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Saturday Night Racer >> RACE TECH >> Limited Slip
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Message started by triplexl46 on 06/18/13 at 7:54pm

Title: Limited Slip
Post by triplexl46 on 06/18/13 at 7:54pm

Just curious as to why a lot of tracks have them in their rules as not allowed but they allow a full locker in most Hobby Stock classes. Wouldn't it be a down grade to run LSD instead of a locked rear? Or might there actually be some advantage in running a LSD like a TrueTrac? It's been a question I've always wondered about but could never get a straight answer.

Title: Re: Limited Slip
Post by dirtmopar44 on 06/19/13 at 5:19am

I would think LSD would not stear the car as good as a locked diff. With a locked diff you would allways have the same rear stear effect because the wheels will always be locked together. You could set up a LSD very tight (add more discs and heaver springs) to have the same stearing efect but it would be heaver and not as reliable. Remember we are trying to stear the car with the rear end.

Title: Re: Limited Slip
Post by triplexl46 on 06/19/13 at 7:26am

The thing about LSD rears though is it opens in the corners supposedly helping it turn itself then locks again under power. A traditional "open" rear would transfer the power to the wheel with less resistance in the corner and it was always the left rear which was difficult to set up for. A unit like a TrueTrac advertises however that it will transfer the power as needed to each wheel always making the load on the wheels the same so one wheel never has too much load and one wheel never is freewheeling. So it always levels the power out.

The traditional open rear your open all the time. A LSD your open in the corner and locked while under power on straights. TrueTracs your locked on straight power and both are spinning in the corner but just at different speeds to even themselves out. I know their popular on asphalt cars and in road racing.

Title: Re: Limited Slip
Post by Andrew on 06/19/13 at 7:38am

This rule makes sense on pavement, not on dirt. A TrueTrac works incredibly on pavement. But on pavement you're NOT spinning the tires. On dirt, they're unpredictable. In theory, unlocked in the corner, locked under power sounds great, but when it locks and unlocks it makes the car do funny stuff. I'll never admit how I know this ::)

Title: Re: Limited Slip
Post by OLD SCHOOL#6 on 06/19/13 at 9:26am

triplexl46 wrote on 06/19/13 at 7:26am:

Hey triplex146 -- Is it possible you are confusing the LSD with a Detroit Locker? The LSD has a clutch pack and springs in it and never completely opens or completely locks up. They are used a lot in pick- up trucks. The Detroit Locker has springs and locking dogs in it, and does exactly what you are describing. It completely unlocks under deceleration and completely locks up under acceleration. We used to use them back in the old late model days when we had no tire stagger available to us. It would unlock going into the turns allowing the car to rotate, and when the throttle was picked up, it locked. Sometimes a little unpredictable, but they served the purpose.

Title: Re: Limited Slip
Post by racincowboy3 on 06/19/13 at 11:23am

A LSD transfers power back and forth between wheels as one tire begins to spin at a high rpm then the other... I don't know in higher classes that it would be any advantage but in the factory stock classes its a big help. take the driver out of the equation some to where you can "stomp and steer"

Title: Re: Limited Slip
Post by triplexl46 on 06/19/13 at 7:09pm

Andrew, your funny. Lol. Old school, it's very possible. I just recently started learning about rears and what they do. I was mostly interested in finding out if anybody knew about the TrueTrac rears bc they claim to be a different type of limited slip working opposite of how a traditional LSD works. The other wheel turns and it never truly loses it's posi. It always spins both just compensating for the different amounts of spin needed for each wheel in the corners.

And the original question was as to why tracks that allow a fully locked rear often have it in their rules that LSD are illegal. Why make it illegal if it's a downgrade. My local track has always had it in their rules. Just another antiquated rule? Lol

Title: Re: Limited Slip
Post by racincowboy3 on 06/20/13 at 8:00am

A LSD takes the driver out of the equation to a point but adjusting to wheel spin and whatnot... A locked up rearend makes the wheels turn together and thus needing more driver input... its not that it is an advantage for overall power, but that the drivability is easier

Title: Re: Limited Slip
Post by triplexl46 on 07/11/13 at 3:30pm

So would a LSD or a TrueTrac make the car looser or tighter?

Title: Re: Limited Slip
Post by racincowboy3 on 07/16/13 at 8:22am

Dont think of it as a handle resolution... more as a power management tool