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David Pozzi
09-12-2004, 10:01 PM
I went to the Trans-Am races at Laguna Seca last Saturday. I checked out all the TA cars, and they all use the three link suspension. The lower links appear to be around 1 3/8" or 1 1/2" diameter and around three and a half to four feet long! They run forward to near the center of the door on each side.

The upper links are offset to the right of center just a little, either to bias traction to the right to offset rear axle torque or to clear the driver's elbow. The upper link is around three feet long and intrudes about a foot inside the ****pit passenger side. (forum software won't let me say cocpit!)

Most of the upper links had a neat screw adjuster on the front attachment point that was like a NASCAR jack bolt. It allows raising or lowering the front mount to vary the geometry.

I talked to one driver who converted his car to three link from four link and he said he likes the three link better, but I wasn't able to get more details.

Oh, and not a drilled rotor in sight!
David

Ralph LoGrasso
09-12-2004, 10:11 PM
Sounds like an awesome time checking out all the badass cars!

I'm glad I decided on the 3-link. :)

PTAddict
09-13-2004, 07:25 AM
Notice the length of those links. What the longer links do is keep the various parameters fairly constant through the suspension travel. One of the concerns I'd have with a 3-link in a PT car is that the links might be quite short for packaging reasons, leading to big changes in instant center, etc. as the car squats or rolls. The only way to work this out is to do the calculations, preferably with a suspension program.

One design I think is pretty good is the 4-link with angled upper arms that Art Morrison uses in its chassis. The angled upper links remove the need for watts or panhard, and otherwise give very similar geometry to a 3-link. Adapting this design to a uni-body, though, means reframing the rear or engineering some kind of bolt-in cassette with the necessary strength at the upper control arm mounts.

And I still think a torque arm setup might represent the best set of compromises of all.

68protouring454
09-13-2004, 07:46 AM
david i love reading your posts, i have learned alot, but whats this no pics
???
:postpics:

David Pozzi
09-13-2004, 02:16 PM
here is a side view of Tommy Drisi's TA car.

David Pozzi
09-13-2004, 02:21 PM
here is the upper link with adjuster, pretty neat system! :)

nancejd
09-13-2004, 05:21 PM
I love how the axle is between the upper and lower frame rails in the car!

CoryM
09-13-2004, 06:00 PM
The TA guys do some neat stuff. They also run blade type swaybars I believe. Id like to know where they get the blades. Any ideas? Its too bad the TA racing is not as entertaining as other classes. Some fast cars out there.

dennis68
09-13-2004, 06:27 PM
I personally think TA racing is WAY more entertaining than NASCAR, if they wanted to eliminate a series it should have been BUSCH. I don't even watch motorsports on TV anymore unless it's NASCAR at Infenion or Watkins Glen.

dennis68
09-13-2004, 09:22 PM
Notice the length of those links. What the longer links do is keep the various parameters fairly constant through the suspension travel. One of the concerns I'd have with a 3-link in a PT car is that the links might be quite short for packaging reasons, leading to big changes in instant center, etc. as the car squats or rolls. The only way to work this out is to do the calculations, preferably with a suspension program.
I was going to question this, is the additional length of the arms THAT advantageous to the design? For example, how much of a disadvantage would you think running 30" LCA instead of 48" LCA would have? Does running a shorter LCA somehow negate the advantages of running a 3-link?

MrQuick
09-13-2004, 10:29 PM
Dennis all that info would be best figured on a program as stated earlier. Remember these 3 link systems on TA cars are built for optimum performance,im not sure if they are limited by rules as much as stock cars are. With that said space limitation isn't a problem since these guy are practicaly sitting on the upper link. It would be nice to seeing what difference it would make 24" LCA's verses 40". Im gonna start with my 24" lowers and a 18" upper.

Norm Peterson
09-14-2004, 03:08 AM
All you need to know is the length and inclinations of the links and the PHB pivot elevations to determine the anti-squat and roll steer. If you also know the brake bias you can work out the anti-lift. All stuff that can be done in a spreadsheet, including plots showing how it varies over suspension travel.

