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Old 03-28-2005, 08:55 PM   #51
RockyMtnRay
TrailManor Master
 
Join Date: Jul 2001
Location: Colorado Springs, CO
Posts: 816
Default Sounds like trailer induced oversteer

Quote:
Originally Posted by BobRederick
On my last trip with my GMC Envoy pulling the TM 3326, I had a very eerie feeling when I came to a curve in the road. This particular 2-lane road had several such curves. It felt like the TM was pushing me into the turn and like I had to counter steer to keep the TV on track. It felt like the force normally needed on the wheel in a turn was reduced. I towed it 2000 miles on the first trip and had not felt this before. The two variables I think are important are a) the freeway curves of the first trip are more gentle and b) I had readjusted the WDH to put less weight on the front of the TV (it had been seriously incorrectly adjusted by the dealer).

After reading these posts, I am wondering if my TV wheelbase is too short for this trailer. Also, to agrivate this effect, the hitch looks to be extra long between the ball and the TV. I can even get into the rear of the TV with the TM open. The hitch measures 12 inches from where it exits the receiver to the ball.

Any words of wisdom on this subject from the mathematical wizards out there would be appreciated.

Bob
When a rig enters a tight corner in a decellerating (or descending) situation, the momentum of the trailer causes it to want to continue in a straight line. Since the tow vehicle is now at an angle to the trailer...and the hitch ball is well behind the tow vehicle's axle, that trailer momentum will tend to push the rear of the tow vehicle toward the outside of the turn...which will pivot the TV around it's rear axle and cause the front to move toward the inside of the turn...a classic case of oversteer. In an accelerating/ascending (power on) situation, the trailer's inertia has the opposite effect...it will tend to pull the rear of the tow vehicle toward the inside of the turn and the front will pivot toward the outside of the turn...a classic case of understeer.

The solutions are multiple...

First, be sure to slow down well before entering any sharp turn (especially a descending sharp turn) and try to hold neutral or slightly power-on throttle through the turn. That will result in minimal under- and over-steer.

Second, it definitely helps to reduce the distance between the hitch ball and the tow vehicle axle...that reduces the lever arm the trailer works through to effect the tow vehicle's under/over steering. If you can, try to slide the hitch bar further into the hitch receiver. Most WDH that I've seen have at least 2 pin positions on the bar.

Third, yes, wheelbase does matter...the farther the steering tires are from the rear axle (which is where all the pivoting occurs), the greater leverage they will have on the entire rig. Furthermore, if the front suspension is well weighted (or at least not unweighted) by a WDH, those front tires will have greater road force and will provide better control. Since you can't stretch the Envoy's wheelbase (which is borderline short for 26 foot trailer), at least do a careful relook at your WDH's adjustment to get as much weight as you can tolerate on the front tires.

I towed my 2720SL for two seasons with a very short (only 100 inch) wheelbase Jeep Cherokee over some very steeply descending and sharply curving mountain passes (the worst combination for experiencing trailer induced oversteer). Although I never once had to consciously compensate for that potential oversteer (mainly because I slowed down to about 15 mph on some of these turns), I was well aware there was a distinct possiblity it could occur...and I had my hand resting on the trailer brake controller's manual override (increasing trailer braking relative to truck braking will instantly minimze an over steer situation). One of the reasons I upgraded to my Tundra was to get a longer (128 inch) wheelbase...the other (main) reason was to get about twice as much torque for climbing mountain grades.
__________________
Ray

I use my TM as a base camp for hiking, kayaking, mountain biking, and climbing Colorado's 14ers


The Trailer: 2002 TM Model 2720SL ( Mods: Solar Panels (170 Watts), Dual T-105 Batteries, Electric Tongue Jack, Side AC, Programmable Thermostat, Doran TP Monitor System)

The Tow Vehicle: 2003 Toyota Tundra V8 SR5 4X4 w/Tow Package (Towing & Performance Mods: JBA Headers, Gibson Muffler, 4.30 gears, Michelin LTX M/S Tires, Prodigy Brake Controller, Transmission Temperature Gauge)


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