Zandcwhite

Well-Known Member
First Name
Zach
Joined
Sep 4, 2019
Messages
1,064
Reaction score
1,465
Location
Patterson, ca
Vehicle(s)
2019 jlur
You have that exactly backwards, low range first gear gives the tires minimum mechanical advantage, if the road surface was wet theres a good chance they wouldn’t have turned at all.
You do realize gearing works in both directions? The same gearing that gives the engine maximum torque to the tires gives the tires maximum torque to the engine when the wheels are being driven and the engine is off.
Advertisement

 

cnapierala

Well-Known Member
First Name
Chris
Joined
Nov 9, 2020
Messages
79
Reaction score
67
Location
Omaha, NE
Vehicle(s)
2020 JLR
So do you think they got to their destination and tried to start it before they figured out there was a problem? Just imagining the poor folks popping the hood to see what was going on all to see half the engine gone! Ha ha!
 

Arterius2

Well-Known Member
First Name
Jerry
Joined
Dec 29, 2018
Messages
3,483
Reaction score
4,540
Location
Vancouver, BC
Vehicle(s)
2018 JLU Sahara 2.0L
You have that exactly backwards, low range first gear gives the tires minimum mechanical advantage, if the road surface was wet theres a good chance they wouldn’t have turned at all.
Yep, 4lo and 1st gear gave it highest engine compression ratio.
This is why when descending from a hill, putting it into 4lo and 1st gear can maximize your engine braking.
I'm surprised they didn't realize how difficult it was to tow that damn thing before it reached 70mph.
 

Zandcwhite

Well-Known Member
First Name
Zach
Joined
Sep 4, 2019
Messages
1,064
Reaction score
1,465
Location
Patterson, ca
Vehicle(s)
2019 jlur
Yep, 4lo and 1st gear gave it highest engine compression ratio.
I'm surprised they didn't realize how difficult it was to tow that damn thing before it reached 70mph.
Compression ratio doesn't change with gearing. If it takes 50ftlbs to turn the crank with the engine off the torque multiplication reduces the effort at the wheels to turn the motor over. Picture a longer ratchet on the crank bolt, that is what the gearing was doing.
 

Arterius2

Well-Known Member
First Name
Jerry
Joined
Dec 29, 2018
Messages
3,483
Reaction score
4,540
Location
Vancouver, BC
Vehicle(s)
2018 JLU Sahara 2.0L
You do realize gearing works in both directions? The same gearing that gives the engine maximum torque to the tires gives the tires maximum torque to the engine when the wheels are being driven and the engine is off.
I don't think that's the case here.
Imagine descending off a hill, you put the vehicle into 4lo and 1st gear to maximize engine braking, providing highest rolling resistance.

Just replace that downward descend force with a vehicle trying to tow you, you would still offer highest rolling resistance to that said vehicle towing you. No?
 
Last edited:

Zandcwhite

Well-Known Member
First Name
Zach
Joined
Sep 4, 2019
Messages
1,064
Reaction score
1,465
Location
Patterson, ca
Vehicle(s)
2019 jlur
Engine braking doesn't work with the engine off. With the engine off the drive train is just a lever on the crank shaft. More gearing, larger lever.
 

Arterius2

Well-Known Member
First Name
Jerry
Joined
Dec 29, 2018
Messages
3,483
Reaction score
4,540
Location
Vancouver, BC
Vehicle(s)
2018 JLU Sahara 2.0L
Engine braking doesn't work with the engine off. With the engine off the drive train is just a lever on the crank shaft. More gearing, larger lever.
Sure it does.

Imagine 2 scenarios (with wheels spinning 1 full revolution when towed):

Scenario A (low gearing) - small gear turning a larger gear with 3x more teeth - small gear turns 1 rev, large gear turns 1/3 rev, due to the force multiplying nature of the gearing system, relatively less force is required to turn the small gear 1 rev.

Scenario B (high gearing) - large gear with 3x more teeth turning a smaller gear - large gear turns 1 rev, smaller gear turns 3 revs, you would feel 3x more resistance at the input end of the large gear.

When towing the Jeep in 1st gear, it would be something akin to scenario B.
 
