Trying to Learn squat....

[Norm Peterson]

If you're talking about the 5th wheel rising while pulling a trailer, I think that's just the reaction from the high CG load it's pulling.

I'll have to grab a few pictures of the rear suspensions on the trucks my son and son-in-law drive for a better view of anything I can find online, but it looks like one Class 8 arrangement is a sort of upside-down torque arm type (the control arm picks up above the axle and the "torque arm" itself is a link-style that attaches below the axle, the link being that curved component). That would put the SVIC above axle height close to the control arm's chassis side pickup forcing the antisquat construction line slope to be somewhere in excess of 45°.

Watch a semi's tractor running bobtail sometime.




Norm

 

[blacksheep-1]

OK guys, I may sound like a heretic, but why all the issues with "squat"..it's not a bad thing, drag racers have mastered it, if you don't want squat then weld the suspension solid and you won't have to worry about squat..dive..roll or anything else, it will be a go kart (which in reality is an extremely complex torsion bar).


The unlimited late models are all bump steer cars..very little movement, and I believe the only reason the have any suspension is to manage the ability of the chassis to sit as light as possible on the bumps. FWIW back in the day, it was rumored that this is what killed Neil Bonnet at Daytona, the car was going through the banking with the right rear shock completely collapsed (as designed) and the shock bracket broke. This made NASCAR revisit the rules and basically forbidding bump stop usage on high banks....although, I'm sure by looking at the cars at full compression it has made a comeback.

What I want you to look at in this pic, is the left front tire and it's massive positive camber...


now here is the same class of car, in the corner..actually a good pic of corner entry and mid corner...


You can see the difference between the red 02 and the 44 who are on the stops and the blue 14 car that appears to be just starting to accelerate and the left front is starting to move back towards the positive camber position.

It would appear that the center of the corner is the least important aspect of the corner, down south we call that the "cut" as in the "the car won't cut in the center of the corner" at that point you just want the car to turn sharply, nothing else really matters and it's at the slowest point the car will ever go. What is important, is the car's entry and exit..fast in..fast out..not so much in the middle. which looks a lot like the car Phoenix (and others ) build. The big advantage over strut suspensions, (McStruts we call them) is that you can build in camber gain by manipulating the angle of the upper control arms in a stock car.. I believe this is one place where the mid 60s Camaros in Trans Am had it all over the Mustang front suspensions.
So I would suggest, that the inside tire is really not loaded, and is simply along for the ride in most cornering cases..what seems to be important is the ability of the car to squat and go on acceleration. The only time you need 2 front tires is under braking..which of course, all the dimensions..dive in particular, come into play.
IMO this is why shocks are so important, maybe more so than spring rate..the difference between a separate shock/spring combination..as used on limited late models, and the coil over shocks used on super late models is huge, walking through the pits, you can almost tell a super from a limited by simply looking at the attitude of the suspension and the range of travel.
One of the most enlightening conversations I had was at Mosport talking to some CASCAR guys about the difference between their cars and ours.. and the attitudes of the cars in the corners, being 2 different types of suspension, nothing was really transferable (that I'm going to mention) but to watch both types of cars was pretty informative, and those guys didn't use coil overs. I would bet a super late model..set up square, using coil overs, would walk the dog on just about anything short of an open wheel car there.
So, the point is, why fight the squat?, why would you try and eliminate something that is going to help launch the car off the corner? what you need to do IMO is manage it, not eliminate it.

 

[Grant 302]

But that particular sketch was only intended to show the force equilibrium side of the discussion. The SVIC is "virtual" in this very specific situation - out there "at infinity" in a purely horizontal direction for 0% antisquat.

Understood that it was just an example. But it does conveniently show how a 0% AS condition exists that is above the ground plane.

If you start with that sketch and drop only the chassis-side pickup elevations down by the same amount (lowering the ride height a little), the UCA will change slope faster than the LCAs. The SVIC now has some real location and anti-squat now has some non-zero value (the situation that starts out with all of the arms/links horizontal actually goes into "pro-squat" with lowering).

This is why I see anything under 100% AS as being 'pro-squat' (IMO-arguable) because any dynamic squat increases until a relatively 'steady state' is reached.

This also 'proves' that actual AS is non-existant when the IC below the LCA connections and above the ground plane, *despite* the conventional definition that would put it between 0% and say 20-30% depending on the lowering of the particular car.

