Apparent proof that tire weight affects Dynojet results
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Stellar HDF Member
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From: Lethbridge, Alberta Canada
The stock Dunlop tire has an actual diameter of 25.91 inches.
The Pirelli Diablo tire has an actual diameter of 25.75 inches.
The difference is tiny, being 0.16 Inch or just over half of a percent (0.6 of one percent).
Jim G
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From: Triune, TN
That is precisely the point. The engine is not producing more power than it was - no change in tune or anything else in the engine. Yet, the Dyno is REPORTING more power, due simply to the change in tire.
That's not old news. It's confirmation of a theory I have long held.
Jim G
That's not old news. It's confirmation of a theory I have long held.
Jim G
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From: North Texas
Yes, when choosing a new tire, I examined actual (not "nominal") diameters.
The stock Dunlop tire has an actual diameter of 25.91 inches.
The Pirelli Diablo tire has an actual diameter of 25.75 inches.
The difference is tiny, being 0.16 Inch or just over half of a percent (0.6 of one percent).
Jim G
The stock Dunlop tire has an actual diameter of 25.91 inches.
The Pirelli Diablo tire has an actual diameter of 25.75 inches.
The difference is tiny, being 0.16 Inch or just over half of a percent (0.6 of one percent).
Jim G
The cool dense air contributed more to true engine performance. The tire's weight and diameter stole less energy than the larger, heavier tire.
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From: Stuttgart, Germany
That is precisely the point. The engine is not producing more power than it was - no change in tune or anything else in the engine. Yet, the Dyno is REPORTING more power, due simply to the change in tire.
That's not old news. It's confirmation of a theory I have long held.
Jim G
That's not old news. It's confirmation of a theory I have long held.
Jim G
And sorry, but your little project has yet missed to provide sufficient 'proof' that the lighter tire is the cause of the marginal power gain...too many variables were disregarded, just my .02.
But nonetheless, if you feel happy with your experiment and the alleged proof for your theory, just don't worry about anybody telling otherwise.
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Stellar HDF Member
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From: Lethbridge, Alberta Canada
Not trying to be disrespectful Jim, but this is old news. It has been known for decades. Why do you think horsepower at the rear wheel is less than hp at the crank? Its beacause of the friction and weight of the drivetrain. ANY decrease in weight or friction will result in more power to the ground. The dyno is simply measuring the power you put to the ground.
Jim G
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Stellar HDF Member
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From: Lethbridge, Alberta Canada
Actually, that's a 1 percent different in diameter. It's also smaller, which gives less moment arm for the ground to act against the drive train.
The cool dense air contributed more to true engine performance. The tire's weight and diameter stole less energy than the larger, heavier tire.
The cool dense air contributed more to true engine performance. The tire's weight and diameter stole less energy than the larger, heavier tire.
One precent of 25.91 is 0.2591 inch. The difference between the Pirelli and the Dunlop is 0.16 inch - just over half of that one percent. Check your math.
The cooler denser air was supposedly allowed for by the correction factor. If you don't believe in the effectiveness of correction factors, then you don't believe in the value of comparing dyno reports, and therefore you don't believe in the value of DOING dyno tests in the first place, because not every day is a "standard" 77 degree SAE day.
Jim G
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Stellar HDF Member
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From: Lethbridge, Alberta Canada
Jim, that so-called theory of yours respectively your conclusion is old hat as FLS103 stated. That is the reason why e.g. -at least here in Germany- the power of a vehicle has always (for decades) been stated as crank hp and never as rwhp.
And sorry, but your little project has yet missed to provide sufficient 'proof' that the lighter tire is the cause of the marginal power gain...too many variables were disregarded, just my .02.
But nonetheless, if you feel happy with your experiment and the alleged proof for your theory, just don't worry about anybody telling otherwise.
And sorry, but your little project has yet missed to provide sufficient 'proof' that the lighter tire is the cause of the marginal power gain...too many variables were disregarded, just my .02.
But nonetheless, if you feel happy with your experiment and the alleged proof for your theory, just don't worry about anybody telling otherwise.
I never claimed total control of all variables. That is not within my practical capability. I do not own the dyno, note the facility, nor can I control the weather, nor can I think in advance to warn a certified experienced mechanic to not over oil the air filter. I do the best I can. I think the results are clear enough despite the limitations.
Jim G
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From: Triune, TN
Replace the belt drive with a chain drive and you will also realize a gain in RWHP with no gain in crank HP. Replace the belt drive with a shaft drive and you will lose RWHP...