Class 8 Wheelbase

Ricky · Dec 25, 2005

I would like some information from all of the class 8 expediters.

1. What is the best wheelbase for a tandem axle tractor with a 22' box and why?

2. How many inchs or feet do you need from the sleeper to the end of the frame rails for the same size box?

3. What is the best gear ratio with a autoshift and why?

4. Can a person find a class 8 tractor from factory with long frame rail without having to add to the frame?

5. Is there a resale book on tractor like the kelly blue book for cars?

Any more information on a class 8 is greatly welcomed!!

Thanks for all the information and time on this subject.

Ricky

LDB · Dec 25, 2005

The wheelbase, in my opinion, should be as short as possible while still providing adequate support to the cargo box. That said, the center point between the two axles should be no farther forward than the center point of the cargo box. The reason I like the shorter wheelbase is to give a smaller turning radius. The wheelbase on my truck is 306" and puts the center points in vertical alignment.

You need frame out to the back of the box. If you spec to have about 39'11" from bumper to the end of the frame rails they can cut off an inch or two when they install the cargo box if they need to. That is what they did with mine but that way the rails weren't too short and the end of the box wasn't unsupported.

The gear ration should put the engine at the sweet spot at the cruising speed you intend to use most. That most likely would be 1350-1400 rpm. If the truck has a 13 or 18 speed it has 2 overdrive gears. I went with an 18 just to get the two overdrives. Mine is geared to run 1350 at 60mph and 1350 at 70mph depending on whether I'm in 17th or 18th. You could do something similar with 12th and 13th.

It is very unlikely you will find a chassis with an extended frame on a lot anywhere although with enough searching and patience it might happen.

I personally don't know of a "blue book" for class 8 vehicles. The closest I'd know of is truckpaper.com or the printed version of same. Good luck to you.

Leo Bricker, owner trucks 3034, 4958
OOIDA 677319
73's K5LDB
EO Forum Moderator 1+ Years of Service
Expediters Online.com - The Best is Getting Better!
-----
Support the entire Constitution, not just the parts you like.

greg334 · Dec 25, 2005

4. Can a person find a class 8 tractor from factory with long frame rail without having to add to the frame?

yes, BUT dealers don't normally have them and most stocking requirments of the dealer don't provide for them in their inventory. (Source FL)

Truthfully you can order any length of frame you need, the factory will build the truck as you order it. Kenworth i know will allow an order by inches, i think Mack is the same. FL i think has standard lenghts as does Ford, so cutting may be somehting to have done.

5. Is there a resale book on tractor like the kelly blue book for cars?

there is a process where the banks and underwriters have to estabish the value of any truck, not a book. I know when I looked at several trucks in the past, I would bring in the specs with photos to have my bank to determine the value. I must add that these are not retail values but loan values which sometimes runs under 15% of the retail value, more or less.

Ricky · Dec 25, 2005

Thanks LDB and greg334 for the reply.

LDB,

I have found a Century with a 298" wheelbase but a little high on price for it, I think. Do you think this one would make a great truck?

Trying to find out what the measurement are from the sleeper to the end of the frame rails.
Did your KW come from factory with that wheelbase or did you add to it, if so how much and the price for the job?

Thanks,

Ricky

LDB · Dec 26, 2005

I ordered my truck to spec. It's a new 2006 model. I thought you were talking about a used truck in which case I think it will be very unlikely to find one with a long enough frame for a full size cargo box. If you are talking a new truck that's a whole different story. Again, I don't think you'll find one sitting on the lot ready to build on but you can order it whatever length you want. For anyone considering a new truck I STRONGLY urge calling Fred Sargent at Performance Kenworth in Houston. He will help you put together a great chassis to build out your truck on. Their number is 713-844-7111. For an "off the shelf" truck I'd also recommend Jon Mosier at Freightliner of Knoxville.

Leo Bricker, owner trucks 3034, 4958
OOIDA 677319
73's K5LDB
EO Forum Moderator 1+ Years of Service
Expediters Online.com - The Best is Getting Better!
-----
Support the entire Constitution, not just the parts you like.

Ricky · Dec 27, 2005

Hey Leo,

I was talking about a used truck.

The truck has a 160" from back of sleeper to the center of the tandems. If I centered the box and tandems up together with a 22' box on it, that leaves a 7' section of frame rail I would have to add. What is your thoughts on this!

