Watts Link for improved street manners

modernbeat

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...Should we assume (or not, LOL) that the suspension kits offered by various manufacturers practice matching springs and dampers? Wouldn't adjustable dampers be compatible with most springs? As you can "tune" them to the spring rate?

Nope.

We've found that first, most manufacturers don't do a good job of matching springs and dampers. And next, that adjustable dampers have a range, sometimes large, sometimes small, that they work in. If you want to go outside the range, it's time for a revalve. Even working inside the range, but changing the spring rate might force you to run almost all the way stiff, which turns your adjustable shock, into a fixed valve shock, because it won't work well when turned down to match conditions.

And there is more to it than that. Some shocks and struts, like the MCS we work with, are shortened to work best with lowered cars and stiffer spring rates. But if we tried to put a soft-ish stock-like spring on them, we would run out of stroke. So for "stock" class cars, we have them custom made with long, stock-like lengths.
 

Candy10

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Nope.

We've found that first, most manufacturers don't do a good job of matching springs and dampers. And next, that adjustable dampers have a range, sometimes large, sometimes small, that they work in. If you want to go outside the range, it's time for a revalve. Even working inside the range, but changing the spring rate might force you to run almost all the way stiff, which turns your adjustable shock, into a fixed valve shock, because it won't work well when turned down to match conditions.

And there is more to it than that. Some shocks and struts, like the MCS we work with, are shortened to work best with lowered cars and stiffer spring rates. But if we tried to put a soft-ish stock-like spring on them, we would run out of stroke. So for "stock" class cars, we have them custom made with long, stock-like lengths.

Thanks for the input. I've been looking at your website alot lately.

....and alot of little things just clicked in my head. Learning lol.
 

SoundGuyDave

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Hey, Kelly! I agree with all your points, however we all need to keep in mind that the discussion was focused on "daily driving situations at regular speeds." To my mind, we're talking about 0.2G lateral, or less. The OP mentioned ruts, frost heaves, dips, etc. I don't think we're talking about huge amounts of assymetrical suspension motion here, but primarily in pure pitch/heave. That tosses most of the roll-steer factor right out, and comes back to the PHB controlling lateral axle motion pretty well. Granted, not with the precision of a Watts, but really we're talking soccer-mom driving pace here, not a TT session or a slalom pushing past the 1.0 LatG point. You make a good point about the accumulation of tolerances/variances through the range of suspension motion. With the Nerf-grade springs on the car, the range of travel is most likely excessive. If he had proper spring rates, though, that range of motion is cut down to something reasonable, which also plays into reducing/minimizing that accumulation... "Everything depends on everything else," right?

Regardless, the first step HAS to be to get the car on proper springs, with proper dampers. Again, doesn't have to be race-car stiff, nor do the dampers have to cost $X,000. All they really have to do is keep the car OFF the bump-stops under normal circumstances, and have damping to control the spring oscillation. THEN we can start talking about suspension geometry and axle location techniques.

Let's face it, there are fast Mustangs with Watts links out back. There are also fast Mustangs with Panhard bars out back. Whether one is superior to the other at the very bleeding edge is completely besides the point when talking about taking a dip in the road at 35mph in pure pitch/heave. The axle doesn't shift enough to contribute to a thrust-angle problem, there is no practical change in roll-steer, and the roll center change is a moot point as well. Either solution will work well under those conditions, assuming that the car isn't on the bump-stops.
 

Shotokan1509

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Guys are killin' me, I have to replace panhard bar but don't really have the car budget (stupid house) to step up to the watts. The current panhard is a reputable company but basically the only non-bmr part that they make a part for.
 
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jraskell

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I'm going to chime in with the group saying get better shocks and springs first. I'm running Steed Ultralites on Koni Sports, and my car handles rough roads just as well as, if not better than stock. The ride is not at all harsh, just firm, which IMO is better than stock.

And while I will eventually be installing a Watts Link for Autocross, panhard bar is perfectly fine for street driving and I believe has no bearing whatsoever on your ride quality problems.
 

Sky Render

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Still running the BMR combo?

Yep.

I think a lot of the people who put a watts link on are swapping from the stock squishy panhard rod, so a lot of the difference they see is the lack of lateral movement caused by the squishiness of the bushings.

A good rod-end panhard bar has very little lateral deflection. As a few others have said, you get more lateral deflection from the tire carcass.
 

