds it has headshake that will quickly develop into a tank slapper if I'm not careful. Steering is stock but quite light as is, so I just live with it. I could fit a steering damper, but am worried about it coming apart (that'd be outright dangerous!), and possibly taking some of the fun out of what has turned out to be a really enjoyable rig to go country cruising with. If you've got the rig setup correctly now so it tracks straight and steering effort is low, I'd give it some more time to get used to it. If steering effort is high, and the headshake is really something you don't want to live with, suggest you need to look into trail reduction mods.

[jaydmc]

Looks like you have the aligment done well, Make sure that they used a sub frame as the frames on these bikes are known to fail over time with out a sub frame, It sounds to me like they did not have a clue on alignment when they hooked it up. I would hope that they did not charge you for this or are giving you your money back as while it is not uncommon to have to fine tune lean out for you weight you should not have to make any other changes if the sidecar was properly installed. Claude covered pretty much every thing to check. One other thing you can do that helps is to switch the front tire over to an Avon sidecar triple duty. This some times helps with head shake. It also helps with braking traction.
We imported a few of these sidecars for a while, We were not all that happy with the quality and stoped importing them. I really did not care for the way that the trunk lid was held up when used as a seat. We found that the wire spoke wheels were seldom true which will make it hard to set the toe and keep the bike from having a head shake. The cast wheels were much better (we still have a few cast wheels in stock) I would make sure that you have the brake on the sidecar working. This is a heavy sidecar, even more so with two people in it.
We finished up an R100RS about two weeks ago that is being picked up today by the trucking company to deliver it to California, we did not need any damper on it. We ran one of our M72D sidecars on this bike with a disk brake tied to the front brake. The cable drum brake on your sidecar is fairly easy to hook up if your bike had a rear drum brake but as it should be a disk on the rear it is not so easy to make it work well. If we were doing it we would make a pedal for the sidecar brake that sits next to the bikes rear brake pedal.
Let me know if we can be of any help at all.
Jay G
DMC sidecars
www.dmcsidecars.com
866-638-1793
jay@dmcsidecars.com

[XL-erate]

Just a thought here and I'm no expert at all. Hopefully Claude, Jay or others will correct if I'm in error.

On all my bikes I like to set the preload on steering stem bearings so that they're snug, with just a slight resistance to turning. I lift the front and after repacking stem bearings will tighten the steering stem nut etc. I usually find that bikes are set up so that with wheel straight ahead just a touch on the bars causes wheel to flop all the way over to the side. I prefer to setup so that it's tight enough that it takes a nudge to keep the fork turning side to side, just a slight preload resistance. That if you move bars a couple of inches the front wheel stays there unless you give another very gentle push. This of course with properly lubed stem bearings.

I'm unfamiliar with your stock steering damper and how the stem is set for preload. You might want to investigate what kind of preload is going on with damper backed all the way off and VW Damper disconnected. Establish what kind of resistance is present at zero damping setting, and also at progressively more dampened settings, to see where you're really at. From there you may be able to add just a wee bit of preload when in the zero setting and eliminate unwanted play in steering stem, but not to cause binding.

While you're at it you can spin front wheel a few times to see what the wheel & tire balance looks like. See if the same part of wheel always ends up at bottom. Also check lateral side play in the whole wheel assembly.

With the chair's shock/spring disconnected & wheel off the ground I'd check to see what kind of play may be present in sidecar swingarm assembly? You could check to see what amount of damping is offered by sidecar's shock & spring too, that it's firm enough?

As the experts said, sounds like you're pretty close right now, maybe just some minor issues. Happy adventures to you!

.

[claude]

XL-erate wrote:
>>On all my bikes I like to set the preload on steering stem bearings so that they're snug, with just a slight resistance to turning. I lift the front and after repacking stem bearings will tighten the steering stem nut etc. I usually find that bikes are set up so that with wheel straight ahead just a touch on the bars causes wheel to flop all the way over to the side. I prefer to setup so that it's tight enough that it takes a nudge to keep the fork turning side to side, just a slight preload resistance. That if you move bars a couple of inches the front wheel stays there unless you give another very gentle push. This of course with properly lubed stem bearings.<<<

I agree with this. Tighter bearing will give a good dampoening effect. However one must be carefull if ball bearings are used in the steering head as these can become an issue if overtightened.

Just a note As far as telescopic type dampers go. These can be an issue if installed wrong. When installed on tele forks Bump steer can be present if suspension travel comes into play that moves the damper in and out.This is not always the case but should be checked for. The damper should be 90 degrees to the fork tube when viewed from the side if possible and as close to the fork tube as possible. How much travel the damper goes through will dictate how much steering effort it may add. Of course if the damper can be mounted apart from suspension travel this is best but is not always possible. Once a damper is installed it should be checked for proper movement during steering input and also through suspension travel.

[XL-erate]

Thanks, Claude, good to know about the ball bearings, a good foot note to my partial knowledge!

[3legs]

Does it have a leading link? If so check the bolts that hold the swingarm to the down tubes are firm. Not so tight that the smingarm can't move but firm enough to have some slight resistance. I know when mine start to loosen up as that is when the front end starts to wobble. A quick tighten of both bolts and no more head shake. Thankfully I don't have to do it too often.

3legs

[Jetblast]

Thank you everybody for your suggestions.

Bearings are new. Steering head was tighten. Alignment of the tub wheel was checked when I installed a new tire.

There is no brake on the side car. The bike has front double disks and rear single disk. I'd like to see a picture of your wheel Jay if you can send me one.

I was seriously considering a subframe for the reasons mentioned here. I started to look around for options.

I will experiment more and see if I can eliminate the wobble.

Cheers!

[cathouse willy]

I recently mounted a dmc car to my 01 Bonneville and had a bad case of head shake. after rechecking all the settings it was still scarey to ride.I mounted an Avon triple duty tire on the front of the bike and cured 90% of the wobble.There is still a bit at low speed but that is supposed to be normal

[Biebs]

I had a low speed wobble would be a tank slapper if handle bars were let go - The VW steering Dampener to front fork from sidecar mount is the solution - unless you want to add a leading link fork setup just the nature of the beast.

See my build thread if interested - no brakes on sidecar.

http://advrider.com/forums/showthrea...ighlight=biebs

[bmweuro]

With the stock BMW front end you have to much trail. You can start with checking wheel bearings, swing arm bearing, steering head bearings and tire pressure but at the end of the day you will need a steering damper.

Most leading links with close to zero trail a lot of the time do not require a damper and go down the road without wobbles.