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-   -   [240] Show us your Panhard mount relocations (https://forums.turbobricks.com/showthread.php?t=348039)

DrZiplok 03-07-2019 10:04 PM

[240] Show us your Panhard mount relocations
 
Ok, long shot. Thanks to the folks that commented in my previous thread about RR wheel lifting plus far too much internet self-study time, I think we need to raise the body-side Panhard bar mount point. A lot.

This looks messy. Like it will involve cutting up the existing mount, fabricating things, relocating fuel lines, etc. I would love to learn from others' mistakes.

Have you done this? Did you regret it? What would you do differently? Or was it f'ing awesome? I'd love to know...

cwdodson88 03-07-2019 10:32 PM

Why move it up?

Overkiller 03-07-2019 11:38 PM

If you're thinking about cutting stuff up I'd go watts link personally.

RvolvoR 03-08-2019 02:04 AM

Quote:

Originally Posted by cwdodson88 (Post 5924650)
Why move it up?

to adjust roll center.

RvolvoR 03-08-2019 02:09 AM

Quote:

Originally Posted by DrZiplok (Post 5924637)
Ok, long shot. Thanks to the folks that commented in my previous thread about RR wheel lifting plus far too much internet self-study time, I think we need to raise the body-side Panhard bar mount point. A lot.

This looks messy. Like it will involve cutting up the existing mount, fabricating things, relocating fuel lines, etc. I would love to learn from others' mistakes.

Have you done this? Did you regret it? What would you do differently? Or was it f'ing awesome? I'd love to know...

you might be able to just drill another hole 1" up and maybe clearance the mount...but it really depends on (this is what I have been reading as well, so take it with a grain of salt) the type of driving and how big or small of a track youre on.

shoestring 03-08-2019 09:12 AM

I can't envision what it looks like back there right off the top of my head, but couldn't you raise the mounting point on the rear axle and achieve the same goal of lifting the rear roll center? That would also minimize lateral axle movement by bringing the panhard bar closer to parallel with the ground. Problem with this might be unintended consequences of moving the roll axis.

Is this the budget race car with the Randy Pobst vid and the TruTrac complaint?

Uncleknucklez 03-08-2019 09:50 AM

I can't remember without checking my notes, but lowering the mount on the axle would do the same thing?

DrZiplok 03-11-2019 08:01 PM

Quote:

Originally Posted by shoestring
Is this the budget race car with the Randy Pobst vid and the TruTrac complaint?

It is.

Quote:

Originally Posted by cwdodson88
Why move it up?

As it stands, it contributes to jacking the RH rear wheel off the ground in RH corners. With the RH wheel in the air, there is a distinct lack of acceleration on corner exit, which inhibits our otherwise absolute domination of the crapcan racing series we compete in.

Quote:

Originally Posted by shoestring
I can't envision what it looks like back there right off the top of my head, but couldn't you raise the mounting point on the rear axle and achieve the same goal of lifting the rear roll center? That would also minimize lateral axle movement by bringing the panhard bar closer to parallel with the ground. Problem with this might be unintended consequences of moving the roll axis.

To get the arm back to the same angle, you'd want to lower the mount on the axle end, but now the arm is at a different height relative to the contact patch, so you still end up with different geometry. Also and less important, we'd have to repeat this for our spare axles, which we change slightly more often than our chassis.

Quote:

Originally Posted by overkiller
If you're thinking about cutting stuff up I'd go watts link personally.

Is this a thing you've done or seen done (if so, I'd love to see some pictures)? Because really if I was thinking about cutting stuff up without a plan I'd be putting an E46 subframe in the back and going IRS... 8)

Quote:

Originally Posted by RvolvoR
you might be able to just drill another hole 1" up and maybe clearance the mount...but it really depends on (this is what I have been reading as well, so take it with a grain of salt) the type of driving and how big or small of a track youre on.

Not circle track. Road racing. I've read all those things, and they're only marginally helpful because we turn both left and right. 1" won't be anything like enough to get back to the original geometry (assuming that was more or less good) given how far we have dumped the rear.

https://i.imgur.com/s11lfbQ.png

Still interested in your experiences / suggestions...

cwdodson88 03-12-2019 12:32 AM

The reason I asked why, is that its been getting more and more "I read this on the internet" but the person asking the question has no idea why they are wanting to make a change or modify something... With rear axle hiking in one corner vs the other, I don't really feel like moving the roll center up or down is going to change that effect that much. How is the panhard bar currently set? Angled? Chassis side high?

How is the suspension currently limited under droop? When you lift the car and let the axle dangle, does it dangle even? Higher on the chassis mount side or axle mount side?

Going to a watts link could solve this, moving to a watts link with the pivot on the chassis and arms on the axle seemed to work well in a similar regard with my 122, but I was focused on roll center>center of gravity vs roll center>contact patch. The only downfall was space constraints, so usually its easier to place the pivot on the axle.

I would take a look at turnology, they did a few wiriteups on the key differences and the cause:effect of them.