Saleen304

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Years ago when I originally switched from a BMR panhard bar with urethane bushings to a Saleen watts link with urethane bushings it was night and day difference. That was all I changed at the time. Stock Saleen suspension, etc. Before the watts link I would notice the ass end bouncing laterally going onto a bumpy on ramp and afterwards it was planted. No more drama. I have since moved to the Cortex setup, but the watts link for me was a great upgrade for the street.
 

Gabe

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Yep.

I think a lot of the people who put a watts link on are swapping from the stock squishy panhard rod, so a lot of the difference they see is the lack of lateral movement caused by the squishiness of the bushings.

A good rod-end panhard bar has very little lateral deflection. As a few others have said, you get more lateral deflection from the tire carcass.

On my fiancée's Shelby we switched from a poly-end BMR panhard bar to the poly-end BMR Watts and there's a huge difference in how the car drives.
Selling the bar now since there's no way it's going back on
 

BMR Tech

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Hi there Dave! Always good seeing your posts, and I think we both agree completely with each other. I am 100% certain that the OP is likely experiencing the effects of rate, dampening and "bottoming out" possibly.

I just wanted to post up and clarify that Dylan was just addressing a few of the questions in the original post, about the Watts in a street or daily manner.

Shooting from the hip, errr kinda sorta....I would say the OP should get into some springs with mid 200ish rates up front, and 200ish out back...with some Bilsteins. Springs preferably Linear during use and no more than 1.5" drop. For OEM style dampers, I think a 200lb/in rear spring is a homerun for all around use, personally.

And yes, that combo would work well for soccer game commutes!
 

Pentalab

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Getting back to the OPs original intent, which was a "discussion about the benefits (or lack thereof) of a Watts Link in daily driving situations at regular speeds."

Point 1: Under "normal" conditions, the car does NOT "have 300 lbs of axle swinging around like a pendulum under the car" as Dylan posits. Do the math. Simple Pythagorean Theorum will tell you that with a compression/rebound cycle of 1" or so from static ride-height, the axle will only move laterally a handful of thousandths of an inch. If you compare that to what you get from bushing deflection or tire carcass and tread block squirm, and you have the axle motion lost in the noise.

So why is it, when you lower the rear 1", that the axle shifts 3/8" to the driver's side ? I fixed that issue with the BMR adjustable PHB + brace. The PHB uses poly. Stiffer bushings + axle centered was an improvement over stock. Then replaced the BMR PHB..with a WL watts link. Back end of car feels more solidified for dd use. Axle doesn't budge. Hit bumps flying around corners, and back end doesn't do the skitery dance routine.

Did you see the auto cross video with the go-pro mounted just aft, and above the driver's side wheel well ? That was using a poly PHB. On sharp right turns, the tire vanishes into the wheel well. On sharp left turns, you can see the top of the tread. And that's the top of the tire. That's a helluva lot more than a few thousands of an inch.
 

Sky Render

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So why is it, when you lower the rear 1", that the axle shifts 3/8" to the driver's side ? I fixed that issue with the BMR adjustable PHB + brace. The PHB uses poly. Stiffer bushings + axle centered was an improvement over stock. Then replaced the BMR PHB..with a WL watts link. Back end of car feels more solidified for dd use. Axle doesn't budge. Hit bumps flying around corners, and back end doesn't do the skitery dance routine.

Did you see the auto cross video with the go-pro mounted just aft, and above the driver's side wheel well ? That was using a poly PHB. On sharp right turns, the tire vanishes into the wheel well. On sharp left turns, you can see the top of the tread. And that's the top of the tire. That's a helluva lot more than a few thousands of an inch.

Tire carcass deflection and bushing compression.
 

Pentalab

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Hi there Dave! Always good seeing your posts, and I think we both agree completely with each other. I am 100% certain that the OP is likely experiencing the effects of rate, dampening and "bottoming out" possibly.

I just wanted to post up and clarify that Dylan was just addressing a few of the questions in the original post, about the Watts in a street or daily manner.

Shooting from the hip, errr kinda sorta....I would say the OP should get into some springs with mid 200ish rates up front, and 200ish out back...with some Bilsteins. Springs preferably Linear during use and no more than 1.5" drop. For OEM style dampers, I think a 200lb/in rear spring is a homerun for all around use, personally.

And yes, that combo would work well for soccer game commutes!

