Any regrets going automatic?

AnnDee4444

Well-Known Member
Joined
Jan 14, 2019
Messages
1,707
Reaction score
1,628
Location
Earth
Vehicle(s)
Jeep
C/D testing suggest the manual is faster. That would make sense as there's less power loss and the lower gearing.
The torque converter acts as an additional gearset somewhere in the 1.8:1 - 2.5:1 range, and 1:1 is 6th in the automatic vs. 4th in the manual. Those two additional gears keep the motor right in it's powerband the whole time.

Even if the efficiency losses are greater, the automatic should have a pretty big advantage over the manual when it comes to acceleration, with the exception of dead stop clutch dumps.





Advertisement

 

PatrickR

Well-Known Member
First Name
Patrick
Joined
Jan 8, 2020
Messages
72
Reaction score
35
Location
North Carolina
Vehicle(s)
2018 JLU
The torque converter acts as an additional gearset somewhere in the 1.8:1 - 2.5:1 range, and 1:1 is 6th in the automatic vs. 4th in the manual. Those two additional gears keep the motor right in it's powerband the whole time.

Even if the efficiency losses are greater, the automatic should have a pretty big advantage over the manual when it comes to acceleration.
On starting acceleration a clutch functions the same way. Also, your stall speed is fairly low on standard torque converters for the street so you really aren't gaining any extra gearing.

On gearing, more gears isn't necessarily going to make you faster. The purpose of 8 and 10 speed transmissions has more to do with optimization for efficiency while cruising and smooth shifting.
 

Chrysler-Factory-Warranty

Well-Known Member
Rock Sponsor (Level 1)
First Name
Sam
Joined
Aug 29, 2019
Messages
75
Reaction score
69
Location
Munice IN
Vehicle(s)
Jeep Grand Cherokee
None in this department, current-day automatic transmissions are buttery smooth and you can change your tire size without ever having to re-gear!
 

Rodeoflyer

Well-Known Member
First Name
Bert
Joined
Dec 16, 2019
Messages
496
Reaction score
295
Location
Conifer, Colorado
Vehicle(s)
2020 Jeep JLUR; 2016 Ram Powerwagon
Vehicle Showcase
1
Yeah but can you shift gears on that manual transmission in 200ms? ;)
Never need to, this is an offroad vehicle. Nor would I ever want to in an offroad situation.

just an observation. not that fast shifts aren't nice on road. I've paid the $5k for auto rebuilds and just refuse to deal with it again.

Is it true you can't open the doors while moving with the auto?
 

AnnDee4444

Well-Known Member
Joined
Jan 14, 2019
Messages
1,707
Reaction score
1,628
Location
Earth
Vehicle(s)
Jeep
On starting acceleration a clutch functions the same way.
In my opinion starting acceleration is the only place that the clutch has the advantage, and it's nothing like a torque converter. It's advantage is because you can use the flywheels momentum instead of just relying on the power of the engine to accelerate. Riding the clutch won't get any torque multiplication, and will only cause heat & wear. I guess you could technically flat-foot shift every gearchange for a slight advantage, but I'm not sure about longevity...

Also, your stall speed is fairly low on standard torque converters for the street so you really aren't gaining any extra gearing.
OK, lets to the math. If the stall speed was extremely low, like 1.1:1, and first gear in the automatic is 4.71:1, the apparent gearing after torque multiplication would be 1.1 x 4.71 = 5.181. The manual's first gear ratio is 5.13:1. I'm not sure exactly when the torque converter locks up, but the automatic's first gear definitely has an advantage in apparent gearing.

On gearing, more gears isn't necessarily going to make you faster. The purpose of 8 and 10 speed transmissions has more to do with optimization for efficiency while cruising and smooth shifting.
Ture, more gears don't necessarily make acceleration faster, and the most companies are doing it for efficiency reasons rather than acceleration. However all else being equal, the fastest acceleration is going to be achieved when the most work is done, which is by remaining at the highest horsepower for as much time as possible.


I put this graph together a while back, but haven't shared it much since people get all bent out of shape about how the engine power was being calculated. I didn't calculate it, it's was obtained here.

Basically what I've done is graph out the pounds of force that the tire exerts on the road in each gear. This doesn't account for drivetrain loss, torque converter multiplication, or flywheel inertia... so it's probably best to ignore first gear. The only place where the Manual transmission exerts more force to the road is between 49-58 MPH, and from 90-95 MPH (which is the speed limiter on the Rubicon). At all other speeds, the automatic has the gearing advantage.

Solid line = Manual 3.6 Rubicon
Dashed line = Automatic 3.6 Rubicon
Pounds of Road Force by Gear.png
 

Rodeoflyer

Well-Known Member
First Name
Bert
Joined
Dec 16, 2019
Messages
496
Reaction score
295
Location
Conifer, Colorado
Vehicle(s)
2020 Jeep JLUR; 2016 Ram Powerwagon
Vehicle Showcase
1
Drivetrain loss from the converter needs to be added to your graph. There's a lot of parasitic drag in an auto trans.
 

