Watts Link vrs Panhard Bar "aka..Old Reliable"

[SoundGuyDave]

I know I've said this before, and I'll say it again, just for full disclosure: I am NOT suggesting that a Watts link is an ineffective mod, particularly in an autocross setting; I'm playing devil's advocate at this point, hoisting the PHB flag...

That said, I'd like to suggest that we throw some numbers out there and actually quantify the benefits (or lack thereof) gained with the Watts link. My car is inaccessible at the moment, so I have nothing to measure. I think, though, if we can come up with a rough length of an installed PHB, using Pythagorean theorem, we can determine EXACTLY how much axle displacement we're really talking about at a variety of suspension jounce/rebound heights. I'll go out on a limb, and say that with a suspension that's tightened down (race mode) to around 3" total variance, we're not going to see that much motion.

Next topic: For modeling purposes, what should we use to factor in bushing displacement between rubber, poly and steel (Heim)? I'm thinking we can use a percentage of total bushing outside diameter and simply add that to the net displacement. For example, with a Watts you will have a theoretical ZERO lateral displacement from the geometry, and have only bushing displacement. If we assume a 2" bushing diameter (actual measurements, anyone?), and 6.25% displacement with poly bushings, that equates to a 1/8" net lateral movement. Per bushing. Assuming four bushings in play (two ends, times two lateral link members), that equates to a full 1/2" of lateral motion. Now, with a rod-ended PHB, we'll assume theoretical ZERO bushing compression, and just work the geometry. Assuming a roughly flat nominal bar angle, and a 38" length, which becomes the hypotenuse under suspension deflection, and looking for that same .500" lateral displacement, you would need something like 6" of vertical suspension motion at the PHB chassis-side mount. 6"? Really? To get the same amount of "slop" as you would from a poly-bushed Watts? Hmmm... Even if you use a poly-bushed PHB, with the same compression factor, two bushings for a net 1/4" displacement, then the remaining 1/4" of axle offset would require more than 4" of vertical travel. Somebody PLEASE check my numbers!!!

Total deflection is 1/2" (.500). 1/4" is bushing deflection, therefore, the remaining 1/4" must come from the geometry shift. Asq+Bsq=Csq. A is the distance between the chassis- and axle-side Panhard bar mounts as measured on the ground, B is the vertical rise (or droop) of the chassis vs. the axle mount, and C is the length of the Panhard bar.

To get 1/4" of lateral offset, we need to have the A distance being .250" shorter than the C distance of 38" (actual length TBD), thus, 37.750". Csq (1444) minus Asq (1425.063) yields a Bsq of 18.9375, and the sqrt of that yields a B dimension of 4.35. With a locked-down suspension, with race-level spring rates, I seriously doubt you're going to see that much suspension travel. I seriously doubt that there's even that much compression stroke available from the dampers. Remember, these numbers are at the PHB mounts, NOT the quarter panels! If you extend the base leg of the triangle by 18" (guess at distance), that would yield more than 5-1/4" of travel relative to rest to get 1/2" of axle displacement...

 

[csamsh]

Interesting math. This seems to be hard to quantify.

We need somebody too do a test- get some times with a phb, then install a watts real quick and go do the same course/track/whatever.

 

[jsimmonstx]

Interesting math. This seems to be hard to quantify.

We need somebody too do a test- get some times with a phb, then install a watts real quick and go do the same course/track/whatever.

It ain't exactly a "real quick" kinda task to install a watts link. It would be faster to uninstall the watts link and replace it with a phb/brace, but still, you're should at least an hour or two to make the swap (if you're starting with the watts link installed).

 

[jsimmonstx]

I know I've said this before, and I'll say it again, just for full disclosure: I am NOT suggesting that a Watts link is an ineffective mod, particularly in an autocross setting; I'm playing devil's advocate at this point, hoisting the PHB flag...

That said, I'd like to suggest that we throw some numbers out there and actually quantify the benefits (or lack thereof) gained with the Watts link. My car is inaccessible at the moment, so I have nothing to measure. I think, though, if we can come up with a rough length of an installed PHB, using Pythagorean theorem, we can determine EXACTLY how much axle displacement we're really talking about at a variety of suspension jounce/rebound heights. I'll go out on a limb, and say that with a suspension that's tightened down (race mode) to around 3" total variance, we're not going to see that much motion.