If you don't want the 1.5" drop of the BMR GT springs, the BMR GT-500 springs (handling or performance versions) will apparently provide for a .5" front drop...and a 1" rear drop, when used on a GT. Then use the Vorshlag Bilsteins. With a blower, the front may end up being a .7" drop.

http://www.bmrsuspension.com/?page=products&productid=1468&superpro=0 220 front /200 rear. (performance)

http://www.bmrsuspension.com/?page=products&productid=1470&superpro=0 260 front / 220 rear (handling)

http://www.vorshlag.com/product_info.php?cPath=141_142_179&products_id=642 (allows for more bump travel)

Use a strut mount with some adjustable camber, after market front + rear sway bars... and I believe the above items will be a winner. I will attempt this combo early next spring.

Of course you can buy BMR front springs separate from rears, to make any combo you want... like 260 /200 or 220/220
 
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Norm Peterson

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Tire carcass deflection and bushing compression.
Also there's a bit of an illusion going on, since the body motion relative to the axle is mostly roll instead of the purely straight up-straight down "heave" suspension movement that would duplicate the effect of lowering.


Norm
 
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Pentalab

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Tire carcass deflection and bushing compression.

I drew this all out on paper, with extreme sidewall deflection, and even with the... 'tire carcass deflection / side wall deflection', I still can't see the axle / body shifting. What am I missing here ? Any sidewall deflection will be at the bottom, at the 6'oclock position.....meanwhile the go pro is pointed at the 12'oclock position.

Sure, even with extreme sidewall deflection, the entire back end of the car can flex side to side, but the axle will still be centered between the 2 x wheel wells.....IF a watts link is used.

If a 35 series tire used, and wheels that are say 1/2" wider then their 'measuring width', I can't see a heck of a lot of sidewall deflection happening.
 

SoundGuyDave

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You can get up to 1" (yes one inch!!) of tire carcass deformation, even with a 35-series sidewall on a properly sized rim. You've seen the undercar videos of AI cars (Toyo RR) digging into a corner, and seen the entire carcass shift towards the inside of the car (outside front wheel), more at the bottom than at the top, but the entire carcass is moving back and forth relative to the wheel centerline.

What you're missing is the axle pivoting around the roll center of the rear suspension. Rear roll center with a Panhard is essentially defined as the point where the track bar crosses the center of the differential housing. This will move vertically, slightly, depending on whether it's a left or right turn, but honestly not all that much with properly selected spring rates. With a Watts, the RC is essentially defined as the center of the pivot bolt. That will move relative the axle, or not, depending on whether the pivot is fixed to the rear cover (Griggs) or is mounted to the sprung chassis (Fays2). With the camera on the car fixed to the chassis, visually, the axle is moving around the roll center. When it does, the position of the wheel relative to the wheel well NECESSARILY has to change, regardless of locating mechanism.

page01.jpg

Black line is the chassis plane, static relative to the camera in the video. Green is the axle and tires with no side load. The dot in the middle is the roll-center. Red is the axle under pure roll conditions, with no pitch (throttle or braking induced load transfer).

As you can pretty clearly see, the tire "appears" to move in and out of the wheelwell (relative to the black chassis plane), when in reality it really doesn't. It's just a function of the visual angle. This is somewhat compounded by the carcass deformation, where the outside tire, the left in this case, will have the contact patch shoved violently inward (the aforementioned 1"), with the outside tire being shoved slightly the other way (light load, small carcass centerline shift). In terms of the video, those two "stack up" (thanks Kelly!!) and you have what appears to be an axle shifting back and forth dramatically. If this were actually the case, where the entire housing was moving laterally relative to the chassis by inches, you would see it not only at the wheel, like in the famous video, but also TO THE SAME EXTENT right at the roll center. In the undercar video though, if you focus on the center of the diff, it isn't moving much relative to the rest of the chassis, which means that the axle itself isn't moving much. Looking at the roll center will show you how much lateral migration there really isn't. If you catch my drift.

Does the Watts control the lateral position of the axle better than a Panhard bar? Yes. That's not up for debate, at all. Is it 0.1%, 1%, 10%, 100%, 1000% better? THAT is what is up for debate, particularly when you're talking about a street-driven car, when NOT driving like you're an ass-hat. Think in terms of taking a corner with a MOST a 0.20G lateral load, not a 1.0G autocross turn...

Trivia quiz: Name the SPEC SERIES, professional level, that allows the use of either a Panhard bar or a Watts link. Hints: V8s, tube chassis, quick-change rear end. Both Watts and PHB are available, and to the best of my knowledge legal. If it was such a night-and-day difference, wouldn't that be as closely regulated as everything else on the car, as is typical of a spec series?
 

