length to wheel base ratio

[Michigander]

I seem to recall a thread about 8 years ago concerning the best ratio for handling and I can not find it. Does anyone know the best length to wheel base ratio? Thanks!

[SoCalDesertRid1]

wolfe10 wrote:

SoCalDesertRider wrote:

I never understood why diesel busses and motorhomes don't place the engine in front of the rear axle, instead of behind it. The rear could be used for storage, which is much lighter than an engine. With the heavy diesel engine mid-ship in the chassis, it will have far better handling than a rear engine or front engine chassis.

Actually, Spartan DID make a "mid engine" diesel chassis, the Me2. A few made "garage model" motorhomes on it.

Sadly, no one saw the advantage of making a short (like 30-32') high end coach on it. Wheelbase would have been within a few feet of full chassis length. The perfect "downsize" coach for many 40' DP owners as they age.

Here is the press release: http://www.prnewswire.com/news-releases/spartan-motors-introduces-new-mid-engine-rv-platform-7590750...

Google will get you more hits.

That does sound interesting. The hydraulic rear garage is quite innovative for use as a toter-home. Too bad it didn't catch on.

[Ivylog]

SoCalDesertRider wrote:

wolfe10 wrote:

Ivylog wrote:

SoCalDesertRider wrote:
I
.

Also, a single tire axle with 22.5 wheels can have as much as 12,000-14,000 lbs load on it.

If it has that much on the tag it will have 24,000 on the drive axle... Newell/Prevost

[Cloud_Dancer]

You first make it as complicated as you want, but then you tend to lean towards the practical. You can say that the the CG has no height, but the center of mass does. You can say that the front(steer) tires should be loaded close to their max capacity, so that you can enjoy maximum camber and toe-in authority,...such that both will be able to enhance the vehicle's directional stability(which is ONE component of "handling", in motorhomes).
My way of "keeping it simple" is to buy one with the longest wheelbase and shortest rear overhang (in the size of DP motorhome that you prefer). then, you will find out that loading the front tires to the maximum allowed,....is not a problem.

[wolfe10]

SoCalDesertRider wrote:

I never understood why diesel busses and motorhomes don't place the engine in front of the rear axle, instead of behind it. The rear could be used for storage, which is much lighter than an engine. With the heavy diesel engine mid-ship in the chassis, it will have far better handling than a rear engine or front engine chassis.

Actually, Spartan DID make a "mid engine" diesel chassis, the Me2. A few made "garage model" motorhomes on it.

Sadly, no one saw the advantage of making a short (like 30-32') high end coach on it. Wheelbase would have been within a few feet of full chassis length. The perfect "downsize" coach for many 40' DP owners as they age.

Here is the press release: http://www.prnewswire.com/news-releases/spartan-motors-introduces-new-mid-engine-rv-platform-7590750...

Google will get you more hits.

[SoCalDesertRid1]

wolfe10 wrote:

Ivylog wrote:

SoCalDesertRider wrote:
I suppose a motorhome manufacturer can list it in whatever unconventional way they want. For commercial trucks, the standard is center of tandems, on a 3 axle tractor.

:S A tag axle DP only has two tires on the tag unlike your truck example. The four tires on the drive axle with 20K lbs on them will win over the two with only 7K on them when a DP is turning... even without decreasing the tag's air bags pressure. The MH manufactures know the correct numbers.

Agreed, in terms of effect on turning radius.

But, in terms of stability/straight line handling, a tag DOES count. That is where the 1/2 the distance between drive and tag gives relevant information.

Also, a single tire axle with 22.5 wheels can have as much as 12,000-14,000 lbs load on it.

[SoCalDesertRid1]

barmcd wrote:

RLS7201 wrote:

barmcd wrote:

RLS7201 wrote:
Wheel base to over all length ratio is more forum/internet nonsense.
MY 95 Bounder has a ratio of .479 and it drives great! 190" wheel base, 33' long. Best thing is the turning. Then there is the diesel owners talking about rear over hang on the gassers. My gasser has a 13' over hang. Diesel pushers have a 12'+ over hang, depending on chassis. More forum/internet chatter. Bah Humbug!
You'll see folks telling how horrible or how great their rig drives, no matter the ratio or total length. No one can document the ratio thing.
If set up correctly, they all drive well.

Richard

It's called physics.

OK, any one can say a work. Can you detail what you said?

Richard

Sure, the formula for figuring out the dynamic forces on a wheeled vehicle includes the following components: center of gravity, weight of the vehicle, wheelbase of vehicle, height of components above ground level, acceleration or deceleration of the vehicle and a gravity constant.



While it seems like the size of the rear overhang won't make a difference in the handling of a vehicle, it does affect the forces the wheels experience because one component is the distance between the center of gravity and the axle ("d"). A large rear overhang moves the center of gravity toward the rear of a coach.

Agreed. And the forces are further complicated by a large sail area behind the axle for cross winds or wakes from passing trucks to act upon. Then it gets even more complicated when you tow something behind the motorhome, with down force on the tail of the chassis from tongue weight, also side forces when the towed vehicle or trailer pushes on the rear of the chassis at an angle during braking, as well as from any swaying action the trailer or towed vehicle experiences while towing.

