The tire diameter is most certainly part of the gearing equasion.

Tell me what the difference would be if instead of shifting gears, you could change tire size on the fly? There is no difference. Torque multiplication is delivered to the ground the same in both cases.

Lets say you were towing a given weight up a hill with a given amount of engine torque. Lets say you began to lose speed.... If you could instantly reduced your tire diameter to maintain the engine RPM developing your given torque value, wouldn't that be multiplying torque?

Here is an excellent explanation of torque pulled from elsewhere on the net:

Horsepower and torque are two different ways of describing force (or torsion), hp is time dependent, torque isn't. It's like comparing distance and velocity, velocity is time dependent, distance isn't. Torque would be most analgous to distance, while horsepower to velocity. Horsepower is the rate of change of torque with repect to time (dT/dt), just as velocity is the time-rate of change of distance.

Think of the torque curve as the twisting *force* (or torsion) produced by the crankshaft at various rpm's. Since torque is the applied force x distance (or radius), you can convert this torque to a force at the rear tires if you know the overall gear ratio and tire radius. Therefore, applied force to move the vehicle = torque at given rpm x effective gear ratio / radius of tire. Since acceleration = Force / mass, if you double the torque, you will double the acceleration at a given instant. A high crawl ratio simply increases the force available to push the vehicle.

To optimize acceleration, you want to shift the torque curve the right, or upwards, or both, i.e. to the upper right. This will shift the peak of the torque curve to the right, at a higher rpm. Since horsepower is a product of rpm's and torque, it increases your horsepower. A diesel (usually) has low acceleration because it's ultra-high torque value occurs at a low rpm, hence it has lower horsepower as opposed to an engine which revs high and has high torque (monster truck, drag car).
A high crawl ratio results in low acceleration even though the force is high, because the engine revs very quickly, and the torque quickly reaches a maximum and declines as a result of the drop in the torque curve as the torque "peaks out" quickly. A CVT (continuously variable transmission) results in high acceleration for this reason, it can be tuned to always stay at the peak of the torque curve, with no need to "shift gears" and fall off of the peak of the torque curve.

Maybe we're getting semantics confused here. Lets just say force delivered to the dyno does not care about tranny ratios any more than it cares about tire size, it all calculates out the same. Anyway, on to the next topic.

In drag racing it's not that the transmission is overdriven that matters, overdrive simply does not equate to holding the engine at peak torque at speeds less than Mach 1 without horrendously low rear end gears, which makes the lower gears (in the tranny) so torquey and short to render them useless, especially in a V8 application that has a broad torque curve. OD is setup for street use, it's a completely different discussion all together and does not apply.

What would you like to discuss about oil?

 

The tire radius and secondary gearing does not "make" more or less torque. Overdrive in a car or quad is the same thing. 5th gear for the raptor is .904.....this is overdrive, and the reason for the initial post concerning dyno's. I noticed Hak's post...did you get kicked off? What for?

 

Like I've been saying, it depends on where you measure at....

If you're measuring at the contact patch of the rear tires, like you would on a chassis dyno, the tire diameter, secondary gearing, etc... all factor into the equasion of how much force is applied at the contact patch of the tire before the dyno (but do not affect the final readings of the dyno appreciably due to reasons outlined below).

The force (that is read as torque) applied at the contact patch of the tire is affected (multiplied) by all aspects of the gearing (tires included), but is filtered thru the calculations of the Dyno's software. The rate of acceleration of the drum is compared against the known drum diameter, mass of the drum, rotation speed of the drum, engine RPM, and time. With these inputs, gearing is a non issue and is not needed for the calculation. This is good because very seldom will it ever be constant between vehicles because differences in final drive and tire diameter will be different for every vehicle being measured, the only issue that arises with gearing is that some gears are better suited for pulling an accurate reading than others, simply because they allow for more controlled acceleration of the drum.

If you measure at the axle, the no, the tire diameter will have no affect (other than inertia) on torque.

It seems we are talking about 2 different things and getting off topic from the original question.

 

Seem to keep going over the same thing over and over with no resolution. Thanks for the replys anyway Gabe.