DW! Need longer arms for more caster

[JCrockett]

Hell yes!! Where do I sign up! I have gotta get down that way... ... ... ... soon, and preferably with my truck! You guys get to have WAY too much fun down there. :-laf

 

[kentkroeker]

I hate to admit it - but that story Greg just told is 100% true. When we hit that jump, I was trying to be cool - I was slouching and didn't even change position - which would have been a sign of weakness.



JCrocket,



It's not always fun - I think he may have torqued one of my ribs - although I didn't tell him until later.



Additionally, Boardman obliterated the part we were testing - which set a new record for him. Usually it takes a couple of months. This time it took him less than 24 hours.



When we release the production units - the first batch of which should be here tomorrow - I'll post pictures of what Boardman did to one of the prototypes.



-Kent

 

[rbattelle]

My favorite one is this eight inch curb to a four foot drop-off I hit at 60 mph - from the highway. Nobody expects it. I say, "look at that llama. " It distracts them for a second and when I launch the truck off the pavement they think the steering column snapped or something. It's so funny - we laugh and laugh and laugh...

You routinely drive over an 8" curb at 60? Without damaging anything? I would think that would at least bend a wheel!



-Ryan

 

[RKerner]

HLewallen,



But I digress. The issue is DW and DW probably isn't going to be cured by adjusting your caster. Caster gives your truck stability and return-to-center. It also affects several other geometric properties of steering. But I wouldn't focus on this to solve your problem.



A lot has been said about running E-rated tires. As we've learned, the E-rating is a measurement of sidewall strength/flex and not simply load rating. An E-rated tire has a stiffer, less compliant sidewall than a D-rated tire.



We know that some trucks DW because of bad components. This explains why some trucks DW from the showroom. We also know that some trucks DW because of bad tires - "switched to Hummer takeoffs and now I've got DW. " In addition, proper tires mask the effects of bad components and proper components mask the effects of bad tires. This explains why some trucks never DW, even with D-rated tires.



So far, nobody has explained precisely why the tire with the weak sidewall can cause DW. We just know from experience that that switching to a better tire can cure it.



Now I'm going to totally geek out:



As your suspension moves up and down (lifted, long travel, or stock) your toe changes. You get an increase (positive) on the down stroke and a decrease (negative) on the up stroke. That's just how your suspension works. A stiff sidewall with a narrow contact patch (OE tire) or the Rickson 19. 5 set up is inherently anti-DW because, even in a high traction situation on pavement, the tread is permitted to rotate slightly around its axis as toe changes during normal suspension cycling. Now, switch to a larger contact patch - the number 315 comes to mind - that's width in millimeters - and a weaker sidewall - the letter "D" comes to mind - that's "ply rating. " Anyway, now you're increasing traction while simultaneously decreasing sidewall stiffness. The result is that instead of transmitting the rotational forces of toe change to the tread, the tread stays planted under 4660 lbs. (front axle - 3rd Gen. ) of diesel beast and every bit of that rotational force gets distributed into the sidewall of the tire. Next you get a harmonic that develops in the sidewall that spreads into your steering and throughout the entire vehicle - DW. Interestingly, it's nearly impossible to get sidewall-induced DW while off-road in low traction situations. The low friction coefficient of good old dirt permits the tread to rotate, so the sidewall doesn't have to bear the brunt of toe change.





Here's the point to all this: As you go up in tire size, your contact patch increases. Correspondingly your traction increases thereby necessitating an even stiffer sidewall to transmit normal suspension and steering movements to the ground where they can be dissipated harmlessly instead of into your vehicle where the effects are manifest as DW.



Combine this tire phenomenon with a loose tie rod end or sloppy drag link and you get a pretty scary truck - a truck even scarier than Boardman's off-road driving.



That's what we know so far.



