Wheelbase and length

[kerrlakeRoo]

In Researching motorhomes in general, I ran into something I dont understand.
We have started looking at units both Class A and C with roughly a 30' box, and 32 or so foot total length.
Why are the Class C units in this size 220 - 228 wheelbase and the class A units 190 to 208.
For instance the 29' to 31' Jayco Greyhawks have a total length of 32'3 and a wb of 223
And I commonly see Class A's like the Georgetowns with total lengths about the same but wheel bases of 190 or 208.

Comments about sway problems on the class a 's frequently talk about the tail swing and cases of sway from a long tail so why are they almost always shorter wheelbases?

[pusherpilot]

wolfe10 wrote:

kerrlakeRoo wrote:
Is the idea on the smaller A's that having a longer tail shifts weight off the front axle?

Certainly weight distribution is one factor.

So is affect of wind on that long overhang-- think of it as the "tail" on a wind vane.

Cross winds are really dangerous on many of the older gas chassis MHs. I've seen many of them going down the road crossed up so bad that they are overhanging the adjacent lane. In our DP in the same wind it's unusual to fight the wind and many times the only way to tell if there is a cross wind is the steering wheel position or stuff blowing across the road.

[kerrlakeRoo]

I continued looking and apparently its also a matter of total capacity. With the Coachmen Mirada, even of a smaller model 32ss the wheelbase was up to 228, but the gcwr was up to 26000 instead of 23000, gvwr had also gone up by 2500 lbs. so maybe in the f-53 models WB closely follows load.

[wolfe10]

rgatijnet1 wrote:
The design of the HOUSE and the placement of fuel tank plus the water and waste tanks, all determine the placement of the rear axle/wheelbase. It has nothing to do with cost and everything to do with making sure that both the front and rear axles are properly loaded per the manufacturer's specification.

I respectfully disagree. Many times the sales department rather than the engineering department makes critical decisions on cost as well as layout. Certainly, number and size of slides, where the galley is placed, etc materially affect weight distribution and therefore handling.

[rgatijnet1]

The design of the HOUSE and the placement of fuel tank plus the water and waste tanks, all determine the placement of the rear axle/wheelbase. It has nothing to do with cost and everything to do with making sure that both the front and rear axles are properly loaded per the manufacturer's specification.

[wolfe10]

kerrlakeRoo wrote:
Is the idea on the smaller A's that having a longer tail shifts weight off the front axle?

Certainly weight distribution is one factor.

So is affect of wind on that long overhang-- think of it as the "tail" on a wind vane.

[kerrlakeRoo]

Is the idea on the smaller A's that having a longer tail shifts weight off the front axle?
Putting the extra weight on the rear must be the cause of the handling issues that folks complain about with the F-53 chassis.

I went through photos and the F-53 vs the E-450,
difference of the amount of rig forward of the axle only appears to be about 6 to 9 inches. Seating position of the driver is irrelevant.
So most of the additional 30" of rig outside the wheelbase is off the rear.
Thanks all, you got me to thinking a little differently on it. And better understanding the need for stiffening the rear to the extreme.

[pusherpilot]

Back in the late 90s there was great controversy over the length to wheelbase ratio. Ratios over 50% and preferably over 55% were considered safe. The wheelbase must be over 50% of the total length of the unit. Mfgrs started lengthening the wheelbase on most models to get over that magic figure. Another issue was the weight distribution front to rear. Before the controversy started the generators and fuel tanks on most Diesel pushers were mid chassis or further to the rear. On my 2004 HR Imperial the fuel tank 120gal, propane tank and the water tank, 100 gal is just behind the front axle. The generator is in front of the axle.

[Dale_Traveling]

kerrlakeRoo wrote:
Yes, thats why I thought it odd
From www.jayco.com class C
Greyhawk 29 MV 223" wheelbase
Forest River Forester 3011ds
220" Wheelbase.

I assume the builders are cutting and extending the chassis for these, but Coachmen, Winne, they all are longer than 200" on most 29-32' Class C units.
Yet they will build Class A gassers 30 - 34' long with only a 190" wheelbase.

I never research Class C's that deep but you're right 200"+ wheel base E-450 based rigs. I knew Morryde was doing chassis mods for builders but never suspect they were that busy. About the only mod you'll see on the F53 is tail end frame extensions. Haven't heard of any Class C's breaking in half so I guess the mod works.

Morryde Chassis Division

[Dutch_12078]

kerrlakeRoo wrote:
Akrv, I should have specified, gas class A's. There isn't much forward of the axle on those, it appears similar to the E-450 van fronts on the Class C's.

A Class C has the front seating ~3' behind the axle. Gas Class A's have the front seating over the axle, and in our's the drivers door is directly over the axle, while a Class C drivers door is behind the axle. It's ~4' from the front of our coach to the axle, and the space from the dash back is part of the living area when stopped. Nearly all of our engine sits forward of the axle, versus a Class C where the axle is closer to the front of the engine. I'm not saying one is better than the other, just that there differences in the body/chassis balance.

[kerrlakeRoo]

Dale.Traveling wrote:
For the current model year the F53 comes in wheelbase lengths from 158" to 252". It's up to the builder to choose which length to build on. Bigger the wheel base the higher the cost so builders will go as small as they can.

Also Ford E series, cutaway or stripped chassis the choice of wheelbase is 138" 158" or 176". At least for model year 2018. Are you sure about the 220"-228" lengths?

Dimensional data from Ford is listed here - 1997-2018 Ford Body Builders Layout Book(s)

Yes, thats why I thought it odd
From www.jayco.com class C
Greyhawk 29 MV 223" wheelbase
Forest River Forester 3011ds
220" Wheelbase.

I assume the builders are cutting and extending the chassis for these, but Coachmen, Winne, they all are longer than 200" on most 29-32' Class C units.
Yet they will build Class A gassers 30 - 34' long with only a 190" wheelbase.

[Dale_Traveling]

For the current model year the F53 comes in wheelbase lengths from 158" to 252". It's up to the builder to choose which length to build on. Bigger the wheel base the higher the cost so builders will go as small as they can.

Also Ford E series, cutaway or stripped chassis the choice of wheelbase is 138" 158" or 176". At least for model year 2018. Are you sure about the 220"-228" lengths?

Dimensional data from Ford is listed here - 1997-2018 Ford Body Builders Layout Book(s)

[kerrlakeRoo]

Akrv, I should have specified, gas class A's. There isn't much forward of the axle on those, it appears similar to the E-450 van fronts on the Class C's.

[akrv]

The class A have a shorter wheel base because more weight is forward of the front axle than in a class C. You want 2/3 of the weight on the rear axle and 1/3 of the weight on the front axle. Also have most of the weight between the axles for the best ride and handling.