Whiteline Watts Link Failure

[SoundGuyDave]

To add to that, I still want someone to do A/B testing with an awesome link vs a PHB using the same roll center height.

I'll volunteer my car if there's somebody near Chicago that wants to actually do some instrumented testing in either Time Trial or race-group conditions... As mentioned, the roll center has to stay the same, though. It's not hard to swap a PHB, and from looking at it, not that hard to put on a Watts link either. I'm thinking start with the Watts, run a session, then pull it and swap in the pre-adjusted PHB (and stock brace), and re-run. No other changes. No spring rate, no damper adjustments, no tire pressure adjustements, just the rear lateral-location device. Highest peak-G and/or lap time wins? If no difference at all, then does the PHB win because it's cheaper and lighter? Assuming proper licensing and seat fitment (think skinny!), I'll even let the guy with the Watts drive both, and then we can compare data and notes to remove any potential (unintentional) bias. Can't get more fair than that. Two drivers, two different parts, no other changes, all on the same day at the same track with the same car. If there's a "ride quality" improvement to be found, I would bet it would show up on the Z-axis accelerometer.

 

[jmauld]

There's no point in that comparison. You should do the comparison with the suspension optimized for the phb vs the suspension optimized for the the watts link. Not optimizing the setup for each device would be a comparison of subpar setups.

 

[SoundGuyDave]

Well, maybe I'm off base here, but exactly what would you want to change to optimize for a Watts versus a PHB? At the end of the day, they're both lateral links that positively locate the rear axle relative to the vehicle centerline. There's no magic in either. The point about keeping the roll center the same is to eliminate a very LARGE variable. In fact, you CAN tune roll center height with a PHB but it requires relocation brackets to raise or lower the bar. By specifying that the Watts keep the same RCH as the PHB, that simply eliminates the tuning variable. If one shows a dramatic difference from the other with all other variables being held the same, then we have positive proof of the advantage to one or the other. If you were to, say, drop the roll center with the Watts, then it wouldn't be a direct comparison, and that's really the whole point.

 

[Gray Ghost GT]

When people talk about "significant ride improvement" in their daily driver when installing a watts link, I wonder how many actually notice the difference when that watt's link provides symmetrical handling response in performance driving conditions with the ability to "tune" the suspension by adjusting the roll center, whereas a Panhard is slightly asymmetrical with no roll center adjustment.

Another benefit of the watts link (chassis mounted) is symmetry in jounce and rebound, in that the "roll couple" - the distance between the center of gravity and the roll center - remains constant. The roll couple has a direct effect on the amount of roll each end of the vehicle experiences during a turn. There is nothing to optimize in the suspension setup for a watts link vs. PHB comparison.

The Z-axis accelerometer could demonstrate the benefits of a chassis watts link vs. a differential mounted watts link vs. a PHB. The differential mounted watts link = the motion of the axle moves in a straight line relative to the body of the car, e.g., if the car is leaning, so will the direction of bump travel (or Z-axis). The relationship between the roll center and the center of gravity changes during bumps too.

A chassis mounted watts link places the pivot on the chassis, which allows the axle to move straight up and down (Z-axis) relative to the surface of the road (not the lean angle of the car), no matter how far over the body is leaning in the turns and esses. The cars roll center and center of gravity do not change in relation to each other. Its the geometry of what each one does that impacts suspension performance.

 

[jmauld]

By specifying that the Watts keep the same RCH as the PHB, that simply eliminates the tuning variable.

Okay, I'll give you that, assuming that you can adjust the roll center with the PHB to an ideal location, whatever that may be.

Which would require the purchase of adjusting brackets for the PHB. Don't just set the roll center of the watts link to match that of the factory PHB location. Because then you're giving up one of the reasons for buying a watts link.

Also, I think you could get away with a softer spring with a Watts link, vs a PHB, simply because the less that PHB moves around, the more consistent your handling will be. But I might be off on that.

With that said, this comparison would be nice to see done. I'd like to see a professional driver and a grassroots driver have a go at it, to see if there is any advantage to one setup in the hands of different skill levels. I'm surprised that no one has done this and published the results yet. It seems like a simple test and perfect for a magazine like GRM to do.

