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Hi Bob,

That was fun. I have a predilection for Volvos - my first car was a '71 164. Car was a joy to drive - 3L-PHR Dana rear, SLA-IFS, But the car was tall and narrow by today's norms, and the skinny stock tires resembled bicycle tires more than car tires. Unibody. Yeah! Around 2,800 pounds as I recall with a straight six, with an interior cabin volume that was close to that of an A/G body. The Volvo in this video is an older model (122?), but still, quite tall and narrow by today's standards. I haven't watched any of his other videos but I'm sure packaging wide-body C4 things into a narrow-body Volvo was a MAJOR headache. (An A/G body is somewhat intermediate in width compared to a C4 and a Volvo.)

So he describes two ways of getting the RCH: one by getting an instant center as defined by the links as they move in response to vertical suspension motion, and another by plotting the lateral migration of the center of the contact patch as the suspension moves up and down. It's a shame he didn't plot this in the same way as he did for the link-centric definition, but his method amounts to constructing a normal to the path of this CPC migration, and seeing where that normal intersects the vehicle centerline, where the height of that intersection point would be the CPC RCH. So, two different methods, and two different RCHs.

Note that the first method is independent of the lengths of the links. But the latter is highly influenced by the length of the links. In fact, the latter is a function of the former, but with the modification of link length.

So I think (and I hope SSM comments) that the real question is, if the two methods are related but different, which one is more relevant? Which "counts" more? Or more fundamentally, why do we even care about RCHs?

First, let me use acronyms to reduce typing. I'll call the first method, which is the one we see in videos and in texts, the "LIC" (Link Instant Center) method, and the latter the "CPC" method (his acronym - Contact Patch Center.) Let me use another acronym as well: LLT (Lateral Load Transfer.) I'll further take this to be considered per unit transverse acceleration, which amounts to the car's lateral acceleration at a given constant speed in a turn of constant radius. We could take that acceleration to be 1g, for example. LLT is more-or-less directly proportional to lateral acceleration, so I'm talking about the ratio of the former to the latter.

If we ultimately care about LLT in a turn (btw, SSM, your previous reference to roll stiffness is really a reference to LLT) then the LIC method is what counts. The CPC method is a measure of lateral tire scrub and amounts to a forced tire slip as the tire rolls over bumps or the car rolls. It only has a transient effect on forces imparted to the car as the suspension moves up and down. That is to say, it has no steady-state consequence. LLT, on the other hand, has very important consequences in a steady-state turn. This is because it determines the difference in vertical tire loading between the two tires on a given axle (that, plus the spring/sway-bar contributions in roll.) And this difference determines things like ultimate lateral grip (going back to how tries don't obey the laws of Coulombic friction,) and induced tire slip angles, which brings us to the matter of understeer/oversteer when we also consider what the other axle is doing. LLT is gotten from the LIC method plus the spring/sway-bar contributions in roll.

Again, CPC is a transient-only effect and I think is relatively unimportant. LIC has transient and steady-state effects. CPC does matter for transient bumps, because it imparts a lateral force to the car which, in turn, is reflected back to the wheel as a modulated coupling mass. I wrote about this a lot with respect to live axles with a high (LIC) RCH, in that a high RCH couples a surprisingly high fraction of the car's sprung mass to the unsprung mass of the bump-affected wheel.

Anyway, that's my top-of-the-head reaction - I'm probably forgetting something...

Best,
MAP

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Incidental remark, just to muddy the waters even more, as if they weren't already sufficiently muddy:

Bob, two posts ago, I said that one effect of tire compliance is that it causes the car's true roll axis to migrate toward the ground. Generally speaking, but not always, this migration is a good thing. In the case of an A/G body and its stock geometric RCHs of about -2" in the front and about +18" in the rear (or about +6" for the roll axis height at your COM location, disregarding tire compliance,) this is certainly a good thing, at least with respect to handling over bumps at the car's rear.

