Hey for the Virtual Dyno settings on evoscan... is the tire diameter referring to the actual diameter of the wheel (25.7" or so) or is it looking for the distance from the center of wheel to the ground multiplied by 2 ?

 

Geez 40+ views and no answer?!?

My thought is that the power that is being calculated is the power being applied to the road... SO the question is does this calculation assume that there is a vector going tangent to the tire where it meets the road. And that the vector is 1/2 diameter away from the axel's center?

Or has the fact that the tire isn't perfectly round when the car is sitting on the ground been included?

 

Just input tire size.. let it calculate the decimal

 

While I agree that splitting hairs isn't going to gain you much in a virtual dyno I'd say use your best scientific guess. If you feel the tire "grows" at speed and provides less contact patch then use center to tire height (top). If you think it doesn't then use center to bottom. If you want to be a normal person just measure the tire.... your eye isn't going to be too terribly accurate about the difference anyway unless you are using a caliper.

It is true that the size on the tire wall doesn't always translate to an accurate height.

 

Weight of the car squishes the tires down. Most tires that people would run on the Evo have very stiff side walls. These tires are not the squishy wrinkle wall tires that drag cars use. Nor are we spinning them up to 300 mph.

There are other ways to make VD read higher. But you can make the tire bigger if it inflates your ego.

 

I'm just trying to figure out whats right. It is a decent difference the distance with the weight of the car versus the distance without... So i was hoping whoever setup these formulas would chime in what would be most accurate.

 

VD should be used less as a measure of actual power and more as a measure of comparison between 2 runs with as many of the same variables as possible. To know what the output should *really* be you would have to do a run on a real dyno (which is also just a tool) and measure against it, but remember that any real dyno will also read higher or lower than the same make/model somewhere else.

 

VD has been proven to be nearly identical to DynoJet numbers on many occasions.

We've put a car on the dyno, did 3 pulls and then took it out on the road to do some logged pulls. VD results were nearly identical to the DJ results. Evo 8, 9, and 10's have proven this.

So... The tire diameters that come with the app must be pretty damn close.

 

Exactly my point?

No dyno is the same, and VDR is not a dyno... its a virtual dyno. A well tuned one in our case, but to know if your tire measurement was "correct" (assuming all other variables were correct) you would have to compare to a real dyno (and your results would still be virtual and no more than a damn good estimate).