Wheelbase to length ratio - how important?

We're looking at new gas class A's.  Specifically the Winnebago Vista 31KE and the Itasca Tribute. In each case the wheelbase to length ratio is 51% which is ranked as "fatiguing". Should we be concerned about it?  If so, just what would be some examples of Winnebago/Itasca class A in the 28-32 ft. range that have any better rating?

Somewhere around 54% is a good target, but I don't know any meaningful way to compare the "fatigue" factor of driving a coach that has 51% vs 54%. More is better, but trying to compare small differences is an exercise in futility since other factors could easily cloud whatever tiny difference the wheelbase made. Some examples might include tire size and type, steering gear ratio, size of anti-iroll bar(s), suspension stiffness, weight distribution, etc. If we could get Winnebago to build the exact same rig with two different wheelbases on otherwise identical chassis, maybe a difference could be measured. Maybe...

I realize this isn't a very helpful answer, but I don't think you can isolate one small factor like this and make any judgements based on it.

Sounds like you are reading that guide where you enter wheelbase, overall length etc, cost a bit to get this guide.  If the one I am thinking the formulas make a lot of assumptions and then make statements like fatiguing.  If this is where you are getting this, try to get your money back.  Drive the coach, check it all out. As Gary says, a bigger ratio would be better, so the guide isn't completely off, but they tend to be really offputting, and turn folks away from a perfectly good coach because of very subjective viewpoints.

Think about this, if the ratio were 30% well it would be a teeter totter, if it were 100% you would need 40 acres to turn the rig around.  The reality is for the most part, there are standard wheelbases on the market, having a weight rating.  Up to the coach builder to match the house to the chassis.  The drive will tell you if they got it right.

Excellent feedback. Even my engineer husband agreed to put away his calculator on this one.
And, yes, we had used "that guide".

"Overall length"? I would think any portion of the overall length ahead of the front axle would be a plus. Why should that figure in? Or does the formula account for that?

Dan, that is ONE of the reasons I asked about 'that guide'.  The guy that wrote it for the unsuspecting has not exactly gotten rich on it, but he probably financed his next coach with the proceeds.  I don't remember the name of the guide, or his name, but while having some good information, it is heavily biased by his own often misinformed opinion, all under the guise of 'science'.

PancakeBill said:

Drive the coach, check it all out. ..

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It is my belief that the ratios are indeed a general guide to handling ease at each end of the scale but in the middle of the ratio bell curve the differences are probably very subtle. For test drives, it's important to drive in a variety of environmental conditions, different road surfaces and especially test the unit in crosswinds.

If there is a long overhang (the house that extends aft of the rear axle), expect a "tail wagging the dog" effect.  All of that overhang acts as a lever to push the front around requiring lots of steering inputs which can be tiring.  Another disadvantage of a long overhang is when maneuvering - you have to be very aware of the swinging radius of the overhang.

As far as wheelbase length, I have a real world example contrasting my long wheelbase F-250 truck and our old short wheelbase Jeep Liberty.  The truck requires very few steering inputs and we can easily drive it 500 miles a day and not feel beat-up.  The Liberty on the other hand requires lots of steering inputs and is very tiring to drive more than 100 or 200 miles.

Having said all of that, even shorter wheelbase units can handle very well but that probably varies from model to model depending on how the house builder distributed the weight and how long the overhang is.  One more point about overhang - the long overhangs are used to unload the front axle to keep the weight within axle limits.

Conclusion: test drive the units (I'm talking about a 45-60 minute test drive) and talk to owners to get their feedback.  Congratulations on doing your homework.

There are at least two basic things going on with wheelbase vs overall length: First is front to rear weight balance and the second is the polar moment of inertia when turning.

After that, there is a host of other real-world issues like tail swing and crosswinds as previously mentioned.

My own rig (quick measurements) are 180" wheel base, 130" rear overhang and 359" overall length. To say that the overall length measurement that includes a lot of air behind the front cap should be taken into account equal to the tools I carry in the rear storage compartment is just plain silly. At present, I think most here in this thread likely agree.

However, even with all my negative comments on the issue, there is some heat in the arguments even if the calculations might shed more heat than light. I've looked at quite a few MHs and thought to myself: that rig doesn't look right and moved immediately to considering a different one.

All the above being said, there is a difference. You may occasionally encounter a coach that is somewhat lower priced than other, seemingly similar, models. With rice price competition in the RV market so aggressive, you can be sure the less expensive model left somethings out or scrimped a bit here and there, usually in places that are out of sight to the casual buyer. The chassis capability is one of those places, and you may note a shorter wheel base, lower GVWR and/or GCWR, smaller engine, maybe an Allison 2400 or 2500 instead of a 3000 or 4000, steel wheels instead of alloy, and so on. None of these things are inherently bad, but the cumulative effect of cost-cutting is likely to show up in handling, ride, future maintenance costs, and so forth.

So, pay attention to factors like wheelbase ratio when comparing models, but use them as clues to overall design and build quality and not as a single make-or-break decision.

Gary RV Roamer said:

.. With rice competition in the RV market so aggressive, ..

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Uncle Ben's is #1 

As for this specific model (Vista/Tribute 31KE), I would count the 190" wheelbase as a slight negative. Notice that the larger 35 foot models (35B & 35F) have 240" and 228" wheelbases. That's an additional 50" or 38" of wheelbase for a mere 62" or 49" of extra overall length, increasing their wheelbase ratio to a more respectable number and improving it. Ford makes that same 18,000 lb F53 chassis in 208" and 228" wheelbases and Winnie would have done much better using the 208" for these coaches. I don't know the cost difference in Winnie's contract with Ford, but you can be assured there is one.