In reality, it would only be a momentary unweighting of axle weight off the ground. I think you'd have to look for a very brief decrease in vertical tire deflection down at the ground before the real, physical weight over the rear axle drives it back down. Kind of self-correcting.

Agreed that it happens in the brief time that it takes for the jerk to happen and suspension to load. Measureable in the mili to hundredths of a second. And it only happens if and when the lower arm is pointing below level. 'Self-correcting' is a good way to look at it. I understand that this is a problem for drag racers and possibly inducing hop off the line, but I've never seen it have any issues for road racers.

With my recent driving comparing the +3º LCA GT and the -2.2º Boss, I see difference as the rate which you can apply throttle. Mid turn, the GT can take a rapid 'stab' of the throttle and the Boss needs to be 'rolled' into. Right now it seems the Boss can take more throttle and ultimately put power down better, considering it's stock and doesn't corner as fast as the GT.

OK guys, I may sound like a heretic, but why all the issues with "squat"..it's not a bad thing

Rob, I want to credit you with shining a LOT of light on this subject over the years here without making any of us feel dumb/bad/stupid about this. Thank you for *everything* you've taught me so far. You are a true asset to TMO.

Ultimately, I think one of the issues is the drag race oriented aftermarket for the Mustang community has effectively sold a lot of us on running enough anti-squat to launch the cars and little else regarding road racing. Feeling the benefits of a better launch and hop reduction sealed the deal for many of us. Winning at stoplights didn't help either. I certainly drank the anti-squat kool-aid.

 

[Grant 302]

Some one has two mustangs!! On the 23/24 I will have two days at the track so I can try swapping the LCA angles and see what my times give....

Guilty. I haven't wanted to swap LCA brackets on the GT/FakeR to make it happen. I have the 4" Whiteline bracket on there and need to put the FRPP 2"/3" on there to make any adjustments while keeping the rear relatively lowered and level. And this vacation killed at least two track day opportunities for me, including this weekend for Chuckwalla. No way I was gonna have the car prepped on time and I'm still feeling the jet-lag and an additional hour for daylight savings that kicked in while we were gone.

Looking forward to your results next week!

 

[blacksheep-1]

Back in the day there were 2 trains of thought for suspension..a guy named Dick Guldstrand..( http://archive.constantcontact.com/fs032/1102766514357/archive/1110820883755.html) who was a brilliant Corvette guy would try and get all the parts to complement each other and work in harmony, the other guy..Herb Adams..(https://www.hemmings.com/magazine/mus/2011/12/Herb-Adams/3706751.html) who basically said who cares about spring rates, run the softest possible and fine tune with shocks and bars. I always thought Guldstrand's stuff was ultimately faster, but when you needed something to work RIGHT NOW ..you could not beat the Herb Adams approach. For that simplistic reason I've always run the softest springs possible, even 6 cylinder springs to get the stick axle to conform to the track. It's fast and dirty but it works and you don't need days to develop it. with regards to auto crossing, which is generally on the gas on the brake switch backs, the Adams approach is the only way to go. As long as it doesn't violently bottom out..sign me up.

 

[Norm Peterson]

OK guys, I may sound like a heretic, but why all the issues with "squat"..it's not a bad thing,
<snip>
So, the point is, why fight the squat?, <snip>
what you need to do IMO is manage it, not eliminate it.

This ↑↑↑ .

It's OK to let the suspension actually move when you change the loadings around. It's probably the reason I don't pay a whole lot of attention to squat as something you see whether I'm running an analysis or driving the car.


Norm

 

[Norm Peterson]

Understood that it was just an example. But it does conveniently show how a 0% AS condition exists that is above the ground plane.

Yes, it does. But be careful - it only applies when all of the arms/links are horizontal. Incline the upper without changing the inclination of the lowers and AS% goes to some finite, positive value. Works the same way for the triangulated 4-link Fox/SN95/GM RWD intermediates arrangement, too.

This is why I see anything under 100% AS as being 'pro-squat' (IMO-arguable) because any dynamic squat increases until a relatively 'steady state' is reached.

Maybe we should just retire the term "pro-squat".

