|
Thank for the thoughts so far.
Yes, the Grand Cherokee SRT shares the platform architecture with the Mercedes equivalent.
And yes, I’m quite pleased with it. It is on the indulgent end of things for me, as I’ve grown used to older and more modest vehicles.
I took my 12.5hr trip from the NJ coast to South Haven Michigan yesterday. I was able to manage 21.8 mpg average on the first 482 mile leg heading out running from 65-78 mph depending on speed limits. There were not many truly flat sections, mostly slowly rolling up and downs. I spent the bulk of the time in the 78mph setting under a 70mpg speed limit. It matched the measured mileage/fuel used mpg I calculated by hand compare to the dash data display when I fueled up within a very small margin. That is encouraging.
While running the flat sections at 78mph, 24mpg was about the average. The rest was a bit over 21mpg.
I did find that most of the semi trucks were sticking with 65mph or so, not helpful for me to draft behind. I had better luck with the occasional lead foot 5th wheel RVs, Big motor home RVs, and trucks pulling big cargo trailers running 70-75mph. I was able to set the ACC (adaptive cruise control) and shadow behind them for a stretch at about 75ft behind. The ACC did a great job keeping a constant matching distance behind. The mpg numbers jump 3-4 mpg consistently for the rare times I was able to locate one going fast enough to draft behind for a bit.
I put what info I knew into the Aerodynamic and rolling resistance calculator, adjusted to get for 24mpg at 5200lbs (bare SRT, flat road, 75mph) and added the 2700 all up trailer weight only and and up with 21.2 mpg.
21.5mpg at 5200lbs (bare SRT, rolling elevation roads, 75mph) when adding 2700 lbs came to 19.1 mpg.
So assuming the aero of the SRT/trailer combo is equivalent to the bare SRT(big if), real world roads would bring me from about 21.5mpg down to about 19mpg(probably a little less when accounting for the minor extra rolling resistance of the two trailer tires. That would represent about a 12% drop in overall fuel efficiency.
That would be great if true.
There is certainly greater aero potential than what I specced out for the trailer. The design was the result of my needs logistically(two race bikes loaded from the rear, equipment, tools, spare race engine, small generator, spare race wheels/tires, small air compressor, 10x10 EZ UP tent, camping gear, race fuel, etc.
Still, I think it may be possible to satisfy my logistical needs and create an SUV/trailer package capable of hitting my goal of 20-22 mpg on flat roads at 75mph, and giving me 18-20mpg on more typical roads(modest rolling elevation changes).
That’s really encouraging.
My friend has a new setup this year with a Ford F-150 super crew with the 3.5 Ecotec engine, pulling a standing headroom 7x16 v nosed dual axle cargo trailer(sharp edges all around) with about the same cargo inside (two race bikes and gear) as me with a 3600lb all up weight (his trailer is much heavier, plus two axles) and he also favors 75-78 mph on his trips. He reports roughly 21mpg truck only at that speed but a rather shocking 7.5mpg with the loaded trailer. He runs a tonneau cover, so the bulk of that frontal area of the trailer is fully exposed and draggy.
That’s a horrendous drop in FE and what inspired this whole thing. His first three trips came up with nearly identical numbers each, both from the dash instruments and the hand calcs.😳
9000 miles at 7.5 mpg at $3 gallon fuel is $3600 per year going to and from the races.
9000 miles at 20 mpg at $3 gallon fuel is $1350 per year. That $2,250 savings potential isn’t my the driving force behind my interest, but rather the challenge it represents and the potential uniqueness of the end result.
Anyway, I look forward to exploring this further.
George
|