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Old 12-18-2008, 02:26 PM   #19
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What's up with all you Canucks?!? Do ya gotta argue about everything?!?

Just kidding, of course! For TLyttle, I do understand that a wider tire offers greater rolling resistance, therefore reduces fuel efficiency; but you neglect to mention that there are benefits over a wider tire such as cornering traction. By the way, you got it confused, the diameter of the tire is the distances encircling the tire, not the width. We are talking about taller tires on here, not wider ones; but the truth is that taller tires do require greater effort to get moving, hence the need to regear in Jeeps when adding much larger wheels.

For my buddy thebarber, the speedo and odometer being off by 7% is not a big deal. I can easily computer how fast I am going and I also have a GPS that gives me a more accurate reading than any speedometer would (I left the speedometer error discussion out of this as it applies pretty much equally to all cars). I work with a guy who has a stock Yaris with an AT, maybe one day I will challenge him to a drag race so we can see how much faster the smaller tires make it. I doubt it is much, and I would have him at some point as the taller tires will give my car a greater top speed. But all that is a moot discussion when talking about an economy car such as the Yaris. The larger wheels are more of a 'looks' thing than they are a 'performance' mod. And I am not one of those 'hypermilers' who play every trick in the book to squeeze an extra mile or two out of a gallon of gas. A gallon costs $1.45 here in Texas at the moment, and I would rather enjoy driving the car. I speed (80+ MPH), I take off from stops faster than a snail and I don't shut down at stop lights or drag off the back of large trucks.

I bought my Yaris because it is a fun little car to drive, and I put the bigger wheels and tinted windows on it to make it unique. I parked next to a stock Yaris the other day and there is a distinctive difference between it and mine.

And most of all, I am happy with it. That's all that matters. Oh, and if I want performance, I jump on my 150 HP litre-class sportbike. After riding that, nothing else feels fast...
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Old 12-18-2008, 02:50 PM   #20
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MadMax,

Please remember that this is the Fuel Economy forum. The Cosmetic Modifications forum can be found from the main page.
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Old 12-18-2008, 04:34 PM   #21
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BailOut

I didn't drive this discussion, I originally just added the fact that 17" wheels are larger than stock; so if anyone was comparing the two then they need to factor in the 7% increase in diameter....

But you are right, this isn't my area of interest and I wandered in here by mistake...so adios, amigos!
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Old 12-19-2008, 09:40 PM   #22
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Yup, we don't have much else to do up here in the winter..;-)

I have never been a fan of wide tires on small, low-powered vehicles; I am very aware of the cornering benefits of wide tires, and it would suit me if the only thing we required of our cars was cornering power. However, we need tire stability in the wet (hydroplaning is truly exciting alright, but not always desirable), and traction in the snow where wide tires are a disadvantage (hence my Model T analogy). We also fight for FE, and wide tires are again a disadvantage. The tire companies fight with these opposites every day, looking for the perfect combination of FE, traction, and long wear, under ALL weather conditions. Now there's a challenge...

I spent some time calibrating speedometers for a living, and I have intimate knowledge of how much difference an inch of diameter can make!
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Old 12-19-2008, 10:32 PM   #23
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I'm running 205x40x17's so my speedo reading should be pretty close to stock. I have a GPS hockey puck antenna that I can hook up to my laptop and see how they compare. Maybe I can do that this weekend. Anyway, calculating my mpg using the trip meter of the car divided by the total gallons used for a fill up has ranged from a low of 29.7 (I had FUN with that tank! ) to 35.2 at the high end. Usually I see an average of 32 mpg. I totally enjoy driving this car with the mods I've made. I'm really not concerned with my mpg as it is so much better than my 2001 Tundra 4x4 that gets about 14 mpg.

The Yaris is my daily driver (since June of this year) and the Tundra has gone into semi-retirement. So I'm ecstatic to get anything over 30 mpg. By the way, the mpg did drop when switching to the 17's and a wider tire. If I recall correctly, the 17's with the tire mounted weighed about 6 lbs more per tire than the stock 15's that came with the 'S' version of the sedan.

As a side note, I'm running 35's on the Tundra. I regeared to 4.88's and I'm using a Superlift Tru-speed speedometer recalibrator. It is infinitely adjustable and I was able to set it using the GPS/laptop combo, so the speedo is spot on. I have not looked to see if there is a similar product available for the Yaris.
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Old 12-20-2008, 05:22 PM   #24
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Today was a perfect day to transfer the GPS hockey puck out of the Tundra and over to the Yaris. Booted up the laptop, connected the GPS to the laptop via the USB port, launched DeLorme Street Maps 2008, acquired a signal and took off for a nearby highway.

The highway is nice and straight for about 6 miles. I tried different speeds and held that speed long enough to get a good reading from the laptop. Here's the results with my size tires (205x40x17):

Yaris speedo__________GPS
50 mph................................49 mph
55 mph................................53 mph
60 mph................................58 mph
65 mph................................63 mph
70 mph................................68 mph

So at highway speeds it was pretty much a 2 mph difference. At lower speeds the difference was more like 1 mph. Take the above info for what it's worth.
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Old 12-20-2008, 07:17 PM   #25
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I have 18" and I'am getting 30mpg on city. On the speedometer... I have no idea if its off but I have pass by cops at the speed limit according to my speedometer and no problem yet so I shouldn't that off.
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Old 12-20-2008, 08:54 PM   #26
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(Yeah, I know I said I was bowing out of this thread; but I will keep this fuel efficiency related...)

Herbicidal

I did the same thing, I pulled the Nuvi 350 out of the Jeep and found that the speedo is alot closer than I thought. But that begs the question, how off is it with the stock sized tires?

For example, as with 17" tires we both have found that the speedo is actually near accurate; wouldn't that mean with smaller tires it would be more optimistic? For example, it would read 60 mph when possibly traveling at only 55 mph. As such, instead of traveling 60 miles in an hour, a person was traveling 55 miles, so their odomoter reading would be five miles higher than it should. For a tank of gas, that would equate to 30 miles that should be reduced if one is only using the odometer to compute their gas mileage!

I am going to have to go back and re-adjust my figures, it sucks that my Yaris isn't getting as good gas mileage as I thought (34-35 mpg); but with the wider tires and my driving habits, I am still doing alright. But the folks that are only using their odometers might find they aren't getting as good of gas mileage as they thought either!

And don't ScanGauge readers pull data from the same source as the instrument cluster (since the car is all electronic)? If so, those figures may be off as well.

Thoughts?

Oh, and the funny thing is that when I went with bigger tires on my Jeep; my speedo became more accurate as well!

Cheers! M2
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Old 12-20-2008, 09:48 PM   #27
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MadMax, perhaps we need someone with stock wheels and a GPS to post some numbers and see what we get. Anyone?

YarisPR - you have 18's, but what is the tire size? If they are lower profile than a 40 series, then your speedo may not be that far off.
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Old 12-20-2008, 11:44 PM   #28
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Being the same weight, if not lighter, than the OEM steelies, I actually saw a small increase in FE.
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