This also 'proves' that actual AS is non-existant when the IC below the LCA connections and above the ground plane, *despite* the conventional definition that would put it between 0% and say 20-30% depending on the lowering of the particular car.

What *not much* AS% means in terms of observable squat is that you're not getting quite as much squat as you would if the AS% was 0%. Any load transfer that's going through the geometry is load transfer that can't make the springs compress all the way down to where they'd go with 0% AS. Hence in the same car, the amount of squat has to be less at, say 20% AS, than it would be at 0%. Maybe it won't be much less, but it will still be less.

Load transfer is the independent variable here, squat is only a consequence, simply the visible evidence (in most cases) that load transfer is happening. I think it's the load transfer itself that you're actually managing - and managing that with respect to time.


Norm

 

[Grant 302]

Yes, it does. But be careful - it only applies when all of the arms/links are horizontal. Incline the upper without changing the inclination of the lowers and AS% goes to some finite, positive value. Works the same way for the triangulated 4-link Fox/SN95/GM RWD intermediates arrangement, too.

That's only a 'finite positive value' as defined by convention. What I mean is that there is no actual net upward force even with the LCA horizontal and the UCA pointing down. As squat lowers the LCA angle the UCA vertical component only matches the LCA component less the amount that the spring compresses. Some arrangements can even have both LCA and UCAs in compression to counter the total spring compression. I would call this condition 'pro-squat' despite the conventional terms and percentage >0.

Maybe we should just retire the term "pro-squat".

But I found a use for it now.

What *not much* AS% means in terms of observable squat is that you're not getting quite as much squat as you would if the AS% was 0%. Any load transfer that's going through the geometry is not making the springs compress the still further (and the car visibly squatting even more like it would if the AS% was zero or "non-existent").

That might be a good way to explain it, but in those conditions with the IC under the LCA, there's nothing 'anti' about it.

Load transfer is the independent variable here, squat is only a consequence, simply the visible evidence (in most cases) that load transfer is happening. I think it's the load transfer itself that you're actually managing - and managing that with respect to time.

Most of the load transfer management with respect to time is handled by the rear shocks. This is one of the reasons why I suggest people spend for more adjustability and control there.

Control over the time for shock and jerk is better controlled by the type of joints used. Heim joints being fast and OEM rubber being slow.

 

[Norm Peterson]

If you look at this in terms of time, the geometric 'anti' occurs first (almost but not quite instantaneously). Next to peak is the shock contribution because suspension velocity increases and then drops as the suspension approaches/reaches its new equilibriun position. Last to peak is the spring contribution because that has to wait until the suspension has reached its final position. I'm assuming no bumps for simplicity.


When the UCA points down (from the axle toward the chassis) and the LCAs are horizontal, the upward component of UCA force - remember that the UCA is in tension here - certainly is pulling upward at the UCA's chassis bracket. Upward geometric load is not limited to coming from the LCAs alone. It's getting too late for me to draw that diagram.


Happy St. Pat's Day, what's left of it.


Norm

 

[Grant 302]

If you look at this in terms of time, the geometric 'anti' occurs first (almost but not quite instantaneously). Next to peak is the shock contribution because suspension velocity increases and then drops as the suspension approaches/reaches its new equilibriun position. Last to peak is the spring contribution because that has to wait until the suspension has reached its final position. I'm assuming no bumps for simplicity.

I agree on the flow of reactions. I'd break down the geometric reactions to the LCA first because of the initial torque reaction. Through the chassis and then to the UCA.

When the UCA points down (from the axle toward the chassis) and the LCAs are horizontal, the upward component of UCA force - remember that the UCA is in tension here - certainly is pulling upward at the UCA's chassis bracket. Upward geometric load is not limited to coming from the LCAs alone. It's getting too late for me to draw that diagram.

That's generally true for our setup. But steepen the UCA into 100%+ AS range and it'll go slack or into compression over that. When the LCA is horizontal, the only opposing vertical reaction is from the springs.

Happy St. Pat's Day, what's left of it.

Thanks...still a wee bit more over here! The kids are 1/16 Irish...so of course we had to celebrate!

 

[Norm Peterson]

That's generally true for our setup. But steepen the UCA into 100%+ AS range and it'll go slack or into compression over that. When the LCA is horizontal, the only opposing vertical reaction is from the springs.