 

[csamsh]

I'll volunteer my car if there's somebody near Chicago that wants to actually do some instrumented testing in either Time Trial or race-group conditions... As mentioned, the roll center has to stay the same, though. It's not hard to swap a PHB, and from looking at it, not that hard to put on a Watts link either. I'm thinking start with the Watts, run a session, then pull it and swap in the pre-adjusted PHB (and stock brace), and re-run. No other changes. No spring rate, no damper adjustments, no tire pressure adjustements, just the rear lateral-location device. Highest peak-G and/or lap time wins? If no difference at all, then does the PHB win because it's cheaper and lighter? Assuming proper licensing and seat fitment (think skinny!), I'll even let the guy with the Watts drive both, and then we can compare data and notes to remove any potential (unintentional) bias. Can't get more fair than that. Two drivers, two different parts, no other changes, all on the same day at the same track with the same car. If there's a "ride quality" improvement to be found, I would bet it would show up on the Z-axis accelerometer.

Finally somebody proposes some data generation. I await this with baited breath.

 

[SoundGuyDave]

Jmauld: It sounds to me like you're identifying the major benefit of a Watts to be the roll center relocation, and that's something that I STRONGLY suspect is true. In this thread (as well as others) there have been a large number of assertions that a Watts is a night-and-day difference compared to a Panhard bar, and I'm proposing that it just isn't so... Is a Watts easier to adjust roll center with than the stock-bracketed PHB? Yes, I will give you that without reservation. I will, however, stand by my position that absent the roll center relocation, there will be little, if any practical difference where the rubber meets the road on an open track. From what a number of Watts link "fan-boi" types have said, it's a virtual miracle that the S197 can actually get around a corner without the axle falling out of the car with a PHB. THAT is the assertion that I'd like to test. The Watts is a lateral locating device for a solid rear axle. A Panhard bar is a lateral locating device for a solid rear axle. Roll center adjustments can be made with both (albeit easier with the Watts), so as a result, we should remove that variable from the equation. For the purposes of this test, I have no interest whatsoever in modifying my car to allow RCH adjustment with a PHB, just so that we can call the setups "optimized." Roll center optimization has nothing to do with the type of lateral locating device, and everything to do with driver preferance and dynamic chassis balance. We're not shooting for a "best possible case" scenario here, we're trying to test the REAL difference between a proper Panhard bar (with rod ends) and a Watts link. My money is on the instrumentation showing ZERO change in peak lat-g, Vert-G or raw lap times. At least to me, those are the only metrics that matter. If there's ZERO gain, I would rather spend less money and carry less weight by sticking with a PHB, even if I had to add brackets to relocate the roll center.

Csamsh: Well, the offer is out there... It'll just take somebody PM'ing me that has a Watts in a box and a desire to spend a day at the track. The offer is there, and at this point I'm just waiting... I consider myself a decent grass-roots level driver, and if anybody wants to bring a pro to the table, that's just fine with me. I know one, but I would hesitate to ask him to jump in on something like this. I think I would get an "implied facepalm" out of the request.

 

[NoTicket]

Yes, the Stig is needed.

 

[kona302]

Finally somebody proposes some data generation. I await this with baited breath.

We need the stig! Some say,"if he caught on fire he would burn for 1000days."

 

[csamsh]

If I still lived in Champaign I would be at Autobahn yesterday

 

[jmauld]

Jmauld: It sounds to me like you're identifying the major benefit of a Watts to be the roll center relocation, and that's something that I STRONGLY suspect is true.

I do think it is a benefit. I don't know if it's THE major benefit. I am skeptical of the watts link as well, for the same reasons that you are. Theoretically, the watts link should provide consistent handling in both directions, where the phb will not. However, I can't quantify that, and I suspect that the majority of the people on this board wouldn't be able to feel that inconsistency on a track. While a professional driver might.

I also think that a stiffer sprung setup will show less of a difference between the two.

 

[Norm Peterson]

And I STILL want to know exactly HOW changing a lateral-location device dramatically improves ride quality... Particularly on the street, where vertical motion is most likely less than +/- one inch of suspension travel...

The discussion seems to have drifted a bit from Dave's original point of curiosity.

I think we first really need to know more about the kind of PHB those claiming this sort of benefit swapped, away from along with any other rear suspension mods on their cars.

Rear spring rate will certainly influence how big the differences between the two varieties of WL and the PHB are.

I doubt that anybody would really question the value of symmetrical behavior if everything else about the car and its rear suspension loading was symmetrical as well (which it isn't).


Norm

 

[Whiskey11]

Dave, I think one area that the watts link might have an advantage is in perceived head toss over rougher pavement. Even with rod ends you are still talking about a several hundred pound axle moving laterally under the car which is going to pull and push the chassis around as it moves laterally. The watts link will not do this. Obviously a rod ended PHB is going to be a lot less movement then say a Poly one but there is still a lateral displacement going on. That helps with driver confidence too.

