GT40s.com
MK-I  MK-II  MK-III  MK-IV  GULF  MIRAGE  J-CAR  LOLA
GT40s.com
Home Forum Gallery Support GT40s.com  
Register FAQ Advertisers Search Today's Posts Mark Forums Read

Go Back   GT40s.com > GT40 Technical Forums > GT40 Tech - Chassis,Brakes,Tires,&Wheels


GT40 Tech - Chassis,Brakes,Tires,&Wheels Chassis and Handling.

Reply
 
LinkBack Thread Tools Display Modes
Old 11th September 2004, 09:22 AM   #1 (permalink)
JohnD
A Tenth
United States
 
Join Date: Feb 2004
Location: Virginia USA
GT40: None yet, just a '68 Camaro, Datsun 240-Z and Nissan 300ZXTT.
Posts: 134
solid axle rear suspensions?

Hey everyone. In addition to loving the GT40s, I happen to be a big fan of old muscle cars... pretty much all of which are solid live rear axle cars.

In the interest of increasing cornering performance, I'm curious what you all think or know about rear suspension designs for these kinds of cars...

My '68 Camaro has leaf springs at present, which can handle pretty well, but I'm interested in the possibilty of something like a triangulated 4-bar or the like.

Just a theoretical discussion to help out a guy who is kind of a novice at this stuff. [img]/ubbthreads/images/graemlins/grin.gif[/img]

Cheers!

John
JohnD is offline  
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiTweet this Post!
Reply With Quote
Old 11th September 2004, 11:07 AM   #2 (permalink)
llarsen's Avatar
llarsen
Admin
United States
 
Join Date: Jun 2003
Location: Raleigh, NC
GT40: Sabre
Posts: 2,076
Re: solid axle rear suspensions?

John,

Sounds like you want to convert your muscle car into a "G" car. I believe there may be magazines and/or web sites that deal with building G cars and that is where I would start looking if I were you. Their main focus is handling, so they would probably be aware of anything out there that would help you in making a Camaro handle better.

Regards,
Lynn
llarsen is offline  
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiTweet this Post!
Reply With Quote
Old 11th September 2004, 01:27 PM   #3 (permalink)
JohnD
A Tenth
United States
 
Join Date: Feb 2004
Location: Virginia USA
GT40: None yet, just a '68 Camaro, Datsun 240-Z and Nissan 300ZXTT.
Posts: 134
Re: solid axle rear suspensions?

Yeah, I'm a member over at Pro-Touring.com and most of the people have first gen Camaros that they are turning into G-machines. There is a lot of disagreement regarding what the best setup might be though... some people are really keen on truck arms, some like the parallel 4-bar, some the three link, etc, etc.

Just curious if any of the suspension gurus on this site have opinions on the subject. = )
JohnD is offline  
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiTweet this Post!
Reply With Quote
Old 11th September 2004, 02:26 PM   #4 (permalink)
Howard Jones's Avatar
I Have No Life
United States
 
Join Date: Jun 2002
GT40: San Francisco Bay Area California USA
Posts: 3,356
Re: solid axle rear suspensions?

To start with I would do reserch on the orginal TRANSAM cars. These were just what you wamt with softer springs and maybe a little more travel in the suspension. Then I would look att currwnt roadrace spec NASCAR.

First settle on rires and rim width and design from there.
Howard Jones is offline  
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiTweet this Post!
Reply With Quote
Old 11th September 2004, 10:15 PM   #5 (permalink)
JohnD
A Tenth
United States
 
Join Date: Feb 2004
Location: Virginia USA
GT40: None yet, just a '68 Camaro, Datsun 240-Z and Nissan 300ZXTT.
Posts: 134
Re: solid axle rear suspensions?

The original Trans Am Camaros ran leaf springs out back. NASCAR as far as I know uses truck arms because they are required by the rules. I'm not sure if it is the best setup though... seems that on a surface with any irregularities the truck-arm is going to bind to some extent... unless you use soft rubber bushings that will deflect.
JohnD is offline  
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiTweet this Post!
Reply With Quote
Old 12th September 2004, 12:53 AM   #6 (permalink)
A Tenth
United States
 
Join Date: Jul 2004
GT40: Silicon Valley
Posts: 121
Re: solid axle rear suspensions?

A lot of people are using torque arm/ panhard bar setups. The late model Camaro's had them and a lot of Mustangs install them to improve their handeling.

I think that they are popular because you don't have to add heim joints every where to make it handle.

