Quote:
Originally Posted by nikitopo
The length of the "lever" is almost the same (rim+tire). The distribution of the weight is changing mainly. I am just trying to show you that in reality (not in a lab or by using a thought experiment) different unexpected results are happening.
Racecomp Engineering gave you another example on the same dyno. Not different dynos with different calibrations and let's not start the silly discussion about noise. A good dyno on a 200hp car can be reliable up to 1/2 hp.
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The difference in gearing is more significant than the difference in weight. When the crank puts out effort to turn the wheel the 2700lb car is where the VAST MAJORITY of the work is coming from.
There are other factors at play too. The fact that the car gets identical 0-60 times is telling too. If I were to ignore the gearing and friction difference between the two tire sizes and compounds, I could point to the time as proof that there is no difference between the two, but there are differences. One has a gearing advantage and the other has a friction advantage.
As for dyno accuracy, my 350Z was on 4 different dynos and no two runs (not even back-to-back runs on the same dynos) were ever within 1/2hp of each other.
If I were to put your car on jack stands, blindfold you and ask you to turn two different weight wheels by hand, you might be able to tell me if one wheel weighed 5lbs more than the other. This is the simplified way most people visualize this question, and it holds true.
However if I do the same thing but put the car on the ground, you would have no idea if one wheel was heavier than the other. The effort required to move the
freaking 2700lb car now dwarfs the effort required to move the wheel itself.
A lighter lever is better, yes. And where the weight is located on the lever also matters too, but when the lever is just 0.01% of the weight you are moving, making the lever 0.014% is not that big of a change in the work load.
I think the gyro effect of a spinning wheel and it's resistance to lateral changes (like when you turn the car) are far more noticeable from behind the wheel.
*edit* just checked the article for the track test and they cover the gearing issue vs top speed as well.