LSD Installed
Three Wheelin'
Joined: May 2009
Posts: 1,720
Likes: 5
From: West Sussex
Aside from the basic operation of a plate diff described above, there's a few other variables that change the handling impact:
Good explanation here,
http://www.intothered.dk/simracing/differential.html
the references to GPL relate to a racing sim Grand Prix Legends - one of the first to really model suspension physics AND let you play with everything. The difficulty in this game is fierce, basically it's slightly more difficult that actually driving a real 60's F1 car!
Good explanation here,
http://www.intothered.dk/simracing/differential.html
the references to GPL relate to a racing sim Grand Prix Legends - one of the first to really model suspension physics AND let you play with everything. The difficulty in this game is fierce, basically it's slightly more difficult that actually driving a real 60's F1 car!
Three Wheelin'
Joined: May 2009
Posts: 1,720
Likes: 5
From: West Sussex
Lol, let me google that for you....
Option 220 is a "40% lock" - which apparently means 30deg ramp angles on both accel and deccel.
The racey RS and Turbo option is "20/100", the numbers aren't the ramp angles but again the "% lockup" - so its pretty mellow on accel and locks up fully on deccel (or when reversing)
Option 220 is a "40% lock" - which apparently means 30deg ramp angles on both accel and deccel.
The racey RS and Turbo option is "20/100", the numbers aren't the ramp angles but again the "% lockup" - so its pretty mellow on accel and locks up fully on deccel (or when reversing)
Pro
Joined: Sep 2004
Posts: 621
Likes: 25
From: Norfolk, UK
Please could you explain that in a bit more detail? I've always understood it that a normal diff exists for precisely the reason that turning requires the driven wheels to cover different radii - so having a solid rear end (like the Moby Dick 935s!) means that at least one wheel MUST slide to go around a corner making such a car useess in the hands of a non-racing driver.
Likewise my understanding of the LSD is that it (kinda like the name implies) limits the amount by which the 2 axle speeds may differ: as a wheel starts to spin, the axle progressively locks up to force the other wheel to turn- so you won't experience the classic "one wheel still & undriven and the other spinning" but more importantly high speed cornering will be more controlled.
Sounds like I may have this wrong - can you help?
Z
Likewise my understanding of the LSD is that it (kinda like the name implies) limits the amount by which the 2 axle speeds may differ: as a wheel starts to spin, the axle progressively locks up to force the other wheel to turn- so you won't experience the classic "one wheel still & undriven and the other spinning" but more importantly high speed cornering will be more controlled.
Sounds like I may have this wrong - can you help?
Z
RL Technical Advisor
Joined: May 2001
Posts: 11,870
Likes: 75
From: Portland Oregon
The value of an LSD (clutch-type) isn't wheel spin control; after all, you can control that with your right foot, ala "traction control" of sorts.
The real value of an LSD is its ability to keep the rear wheels rotating at the same speed under hard braking. This eliminates that side-to-side wiggle these cars have during this period that destabilizes the chassis at a critical time.
Open differentials as well as Torque-Sensing diffs allow the rear wheels to operate independently under trailing throttle and these cars (with their 63% rear weight bias) do not feel very stable under hard braking and an LSD fixes that immediately.
Naturally, an adjustable type such as the Guard ones allow one to fine tune the LSD to one's preferences and chassis setup. Typically, these can be adjusted to either 40/60 or 50/80 pretty easily, depending on how much power one has and how the car is setup.
The real value of an LSD is its ability to keep the rear wheels rotating at the same speed under hard braking. This eliminates that side-to-side wiggle these cars have during this period that destabilizes the chassis at a critical time.
Open differentials as well as Torque-Sensing diffs allow the rear wheels to operate independently under trailing throttle and these cars (with their 63% rear weight bias) do not feel very stable under hard braking and an LSD fixes that immediately.
Naturally, an adjustable type such as the Guard ones allow one to fine tune the LSD to one's preferences and chassis setup. Typically, these can be adjusted to either 40/60 or 50/80 pretty easily, depending on how much power one has and how the car is setup.
Three Wheelin'
Joined: May 2005
Posts: 1,335
Likes: 0
From: Reston, VA
The value of an LSD (clutch-type) isn't wheel spin control; after all, you can control that with your right foot, ala "traction control" of sorts.
The real value of an LSD is its ability to keep the rear wheels rotating at the same speed under hard braking. This eliminates that side-to-side wiggle these cars have during this period that destabilizes the chassis at a critical time.
The real value of an LSD is its ability to keep the rear wheels rotating at the same speed under hard braking. This eliminates that side-to-side wiggle these cars have during this period that destabilizes the chassis at a critical time.
I.E. (making up arbitrary numbers for learning purposes) lets say you are coming out of a hard turn with an open diff and experience inside wheel spin at 75% throttle, and fund you have to decrease that to 60% throttle in order to eliminate inside wheel spin. Then you take the same car in the same conditions through the same turn (only with an LSD installed this time), and applying 75% throttle at the same exit point, you find the LSD is preventing the inside wheel from spinning. Wouldn't the 2nd scenario be an example of a benefit to an LSD, and in turn a faster car?
I've always thought that was a large advantage to having an LSD. I know at the autocrosses I've competed in, I've at various times simultaneously sworn at the LSD equipped cars and chastised my own for not having one.