The 4 link suspensions are theoretically superior in geometry and unsprung weight, but the deflection of the bushings eliminates that advantage unless you add the heim joints, then you will start pulling the suspension mounting points out of your floor pan and transfering a lot of vibration and noise in to the interior.
killroy is offline  
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiTweet this Post!
Reply With Quote
Old 12th September 2004, 10:34 AM   #7 (permalink)
llarsen's Avatar
llarsen
Admin
United States
 
Join Date: Jun 2003
Location: Raleigh, NC
GT40: Sabre
Posts: 2,076
Re: solid axle rear suspensions?

This is just a hair brained idea, but it occurred to me that a lot of guys pull the IRS rear ends out of Corvettes and the later Mustangs and, for drag racing, replace them with solid axles. If you are moving the other way, would it make sense or be possible to put a Corvette IRS rear suspension in a Camaro? Rather than the single transverse leaf spring, it might be easier to go to coil over setups or coil & shock, at least.

Lynn
llarsen is offline  
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiTweet this Post!
Reply With Quote
Old 12th September 2004, 11:52 AM   #8 (permalink)
JohnD
A Tenth
United States
 
Join Date: Feb 2004
Location: Virginia USA
GT40: None yet, just a '68 Camaro, Datsun 240-Z and Nissan 300ZXTT.
Posts: 134
Re: solid axle rear suspensions?

There are actually kits now to put a C4 'Vette IRS into a 67-69 Camaro and it is a popular swap. I like the idea of keeping a solid axle in the car though (since I already have one).
JohnD is offline  
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiTweet this Post!
Reply With Quote
Old 15th September 2004, 01:02 PM   #9 (permalink)
Hemipanter's Avatar
Rookie
Sweden
 
Join Date: Mar 2004
Location: Being working sportscar since 1970, and building guitars since 1960.
GT40: Stockholm Sweden
Posts: 62
Re: solid axle rear suspensions?

A live axle can be mad to work quite good. One drawback is weight and the other is roll centre that tends to be high.
An easy side lokator is a Panhard rod, but even better is a watts link.
A fourlink as on drag cars is NOT for road racing. Those likage is blocking themselfes in roll depending on settings. As the car rolls one side goes up and the other down, and this creates oposite twisting motion in the axle. As the axle dont twist, roll is then blocked totally if linkarm is out of paralell. Rubber bushings may work for roll motion but not for racing where balljoints should be used.
Goran Malmberg
Hemipanter is offline  
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiTweet this Post!
Reply With Quote
Old 15th September 2004, 03:58 PM   #10 (permalink)
A Tenth
United States
 
Join Date: Jul 2004
GT40: Silicon Valley
Posts: 121
Re: solid axle rear suspensions?

Have you ever seen a mumford link, it lets you put the roll center where ever you want it, even under ground.

Drag racing style 4 links are completely different from what you see on the street and on a race track. They have the upper and lower links almost parallel.

Street style has the upper arms angled inward about 45 degrees. The upper arms usually serve to locate the axle side to side as well as controlling the pinion angle.
killroy is offline  
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiTweet this Post!
Reply With Quote
Old 15th September 2004, 05:39 PM   #11 (permalink)
JohnD
A Tenth
United States
 
Join Date: Feb 2004
Location: Virginia USA
GT40: None yet, just a '68 Camaro, Datsun 240-Z and Nissan 300ZXTT.
Posts: 134
Re: solid axle rear suspensions?

That is the type of 4 link I was considering... I've heard it referred to as the "triangulated" 4 link... where the upper arms angle in.

I'm not familiar with a mumford link, and I've heard of the watts link, but am not really familiar with it. Any more info on these?
JohnD is offline  
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiTweet this Post!
Reply With Quote
Old 15th September 2004, 06:39 PM   #12 (permalink)
A Tenth
United States
 
Join Date: Jul 2004
GT40: Silicon Valley
Posts: 121
Re: solid axle rear suspensions?

It's hard to describe, it's a linkage that attaches to both axle tubes and a bracket behind the center section of the axle.

It's like a weird watts link.

Try a google search for mumford link and you will see pictures and illustrations.
killroy is offline  
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiTweet this Post!
Reply With Quote
Old 16th September 2004, 02:19 AM   #13 (permalink)
Russ Noble's Avatar
Russ Noble
Lifetime Premier Supporter
New Zealand
 
Join Date: Jul 2004
Location: Christchurch,NZ
GT40: Scratch Kiwi 40
Posts: 2,033
Re: solid axle rear suspensions?

