# Watt??



## spdas (Nov 28, 2009)

spdas said:


> With my Yaris (Calb 46x180, Zilla, Warp @2700# and mostly 55-65 mph), one surprising thing is the Rolling Resistance. I had WIDE 195-50-15's and got just under 195/watts per mile. I upgraded to 185-60-15 Bridgstone Potenza (my set that had 8000 miles on them and came with the car) and now am getting 230 Watts per mile. As soon as i find some on Craigs I am going to 215/45/17's to see what happens. And then coroplasting (sp) the underside later. I would like to see 175-200 w/mi. or under.
> 
> francis


OK, a contest...... I just installed 4 new Nexen 8000's 215/45/17. Purported to be ultra performance to the Audi/WRX crowd. Took it for a 10 mile run just now and the tires are a bit mushy, quieter on the freeway, smooth & quiet running over tar strips, and seem to roll much longer when you "let off the gas". Although mushy, the oversteer is much more manageable than with my set of 185/60/15 Bridgestone Potenza. Here is a photo of the "pimped ride" and a photo of the enormous open tread design..... 

So what do you guess? 

Will my watts per mile be down to around 200 or stay around 230 or get worse up to 250 watt/mile?
I will test on the exact route I go every week, tomorrow.

Francis


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## spdas (Nov 28, 2009)

gottdi said:


> Your pimped ride looks good. Excellent work. Hows the warp motor working out for you? Do you continue to lift those wheels off the ground for fun?
> 
> Pete
> 
> My guess if you pump them to the max pressure you should still get about 200. I'd like to see less.


 Yup, hoping to get back under 200, but will see. The warp works great, but I need to sort out the Zilla because at 2800 rpm the zilla seems to kick in with 25-50% more power. Can't lift the front wheels as it is FWD, but 40-60mph takes only a couple of seconds.

And I guess I am getting used to the power on takeoff because although it seems sluggish, when I look at the speedo, it is reading 55-60 mph and flips up to 85-90 easily. 

Francis


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## spdas (Nov 28, 2009)

spdas said:


> Yup, hoping to get back under 200, but will see. The warp works great, but I need to sort out the Zilla because at 2800 rpm the zilla seems to kick in with 25-50% more power. Can't lift the front wheels as it is FWD, but 40-60mph takes only a couple of seconds.
> 
> And I guess I am getting used to the power on takeoff because although it seems sluggish, when I look at the speedo, it is reading 55-60 mph and flips up to 85-90 easily.
> 
> Francis


Nope, no such luck. Ended up the journey at 252 watt/hr per mile. This is a measured journey, so I use a constant 69.3 miles for the distance regardless what actual size tire I have installed.
The tires are extremely quiet and very smooth over cats-eyes in the road. Now the loudest thing is the wind buffeting and the transmission has a slight whine.
I am at 42# pressure and i understand with tire aging, a person gets better mileage. I will pump up to 50# or the max and give it a go.
Then on to underskinning the car.

francis


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## spdas (Nov 28, 2009)

Aloha, here's what I get in w/mile for three different tire sizes:

a) 11 journeys average of 226.24 w/mile for the 195/50/15 old tires

b) 6 journeys average of 226.07 w/mile for the Potenza 185/60/15 80% new

c) 4 journeys average of 245.60 w/mile for the Nexan 215/45/17 New
@ 42psi nice smooth ride and 50psi much harsher ride and not much change in w/mile

francis


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## major (Apr 4, 2008)

spdas said:


> Aloha, here's what I get in w/mile for three different tire sizes:


And 



spdas said:


> Ended up the journey at 252 watt/hr per mile.


I know you mean well and thanks for sharing, but please use the correct units. I am sure this has been brought to your attention before. It is the energy consumption per unit distance and commonly given in "Watt hours per mile" or Wh/mi.

It is not Watts per mile or watt/hr per mile or w/mile.

A watt/mile is as meaningless as a horsepower/inch.

Please try to help us out on this forum and get the units correct. Please.

major


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## spdas (Nov 28, 2009)

major said:


> And
> 
> 
> 
> ...


Yeah I will try and get it straight. It confuses me every time! 
Francis


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## GizmoEV (Nov 28, 2009)

spdas said:


> Yeah I will try and get it straight. It confuses me every time!


Well, it doesn't help that many people, even ones who claim they know better, get sloppy with the units.

Part of the confusion could be because of units like miles/gallon or miles/hour and many people really don't understand them either. It might help to know that a Watt is actually a single word for Joules/second so when you use the term Watt it already has the /second part in it. Note that it is like miles/hour where there is a unit over time in it meaning it is a *rate* based on time. When you want to figure out how much energy is used or work is done to move your car a given distance (much like gallons/mile) the unit above the distance needs to be an energy or work unit. Since Watt = Joules/second is a rate and time is in the denominator of the fraction it must be multiplied by time to "cancel out" the time units. It turns out that it isn't convenient to use seconds for typical time measurements, after all, people aren't even overly concerned with individual minutes as evidenced when some one says it is quarter to 10 even if it isn't exactly 9:45. It is much easier to use hours, at least that is what most people are comfortable with since the numbers are smaller. So to "convert" the Watts back to an energy unit we merely multiply by the time in hours and hence we get the Watt hour or Wh. Once you have that you can then see how many are used in a mile and give you the Wh/mi unit.

Hope that wasn't too confusing. Maybe just make a list of units you use for different situations and refer to it when you need to be reminded what unit to use. I've had beginning Physics students do this until they got the hang of things.

BTW, you might want to go back through your posts and edit the units so that others who are trying to learn wont get thrown off my the incorrect units.


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