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[240] Show us your Panhard mount relocations

Its also better to drop the axle side vs the body side because it will help lower the Roll center of the rear.

Well, as long as the point where the bar crosses the centerline of the car is lower, it lowers the roll center. If you run the bar parallel to the ground, it impacts lateral loading the least, provided that at rest the car is halfway between full bump and full droop. This doesn't necessarily mean that is the best position for this application.

I have to wonder about the corner weights and roll stiffness on this car as was pointed out earlier. If it's rolling over on the left front a lot and really unloading the right rear, I might be tempted to resolve that first. Maybe combine that with a rear roll center or roll bar change to try to maintain a good handling characteristic.

I would absolutely try to diagnose and cure causes rather than symptoms, first.

Keep us posted. This is interesting.
 
I have to wonder about the corner weights and roll stiffness on this car as was pointed out earlier. If it's rolling over on the left front a lot and really unloading the right rear, I might be tempted to resolve that first. Maybe combine that with a rear roll center or roll bar change to try to maintain a good handling characteristic.

I would absolutely try to diagnose and cure causes rather than symptoms, first.

Keep us posted. This is interesting.

Agreed...in the previous thread I linked above (didn't happen to notice if you were involved in that one too), I asked about front springs, they're cut IPDs, and I suggested a front spring rate somewhere between the 475lb and 700lb that I had tried on our lemons 240 wagon.

500lb front springs, 25 or 28mm front bar, reasonable ride height (control arms pointed just slightly down, not slammed-low), and lower the rear on relatively soft springs (<200lb)...it might get better than what they showed in the video. IPD lowering springs are a joke for roll stiffness, so it's going to dive onto the outside front and hike the inside rear.

One very old post about lowering / softening the rear. I already have stiff front springs...
http://forums.turbobricks.com/showthread.php?p=3726316&highlight=rear+roll#post3726316
 
The only way to fix it is lower the rear roll center. You can reduce the sprung weight transfer in the rear to zero, and still have a problem if the roll center is high enough (which it may be, on the 240). My math says that on a stock 240, the roll center contributes 16% of the front weight transfer, and 46% in the rear. Lowered it's even worse. On a lowered 240, the front RC is <4" off the ground, often near or below ground. The rear RC is the center of the panhard bar, so 11-13" off the ground.

One option is the somewhat spooky but highly effective Mumford Link:

21PETEB.jpg


The RC is at the intersection of the two long links.
 
Agreed...in the previous thread I linked above (didn't happen to notice if you were involved in that one too), I asked about front springs, they're cut IPDs, and I suggested a front spring rate somewhere between the 475lb and 700lb that I had tried on our lemons 240 wagon.

We have more front spring now (though not quite up to your 700# number). Still the same result.

I appreciate the suggestions and reading material, but please do bear in mind that the car is very close to evenly balanced left/right. Any theory needs to account for how this *only* affects the RR. The LR does not unload in anything like the same fashion.
 
I have to wonder about the corner weights and roll stiffness on this car as was pointed out earlier. If it's rolling over on the left front a lot and really unloading the right rear, I might be tempted to resolve that first. Maybe combine that with a rear roll center or roll bar change to try to maintain a good handling characteristic.

I would absolutely try to diagnose and cure causes rather than symptoms, first.

Keep us posted. This is interesting.
In drag racing, it is amazing how much the front suspension effects rear traction due to weight transfer. Front shock settings can make a car go left, right, smoke the tires or plant and haul. This front to back traction issue is not nearly the problem to road racers, though it does come up. Specifically when the car dives in breaking for a corner, and then squats coming out of it. It is entirely possible that the panhard is not the real problem and the spring rates and the rebound speed of the front suspension is. Incorrect spring weights and damper valving can cause odd weight transfer behavior, possibly loading and unloading the rear tires.

Id also check that the rear swaybar is not bent. If it is twisted, it will lift one side and load the other.
 
Any theory needs to account for how this *only* affects the RR.

This is a thing that Panhard bars do. Your options are:
  1. Move the right side of the panhard bar downward.
  2. Switch to something symmetrical instead of a Panhard bar like a Watts link, Mumford, IRS, etc.