As I'm sure has come up before though, I think that a PHB's disadvantages are less noticeable on big open road courses where the differences are quite profound in an autocross environment. You can actually feel it plant and unplant the rear wheels in quick transitions and it is a disconcerting feeling when you are trying to navigate a slalom quickly or the course you are on is transition heavy.

 

[Sky Render]

Steeda makes a weld-in "competition" panhard bar that allows roll center adjustment...

http://www.steeda.com/store/steeda-mustang-adjustable-panhard-bar-555-2552/

 

[SoundGuyDave]

I do think it is a benefit. I don't know if it's THE major benefit. I am skeptical of the watts link as well, for the same reasons that you are. Theoretically, the watts link should provide consistent handling in both directions, where the phb will not. However, I can't quantify that, and I suspect that the majority of the people on this board wouldn't be able to feel that inconsistency on a track. While a professional driver might.

I also think that a stiffer sprung setup will show less of a difference between the two.

I did the math in another thread, somewhere, but... Assuming a roughly 40" length, and using basic Pythagorean Theorem, you get this:

Travel Shift
2 0.050
1.75 0.038
1.5 0.028
1.25 0.020
1 0.013
0.75 0.007
0.5 0.003
0.25 0.001
0 0.000
-0.25 -0.001
-0.5 -0.003
-0.75 -0.007
-1 -0.013
-1.25 -0.020
-1.5 -0.028
-1.75 -0.038
-2 -0.050

Now this is in pure bump or rebound. However, the numbers still don't lie.... With a total of 4" of stroke cycle, you're only looking at 0.100" of axle displacement. In a roll condition, where one side is up, and the other is down, I would posit that you could just double those numbers. In a situation where one side is at 2" of compression, and the other at 2" of extension, you're still seeing less than 1/4" of total axle displacement from rest. Given that tire carcass deflection is several multiples of that, I bet it would take somebody like The Stig to actually feel the difference. At that level of loading, I would bet that you would be getting wheel flex that would approach the amount of axle displacement allowed by the PHB. Given the (relatively) small amount of axle offset involved, I would hardly say that the handling is appreciably asymmetrical, but I will grant that on rapid direction changes (slalom), even that amount of mass motion might be appreciable.

I'm still pretty convinced that the "big change" that everybody keeps talking about with the Watts comes from roll center height tuning, and NOT from a "more stable" rear axle position relative to the chassis.

The proof will be in the pudding, but until somebody steps up with the hardware, I doubt that the two camps will come to a consensus.

 

[jmauld]

The discussion seems to have drifted a bit from Dave's original point of curiosity.

I think we first really need to know more about the kind of PHB those claiming this sort of benefit swapped, away from along with any other rear suspension mods on their cars.

Rear spring rate will certainly influence how big the differences between the two varieties of WL and the PHB are.

I doubt that anybody would really question the value of symmetrical behavior if everything else about the car and its rear suspension loading was symmetrical as well (which it isn't).


Norm

I've been doing some binging and reading this morning, and saw that you've had a similar discussion with another group back in 2005.

It still surprises me, that I can't find a back to back comparison, with raw data. Perhaps that speaks to just how little of a difference there is between the two setups?

 

[NoTicket]

The discussion seems to have drifted a bit from Dave's original point of curiosity.

I think we first really need to know more about the kind of PHB those claiming this sort of benefit swapped, away from along with any other rear suspension mods on their cars.

Rear spring rate will certainly influence how big the differences between the two varieties of WL and the PHB are.

I doubt that anybody would really question the value of symmetrical behavior if everything else about the car and its rear suspension loading was symmetrical as well (which it isn't).


Norm

I have zero other suspension modifications. Right now as my car sits in the driveway it is completely stock other than an MGW shifter and the Whiteline trans mount insert. I had the Whiteline Watts on, but took it off and sold it.

For those not familiar with the freeways and expressways of the San Francisco bay area it is very easy to have well over an inch of suspension travel just driving to work on stock springs. One of my favorite test areas is a rather screwed up dip in an overpass that causes the rear to lift and then nearly bottom out coming down at around 55mph. In stock form the rear end shimmies back and forth during every bump/rebound cycle. Now I understand that going to a better PHB would eliminate the slop in this motion but the motion itself will still be there due to the nature of the PHB geometry.

I have a 20 mile (each direction) commute every day over some pretty shitty road conditions. I encounter more suspension travel here than anywhere outside of some particularly large berms at some courses.

