Why does running one size bigger tires increase fuel economy?

[SVOboy]

I don't understand the issue with rotational mass and FE. Sure, you invest more energy to accelerate, but you get it back while coasting.

When I studied physics last year and we were doing intertia one of the first things was about a car that had a 2000 pound mass and 1000 pound flywheel. If you invested in getting it up to speed it would take four km to wind down or something. However, you gotta know that eventually you will lose that energy to braking, much like having a heavier car. If you invest in moving 300 extra pounds you gotta stop it sometime and that investment will be wasted.

If I hung 10 pounds on my rims and it didn't affect drag the coasting would probably last longer, but seeing as how energy is not converted perfectly to get the wheels moving the savings wouldn't be there in my mind.

[krousdb]

Originally Posted by SVOboy

However, you gotta know that eventually you will lose that energy to braking, much like having a heavier car.

Brakes? You use brakes?

I agree that if you use your brakes a lot, lighter wheels would make a difference. But I use my brakes so little that I doubt the difference for me would be measureable.

It's too bad Matt didnt hove those HX wheels on ebay about a month ago. I would have had those light weight wheels and lighter weight 14" tires. Oh well. I can't complain with what I have.

[SVOboy]

Get some damn vx rims, mine will be delivered tomorrow.

[krousdb]

Originally Posted by SVOboy

Get some damn vx rims, mine will be delivered tomorrow.

If I decide to go all out then maybe VX rims. But that also means stripping the interior, filling the tires with helium and switching to aluminum wheel weights. ;-)

By the way, did you finish the rear springs? Post some pics.

[SVOboy]

I would not call 100 for sexy *** rims all out and helium is just being lazy about checking/filling.

I finished the ****, had to jack the car back up a bit. Will post some pictures tonight and write the DIY tomorrow night for lack of time tonight.

Need to align it myself, which should be fun! DIY on that too.

Also, I found some coilovers for you if you want them.

[krousdb]

Originally Posted by SVOboy

I finished the ****, had to jack the car back up a bit. Will post some pictures tonight and write the DIY tomorrow night for lack of time tonight.

Need to align it myself, which should be fun! DIY on that too.

Also, I found some coilovers for you if you want them.

Look forward to the DIY's. Thanks for offering the coilovers, but I won a set on ebay and they will be here on Wednesday.

[SVOboy]

Haha, damn, was gonna get this set for 20 and they sell for 150 shipped on ebay,

[Compaq888]

LOL you get everything for low price. Too bad you can't get altima parts that cheap. I've been looking for G20 rims that weigh 13lb stock for a while now.

[MetroMPG]

note, see new related "experiment" thread:

rpm/gear choice VS MPG at constant speed

[philmcneal]

damn all this tire talk, all i know what to do is pump them near the 50 PSI limit. By the way do alloy wheels cost more to replace than standard steel wheels?