We all know it doesn't take much to make our LSD start to slip, it's just not tuned very tightly at all. The factory spec for the 2000 Xterra is 138-180 ft-lbs. of torque needed to make it slip. I was shocked to see that the 95 Pathfinder with an H233b LSD has a 260-289 ft-lb. breakaway. I've seen them in action, they do work much better, I'd love for mine to be up there or even around 300 ft-lbs. (see my how-to in the backyard mechanic section)
Now, here's the shocker. The 2001 and 2002 Xterra have the same 138-180 ft-lb. spec. However, the 2003 and 2004 have a PATHETIC 29-43 ft-lb. breakaway torque specified in the service manual. That's essentially useless, why even bother...


Brent

Whats that mean Brent? The torque (#'s) of resistance against the "gripping" wheel required to make it stop is only 30-40 #'s?

Pretty much. In practicality, it's an expression of how much force the tire with better traction is able to provide towards making progress before the other tire starts to spin and takes most of the power away from it.

Thanks, and I find that incredibly weak too, and strange. In that it requires less then 40# of pressure to rip someones ear off. I'm just glad I've got square headlights

To test a limited slip diff. all you have to do is lift one rear wheel off the ground and give it a twist to brake the clutches. With the other rear wheel on the ground a lsd with nuts will take some serious nuts on your part to turn the up wheel. My 2000 has a LSD and it is a piece of cake to twist using this method. The clutches are set loose to eliminate any form of chatter when cornering. Remember these units are built for the highway with an occasional trip on slippery roads. If you go where you are concerned about returning or need positive traction on an upcoming adventure, change out to a set of Detroit lockers. Those puppies do make noise on corners, but they are easy on tires. A normal Dana LSD has a break of over 600 lbs. I used to add clutches until the wheels hopped on corners and then backed off a clutch or two. This was not an exact science and depended on the weight of the rig, but it made for positive drive to both rear wheels. Good in most conditions; not ice, not packed snow. The Detroits were by far the best LSD for me.

Bang for your buck you can't beat a spool. They aren't as ba as people try to make them out to be, just run 50 psi on the street and you're golden.

Justin

Yea, and your teeth fall out and your traction and handling go to shit.

Good thing I have a 2002!

I have a LSD on a 2003 and I completely believe those torque ratings. I've tried it one side on ice and the other on dry pavement many times. It just slips like crazy with little throttle but eventually gets moving. My Subaru Outback with a rear LSD seems to do much better in the same situation.

Square headlights are looking better now.

I run a spool in my ex-daily driver (daily drove it with a spool for beter than a year), the only time you really notice it is when pulling parking lot maneuvers, but it is entirely liveable. Running 50 psi makes for HORRIBLE traction with an open diff, but with a spool you have to apply double the torque to the axle to bust the ass loose, so you don't really lose much. There's a particular corner by my house that my truck would always spin the tires on going around the corner, wet, dry, no matter what (this was at 30 PSI and an open diff). Now i run 50 with the spool and haven't turned a tire yet. as for handling, these things ain't sports cars. just turn a little earlier than usual and you're good. If you're serious about playing, you gotta BE serious about playing.

I've never tried 50 psi in my X, so i dunno about the teeth falling out part, but in my truck (which is actually lighter than the X by almost 1,000 lbs) the ride is entirely acceptable. I'll throw 50 in the X in the next day or so, see how it feels.

Justin

You may find the ride acceptable, but so little of the tire is actually touching the ground at 50 psi. Your contact patch is miniscule on anything smaller than tank treads. At that high of pressure your tires are slipping because they can't remain in contact with the ground.

No way I would reduce my footprint like that, it would be a nightmare on wet roads and compromised even on dry.

You run 50 lbs so the tires do slide cross the pavement, otherwise you start breaking axles. Even at 50 psi the center three rows of tread on my tires were wearing evenly and as i said before, this is with at least 1,000 lbs less on the tires. that means my rear contact patches are probably about 3-4 square inches parked, which really isn't that bad. My last car had about 2 sq. inches parked and about 1/2 square inch contact at 60 mph (and that's the way it was supposed to be )

All you have to do is not drive like an idiot and you'll be fine. I never lost my truck ever. Not in the rain, snow, ice, dry, anything. The reduced contact is no big deal if you know you have reduced contact and drive accordingly. Other big part is to go into an empty parking lot and find out when he tail breaks out. you find this out and you'll never lose it.
(unless you want to )

Justin

2 square inches of contact patch on a 3000 pound car would require each tire to be inflated to about 187.5 PSI. At 1/2 square inch, you would need 750 PSI.

Please try again.