So have you thought of testing unusually soft tires in the rear, such as what you get with a tall sidewall? Soft tires make the car's steering response more sluggish, but they will improve handling over bumps and reduce your car's understeer. It might ultimately be a faster way around turns, and even better, you may not have to change your rear at all. To test this, you could swap a set of stock MCSS tires for the rear. Of course, ultimate grip in a turn will be reduced (to restore that, go with wider tires and softer compounding,) but it will tell you a lot about handling characteristics over bumps and the car's understeer/oversteer balance.

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Cool video, and methodology thanks for sharing. I hope all this produces a serious recipe for you Bob.


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Heads up: the fun starts when trying to apply the CPC method to the stock rear. Depending on how the rear is constrained, you either get a very low or a very high RCH (!)

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I take everything as food for thought. Craig is one of the most interesting builders you will ever meet, talented, smart, persnickety and PPPppppaaaaaatttttiiiieeeennnnttt, patient.
Episode 47 on his sway bar build I watched a dozen times for inspiration.


Had a little time today and being a beautiful day put an easy 30 miles around the block. A stop at a used car lot looking for my quest for a cherry Trailblazer, some cheap Sunoco 94 octane, a blow through at the car wash to clean the rubber off the tailpipes and a trip to see my friend with the 65 Olds wagon. Looks like we will be swapping the converter soon in it.
Back in the shop sitting full tank, ride height, with a bullseye on the drivers door to mark CG height, fore-aft. That on a black door, with ok old gloss, and a white China marker + to stare at for the next couple months. I then lean back in the comfy shop chair, stare at the car and wait for that epiphany. There will be a lot of that going on before something changes in the rear susp.

This Sat morning coming is autox in Harrisburg, Hurricane Ian, may have something to say about that. To early to tell but the weather forecast didn't look good for Sat. Haven't driven the Falken RT660 in the rain, it's said they are ok in the wet, don't need to find out. Autox is a 160 mile round trip.

If I go it will be a cold morning, only 70 for a high, won't need to spray tires. All four previous 16 run days were 90 or higher, we sprayed the last event.
Setup:
Front shocks cranked up, 14 Comp - 14 Rebound.
Rear shocks 0 L Comp, 0 H Comp, 8 rebound to start. Will back down if, when hop shows up.
Spohn adj rear sway bar is currently and at last event on it's middle setting. As a S&G experiment with nothing to lose will set it to full stiff. I need to see if I can tell how much effect a lot of rear bar has on a car that had oversteer. Set at a full stiff rear bar I have driven the car on many times, it was my drag race setup. For some time after drag racing i would leave it full stiff. Along with that bar setting the LCAs in the rear were dropped to improve the drag racing IC. I never liked the way the car drove on the street with that drag racing combo. Better at the track, yes, also ran a right side bag, and bias slicks. But I had never driven the car with the bar at full stiff and my normal street LCA angle, middle hole.

So nothing to lose, crank up the rear bar maybe tomorrow and be able to burn some more of that 94 before the weekend.

Oh, forgot. In the shop, just staring at the car from all corners imaging how the attitude of the car is as it navigates high speed corners. Sitting back in the chair, staring at the left fender from the front, close the eyes and watch that front left corner as it turns into you, you visualize all that jacking, wow that's a lots, the result of all that caster, how much weight is that pulling off the left rear as that body lifts on that left side, man, that's the inside rear tire.

Good thing there is a couple months to just sit back and think about if there is any hope.

If you take the time to watch a few of Craigs suspension follys, you get a good grasp of how difficult it is to make changes to benefit all aspects needed. Compromise. An effort was made by him and suspension software modeling to try and find his way. He does point out something I've know for a long time and that is life is 3D, suspensions are 3D, to much concept is 2D. In his own way Mark has said that.