Even in that case, the UCA is still in tension. And it's doing more than just splitting the rearward load transfer with the springs - it's actually unloading the springs because once you're over 100% AS you're getting 'rise'. The UCA starts out lifting up harder than the amount of rearward load transfer is pushing down, and gradually shares the upward force to the chassis with the LCAs as the rear rises and the LCAs start inclining uphill toward the chassis.

Though I can see a UCA going slack during wheel hop.

Thanks...still a wee bit more over here! The kids are 1/16 Irish...so of course we had to celebrate!

While my wife is 1/4 Irish, I doubt I've got more than a tiny scrap of it in me. But a local family-owned and run Irish tavern was THE place to be last Saturday afternoon no matter your roots. Smithwick's (pronounced Smiddick's) from the tap, of course.


Norm

 

[Grant 302]

Even in that case, the UCA is still in tension. And it's doing more than just splitting the rearward load transfer with the springs - it's actually unloading the springs because once you're over 100% AS you're getting 'rise'. The UCA starts out lifting up harder than the amount of rearward load transfer is pushing down, and gradually shares the upward force to the chassis with the LCAs as the rear rises and the LCAs start inclining uphill toward the chassis.

Though I can see a UCA going slack during wheel hop.

I'm pretty sure that's how it gets to steady state with compression in the UCA when AS starts over 100%. The LCA does the majority of the lifting and progressively more until it eventually gets enough opposing vertical reaction from the UCA. With the UCA pointing down/forward, I think that has to reach compression for the steady state when the body stops moving up. I do think that it makes sense that the initial jerk reaction is in tension for most setups and should stay in tension for a squatting setup or any setup that reaches a steady state with both LCA and UCA pointing forward/down.

I think this is also why hop issues can be solved for the floppy OEM UCA bushings with enough AS.

While my wife is 1/4 Irish, I doubt I've got more than a tiny scrap of it in me. But a local family-owned and run Irish tavern was THE place to be last Saturday afternoon no matter your roots. Smithwick's (pronounced Smiddick's) from the tap, of course.

It's Muldoon's in here in Orange County. Doesn't need to be St. Paddy's for us to go down there for Pot Roast and Guinness!

 

[Mad Hatter]

Ok, had a long day at the track and a great first day of wheel two wheel racing. We had three runs during the day. two of 10 min and then a 15min race. Managed to get third overall!!! First was a Aston GT3...... saw it only as a far away spec in the horizon!!

The suspension was with the LCA on the highest setting so well under the 100% squat line...

The car felt very well planted with good corner exit and was able to get on the power sooner the before.... On the last race I had a Cayman GT4 Clubsport stuck to may tail for 10 laps. He got me on braking but corner exit would leave him behind quickly. Great introduction to wheel to wheel!

My times were almost a two seconds off my best at this track.... So need to test the LCA with a little more anti-squat next time. But then again thats with R7's that are going on to 20 heat cycles

If it was the tires, that would mean the more squat inclined suspension. was a big success because I had no problem with rear traction on cycled out Hooisers. OR maybe leave it all alone and get new tires......

 

[Grant 302]

OR maybe leave it all alone and get new tires......

Go for broke! I say new tires and LESS anti-squat! But maybe that's just the crazy talking!

 

[Mad Hatter]

It will probably be just the tires and leave well enough alone for now

Had ten minutes of this today.... longest dam 10 minutes....

...

https://www.facebook.com/video.php?v=10213646673619881

 

[Grant 302]

Can't see the video. Probably an issue on my end?

It will probably be just the tires and leave well enough alone for now

There's too much reason and common sense in that proclamation!

 

[Grant 302]

Drove the Boss around this morning...it's an education learning to drive my two cars differently. I just might have to make the hardware changes to the FakeR before my next track day.

 

[Mad Hatter]

I just looked at the date I bought and mounted my current set of R7's...... Dec 2016!!! Even though they were worn out, It was still much harder to break the tail loose then before.... Before being with lots and lots of antisquat

 

[Mad Hatter]

Can't see the video. Probably an issue on my end?

Not sure why I can't post it.... have the rules changed and you can not repost facebook videos any more???

 

[DocB]

The suspension was with the LCA on the highest setting so well under the 100% squat line...

Is your car lowered now and by how much?
How much is the "highest setting" lower than OEM and how many holes below that one?