towing mileage of trucks

rbcamping wrote:

laknox wrote:

Cummins12V98 wrote:
My 98 with 3rd gen take offs for tires I had to add 5% to my miles driven then divide by gallons to be ACCURATE.

Going from the OEM 245s to 265s on my truck puts me 4% =under= actual on the speedo/odo. I add 4 miles for every 100 when calc'ing mpg. It DO make a difference! For speed, I use my ScanGauge II, which is calibrated to read 4% over indicated and is within 0.5 mph of my GPS. OTOH, my '11 Sonata reads 4% HIGH, so I get even worse mileage than the liar, er, dash reports. Before I realized the odo error, I would get 1-1.5 mpg LESS than the dash reported, around town. On the highway, it's about 1.5-2.5 mpg difference. Add that 4% error on top, and I lose about 12 miles per highway tank, which boosts that difference to 2.5-3.5 mpg. Hyundai keeps telling me that I'm "within spec". Yeah, right... Oh, tires are OEM size.

Lyle

This is mostly true for gas, not diesel. diesel engines are true heat engines compared to gas engines, they only need an amount of fuel (energy, fuel) to move their parts. There are several things that affect fuel efficiency in a diesel engine which are friction, and power efficiency from fuel burn. EGRs affect efficiency, Injection events and timing affect efficiency, and heat loss affects efficiency

So if you have more injection events that happen after top dead center, you burn more fuel, if your egr is running, you burn more fuel because you lose power and must make it up by adding more fuel. Friction losses and engine design are pretty obvious

First off, what does this have to do with the fact that my tire size is different than the OEM, so throws everything off? Second, what does this have to do with the fact that my Sonata's speedo/odo is so far out of whack? :h

I've never been able to figure out why it's so hard for the mfrs not to use a "net fuel" type mileage readout. I mean, it's pretty easy to measure fluid flow in a pipe; you've got fuel going to the engine and excess fuel returning to the tank. Net the in and out fuel and divide by the distance. D@mn simple, if you ask me and, basically what you do with a hand-calc. Now, if your odo is off, you'll still get errors, so this is where GPS distance is useful.

Lyle