Cool thing is I'm doing my homeroom reading, trying to find a pertinent chapter in the Milliken RCVD to read 10 times to understand those boys. it's seem every time those boys did something they built it and beat the snot out of it, then formed opinion and finally some truths from the results.
Bob

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I watched the roll center video in bits and pieces last night. Getting 25 minutes uninterrupted to myself during the week is rare these days! This is some very interesting content. I think I understand what he is doing to calculate RCH via the CPC method... he's essentially getting a gradient of dY/dZ of the contact patch and then multiplying that by half the tread width to get the height of the pivot point above the tire contact patch, at the vehicle centerline. That calculation simplifies nicely.

So as MAP said, the LIC method is not affected by the link lengths, and it also does not require you to move the suspension. It is a snapshot, so to speak, of the point about which the chassis kinematically rolls at a given instant. As Craig notes, the RCH moves around as you exercise the suspension. So by using measurements at different heights, he is approximating the average RCH location over a range of vertical suspension height. I suspect that if you differentiated the curve to get the gradient at each point instead of taking a gradient from two points at +1" and -1", you would end up with the same RCH at each vertical suspension position as the LIC method. The trouble is there is some noise in his measurements which gets amplified during differentiation, so a simulation would prove that better than real data. If I'm right, the CPC method gives you an average of the RCH over the range [-1", +1"].

I disagree with Craig that an analysis of the pivot points is inferior to his method. By the looks of it, he would have been time ahead to have measured the link positions and simulate it. He seems pretty sharp, and I bet he could develop a spreadsheet to determine the instant center locations using 3D coordinates if a 2D simplification doesn't satisfy him. A 2D simplification to find the Y/Z coordinates of the inner arm pivot would be to take the intersection of a vertical-transverse plane passing through the arm's ball joint with the axis of rotation of that arm. If you want it more precise, you have to define the plane of each arm using the 3 measured points (your two arm bushing points can be anywhere on the axis of rotation, so no need to estimate the center of a bushing or rod end, just use the end of the shaft), then find the intersection of the upper and lower arms which defines an instant axis, and then find the intersection of that axis with a vertical-transverse plane through the wheel center to find the front-view instant center.

https://www.eng-tips.com/viewthread.cfm?qid=374074

See the 6th post down, by Jack Action, with some links to how to determine this mathematically. The last link to use the instant axis to determine the front-view instant center is dead, but extrapolating the axis to a given X location is the easy part. You could make a spreadsheet using these equations and have it spit out the IC and RC locations.

Having a high RCH not only makes the car handle awful over bumps, but it also makes the car act like it has a bind in lateral transients. When you turn in, the rear tires develop lateral force before the body starts to roll. The lateral force, with a high RCH, causes the tires to transfer load to the outside instantly. With a low RCH, you don't get this and the tires don't transfer load until roll rate creates damper forces and roll angle creates springs and bar forces. That can cause imbalances in tire lateral load transfer distribution during transients (turn-in, slalom, etc) and upset the balance of the car.

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Bob, I think you'll find that more rear bar will spin the inside tire on corner exit. The Trutrac acts like an open diff at some point if you don't have load on the inside tire. I think I commented to Jason that I felt it doing that when I drove it.

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I would disconnect the rear bar completely before I'd put it at full stiff.

Speaking from a LOT of experience, these cars do NOT like a lot of rear sway bar entering, mid turn, or exiting a corner.

I like your shocks settings...leave them there. But soften the rear bar way up, trust me on this...


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Bob, try the soft rear tire experiment. This is incredibly low-hanging fruit.

To be very clear: a high rear RCH means the CPCs of the two tires do a lot of lateral scrubbing as the rear works over bumps. (Yes, at higher, mass-controlled frequencies where the body is essentially grounded.)

With short, stiff sidewalls, that scrubbing "spends" a lot of the tire's traction circle to stay attached to the pavement. If you hit bumps in that condition, you could break loose, and that's not a good outcome in a turn or with throttle or brakes, or some combination thereof.

