Help, different rider, different shake

@Aby Don, more info is needed, otherwise all you will receive is subjective guesses.

Does the bike have a modified front end, such as trail reducing triple trees, or Leading Link front end ?

What TYRES is the bike using, on all 3 wheels, but most importantly on the bike's front wheel ??

What tyre PRESSURE are you using in all 3 tyres, but most importantly in the bike's front tyre ???

How many miles/kilometers are on the FRONT tyre of the bike ?????

One of the first things others will tell you is that it is usually beneficial to have added WEIGHT in the sidecar, and the quantity of weight varies, depending on the rig. Anywhere from 40 lbs to 100 lbs will make a big difference, simply as ballast to maintain better handling characteristics of the entire sidecar rig.

I notice two things in that singular picture you posted...

# 1: The front end of that Triumph appears to be STOCK, with no modifications at all, other than you states it had a steering dampener.  If in fact that front end is still stock, with no reduction of the original TRAIL, that is a problem, that CAN be fixed. Having a stock front end adds to steering difficulty, and adds to head shake, both of which can be fixed by reducing the TRAIL so that the axle of the front wheel is "approx" 2.5 inches, or 60mm forward of the original location. Several ways of doing that....

# 2: It appears that the sidecar wheel has very little lead compared to the bike's rear wheel. Generally....it is recommended that the sidecar wheel be a bit more forward than the motorcycle rear wheel. I can see it is not as far BACK as the motorcycle rear tire, but IMO that is not much lead....meaning...IMO it should be more forward than it is.

Much easier to address item # 1....than to address item # 2.

Can you please post a LOT more pictures of the entire rig, as in...show us the front end of the bike, show us tyre WEAR on the front tyre, tell us tyre pressure in the front tyre...

I'll have a little different spin than FM.  He is certainly right about #1 and #2, but it doesn't explain why one rig handles OK and the other one doesn't.

You say both rigs are identical built by the same builder.  If you really mean that -- that they are literally identical -- and yet they handle differently -- then there must be something different in either the setup (most probable), shocks, bearings (steering head, wheels, etc), or tires.

If it was me, I'd get both rigs on the same garage floor and start measuring the setup on each rig -- actual lean (or tilt), lean out and toe-in of course, and wheel lead.  I'd also check sag front and rear to eliminate the shocks/forksprings as the source of the problem.  While doing that, making sure that all the strut connections are tight and the subframes are installed the same and with no broken parts.  I expect you'll find that they are NOT set up the same.  But, if I'm wrong, then start scrutinizing the bearings and tires.  Don't forget the rear wheel and axle -- it can be the culprit in head shake issues.

Thank you for the response. Good noticing about the stock front end and the position of the sidecar in relation to the motorcycle. We will get some more pictures posted.

In the meantime, we did a some testing today.

1) Specifically, I, the short one of the two of us, am 6 pounds lighter than my partner so say the scales. 

2) we added weight to the seat of the sidecar. We started with 50 pounds and each took it for a ride. For my partner, the shake at 20 KM/hr was almost gone; the very slight shake at 40 KM for me was totally gone. We increased the weight to 70 pounds and shake no more, albeit the expected. We are both smiling wide. 

Thank you again for your suggestions. More to come.

Well, I have an explanation for why the extra weight reduced the headshake but let me the first to say that I don't like my own explanation! LOL

If you lower the bike's frame in the rear by using a shorter shock, or a softer spring, or by loading it up with weight (making it "squat"), this will act to reduce trail because the angle of the forks changes.

But for that to happen with only 70 lbs of ballast?  Seems unlikely.  But maybe.

@Aby Don, first, that is great that you did some experimentation, and found a way to reduce or eliminate the head shake. Good on you for doing that !

Second, that olde, olde man @DRONE, was attempting to teach you advanced physics, when he should have checked first (as I did) to see if you understood the basics of math, before wandering off into applied geometry. (laugh DRONE....it was funny back in 1960, and still is today)

Aby, as you stated, you added weight to the seat of the SIDECAR...and the vast majority of sidecar owners find that added weight helps them. Many find ways to keep permanent weight in the sidecar, but it is just as easy to add a 50 lb, or 80 lb bag of sand, like the sand tubes...in a bag.

Okay, you found a "bandaid" to remove or reduce the head shake, but if you want to make it even better, and more permanent, give serious consideration to reducing the trail on the front end of each bike.

