LSD Talk - Explain the term "Lockup"

[RobertK]

I've ben looking into LSDs for my car and I hear the term "lockup" used alot with a percentage before it.. I'm still learning alot about my car so I was curious if maybe someone could clue me in.

[StereoInstaller1]

"Lockup" applies to all LSD or locking differential devices, not just your car.

Simply enough, a "spool", which connects the ring gear directly to both axels, thus both wheels, is a 100% lockup. Dragstrip or 4X4 only, lemme tell ya!

An "open" diff, like most all vehicles come with, are basically 1 wheel drive, meaning no actual torque is applied to the non-driven wheel. The "percentage" is a term used to define just how much power is applied to the other wheel. (tranfser of torque)

If both wheels are locked together, turning corners on asphalt is much more diffucult, due to one wheel having to turn a larger circumference corner than the other, making the car damn near undriveable.

More info can be found at http://auto.howstuffworks.com/differential.htm

HTH,
Luke

[RobertK]

What is a good percentage of lockup for street usage?

[kylebes1]

I am going to a 35%

I think 45% would be about he highest.

What happens in a turn is the inside wheel has less resistance through the driveline, so an open diff ends up turning it alone. That is why it is hard to get an open diff car to do a doughnut.

with an LSD the locking mechanisms force power to the wheel with relatively more resistance, the outside wheel...

The new Ferrari f430 (sex on wheels) has what is called E-diff. It has zero to 100% lockup. In a straight line it evens the torque. In a turn it sends up to 100% of the power to the outside tire, which also has more traction availble for forward motion that the inside tire.

[MR 325]

"It spins 2 tires"

[bmw332i]

I am going to a 35%

I think 45% would be about he highest.

What happens in a turn is the inside wheel has less resistance through the driveline, so an open diff ends up turning it alone. That is why it is hard to get an open diff car to do a doughnut.

with an LSD the locking mechanisms force power to the wheel with relatively more resistance, the outside wheel...

The new Ferrari f430 (sex on wheels) has what is called E-diff. It has zero to 100% lockup. In a straight line it evens the torque. In a turn it sends up to 100% of the power to the outside tire, which also has more traction availble for forward motion that the inside tire.

40% lock-up sems to be about right on my 3.23 MCoupe LSD. Quaiffe also makes one hell of a diff. My bro has one on his 1995 Euro 3.8l M5, and it's great for his app.

[Mystikal]

The new Ferrari f430 (sex on wheels) has what is called E-diff. It has zero to 100% lockup. In a straight line it evens the torque. In a turn it sends up to 100% of the power to the outside tire, which also has more traction availble for forward motion that the inside tire.

BMW did it first with the E46 M3.

I beleive most stock BMW LSDs were 25%.

[kylebes1]

The new Ferrari f430 (sex on wheels) has what is called E-diff. It has zero to 100% lockup. In a straight line it evens the torque. In a turn it sends up to 100% of the power to the outside tire, which also has more traction availble for forward motion that the inside tire.

BMW did it first with the E46 M3.

I beleive most stock BMW LSDs were 25%.

BMW had an e-diff?

cool

[Erick]

e-diffs..... next thing you know you must have a Ph.D in Computer Science to mod your car.

[RobertK]

I hear alot about the different ratios like the 3.73 and the 4.10.. I've read the "How Stuff Works" website but what I don't understand is what or how exactly does the ratio effect acceleration, Top Speed, etc?

[erik325i]

I hear alot about the different ratios like the 3.73 and the 4.10.. I've read the "How Stuff Works" website but what I don't understand is what or how exactly does the ratio effect acceleration, Top Speed, etc?

The higher the number, the lower the gear. The stock 325is ratio is 3.73 so if you put in a 4.10 you will have a lower gearing. Imagine riding a mountain bike. You have 27 speeds for example. If you drop down to a low gear, it would be like putting in a 4.10 LSD. You would be able to excellerate good, but would reach your top speed quickly because your legs can't pedal that fast (redline).

So, to sum everything up, using a lower diff (3.91, 4.10) will give you faster excelleration, at the expense of your theoretical top speed, and gas milage.

Hope you understand.

[erik325i]

"It spins 2 tires"

Great explaination MR Obvious :roll:

[RobertK]

So if I were looking to use my car for some daily driving as well as maybe some street usage I wouldn't want to go all the way by getting the 4.10 right?

[Mystikal]

So if I were looking to use my car for some daily driving as well as maybe some street usage I wouldn't want to go all the way by getting the 4.10 right?

Plenty of guys do it, but to me I rather like my 5th gear cruising RPM as it is. If I didn't do a lot of high-speed highway driving I'd consider the 4.10 rear.