Thanks,

Ricky

davekc · Dec 27, 2005

If it is 7 feet addition from the center of the tandems back that would be ok. If it is a additional 7 feet from the end of the frame it would likely be too long. This would pose problems with a heavy load. That would set your over hang at possibly 8 feet. Additionally, they would have to double frame that length and of course remove the tandems and a host of other items.
The other issue is the back of cab to the box. A minumum of three inches to twelve inches is needed depending on the cab configuration.
That would move the box back farther on the frame thus needing additional frame length.
I would highly advise having a manufacturer engineer look at making that type of alteration. A computer and water test would tell you how viable of a option this is.
Most of the time these tractors are stretched in the middle for these reasons.
Not sure if I helped or hurt?

Davekc
owner
21 years
PantherII
EO moderator

Ricky · Dec 28, 2005

I guess you could say it helped and also made me think a little more about it. Just trying to get an idea where the box will be for the best benefit and how much frame I will have to add if any!!
Thought about putting a 20' box but there goes 2' of cargo room.

LDB · Dec 28, 2005

If it is 160 inches from the back of the cab to the center of the tandems that would probably make the frame length from back of cab to end of frame somewhere around 18x inches. That would let you put about a 14 foot box and run as a C unit without doing anything to the frame. You would have to add extra frame to get to a 22 foot cargo box, provided that doesn't exceed the 40 foot overall length. As already mentioned, you need to talk to an engineer or to a business that does frame stretches all the time and can give you proper advice on it. Good luck with it.

Leo Bricker, owner trucks 3034, 4958
OOIDA 677319
73's K5LDB
EO Forum Moderator 1+ Years of Service
Expediters Online.com - The Best is Getting Better!
-----
Support the entire Constitution, not just the parts you like.

Ricky · Dec 29, 2005

Did a little more checking on it today, check out these numbers.

Front of bumper to center of tandems is: 343"
Add the 2 axle 48" + 10" for the original frame is: 58"
Add the extra frame rails is: 58"
Total lengh is 459"/12" = 38.250'
Center of front axle to center of 2 axle is 319" / 12" = 26.5833

Added a extra 58" frame rails to the support the 22' box.
With all of that said could this be a big problem?

LDB · Dec 29, 2005

>Did a little more checking on it today, check out these
>numbers.
>
>Front of bumper to center of tandems is: 343"
>Add the 2 axle 48" + 10" for the original frame is: 58"
>Add the extra frame rails is: 58"
>Total lengh is 459"/12" = 38.250'
>Center of front axle to center of 2 axle is 319" / 12" =
>26.5833
>
>Added a extra 58" frame rails to the support the 22' box.
>With all of that said could this be a big problem?
>

Confessing again that I'm not an expert on frame stretches, some numbers that are significant are bumper to back of cab (BBC), back of cab to centerpoint of tandems and back of cab to end of frame rails. You will need to add 4 inches to the BBC length for the gap to the cargo box. Your BBC max for a 22' box would be 211". Your cargo box can't extend more than a couple of inches beyond the frame rails at most or the lift going in and out will destroy it eventually.

The centerpoint of the tandems should be no farther forward than the centerpoint of the cargo box. I don't know if it's possible to fit a rail inside the current rail and have it extend far enough to support the box to the max legal length or not. That would obviously be a smaller rail than from the factory and may not be large enough. Another option is to consider the same chassis and a smaller box. It is pretty rare to fill a 22' box. Probably around 90% of your loads would be fine in an 18' box and would make the stretch a little easier and the truck a little more maneuverable too.

The most important thing is to find someone who has done scores of these conversions and can give you references to contact about their work.

Leo Bricker, owner trucks 3034, 4958
OOIDA 677319
73's K5LDB
EO Forum Moderator 1+ Years of Service
Expediters Online.com - The Best is Getting Better!
-----
Support the entire Constitution, not just the parts you like.

Ricky · Dec 29, 2005

Confessing to you, just trying to get a picture on it!!!

Truck dealer gave me some more detailed information on the measurement.
He told me that from the back of the sleeper to the end of the frame rail is going to be 268 inches, that is with a extra 50" (4 feet. / 2 inches) frame rails added and counting 4 inches for the sleeper to box clearance. Tried to get a picture of this, it would put the center of the 22ft. box over the center of the front axle.

Any thoughts on project or input on the weight factor!!

Tennesseahawk · Dec 30, 2005

Since I'm an idiot on these matters, I'll just suggest where you can find wheelbases of trucks already built. Check out truckpaper.com. Looking at a number of them, I'd say the front drive axle being at the midpoint of the box is pretty close.

davekc · Dec 30, 2005

On the surface it is starting to sound ok. The next place I would look is at the front end weight.
It would be depressing to go through all that and can't haul the first load because the front is too heavy.
It has certainly happened more than once.
Who ever is going to do the alteration, really needs to see this truck. And preferrably, not the guy that is trying to sell it.

Davekc
owner
21 years
PantherII
EO moderator