A tire with lots of lateral compliance "spends" less of its traction circle fighting that lateral scrubbing, yielding better traction over bumps. It also yields a softer ride, but I know you're not much concerned with NVH.

A soft tire does yield a slower, duller steering response, but I'm guessing not of a magnitude that's likely to be significant in a road race scenario. In fact, the reduced understeer and improved traction over bumps (back to the street in this case) could actually make the car faster.

The trick is to maintain the rear traction you have now, so the recipe would be a tire with a tall, soft sidewall, but with the widest, stickiest tread you can fit.

A stock MCSS tire will likely give you the first two out of four, so you'll get a good sense of handling over bumps and some sense of a new understeer/oversteer balance.

Based on past experience, I know you like to stay inside the box, but breaking out of the box can sometimes bring surprising dividends...
__________________________

Further about the CPC RCH: the center of the contact patch traces a smooth curve as the suspension translates up and down. The curvature of this path is likely to be so small that it could be well approximated by a straight line, at least for modest translations like +/- an inch. The inward-projecting bisecting normal to this line creates an RCH based on its intersection with the car's centerline. We could certainly get mathematically precise about this by invoking derivatives (of first and higher orders,) but this simple geometric method could be done with a pencil and a ruler.

On edit: Yet another occasion where I wish we could all be standing in front of whiteboard! This is very cumbersome to convey with words, but a picture or two would make this easy for even a third-grader to understand. The CPC RCH method is literally child's play, it's so simple. But anyway...

__________________________

Also, to amplify a bit of what SSM said: the vertical forces imparted to the wheels in a turn could be classified into two broad camps: one of horizontal link-transmitted forces that act instantaneously as the car turns, and another where (ignoring damper action for now,) spring/bar forces develop in response to the relatively slow accumulation of roll as the car starts a turn. Tuning the rear involves finding a comfortable balance for the driver between the instant "kick" of link-transmitted forces, and the slower "thud" of spring/bar-transmitted forces.

If good handling over bumps were the whole object, the rear RCH should be zero. But steering response would likely be judged to be slow, so that upon initiating a sudden turn, we would get a distinct transient response from the front of the car, followed by the rear "falling in" a noticeable fraction of a second later. A one-step two-step response, if you will. Or a zig followed by a zag, if you also will. Raising the rear RCH amplifies the link-transmitted "kick", but it comes at the price of good handling over bumps. So the driver needs to find a subjective balance that works best for him. That's why I recommended starting with a rear RCH of around 8" - 9" to explore this balance.

Btw, needless to say, as the rear RCH is dropped, you need to increase roll stiffness in the rear suspension to conserve LLT.

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Continued.

So yesterday's video with its CPC RCH was new to me. I've been thinking about this a bit more, and just to share:

The LIC method, which is what we're all used to for determining RCH, is the one I believe rightly deserves the lion's share of attention. From it we get link forces and can deduce LLT in a steady-state turn.
The CPC method matters only in a transient state when a wheel is going over a bump. The lower this RCH is, the lower the tire's lateral scrub, and the lower the fraction of sprung mass that's reflected back to the wheel, which is a good thing. I believe the goal with the CPC RCH is always to minimize it.

Tuning the LIC RCH is more important and more nuanced. Making this RCH zero is not necessarily the best solution, as partially evidenced by the kick vs. thud balancing exercise.

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I think the RCH derived by the CPC and the LIC methods arrive at the same answers (as a function of suspension position), as the distance between the two measurement points for the CPC method approaches zero. You can't minimize one RCH without minimizing both, as they are really two ways of measuring the same geometric roll center.

Multiplying by half the track width in the CPC method interpolates the line from the tire patch to the IC that the LIC method defines.

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Originally Posted by SSLance
I would disconnect the rear bar completely before I'd put it at full stiff.

Speaking from a LOT of experience, these cars do NOT like a lot of rear sway bar entering, mid turn, or exiting a corner.

