Suspicious (Poor) 0-60 Times

[RowsKing]

He’s questioning if his Braptor is making as much power as it should by comparing 0-60 times. Makes perfect sense if one doesn’t have access to a chassis dyno.
You acted like what he’s doing is a waste of time on an offroad vehicle. So that seems to me that you don’t value hp in said off-road vehicle.

I’d value torque more in an off road vehicle.

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[Spooled]

I run consistent 4.8-4.9's to 60 with the ZFG 93 tune. There's diminishing returns doing 4hi boosted launches as well since the suspension is so soft it squats so hard and unloads weight off the front then spins. it's just a big heavy beast

 

[swamp2]

Are your times correctly measured ?

I think OBDII + Torque App should be within a couple tenths of actual.

almost all car manufacturers are list 0-60 times not consistent with the real world unless all conditions are ideal

I've found that magazine times are typically obtainable or very close. I've got great temps and pressure around here.

 

[Finbox]

Did you make your runs with 93 octane?

 

[swamp2]

Did you make your runs with 93 octane?

91. It sounds like the SAE J1349 standard which Ford adheres to, uses 92 octane. Odd, it should be 91 since 93 isn't widely available.

 

[swamp2]

I did some BOE (back of the envelope) calculations on my wheel weight vs. stock and concluded that could not be meaningfully contributing to my lower than expected performance.

The added weight of the wheel changes is 45 lb (9 lb x 5 wheels). This is 0.75% based on a 6000 lb total (vehicle+driver). Call it a 1% change.

Now lets look at inertia. The heavier wheels consume (and store) more power spinning them up to a given speed under a given acceleration. This is most often described in equations as an effetive force or power loss, although the power is definitely not being lost.

Following equation (2-9b) in "Fundamentals of Vehicle Dynanics" text book by Gillespie (a very good read), we can compare the accelerative force from the engine vs. the effective force "losses" from wheel weight (inertia really not actually a true loss). The engine force term (in english) is

Force = (engine crank torque) x (trans ratio) x (final drive ratio)/wheel radius

These (in metric, of course) are 600 Nm, 4.7, 4.7 and 0.47 m respectively, giving us 28200 N

The inertial force "loss" from the wheels (all 4) is:

F = 4 x (wheel moment of inertia) x acceleration / (wheel radius)^2

We can approximate the wheel as a uniform disc (beefy aluminum for the rim, less dense rubber with heavier steel belts for the tire sidewalls and tread), thus moment = 1/2 mass x (wheel radius)^2

We'll use an average acceleration of 4 m/s^2 (0.4g) from 0-60. The actual ranges from about 0.7 - 0.3. The wheel radii cancel and the result is

F = 2 x mass of single wheel x acceleration, 2 x 50 kg x 4 m/s

The (rounded) result is 400 N.

This is 1.4% of the engines applied force (ignoring the other drive train inertial "losses").

My KMC wheels+OE tires are 113 lb each and they are 9 lb heavier than the OE wheel+OE tire. So, basically about a 10% change.

10% of 1.4% is about 1/10th of 1 percent.

This is the overall size of the expected change due to increased inertia. Whether you consider this a change on torque, force, acceleration, whatever, the effect is completely negligible.

So the entire effect is basically just mass, not inertia and its a 1% change.

This was not the cause of the unexpectedly low performance.

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