No. In fact, in the other Dyno thread you'll see that David Weaver states to increase pressure to 35 lbs to get rid of any sidewall flex. Flexing that sidewall is sacrificing power to increase traction and reduce the moment arm of the axle around the tire. As the tire's RPM increases, the moment arm can increase.Torquemonster said:Fair enough Mark - but by your figures - how many hp would it take to shoot a 2200lb dragster 6" from a stop in 0.5 seconds running the gearing they run?
I submit it is measureable - and that maintaining that deflection on the tire on a rolling dyno will pick it up...
Wouldn't prima face' evidence be that others have done just that?
Seeing how they 60 foot in under a second and reach over 100MPH before that mark it is one hell of a lot of power. :nod:Torquemonster said:Fair enough Mark - but by your figures - how many hp would it take to shoot a 2200lb dragster 6" from a stop in 0.5 seconds running the gearing they run?
I submit it is measureable - and that maintaining that deflection on the tire on a rolling dyno will pick it up...
Wouldn't prima face' evidence be that others have done just that?
OK, this is true. I was saying that about stored energy before.GTS Dean said:If there wasn't a lot of useful energy stored in the tire sidewall, they wouldn't need beadlock screws to keep them from slipping on the rim. You can either do it with screws, or internal pressure. The correct engineering term for this phenomenon is "rimpull."
No Clint, remember it's a decreasing RADIUS issue. The only (easily changeable) distance that affects output torque is the effective loaded radius of the tire.Clint Sever said:Dean - that makes perfect sense, I wasn't thinking of it in a decreasing-diameter sense,
Ahh, good point Dean. /images/graemlins/freakGTS Dean said:No Clint, remember it's a decreasing RADIUS issue. The only (easily changeable) distance that affects output torque is the effective loaded radius of the tire.Clint Sever said:Dean - that makes perfect sense, I wasn't thinking of it in a decreasing-diameter sense,
Ah but yes it does.Clint Sever said:By the way Barry, that stored up energy in the tire isn't ever released as power measured on the dyno. That's because as that tire flexes, it remains flexed althrought the run; the power transferred the the wheels increases and increases throughout the run and the tension on the sidewall isn't released until after the power is disengaged at the end of the run.
That stored energy in the sidewall doesn't show up on the dyno.
Jerome said:Ah but yes it does.
Remember we are not talking race slicks so the amount of wind-up will be very small, but enough to have an effect.
God I wish I could explain this. :bonk:
I forgot wtf I as talking about /images/graemlins/laughing.gifMark Young said:Jerome said:Ah but yes it does.
Remember we are not talking race slicks so the amount of wind-up will be very small, but enough to have an effect.
God I wish I could explain this. :bonk:
You can explain it fine. What are you talking about, a Viper on a dyno or what?
Mark, hate to disagree with you but you're wrong on a number of counts here. JPH was correct that the inertial dyno (like a Dynojet) measures the rate of acceleration (change in drum speed between discreet time samplings) of the drum and back-calculates torque from it. Torque is a static property that cannot be measured directly from a rotating device like a dyno drum. So although Hp seems unreal to many of us and we dismiss it as nothing more than a derived entity, in actual fact the dyno only measures power and reports torque as the *mathematical* afterthought.Mark Young said:Holy crap, in the time it took me to type my post the levee broke on this thread.
To highlight:
A dyno measures TORQUE, not hp -
Changing drive ratio, overall tire diameter, etc, changes the Torque reading at the wheels, and thus the dyno gives a different reading.
Its simple physics people.
That's what I'm saying Jerome.Mark Young said:Same OD (and weight) = same reading by laws of physics.
However, I think your point was that due to the greater sidewall flex of the 16" combo, the reading will be different. Assuming you pump up the 16" combo adequately, the flex will be neglibible and the difference will be lost in the noise of any series of dyno pulls. And if you did not pump up the 16" combo, the reading would be less, because energy is wasted in the tire flex instead of being transferred to the drum (there is no traction issue here like with the dragster from rest).
Eric is right. I was under the impression that the dyno drum worked like a torque wrench does, but it does not. It does in fact measure horespower and extrapolate torque using the rpm sensor of the engine.SeriousEric said:Mark, hate to disagree with you but you're wrong on a number of counts here. JPH was correct that the inertial dyno (like a Dynojet) measures the rate of acceleration (change in drum speed between discreet time samplings) of the drum and back-calculates torque from it. Torque is a static property that cannot be measured directly from a rotating device like a dyno drum. So although Hp seems unreal to many of us and we dismiss it as nothing more than a derived entity, in actual fact the dyno only measures power and reports torque as the *mathematical* afterthought.Mark Young said:Holy crap, in the time it took me to type my post the levee broke on this thread.
To highlight:
A dyno measures TORQUE, not hp -
Changing drive ratio, overall tire diameter, etc, changes the Torque reading at the wheels, and thus the dyno gives a different reading.
Its simple physics people.
Changing the ratios of the above (gear ratio, tire size, etc) affects the curve for sure, but I can see that it should not affect the peak readings. However, gear swaps rarely result in similar dyno measurements, but I'm happy to chalk this up to different driveline loss and/or just typical dyno differences between trips.SeriousEric said:Changing the drive ratio and tire diameter does have an affect on the force that your tire applies to the ground and hence to the dyno drum but I will reiterate that the dyno does factor this out in it's calculations of flywheel Hp and Tq. You said earlier that it couldn't be doing this because there's no way to enter drive ratio and tire diameter into the dyno program. My response is that you don't need to enter that crap because the dyno has a much more simple and elegant way of factoring out the torque multiplication due to gearing and tire and it does so using the ratio of engine rpm to drum rpm. If your crank were hooked directly to the drum axle with no gearing induced mechanical advantage they would rotate at the same speed, right? If your motor rotates the drum at half the engine's rpm then there's a mechanical advantage (torque multiplier) of 2:1 at work somewhere in the driveline, correct? The dyno doesn't give a shit whether that multiplier is due to tranny, diff and/or tire size. It simply knows to divide it's measured power/Tq numbers by 1/2 to get the flywheel values ... it's really a beautifully elegant system when you realize how it works.
As far as why we put the tranny in 4th (1:1) to run dyno pulls? It's not because 1:1 is necessary for the calculation to work, it's because in direct drive (1:1) you get less power loss through the clusters than you do when it's in some other gear. You could perfectly well do a pull in first gear or in 6th but the "rule of thumb" loss figures that we all apply would be wrong.
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Well I don't have a dyno, rwd car, and two sets of rims/tires so I can't prove this. But I have seen it in person, I try not to talk out my ass, but well at times... /images/graemlins/laughing.gifMark Young said:Same OD (and weight) = same reading by laws of physics.
However, I think your point was that due to the greater sidewall flex of the 16" combo, the reading will be different. Assuming you pump up the 16" combo adequately, the flex will be neglibible and the difference will be lost in the noise of any series of dyno pulls. And if you did not pump up the 16" combo, the reading would be less, because energy is wasted in the tire flex instead of being transferred to the drum (there is no traction issue here like with the dragster from rest).
You graciously fold in the face of my undeniable rightness, just like that? Turn in your Alley membership card and get out!Mark Young said:So I humbly drop trou and offer up my lilly white ass for a public VA caning, and can only add this link with a good writeup of how the whole thing works:
(I'm stickin to my guns on the drag tires though!)
