Quote:
|
Originally Posted by Cobra500
I'd guess the type of rear suspension is as important (or more) than the axle to hitch length.
|
It would be a very, very bad suspension to have equal importance...yes, some suspensions have lateral movement but it's unlikely to be more than half an inch...which is about the same lateral flex in the sidewalls of P series tires.
Quote:
|
Some "performance" suspension designs (with lots of wheel travel) allow more side to side movement than others- a panhard bar would help to control lateral movement as much as anything. Soft coil springs (independant suspension/ McPherson struts) are probably bad, leaf springs with overload supports possibly better.
|
Worst case would be coils on a live axle with a panhard rod. All independent suspensions (including McPherson or other strut designs) use a lower control arm where the only lateral movement will be the minor amount allowed by the arm's pivot bushings.
Quote:
|
My guess is that simple leaf designs with stiffer springs are what make pickups better tow vehicles than many SUVs with softer springs. Your overhang theory would suggest SUVs are 25% more stable while towing???
|
No, not even close to a 25% difference. It''s
not the overhang itself but the
ratio of wheelbase to overhang...and the higher the ratio, the greater leverage the steering can exert.
Typical midsize SUVs have wheelbases in the 110 to 120 inch range and an overhang of about 36 inches. Typical half ton trucks have wheelbases between about 130 and 150 inches and an overhang of about 48 inches. That computes to a steering leverage ratio of about 3.2 for a 115 inch wheelbase SUV and a leverage ratio 2.91 for a 140 inch wheelbase truck...a slight (10%) advantage for the SUV...but if that SUV had just 4 more inches of overhang, it's ratio would be 2.88. And if the truck had just 4 inches less, it's ratio would be 3.18. Real hard to derive any cross-the-board differentiation between SUVs and pickups on this factor.
However, trucks tend to have more front weight bias (when lightly loaded)...which improves steering control...and they also usually have LT tires with stiffer sidewalls...a factor that definitely improves lateral stability when towing.
In any case, I've yet to see any conclusive, widely reported evidence that pickups make better tow vehicles for travel trailers than equivalent sized SUVs...or vice versa. I've also not seen any widely reported conclusions that different types of suspension make a huge difference in towing stability. I have, however, seen a number of anecdotal reports that suggest that stiffer sidewall tires (in particularly "LT" light truck series tires)
do make a noticeable difference in towing stability.
For a very indepth analysis of suspension, overhang/wheelbase ratio, and tire effects on towing, please read
this post on the RV.NET towing forums. It was written by an RV dealer in Canada who has enormous amounts of experience and knowledge regarding what works and what does not work for trailer stability.
For instance, on the wheelbase/overhang ratio I keep harping on, he writes:
"What we have found is that we do not look at wheelbase alone but also its relationship to rear overhang so we measure the rear overhang as a percentage of the wheelbase. So a Front Drive van with 120" wheelbase and a 30" overhang has an overhang to wheelbase percentage of 25% where as a Suburban with a 131" wheelbase and a 49" rear overhang has an overhang percentage of 38%. An interesting comparison that I have found is a Suburban and a Tahoe that have identical suspension have equal overhang percentages when you use a welded ball mount. Even though the wheel base is 131.5 for the Suburban and 116 for the Tahoe if you connect identical trailers to both vehicles they will handle the same."
On SUVs (especially the import SUVs you don't seem to think much of) and independent suspensions, he writes:
"Some SUV’s work quite very well the BMW X5 and the Mercedies ML handle extremely well. Someone posted a picture of a Lexus RX300 /25' Airstream combination. I doubt many if any of the combinations that I see people here own could match it in stopping distance emergency handling or straight line stability in fact this combination will likely outperform most large trucks solo. Trust me the owner of this combination is very particular about the performance of his vehicles he has raced and owned some exotic sports cars. He is also in the position to tow with what ever he pleases
The new Ford Expedition and Explorer with independent rear suspension are also quite good if you get rid of the balloons they call tires."