I remember seeing your rear wheel off the ground I believe from too much rear bar.

Last edited by 1 Slow SS; 09/28/22 11:57 PM.

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SSM, on thinking further about this, I think I agree with that. In the y-z plane, as the wheel moves up and down, it is always virtually revolving about the intersecting construction lines running through the UCA and LCA pivot points. Since the wheel is a rigid body, the path of translation of any point in that wheel would have to yield the same effective center. Where things get squirrely from a motion standpoint is that especially for short, unequal-length UCAs and LCAs, suspension travel can cause that IC and thus its RCH to drift in space a lot. For example, for a restricted portion of suspension travel, the instant RCH might draw close to the ground, even though we might consider the nominal RCH to be quite different. So the CPC method immediately reveals the squirreliness of the IC as the suspension moves up and down, while the LIC method tends to be thought of mostly with the suspension near its rest position, where the IC location is relatively stationary. (Btw to get the full IC locus, one needs the first and second derivatives of the y,z path. So we can get quite sensitive to measurement noise.)

Anyway, point is, these different perspectives yield different impressions of what's happening to RCH (as it did to me,) but the same information in a global sense. Another important distinction: we have to remember that the location of the IC derived from the CPC method will be relative to the location of the CPC, and not relative to a frame of reference ["FOR"] fixed to the ground. OTOH, the LIC method customarily uses a FOR fixed to the ground.

So where this gets really interesting is for a live axle rear. With an IFS or IRS, plotting the IC and thus the RCH is simple because it can be seen as a one-wheel system.

Not so with a live axle.

We have to choose how to constrain the motion of the entire rear. We can either anchor one wheel's CPC, in which case the CPC defines the IC, so we get zero RCH as the other wheel moves up and down, or, we can laterally anchor the car's sprung mass, in which case the RCH will be our famous 18-ish inches above the ground at nominal ride height. The former creates a lot of lateral body motion with no lateral tire scrub, while the latter does the reverse. The former amounts to the compliance-controlled low-frequency regime, and the latter to the mass-controlled high-frequency regime, and comes from a Hamiltonian constraint of minimized energy. Bumps usually fall in the high-frequency regime, so this is where soft tires to accommodate lots of lateral tire scrub can really help us. As well, it can restore a more neutral understeer/oversteer balance with a front-heavy car. Or, we can instead drop the rear RCH and increase rear roll stiffness for conserved LLT, reducing the "kick" part, but making the "thud" part sharper. (Softer tires also reduce the "kick" by dropping the rear of the effective roll axis.)

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Ron, Lance - that's my recollection too. With limited rear traction, start with the least possible rear roll stiffness and work up carefully from there. Reducing the rear RCH helps too if that's an option.

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[Linked Image from i.imgur.com]

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Hi Brent - could you explain that further? Thx. Also about two different RCHs, that's true for any suspension. We normally jump immediately to the fixed-body scenario, so that's where the suspension's effective point of rotation (i.e., that IC) with respect to the body comes into play. The IC at one CPC on an un-bumped wheel thing (i.e., the trivial case of the suspension and body rolling as a unit over a one-sided bump) prominently comes up in the case of a live rear because we're immediately confronted with how to apply motion constraints with two coupled wheels. And must say it's quite useful to think about this in the frequency domain...

But anyway! Hope I'm not making this too sticky and boring.

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I need to apologize to Brent, sorry.

That pic is a chart of my scaling of my 86. Brent just helps me out at times posting a pic. Of the dozens of times the car was scale i could break it down to three areas of interest.
First is the three top weights. This were done with four sold shocks, 4SS.
No driver, ride height.
Second is driver, ride height.
Third scaling is no driver, rear raised 11.5" and shows a 20.5" CG on the scale.

Second set of four scalings are rear springs swapped side to side and no shocks at all.
Notable is how the crossweights got a whole lot better and how that 20.5" CG number appeared again.

