A lesson from the Master on LSD set up...
09-26-2007, 01:58 PM
#1
Rennlist Member
Thread Starter
A lesson from the Master on LSD set up...
Quite unexpected, I just received the note below from Paul Guard, in BLUE, on LSD set up. His note was precipitated by a post a put up a few days ago about the change in my car with a rebuilt LSD.
Please note, I in no way wished to imply that the LSD rebuild was in any way contributory to the ill handling of my car....that came about due to the sway bars and front drop links I am using. My front sway bars are to large 25mm...and the front drop links, stock 993, are too long. I will replace them with the Tarett adjustable drop links in the near future. The rear drop links are 993 RS...they seem to be fine.
Here is what Paul Guard has to say on LSDs and handling in general:
Just to clarify a few things for the recent LSD thread on Rennlist:
Your LSD is NOT a Motorsports 40/60 unit. While yours has the same body as the Motorsports version, yours is one of the street versions with 20/80 ramps (or something close to that).
Regardless, the ramp angles are very much secondary to disc, plate, and pre-load settings of the LSD. The perception that the 20/80 is not nearly as effective as the 40/60 is because they didn't come equipped with "racing" friction discs, and they were set with very little pre-load. For these two reasons, these street LSDs didn't function nearly as aggressively as the 40/60 Motorsports unit.
For the record, there isn't a pro driver alive who can positively discern the difference between a 40/60 and a 50/80 setting, all other factors being the same. They "think" they can, but they absolutely can not. Over the years, we have seen more attributed to (or blamed upon) the LSD, when it has in fact been the suspension / tires that have been the FAR greater contributing factor. Yes, a working LSD is an important part of the equation, but it is the overall set-up of the car that is of greatest importance.
We are always happy to set up an LSD "different than standard", if this is what the customer specifically requests ..... and some guys may wish to experiment with low or "zero" preload settings, which MAY make an LSD more versatile for different types of track. A zero pre-load LSD would typically have a more "neutral" feel in light throttle situations .... as when maintaining speed through a turn .... yet have an aggressive lock-up on acceleration or deceleration.
In ALMS racing, we have seen the full spectrum of set-ups, from dual Belleville washer per side (virtual spool), to more recent uses of "zero" preload settings. This sort of experimentation should be done by someone who thoroughly understands suspension set-up, as it involves a lot more than just the LSD. This is way beyond our area of expertise.
And no ...... the ONLY asymmetrical LSDs that can have their ramps reversed are some of the Guard LSDs. NONE of the Porsche asymmetrical units can have their ramps reversed, as there is a 0.5mm difference in ramp dimensions that will purposely prevent this.
Thanks again Paul for the clarification...I have my LSD rebuilt by you again in a heart beat!
Please note, I in no way wished to imply that the LSD rebuild was in any way contributory to the ill handling of my car....that came about due to the sway bars and front drop links I am using. My front sway bars are to large 25mm...and the front drop links, stock 993, are too long. I will replace them with the Tarett adjustable drop links in the near future. The rear drop links are 993 RS...they seem to be fine.
Here is what Paul Guard has to say on LSDs and handling in general:
Just to clarify a few things for the recent LSD thread on Rennlist:
Your LSD is NOT a Motorsports 40/60 unit. While yours has the same body as the Motorsports version, yours is one of the street versions with 20/80 ramps (or something close to that).
Regardless, the ramp angles are very much secondary to disc, plate, and pre-load settings of the LSD. The perception that the 20/80 is not nearly as effective as the 40/60 is because they didn't come equipped with "racing" friction discs, and they were set with very little pre-load. For these two reasons, these street LSDs didn't function nearly as aggressively as the 40/60 Motorsports unit.
For the record, there isn't a pro driver alive who can positively discern the difference between a 40/60 and a 50/80 setting, all other factors being the same. They "think" they can, but they absolutely can not. Over the years, we have seen more attributed to (or blamed upon) the LSD, when it has in fact been the suspension / tires that have been the FAR greater contributing factor. Yes, a working LSD is an important part of the equation, but it is the overall set-up of the car that is of greatest importance.
We are always happy to set up an LSD "different than standard", if this is what the customer specifically requests ..... and some guys may wish to experiment with low or "zero" preload settings, which MAY make an LSD more versatile for different types of track. A zero pre-load LSD would typically have a more "neutral" feel in light throttle situations .... as when maintaining speed through a turn .... yet have an aggressive lock-up on acceleration or deceleration.
In ALMS racing, we have seen the full spectrum of set-ups, from dual Belleville washer per side (virtual spool), to more recent uses of "zero" preload settings. This sort of experimentation should be done by someone who thoroughly understands suspension set-up, as it involves a lot more than just the LSD. This is way beyond our area of expertise.
And no ...... the ONLY asymmetrical LSDs that can have their ramps reversed are some of the Guard LSDs. NONE of the Porsche asymmetrical units can have their ramps reversed, as there is a 0.5mm difference in ramp dimensions that will purposely prevent this.
Thanks again Paul for the clarification...I have my LSD rebuilt by you again in a heart beat!
