rolling resistance ?

Yes. That's why economy cars have the thinnest, highest profile tyres possible. In fact the increase in cornering grip from wide tyres is nothing like as much as the increase in drag and fuel consumption.

Dave Baker - Puma Race Engines

I'm not at all sure why women like men. We're argumentative, childish, unsociable and extremely unappealing naked. I'm quite grateful they do though.

| Yes. Disagree. In 12-93 my Accord came with 185/70/R14 Goodyear eagle ( had just 165mm width, I reported Goodyear M'sia to ministry of trade ) &

5" wide steel wheels. In 1-94 I fitted 195/70/R14 Dunlop JCinq on these 5" wheels, rolling resistance (rr) did not rise noticeably, same again in 4- 98 on 6" wide alloy wheels ( each with these JCinq weighs 16kg ). Now with 195 & 205/65/R15 Michelin mxv3a on 6½" wheels ( each with tyre weighs 18-19kg ), rr is significantly lower than from Goodyear / Dunlop, same result in 6-02 with a heavier Michelin model of 205/65/R 15 ( with wheel weighed 20kg ) Every tyre used had / has the same pressure ( 2.3 kg/cm² when cool ). This Accord has been parked on level ground under my porch, pushed to & fro to e.g. chk rr / brake bind or to get a rinse fr rain, daily since 1-94, no brake part changed. Tyre brand / model / pressure / toe-in makes a far bigger difference in rr, than width / weight can ( certainly cannot cut mpg by 12%, from just a change fr 185 to 205mm width / weight ).

| That's why economy cars have the thinnest, highest profile tyres i] thinnest tyres are the cheapest ii] cheap cars have narrow e.g. 4½" width wheels which cannot hold broad tyres well : tyres' side walls will not flex = hard ride, outer sides of thread will not touch tarmac =

No you don't.

So, they won't flex? I see.

That sounds like a lower rolling resistance to me. Where do you suppose the energy to flex the tire comes from?

New, larger wheels are probably heavier, too. From 14 to 16" represents roughly 15% increase in diameter, but roughly 30% increase in area. If the new wheels are wider, that adds more weight. Also, weight on the wheels further out from the center (larger diameter) requires more horsepower/ torque to accelerate.