Also, RPM Net did a tech article explaining the typical handling characteristics of a few different panhard locations.

towerymt 03-12-2019 09:28 AM

May want to reference the previous thread:

[240] Right rear spins turning right, left rear does not spin turning left. Wut?
http://forums.turbobricks.com/showthread.php?t=346516

towerymt 03-12-2019 10:00 AM

Watts:
https://pbase.com/towerymt/image/6919205.jpg

https://pbase.com/towerymt/image/6919207.jpg

Group A 242:
https://pbase.com/towerymt/image/9401834.jpg

Other side, from Anthony Hyde's page:
http://people.physics.anu.edu.au/~am...K8axlesusp.jpg

http://people.physics.anu.edu.au/~am...olvo_specs.htm
(also note his link to my pbase gallery :lol:
Photos - Pirate site showing a wide variety of nicked GpA pics (how about thanking the contributors))

https://240grupp-a.se/

Another shot of a rear axle, parallel panhard:
http://240grupp-a.se/wp-content/uplo...0/then_un1.jpg
From here: https://240grupp-a.se/bengt-thenander/

Another grpA 242 rear axle (full droop, hence not parallel w/axle/ground):
http://240grupp-a.se/wp-content/uploads/2018/03/88.jpg
From here: http://240grupp-a.se/sa-byggdes-en-grupp-a-volvo/


More fun pictures to look at:
https://pbase.com/towerymt/240_racing&page=all

Just buy this and dominate:
https://racecarsdirect.com/Advert/De...-turbo-group-a

Not much help...looks like they leave the chassis side alone and move the axle side down.

RvolvoR 03-12-2019 10:14 AM

Quote:

Originally Posted by DrZiplok (Post 5925845)
Not circle track. Road racing. I've read all those things, and they're only marginally helpful because we turn both left and right. 1" won't be anything like enough to get back to the original geometry (assuming that was more or less good) given how far we have dumped the rear.

I'm not talking roundy-round. I suggest you read this to study what the effects of moving the panhard around do:

http://lateral-g.net/forums/showthread.php4?t=42568

Also, a few of us have done this style mount (stole pic from hackster), but none of us have tested it yet:
http://i1133.photobucket.com/albums/...psiqwoonus.jpg

blkaplan 03-12-2019 10:34 AM

If it were me, I would drop the axle side. Ive always wanted to release a bolt on axle bracket to relocate the panhard bar lower, just not enough time to get to it yet.

shoestring 03-12-2019 10:52 AM

You could also move either of the mounting points inboard to reduce the leverage the panhard has on the RH side of the axle. Alternatively, if you move the body side mount down and/or move the axle side mount up so that the panhard bar is inclined from driver's side to passenger's side, won't that pull down on the RH side of the axle in RH turns? Someone correct me if I'm wrong.

RvolvoR 03-12-2019 11:47 AM

Quote:

Originally Posted by shoestring (Post 5926017)
You could also move either of the mounting points inboard to reduce the leverage the panhard has on the RH side of the axle. Alternatively, if you move the body side mount down and/or move the axle side mount up so that the panhard bar is inclined from driver's side to passenger's side, won't that pull down on the RH side of the axle in RH turns? Someone correct me if I'm wrong.

Moving the mounting points inboard is bad juju as it will just exacerbate the side to side movement of the axle on articulation.

crogthomas 03-12-2019 12:23 PM

Quote:

Originally Posted by towerymt (Post 5925994)
Not much help...looks like they leave the chassis side alone and move the axle side down.

Most likely because Group A cars weren't allowed to move suspension mounting points. If you've got the freedom to move them (which I assume you have in 'crapcan' racing) then do whatever is the most practical.

cwdodson88 03-12-2019 12:28 PM

Quote:

Originally Posted by RvolvoR (Post 5926029)
Moving the mounting points inboard is bad juju as it will just exacerbate the side to side movement of the axle on articulation.

but instead of loading R>L tire unequally moving the bar axle mounting location toward the center equalizes the loading between the two tires. It doesnt seem like it would be exacerbating side to side movement of the axle unless its seeing full compression then full droop, that would go through the entire lateral range of the bar. But L high R low articulation would be "free-er" to move about since the locating point is centered.

http://rbmn.free.fr/PL_barre_US.html

blkaplan 03-12-2019 12:37 PM

moving the mounting inwards does make the panhard bar have less jacking forces on the axle but it will create more side to side movement.

Its all a balancing act.

740s use a shorter panhard bar than the 240s and they have a wider axle.

DrZiplok 03-13-2019 01:54 AM

Quote:

Originally Posted by towerymt (Post 5925994)
Not much help...looks like they leave the chassis side alone and move the axle side down.

On the contrary, that's a ton of help - and thanks, I have been looking for GpA pictures of this part and failing. If it worked for GpA, it ought to work for us.

Quote:

Originally Posted by RvolvoR
a few of us have done this style mount (stole pic from hackster), but none of us have tested it yet:

Will definitely be interested to hear about your results, and many thanks for that link - not one I had surfaced and plenty of pertinent material to digest.

Quote:

Originally Posted by blkaplan
Ive always wanted to release a bolt on axle bracket to relocate the panhard bar lower

Noted. If you need an excuse to get to it, you know where we are. 8)

blkaplan 03-13-2019 11:03 AM

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

shoestring 03-13-2019 12:30 PM

Quote:

Originally Posted by blkaplan (Post 5926507)
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.

towerymt 03-13-2019 02:14 PM

Quote:

Originally Posted by shoestring (Post 5926540)
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/showth...ll#post3726316

mck1117 03-13-2019 10:05 PM

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:

https://imgur.com/21PETEB.jpg

The RC is at the intersection of the two long links.

DrZiplok 03-14-2019 01:04 AM

Quote:

Originally Posted by towerymt (Post 5926592)
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.

NotSoFresh 03-14-2019 01:09 AM

Quote:

Originally Posted by shoestring (Post 5926540)

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.


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