IMHO the Mumford link though very interesting is too complicated and has too many moving parts, and do you need a rollcentre close to or below ground level.OK for a racing U2 or Seven type car.I'm a great believer in the KISS principle.

With regard to the suggested upper triangulated four link IMHO the roll centre is too high, it is at the height of the mounting point on the housing which of course is above the axle.Causes massive oversteer in my TR7V8. The opposite setup with the top links parallel and the bottom links angled in gives a much lower roll centre which is at the height of the mounting points which are below the axle housing, this IMHO is much more ideal.I would think this would be an excellent solution provided engineering the forward pickup points was not a problem.FWIW I am at this very moment converting the TR7 to four parallel links and panhard rod with multiple pickup points to allow variable rideheights, antisquat, rollcentres etc.
Russ Noble is offline  
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiTweet this Post!
Reply With Quote
Old 16th September 2004, 08:58 AM   #14 (permalink)
nota2266's Avatar
nota2266
Lifetime Premier Supporter
Australia
 
Join Date: May 2004
Location: Kurrajong, Aust
GT40: Frank Wigg Mono
Posts: 595
Re: solid axle rear suspensions?

IMHO. A parallel 4 link system is without doubt the best way to control a solid rear axle. The links must be parallel in the horizontal plane and preferably a perfect pantograph in the vertical plane. This will give no geometric interference as the body rolls and spherical joints can be used for all of the pivots. In the event that the top arms or the bottom arms are converging in plan view you will get geometric interference and if you use spherical joints you will break and or twist something. The links arranged in this manner become a part of the springing medium which is undesirable. To allow for the geometric interference compliant bushes must be used at the pivot points, this then allows undesirable movement of the axle under accelerating, braking and cornering loads. In the event that the links form a pantograph in the vertical plane the pinion angle will not change relative to the body/chassis. The longer the arms the better but the longer they are the stiffer they need to be to cope with the torque reaction of the rear axle. In terms of transverse location a watts linkage provides the better solution for a road going car. The pivot point of the centre link is the roll centre of the rear suspension. The pivot for the centre link can be mounted on the rear axle or on the body/chassis. A simpler but less effective method is a panhard bar as long as is practically possible. The roll centre with a panhard bar is the point where the axis of the bar intersects the midpoint of the wheel track. ie If the panhard bar is parallel to the ground (as it should be) and equal in height to the wheel centreline the roll centre is at the centre of the rear axle in height. A mumford linkage system is high maintenence and not really suited to a large sedan type vehicle, they are very good on lotus seven type vehicles as ross noble mentioned. In all of this what is very important is the roll axis of the vehicle. This is the axis thru the front and rear roll centres. It is this that will govern the handling characteristics of the vehicle. Assuming that the cg of the whole of the vehicle is above the roll axis- A front roll centre higher than the rear roll centre gives less weight transfer to the front outside wheel than does a front roll centre being lower than the rear roll centre. The amount of roll can be controlled by (adjustable) anti roll bars front and rear. Converting the rear of an existing vehicle you are limited by the front suspension and its designed roll centre. The original leaf spring setup roll centre height will be at the centre line of the rear axle. Whether tou use a panhard bar or a watts linkage I would suggest you start with the roll centre at the centre of the rear axle and adjust it up an down to suit your driving preference. You will notice an improvemant in handling just from the more accurately controlled rear axle. To understand all of this I suggest you go to a model shop and purchase some ball joints (plastic), some coil shock units, and build a small block model of a vehicle. An accurately located solid rear axle is a very good system, after all Jim Hall used them in his Chaparral Can Am cars
Hope this helps,
Trevor
nota2266 is offline  
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiTweet this Post!
Reply With Quote
Old 16th September 2004, 02:29 PM   #15 (permalink)
A Tenth
United States
 
Join Date: Jul 2004
GT40: Silicon Valley
Posts: 121
Re: solid axle rear suspensions?

A mumford link has five moving pieces which isn't that many, it has all of the advantages of a watts link (three moving pieces) with the added ability to put the roll center any where you want. I believe the unsprung weight is about the same as a panhard bar, so it is the best of both worlds and then some.

I have seen one on a 700 hp car weighing nearly 4,000 lbs, so they aren't just for Lotus 7 replica's.

The parallel link system can work well, but if they are truly parallel, the two upper arms can be replaced by a single upper arm in the center of the axle.