The bottom set of three scaling was to see if the concrete floor level effected the scaling. Both the car and the scales were turned around in the shop bay. The individual scales are specific, LF, RF, LR, RR. i found a little deviation in gross weight of 8-9 lb, crossweights not effected much and still got the same 20.5" CG.

As someone said the ideal place to scale a car is on an alignment rack that is dead level. If i had more time with the scales i could have got my water level out and did the dead level shimming necessary to get all four dead level to each other. As this is termed silliness doing all this weighing I felt the water leveling would just be pushing the weighting into the funny farm crazy realm. I may be off a lb or two here or there but still think there was very useful info obtained.

Got state inspection stickers on the car yesterday. Unfortunately the shop latest and greatest Hunter alignment rack is waiting for a service call because of a dead head. So no rack time for the 86. I need to know that rack is spitting out good numbers, and I'm especially interested in what the rear suspension numbers are. As we know the solid axle rear still has camber, toe and thrust to measure and deal with.

After stickers put 40 miles on the car, needed to see an old guy about a ZL1 67 Vette he put together. Today another 35 miles on the car. Tomorrow was supposed to be an autox event, it's already raining, Ian is coming this way.
Being i had the rear sway bar at full stiff and the rear TA shocks set at 8 rebound I wanted to put miles on the car to get a feel of that setup. So far haven't found a corner that the evil rear bar shows up but I'm still pushing on the car. I can say that 8 rebound setting causes even me to be totally bothered by the ride quality. Every irregularity in the highway is transmit to the car, busy is not the word for it. Finally late this afternoon i pulled into a parking lot and cranked the 8 down to 2 in the rear and presto, tolerable, NOTICEABLY better. Comps the entire time was set at 0 - 0.
I'll drive, play with the car in that setup for a couple weeks coming.
Bob

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Hi Bob,

Thanks! Those videos are a lot of fun, btw. He does a great job with them.

Back to the numbers: if you can just share your front and rear axle heights, we can confirm the COM height. Your garage floor doesn't need to be exactly level to calculate this number with good accuracy, as long as you're initially level to within a degree or two (most garage floors are canted about one degree for fluid drainage.) But, front/rear weight balance will show some sensitivity to this inclination.

Need to say it once again: if you've got some soft, skinnier tires to try in the rear, you should test them. Put it this way: you're probably thinking about the 3L-PHR in order to drop the rear RCH from the stock towering 18" (+/-) to something lower, like 8" to 10" as a first guess.

But I've repeated what Greg Locock said: a car "...doesn't roll about its roll centers." That's because we have compliance elements in the force transmission chain between the ground and the sprung mass, chief of which is tires. One effect of tire compliance is to reduce the true roll axis height. And the amount of that dropping could be quite significant depending on how soft the tires are, possibly even comparable to what a 3L-PHR might do for you. Now softer tires wouldn't yield exactly the same changes as a 3L-PHR, but the overlap is significant enough to be well worth exploring. Plus, you'd get a softer ride. Plus, you'd probably need less dampening at the rear. Plus, the inner tire would be less likely to part with the ground in tight turns. Plus, you'd get some free reduction of understeer, which you probably have in spades.

Again, this is just for experimental purposes. If you really like it, just go a lot wider and stickier.

What do you think?

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No apologies needed Bob. When I posted the picture I meant to put a description with it, something came up and I completely forgot to come back and edit.

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The evil rear bar shows up on a heavy braking corner with a quick turn in. I used to recreate it in a church parking lot.


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If you liked Craig's other video of the RC his follow up is a necessity. So many thing he puts in prospective as he simplifies the front suspension pickup points for his car.


Ya know it took me a long time to find his name and who he was, is. You won't find that anywhere on his Throttle Stop Garage channel. I can read some of his facebook page, you won't find personnel on him there either.
I drink coffee, have said a dozen times I should order one of his coffee cups, time is now.