Next topic: For modeling purposes, what should we use to factor in bushing displacement between rubber, poly and steel (Heim)? I'm thinking we can use a percentage of total bushing outside diameter and simply add that to the net displacement. For example, with a Watts you will have a theoretical ZERO lateral displacement from the geometry, and have only bushing displacement. If we assume a 2" bushing diameter (actual measurements, anyone?), and 6.25% displacement with poly bushings, that equates to a 1/8" net lateral movement. Per bushing. Assuming four bushings in play (two ends, times two lateral link members), that equates to a full 1/2" of lateral motion. Now, with a rod-ended PHB, we'll assume theoretical ZERO bushing compression, and just work the geometry. Assuming a roughly flat nominal bar angle, and a 38" length, which becomes the hypotenuse under suspension deflection, and looking for that same .500" lateral displacement, you would need something like 6" of vertical suspension motion at the PHB chassis-side mount. 6"? Really? To get the same amount of "slop" as you would from a poly-bushed Watts? Hmmm... Even if you use a poly-bushed PHB, with the same compression factor, two bushings for a net 1/4" displacement, then the remaining 1/4" of axle offset would require more than 4" of vertical travel. Somebody PLEASE check my numbers!!!

Total deflection is 1/2" (.500). 1/4" is bushing deflection, therefore, the remaining 1/4" must come from the geometry shift. Asq+Bsq=Csq. A is the distance between the chassis- and axle-side Panhard bar mounts as measured on the ground, B is the vertical rise (or droop) of the chassis vs. the axle mount, and C is the length of the Panhard bar.

To get 1/4" of lateral offset, we need to have the A distance being .250" shorter than the C distance of 38" (actual length TBD), thus, 37.750". Csq (1444) minus Asq (1425.063) yields a Bsq of 18.9375, and the sqrt of that yields a B dimension of 4.35. With a locked-down suspension, with race-level spring rates, I seriously doubt you're going to see that much suspension travel. I seriously doubt that there's even that much compression stroke available from the dampers. Remember, these numbers are at the PHB mounts, NOT the quarter panels! If you extend the base leg of the triangle by 18" (guess at distance), that would yield more than 5-1/4" of travel relative to rest to get 1/2" of axle displacement...

A car with a PHB can't truly be "locked down", and I think that any unintended movement is not desirable and should be avoided when possible.

 

[csamsh]

It ain't exactly a "real quick" kinda task to install a watts link. It would be faster to uninstall the watts link and replace it with a phb/brace, but still, you're should at least an hour or two to make the swap (if you're starting with the watts link installed).

yeah...a little tongue in cheek was intended

 

[SoundGuyDave]

A car with a PHB can't truly be "locked down", and I think that any unintended movement is not desirable and should be avoided when possible.

I was saying "locked down" to indicate a race-level prep, not a dual-purpose or strictly street car... 300+lb/in rear springs, high-grade dampers, etc. That type of car typically has CONSIDERABLY less chassis motion that a street car, as it generally doesn't contend with potholes, driveway lips, etc. I get where you're coming from, but by that metric, NO car can be "locked down" if it has a sprung suspension.

I will also agree that unintended movement is both undesirable, and should be avoided, but I'll change the last part to "where practicable." Yes, a Watts (with Heims) will allow less lateral axle motion than a Panhard bar in jounce/rebound conditions, but the real question is whether or not the added weight, complexity, and cost are justified compared to the amount of motion that is reduced. If, for (extreme) example, I could hang a "widget" on your car that would ABSOLUTELY eliminate ANY lateral rear axle motion, but it weighed 2000lbs, would you do it? How about 200lbs? How about 20lbs? Next question would be "what is the viable maximum lateral motion that you're willing to accept at a given weight/complexity/cost penalty?" If it's $200 to keep the axle to under +/-1/8", but it's $2000 to narrow that to +/-1/16", would you do it?

It's all (obviously) down to each of us to determine the bottom line in a cost/benefit analysis, and the main reason for my contrarian opinion is to make people think about exactly that. Take my car, for example... Full rod-end rear, race prepped, track duty only, no autocross, scales at 3306lbs. IF my math is right, and I'm seeing no more than a 5" range of motion from jounce to rebound, that equates to approximately 0.080" of lateral motion in either direction. Given that carcass shift, even with race tires, is a GREAT many multiples of that amount, it really isn't worth $1000, 28lbs, and all the added complexity to potentially reduce. In my case, I could pretty easily argue that the Watts would be a fix for a problem that doesn't exist.

