BAE SD Brazos Chassis now available through GXV

[762X39]

And IMHO if you have one of these and you need to rush around you've got your priorities wrong.
But that's just my opinion.

This is a good observation and one that holds a lot of weight with me. I went a couple of hours from my home on Saturday to help put up trail markers and clean up some trails. On the way, I had to perform some evasive driving (I was on a secondary highway going about 80k) to prevent t-boning a vehicle that forgot to look before it pulled onto the highway.Since these vehicles are actually someones home away from home (or home period in some cases), high speed travel is probably low on the priority list.Control of your vehicle, comfort and safety likely rate higher.

[charlieaarons]

Could one not simply put on an over the road truck tire?

You can get them with a pretty meaty tred pattern, so why not just go with that? Those tend to be spead rated for something like 80-85 and would certainly do the job.

No such tire exists in 395/85R20, as I previously stated. Or in any size of similar diameter that fits a 20X10 rim. Yes, one could fit 22.5" rims with duals on the back and over-rev the engine because of the low axle gearing and smaller diameter tires after disabling the speed governor in the ECU. But that would be sort of silly, why not buy a Prevost or similar instead?
Oh, and with the axle and transmission gearing the final drive ratio in top gear is 4.9:1, so RPM at 60 mph is 2200. The engine is only good for 2400 or so. While you're at it, change the axle gearing and or put in a gasoline V8 with 550 cubic inches so it can rev faster?
Try driving one of these yourself and then tell me how comfortable you'd feel at 85mph.

Charlie

[Ford Prefect]

LukeH

Thanks a lot, great information, and I understand. I had not considered the longer suspension and the softer ride.


Charlie,

Perhaps not your intention, but it came off very rude. If that was intentional, well there is just no call for being like that when I only asked a simple question.

[charlieaarons]

Well, I'm really sorry, but there are so many things about these big trucks that are engineered differently than a chassis designed to run at >75mph on an Interstate...I wanted to make that clear. I thought I did make it clear that there were no tires available in that size designed for over 70mph in a previous post in this thread.

Charlie

[charlieaarons]

I'm sorry, my guess of final drive ratio of 4.9 was too low. It has a 3.9 diff, 2.0 planetary hubs for 7.8 axle ratio, times 0.78 (http://www.allisontransmission.com/i...ies/3700sp.jsp) 7th gear ratio = 6.08 final drive = almost 2700 rpm at 60 mph - really winding the Cummins out past its' peak efficiency. 50-55 mph would give one better fuel economy and is a fine speed for anywhere in the world except US interstates.

Charlie

[Ford Prefect]

On another note: Ford Perfect... To me! It sounds like you are "coming off" like you are a person that has lots of experience with your own medium heavy-duty 4x4 rig. Have you bought one and put it through thousands of miles of on & off-road use... And not felt like posting a thread about your new rig?

Or are you being a "drug store cowboy"?

Maybe it would be wise to listen more and speculate less. Because unless you actually own a medium heavy-duty 4x4... FACE IT, you are just speculating!

No Jack, I am acting like I have driven OTR trucks over several thousands of miles on and off road. That is all I have said, just information particular to that type of driving. Beyond that I have also got several thousand miles in dumptrucks, tandem dump trucks, so I am also giving my thoughts on how this particular vehicle would work in that arena. I have made no claims as to the ability of this truck as an expo rig, in fact I have asked a lot of questions about the topic because I am curious. Further I have asked why this vehicle is deemed by some as bad for various purposes and I Have received answers to those questions. I might add that they have come from people with actual (imagine this one for a second) respect for other people and their right to ask questions and learn for themselves. Go figure, a guy on a forum, trying to gather information. Unheard of. Shocking. Amazing. Really can you imagine a guy trying to ask a question on a forum of people who might actually know better than he? And LukeH was more than happy to answer my most recent question without the arrogance that Charlie has displayed. I know some people on here think they are god's gift to expedition traveling, but I say they need to get over themselves, OR stop web wheeling and go drive the rig they like to brag about so much on here.

Oh and I will also add that I have driven a myriad of 4x4's from dedicated trail buggies to plane Jane stock SUV's on a great number of off road situations. I like to understand things in context of my experience, so I have asked and spoken from that background as well.

Regards
Brian

[Ford Prefect]

Well, I'm really sorry, but there are so many things about these big trucks that are engineered differently than a chassis designed to run at >75mph on an Interstate...I wanted to make that clear. I thought I did make it clear that there were no tires available in that size designed for over 70mph in a previous post in this thread.

Charlie

No worries Charlie,

yes you made it abundantly clear that you know of no tires available in that style that will rate for speeds of 70 mph +. I said that one could use an OTR tire, in other words NOT of that style, and they might see favorable results. Again Luke made it plain that this would not be the case. This was all I was saying, that a differently rated tire is available.

As for the gears in the rear end, I did not know that the change of the tire would cause such a concern. I did not realize (nor honestly take the time to look at it) that the gears were such as to cause such a problem with those tires sizes. I do not really know the axles well enough to be versed in them, so obviously I was erant in my thoughts. Thank you for pointing out why that idea of mine would not work. Speculation, after all, is what gets a LOT of things done in the expo world. Look at most of the trucks out there, they all have some neat idea that someone, someplace, thought they would give it a try. Some work, some do not. Some (like these tires) would be wise to be thought out thoroughly prior to implementation. Again, thank you for your thoughts and for educating me on why that would not work.

Regards,

[charlieaarons]

And LukeH was more than happy to answer my most recent question without the arrogance that Charlie has displayed.

Except for the fact that your question was about tires, and LukeH's kindly appreciated answer addressed speed in general but not tires in particular, and I had already stated there is no 395/85R20 with a speed rating over 70mph; unless, you are ready to start redesigning the vehicle with new size wheels, tires, gears etc. Call that rudeness or arrogance if you like, though I'd suggest you get off your high horse, please.
Incidentally there is one tire modification that would lower 60mph rpms though not increase legal/engineering speed rating: the 11 ton FMTVA1 demonstrator used stock wrecker axles (probably for a greater GAWR rather than tire size increase) but 14.00R20 XZLs, which are about 6.5% taller than 395s, which would lower rpms by about 200 at 60 mph.

Charlie

[LukeH]

Now lets calm down and stop the personal jabs. I didn't say anything about tyres because I don't have that information available. The gearing considerations (and consequences) are important.
I seem to recall that Gertenbach's Bigfoot was on roadgoing 22.5s that replaced equivalent 14.5 x 20.
Actually Michelin DO make the big /20 XZLs rated to 160 km/h but it is very clearly stamped "competition use only" on the sidewalls and if you're caught with them on your truck outside of an event you walk home. The drivers that use them in events like the Dakar have balls of steel and spinal columns of titanium! Before the power was restricted these FC trucks placed regularly among the top ten CARS.

[charlieaarons]

.
Actually Michelin DO make the big /20 XZLs rated to 160 km/h

That's an interesting fact about big Michelins I didn't know. Do you know if they are de-rated as far as load, and if it is the same casing as the 90/100/110kph versions, or thinner in order to heat up less at speed?
One thing I do know: there are more than one true horror story regarding driving too fast on these large tires, especially if a little low on air. Involving very serious injuries.
I tried uploading my "Michelin Truck Tire Specifications" file but it was 500kb too big. It has sizes, speed and load ratings on the military type tires, OTR type truck tires, etc.

Charlie