Mark as far as tires go only have two different tires for the rear. The autox tire, Falken RT660 is a 275/40x17, 200 rated which I've run at 32 predominantly, street and race. It's a super sticky tread and a pretty stiff sidewall. My other tire is a 7 year old BFG Comp 2 Summer in a 255/50x16, when new a 315 rating and now with old age not as good. Old, tired, and not good at the autox but OK for the street for every day use for another year. I ran 36 psi rear pressure with the Comp 2 tire. I had Hoosier A6 which I gave away, had Hoosier QTP slicks which i threw away, has Mickey drag radials which i gave away. Forgot about the M60x15 a friend gave me just to see if i could burn them off. They were so old and hard you couldn't burn them out, just could constantly haze them.
So yep had a few different tires in the back and got an idea how a soft tire feels as the rear rotates around.

I don't see any tire available that could just be thrown on the rear to try. When the Rt660 are gone the replacement will possibly be these Continentals.
https://www.tirerack.com/tires/tire...vehicleSearch=false&fromCompare1=yes

I'm still looking for a place that has lots of flat,good looking blacktop that doesn't mind a guy doing a couple spin outs at high speed.

Bob

Last edited by mmc427ss; 10/02/22 06:11 AM.
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Too bad you don't have something you could throw on. I'm not sure what to say - maybe try running a very low tire pressure? You can actually get an idea of tire vertical stiffness by measuring axle height as you lower that end of the car to the point of barely touching the floor, then releasing the jack entirely and measuring the axle height in that fully-loaded condition. The difference in height will be kind of proportional to vertical tire compliance.

It's a shame you couldn't the original A/G body tires, which were 195-75R14s - soft as a pillow.

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Hi Bob,

Just a bit further to say that the easiest way to soften your tires is to let the air out of them, to a point. (10psi? Wild guess only.) I'm sure you'll find that point sanely and safely.

I really like Craig's videos. On that last video, though, couldn't say I agree with all that he said (!) but still, a great video.

Have fun,
MAP

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I find Craig's approach to most everything he does entertaining, enlightening and it's his quest to figure stuff out and produce from scratch that I like. Although his garage is really tiny he has a wealth of knowledge and tools stuffed in it. It a shame that restrictions from Rona, and the difficulty and expense to get things across the border slows everything he's done down. I've watched more than 1/2 of his videos.
Ordered a coffee cup from his today to help support just a little.

Having rained now for most of Sat and Sun spent time surfing and reading pieces of my new book, RCVH. One of the interesting points made in several sections is about CG and how you need to know where it is is you want to play with improving handling. Even pages of how exactly to arrive at a CG, and how my procedures mimic their process. Exception is I didn't need to struggle with trig, the scale processor and the calculators on line did the hard part.

I email Susq SCCA to see what their last event of the season is, Oct 29. I may be able to make a few more runs on the car then. We'll see.
My friend with the 65 Olds station wagon is in process of swapping in his old torque converter, a 9" 3500 stall, to see if the 8" 3500 stall converter in the car now is WAY to loose. Intent is a mid 10 second boat in the 1/4. If he make a trip back to Cecil County I may go with him and also make a couple more passes on my car. Just to see if I can get my truck engined, single exhaust, 3700 lb turd to run low 12 on the Falkens. In another month or so the Summer only Falkens need to be removed and my old Comp 2 Summer go on for the Winter driving. That may sound contradicting, it is, but it's not.The Falkens need to be stored about 50 degrees for the Winter, the Comps are soon retiring.

Oh, only about 50 miles needed to drive to hit my 2000 miles annual goal on the 86. It's why i still have the car, because i like to drive it, and do drive it, sometimes pointlessly, just to, drive it. To many of my car friends have cars they put 100 miles on a year, just don't see the point to owning a garage queen.
My car will soon hit 175K, bought almost new with 9200 in 1991. It's been a toy car since 12/01, the wife says money pit, but being a toy I can play with it any way i want. Sure would be fun to run a road course someday.