There are, of course other factors involved with the go/no-go decision. The relative ease of tuning roll centers, for example. Terry Fair's rear tire clearance issues with steamroller meats is another. Or, for the guy with the bone-stock rear suspension, the cost differential between the Watts and a Panhard is a lot less than somebody that is already vested.

Again, all I'm trying to do here is provoke some thought. I'm not saying the Watts link fans are wrong, and I'm also not saying that a Panhard is a superior locating device. I'm just suggesting that anybody considering a Watts take a hard look at the numbers and their goals. We've all seen the "hysteria" in the past with different parts, and I just don't want a newbie to think that "Oh my God! If I don't have a Watts, and try to take a corner on the way to the store, the rear axle will shoot out the side of the car and run over the old ladies on the sidewalk!" The difference, both from personal opinion as well as from this thread, between a Watts and an aftermarket Panhard simply isn't a night and day affair, like a rear gear change, or going from all-seasons to Hoosiers.

 

[Norm Peterson]

I know I've said this before, and I'll say it again, just for full disclosure: I am NOT suggesting that a Watts link is an ineffective mod, particularly in an autocross setting; I'm playing devil's advocate at this point, hoisting the PHB flag...

That said, I'd like to suggest that we throw some numbers out there and actually quantify the benefits (or lack thereof) gained with the Watts link. My car is inaccessible at the moment, so I have nothing to measure. I think, though, if we can come up with a rough length of an installed PHB, using Pythagorean theorem, we can determine EXACTLY how much axle displacement we're really talking about at a variety of suspension jounce/rebound heights. I'll go out on a limb, and say that with a suspension that's tightened down (race mode) to around 3" total variance, we're not going to see that much motion.

Next topic: For modeling purposes, what should we use to factor in bushing displacement between rubber, poly and steel (Heim)? I'm thinking we can use a percentage of total bushing outside diameter and simply add that to the net displacement. For example, with a Watts you will have a theoretical ZERO lateral displacement from the geometry, and have only bushing displacement. If we assume a 2" bushing diameter (actual measurements, anyone?), and 6.25% displacement with poly bushings, that equates to a 1/8" net lateral movement. Per bushing.

I think I'd rather estimate lateral loads and assume a bushing stiffness of something like 10,000 lb/in in rubber and maybe an order of magnitude higher for poly. 1500 lbs lateral at the rear will be slightly over 1.0g, probably closer to 1.25g (you deduct the rear unsprung weight from rear total weight for this). That would give 0.15" per rubber bushing in a PHB, and 0.075" per rubber bushing if anybody made a Watts link with rubber bushed links. But since everybody making Watts links uses something of polyurethane stiffness or higher at the ends of the links I doubt that bushing compliance effects for a Watts amount to more than about 0.02" per bushing.

For reference a set of rubber PHB bushings would deform a total of 0.30".

Assuming four bushings in play (two ends, times two lateral link members), that equates to a full 1/2" of lateral motion.

Four bushings, yes, but a Watts link is really two links in parallel, with only half of the rear lateral load being carried by each link. IOW, each link sees only 750 lbs and would have a total bushing deformation (using poly) of 750/100000 * 2 = 0.015".

Now, with a rod-ended PHB, we'll assume theoretical ZERO bushing compression, and just work the geometry. Assuming a roughly flat nominal bar angle, and a 38" length

I think the S197 PHB is closer to 40.25" long. I don't see any point in computing a PHB inclination to match a rubber-bushed Watts link (that nobody makes). Or particularly to match the 0.015" poly bushing compression number either, since it's such a small fraction of the 0.30" rubber bushing deformation that's on the PHB side of the comparison here (5% = strictly noise).


Norm

 

[SoundGuyDave]

Well said, Norm! I'll still argue that the difference between a Watts and Panhard in a "race car" application (please note that I did say "rod-end Panhard," not stock, rubber bushed) is still fairly trivial in terms of lateral axle shift. Comparing your specified 0.030" (Watts with poly) to my 0.080" (Heim-jointed Panhard) is still so bloody close... Yes, the Watts is more than two times more effective, but that 0.050" difference in distance is still visually indistinguishable (videos) and is as you indicated "noise" in the big scheme of things, like carcass shift.