Those of us on these forums are well educated and well versed in the different methods of reducing trail on bikes, and whilst there are several different ways to do it, it really comes down to how many dollars you have to spend...to make sense of what you are doing.

The least expensive way will cost you approx. $ 300.00. The next step up will cost you approx $ 1,200.00. And the most expensive way will cost you approx $ 4,500.00. Now, reality.....the best way is also the most expensive way, which is having a set of Leading Links built for the bike. It will handle like a dream, much easier to steer, better driveability, and that will last the life of the bike.

But not everyone can afford to put out $ 4,500.00 for a Leading Link front end.

My personal recommendation, if the dollars won't allow you to spend that combined $ 4,500.00 for a Leading Link front end custom built for you.....is to buy a SET of trail reducing Triple Trees (we know people that make them), and install them yourselves onto the bike.

BTW, olde @DRONE and I are friends, so no bad blood there...just razzing him.

Oh, and you ABY still owe me pictures of the front tyre, and air PRESSURE run inside the front tyre.

I realized I need to clarify something. When I said initially that there are two riders on the Triumph sidecar rig I literally meant two different riders on one unit. We have one motorcycle and one side car, not two. That was why it was so confusing when I rode it solo and my partner rode it solo with different results. As has been stated, the ballast seems to have worked. We are going to talk through the modification suggestions. Oh, and the friendly banter makes me smile. 

I am curious as to why the Steering damper didn't mask the effects. They are usually pretty good at masking any deficiencies 

Quote from Aby Don on July 4, 2023, 1:47 pm

I realized I need to clarify something. When I said initially that there are two riders on the Triumph sidecar rig I literally meant two different riders on one unit. We have one motorcycle and one side car, not two. That was why it was so confusing when I rode it solo and my partner rode it solo with different results. As has been stated, the ballast seems to have worked. We are going to talk through the modification suggestions. Oh, and the friendly banter makes me smile. 

Well...young lady...you certainly had all of us fooled. We thought you had two matching sidecar rigs.

Oh, Aby...oh, oh Aby.....

Quote from Aby Don on July 4, 2023, 1:47 pm

I realized I need to clarify something. When I said initially that there are two riders on the Triumph sidecar rig I literally meant two different riders on one unit. We have one motorcycle and one side car, not two. That was why it was so confusing when I rode it solo and my partner rode it solo with different results. As has been stated, the ballast seems to have worked. We are going to talk through the modification suggestions. Oh, and the friendly banter makes me smile. 

LOL!  That's hilarious!  Just went back and read Post#1 again!  One rig, two riders!  LOL--totally obvious now that you point it out.  Me and Monkeys are idiots. You hear me Monkeys?  We're idiots!

This being the case, your experiences with the two different riders makes no sense to me unless one of you is a one-arm sidecarist.  Or has Parkinsons. One being taller and one being shorter should have no effect on anything, other than maybe wind drag, but wind drag doesn't really affect handling below maybe 65kph (40mph).  Not in my experience anyway.  Very strange.

Here I thought I readied something wrong, but I guess I didn't.   

Quote from DRONE on July 4, 2023, 10:57 pm

Quote from Aby Don on July 4, 2023, 1:47 pm

I realized I need to clarify something. When I said initially that there are two riders on the Triumph sidecar rig I literally meant two different riders on one unit. We have one motorcycle and one side car, not two. That was why it was so confusing when I rode it solo and my partner rode it solo with different results. As has been stated, the ballast seems to have worked. We are going to talk through the modification suggestions. Oh, and the friendly banter makes me smile. 

LOL!  That's hilarious!  Just went back and read Post#1 again!  One rig, two riders!  LOL--totally obvious now that you point it out.  Me and Monkeys are idiots. You hear me Monkeys?  We're idiots!

This being the case, your experiences with the two different riders makes no sense to me unless one of you is a one-arm sidecarist.  Or has Parkinsons. One being taller and one being shorter should have no effect on anything, other than maybe wind drag, but wind drag doesn't really affect handling below maybe 65kph (40mph).  Not in my experience anyway.  Very strange.

 

Well, @DRONE, I will admit that I am the Idiot. You are just a nice olde man.

I was duped.....duped I say....by the charm of Aby, despite her having a too tall of a man in her life.