Regarding wheels...
 

You may have talked about this before, but since I'm new, I need some clarification. I bought a Toyota Yaris Liftback automatic in January. It's now got 1024 miles on it. On one of the upgrade packages, (Convenience Package), I got 15" wheels instead of keeping the stock 14" wheels. Was this a mistake for getting better gas mileage? I'm already experimenting with coasting since the shift knob is so easy to use. I've begun shutting off the engine at lights. But I've still a concern about whether the larger wheel is better or worse - not that I can do anything about it right now anyhow. Any suggestions, comments, hints, etc.?

there are two really easy to get numbers that are going to give you an idea, first number is how wide the tires are, to find this out you look at your tire size it will be something like 205/65 R15 that first number is width, 2nd number is aspect ratio (hight in precentage of width), normally when you make something narrower it also gets lighter, fiddle around on some of the tire sites like tirerack.com and check out the specs of the tires, they normaly give the weight.
larger rims are heavier then smaller rims, and the extra rubber twards the center of the tire doesn't normaly make up the extra weight of the metal in the rim, so if you own any sort of scale that goes over 40lbs (bathroom scales work) you can pull a wheel off and weigh it, my civic vx has wheel/tire combo that weigh around 23lb's each, 9 pound rim, 14 pound tire.

If the 15's are taller overall than the 14's this will effectively increase (decrease, numerically) your overall gearing slighty: Good

Unfortunately they're probably a size or two WIDER than the 14's which increases rolling resistence: Bad

The good news is that depending on your rim width you can buy some narrower 15's when replacement time rolls around.

Yaris1 -

I just went here :

https://www.toyota.com/yaris/specs.html

And saw these numbers :

P175/65R14
P185/60R15

I plugged them into this tire calculator that *assumes* you are switching tires, so ignore the speedometer comments :

https://www.carbibles.com/tyre_bible_pg2.html
Attachment 1189

Now, from what I can see, your tire upgrade means your 15" tires are bigger. Sooooo, you should be getting better MPG. One thing I don't know is the weight of the rims. I think the 15" alloys would be lighter as a rule. From what I can tell, you have steel rims :

The 15" steel wheels should be heavier than the 14" steel wheels. The heavier wheel may negate the bigger tire size. If you had the 15" alloys, they might have been lighter.

CarloSW2

stock 14" wheels without tires are 6.4kg or 14 pounds, I couldn't find 15" wheel weight, altho tirerack.com wheel weight seemed to jump by almost 3 pounds when you change from 14" to 15" so I checked the weight of the alloy wheels on tire rack they ranged from 10.2lb ($350 each!) and go up to over 19 pounds each for 15" alloy!
of course they use the same 4-100 bolt pattern that pre 2005 hondas use, so getting some insight, civic hx, or early miata wheels would all fit and alow you to use narrow LRR tires.
tires also jump from 15lb for 14" and 18lb for 15" for OEM tires, so you gained around 24 pounds with the larger rims and wider tires, and the rule I know for rotating weight is that a pound of rotating weight is like 3 pounds of weight on the car as far as acceleration goes.

I used the calculator mentioned above and the 205/60/16 tires I'm looking at are .72% larger than the 215/55/16 I currently have.... Very interesting.

On a side note LRR tires in 16 inch are non-existent. Is the treadwear rating in any way related to RR if so I'll go for some 600+ treadwear tires and be done with it.

Unfortunately although there may be some correlation between treadwear and rolling resistance, neither is an indicator of the other. When I was shopping for tires for my Escort, I found some with higher treadwear ratings but higher rolling resistance than the HTR T4s I ultimately chose.

I think that as a general rule, lower profile will reduce rolling resistance in the same treadwidth, but that doesn't mean a manufacturer will not compromise on sidewall stiffness to make the lower profile tire a 'more comfortable ride'.

Unfortunately I've found that true of most of the 16 inch tires. If I can find some 15 inch steel wheels for this car I can get some real LRR tires. So far that search has been fruitless.

I was shopping for tires last fall and also found little info on the rolling resistance of 16" tires. So I tried to feel the difference in sidewall stiffness of a few different unmounted tires while shopping in the tire store. I know this isn't scientific, but generally I found that tires with high speed ratings (Z, W, Y) have stiffer sidewalls, and tires rated for lower speeds generally have softer sidewalls, which would reduce RR because there's less rubber flexing in the sidewall.

I replaced my old Z rated tires with a set of H rated tires. They have an added benefit- they're slightly more comfortable, so I raised the pressure a little more. :)

Thanks!
 

You all have given me a lot of info. But primarily what I got out of what you'd said is that the bigger/thinner the tire is the better the FE. The smaller/wider the tire is the lower the FE. That's great for straight aways, but what about handling going around those curves? Granted, when others are behind me wanting to increase speed, doesn't make for good road handling. I've already forgotten the intimidation factor, I just simply slow down. I eventually, probably will stiffen the shocks for handling sake anyway. But do I understand all of you correctly?

Regards.