Wheelbase to length ratio. What does it mean?

ferndaleflyer wrote:
I once rode from Baltimore to the Carolinas in a C class that if you looked at it from the side the rear wheels were right in the middle, or 1/2 way between the front and rear bumper. That thing swerved if a car passed and you can imagine what it was like passing a truck.....I flew back home. Better yet try towing a trailer behind anything with a lot of over hang.....must have a death wish.....

Hauled 25 of the 16' cattle panels on a 12' single axle trailer behind and S-10 this summer under a time deadline. Tail long and heavy with negative tongue weight is BAD. Thankfully it was relative light. It was fine at 35 MPH, fair at 40, wiggle at 42 and a full dance at 45 (only did that once however but it was on a bridge. :(

I just calculated the ratio for my coach. It is 53%, however, the wheels (all independent suspension) are more centered to the coach body than most. See the picture in my signature. You can see that the drivers door is in front of and not over the front wheels. Also, due to the independent rear suspension the drive line is only six inches long so the rear wheels are closer the rear of the coach than other rear engined units.

I do know that it handles great and cross winds etc. do not bother it. I have never gone over 82 mph unintentionally.

I once rode from Baltimore to the Carolinas in a C class that if you looked at it from the side the rear wheels were right in the middle, or 1/2 way between the front and rear bumper. That thing swerved if a car passed and you can imagine what it was like passing a truck.....I flew back home. Better yet try towing a trailer behind anything with a lot of over hang.....must have a death wish.....

Another way of viewing poor WB/OL coaches is to picture the wind vane on top of the barn.

Most of the surface is behind the fulcrum. So, the slightest wind makes it point toward the wind. Lots of rear overhang acts the same way in a cross wind. Again, not a Class A, C, diesel or gas issue.

Can engineering overcome this-- sure. A good example is the Foretravel 34'. Poor WB/OL ratio, BUT (yes, big but) it has 8 outboard air bags and 8 outboard shocks that help defy physics.

Think of it as the tail wagging the dog. That issue will only get worst the more weight that is placed in the rear (i.e tanks.)

TechWriter wrote:

berreez wrote:
When you divide the wheelbase by the length of the motor home, you should have a wheelbase-to-length ratio of 53%. This ratio gives us a good idea of the handling characteristics you can expect from this vehicle.

From the above statement, is it better to have a number lower or higher than 53% if you what better handling?

What does it mean? Buy a diesel.

A ratio of 53% is just fine.

And there are both gas and diesels with poor and those with good WB/OL ratios. Not necessarily an "engine" thing-- or even Class A vs Class C thing.

Buy a deisel isn't always the choice either....

A gasser typically has the front wheels pushed very far toward the front. The engine is up there, a lot of weight is up there, this is what works. Everything else follows, so to speak.

In a diesel, the distance from the center of the rear axle to the rear bumper is pretty much fixed. Regardless of the totl length or the wheelbase, the axle, driveshaft, trans and engine is "this long", period.

As gassers get bigger, the rear overhang gets longer, and the odds of getting a poor handling coach increases, depending on what the manufacturerdecides to do with the wheelbase.

With diesel, it is the opposite. Since the rear axle to tail is fixed, as the coach (and wheelbase) get shorter, you are more likely to get "tail wagging the dog" issues.

berreez wrote:
When you divide the wheelbase by the length of the motor home, you should have a wheelbase-to-length ratio of 53%. This ratio gives us a good idea of the handling characteristics you can expect from this vehicle.

From the above statement, is it better to have a number lower or higher than 53% if you what better handling?

What does it mean? Buy a diesel.

The tail can wag the dog for sure. Our 32'1992 P30 chassis handles well but GBM took the 190" wheel base to 208" before building the house. Your ratio is awesome.

Confused about the ratio. Never good at math. lol. I DO know that too much coach behind the rear wheels WILL cause handling problems, especially when trucks are passing you. Will cause the rear to sway & U'll be trying to correct steering. This is my 5th. motorhome. Its the 1st. one I've owned that didn't look like the rear wheels were almost in the middle of the coach. It is 2006 Ford F53 chassis, 34' Class A with 228" wheelbase. It is the 1st one I haven't had a swaying problem with. You do the math.