The lateral-g link above explains this pretty well, in the middle of this post (heading "If the car is working the rear tires different in RH corners versus LH corners"): http://lateral-g.net/forums/showpost.php?p=497568&postcount=6
 
And a drawing:

J0UA8Ve.jpg


This is an extreme case for sake of explanation, but it illustrates the point. If you lower the car so far that the panhard bar points straight at the left hand contact patch, a right hand corner will pull on the panhard straight toward the left contact patch. If that force vector is pointed at the left tire, the right tire is doing diddly squat.

A more level panhard (right side down) allows the right spring to keep the right tire on the ground.

Edit: and in left hand turns, the force vector points high and to the right, so both tires get loaded more evenly.
 
Incorrect spring weights and damper valving can cause odd weight transfer behavior, possibly loading and unloading the rear tires.

Per my note above, this doesn't account for the left vs. right difference.

Id also check that the rear swaybar is not bent. If it is twisted, it will lift one side and load the other.

That's easy to check, because it's sitting on the shelf. No rear sway on this car.
 
The lateral-g link above explains this pretty well, in the middle of this post (heading "If the car is working the rear tires different in RH corners versus LH corners"): http://lateral-g.net/forums/showpost.php?p=497568&postcount=6

Yes, sorry, did not mean to address your comments / references with mine; just wanted to encourage folks offering ideas about front spring / damping to think about how to square those suggestions with the very asymmetrical behaviour we observe.

As an aside, I just (re) discovered Vsusp courtesy of the Retropower series about Gordon Murray's Mk1 Escort, and was sad to see it still doesn't have any support for solid axles. 8(
 
just wanted to encourage folks offering ideas about front spring / damping to think about how to square those suggestions with the very asymmetrical behaviour we observe.

Me too, as I've also observed my rear-slammed-240 to pick up the right rear when in hard right hand corners. Which I observed at an autocross after installing some suspension before I prove out the suspension...at a Lucky Dog race. See you there!
 
Yes, sorry, did not mean to address your comments / references with mine; just wanted to encourage folks offering ideas about front spring / damping to think about how to square those suggestions with the very asymmetrical behaviour we observe.

Is this not just the standard behaviour of a car with a solid rear axle due to the torque reaction through the engine/propshaft?
The standard way of dealing with that (for drag racing at least) is to add some pressure to the right rear tyre by raising the ride height slightly on that side. I'm not sure how appropriate to circuit use that is, but have you tried it?
 
Is this not just the standard behaviour of a car with a solid rear axle due to the torque reaction through the engine/propshaft?
The standard way of dealing with that (for drag racing at least) is to add some pressure to the right rear tyre by raising the ride height slightly on that side. I'm not sure how appropriate to circuit use that is, but have you tried it?

Remember, for there to be torque applied to the driveshaft, there has to be grip. If the right rear wheel is spinning, there can't be any meaningful amount of torque being applied to the driveshaft.
 
My kid and I were talking about this last night and wondering if the driver's weight and location were being taken into consideration. I wonder what swapping the mount points left to right would do? That is to say, axle mount on the driver's side and body mount on the passenger's. If the car then had the tendency to spin the LH tire, you'd have ~200lbs on that side to help counteract it. That's probably 7-8% of the car's weight.
 
Common in road / endurance racing with a clutch diff for sure. I've heard of some BMW lemons teams running diff coolers. All sorts of systems, from added fins to the diff cover to actual pumps & oil coolers like that one.
 
Common in road / endurance racing with a clutch diff for sure. I've heard of some BMW lemons teams running diff coolers. All sorts of systems, from added fins to the diff cover to actual pumps & oil coolers like that one.

We have been considering this as well, but wanted to put a sensor in first to be sure it was worth it. The rear end (with the TruTrac in it) does run "very hot" but we have no real way to quantify it. We ran the last race with Swepco 210 in it, haven't taken a sample to see how it held up...

My kid and I were talking about this last night and wondering if the driver's weight and location were being taken into consideration. I wonder what swapping the mount points left to right would do? That is to say, axle mount on the driver's side and body mount on the passenger's. If the car then had the tendency to spin the LH tire, you'd have ~200lbs on that side to help counteract it. That's probably 7-8% of the car's weight.

BMW kind of took this into account when they slanted our motor over; the bulk of the mass of the block and head are to the right of the vehicle centreline. Closer to the centre, but closer to the front. Battery is also in the passenger footwell for the same reason (well, that and it's the only sensible place to put it).
 
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