Rodeoflyer

Well-Known Member
First Name
Bert
Joined
Dec 16, 2019
Messages
496
Reaction score
295
Location
Conifer, Colorado
Vehicle(s)
2020 Jeep JLUR; 2016 Ram Powerwagon
Vehicle Showcase
1
Good question but no, I just know it def exists. A lot of parasitic drag in an auto trans and probably 200lb of extra weight
 

AnnDee4444

Well-Known Member
Joined
Jan 14, 2019
Messages
1,707
Reaction score
1,628
Location
Earth
Vehicle(s)
Jeep
Numbers I'm finding online are showing around 15% drivetrain loss for a manual, and 18%-21% for an (older) automatic drivetrain. ZF did quite a bit to reduce losses in the automatic, so for argument's sake and ease of manipulating the numbers, I'll just make a high guess and say that the manual transmission itself is 100% efficient and the auto is 95% (at all engine speeds). Apparently the differentials aren't very efficient... probably has something to do with the 90 degree change in rotation.

With this complete guess of efficiency, the manual's gearing advantage is from 49-58 MPH and 83-95 MPH. The only change from the previous graph was 83-90 MPH.

I'm not going to quantify the weight or the automatic's shift times, mostly because I don't know how but also because it would just be easier to find two appropriate Jeeps and race them.

Pounds of Road Force by Gear 95%.png
 

AnnDee4444

Well-Known Member
Joined
Jan 14, 2019
Messages
1,707
Reaction score
1,628
Location
Earth
Vehicle(s)
Jeep
Also it's worth mentioning (but not quantifying): If the Jeep has eTorque, the auto would have a couple more slight advantages. First being the initial electric boost from dead stop, second being the the reduction of engine speed during shifts which further reduces shift time (at least that's what they claim). The weight penalty probably balances all this out anyway, but some may find it interesting.
 

Rodeoflyer

Well-Known Member
First Name
Bert
Joined
Dec 16, 2019
Messages
496
Reaction score
295
Location
Conifer, Colorado
Vehicle(s)
2020 Jeep JLUR; 2016 Ram Powerwagon
Vehicle Showcase
1
Well I love your analytics sir! Its hard to quantify but you're def helping.
 

PatrickR

Well-Known Member
First Name
Patrick
Joined
Jan 8, 2020
Messages
72
Reaction score
35
Location
North Carolina
Vehicle(s)
2018 JLU
In my opinion starting acceleration is the only place that the clutch has the advantage, and it's nothing like a torque converter. It's advantage is because you can use the flywheels momentum instead of just relying on the power of the engine to accelerate. Riding the clutch won't get any torque multiplication, and will only cause heat & wear. I guess you could technically flat-foot shift every gearchange for a slight advantage, but I'm not sure about longevity...

OK, lets to the math. If the stall speed was extremely low, like 1.1:1, and first gear in the automatic is 4.71:1, the apparent gearing after torque multiplication would be 1.1 x 4.71 = 5.181. The manual's first gear ratio is 5.13:1. I'm not sure exactly when the torque converter locks up, but the automatic's first gear definitely has an advantage in apparent gearing.

Ture, more gears don't necessarily make acceleration faster, and the most companies are doing it for efficiency reasons rather than acceleration. However all else being equal, the fastest acceleration is going to be achieved when the most work is done, which is by remaining at the highest horsepower for as much time as possible.


I put this graph together a while back, but haven't shared it much since people get all bent out of shape about how the engine power was being calculated. I didn't calculate it, it's was obtained here.

Basically what I've done is graph out the pounds of force that the tire exerts on the road in each gear. This doesn't account for drivetrain loss, torque converter multiplication, or flywheel inertia... so it's probably best to ignore first gear. The only place where the Manual transmission exerts more force to the road is between 49-58 MPH, and from 90-95 MPH (which is the speed limiter on the Rubicon). At all other speeds, the automatic has the gearing advantage.

Solid line = Manual 3.6 Rubicon
Dashed line = Automatic 3.6 Rubicon
Pounds of Road Force by Gear.png
Dude you don't understand how a torque converter works... Torque multiplication only happens at low speed, and maxes out at stall speed, which is given in rpm... Not a ratio.

Also, you don't get that for free, it's quite inefficient, which is why most modern autos are locking- to include the zf. When you are accelerating along your converter is most likely locked.... Your chart is way way wrong
 

Rodeoflyer

Well-Known Member
First Name
Bert
Joined
Dec 16, 2019
Messages
496
Reaction score
295
Location
Conifer, Colorado
Vehicle(s)
2020 Jeep JLUR; 2016 Ram Powerwagon
Vehicle Showcase
1
I love anndees charts but yes, you're correct., lets provide him the data to make a correct chart. Driveline loss is severe with the auto trans.
 

PatrickR

Well-Known Member
First Name
Patrick
Joined
Jan 8, 2020
Messages
72
Reaction score
35
Location
North Carolina
Vehicle(s)
2018 JLU
I love anndees charts but yes, you're correct., lets provide him the data to make a correct chart. Driveline loss is severe with the auto trans.
Well, that's going to be tough, you'll need to know stall speed, and the torque multiplication and loss from whatever your launch is to when it locks. I would bet it locks up pretty early... I know it's locked when you're cruising at 1200 rpm, but I have no idea on the logic at a hard launch.

However, data on old autos shows torque multiplication is essentially gone by 2k, so you could plot the stated ratios from 2k rpm and above and be accurate. To account for losses, the zf is pretty efficient locked up, so I would estimate 1-2% off the auto...
 

Advertisement




Dwayne Lane's Chrysler Jeep Dodge
 



Advertisement
Top