Panhard Bar Roll Axis

Yotaonly · 11-10-2002, 07:10 PM

Lately we have seen a lot of threads dealing with linked suspension geometry and all the fun stuff that comes with it. But what I have yet to learn is how to figure the roll axis of a link suspension with a panhard bar.

Now I know it's kinda pointless, cause for me atleast, the panhard bar is gonna go on the same plane as the drag link, but I'm curious.

So whatta ya say, if your not to tired of discussing link suspension, lets here some info on this from the experts out there. PIG, elf_cruiser, I'm looking in your direction.

Thanks, Jesse

elf_cruiser · 11-10-2002, 08:04 PM

ya got me on that one...

I have never really thought about it that much, sorry...

someone has to know though... I think that TPIJeep said something like the roll center is the midpoint of the upper panhard mount and the lower panhard mount. THis seems to make sense to me*shrug*

Yotaonly · 11-10-2002, 09:56 PM

Yeah, TPI's comment kinda makes sense, but I was thinking.

Say your passenger side is at full stuff and the driver side is drooping. The axle would be pivoting off of the panhard rod mount to the axle. But if the drivers side is stuffed, the the axle would be pivoting off of the panhard rod mount to the frame, kinda. What that does to the roll axis, I have no idea. I'm thinking that for the most part, the axle pivots off of the panhard rod mount to the axle, so could that be where the roll axis is. That would suck, all off to one side and way too low. I wish my rig could be trailered so I wouldn't have to worry about bump steer, then I could just do it right.

Suprdlux · 11-11-2002, 06:21 AM

If I remember correctly in the side view of the vehicle the roll axis runs from the point where the panhard connects to the frame to the point where the links converge in the top view. The roll center would be the point on the axis at the midline of the tire.

Gordon · 11-11-2002, 09:30 AM

The roll axis with a panhard and a three link goes from the point in the middle of the panhard to the other horizontal restraint point, which is found just like in a four link ie top view intersection of the lower two links.

That makes the panhard bar rear suspension pretty neat, by raising and lowering the panhard bar you can adjust the roll steer without affecting any of the anti squat anti dive.

The two bad characteristics of the panhard is it makes the axle move sideways and asymetrically as the suspension compresses. and if it is not exactly level then it can pull up on the chasis when turning one way and pull down when turning the other

JohnnyJ · 11-11-2002, 02:23 PM

Here's a pic to try and help clarify what others have said:

Gordon · 11-11-2002, 02:35 PM

Johnny J,
Miliken couldn't have said it better himself.

JohnnyJ · 11-11-2002, 02:37 PM

Actually, that's a pic from an SAE book "Fundamentals of vehicle dynamics" by Thomas Gillespie. He must have been a good copy of Milliken.

I've got to find a copy of the Milliken book.

Scott@Rockstomper · 11-11-2002, 03:08 PM

Quote:

Originally posted by Gordon
The two bad characteristics of the panhard is it makes the axle move sideways and asymetrically as the suspension compresses. and if it is not exactly level then it can pull up on the chasis when turning one way and pull down when turning the other

This isn't necessarily all bad... I swapped back to a panhard bar rear suspension on the Mantis because of tire-to-frame clearance issues. A panhard bar with a noticeable angle (I'm entirely too fried to engineer-speak this, sorry) on it, is one of relatively few suspensions that pushes the stuffed tire (on articulation) outboard. Since my rear tires pulled too far inboard, and crunched into my quarterpanels, I wanted something that wouldn't do that.

So... almost perfect setup ended up being, panhard approx 3.5 ft. long, approx 10" of vertical offset from frame mount to axle mount, with the axle pulled off-center (panhard 1/2" too short) slightly. Redneck engineering, but fuel for the fire nonetheless. I couldn't come up with a suspension that would tend to push the stuffed tire outboard more than this, and still fit within the confines of my frame arrangement.

For obvious reasons, at-speed handling is of almost no concern to me.

Brutpwr · 11-11-2002, 04:19 PM

Not sure if this is applicable or not but I used to street canyon race a lowered Toyota truck. It was dialed to perfection spring, shock and sway bar wise. I decided to add a panhard bar and it made the truck spooky to drive at anywhere near the limit (cornering). It would make my rear end come around like I was on the bump stop--not sure why cause I took it off after one week. I was thinking of reversing the link left to right thinking the bar was loading/unloading the suspension in reaction to engine torque but the bar was horizontal and the truck usually did not corner with more than 2 1/2 degrees of lean so since the truck handled beautifully w/o it I never tried mounting it in the opposite direction. With the above thinking in mind as far as off-road especially with long travel I'd think the panhard bar would
really mess up any designed in anti-squat and other good stuff--ie when your off camber on a slippery rock and you gassed it you might have a tendency to slip right off. Thats what my lowered street truck did. I spun around 4 times that week when before I had really only spun it out accidently once in the rain in all the years I drove it (over 500,000 miles between 3 toyota trucks)--that's all on DOT race rubber so when you spin something is way off on your set up!

Jason

PIG · 11-11-2002, 05:19 PM

Quote:

Originally posted by Gordon
Johnny J,
Miliken couldn't have said it better himself.

You took the words right out of my mouth Gordon.

Gordon · 11-11-2002, 05:28 PM

Scott. I dig panhards. My current thoughts are I am going to start with one on the rear of my buggy. The main reason is I want to offset the upper link of the 3 link to eliminate the body roll due to driveline torque. but also it makes it easy to adjust roll steer and anti-squat independantly.