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Burning Brakes
Joined: Jun 2011
Posts: 977
Likes: 1
From: Sydney Australia
Point understood Steve, but wouldn't reduced wheel spin in a turn still be a fairly big advantage to an LSD? Sure you can control wheel spin with your right foot, and decrease throttle if necessary, but doesn't an LSD help with NOT having to reduce that throttle, allowing one to get on the gas a bit harder and a bit earlier with an LSD?
I.E. (making up arbitrary numbers for learning purposes) lets say you are coming out of a hard turn with an open diff and experience inside wheel spin at 75% throttle, and fund you have to decrease that to 60% throttle in order to eliminate inside wheel spin. Then you take the same car in the same conditions through the same turn (only with an LSD installed this time), and applying 75% throttle at the same exit point, you find the LSD is preventing the inside wheel from spinning. Wouldn't the 2nd scenario be an example of a benefit to an LSD, and in turn a faster car?
I've always thought that was a large advantage to having an LSD. I know at the autocrosses I've competed in, I've at various times simultaneously sworn at the LSD equipped cars and chastised my own for not having one.
I.E. (making up arbitrary numbers for learning purposes) lets say you are coming out of a hard turn with an open diff and experience inside wheel spin at 75% throttle, and fund you have to decrease that to 60% throttle in order to eliminate inside wheel spin. Then you take the same car in the same conditions through the same turn (only with an LSD installed this time), and applying 75% throttle at the same exit point, you find the LSD is preventing the inside wheel from spinning. Wouldn't the 2nd scenario be an example of a benefit to an LSD, and in turn a faster car?
I've always thought that was a large advantage to having an LSD. I know at the autocrosses I've competed in, I've at various times simultaneously sworn at the LSD equipped cars and chastised my own for not having one.
What a 911 benefits more from, is stability under braking to tame the natural turn-in tailswing, which then allows you to carve a higher and more consistent entry speed. Both the 40% and 20/80% factory LSDs will help in this regard.
So fitting an LSD to a 964 will benefit you more in corner-entry stability, than corner-exit powerdown.
RL Technical Advisor
Joined: May 2001
Posts: 11,870
Likes: 75
From: Portland Oregon
I think what Steve is alluding to, is that the traditional reason for having an LSD (ie, reduced inside wheelspin under power) isn't a big issue in a 911 because of the rearward weight bias and naturally-good traction.
What a 911 benefits more from, is stability under braking to tame the natural turn-in tailswing, which then allows you to carve a higher and more consistent entry speed. Both the 40% and 20/80% factory LSDs will help in this regard.
So fitting an LSD to a 964 will benefit you more in corner-entry stability, than corner-exit powerdown.
What a 911 benefits more from, is stability under braking to tame the natural turn-in tailswing, which then allows you to carve a higher and more consistent entry speed. Both the 40% and 20/80% factory LSDs will help in this regard.
So fitting an LSD to a 964 will benefit you more in corner-entry stability, than corner-exit powerdown.
Three Wheelin'
Joined: May 2009
Posts: 1,720
Likes: 5
From: West Sussex
Hehe just playing, I asked myself the same question, only was too impatient to wait for someone who knew to answer 
In the course of my googling I read somewhere that the 917 and many Porsche racecars since have spool axles ie 100% lock at all times, and on the 917 this was addressing lift off oversteer. Which I guess is in a similar vein to what Steve is talking about.
Also read that the reversing noises in a turbo are common because the diff is wanting to lock.
Locking a diff on the power side mid turn will make the car push upto a point and eventually give oversteer. Probably less desirable in a 911 due to the natural characteristics.
Drift guys on the cheap will weld up an open diff creating a spool, and work around the understeer, Babalouie may have come across that maybe, he's not averse to a bit dori action.
In the course of my googling I read somewhere that the 917 and many Porsche racecars since have spool axles ie 100% lock at all times, and on the 917 this was addressing lift off oversteer. Which I guess is in a similar vein to what Steve is talking about.
Also read that the reversing noises in a turbo are common because the diff is wanting to lock.
Locking a diff on the power side mid turn will make the car push upto a point and eventually give oversteer. Probably less desirable in a 911 due to the natural characteristics.
Drift guys on the cheap will weld up an open diff creating a spool, and work around the understeer, Babalouie may have come across that maybe, he's not averse to a bit dori action.
Three Wheelin'
Joined: May 2005
Posts: 1,335
Likes: 0
From: Reston, VA
I think what Steve is alluding to, is that the traditional reason for having an LSD (ie, reduced inside wheelspin under power) isn't a big issue in a 911 because of the rearward weight bias and naturally-good traction.
What a 911 benefits more from, is stability under braking to tame the natural turn-in tailswing, which then allows you to carve a higher and more consistent entry speed. Both the 40% and 20/80% factory LSDs will help in this regard.
So fitting an LSD to a 964 will benefit you more in corner-entry stability, than corner-exit powerdown.
What a 911 benefits more from, is stability under braking to tame the natural turn-in tailswing, which then allows you to carve a higher and more consistent entry speed. Both the 40% and 20/80% factory LSDs will help in this regard.
So fitting an LSD to a 964 will benefit you more in corner-entry stability, than corner-exit powerdown.
I get a bit of wheelspin in AX, but on a track considering the higher speeds and wider turns it I guess it isn't as big of a problem!