Last edited:

Sydwaiz

Well-Known Member
First Name
Mark
Joined
May 11, 2020
Messages
230
Reaction score
195
Location
Torrance, CA
Vehicle(s)
2021 JLURD, 73 CJ-5
Engine braking doesn't work with the engine off. With the engine off the drive train is just a lever on the crank shaft. More gearing, larger lever.
Whut? The engine is still compressing air in the cylinders even if you aren't adding fuel and ignition. That is engine braking. Do you think the valves miraculously remain open when the engine is off letting the motor spin freely with no compression?
 

Vinman

Well-Known Member
First Name
Vince
Joined
Oct 19, 2020
Messages
303
Reaction score
654
Location
Calgary, Alberta
Vehicle(s)
2021 JLU Rubicon
Whut? The engine is still compressing air in the cylinders even if you aren't adding fuel and ignition. That is engine braking. Do you think the valves miraculously remain open when the engine is off letting the motor spin freely with no compression?
The valves in the Jeep in the original post definitely remained open.....🤪
 

Zandcwhite

Well-Known Member
First Name
Zach
Joined
Sep 4, 2019
Messages
1,064
Reaction score
1,465
Location
Patterson, ca
Vehicle(s)
2019 jlur
Sure it does, the nature of the cantilever/pulley system still exist when engine is off.

Imagine 2 scenarios (with wheels spinning 1 full revolution when towed):

Scenario A (low gearing) - small gear turning a larger gear with 3x more teeth - small gear turns 1 rev, large gear turns 1/3 rev, due to the force multiplying nature of the gearing system, relatively less force is required to turn the small gear 1 rev.

Scenario B (high gearing) - large gear with 3x more teeth turning a smaller gear - large gear turns 1 rev, smaller gear turns 3 revs, you would feel 3x more resistance at the input end of the large gear.

When towing the Jeep in 1st gear, it would be something akin to scenario B.
I was definitely thinking of that backwards, force multlication vs force division. It would take 80 times the force to turn the engine from the wheels. That 10 ftlbs it would take to turn the crank would be ~800 ftlbs at the wheels. Regardless, the wheels would rotate under enough force which is why on an auto I always leave the trans in park so that nothing upstream of the t-case can be spun when flat towing.
 

Zandcwhite

Well-Known Member
First Name
Zach
Joined
Sep 4, 2019
Messages
1,064
Reaction score
1,465
Location
Patterson, ca
Vehicle(s)
2019 jlur
Whut? The engine is still compressing air in the cylinders even if you aren't adding fuel and ignition. That is engine braking. Do you think the valves miraculously remain open when the engine is off letting the motor spin freely with no compression?
Rather, engine braking is minimal at low rpms. Which is why lower gears increase engine braking as the rpms are higher.
 

Petey

Well-Known Member
First Name
Pete
Joined
Oct 10, 2020
Messages
448
Reaction score
230
Location
Miami
Vehicle(s)
2020 jl sport manual
I was eating noodles for lunch and when I read this on the drive and I literally laughed so much I got noodles coming outta my nose.

I am a noob when it comes to vehicle but heck I would do enough research before doing stupid $hit like that!! :LOL: :LOL: :LOL:

Look at their engine!! Look like a relic that came out from some Aliens movie!!! Hahaha.

message-editor_1615869694240-20210316-jeepwranglertowingsubhero3.jpg


P.S: Noodles from my nose! No I am not eating that!

20210316_135258.jpg
thats not a noodle sir ..please see a doctor
 

Headbarcode

Well-Known Member
First Name
Mike
Joined
Aug 16, 2018
Messages
4,622
Reaction score
8,817
Location
LI, New York
Vehicle(s)
2019 JLUR Stingray 2.0 turbo
Vehicle Showcase
1
Being in a higher gear will give more mechanical leverage to the tires over the non running motor. Think of push starting a vehicle. If it was in 1st when the clutch gets popped, the vehicle would abruptly stop and the poor soul pushing it would eat the trunk. The trick was to have it in, say 3rd, and once it fires the clutch is pushed in before it stalled due to being in too high of a gear.
 
Advertisement

ATO4x4
 
Advertisement
Top