11-10-2002, 07:10 PM	#1
Yotaonly Registered User Join Date: Feb 2002 Member # 9873 Location: Vancouver, WA 98683 Posts: 934	Panhard Bar Roll Axis Lately we have seen a lot of threads dealing with linked suspension geometry and all the fun stuff that comes with it. But what I have yet to learn is how to figure the roll axis of a link suspension with a panhard bar. Now I know it's kinda pointless, cause for me atleast, the panhard bar is gonna go on the same plane as the drag link, but I'm curious. So whatta ya say, if your not to tired of discussing link suspension, lets here some info on this from the experts out there. PIG, elf_cruiser, I'm looking in your direction. Thanks, Jesse __________________ '87 4Runner in the works with all that junk

11-10-2002, 08:04 PM	#2
elf_cruiser Registered User Join Date: Jan 2001 Member # 2857 Location: Phoenix, AZ, USA Posts: 3,319	ya got me on that one... I have never really thought about it that much, sorry... someone has to know though... I think that TPIJeep said something like the roll center is the midpoint of the upper panhard mount and the lower panhard mount. THis seems to make sense to meshrug __________________ I was a dog. But - I was really good, so they let me come back as a human. Sort of...

11-10-2002, 09:56 PM	#3
Yotaonly Registered User Join Date: Feb 2002 Member # 9873 Location: Vancouver, WA 98683 Posts: 934	Yeah, TPI's comment kinda makes sense, but I was thinking. Say your passenger side is at full stuff and the driver side is drooping. The axle would be pivoting off of the panhard rod mount to the axle. But if the drivers side is stuffed, the the axle would be pivoting off of the panhard rod mount to the frame, kinda. What that does to the roll axis, I have no idea. I'm thinking that for the most part, the axle pivots off of the panhard rod mount to the axle, so could that be where the roll axis is. That would suck, all off to one side and way too low. I wish my rig could be trailered so I wouldn't have to worry about bump steer, then I could just do it right. __________________ '87 4Runner in the works with all that junk

11-11-2002, 02:23 PM	#6
JohnnyJ Low Range Drifter Join Date: Nov 2001 Member # 7903 Location: SE Michigan Posts: 2,133	Here's a pic to try and help clarify what others have said: __________________ 2001 TJ Now with 4.7 V8 power : 1975 Wagoneer

11-11-2002, 02:37 PM	#8
JohnnyJ Low Range Drifter Join Date: Nov 2001 Member # 7903 Location: SE Michigan Posts: 2,133	Actually, that's a pic from an SAE book "Fundamentals of vehicle dynamics" by Thomas Gillespie. He must have been a good copy of Milliken. I've got to find a copy of the Milliken book. __________________ 2001 TJ Now with 4.7 V8 power : 1975 Wagoneer

11-11-2002, 06:21 AM	#4
Suprdlux Registered User Join Date: Feb 2002 Member # 9762 Location: Iowa City, Iowa Posts: 61	If I remember correctly in the side view of the vehicle the roll axis runs from the point where the panhard connects to the frame to the point where the links converge in the top view. The roll center would be the point on the axis at the midline of the tire.

11-11-2002, 09:30 AM	#5
Gordon Registered User Join Date: May 2000 Member # 929 Location: Santa Rosa, Ca USA Posts: 2,801	The roll axis with a panhard and a three link goes from the point in the middle of the panhard to the other horizontal restraint point, which is found just like in a four link ie top view intersection of the lower two links. That makes the panhard bar rear suspension pretty neat, by raising and lowering the panhard bar you can adjust the roll steer without affecting any of the anti squat anti dive. The two bad characteristics of the panhard is it makes the axle move sideways and asymetrically as the suspension compresses. and if it is not exactly level then it can pull up on the chasis when turning one way and pull down when turning the other

11-11-2002, 02:35 PM	#7
Gordon Registered User Join Date: May 2000 Member # 929 Location: Santa Rosa, Ca USA Posts: 2,801	Johnny J, Miliken couldn't have said it better himself.

11-11-2002, 04:19 PM	#10
Brutpwr Zeus of the Sluice Join Date: Mar 2000 Member # 481 Location: San Jose, CA, USA Posts: 3,687	Not sure if this is applicable or not but I used to street canyon race a lowered Toyota truck. It was dialed to perfection spring, shock and sway bar wise. I decided to add a panhard bar and it made the truck spooky to drive at anywhere near the limit (cornering). It would make my rear end come around like I was on the bump stop--not sure why cause I took it off after one week. I was thinking of reversing the link left to right thinking the bar was loading/unloading the suspension in reaction to engine torque but the bar was horizontal and the truck usually did not corner with more than 2 1/2 degrees of lean so since the truck handled beautifully w/o it I never tried mounting it in the opposite direction. With the above thinking in mind as far as off-road especially with long travel I'd think the panhard bar would really mess up any designed in anti-squat and other good stuff--ie when your off camber on a slippery rock and you gassed it you might have a tendency to slip right off. Thats what my lowered street truck did. I spun around 4 times that week when before I had really only spun it out accidently once in the rain in all the years I drove it (over 500,000 miles between 3 toyota trucks)--that's all on DOT race rubber so when you spin something is way off on your set up! Jason Last edited by Brutpwr; 11-11-2002 at 04:20 PM.

11-11-2002, 05:28 PM	#12
Gordon Registered User Join Date: May 2000 Member # 929 Location: Santa Rosa, Ca USA Posts: 2,801	Scott. I dig panhards. My current thoughts are I am going to start with one on the rear of my buggy. The main reason is I want to offset the upper link of the 3 link to eliminate the body roll due to driveline torque. but also it makes it easy to adjust roll steer and anti-squat independantly.

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