 

[Sky Render]

I think most of the lateral deflection you're seeing in those videos is a result of the rear axle moving in an arc and tire carcass deflection. That's just a hunch, though.

I'm more than willing to swap from my polyurethane panhard bar to a full rod-end panhard bar between morning and afternoon autox runs if someone has a rod-ended PHB I can borrow.

 

[2013DIBGT]

I love seeing these gory details of calculating total axle displacement between the two parts: I'm an engineering geek myself but I deal with 1's & 0's verses mechanical ..etc

BUT, what if we ignore the numbers for a moment and think about how each device actually "Feels" to the driver on the road or track under conditions such as mid corner bumps and road irregularities. Does one device offer or inspire more confidence in the driver when they encounter these less then ideal surfaces at high rates of speed?

Does an axle moving in an almost perfect Up/Down motion with no arching motion involved (ie..Watts) "Feel" or shrug off lousy road surfaces better then a Panhard bar which has no choice but to arch during its range of motion?

Last question, I hear people using the term "Carcass" and the first thing that comes to my mind is dead bodies. What the hell is Carcass?

 

[csamsh]

Last question, I hear people using the term "Carcass" and the first thing that comes to my mind is dead bodies. What the hell is Carcass?

Structural portion of a tire=carcass

 

[2013DIBGT]

Thanks for the clarification

 

[Norm Peterson]

BUT, what if we ignore the numbers for a moment and think about how each device actually "Feels" to the driver on the road or track under conditions such as mid corner bumps and road irregularities. Does one device offer or inspire more confidence in the driver when they encounter these less then ideal surfaces at high rates of speed?

Does an axle moving in an almost perfect Up/Down motion with no arching motion involved (ie..Watts) "Feel" or shrug off lousy road surfaces better then a Panhard bar which has no choice but to arch during its range of motion?

I'm sure that "feel" and driver confidence is related in some way to the path that the rear of the car follows, as that is the end that you don't have any direct control over. You want it to move predictably, and when it doesn't there will be a small acceleration or two that you will feel even when very little movement is occurring. For lack of a better description, they can make you just a little uneasy at least on a big track.

It doesn't have to be lousy pavement, either. T1 at NJMP's Lightning is a right-hander that involves cresting a small hill, so the car tends to go light and come down again as you're tracking out (you'll still be at a small roll angle). In a stock-ish Mustang, the little wiggle there will get your attention, every lap. Just how much of that is due to the behavior of a 100% OE PHB and how much is due to the changes in axle roll steer that also occur as a function of rear ride height - I have no idea.


Norm

 

[Department Of Boost]

In regards to “feel” I think I can unequivocally say the Watts Link will inspire more driver confidence……….But, you have to push the car REALLY hard to get it to the point where the PHB will “scare” you.

On the street if you are driving your car fast enough to make the PHB and axle location an issue you are driving WAY TOO FAST!

On the AutoX course its clear the axle will move a lot. But you are not going very fast and in most cases there is nothing to crash into on an AutoX lap so the scary/consequences factor is relatively low.

Lapping a “big” track on the other hand at a brisk pace could get a little sketchy, especially for someone who doesn’t have a good amount of track time. A new driver it will scare a little, a experienced driver will just log it away as data and keep on going.

 

[NDSP]

Based on the deflection calculations it seems there is little difference between the two on that particular metric. Especially on a track only, stiff suspension car. So "if" the main benefit to a watts link is a better locating of the rear axle, then a dual purpose street/track car would benefit the most from that. Correct? Since it would have more movement in its suspension. Also with some watts links you can adjust the roll center, how benefitial is that? Would a dual purpose car ( and the average Joe driving it ) be able to fully take advantage of this adjust-ability?

 

[Pentalab]

Mine is just a street car. But I went from oem Pan hard bar + mating brace....to the on car adjustable BMR pan hard bar + mating BMR bace. Oem ford PHB is full of SAND, when you cut the end off. ( on my 2010). That's a huge improvement...esp since the axle was sticking out 5/8" to the drivers side on the oem ford setup.

Next step was to replace the BMR setup with the WL watts link..AND also an eaton tru-trac differential, both those items installed at the same time. Yikes, the difference and improvement in handling is apples + oranges. IMO, the WL watts link is a huge benefit for street use.