Frankly, though I would like to contribute to the knowledge base more than I currently have, I am not really that interested in convincing people of the benefits of the Watts. I personally felt a big enough difference after installing it that I didn't feel the need to do much else to the car. I would like it if I were able to do a comparison with a rod ended panhard. Unfortunately I don't have one available, and since I already know how a watts feels in comparison to the stock phb am reluctant to waste the money finding out, since I'm fairly certain with the road conditions around here it is at least partially a geometry problem and not entirely a slop problem.

 

[NoTicket]

I've been doing some binging and reading this morning, and saw that you've had a similar discussion with another group back in 2005.

It still surprises me, that I can't find a back to back comparison, with raw data. Perhaps that speaks to just how little of a difference there is between the two setups?

It speaks to the lack of resources of internet forum posters more than anything. Griggs claims a 2 second improvement all else being equal, but they are a manufacturer with a vested interest. So are most other parties that have the time and money to swap out various suspension parts while at the track.

The only proper way to get reliable data is to have two of the same cars set up the exact same way, except the watts, with the same driver doing laps over multiple days while not being told which car is which. Lap times can change for too many reasons, one of them being track temp, which changes so quickly and frequently it is nearly impossible to get reliable data in just one day.

 

[Whiskey11]

I did the math in another thread, somewhere, but... Assuming a roughly 40" length, and using basic Pythagorean Theorem, you get this:

Now this is in pure bump or rebound. However, the numbers still don't lie.... With a total of 4" of stroke cycle, you're only looking at 0.100" of axle displacement. In a roll condition, where one side is up, and the other is down, I would posit that you could just double those numbers. In a situation where one side is at 2" of compression, and the other at 2" of extension, you're still seeing less than 1/4" of total axle displacement from rest. Given that tire carcass deflection is several multiples of that, I bet it would take somebody like The Stig to actually feel the difference. At that level of loading, I would bet that you would be getting wheel flex that would approach the amount of axle displacement allowed by the PHB. Given the (relatively) small amount of axle offset involved, I would hardly say that the handling is appreciably asymmetrical, but I will grant that on rapid direction changes (slalom), even that amount of mass motion might be appreciable.

I'm still pretty convinced that the "big change" that everybody keeps talking about with the Watts comes from roll center height tuning, and NOT from a "more stable" rear axle position relative to the chassis.

The proof will be in the pudding, but until somebody steps up with the hardware, I doubt that the two camps will come to a consensus.

The S197 8.8, assembled and lubed without wheels/tires weighs in at 175lbs. Lets say the wheels/tires are 50lbs each for the sake of simplicity (although that number isn't that far off from a decent wheel/tire setup). 275lbs is accelerating, in some fraction of a second, laterally .05". I don't think that number is insignificant although the math hurts my head at this time in the morning.

I like to think of what the PHB is doing in terms of force vectors and how those force vectors are changing. In the PHB arrangement at factory height there is this awkward planting/unplanting thing going on in a corner through the forces in the PHB interacting with the chassis. My ever so popular MSN Paint picture:



You can see the force vectors associated with the stock PHB configuration. Obviously this effect is reduced if the PHB is level (like it is supposed to be) but it will still change depending on the variations in the height of the PHB's chassis mounting point relative to the axle point. A watts link doesn't have those effects because the arms on the watts link are equal and opposite in angle and the forces cancel each other out.

If I wasn't going through the academy this summer I'd be thrilled to compare the two back to back but I'm not sure I will have time to test the two, or the funds for that fact to test the rod ended PHB vs the watts linkage.

 

[Gray Ghost GT]

My money is on the instrumentation showing ZERO change in peak lat-g, Vert-G or raw lap times. At least to me, those are the only metrics that matter. If there's ZERO gain, I would rather spend less money and carry less weight by sticking with a PHB, even if I had to add brackets to relocate the roll center.

I think that a PHB's disadvantages are less noticeable on big open road courses where the differences are quite profound in an autocross environment. You can actually feel it plant and unplant the rear wheels in quick transitions and it is a disconcerting feeling when you are trying to navigate a slalom quickly or the course you are on is transition heavy.

I think the differences between a PHB and any watts link become more evident on those road courses that have more tighter turns and esses vs. those circuits with long straights and high speed esses - all other suspension factors being equal. The more technical courses often require the car to make quicker transitions; fighting to keep the wheels planted as the weight and momentum of the car shifts - symmetrical vs. asymmetrical motion - that should lead to better lap times or improved session times after a 20 to 30 minute stint. It would be interesting to see the data though... an interesting physics and geometry problem to assess.