first report new springs with a surprize result

[pianotuna]

Hi,

I replaced the springs and had a leaf added on each side.

There were air bags that may have been improperly installed from the get go--7 inch bags in a 5 inch space, so the brackets torn away from the frame.

The air bags have been replaced with timbrens, which do not touch the frame--but might if I had full water tanks (66 gallons).


I put on new monro shocks at the rear.

Results (big surprize).

The RV rides 2.5 inches higher at the rear.

Ride is improved

And now the shock. It appears from early results that gas mileage has gone up by about 1.5 to 2 mpg. I've asked one mechanic and he is totally puzzled.

Anyone care to offer an explanation?

[ol_Bombero-JC]

Since you have a Class C MH - you might try posting on that forum.

See if any owners of Class C's have had similar experiences.

:@

[philh]

wopachop wrote:
4. Fuel truck guy accidentally put the high octane into the low octane bladder.

High octane fuel has lower Btu energy. Additional power is made up from higher compression.

But you raise a good point, quality of fuel (including age) can have a huge effect on performance.

[wopachop]

What a fun thread. I have some guesses.

1. New springs and airbags improved aerodynamics and reduced bouncing which might equate to less tire drag friction.


2. Maybe a rear brake pad or e-brake was dragging slightly and freed up from work done to the rear wheel area.

3. You were in snow and driving to Florida. Maybe that first gas tank was mostly downhill?

4. Fuel truck guy accidentally put the high octane into the low octane bladder.

[pianotuna]

Wise advice--and once I'm back to "normal" I'll do just that.

Today 450 miles driving at the speed limit. Totally out of the snow zone but I still need to do pedal to the limit.

drsteve wrote:


I'd say gather some more data before drawing any firm conclusions.

[philh]

pianotuna wrote:
Phil,

It is NOT 20% improvement. I regularly got 9 mpg. Now I'm getting between 10 and 11 *if* I drive 49 mph. (not lie-o-meter, real measurements)

I do have air tabs--but never noted any difference in mileage, except with a tail wind--where they lowered fuel consumption a bit (measured by a lie-o-meter). They helped with cross winds--and large trucks. They helped with noise levels in the cab.

However today I was for some time driving 75 mph. The lie-o-meter was reading about 5.2. At 70 that was 5.8 and at 65 6.4. about 1/2 the trip was at 65 mph.

There was a head wind but not much of one.

I drove 585 miles and consumed 77 US gallons. That works out to 7.59 mpg. My RV weighs 13750 lbs.

9 --> 11 is a 22.2% improvement

[drsteve]

That sounds like a heck of a change just from some aerodynamic tweaking. OTOH, when I bought a new TT my mileage decreased by about 1.5 mpg. The new trailer is virtually the same weight and a bit shorter, but it has 6-7 inches more ground clearance, and the box itself is taller.

I'd say gather some more data before drawing any firm conclusions.

[pianotuna]

Phil,

It is NOT 20% improvement. I regularly got 9 mpg. Now I'm getting between 10 and 11 *if* I drive 49 mph. (not lie-o-meter, real measurements)

I do have air tabs--but never noted any difference in mileage, except with a tail wind--where they lowered fuel consumption a bit (measured by a lie-o-meter). They helped with cross winds--and large trucks. They helped with noise levels in the cab.

However today I was for some time driving 75 mph. The lie-o-meter was reading about 5.2. At 70 that was 5.8 and at 65 6.4. about 1/2 the trip was at 65 mph.

There was a head wind but not much of one.

I drove 585 miles and consumed 77 US gallons. That works out to 7.59 mpg. My RV weighs 13750 lbs.

[philh]

JaxDad wrote:
On he contrary, any improvement in the aerodynamics of a ‘brick’ result in pretty substantial gains. Bear in mind also that as speed increases the drag does NOT increase proportional to the gain. According to Bernoulli's equation, drag is proportional to the SQUARE of THE speed.

Look up “AirTabs” and the gains that can be made by just adding some little plastic stick on tabs to a ‘brick’ and changing the vortices that form BEHIND it.

It's a FREAKING BRICK

There is NOTHING you can aerodynamically change to a FREAKING BRICK to get a 20%+ fuel economy improvement, NOTHING.

Bernoulli at 65MPH? Seriously? We're not talking about radical changes to trailing airflow, you're suggesting a slight change to turbulent airflow underneath will have a 20% improvement in fuel economy.

[Chum_lee]

Just guessing. Did you, by chance, fill your tank with non-ethanol fuel or go from summer to winter blend fuel?

Chum lee

[pianotuna]

It is 176 inches.

At 65 mph am getting 8.1 mpg. Day one is 585 miles to get out of the snow zone. I'll camp here tonight 43.763924, -93.316532

[Harvard]

pianotuna wrote:
The wheels had been aligned less than 1000 miles ago.

If the wheel base were 158 inches, raising the rear end by 2.5 inches would reduce the front end caster by about 1 degree.

[JaxDad]

philh wrote:

JaxDad wrote:
As a pilot with a degree in aerospace engineering I can tell you that “parasitic losses” can manifest themselves in many weird and wonderful ways. Likewise the gains created by eliminating them, witness the little air tabs (originally designed for aircraft) that can measurably increase fuel mileage on a coach.

In this case, I’d say an overloaded suspension created excessive (even if you weren’t aware of it, the slow creep is imperceptible) motion which created the losses you’re now recouping.

At Motorcoach speeds, parasitic losses on a brick aren't going to amount to much. OP said 1.5 to 2 mpg improvement. There was either something very seriously wrong with the alignment or the OP's calculations are a bit off.

On he contrary, any improvement in the aerodynamics of a ‘brick’ result in pretty substantial gains. Bear in mind also that as speed increases the drag does NOT increase proportional to the gain. According to Bernoulli's equation, drag is proportional to the SQUARE of THE speed.

Look up “AirTabs” and the gains that can be made by just adding some little plastic stick on tabs to a ‘brick’ and changing the vortices that form BEHIND it.

[pianotuna]

Hi,

I've now driven about 600 miles and I continue to see improved mileage.

I'm on a long haul to Florida--and tomorrow instead of driving my "economy speed" I need to drive the speed limit.

[landyacht318]

Agree that one data point is nearly useless. Especially when human emotion is is fed through right foot.

I can see a sagging coach body creating more air resistance in between axle and road that is relieved somewhat when raised, but a 2.2mpg increase seems highly unlikely. Report back once you get to Florida and watch the roadside flags for wind direction and make a note of it on your miles per tankful log.