On a road course track, you will know which corners have bumps etc, etc. On the street, you are in for a rude awakening when hitting bumps on corners..when using a PHB. You end up with several hundred lbs of back end sprung weight all of a sudden being shifted laterally by 1/8 to a 1/2" or more. That will take the rear axle along for the crazy ride. No wonder the back end is all over the map with a PHB..and kicks out on bumpy corners.

The drag race folks say they get better launches with a watts link. The street folks just love the watts link...it's a heck of a lot safer. The WL watts link combined with the eaton tru-trac, imo, is the ultimate street setup. Safer, and good for weekend autocross, road course or drag race use.

No wonder the solid axle gets a bad rap from the IRS crowd. The solid axle + PHB is a fubar setup from the beginning. These 600++ hp 2013-2014 GT-500's need a watts link real bad...and ditto with a torsen or a tru-trac.

Between the WL watts link, the tru-trac..and the BMR LCA relocate brackets, BMR UCA + LCA's, welded in steeda triangular sub frame connector's, BMR rear tunnel brace, and a few other suspension mods... like steeda front and rear STB, my car feels "planted".

Every 05-13 car here in town has the axle shifted towards the driver's side..even on car's that have not been lowered..mine included. Funny thing is, after I lowered the car 1", the axle offset didn't get any worse..go figure.

You folks can keep you PHB's..adjustable or oem. I know folks who have sunk $3K in steeda suspension mods...then added the WL watts link dead last. In each case, they all say the watts link made the biggest difference. A PHB + bumpy corners does not inspire confidence.

My only regret is I installed the watts link last...instead of 1st. ( the tru -trac is another winner)

later...... Jimbo

 

[NoTicket]

I am new around here, and this is my first post.

I picked up my 2014 Brembo GT back in May. It has seen 2 track days since.

I decided that I wanted a Watts on this car in addition to other suspension mods.

After a lot of reading I decided that since I will be doing a bunch of suspension work over time, and I knew I wanted a Watts link in the end, AND there is very little info around from people that have the Watts + no other suspension mods, I would do the Watts first.

So far everything is stock except for brake lines and pads, and an MGW shifter.

My next day I'm doing in this car is Oct 3 and I am planning on installing the Whiteline Watts link sitting in my garage within the next 2 weeks. I will report back with any findings.

Sent from my XT907 using Tapatalk 4

 

[NoTicket]

So, here I am the day after Thunderhill. I installed the Watts Link as planned. The handling of the car changed very drastically. I want to make it clear that I have no other mods to the suspension. All I installed in my car is the MGW MT-82 for the first two track days. I am still running the stock Pirelli's that came with the Brembo package. Now I put in the Whiteline Watts Link.

I used the bottom mounting points on the differential cover. The rear felt planted and well controlled. Going around turn 2, which is essentially a fast skid pad, felt excellent, far better than the previous 2 days. Probably my favorite part about turn 2 in this car now is how predictable it will behave when you use the throttle to help steer the car. The car seems to set a lot more cleanly.

Turn 3 and 4 were drastically improved from before. For those that are not familiar, turn 3 is a relatively long off-camber, decreasing radius (slightly) right turn that leads directly in to turn 4 for an immediate left turn. This set of turns used to be pretty challenging to transition between while maintaining proper levels of grip. Now it feels great, and the car takes a set really predictably.

We were running the cyclone configuration for turn 5. You end up approaching it and having to brake while slightly turning, and heading up a hill. Then cresting the hill while taking a sharp left which leads in to turn 5a which is a downhill off-camber turn (it is faster than turn 3). The car was feeling so much better this day (specifically the rear) that I decided to experiment a little on this turn and come in hot, turn more sharply, hit the berm and let the car slide a bit after going over the hill. This ended up working out great, and the car handled hitting that berm with the rear wheels significantly better than the days before.

I am not going to keep going on this analysis of the way the car handled around specific turns, because I feel like the first few turns cover it pretty well. The car feels more responsive, and feels much more stable around turns (especially in fast long turns). No more rear end jiggling about every time I go over a bump.

So outside of the track day, how does it perform? Well, I have a couple of spots around town and near my house that I drive about every time I take the car out. A bunch of them have big bumps around corners, and one in particular is in an express way and there is a rather large dip in the road. Going around corners and hitting bumps has already been covered at the track, and it feels so much better now than it used to. To me, the more significant improvement was when driving around 80mph over a pretty significant dip in the road. I had tested this out 3 different times before installing the Watts Link. And each time the rear of the car shimmied and it felt completely out of control. It seemed like the shocks were working overtime trying to compensate for all of the rapid wait transfer (keep in mind, this is a perfectly straight part of the road, and you go down the hump perpendicular to it). Now, you go down the hump, the car settles immediately, and you move on with your drive.

