Unbelievable... my Yaris showed up!

[Goose]

Well, 2 1/2 weeks after I placed my order, the dealer called and said that my Blazing Blue liftback has arrived! Thank goodness. Hopefully I can pick it up tomorrow.

I'll be sure to post pictures, although it won't be anything exciting yet. Spec is (as far as I know) the Convenience Package with 15" steelies. I'm probably going to drive it for a while before I start to do some basic OEM-type mods, such as the TRD suspension. I might even get raped for the tasty 18" TRD wheels -- they do look nice.

Can't get ahead of myself, though. Anybody care to speculate on what kind of impact wheels/tires like 18's would have on mileage?

[stuffy]

congrats goose!

as far as the big wheels effect on fuel economy, would i be right in thinking that they would require more power to get going? if so, would it be a noticeable difference in fuel consumption (and acceleration time?)

[ricko]

Congrats. The 18's will improve gas mileage somewhat, but I think the real benefits lie elsewhere.

[stuffy]

improve? i would have thought they would have the opposite effect

[ricko]

The 18's will require LESS power to get going, due to less weight.

[ricko]

Remember 18'' alloy wheels have less rubber, and the wheels themselves are significantly lighter than the steelies.

[stuffy]

ahh, i see, i was thinking by just being bigger that they would require more energy to get going, which would probably be the case if the weight were the same

but i'm no physicist, so i could be wrong on that one

[Idjiit]

Originally Posted by ricko

The 18's will require LESS power to get going, due to less weight.

Ummm, no. The 18" rims will be significantly heavier than the stock rims. The difference in tire weight will not balance that out.

[Idjiit]

Originally Posted by stuffy

ahh, i see, i was thinking by just being bigger that they would require more energy to get going, which would probably be the case if the weight were the same

You are correct. Even if the wheels are the same weight, if the wheels is a larger diameter more weight is further away from the axel, which takes more energy for the car to move. Needless to say, the heavier the wheel, the bigger this problem becomes.

[Idjiit]

Here's some sample numbers -

Yaris 15" Steel Wheel/Tire Combo - 37lbs (17lb wheel, 20lb tire)
Toyo Proxes 4 Ultra-High Performance Tires with light Rota SubZero Wheels:
15x6.5 w/ 195/50R15 - 29lbs (12lb wheel, 17lb tire)
18x7.5 w/ 215/35R18 - 39lbs (19lb wheel, 20lb tire)

So, even with a lightweight 18" setup, you're both heavier than stock and a lot of that weight has been moved further away from the axel, so you'll definitely see a drop in performance.

[Ziv]

hum...... tell me if I am dumb. Is that mean bigger wheel is not as fuel consuming?

I know a few basic, the smaller the wheel obviously will have more power to go up the hill and stuff, the bigger the wheel will have better performance. Right?

I am getting confuse.

Oops, sorry where are my manners, Congrats, Goose!

[Idjiit]

Originally Posted by Ziv

hum...... tell me if I am dumb. Is that mean bigger wheel is not as fuel consuming?

Err... you mean, will you get worse mileage with a bigger wheel? You'll definitely get worse mileage with a larger wheel, all else being equal. The car has to work harder to turn the wheel, not sure why this is a difficult concept to grasp.

Originally Posted by Ziv

I know a few basic, the smaller the wheel obviously will have more power to go up the hill and stuff, the bigger the wheel will have better performance. Right?

It depends on what you're defining as "performance". The smaller wheel will have less rotantional mass, which will allow the car to move quicker (assuming the traction is there). But in terms of cornering, the small wheel with larger sidewalls may not have as much grip so having a larger wheel with shorter, stiffer sidewalls will be better.

The best option will be the wheel that gives the best balance between weight and cornering stability. That certainly isn't the 18" option - I would say if you're performance-minded a 16" wheel with a good performance tire would be the best compromise.

[ricko]

I had NO idea the 18's would be THAT heavy. I just know the 16" alloy on my Acura was significantly lighter than 15" winter wheel, and they were only Honda alloys. The extra weight must come from the added width of the tire???? In Canada the 15 inch wheels come with 185/60 tires. How does the rolling diameter compare to that of the 215/35/18's.

[Idjiit]

Winter tires are generally heavier than all-seasons, and depending on the design of the wheels the 15" could actually be heavier than your 16". That's why my comparison uses the same wheel design in different sizes and the same tire in different sizes.

[Goose]

Actually, my first reaction to larger wheels/tires was the effect of the larger contact patch on rolling resistance. Most high-mileage cars are concerned with low rolling resistance, and therefore use skinny, harder compound tires to maximize this benefit. By going to an 18" wheel (with probably at least a 7" width) and similar tires, there's a lot more rubber in touch with the road; contrast this with a 6" or 6.5" wide steel wheel and 185/60 tires, and I assume the performace combo isn't gonna want to roll as easily by comparison.

I assume there's a rolling resistance calculator floating around the 'net somewhere. Just gotta find it.

[Idjiit]

Yes, rolling resistance comes into play as well. Not really sure if there's an easy way to figure that out - it's related to weight of the vehicle and designed of the tread as well.

[Goose]

A quick search found this site:

http://www.geocities.com/CapeCanaver...79/evcalc.html

Obviously, there is no provision for determining the rolling resistance of the wheel/tire, but it's pretty cool anyway. I'm going to keep looking, as I'm sure there's got to be a calculator out there...

EDIT: Rather than start another thread, I'll just tack this on: My dealer screwed up and ordered an AUTOMATIC liftback. Time to reset the waiting clock. It's probably going to be another couple of weeks for me...

[Idjiit]

Oh man, that sucks. Sorry to hear it. :(