An Engineer's Ultimate Guide To 3.21 VS 3.92 Axle Ratio

[BowDown]

Supposedly Truck Trend did a test in 2019 on nearly 2 identical ram 1500 trucks.
One was 3.21 and the other 3.92. (Saw some references but could not find actual TT article.

0-60 mph - 3.21 wins slightly
1/4 mile - 3.21 wins slightly with time and speed

0-60 mph (towing 7500lbs) - 3.92 wins slightly
1/4 mile (towing 7500lbs) - 3.92 wins slightl

Here
3.21 truck was heavier too yet still performed better

https://www.motortrend.com/news/1812-pickup-truck-of-the-year-2019-masterpost-ptoty19/#:~:text=And%20when%20the%20dust%20settled,GMC%2C%20Ford%2C%20and%20Chevrolet.&text=How%20did%20we%20come%20to%20our%20decisions%3F

 

[2021EcoDiesel]

Ahem, 3.92 was on larger tires

 

[Mountain Whiskey]

What

I didn’t know if y’all were serious about pedal commander stuff. I was curious and tried to find some real numbers for comparison.

Don’t get your tights in a wad.

Just jerking your chain. I can't stand that moron.

That dude is annoying as hell. Anyone that goes to him for advice is as bad as the advice he gives.

If that idiot says it everyone should switch to the opposite!

 

[BowDown]

Ahem, 3.92 was on larger tires

And 120lbs lighter

 

[2021EcoDiesel]

And 120lbs lighter

My point exactly, I’m no expert, just poking fun. But I’d bet that tire size makes more difference than the 120 pounds. I’m curious to see what two actual identical (besides gearing of course) trucks would do.

 

[HSKR R/T]

Here
3.21 truck was heavier too yet still performed better


View attachment 176783

https://www.motortrend.com/news/1812-pickup-truck-of-the-year-2019-masterpost-ptoty19/#:~:text=And%20when%20the%20dust%20settled,GMC%2C%20Ford%2C%20and%20Chevrolet.&text=How%20did%20we%20come%20to%20our%20decisions%3F

Imagine that, a truck with bigger tires is slower

 

[BowDown]

My point exactly, I’m no expert, just poking fun. But I’d bet that tire size makes more difference than the 120 pounds. I’m curious to see what two actual identical (besides gearing of course) trucks would do.

Nope.
Each 100lbs is worth about 10hp and the taller tire is a performance advantage over the 20" tire

 

[BowDown]

Imagine that, a truck with bigger tires is slower

Typically, the taller tire is faster and quicker in both the quarter and half mile unless you gear wrong or go too far in tire height which according to the chart posted, the 3.92 and its chosen tire are a performance plus over the 3.21 an 32" tire

The 3.92 truck in the test had 2 advantages and was still slower

 

[2021EcoDiesel]

Nope.
Each 100lbs is worth about 10hp and the taller tire is a performance advantage over the 20" tire

View attachment 176784

Isn’t that 100lbs = 10 hp thing only true in light racing cars? Like ~3000 pound vehicles or so?

 

[Dewey]

Typically, the taller tire is faster and quicker in both the quarter and half mile unless you gear wrong.

The 3.92 truck in the test had 2 advantages and was still slower

Too much tire spin with 3.92’s. Lit em up and couldn’t hook up till 60 mph.

I’ll stand by what I have always said. Unless your towing at the upper end of weight rating there really isn’t much if any advantage with 3.92’s. Getting heavy weight moving from a standstill is all about gearing.

 

[BowDown]

Isn’t that 100lbs = 10 hp thing only true in light racing cars? Like ~3000 pound vehicles or so?

No, weight is weight unless you're talking sprung vs unsprung weight.

What you're referring to is 10th of a second per 100 hp which is accurate down to a mid 10 sec car

 

[2021EcoDiesel]

No, weight is weight unless you're talking sprung vs unsprung weight.

What you're referring to is 10th of a second per 100 hp which is accurate down to a mid 10 sec car

So then the larger tires on the smaller 18 inch wheels would be additional unsprung weight, right?

Plus the Rebel in the test I assume would be on Goodyear Duratracs? And I suppose the Laramie would be on H/L Bridgestone Duelers, right?