Best Regards,



Kent Kroeker

Kent, I've been discussing this with a buddy of mine who has a bit of knowledge with suspensions and steering systems. He helped me understand it a bit better and explained two modes of DW. One seems to be induced by an increase in compliance in front end parts or decrease in sidewall stiffness. Since the suspension is hopefully tuned to not resonate at normal frequencies encountered (like the 70mph bump?), any increase in compliance reduces the natural frequency of the system, allowing unstable motion in the system. The worn parts and/or H2 or D rated tires seem to be the correct diagnosis of this cause. One question, are H2's that much lighter or have significantly different geometry so as not to have heir own DW issues?



The other mode can be described as "wheel fight", where the wheels react funny to a toe change while excited (or the bump thing again). One wheel reacts a bit adversely to its toe position and induces a steering correction all the way to the other wheel which reacts to this input and induces a return reaction. This was described as causing a steering wheel issue where it didn't like to be controlled by your hands. I haven't read where people have had DW and the wheel ripped out of their hands but you describe the toe/traction reaction that fits the wheel fight syndrome. Do you experience the steering wheel feedback in DW? It would be interesting to know if this is one of the DW modes.

 

[kentkroeker]

Ryan,



It doesn't bend the wheel because we're running 37 x 13. 50 rubber on an 8. 5" wide rim on beadlocks. The tires are set to 20 psi cold. This is also with a suspension system we haven't released yet. We're not hitting the curb straight on. Solid axles and trailing arms don't like impacts like this. Surprisingly, you can barely feel the curb - literally, if you were drinking a slurpee, you wouldn't spill any. It's also an asphalt curb, so the top edge is more rounded than a concrete curb you may be imagining. The landing from the launch isn't too bad either - kind of down hill. The key to the maneuver is hitting it at just the right angle at just the right speed. The angle is pretty oblate and the speed is just right to let the tire take much of the curb impact. Then we're flying and the axles droop out all the way, so the full force of the impact gets absorbed by the suspension. It's really fun - and unless you know there's a little dirt trail there, you think you're just launching off into space - scares the pants off people. Greg's been over that one with me at least ten times.



RKerner,



I've experienced a lot of steering wheel feedback during DW. When we're racing it's really important always to keep thumbs pointed up because during DW, the wheel would shatter both thumbs if you gripped it in a normal manner. It can be that bad.



Interestingly, the new Powerwagon comes from the factory with D rated BFG's (here in California). Could be that DC feels the lighter weight of the Hemi won't be as much of an issue when compared to the CTD or the traction of 285's won't cause problems. Or perhaps that tire is constructed differently than the H-2 tire. Just a guess.



Kent

 

[Doubleclutch]

Kent, Greg- you guys remind me of one of my aerobatic flight instructors...



Oh Captain, my Captain, my arse is in your hands,

should they find this vessel at the center of a smoking hole,

pray thee that I died first...



The other Greg

 

[Greg Boardman-RIP]

HLewallen,



Combine this tire phenomenon with a loose tie rod end or sloppy drag link and you get a pretty scary truck - a truck even scarier than Boardman's off-road driving.







Best Regards,



Kent Kroeker

I Knew you were scared :--) :-laf :-laf :-laf :{ #@$%! Kroekers emotions

 

[kentkroeker]

You were scared too!!!



:-laf :-laf :-laf :-laf :-laf :-laf :-laf





Admit it!!! When you errantly mashed into the launch ramp at 80 mph - and the rear of Big Red ended up 4 feet higher than the front, sending your tailgate flying off into space - if you weren't scared you were just being, uh...



Where's the little picture of the guy wearing the dunce cap?



This is the closest one I can find:



hahahah!

 

[HLewallen]

The throttle must have gotten caught in Kent's skirt. That should be your excuse Greg. Next time he scolds you for too much speed just reach down like your fiddling with the pedals and ask him "Is this your purse? Musta got caught in the pedals... "

:-laf

 

[kentkroeker]

The throttle must have gotten caught in Kent's skirt. That should be your excuse Greg. Next time he scolds you for too much speed just reach down like your fiddling with the pedals and ask him "Is this your purse? Musta got caught in the pedals... "

:-laf

Heath, I've gotta admit - that was a good one! :-laf :-laf :-laf





-Kent

 

[Greg Boardman-RIP]

I'm not afraid... ... ... PR