tire aero vs rolling resistance

[moonmonkey]

my question is two parts: if i pay the extra $180.00 , for the bridgestone B381'S will they pay me back in savings from their lrr,as compared to the Sumitomo htr200 also a lrr tire just not as highly rated?, here comes the aero part: my echo runs between 2300-2800 rpm's for alot of my commuteing, if i go 2" taller and 1/2 inch wider will the extra height of the car and weight of the tire cancel out the lowered rpm benifit, my car has front and rear bellypans and while i do some stop and go "not much though" so the moments/reduced leverage/getting the bigger tires up to speed should not hurt me that much,i think. i want to get this right because whatever tires i buy will be on my car until they are showing tread.or resemble onions.

[tasdrouille]

It depends how long they last, but if the RR difference between the two is within 10-15%, it propably does not make financial sense.

What % difference in gearing would that make? You will incurr a small drag penality, but since you already have a belly pan I'd say the longer legs would be worth it.

[Bicycle Bob]

I'll do the calculations if you dig up all the data. We'll need a BSFC on the engine, some wind tunnel tests on the car mods, and all the tire numbers.

[moonmonkey]

cant afford any more wind tunnel rental time ,,,you never know if someone out there has experinced the exact or similar tire swap and know the results just tring to learn bob,