Towing with 335d
Well she's a little dirty, but this is what I'm towing with my car:
A close-up view of some towing hardware:
Source album here on google pics.
My setup is:
Tow limits are:
- Execuhitch Hidden Hitch Replaced with Stealth Hitch (see update notes below)
- Air shocks in rear suspension of TV for load (ride attitude) compensation. Kept front coilovers for good ride control
- Hensley Arrow Cub anti-sway hitch + 600 lb tension (each) load leveler spring bars. The Hensley Arrow projects the hitch rotation point forward by 52". In this case, it puts it right ahead of the TV's rear axle centerline about 1/2"--functionally, it does what a 5th wheel apparatus does, but without raising the TV's Center of Gravity.
- Hayes Swaymaster gyroscope & GPS based electronic anti-sway brake system (interjects full brake command on sway algorithm output in emergency; passes-through on 'normal' conditions)
- Tuson DirecLink 200E OBD-based smart brake controller (always proportional to TV brake pedal % with user-selected biasing values for highway speeds & for slow speeds)
- 10" electric brakes (brand unknown)
- TheUltimateTrailer.com OHT4-X model, air-bagged, RO-RO trailer. Trailer has onboard 12V compressor + manual fill & vent auxillaries
- LED lighting on 7-pin connector: turn signals, brake & running lights
- Break-away emergency brake controller with recycled lithium ion motorcycle battery (can also run compressor for limited time)
- Upgraded tires to Nokian cLine 195/70R15 on upgraded 15" rims (e-trailer I think)
- Custom, shortened stinger I drew & had fabricated locally
- Car - 3890 lbs
- Towbar -4000 lbs
- Stinger-4000 lbs
- TV tires-1929/tire
- TV gross axle limits-2145 lbs front; 2662 lbs rear
- TV% of axle limits(%Safety margins) for F/R - 88% (12% reserve safety margin @ max tongue load) (front and rear)
- TV ride attitude @ max tongue loads - level @ 101 psi to air shocks
- TV corner balances under tow - +/- 50 kg range (needs improvement)
- Trailer Chassis limits - 4300 lbs @ perfect mass distribution; 4150 lbs under typical loading conditions (tolerance 75 lbs? CAD model & actuals testing not yet completed)
- Trailer airbag limits - 5000 lbs at 90 psi
- Trailer brake limits - 4000 lbs
- Trailer wheel limits - 4080 lbs
- Trailer tire limits - 3996 lbs @ max pressure
- Net limit 3890 lbs
Trailer rides @ 16.5" off deck. Empty trailer's center of gravity is below axle center-lines because I placed a custom rack for water & tools under there. Even stock it's Cg is very close to axle center-lines.
Heaviest loads carried so far:
Planned & completed upgrades & when I might do them:
- Moving load--I carried an 8' tall stack of friend's furniture & applicances weighing ~ 1750 lbs about 7 miles
- Static (test) load -- I lifted a friend's 3600 lb car to test airbags & where load Cg must be to overcome their de-leverage factor.
- When I specc'ed this out and started the build I decided to future proof it as much as possible, so there is spare room & load capacity to change e-brakes to hydraulic disc brakes with accumulator & ABS(expensive upgrade). I may do this when towing commercial loads if I ever encounter ice, snow, scary driving conditions, etcetera-- if I calculate it substantially reduces risks.
- There's also room to do one more '+1' tire diameter up-size with higher load index but requires addition of 1/2" hub spacer with longer lug studs
- Within 90 days I will soon be adding 60 gallons fresh water + 60 gallons gray water tanks under the deck w/filla & drain ports easily accessed from the A-frame tonguer
- Soon adding a custom sheet metal, locking tool box for carrying load straps, torque bars, general tools weighing ~21 lbs
I rigged up a temporary solution using a Harbor Freight locking briefcase & magnetic couplings. I may still fab up a custom box of sandwich/aluminum construction because room is tight for all the straps and accessories.
- Soon revising the A-frame's stock spare tire coupler/mount to an angle iron based (more rigid) bar for partly under-the-deck spare storage. This will form the back rigid base of the toolbox as well. DONE. Will add pic later.
- Soon revising my under-deck water rack (trim back for Cg shift toward ideal & keep 13" as special tool racking, etc... DONE
- Soon revising the trailer jockey wheel to a 10" pneumatic, high caster European-style jockey wheel. DONE, but non-pneumatic. Will post item/ catalog # later
- Designing a power movement system for jockey wheel--not ready for release yet
But for my needs so far, I am very satisfied with this setup. The biggest risk is forgetting I'm towing a load. It's very smooth in all regards including braking.
13 October 2019 updates: The lock cylinder and vertical nipple of the Execuhitch failed in rotation, causing the nipple to fall out. This failure happened at around 1 mph, so no damage to my car. My chains engaged the load, and I pulled it to the side of the yard I was at. I had been hauling yard debris to the dump, approximately 2000 lbs.
I think there were two causes: Execuhitch design shortcomings and torque forces exerted by the Hensley hitch. 1.) The Execuhitch design depends exclusively on soft carbon, 1000-series steel. The Execuhitch has a keyed dowel pin, also soft steel. The purpose is to prevent rotation. It is a v-shaped with a U at the top which rides in a female V in the lock hitch. This is the interface that failed when the dowel pin twisted and deformed badly, also damaging the lock cylinder permanently. 2.) The Hensley hitch also induces high torque moments under very certain scenarios: when braking with low TT brake bias, or TT brakes non-functional while doing moderate turns. Lastly, though I'm not sure this contributed, I had been running the Hensley hitch without load leveler bars. The weight of the HH may have causes the keyed dowel pin to engage with the V at a less-than-ideal angle, allowing it to walk out. I will be studying this further with close measurements of angles and such at various load leveling tensions.
I replaced the Execuhitch with a Stealth Hitch. Stealth Hitch has updated the lock cylinder to be made of billet 316L Stainless Steel. All internals are also 316L. The male nipple is a larger, more robust pin design with larger engagement surfaces. I think it's a big improvement. It might not be enough on its own, but I'm going to keep a close eye on it.