Happy motoring.
Bob

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Being it has been raining now for 4 days that's both a bad thing and a good thing. The car has been high and dry since last Thurs, that's the bad thing, the good thing is here in PA I heard they lifted the drought restrictions for most of the state. That's a huge good thing, more important than the car.

So in the shop staring at what the next part of this new Winter project is, will be, the first order of business was finding the static CG, which I believe is done and accurately done. But we know just like every suspension mod we look at in the static mode and drive the car in anything but the static. But ya gotta know what ya got before ya start.
So the process begins with a doing more measuring. And being someone that needs to know asking for what other have for RC is a waste of time. And my car is unlike most others so my numbers only represent my car. Disclaimer.

Was laying under the front of the car and just eyeballing with the help of a straight edge, a digital angle gauge looking for an idea of getting actual, accurate points of interest located. Locating that IC is the key, and think will need to have wheels removed to locate it. That is the difficult part, IC location. I think once you have IC the RC is easy to find.
When I had the entire front suspension out of the car a few years ago I played with RC measurements/location and a 2" number kinda showed up. Looking now to do the exact location.
The front suspension went through major surgery to improve it a few years ago. No need to make any changes up front, just need to know what it's RC is so the rear's RC can play nicely with the front, like more nicerly, ain't a word.

The rear's RC should be easier to find now because I have a pair of those 11.5" cribs built. Put the rear tires up on the cribs, jackstands under the front at #2 body bushing and shim the stands to bring the car to ride height + 11.5" up front. Plumb bobs, tape measures, and angle gauge should make rear RC location not a week long project to get done. May even be able to use the creeper to roll around under the car at that height.
For S&G the 18" rear RC number for stock suspension I've heard, should be interesting to see how that guesstimate fits my car.

Wet weather, colder days and COLD nights is here now. Before that concrete floor in the shop gets to cold to work on gotta get the simple RC numbers on paper. Then I can think about how, if at all, I go drastic change to the rear suspension.
My last chassis project took a year from the first thoughts of the why and what needed to be done to actually done and testing. Oh yes, and a million words written about a simple subject, sway bar.

Yesterday made another mod to my quick stick camber gauge. It's simply a straight 1/4" x 1" X 18.75" alum alloy flat stock, it's used to touch the wheel's alum bead across the center of the wheel, at plumb. The 1/4" thick edge is the straight edge used to measure. The digital angle gauge first is used to plumb the alum measuring off the alum's 1" face. Plumb on any camber gauge is necessary to insure accuracy. Then the gauge is flipped to the 1/4" edge and camber read on the gauge. Worked great for the past couple years. But needed a little more done to make it a 30 second per wheel tester. And it was raining.

Yes i do have a good caster/camber gauge for doing a full alignment. It requires pulling the wheel center caps, and the hub bearing caps to use it. When I found that process as a PITA method the quick stick camber setup was made.

From my sway bar arm's scrap steel ( leftovers ) a 3/4" x 1 1/2" x 1 1/8" block of that steel was whittled with polished parallel faces to .001". This screwed to the center of that alum and dialed in parallel. Now the magnetic digital gauge has three steel faces it can hang on. It was a PITA to lay on the floor while trying to hold the alum plumb while you flipped the gauge 90 degrees to find camber angle. That steel block sure made that easier, but not happy yet.
Holding the alum's 1/4" edge against the wheels bead needed improvement. On one end a Tee has been made. This will allow that T end to have 1 1/4" of surface touching the wheel' s lip, not the 1/4" wanting to rock on a polished surface. The side of the T is curved to match the wheels curvature. I dropped that mod off at the welder's shop this morning for him to glue it together.

That tool when just a piece of alum and a digital gauge worked wells but a couple rainy days and some "nothing to do moments" that tool should be super now, may not even need to lay on the floor to use it. It along with the dozen other suspension tools I've made makes this whole suspension thing a little easier.
Bob

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