Here's a crazy question....

[RedMisted]

But is there anyone out there who races a rear drive car that, for whatever reason, prefers to race with an open differential as opposed to a locked or limited slip?
I'm not completely sold on the merits of running a LSD in my Mustang (UNDERSTEER). A Ford Traction-Loc was recently installed, and I'm wondering if I made a big mistake as the car was already handling like a spec Miata...:eek:
Maybe I should have thought instead about a bigger rear sway bar to help with corner exit speeds. Now that I've got the LSD in my car, I'm going to have to make an adjustment...
As for the adjustment, I can't reduce weight at the front as the car is already bare-boned. Making a sway bar adjustment front or rear makes no sense as all this will do (in my mind) is return the car to its former handling prowess, with the LSD showing negligible, if any, gain. (Spring changes, tire pressure changes, etc...., it'll all be the same to me.):shrug:
Can someone explain in sufficient detail how the LSD is going to benefit me once I dial out the increased understeer that the LSD will initially present???
My assumption is that these LSD things are of more benefit to drag racers than to anybody who drives a road or oval circuit car...
Thanks to any and all replies, as I'm .......STUMPED! :(

[JLawton]

Warning: I am far from being an expert on the topic.....


You need to compensate for what the car is now doing with the LSD. You need to go with a bigger bar or stiffer springs in the rear. Yes, this will take you back to a neutral handling car...........but you'll get out of the corners faster with the LSD. Spinning your wheels out of a corner is not faster.........

[JeffYoung]

Or soften the front, but Jeff's point is right. Spinning a drive wheel (one of them) on corner exit will quickly kill lap times.

If you have a clutch pack diff you can use different ramp angles to get different amounts of lock up on corner entry and under power. Maybe Steve Eckerich, who builds these things, will weigh in on that.

A very "tight" clutch pak will push some on exit, as will a locked. A Quaife or a "looser" clutch pak will push less.

[924Guy]

Decidedly not... you must be lucky enough to race pretty open tracks (no doubt your car's well suited to them!) - with an open diff I was able to spin my inside rear with less than 100rwhp on tap! Of course, keeping the car nice and flat and not overdoing the rear swaybar will help too...

[RedMisted]

Okay, I have a better understanding of the benefits of the LSD, but....

To combat the understeer initially presented by a LSD, is it better to:
a) increase rear sway bar diameter, or
b) decrease front sway bar diameter?

The reason why I ask is because someone told me that if you increase the rear bar, you are basically "decreasing" rear grip. He said that what you really want to do is to decrease the front bar, as this will neutralize the understeer while preserving the rear grip of the car.

My point is, does it make a difference which way you go? Even if you decrease the front bar, it still frees up the rear end in a relative way...Am I right??

And besides, I hate any increase in body roll over the front of the car. (Just my preference.)

[RedMisted]

Vaughan:

Well, Nelson Ledges is about as open as they get!!:D

[erlrich]

I'm no expert either, but what Vaughan said - if you haven't had any problems spinning the wheels with an open diff, you either a) are running a wide open track with no slow, tight corners or b) you aren't going fast enough yet to notice the difference. I originally had an open diff in my 240SX with its piddling 160 or so HP, and when I first started doing track days I never had a problem with spinning, and started wondering what all the fuss was about using an open diff. But as I picked up speed I started to notice in the tighter, slower turns like T7 at Summit or the exit of Oak Tree at VIR I would light up the inside tire with not much effort at all.

One of the things you'll notice as you continue to improve the car and your own driving is that as you make an improvement in one area, you will sometimes expose a weakness in another. I think that's what's happening here - you've increased the traction on corner exit, which is exposing the understeer that wasn't there before. I would work on getting the front to turn better; soften the sway bar a little, soften the rebound on the shocks, dial in some addidional negative camber, play with tire pressures & toe settings (a very slight toe out might help the front to turn), and see if that doesn't help. Just my $0.02.

