It'll definitely have a significant impact. Those Pep Boys tires might not be as bad as some but they're not LRR and certainly not as good as the stockers. You won't be able to use the assist as effectively, it'll take more gas/throttle to maintain highway speeds, and all of this will hurt the gas mileage.
I know from experience.
My Insight has Dunlop Sport 5000 tires (I think it was 5000) that were installed by the previous owner. My friend's 2000 has the stock tires. There are no other differences between our cars other than the color and tires, and his is much easier to "hold" 60-65 MPH without giving it a lot of gas. It also feels zippier because the bigger/stickier tires on mine drag the car down. My car drains the IMA battery quicker, and gets about 5-10+ MPG worse than his car (the difference is more noticeable as I go faster) because it simply takes more gas to keep the car moving.
Granted, these are Dunlop Sports vs. the RE92s and not Pep Boys... but the one clear advantage my car has over his is that it has greatly improved handling. I can confidently drive my Insight so fast through tight corners and twisty roads where his would slide off the cliff if he was even close to my speed. You can also push the brakes a lot harder with better tires before you reach the friction limits of the rubber.
Being a car-nut I weighed the bad vs. good, and settled for 5-10 MPG less in favor of the considerably improved handling... that and I don't want to spend the $300+ on brand new Bridgestones just to throw out perfectly good sport tires.
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2001 5-speed Insight in Silver
S2000 seats, S2000 steering wheel,
Dunlop Sport 5000 (195/65) tires, Porsche 997 Turbo pedals, HID headlights, BetterBattery
Cheap-o non-OEM tires... MPG impact?
These tires barely have 8000 miles on them so I think I'll deal with the mileage hit instead of paying $400 to go back to the stock ones. I'll just replace them with the OEM tires (if they are still around) when I need to.