 

[BowDown]

Too much tire spin with 3.92’s. Lit em up and couldn’t hook up till 60 mph.

Sounds like an excuse to me but the mph at the end of the 1/4 for each displays how the power was better utilized.

Typically the higher mph indicates more horsepower but given we know both engines make the same power, one applied that power more efficiently by staying in the powerband longer vs the other losing time and speed due to shifting more frequently.

Both gears will knock the tires off from a standing start but your premise also assumes motortrend used a driver off the street vs a professional test driver which they typically do.

 

[Dewey]

Sounds like an excuse to me but the mph at the end of the 1/4 for each displays how the power was better utilized.

Typically the higher mph indicates more horsepower but given we know both engines make the same power, one applied that power more efficiently by staying in the powerband longer vs the other losing time and speed due to shifting more frequently.

Both gears will knock the tires off from a standing start but your premise also assumes motortrend used a driver off the street vs a professional test driver which they typically do.

It was a joke

 

[BowDown]

So then the larger tires on the smaller 18 inch wheels would be additional unsprung weight, right?

Plus the Rebel in the test I assume would be on Goodyear Duratracs? And I suppose the Laramie would be on H/L Bridgestone Duelers, right?

No, 18" wheel would be less unsprung weight.
20 and 22 inch wheels are heavier as are the tires.

One iteration of my Z06 made 570 whp (SAE) with 18" wheels.
When I swapped for the 19 inch wheels, I made 558 on the same dyno. More unsprung weight

 

[2021EcoDiesel]

No, 18" wheel would be less unsprung weight.
20 and 22 inch wheels are heavier as are the tires.

One iteration of my Z06 made 570 whp (SAE) with 18" wheels.
When I swapped for the 19 inch wheels, I made 558 on the same dyno. More unsprung weight

So upon doing some quick research the 18” Duratracs (54 pounds) are 17 pounds heavier each than the Duelers (37 pounds.) Do those rims make up for that 17 pounds? Both trucks on a dyno, which one would have more power in your experience?

Also thanks for the answers, and I appreciate the information!! And the civility. I know how easy it is for these forums to derail into nonsense and sh*t talk.

 

[2021EcoDiesel]

I guess also something to take into account for that drag race would be tread pattern and tire pressure. I imagine the Rebel at 55 psi on A/T tires and the Laramie at 36 psi on Highway treads wouldn’t hook up the same from a dig. Especially with traction control on. I’m probably overthinking this at 11:00 pm while I can’t sleep .

 

[BowDown]

So upon doing some quick research the 18” Duratracs (54 pounds) are 17 pounds heavier each than the Duelers (37 pounds.) Do those rims make up for that 17 pounds? Both trucks on a dyno, which one would have more power in your experience?

Also thanks for the answers, and I appreciate the information!! And the civility. I know how easy it is for these forums to derail into nonsense and sh*t talk.

Some tires are heavier, some are lighter. The stock goodyears my truck came with were 6lbs lighter per tire than the Pirellis I replaced them with and they're the same size. I could also feel it, especially in braking; turn in was strangely much better with the Pirelli's even though they are heavier

The wheels are definitely heavier. They are physically larger than a 18, 17lbs heavier, IDK.

I had a rental 3.21 18" wheel truck for a while before I bought my limited, the 18" wheel truck felt faster with the same gear

 

[HSKR R/T]

Way to many variables when comparing different vehicles with different configurations to be an apples to apples test. The real test would have been both trucks being either Rebels or Laramie with the only difference being the gear ratio. But since that's not the case, all anyone here is doing is bench racing and making assumptions

 

[BowDown]

Way to many variables when comparing different vehicles with different configurations to be an apples to apples test. The real test would have been both trucks being either Rebels or Laramie with the only difference being the gear ratio. But since that's not the case, all anyone here is doing is bench racing and making assumptions

Maybe, maybe not but what we do have is known HP/TQ, known weight and known gear ratios. The 3.92 truck should be both faster and quicker however its neither. The only time the 3.92 truck outperforms the heavier 3.21 truck is when loaded with 7500 Lbs. IMO, 3.92s are more gear than this truck needs and while they may "feel" better, they don't seem to actually perform better.

Until someone lines up two identical trucks sans the gears, this is what we have, everything else is just 3.92 jibber jabber