There is a wide range of rolling resistance in tires - up to 60%. That means changing tires could have a large effect on MPG’s - especially when replacing the OE tires. OE tires are designed to the car manufacturer’s specs, not the tire manufacturer’s spec and they typically have low rolling resistance, and they get that by sacrificing treadwear and traction, especially wet traction.
That’s why OE tires are widely criticized for poor wear and low traction.
Further, worn tires have a lower RR than full tread (aka New) tires, even if the same exact tire is used.
So in the OP’s case, he probably took 2 hits in the MPG department - worn to new, and Low RR (OE) to good wear (High RR)
Early-era mountain bicyclists discovered they could go faster on bumpy trails if their bikes had shock absorbers rather than the stiff ride of a no-shocks bike . . Presumably this is the same reason., the higher tire inflation makes the suspension system stiffer and slows the car down.
Different situation: suspension on mountain bikes allows the tire to stay in contact with the trail, hard to get power to the ground when the tire’s in the air. For cars adding a few psi won’t make the tires hop in the air.
Here’s a discussion derived from a Prius forum, they seem to max mpgs at about 40 psi:
Or to retain control for that matter. Same issue, not in contact with the ground, you’ll lose control. Suspension keeps the wheels on the ground at higher speeds than one without it. There’s also the operator- at some point you can’t even hang on due to the shock loads being transmitted to you.
I did a project in the 90s to design front and rear suspensions on a Buick LeSabre to offset the hard ride from 50 psi tires.
The tire and the suspension work together to absorb bumps. High pressure tires act like a stiffer spring so we targeted reduced weight, and more compliance in the suspension to compensate. The rear was a multi link design with an aluminum knuckle, fiberglass and aluminum control arms. Special shock valving in a premuim monotube shock helped as well. Pretty effective.
The front, not so much. It was double A arm design using fiberglass eliptical springs as the control arms. It rode pretty poorly in contrast to the rear.
The tires felt much like run flats. Harsh and not compliant but they were designed to run that high pressure so the centers would not wear out. Overall interesting but the high pressure tires did not fly.
Speaking of the 90’s, anyone here remember the Goodyear Infintred from the 1990’s? It was advertised as the last tire you would need to buy for your car. It was offered with a 100,000 mile warranty, and back then few people kept the same car for over 100,000 miles.
It was the absolute worst riding, handling, and braking tire I have ever seen. Of course they would last 100,000 miles. They were so hard Fred Flintstone would have complained.
