Good Sam Club Open Roads Forum: first report new springs with a surprize result
Open Roads Forum Already a member? Login here.   If not, Register Today!  |  Help

Newest  |  Active  |  Popular  |  RVing FAQ Forum Rules  |  Forum Posting Help and Support  |  Contact  

Search:   Advanced Search

Search only in Tech Issues

Open Roads Forum  >  Tech Issues

 > first report new springs with a surprize result

Reply to Topic  |  Subscribe  |  Print Topic  |  Post New Topic  | 
Page of 4  
Prev  |  Next
jjrbus

FT Myers FL

Senior Member

Joined: 07/19/2008

View Profile


Offline
Posted: 11/17/19 04:20am Link  |  Quote  |  Print  |  Notify Moderator

pianotuna wrote:

The wheels had been aligned less than 1000 miles ago.


Again, not a mechanic. Cannot help but wonder if a vehicle with worn springs can be aligned properly. Guess it is better now, so enjoy the extra mpg.

Huntindog

Phoenix AZ

Senior Member

Joined: 04/08/2002

View Profile



Posted: 11/18/19 03:14am Link  |  Quote  |  Print  |  Notify Moderator

pianotuna wrote:

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?
Raising the rear will change the alignment. Even a low tire will have an effect. In fact the first step a good mechanic does is setting the tire pressures to spec, when doing an alignment.... Having said that. I don't think it would change so much as to cause the results you are seeing. How does it drive? Monitor the tires for unsual wear. If that all checks out, it might be a good idea to get the alignment checked (not changed) so you can record the specs as to where it is set now... And use those specs from now on.


Huntindog
100% boondocking
2021 Grand Design Momentum 398M
2 bathrooms, no waiting
104 gal grey, 104 black,158 fresh
FBP, 3, 8K axles, Disc Brakes
17.5 LRH commercial tires
300 watts solar,
2020 Silverado High Country CC DA 4X4 Big Dually.



pianotuna

Regina, SK, Canada

Senior Member

Joined: 12/18/2004

View Profile


Offline
Posted: 11/18/19 06:44am Link  |  Quote  |  Print  |  Notify Moderator

Hi Huntingdog,

It drives pretty much the same way. The front end has always been on the light side. Once, the folks who rotated the tires put 85 lbs in the fronts. That made it quite uncomfortable to drive--when I went back down to 65 it was back to normal.

I've toyed with the idea of lowering front wheel pressure, but I think that might increase the major cost of my RV which is fuel.

It is early days as I've only driving it about 200 miles.


Regards, Don
My ride is a 28 foot Class C, 256 watts solar, 556 amp hours of AGM in two battery banks 12 volt batteries, 3000 watt Magnum hybrid inverter, Sola Basic Autoformer, Microair Easy Start.

philh

Belleville MI

Senior Member

Joined: 05/11/2015

View Profile


Offline
Posted: 11/18/19 09:41am Link  |  Quote  |  Print  |  Notify Moderator

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.

Huntindog

Phoenix AZ

Senior Member

Joined: 04/08/2002

View Profile



Posted: 11/18/19 04:02pm Link  |  Quote  |  Print  |  Notify Moderator

I have read of cases where bad alignment can cause poor MPGs.... Because the tires can act almost like a brake... But the tires would be wearing pretty fast in that case

Gjac

Milford, CT

Senior Member

Joined: 08/16/2006

View Profile



Good Sam RV Club Member

Offline
Posted: 11/18/19 08:55pm Link  |  Quote  |  Print  |  Notify Moderator

pianotuna wrote:

Hi Huntingdog,

It drives pretty much the same way. The front end has always been on the light side. Once, the folks who rotated the tires put 85 lbs in the fronts. That made it quite uncomfortable to drive--when I went back down to 65 it was back to normal.

I've toyed with the idea of lowering front wheel pressure, but I think that might increase the major cost of my RV which is fuel.

It is early days as I've only driving it about 200 miles.
I think your answer is the 200 miles driven. One tank is not enough to prove a mileage increase like you asked about. I track every tank of gas and tried a lot of different thing to improve MPG. Went from 8.5 to 12.5 mpg one time, after the next tank it went back to 8.7 MP.

pauldub

North of Seattle

Senior Member

Joined: 11/01/2005

View Profile


Offline
Posted: 11/19/19 09:08am Link  |  Quote  |  Print  |  Notify Moderator

One data point is not statistically significant, but we always want it to be when we like the data.

landyacht318

Near a large body of salty water

Senior Member

Joined: 07/11/2007

View Profile



Posted: 11/19/19 10:29am Link  |  Quote  |  Print  |  Notify Moderator

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.

pianotuna

Regina, SK, Canada

Senior Member

Joined: 12/18/2004

View Profile


Offline
Posted: 11/19/19 06:19pm Link  |  Quote  |  Print  |  Notify Moderator

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.

JaxDad

Greater Toronto Area

Senior Member

Joined: 08/02/2011

View Profile



Good Sam RV Club Member

Offline
Posted: 11/20/19 06:02am Link  |  Quote  |  Print  |  Notify Moderator

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.

Reply to Topic  |  Subscribe  |  Print Topic  |  Post New Topic  | 
Page of 4  
Prev  |  Next

Open Roads Forum  >  Tech Issues

 > first report new springs with a surprize result
Search:   Advanced Search

Search only in Tech Issues


New posts No new posts
Closed, new posts Closed, no new posts
Moved, new posts Moved, no new posts

Adjust text size:




© 2020 CWI, Inc. © 2020 Good Sam Enterprises, LLC. All Rights Reserved.