BarmanBean

iTrader: (1)

The salesman I was working with did the same thing via text. I'm nearly certain it was an honest mistake and what he did was just quote me the max possible payload for the 2015 F-150 that we bought, which was like 2200 lbs or whatever. I was hoping it might be a gem and would be a HDPP truck, but checked the sticker when we got there to confirm actual payload was 17xx pounds or so. Was still pretty happy with that.

Gladehound

I found a thesis that compares a model to real world testing and it looks like some interesting weekend reading. From what I've read so far, the understeer gradient is only a measure of the impact of speed / load on steering on a given vehicle compared to the same vehicle at low speed / no load. So to I'm not sure how I would do a cross vehicle comparison - but as I said, more reading to do.

I also prefer oversteer but understand why understeer is the safety standard and appropriate for 99% of people.

Gladehound

Empty, yes. Loaded for a trip, no. GVWR diff of 800 pounds. Ability to swing the TV to TT weight difference by 1,600 pounds through proper loading - and that will make a difference where the tires meet the road.

Regarding Andy T. I wish he would post test results!
Regarding SAE, I wish they would post test results!

BarmanBean

iTrader: (1)

Meh, Andy T also setup a Honda Odyssey to tow a triple-axle airstream. I really liked our Odyssey as a tow vehicle and thought it was very capable with both our pop up and my enclosed utility trailer, but the triple-axle airstream is just silly.

8100hd

As you stated understeer gradient is the effect on vehicle steering from its unloaded state to its loaded state. As you add load to the vehicle there’s only one way for it go and that’s down towards neutral/negative. It’s impossible to return it to its unloaded value by adding weight no matter how it’s distributed. A towing combo with just a driver and hitch load has the stability advantage over the same combo driver and hitch load plus 800lbs of additional payload.
Increasing hitch load will increase sway stability, in contrast it will also reduce understeer gradient and adding more payload in the bed reduces it more. Placing weight as forward as possible in the bed will help but it’s still adding to rear axle load. This principle will apply to any vehicle of course regardless of its weight but a high payload with hitch weight and a light front axle deserves caution not confidence.

Gladehound

And it follows that adding mass forward of the center point between the axles should increase understeer. I did some reading and think I have my arms wrapped around the inertia around the axles and understand your initial comment regarding the balance between trailer stability and cornering.

This once again gets me wondering about ultimate cornering ability. Since friction between the tire and the road does not tend to keep up with inertia with added mass, ultimate corning ability should decrease with increased mass. As such, I wouldn't be surprised if the lighter HDPP truck can out corner any 3/4 ton with the same trailer. The heavier 3/4 ton truck may have a more positive understeer gradient, especially if it's a diesel due to a more forward weight bias. But ultimately it will let go earlier than the lighter truck especially given the higher mass and that these trucks tend to have about the same size contact patch.

This is why I would love to see actual results from the SAE and Andy T's tests. I would not be surprised if the BMW X5 he set up with an 8,000 pound TT would indeed put a 3/4 ton to shame on a handling coarse with the same trailer. I'm not saying I agree with everything he does. There are definitely liability issues and structural strength issues. But it seems there is a trade off with a high mass tow vehicle. Yes, it's more stable. But it also might not be able to avoid an accident when a lighter tow vehicle could.

8100hd

Once you add any substantial hitch weight to the vehicle getting back to the unloaded understeer value won’t happen. As you are starting to get an understanding of the concept you will see that adding any WD at all lowers the understeer gradient. I still have my confidence in the F250 just for the fact that Ford lowered the FALR on the f150 to 25%. Theres only one reason they would do that and that’s to get the truck to pass the cornering stability test. Since the f250 can still take 50% FALR that puts the odds in its favor.

Andy Thompson is a smart man and he can indeed create a combo that can do a slalom at a higher rate of speed then a pickup. There’s nothing magical about his methods, he uses vehicles with very short rear overhangs and a wide stance. The trailers are almost always low CG Airstreams and I am willing to bet he has lowered the hitch weight to 10% or lower on most of these rigs. He almost always has to modify both vehicle and trailer and in turn he makes money doing so which is his primary motivation. In my opinion he focuses to narrowly on this slalom handling, but it makes for a great sales pitch though. He doesn’t like it when you ask or question him about engine, transmission, and transaxle cooling, and vehicle manufactures warranty. Read his articles, there’s some good information there but it’s mixed in with the BS sales pitch.

Gladehound

Yes, I realized that from the start. But was thinking about it only from a weight shift perspective and not considering inertia around the mid point between the axles. Also, in my twisted mind oversteer is good, understeer is bad - so I had no reservations about creating a bias towards oversteer. That's what happens when you spend too much time on dirt tracks. I realize now that is wrong advice to give 99% of people. For example... while I was very comfortable driving my jeep with 18% tongue weight and the WD bars cranked for 14 hour days towing the TT cross country, there was no way I would let my wife in the drivers seat because she has not logged thousands of hours driving loose with an oversteer bias.

In case this is helpful to someone else - my ah hah moment was when I realized I had to think of weight and mass separately. A WD hitch redistributes weight but it does not change the distribution of mass. This is critical when you think about set up. Where the mass is determines the effects of inertia. Where the weight is impacts traction to resist inertia at the tire / road surface interface. You have to think of both of these separately and then put them together to get the full picture of what is going on.

It is very interesting to think about and will change where I pack things. For example, heavy items (like my tools and jacks) that easily fit under the seats in the cab will go there instead of in the bed near the tail gate. Kayaks will go more forward over the cab instead of over the bed. More central mass distribution and less weight distribution through the WD spring bars should result an less pronounced oversteer bias at the limits of traction.

B Brown

Anna. I live in Alaska. Army sent me here and I returned as soon as I could. I would not worry much about a 4 seasons trailer, while nice in the fall and early spring, they are not much more useful in the winter, unless you can store it inside, because once everything freezes up it stays frozen. most people I know that use their RV in the winter dry camp, water in 5 gal jugs and a portable toilet. Most of the campgrounds are not plowed in the winter if they are open. which means your not going in unless you have tracks. Another suggestion, Buy a set of dedicated WINTER tires, Studded tires are legal from 15 sept to 1 may BFG KO's and GY Duratracs while a good tires, are not a good winter tires.

tomt5078

He said 4x4 with a 2900 payload...................Ur right a 2wd could get to 2900.................