Low rolling resistance tires (LRR), my experience

JC68vert300

JC68vert300

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Not about my C body. After having a great ownership experience with my 2012 Dodge Durango R/T, I purchased a new
2022 Jeep Grand Cherokee WK Limited, one less row of seats, but basically a similar vehicle. The Jeep is equipped with 20 x 8 inch wheels with Bridgestone Ecopia H/L 422-Plus LRR tires, size 265/50R20. Under normal conditions, the ride is fine. But coming up on 2 years with the vehicle I can say in wet, damp, or light snow conditions, there is definitely a loss of traction, for a total lack of confidence. Not great because I do a lot of highway driving between NJ and Cleveland and the weather can often be unpredictable. Not used for the daily grind, the Jeep has 18,000 miles on it, about 14 trips to Ohio. According to the manufacturer, the LRR tires should add a 1% increase in mpg, so at an average of 20mpg, that translates into 20.2 mpg, hardly worth it! They will not be replaced with another set of LRR tires. Just a heads up for those who have never heard of them, or have a tire shop try to sell them to you with higher mpg promises. Jim C
 
I call B.S. on this. I'll wager they rewrote tire specs somewhere and upped the normal recommended pressure thus lower rolling resistance. Now marketing kicks in and promotes this at a higher price all the while hiding the math that does not add up. This is new business practice 101. Can't really call them new and they improved like they do with other products. So "LRR" is even better.
Tires are at the best they will ever be when they are black and round, period.
 
Check the specs in TireRack and you'll most probably discover that ALL 18" and UP tires have a tread depth of 8/32" NEW, which will certainly impact wet and snow traction a bunch as the tires wear. Even Michelin Defenders are 10/32" tread depth on their 16" sizes.

THAT plus a slightly harder compound (to get the same wear numbers as normer-tread-depth tires did) is probably where the LRR comes from. Of course, it's an old autocross/road racing trick to use tires with a shallower tread depth for better handling precision as tires with more tread depth will deflect more in corners, which can also mean more power absorption as they roll down the road.

Tire makers (Goodyear that I know of) started to supply tires to the OEMs which took less power to roll down the road. OTHER than just the higher inflation pressure tires. This started in the middle 1990s for the OEM tires to Chrysler and GM. I'm not sure what basis the LRR standard uses for their base model year of comparison.

SO, head over to the TireRack specs for potential replacement tires to check the tread depth specs for tires you're looking at to replace what's on the vehicle now. I mention TireRack ONLY because it's an easy place to find these things, no more, no less.

CBODY67
 
I note that here in Ontario, where our major highways are being upgraded from asphalt to concrete, the concrete surface has been grooved and I consistently note a 1 mpg drop in my '04 300m (instantaneous MPG overhead console readout) when transitioning from one type to another. Road noise increases as well. They are increasing the road surface friction to give better winter traction while sacrificing rolling resistance (and MPG). This will affect all vehicles (ICE and EV's). EV's are heavier and presumably will take more of a hit from this. I have to believe that the relatively new focus on rolling resistance is coming from our forced EV adoption rather than any real need from ICE vehicles.

And as much as I hate gov't regulation, they really aught to put manditory tread-depth requirements on tires, if only from an eco-minded point of view. A very easy way for consumers to get an extra 10, 20% of life out of a tire and ease the disposal / recycling load. I've watched the specs as new tire tread depth has been declining over the past 10 years.
 
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I recently read an article about the low rolling resistance tires EVs are coming equipped with from the factory. I believe they used the hybrid or PHEV Camry and a regular ICE Camry as comparison. They swapped tires in between the two to do a fair comparison due to the extra weight of the EV. They found that there was a slight gain of MPGs on both cars. More noteworthy however was the fact that stopping distances increased on both cars by twelve feet from a 30 mph stop. That's potentially a life and death difference!
 
The very name, "Low Rolling Resistance" implies less traction.

I am assuming to achieve that, manufacturers use a harder rubber compound, stiffer sidewalls to minimize flex and a smaller contact footprint, and higher air pressures. I have my suspicions they are being used for EVs in an attempt to extend range between charges.

When I was growing up, being the typical hot rodder and having a heavy right foot, traction was important to me. Spinning ain't winning. Drag racers rode on treadless slicks, low tire pressures to maximize the tire contact to the road surface, the widest tire we could get away with, and the tires themselves had a much softer rubber compound than typical street tires. Just prior to a race, they would perform burnouts to heat the tires up to make them sticky, this improving launch traction. They aren't just showing off for the crowds, there's a very real reason they do this. Some of our cars didn't even have reverse and had to be pushed back to the starting line, and believe me, a hot sticky tire does indeed present considerable resistance to rolling.

If you compare the tires on a econo car that gets 40+ mpg vs say a Corvette, the specs are dramatically different. Skinny vs fat, tread depth, treadwear numbers, even the speed rating, all of these speak to how "sticky" a tire is with the road. Traction = friction, and thus rolling resistance. If the powers that be (legislatures, designers, engineers) were really serious, we would see tall, skinny tires again like Model As ran.

You want a car that gets 600 to 1000 miles between charges? That's doable, but you won't like it. 40 horsepower, top speed of 35 mph, super hard bicycle profile tires to minimize rolling and wind resistance, in a tight tandem 2 seater shaped like a torpedo to minimize wind resistance. That may very well be what personal transportation looks like in the next 100 years.
 
By observation, the rubber compounds available now, or even in the 1990s, are very use-specific. Just as there are different rubbers in a normal tire . . . the "tread upper" and "tread lower", for example. When the upper, main layer is gone, the rubber under it generally has less traction and wears quicker.

"Z"-rated rubber is different than "S"-rated rubber. In one of our drag racing (stock class) adventures, we found a Z-rated BFG radial that matched the D70-14 tire size, so a club member with a '70 Dart Swinger 340 got a set for his car. The car looked correct, but when he went to the track, the car hooked up quickly and "left". Many wondered what kind of "slicks" he had gotten, from the sound. Not slicks, just normal Z-rated rubber. More than just the inner construction changes with the higher speed ratings.

OEMs have been working on tires with less power absorption since the middle 1990s and the first Goodyear Invictas radials of that time. In many respects, those tires were "un-remarkable", even back then. A total package.

EV tires need to have lower rolling resistance plus a rubber that can live with the heavier weight of EVs. Remember, a harder rubber can effectively become softer when more weight is applied, so performance is still maintained. A harder rubber can have less traction, without the heavier weight, as some LRR tires now do.

Tread design is also a consideration. Solid, or mostly solid tread ribs deflect less in a straight line driving situation. Segmented/blocky tread designs, every tread block will deflect when it hits the road, absorbing power, even several mpg, just as a softer-compound rubber can. 2mpg might not seem like much, but such tires can also make the car seem less responsive off-idle and be harder to push on concrete.

Some thoughts, experiences, and observations,
CBODY67
 
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