I've been noticing some P12w/WHD truck with the same powertrains as the P16/HDX trucks. What is the advantage of one over the other, especially when the "smaller" trucks are available with double and triple frames? Just curious.
ben46a The theory with the flex frame was the frame would flex and follow the contour of the road when coming down around switchbacks where as the rigid frame would not flex and thus would put excess strain on the front springs and rear suspension because something has to move to allow for the twists on switchbacks. What happens with the rigid frame trucks is say you are coming down a hard right hand switchback the left front spring (steering axle) will collapse into the full negative arc position(this gets interesting because the steering tire will bind on the bottom of the front fender) and the weight transfer of the load will lighten up the right rear truck suspension and then the right rear tires on the truck lose traction and start to slide. You have to kind of feel each switchback because they are always changing. If the truck that loaded ahead of you came down say the top swithchback and for some reason one or more of his trailer wheels dragged( on an average load 55% of the load is on the truck and 45% on the trailer) then he is dragging the road material with him so now you might have a trench dug and usually once you are committed you cant stop, so you try a dodge the loose material any way you can. With the flex frame it will flex and twist enough to help eliminate at least some of this action. I will try and get a couple pictures this week of what an HDX or P16 looks like coming down around a couple switchbacks so you can see the twisting action that goes on. Does this help at all or just confuse the issue?
I will be looking forward to your pictures. I enjoy learning about these trucks.
I see exactly what you mean. So were the flex frame trucks preffered in the hills and rigids on the mainlines? Or did they try and modify roads to suit the rigids? SEems to have been plenty of HDX and P16 trucks with the big forestry outfits, moreso than the flex frames.
It really didn't make any difference because everybody just got use to the rigid frame's and adapted to them. Roads today are more driver unfriendly than they use to be because its all about cost saving now. 30% on a switchback was very rare back in the 70's and 80's, Don't get me wrong it did happen but now it becomes all to common a practice. This is directly attributed to the fact that most of the old road engineer's are gone now and the new ones are still learning. I personally loved the WHD but when I got a brand new HDX-- WELL things just looked a whole lot better. Just the cab heater alone made it better. The WHD's had a little square box affair that was called a heater mounted on the firewall whereas the HDX had a man sized thing under the dash that would dry your wet gloves in 1/2 an hour flat!!!!
You can see the difference even in an old Ford compared to a 1990's Toyota pickup. The Toy has a very rigid, welded frame, while the old Ford has a riveted frame that will flex a bit. That is one of the reasons the Toyota pops the sway bar when you go through cross ditches. The suspension takes all the punishment.
I guess I just don't understand why you would want the added cost of a rigid frame truck if a flex frame would do the same job and be easier on parts.
ben46a The thing here is that Hayes made rigid frame trucks starting back in 1954 and they just kept improving on them. Hayes built the first WHD in mid 1964, so they became a favorite of some because they offered the same components as what the rigid frame HDX/WHDX offered. However most logging companies and contractors wanted the rigid frame for the longevity and they knew the success behind the HDX whereas the WHD was kind of new to the scene. Once again it became a choice for what your application was going to be. There are not a lot of WHD's around anymore but there is still a fair number of rigid frame trucks still running out there in the industry. I have one and one of the members on this forum has the one and only survivor of the 10 WHD's that Franklin River got back in 1965-66. Both these trucks are nice examples of what once was and the frames on both these truck's are still in extremely good condition. Kenworth went through the same thing as did Pacific so it was not just Hayes with the flex/rigid frame. I still have not got good pictures for you but I will get them. Where we are in some areas right now you just don't want to stop even if you could to snap a couple shots. Rest assured I will get them for you OK