Wheelbase Question

I am looking at a couple of different coaches one has a 286" wheelbase and the other has a 309" wheelbase. Both are pretty similar otherwise 350 hp engine, 1000 foot pounds of torque. One is 39' the other 41'.

What do I gain/lose with a longer wheelbase? TIA.

Depending on the wheel cut (how sharp it can turn) a longer wheel base will cause the turning radius to be somewhat greater. A longer wheel base will also affect how far inside the rear wheels track when turning sharply, but the wheel cut affects that too, so it's a nice thing to know. A longer wheel base can also make the coach more stable in strong winds, or when being passed by large trucks.

Kev

Elaborating a bit on Kevin's excellent advice, a long wheel base generally rides better than a shorter one if the coaches are otherwise the same (something that is rarely the case).

Both of those wheelbase figures are exceptionally long for the size of the coach, to the point where I wonder if there was a typo or two? Or are these tag axle coaches, where the wheelbase is an imaginary point between the tag and drive axles?  A typical top-of-the-line 39-40 foot coach without a tag would have a wheelbase in the 266-278" range.  But the 350 engine and 1000 lb torque sounds like a lesser coach than that.

The real question is whether the wheelbase is adequate for the coach length. Traditional wisdom for non-tag coaches is that wheelbase should exceed 50% of overall length and 52-54% is typical for better models of DP.  Going much beyond that gets expensive with only modest benefits in ride and handling, and those are traded off against the wider turning radius that Kevin described.  Ideally the wheel cut and wheelbase were wisely chosen such that the turning radius and ride comfort are near optimal. And the engine, tranny and drive axle gearing chosen such that performance and fuel economy are a reasonable balance as well.

Tags are a little harder to put numbers on, especially since there are competing notions as to how to measure wheel base with a tag axle.

This Foretravel coach spec sheet shows a bit about wheelbase with/without tag and resulting turning radius numbers.
http://www.beamalarm.com/foretravel-links/foretravel-past-brochures-specifications-and-manuals.html

I have always looked at wheelbase to length ratio when shopping motorhomes.  Haven't seen many with ratios exceeding 55 to 56%.  My experience has been that dealers and owners often don't have the right numbers.  Both these coaches have wheelbase to length ratio of more than 60%, something I don't recall ever seeing.  If you plan on looking at the coaches, bring a tape measure.

Putting things in perspective, according to the Dec. 2017 issues of FMCA, the wheelbase of a 45 foot Newell is 302 inches.  On their 45 foot coach that equates to almost 56%. 

The coaches I am referring to are the Renegade Verona LE 40'-2" with a 309" wheelbase and if I recall a 63 degree cut, and the Dynaquest DX3 39'-2" with a 268" wheelbase (I said 286" in my original post) I do not know the wheel cut in this coach.

Ahhh! The Renegade Super-C on the Freightliner M2 truck chassis. That does indeed have the huge 309" wheelbase, but I thought the wheel cut was 55 degrees (that's what FTL advertises). 63 degrees would be a big improvement if available.  The "lag" in the turns is going to be monumental with a 309 wheelbase, and the 63 degree wheel cut just makes it possible to cut corners even further.

I had a 40 footer with 268" wheelbase and 56 degree cut and could darn near make a U-turn pivoting the rig on its rear axle.

The Renegade Valencia for 2018 is built on the new Freightliner S2RV chassis and has a 279" wheelbase and the wheel cut is 55 degrees. That is more typical for a 40 footer and makes for a handier driver.

My 40' Allegro Bus has a 276" wheel base and a 60 degree wheel cut. That is on Tiffin's Power Glide chassis. I have noted that the turn radius is as good or better than my 36' Phaeton on a Freightliner chassis was.

Gary RV_Wizard said:

Ahhh! The Renegade Super-C on the Freightliner M2 truck chassis. That does indeed have the huge 309" wheelbase, but I thought the wheel cut was 55 degrees (that's what FTL advertises). 63 degrees would be a big improvement if available.  The "lag" in the turns is going to be monumental with a 309 wheelbase, and the 63 degree wheel cut just makes it possible to cut corners even further.

I had a 40 footer with 268" wheelbase and 56 degree cut and could darn near make a U-turn pivoting the rig on its rear axle.

The Renegade Valencia for 2018 is built on the new Freightliner S2RV chassis and has a 279" wheelbase and the wheel cut is 55 degrees. That is more typical for a 40 footer and makes for a handier driver.

Click to expand...

Gary,

What do you mean by "lag" in the turns? Is it that I would have to travel further into an intersection to make a sharp right turn, or else I would hop a curb?

Yep, and that's where new owners of longer rigs have the biggest learning curve. Especially if you are pulling a toad. Being that the toad is much narrower than the coach it will follow easier in the rigs footprint, but if you catch a curb with the rear tire on a 90 degree turn, odd are good the toad will hit it too.

Yep, that's the "lag", which admittedly is not exactly an obvious term for it.  You crank the steering wheel to one side and the rear axle immediately begins to take a shortcut, the most direct straight line between its present position and where the front end is headed.  It "lags behind" the front end rather than following it through the turn radius, so yes it will hop the curb or strike a pole or even clip a building if you don't pull forward enough to give it room.  The longer the wheel base, the greater the lag.

That negative is balanced against the positive of greater track stability when traveling straight forward and a smoother ride over dips and such.

It's exactly the same offtracking as a 5th wheel trailer exhibits following a pickup truck around turns, except you're driving at the front of the RV instead of being in a pickup towing it.

That's why school buses tend to have short wheelbases and long rear overhangs, while OTR buses are the opposite.  You trade off low speed maneuverability for high speed stability.

When I was in school, I liked to sit in the rearmost row of the school bus and feel the "crack the whip" effect as the bus went around corners.  You'd start by swinging wide towards the outside of the turn, then following the rest of the bus through it.  With an aggressive driver it was almost as much fun as riding the Tilt-A-Whirl at the county fair.

So... we have made a decision to go with the 268" Wheelbase found on the Dynamax DX3 37TS, and forgo the 309" Wheelbase that is associated with the Renegade Verona LE.

The 268" Wheelbase will be more maneuverable in close quarters such as Sunset Bay State Park in Oregon, one of my wife's favorite destination. The Dynamax is just under the 40' mark at 39'-2".

And we found a 2018 that has been reduced significantly, getting ready for the 2019s to arrive.

Very nice! Post up some pics when you bring her home!