Triumph Explorer / DMC M72DX Sidecar Rig - I found my dream rig, now please help me get it together!

LOL Very cool picture. Hope you acquired the correct shocks for the load that will be imposed on them. Bump and rebound is also important of course. The shock angle is also a factor. If remote adjustors can be utilized ans all plaved in a convenient place together that too would be a big plus. I am sure you conferred with Ted or Klaus regarding this but if not you may wish to send them a copy of this picture with the estimated loads included as well as shock angles for proper evaluation. It would seem as though the chosen mattress would also be a big factor along with the number of springs in it as well as their total and seperate spring rates. The spacing of these springs should also be calculated properly so that the ststem as a whole can provide many hours of usage. Maybe Drone or Davebig will chime in with more specific information to consider

It's always hard to beat Ohlins for ride quality

Hmm!!!
The best ride quality?
Nutin to do with Ohlins.

I had a few minutes this afternoon to do some measuring on the rear shock and here's what I found.

• Constructed the Swedish Sag Scale (my family is Swedish) out of a 1/4" dowel and some 1/2" square stock that I planed down with a hand plane.

• Measured with the bike sitting (static sag) and with me on the bike in full gear. I didn't have a passenger in the sidecar; but I typically ride by myself anyway (or one of my kids - they're still <50 lb). The blue marks show the range that I saw depending on me jumping around on the bike (trying to avoid striction inflicted measuring issues).

• Overall measurement from the wood "axle" to the marks:

Shock travel for a 2015 Triumph Tiger Explorer XC

• Front Suspension: Kayaba 46 mm upside down forks, adjustable preload, 7.5 inches travel
• Rear Suspension: Kayaba monoshock with remote oil reservoir, hydraulically adjustable preload, rebound damping adjustment, 7.6 inches rear wheel travel.

So my current sag should be:

• 21.5" - 20" = 1.625" of measured sag
• ( 1.625" of measured sag / 7.6" of total travel ) x 100 = 21.4% sag

So based on this info, it looks like the stock rear shock is handling things just fine (maybe slightly on the heavy side) with just me as a solo rider. I plan to run this test again with different passengers to see how things change. Please let me know if you see any errors or omissions; I'm hoping this serves as a reference for others trying to do the same thing in the future.

Is that the stock Triumph spring ? Does it have a hydraulic preload adjuster ? Do you have that cranked in ?
I would look at the amount of movement at the shock , jack up rig so rear wheel hangs put zip tie on shock shaft, measure static sag as percentage of shock available movement, your relying on accurate advertising nothing could go wrong there.
Except it's hard to believe you add a sidecar and only have 20% static sag .
I'd be aiming at 35% of available shock travel for static sag.

• Q: Hydraulic preload adjuster?
• A: yes, see photo below.
• Q: Cranked in?
• A: Currently all the way hard - my call but may or may not be the right decision.
• Q: Stock shock?
• A: I bought the bike used, but I believe so. Looks like a stock one.

Bike is advertised as having a load capacity of ~400 lbs. I'm ~230lbs in full gear, so I would have figured the addition of the sidecar would have maxed out the rear shock and we would be running at >>30% sag (if it is still stock).

I have no idea why one would check sag with preload maxed out and an unloaded chair, it seems backward the preload adjuster is for adding spring when you have a big load. I have no idea what you plan on hauling around but often sidecar trunk load (tools , tow strap, jack, extra clotches etc etc ) gets to 60 plus pounds then there's a container or two of gas it goes up to 100 pounds pretty fast.
Motorcycle companies have exaggerated there capacities and weights forever why not try real world measuring , crank the preload out fill the gas tank,put the tank bag on load the trunk then start measuring , hell take a couple straps and tied the back of the rig to the ground see how much travel you really have.
Is this all so you can avoid buying a spring ?

Sag should be measured as a % of the travel you want to use. Trying to use all 7.6 inches seems odd for a tall ADV rig. You will get a lot of weight transfer and geometry change with that much travel.