The best plan for good handling is to have a very short rear overhang, particularly if the vehicle is used for towing.

I never understood why diesel busses and motorhomes don't place the engine in front of the rear axle, instead of behind it. The rear could be used for storage, which is much lighter than an engine. With the heavy diesel engine mid-ship in the chassis, it will have far better handling than a rear engine or front engine chassis.

Most high level sport and racing cars use a mid engine configuration, for that reason, be it just in front of the rear axle, or just behind the front axle. Engine hanging out either end is no good for handling.

[barmcd]

BigRabbitMan wrote:
While it has been touched on here, my thoughts are that while wheelbase to length is a factor, a larger one is where the center of gravity is relative to the wheelbase. The farther forward it is, generally the more stable the coach will be. With the heavy rear engine of a diesel, it needs a longer wheelbase to maintain stability than an equal length front engine gasser. Cross winds are a separate factor so the wheelbase issue/number is something to consider, it is not a hard number. The number for my rear engined coach is .52 and it handles fine.

That's what the math says. Not only where the CG is relative to the wheelbase, but how high it is in the coach.

[J-Rooster]

Mile High wrote:

J-Rooster wrote:
I respect all of you, but your getting to technical for my pea brain! I just get in my Class A with a smile and just drive. Before I retired (truckdriver) I had to deal with bridge weights for any State that I drove in. Now life is simple for me just get in and drive!

X2 - I hope some carpet walker did the math on ours before I bought it 🙂

PS - go fast over bridges you are too heavy for - doesn't work for low clearances.

Thanks, Mile High!

[BigRabbitMan]

While it has been touched on here, my thoughts are that while wheelbase to length is a factor, a larger one is where the center of gravity is relative to the wheelbase. The farther forward it is, generally the more stable the coach will be. With the heavy rear engine of a diesel, it needs a longer wheelbase to maintain stability than an equal length front engine gasser. Cross winds are a separate factor so the wheelbase issue/number is something to consider, it is not a hard number. The number for my rear engined coach is .52 and it handles fine.

[wolfe10]

Ivylog wrote:

SoCalDesertRider wrote:
I suppose a motorhome manufacturer can list it in whatever unconventional way they want. For commercial trucks, the standard is center of tandems, on a 3 axle tractor.

:S A tag axle DP only has two tires on the tag unlike your truck example. The four tires on the drive axle with 20K lbs on them will win over the two with only 7K on them when a DP is turning... even without decreasing the tag's air bags pressure. The MH manufactures know the correct numbers.

Agreed, in terms of effect on turning radius.

But, in terms of stability/straight line handling, a tag DOES count. That is where the 1/2 the distance between drive and tag gives relevant information.

[Ivylog]

SoCalDesertRider wrote:
I suppose a motorhome manufacturer can list it in whatever unconventional way they want. For commercial trucks, the standard is center of tandems, on a 3 axle tractor.

:S A tag axle DP only has two tires on the tag unlike your truck example. The four tires on the drive axle with 20K lbs on them will win over the two with only 7K on them when a DP is turning... even without decreasing the tag's air bags pressure. The MH manufactures know the correct numbers.

[Mile_High]

J-Rooster wrote:
I respect all of you, but your getting to technical for my pea brain! I just get in my Class A with a smile and just drive. Before I retired (truckdriver) I had to deal with bridge weights for any State that I drove in. Now life is simple for me just get in and drive!

X2 - I hope some carpet walker did the math on ours before I bought it 🙂

PS - go fast over bridges you are too heavy for - doesn't work for low clearances.

[J-Rooster]

I respect all of you, but your getting to technical for my pea brain! I just get in my Class A with a smile and just drive. Before I retired (truckdriver) I had to deal with bridge weights for any State that I drove in. Now life is simple for me just get in and drive!

[barmcd]

RLS7201 wrote:

barmcd wrote:

RLS7201 wrote:
Wheel base to over all length ratio is more forum/internet nonsense.
MY 95 Bounder has a ratio of .479 and it drives great! 190" wheel base, 33' long. Best thing is the turning. Then there is the diesel owners talking about rear over hang on the gassers. My gasser has a 13' over hang. Diesel pushers have a 12'+ over hang, depending on chassis. More forum/internet chatter. Bah Humbug!
You'll see folks telling how horrible or how great their rig drives, no matter the ratio or total length. No one can document the ratio thing.
If set up correctly, they all drive well.

Richard

It's called physics.

OK, any one can say a work. Can you detail what you said?

Richard

Sure, the formula for figuring out the dynamic forces on a wheeled vehicle includes the following components: center of gravity, weight of the vehicle, wheelbase of vehicle, height of components above ground level, acceleration or deceleration of the vehicle and a gravity constant.



While it seems like the size of the rear overhang won't make a difference in the handling of a vehicle, it does affect the forces the wheels experience because one component is the distance between the center of gravity and the axle ("d"). A large rear overhang moves the center of gravity toward the rear of a coach.