Cummins Publication on Tires & FE

[Diesel_Dave]

Thought some of the Cummins drivers might find this interesting:

Tires and Fuel Economy - Turbo Diesel News -

[gone-ot]

FWIW, I agree 100% with their comments about "tread depth" affecting FE, because (and many people still don't realize this) old, bald tires have lower rolling resistance (Crr) than brand new tires do, and it's predominately due the difference in tread depth--the more rubber there is to flex, the more energy it consumes in flexing it.

[Diesel_Dave]

Yes, as with most things tire-related, there's a trade-off between traction and rolling resistance. For example, bald, over-inflated tires have great rolling resistance, but poor traction, whereas big, nobby mud tires get great traction and have poor rolling resistance.

That being said, I think the trade-off can be affected somewhat by tire compounds and tread designs.

[shovel]

I wonder if there's a rolling resistance difference between a tire that has its continuous ribs under the sidewalls like vs. one that centers a continuous rib & has blocks under the sidewall..

Clearly every pattern is different, and every compound, and even the relationships between the compound and the pattern at a given inflation amount... etc.. so everything we talk about is going to be a generalization.

[oil pan 4]

I wish they went more indepth.
Some lab tested tread pattern info would have been nice.

[trooper Tdiesel]

yea my sidekick got about 27-28 when its tires where new it had just over a 1/2" of tread and there LT rated tires.

now there getting rather bald and im pushing 30+ mpg when its 60F+ out that is. at freezing its still 27 or so.

[redpoint5]

Originally Posted by Old Tele man

FWIW, I agree 100% with their comments about "tread depth" affecting FE, because (and many people still don't realize this) old, bald tires have lower rolling resistance (Crr) than brand new tires do, and it's predominately due the difference in tread depth--the more rubber there is to flex, the more energy it consumes in flexing it.

How much do you think tread pattern contributes to efficiency? If I had thick rubber, but they were slicks instead of having a tread pattern, would they get better or worse economy compared to the same compound tire with a tread pattern?

[Tesla]

Don't think it's all that simple.
I have run BFG all terrains, last two sets, like the first tyre in second post, before that I had the Highway pattern which is less agressive, over the entire period my fuel economy has remained relatively constant, there have been some periodic high's and lows, but it did not correspond to season or tyre changes, probably more driving behaviour & conditions. I think diesels are less sensitive than petrols to extraneous factors like weight, true it is important, but I gutted the 2nd & 3rd row seats a while back, the rear lifted at least 1", but fuel economy remained the same and did a big move a while back travelled over 1,000km loaded to the roof, not far off bump stops, only cabin room for driver, with trailer as well, loaded high, felt the aero braking down hills with the trailer drag, 3 feet above vehicle roof, but economy only went down to 14l/100km vs long term average of about 11.85l/100km. I still maintained normal Hwy speeds, just acceleration to that speed took a lot longer.
I always keep pressures at the higher end, about 45psi, and older tyres do go harder over time, so less rolling resistance, I do have 2 tyres which have been almost impossible to wear out, finally due for replacement, but the only significant changes in fuel economy I have had was a larger intercooler last Nov, dropped numbers by 0.4l/100km and am looking forward to an improvement with recent changes such as grille block, air dam, part underbody cover and cold air intake, vehicle just seems to need less throttle, have good trip coming up so will get some numbers there.
I think as said above harder tyres give better economy, but worse handling vs softer tyres which give the reverse. Hard to do a lot of testing, mine usually go for about 75,000km so it's about a three year commitment, not like mocking up a different airdam every week.

[Diesel_Dave]

Originally Posted by Tesla

I think diesels are less sensitive than petrols to extraneous factors like weight, true it is important, but ....

I have to disagree with you there, diesel vs. gasoline will affect the efficiency of the engine, but factors like weight and rolling resistance determine how much power is required from the engine. The engine determines how efficiently the power is produced, but if you reduce the the power required, it's going to help just as much percentage-wise either way.

[Tesla]

Originally Posted by Diesel_Dave

I have to disagree with you there, diesel vs. gasoline will affect the efficiency of the engine, but factors like weight and rolling resistance determine how much power is required from the engine. The engine determines how efficiently the power is produced, but if you reduce the the power required, it's going to help just as much percentage-wise either way.

I know the science, and don't disagree at all with it.
Just from mine & others experience, diesel vehicles seem to be able to take weight changes with less impact on fuel economy than petrol vehicles.
Science may well explain this in the torque charachteristics of each engine type and the way gearboxes are mated to the engines. I haven't got any proof or done any particular studies on this, it is just personal experiences.
Having said that, I do keep my vehicle light with regular cleanouts, tyres pumped up, no roof racks etc.