So, how about noise? Well, I made sure the grease the everliving sh*t out of the interior and faces of those bushings. The only thing that I have noticed that is different is that when you take out the clutch or let off the accelerator, or both, it seems to transmit the noise of the gears in to the cabin a little bit more than before. No new sounds, no squeaking or anything. But it does transmit that sound a little bit (maybe 3-5db) louder in to the cabin. I am pretty certain this is due to the drop bracket that bolts directly in to the chassis. The only thing that used to be mounted in that location before was the panhard brace. Now there is both the driver side watts link arm, and the new brace.

So, as I am sure you can tell I am incredibly happy with the Watts Link. I was pretty skeptical about the level of improvement that it would offer over the panhard bar. It is, for me, with everything else stock, a drastic improvement. I have heard comments before that the shocks are the reason that the rear end is so unstable, but I can say that if I was not going to slap a coilover setup on this car (still deciding which) the improvement that the Watts Link gave would have convinced me I did not need new shocks.

So, before I part I would like to give a little bit of information about some pains I had while installing this part. First, thanks go to DiMora, a user that posted his step by step installation on this site (and many other Mustang forums). However, his guide did not end up saving me in the end. He says in his write up that the bolt that goes through the passenger side Watts Link arm should get 93 ft-lbs, and the instructions list 129 ft-lbs. However, you are supposed to reuse the panhard brace bolt on this location, and it is supposed to get 85 ft-lbs. No problem at all here (I used the factory manual for spec on that bolt).

However, they supply you with a new class 10.9 m12-1.5x70 bolt with 2 flat washers, a lock washer, and a class 10 nut for the driver side (drop bracket) arm. It also lists in the instructions to torque this bolt to 129 ft-lbs. Well, that is just flat out wrong. The bolt stripped. When I finally got the nut to back out (using a couple of screw drivers and a lot of patience), the threads on the bolt were completely gone. I finally found a torque spec sheet online that lists bolts based on size, class/grade, and thread pitch. It said the maximum spec for that bolt would be 93 ft-lbs. I managed after a few days to get a replacement bolt from Fastenal (did not know the company existed until this install), and the required class 10 nut as well (as it was damaged as well). I torqued it down to 85 ft-lbs, as that is the same as the passenger side, put on an extra nut to hold it in place, and called it a day.

When I called Whiteline to ask them about it, the guy that was tasked with answering my questions was not sure what the actual torque spec on the bolt was. And it took him a while to give me the spec on the bolt. On top of this, he gave me the same answer that others have seemed to be getting, that they are "rewriting the instructions". I told him that the instructions are in a PDF on their website, which would take approximately 5 minutes to update with the proper torque specs. Seeing as this has been the answer people have been getting for a few months (back to March), I don't think they will ever update them.

If I were to buy again I would probably go with the Cortex kit. It is far more adjustable. I do like the Whiteline diff cover and brace. However, their claims that the stresses of the link are distributed over more bolts than the competition. While this may be true for the brace, it really doesn't matter. The main point of stress will be on the mounting point for the propeller. And this is still a single point of failure just due to the nature of rotating things. Granted, it is reinforced, but the Cortex kit also has 2 bolts, to support the center point. I don't know which would is truly stronger, but I have yet to see anyone post that the Cortex kit has actually failed.

So, tl;dr. Watts Link is a vast improvement in handling with an otherwise stock suspension. I would prefer the Cortex kit over the Whiteline kit, but the Whiteline kit IS quiet and seems very sturdy. I will probably stick with it for the time being. It may be an issue trying to get the right roll center once I lower the car though.

 

[2013DIBGT]

No Ticket, thanks very much for posting your impressions and experience with the Watts Link.

 

[jsimmonstx]

One point worth noting - If you're going to autocross your car, your choice of watts link determines the class you complete in. If the watts link you choose involves changing the diff cover (whiteline and others) you will be immediately thrust into the most race-car like class, regardless of what else you have or haven't done to your car. If you get a Fays2-style watts link, you can still compete in the lower tier classes.