Tweaking a Tahoe, the tow vehicle

[Hersbird]

That trailer is cool, how's the inside? I recently gave up a 2005 Duramax with a 12' Lance slide in camper and a 22' pontoon boat that just sat too much. Trying to keep it simple and have only 2 daily driven cars and a small camper and a single waverunner. We usually go to the mountains or Yellowstone to camp and the lake for just quickie day trips on a hot summer day.
When retire I will probably look for something like a sprinter class B to put more miles on.

[autoarcheologist]

Quick update on the trip home. From LA to Portland was just over 1000 miles. We averaged 53 MPH and averaged 11.9 MPG according to the trip computer.

This drive felt harder than the previous drive from Vegas, I swear I could feel the extra drag from the denser air at lower altitudes. We were in 3rd way more often, even on the flatish stretch from LA to Sacramento on I-5.

Once we get the trailer cleaned up and put away I hope to get a rolling baseline for the Tahoe, then try removing the crossbars and front bug deflector and see if that makes any difference.

Slowmover - I found a previous thread about travel trailers. One thing which struck me was the comment that anything above 48" gap between tow vehicle and trailer negates any benefit of the tow vehicle aerodynamics, you might as well be pulling the trailer next to you. If that's the case I'm not sure there is much I can reasonably do to close that gap or improve the combination, other than going with a smaller tow vehicle with a smaller frontal area, like a Roadmaster or Magnum wagon.

I'm still reading and having fun, man I love to do research.

[cRiPpLe_rOoStEr]

Have you never even lurked about a Diesel engine swap?

[slowmover]

Slowmover - I found a previous thread about travel trailers. One thing which struck me was the comment that anything above 48" gap between tow vehicle and trailer negates any benefit of the tow vehicle aerodynamics, you might as well be pulling the trailer next to you. If that's the case I'm not sure there is much I can reasonably do to close that gap or improve the combination, other than going with a smaller tow vehicle with a smaller frontal area, like a Roadmaster or Magnum wagon.

The gap problem is real. But it is back to records to put it all into perspective that matters. One is looking for changes to the average annual fuel consumption, and then as a percentage improvement. One does so by first trip-planning: 1] whether weekly errands combined into one trip and trip route optimized, then driving the remaining miles as best as possible; or, [2] with towing miles which is really control over stops once past travel speed decision as accel/decel events matter.

Towing miles are a subset of annual fuel consumption. Easy to break out. But no truck will provide good numbers, and, handicapped as it is for solo or towing stability, a loser to spend on in order to save be it fuel or extending TV component life. There will not be a silk purse from a sows ear. A 300 Hemi is a far better choice, but stick with HD suspension/touring options. A live axle Buick is not the right choice.

All of which is why I'd say to stick with optimizing the articulated rig n the meantime. Get those numbers ideal. Spring for the better hitch as the gap between a VPP hitch and any other is a difference so wide as to make all other types obsolete. Work the scale numbers. One wants the fewest steering corrections possible. The least amount of driver input to remain lane-centered and upright.

On the TV tires and brakes should last in excess of 70k. Verify alignment, zero steering slop and zero brake drag. Etc.

TT brakes and axle alignment matter. Bearing preload. New shocks and better load equalizers. Etc. Read John Barca threads in DIY on WOODALLS. Better, convert to torsion axles (read Fred Puhn on vehicle handling dynamics, and/or, all of Andy Thomson online). Steamline and Silver Streak did not upgrade suspensions during the 1960's as did both Airstream and Avion. Fully independent suspension is part of better FE . . most any change that increases "safety" increases FE potential.

Same for tire changes. Nearly none of us are willin to use ST tires any more. Means a conversion from 15" to 16". BFGoodrich Commercial T/A an easy choice. Others, too. See threads with contributions by CapriRacer here and on AIR (also, tire engineer Tireman9 on AIR). A tire wipeout is likely more than $6k in damage.

Get the tire load numbers before and after WD is applied. Set the hitch rigging. Know how your combination should feel with optimized numbers. Then TV tire pressure can be played with slightly. Ideal is NOT too high for the load.

Think of your rig as having a lot of loose nuts and bolts. Get the numbers squared away (plus a btter hitch) and then you'll have a tight rig where decisions behind the wheel don't cause the penalties they do now. "Tolerance stack" is not your friend, IOW.

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[slowmover]

Cummins White Paper (online; .pdf)

The power required to maintain a given road speed depends on the sum of the following forces:
 Aerodynamic Drag
 Grade Resistance
 Tire Rolling Resistance
 Engine Accessory/Drivetrain losses


To minimize drag resulting from crosswinds and turbulent air, tractor-trailer gaps should be minimized or aeroskirts should be used to smooth the airflow. Beyond approximately 30 inches, every 10-inch increase in tractor-trailer air gap increases aerodynamic drag by approximately 2%.