Last car, not truck. Car didn't even tip 2000 lbs. But I do admit I mad an error, the 2" was the contact at 60 mph and the other size was at 80. It had a patch of about 8" parked and the truck has a patch of about 17" with the 4.25 at 80 (had the list in front of me, just read everything off one column.) The X would still have a patch of about 21" per wheel at 50 psi as compared to the about 35 at 30psi. 21" isn't bad at all.

All i'm saying is that the spool isn't the spawn of satan that everyone makes it out to be. Running one won't cause the sky to come tumbling down or instantly kill everyone that is on the road when your spooled vehicle drives down it.

When taking into account the cost of lockers, the price of a spool becomes very appealing, and yes, it is worth trying. If you don't like it, take it back out.

Just curious, you ever ran one?

Justin

Why do you think the contact patch changes size at different speeds ? The vehicle still weighs the same amount no matter how fast you're traveling, and can actually weigh more from downforce.

And what car weighs less than 2000 lbs ? The Lotus Elise is the only one I can think of. My WRX weighs 3000. And where did you find a 3000 lb. F-150 ? Ford says they weigh 3700.

Lift. As you drive your car is shaped kinda like a wing with a greater distance across the top of the vehicle than the bottom. The air on top has to travel across a greater distance in the same time as the air that goes under the vehicle. The faster moving air over your car creates a low pressure zone wich allows the air under the car to "push" up on the car hence reducing the effective weight of the car on the road and in turn the size of the contact patch decreases. that is why your cars steering feels lighter at speed because in effect, it is.

Now, if you have an airdam it can provide downforce and maintain your contact patch.

As for weight of the 150, with a full tank of gas and me in the truck it weighs it at 3300 lbs. at the scales. I don't know what ford claims, but that there is what the truck weighs.

1966 VW bug, weighed 1700 lbs with me in it.

Justin

Yes and no... The windshield makes a pretty good airfoil generating downforce.. and as for the steering letting lighter at speed, there is less resistance to turning the wheels, as any loading on the steering system disappears over a few feet, and you are traveling mand feet per second..
75.44 feet per second at 70..

What the hell does this have to do with LSD breakaway torque?

It started with me suggesting the guy try a spool if he wanted a good bang for his buck traction aid seeing as how pathetic the stock Xterra LSD is.

I've been defending my point and this is where we've gotten. Bang for yur buck you can't beat it if you wanna go out and play, if you're worried about how your X is going to corner at 90 then the compromises associated with a spool aren't for you. Otherwise there really is nothing wrong with a spool besides the whole eating tires thing, but that's to be expectd with any fully locking type unit.

Ever notice your vehicle gets blown around by wind more on the highway than around town? Your vehicle is effectively lighter from traveling at speed due to lift. You have less contact area at speed to counteract the side force. That's the most obvious effect.

I still wanna know if any of the people talking bad about spools have actually run one.

Justin

To be honest, I wonder if the breakaway torque on the 03-04 isn't so low as to make calling it a LSD false advertising. I requested the LSD and payed more thinking it would be of some use. Granted... I should have looked into it, but damn, who would really expect a vehicle like the Xterra to have such a pathetic LSD rating?

I'm not bashing the truck (which I love), but I'm a little ticked at corporate Nissan.

Nope. I've never had the wind actually blow my truck or car sideways causing it to skid due to a smaller contact patch. The wind will cause your vehicle to move around due to a large profile though, but it has nothing to do with the contact patch.

Never thought about it until now, & it was actually interesting to think about; here's my .02:

Assume a gust of wind causes a 2 degree drift in your trajectory.
Now, assume a human reaction time to this gust of wind of 0.5 seconds.
At 20 mph (29 1/3 ft/sec), this .5 second reaction time combined with a 2 degree shift off-course results in a lateral displacement of ~1/2 foot; so you have essentially drifted in your lane by 6" before you can correct your vehicle's trajectory. Not too big a deal.
Now, consider the high speed case. The shift off course is linear with respect to speed; therefore, if your vehicle speed is 60 mph (3 times 20 mph), you have drifted in your lane by 3x0.5 = 1.5 feet in that same 1/2 second it took you to react to the wind gust. This is a much bigger drift & is more likely to induce an "Oh $hit!" type of reaction.
These numbers are a little big (1 degree, with 3" & 9" shifts, respectively, are probably more realistic), but they do help to get the point across.
There are certainly other factors involved (i.e. self-aligning torque vs. vehicle velocity), but this to me seems likely to be the dominant effect.

I love it when people can talk intelligibly about a topic and throw in some math for good measure!

I apologize for having nothing meaningful to contribute.

The reaction times I'm use to for simulation run from .06 to .1 second for pilots responding to gusts.