Norm Peterson

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If a 35 series tire used, and wheels that are say 1/2" wider then their 'measuring width', I can't see a heck of a lot of sidewall deflection happening.
Cornering distortion 295 35 on 10.5" & 305 35 on 11". Compare the sidewall shapes of the loaded outer tires against the unloaded RR. These are "measuring width" wheels for the given sizes, but adding another half inch isn't going to eliminate anywhere near all of the distortion you see here. Car is a GT350.

picture.php



Norm
 

Pentalab

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You can get up to 1" (yes one inch!!) of tire carcass deformation, even with a 35-series sidewall on a properly sized rim. You've seen the undercar videos of AI cars (Toyo RR) digging into a corner, and seen the entire carcass shift towards the inside of the car (outside front wheel), more at the bottom than at the top, but the entire carcass is moving back and forth relative to the wheel centerline.

What you're missing is the axle pivoting around the roll center of the rear suspension. Rear roll center with a Panhard is essentially defined as the point where the track bar crosses the center of the differential housing. This will move vertically, slightly, depending on whether it's a left or right turn, but honestly not all that much with properly selected spring rates. With a Watts, the RC is essentially defined as the center of the pivot bolt. That will move relative the axle, or not, depending on whether the pivot is fixed to the rear cover (Griggs) or is mounted to the sprung chassis (Fays2). With the camera on the car fixed to the chassis, visually, the axle is moving around the roll center. When it does, the position of the wheel relative to the wheel well NECESSARILY has to change, regardless of locating mechanism.

View attachment 57278

Black line is the chassis plane, static relative to the camera in the video. Green is the axle and tires with no side load. The dot in the middle is the roll-center. Red is the axle under pure roll conditions, with no pitch (throttle or braking induced load transfer).

As you can pretty clearly see, the tire "appears" to move in and out of the wheelwell (relative to the black chassis plane), when in reality it really doesn't. It's just a function of the visual angle. This is somewhat compounded by the carcass deformation, where the outside tire, the left in this case, will have the contact patch shoved violently inward (the aforementioned 1"), with the outside tire being shoved slightly the other way (light load, small carcass centerline shift). In terms of the video, those two "stack up" (thanks Kelly!!) and you have what appears to be an axle shifting back and forth dramatically. If this were actually the case, where the entire housing was moving laterally relative to the chassis by inches, you would see it not only at the wheel, like in the famous video, but also TO THE SAME EXTENT right at the roll center. In the undercar video though, if you focus on the center of the diff, it isn't moving much relative to the rest of the chassis, which means that the axle itself isn't moving much. Looking at the roll center will show you how much lateral migration there really isn't. If you catch my drift.

Does the Watts control the lateral position of the axle better than a Panhard bar? Yes. That's not up for debate, at all. Is it 0.1%, 1%, 10%, 100%, 1000% better? THAT is what is up for debate, particularly when you're talking about a street-driven car, when NOT driving like you're an ass-hat. Think in terms of taking a corner with a MOST a 0.20G lateral load, not a 1.0G autocross turn...

Trivia quiz: Name the SPEC SERIES, professional level, that allows the use of either a Panhard bar or a Watts link. Hints: V8s, tube chassis, quick-change rear end. Both Watts and PHB are available, and to the best of my knowledge legal. If it was such a night-and-day difference, wouldn't that be as closely regulated as everything else on the car, as is typical of a spec series?

Tnx for the detailed response + diagram.

How much improvement for the watts vs poly PHB ? I don't drive like an ass-hat. The improvement between my former BMR poly PHB and my current WL watts link is most apparent when going over bumps, and imperfections on a road surface....when into corners. The watts keeps the rear planted, the PHB doesn't.

Install lowering springs on the rear, and the axle shifts 3/8" with oem phb. Fix is either an adjustable phb...or a watts link. Fly around a left hand corner..and simultaneously hit a bump (s) with the RR, the axle will shift towards the driver's side if a phb used. RR spring gets compressed. That's no different than the case of installing lowering springs in your driveway, then seeing the axle shift..( cuz the phb is now too long). Of course then you have to factor in rear spring rate + rear shock rate. My rear springs + shocks are both Roush....both are stiffer than oem. I don't have any other possible explanations as to why the Watts works better on the street vs the poly PHB. It's not some subtle difference either.
 
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740weapon

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An alternate idea: Take off the rear swaybar and see if the car is better behaved without it.
 

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