[dickita15]

The reason why I ask is because someone told me that if you increase the rear bar, you are basically "decreasing" rear grip. He said that what you really want to do is to decrease the front bar, as this will neutralize the understeer while preserving the rear grip of the car.

My point is, does it make a difference which way you go? Even if you decrease the front bar, it still frees up the rear end in a relative way...Am I right??

And besides, I hate any increase in body roll over the front of the car. (Just my preference.)
When you change the balance you are actually making one end of the car carry more of the load, do a larger share of the work. To say you are reducing grip is not really right.
I think you answered your own question, if you do not want to increase roll the raise the rear rate rather than reduce the front.
One other thought, you may not see the benefit of a LSD in track days as much but when racing you often need to deviate from the optimum line and an open diff will hurt you there.

[JeffYoung]

Soften the front a bit and see what happens -- softer springs or work the tire pressures. See if you can dial out the understeer by getting more grip up front.

[JLawton]

The bottom line is you must use an LSD to become competative. Put it in, then go from there.

As you keep getting faster, you start fixing the weakest link, which will make you (the car) faster......which will expose another weak link.........and on and on until the car is perfect and you are the regional champ!! Easy, right??

:)

[Rabbit07]

Where are you right now for spring rates and bars? Have you freed up the rear suspension with a Steeda Five Link or a Grigg's toque arm? The Mustang has a poor suspension geometry. Softening the front too much will cause lots of roll which will cause the car to push even more. I have always keep a tuning kit in my trailer for my ITB Mustang. The kit consisted of different rear sway bars. The rear bar is easy to change at the track. Changing front springs and bar is a pain. You may also tune the handling by adjusting the rear ride height. Herb Adam's book discusses roll oversteer and roll understeer. If you read his book and then plot your rear suspension points you'll know which way to adjust to get the desired result.

[RedMisted]

Thanks to all for their replies.
I've a better idea about this LSD-induced understeer thing. I just needed someone to tell me that once you get the car back to neutral handling, the LSD will then begin to really show its magic.
For some reason I happened to think, at least initially, that LSDs or locked diffs are of more benefit to drag cars that often suffer violent, uneven launches off the line.
I'll just try out the new diff and make whatever changes are necessary.:)

[GregMeindl]

I raced 1995 Cobra R Mustangs in Motorola / Grand Am Cup and have raced mustangs for many years. We had a locker in the Cobra R's and a Torsen in the 85-93 bodied cars. Want to be fast in a Mustang get a locker ! Even my 65 mustang vintage racecar has a locker. My T2 2001 Formula Firebird has a Torsen T2R diff.

We used a Steeda front sway bar, poly and custom bushings up front. Stock rear bar. We also had Penske external reserviour shocks valved by Stimola ( SRP). Springs were also Steeda and Afco as well . We bought boxes upon boxes of springs and check them to make sure the rates were 100% equal. We also made adjustable spring perches that sat on the stock control arms. (Now some companies make rear control arms with the adjustable perches built into them.)

We didn't have a Steeda 5 link or a Torque arm as the rules didnt allow for it. The car nadled great and was fast as s.... We won at Daytona and started last. Must have all worked ! We spent a lot of time / money on the shocks. Shocks shocks shocks !!!!!

The 86-93 bodied cars we ran a torque arm.

I still have a pair of front slider struts that you can buy from me and have Penske's built for them. Its a very trick setup and was on all the front running Cobra R's from 99-2002 in Grand Am Cup.

[lateapex911]

In ITE, the rules are rather open, so susp setups will give you more options, but in ITA, etc, I think you can run an adjustable panhard rod on that car, and that will allow you lots of roll center adjustability. one more tool, and one that is different than an ARB.

But, I think road racers need an LSD as much as, or more than drag racers because we try to accelerate as we turn, which makes the inside wheel light, and an open diff will spin it like a pinwheel in a hurricane.

(Always cracks me up when somebody brags about the huge burnouts their new ride will do, then when they demonstrate, it's an one black line special. yea, not a burnout!)