The 2005 Mustang is a good example of a three link with panhard bar.
killroy is offline  
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiTweet this Post!
Reply With Quote
Old 16th September 2004, 06:24 PM   #16 (permalink)
nota2266's Avatar
nota2266
Lifetime Premier Supporter
Australia
 
Join Date: May 2004
Location: Kurrajong, Aust
GT40: Frank Wigg Mono
Posts: 595
Re: solid axle rear suspensions?

A mumford link has 8 pivot points and it is very critical on "no slack" on those pivots. No one has said you cant use them on a heavy car but in so doing its proportions need to be substantial which is not so necessary on a light car. The original post was about a simple system for a road car and a mumford link is not so simple to put into a production type car. Your suggestion of using a single upper central link is ok on low horsepower cars but will allow toe in of the rear wheels under acceleration with high horsepower.
Cheers
nota2266 is offline  
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiTweet this Post!
Reply With Quote
Old 16th September 2004, 09:29 PM   #17 (permalink)
A Tenth
United States
 
Join Date: Jul 2004
GT40: Silicon Valley
Posts: 121
Re: solid axle rear suspensions?

Toe in on a solid Axle suspension?

Now I have heard everything!

Of course, everything on a big car has to be bigger than on a lotus 7 replica. The rod ends don't have to be any larger than what you would use in a panhard bar, and the central four pivots can be roller bearings or bronze bushings. Also the bracket that holds the linkage could be mounted to the chassis with bushings making life easier for those pivots.

It's not as simple as a panhard bar, but it isn't that much more complicated than a Watts linkage (for design and construction). None of these are as complicated as an IRS.
killroy is offline  
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiTweet this Post!
Reply With Quote
Old 17th September 2004, 03:13 AM   #18 (permalink)
Russ Noble's Avatar
Russ Noble
Lifetime Premier Supporter
New Zealand
 
Join Date: Jul 2004
Location: Christchurch,NZ
GT40: Scratch Kiwi 40
Posts: 2,033
Re: solid axle rear suspensions?

Trevor, a very comprehensive post, as you point out a triangulated four link must have compliant bushings, if we are talking a road car, that is probably going to be a requirement anyway and in this situation the influence on roll stiffness may be acceptable.

With regard to the Mumford link, if the reason to consider this option is to achieve a low roll centre whilst maintaining ground clearance then a more valid comparison would be with a Panhard rod rather than a Watts linkage as it is possible to get a much lower roll centre with the Panhard rod than the Watts (given horizontal links) for a given ground clearance.IMHO the slight sideways movement of the axle through normal suspension travel is not a significant effect and neither is difference in rollcentre through left and right hand corners.Thus the comparison to my way of thinking comes down to Panhard versus Mumford. One moving part as opposed to five.IMHO you'd have to be pretty sure that the benefits obtained by the additional complication were going to be tangible and significant.

Regards
Russ Noble is offline  
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiTweet this Post!
Reply With Quote
Old 17th September 2004, 08:38 AM   #19 (permalink)
Mark IV's Avatar
Mark IV
Sponsoring Vendor
United States
 
Join Date: Sep 2001
Location: W. New York
GT40: Superformance
Posts: 2,923
Re: solid axle rear suspensions?

An accurately located solid rear axle is a very good system, after all Jim Hall used them in his Chaparral Can Am cars



[/ QUOTE ]I think what Hall used was a DeDion setup, not a solid axle like a Camaro, very diferent things. And toe in on a solid axle? Yes, you can....Donahue first put camber on a solid axle on the Trans-Am Javelins..Nascar guys runs some camber depending upon the track. In fact when they first started doing they got carried away and put so much in they started to bust differentials that had never before failed! You can put a couple of degrees of camber and/or toe in a Ford 9" rear, the axle splines will allow some slop so it works.

Rick [img]/ubbthreads/images/graemlins/shocked.gif[/img]
Mark IV is offline  
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiTweet this Post!
Reply With Quote
Old 17th September 2004, 12:02 PM   #20 (permalink)
A Tenth
United States
 
Join Date: Jul 2004
GT40: Silicon Valley
Posts: 121
Re: solid axle rear suspensions?

Yes, I know about cambered axles. You could do toe in, but using three links instead of four is not going to bend the axle tubes to create toe in.

Besides, I would not consider a cambered axle streetable in any way. They wear out very quickly.
killroy is offline  
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiTweet this Post!
Reply With Quote
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Display Modes

 
Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On



All times are GMT -4. The time now is 08:13 AM.