The effect of running all tires slightly underinflated (blue line on the chart) is significant. But all tires do not contribute equally. Notice that the trailer tires (green line on the chart) have a larger effect on fuel economy than either steer or drive tires.


tires that run hotter consume more fuel. A majority of this heat is generated by sidewall flex


 High average vehicle speeds with minimum time spent at maximum vehicle speed
 High percent trip distance in top gear (90+ % recommended)
 High percent distance in cruise control
 Minimum percent Idle/PTO operation
 Minimum service brake activity
 Number of Sudden Decelerations
 Service Brake Actuation's/1000 mi


Headwinds and crosswinds can significantly increase aerodynamic drag and reduce fuel efficiency. For every 10 mph of headwind or crosswind, mpg is reduced by nearly 13%. You cannot cheat increasing wind resistance

A TT is always trying to pass the TV. Nature of the beast, of this type of articulated rig. Things boil down to tires. If the load (pressure) is ideal, then much else is quite good, in short. But MUCH goes into ensuring maximum time at TT being aligned with TV. Not so easy (given resistance by RV'ers to sort and correct). Life is easiest on tires (for a given roadway) if mechanical and aero are best. And inputs by driver are short in time and distance to effect changes (and corrections are minimized to the point of nearly-not-existing by combined vehicle lash-up given best design/components). Make sense?

Trip sounds great, and FE looks good. That was an average speed given, correct? The number that matters is at trip end.

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[autoarcheologist]

Originally Posted by cRiPpLe_rOoStEr

Have you never even lurked about a Diesel engine swap?

I toyed with the idea, but we don't drive enough to pay off the cost, and I don't have time.

I would love to do a diesel conversion on a 5 series BMW wagon. I drove one in Germany and it was all the fun of a V8 with 4 cylinder F.E. Would make an awesome tow rig, and I know folks in the UK regularly get 25+ MPG towing with them. Again, no time.

[autoarcheologist]

Originally Posted by slowmover

A TT is always trying to pass the TV. Nature of the beast, of this type of articulated rig. Things boil down to tires. If the load (pressure) is ideal, then much else is quite good, in short. But MUCH goes into ensuring maximum time at TT being aligned with TV. Not so easy (given resistance by RV'ers to sort and correct). Life is easiest on tires (for a given roadway) if mechanical and aero are best. And inputs by driver are short in time and distance to effect changes (and corrections are minimized to the point of nearly-not-existing by combined vehicle lash-up given best design/components). Make sense?

Trip sounds great, and FE looks good. That was an average speed given, correct? The number that matters is at trip end.

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Yup, totally makes sense. I'm happy to chase small changes (brake drag etc) in the name of big changes. I love mucking in the details if it's measurable.

The trip was awesome, and all things considered overall F.E. wasn't bad.

I do remind myself that although % of time spent towing is high on the Tahoe, overall use is low. We drive it less than 10k miles per year, 3-4k per year the last two years have been towing. Since we got back it hasn't moved, I've driven the Alfa or Saab which both get 20+ MPG city.

So for me I think the better metric is not MPG on any vehicle, but overall # of gallons of gas we use per month/year. Throwing $2000 at a truck to save $100 a year just doesn't make sense. And I rarely keep anything longer than 3 years, especially now that we have a dealers license.

Back to details. Tires on the trailer are LT rated Hankooks (I think). I read so much about ST tire problems we went for LT. I keep them just under 50 PSI and haven't had so much as a slow leak yet. I check them before every long tow day and after a few hours. Tires on the truck are Michelin, P rated but extra load. Not sure what load rating that equates to...

The trailer is due for a bearing packing. I will have them check axle alignment as well at the time.

VPP hitch? Propride?

Thanks!
Ian

[Thenorm]

as far as aero drag, here are some areas to target. some aren't practical for a tow vehicle(ie. where thermal management of engine or brakes are concerned)

Major Aero Drag contributors, showing where we can make our improvments.
• 32% Wheels/wheelarches - can maybe do some thing here on truck and trailer
• 30% rear end / wake - included gap between TV and TT
• 12% underfloor
• 10% skin friction
• 7% front end
• 6% Enginebay / cooling
• 3% mirrors

[cRiPpLe_rOoStEr]

Originally Posted by autoarcheologist

I toyed with the idea, but we don't drive enough to pay off the cost, and I don't have time.

The cost rebate after an engine swap, which is a more work-intensive process and has some variable costs invoved, is kinda harder to calculate.

So, since it's the tow rig, have you never lurked about engine mods? A supercharger and a cam regrinding can do wonders in a Chevy V8, and in spite of forced induction being more promoted towards performance, in certain cases it actually also benefits the overall fuel-efficiency.

[slowmover]

The trailer is due for a bearing packing. I will have them check axle alignment as well at the time.

VPP hitch? Propride?

Thanks!
Ian

Money spent on TV not relevant so much as same and more spent on optimizing TT and lash-up details since TV can change.

VPP [virtual pivot point] hitch -- Pro Pride (preferred) or Hensley Arrow -- more or less "lock" the TT to the TV. Nothing happens until TV drive axle changes direction. Huge improvement over any other type. (Been doing this more than 40-years).

The suspension needs to be dis-assembled. Not just bearing re-pack. Big truck spring alignment shop is best, with near-ancient techs (experience matters). Leaf suspensions have many wear points. Think "tolerance stack", again. (Torsion flex replacements (DEXTER dealer) have next to no parts and make for a fully independent suspension system.) My much later Silver Streak has the following from the factory, look into these if not switching axle/suspension type. .

JohnBarca TT Mods

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