The Fleetwood Southwind 32VS uses the 208" wheelbase in a 33'5" overall length, for a wheelbase ratio of 51.9%. Is it better? Difficult to say except that one single factor is a small plus vs the Vista 31KE. It's also 2 ft longer than the 31KE, and that could be viewed as a plus or a minus, depending on your needs and other, individually minute, factors.

Test driving an RV is certainly a good idea; however, it doesn't mean much since the RV will probably be empty. Driving with it loaded can be a whole new ballgame. Unfortunately, the only way to test drive one loaded is to buy it first.

Glad you said that, Bruce! I never felt that a motorhome test drive was very valuable either. It's empty and odds are you are driving on city or interstate roads close by the dealership. Nothing to give you much actual feel for how it drives, nor long enough to get accustomed to it. Short of a glaring defect, e.g. transmission problems or unusual loud noises, you aren't going to learn much.

Gary RV Roamer said:

As for this specific model (Vista/Tribute 31KE), I would count the 190" wheelbase as a slight negative. Notice that the larger 35 foot models (35B & 35F) have 240" and 228" wheelbases. That's an additional 50" or 38" of wheelbase for a mere 62" or 49" of extra overall length, increasing their wheelbase ratio to a more respectable number and improving it. Ford makes that same 18,000 lb F53 chassis in 208" and 228" wheelbases and Winnie would have done much better using the 208" for these coaches. I don't know the cost difference in Winnie's contract with Ford, but you can be assured there is one.

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I agree fully. Why in heck do manufacturers tend to use frames that are a bit too short? (I know: cost.) Don't they realize some of us can differentiate the difference, yet still want a shorter overall length? Or that somewhere down the line a buyer or second owner might want to put something heavy on the rear?

All the above being said, there is a difference. You may occasionally encounter a coach that is somewhat lower priced than other, seemingly similar, models. With rice price competition in the RV market so aggressive, you can be sure the less expensive model left somethings out or scrimped a bit here and there, usually in places that are out of sight to the casual buyer.

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I've seen one (older) long-ish coach that my eye detected some sagging at the rear. Too weak a frame?

Perhaps I can give an example of one particular case I was interested in, the BT Cruiser (2007) from Gulfstream. They made a Ford based version and a GM/Workhorse version that were otherwise identical. The Ford frame was extended by cutting it in two and inserting two pieces , extending wiring and brake lines etc. thus giving it a longer wheel base.  The GM version was extended by adding overhang to the rear of the existing frame. (The Ford version frame mod was NOT done by Gulfstream but through another Ford qualified builder, but the name escapes me at the moment, as Gulfstream informed me, and it was like pulling hen's teeth to get this information as well as the build sheets for a particular vehicle. Don't know about the GM version as I did not pursue it.)

The main observable difference between the two: the engine/transmission used (of course), the longer overhang on the GM version, and the tow hitch capacity; Ford: 5000 lbs and the GM: 3500 lbs.

All this to say that there are definitely differences in the way the frame can be extended and it does affect loading, wheelbase, strength, handling etc.

I've seen one (older) long-ish coach that my eye detected some sagging at the rear. Too weak a frame?

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Yeah, I've seen those too.
As Stu noted, there are two ways to extend the frame for a long body coach. One is called a "stretch", where they cut it in the middle and insert more length, essentially making it a longer wheelbase.  It's expensive and fraught with liability issues for the frame rebuilder. The other method is a simple extend, where the rear is simply extended out with light steel tubing welded to the main frame. It's relatively inexpensive and the extension is typically light duty, for cost and weight reasons. That leads to a limited hitch and tow rating as well as potential issues if too much weight is loaded in the rear. They have also been known to get cockeyed if backed into something at an angle, even at low speeds.

Winnebago has successfully cut and extended frames for some models in the past, not sure which ones or if they still are doing that.  I'm going to move this thread to the Motorhomes board since it's turned into more of a generic discussion. 

With the extended overhang.. (As opposed to the stretched frame) a rear Track Bar become more and more desirable.

Frankly,, My rig is built on a workhorse, and EXTENDED rather than streatched.. This means I can, and have, on occasion parked a 38 foot RV on a 28 foot site (Conditions) rear of site was a cliff, (Ok so it's only a foot or two) and no trees in the way)

I had to use a ladder to hook up and un-hook my long wire antenna, and to take my bicycle down off the rack, but otherwise no problems.

With a Stretched chassis,, I could not have done that.

Most RV builders don't do much actual frame stretching anymore because the chassis builders now offer a wide choice of wheelbases for gas chassis, and diesel chassis can be configured to almost any spec. They do, however, sometimes build their own "bridge" for the diesel pushers. The bridge is the center section that has the storage bays and is essentially just bolted to the front and rear modules, which come complete from a chassis maker such as Freightliner Custom Chassis or Spartan. There is still probably a temptation to stretch a Class C, since the chassis is a standard van model and only available in the sizes the auto manufacturer needs for his own van models.  Class A, chassis, on the other hand, are designed for RVs and medium truck use.

That said, I wouldn't rule out the possibility of almost any sort of chassis extension or stretch. RV builders are well known for taking shortcuts to save a few bucks vs what they can buy ready made, even though those in-house mods have repeatedly bit them in the butt over the years. Their institutional memory seems short, and the very limited warranty saves them from too much pain.

Along this line, I believe this discussion implies a minimum practical length for a diesel rig (I'm pretty well at that limit). That is because, as Gary noted, the front and rear are modules and are of fixed length. The shorter the length, the longer the rear over hang as a percentage of overall length.

Ernie