Cory - The blade adjustment is clearly visible in the first pic. And IMO, the in-car camera sequences of a road course lap are far more entertaining, and the shots through the corners that let you see the line more useful/instructive, relative to most comparable oval-race video.

Norm

ballistic69
09-14-2004, 05:17 AM
here is a side view of Tommy Drisi's TA car.

Hmmmmm.... Looks familar....

CoryM
09-14-2004, 06:11 AM
Oops, I guess I didnt look up enough. I often do that with girls but not usually cars ;) .


the in-car camera sequences of a road course lap are far more entertaining, and the shots through the corners that let you see the line more useful/instructive, relative to most comparable oval-race video.

I certainly wont argue with that. The only oval track racing I find entertaining is sprint cars. The rest I cant be bothered with. However, compared to some good road course series (The older speed vision series, think its the speed channel series now and is not as fun to watch) TA racing is pretty tame. I will give them credit though, in the past few years they have spruced it up a bit. Hopefully soon it will be even better.

David Pozzi
09-14-2004, 02:11 PM
The cars use a short panhard bar from the center bottom diff carrier bolt to the lower frame rail. Some are on the left side, some are on the right side.
David

PAI Racing
09-14-2004, 03:38 PM
Don't know if I didn't read carefully or not, but adjustable blade type sway bars (and just about anything else T/A related) can be found at www.hrpworld.com.

gt1guy
09-14-2004, 09:18 PM
The TA guys do some neat stuff. They also run blade type swaybars I believe. Id like to know where they get the blades. Any ideas? Its too bad the TA racing is not as entertaining as other classes. Some fast cars out there.

That's a driver adjustable swaybar.

http://www.hrpworld.com/index.cfm?form_prod_id=217_1432&action=product


Kevin

Marcus SC&C
09-15-2004, 06:04 PM
Nice pics and info David. The 3rd link adjuster is great,simple PHB adj. hardware and a shifter boot,I like it! :) Interesting that the PHBs are so short. Could it be that their total suspension travel is limited enough that it doesn`t cause the rear to move that much laterally? The 3 link/PHB setup in our test car uses a 40" PHB but we`re using quite a bit of total travel. BTW as far as the length of the links goes...the length of say a Monte SS`s rear UCAs in side view is only about 8" and the lowers 18". Despite the binding inherent in the factory system it still works for the most part. Longer arms would be nice to be sure but IMO lateral axle locating,proper IC and anti squat and rear RC height are all higher priorities. FWIW ours works amazingly well with stock length LCAs and a 3rd link only 2" longer than stock and we still have a back seat. ;) Marcus SC&C

David Pozzi
09-16-2004, 11:48 PM
I don't know the rules for TA these days, but the undersides are flat, the cars carry something like 30 or 35 gallons of fuel! the tank is right behind the rear axle and they place it as close as possible to the rear axle.

There must be a tremendous change in rear weight bias which makes late race traction fall off. The cars got slower by two seconds a lap near the end of the race.

A truck arm suspension would have no room under a TA car and would mess up the aero underneath, plus the driver would have to sit higher up so the link could run under him. The three link allows a much tighter package with flat undertray. The short panhard bar was a suprise for sure! They could use a different type lateral locater but don't.
Tommy Kendall mentioned he spent time "getting the roll-centers right" before the race. I didn't get a good look at his suspension since it was farthest from me, but it's similar to the photo from where I stood.
David

Tig Man
09-17-2004, 04:34 PM
I have in my hands a complete set of blueprints for one of John Millers Corvette's from 2000. I'll try to post some dimensions as well as copies to give you guys some ideas.

Mark

Mean 69
09-17-2004, 05:30 PM
Great post, I tried to post a reply yesterday, typed something long, but the response got kicked out. Frustrating.

I think David (edit: Whoops, it was Marcus, sorry) had it right on regarding the very short PHB, the lateral translation is limited by what I would guess is a very small (relative) vertical translation of the suspension.

The length of the links is not at issue, again, it is the SVSA that is important. It is interesting that they are so long though, with the long links (independent of static IC, anti-squat, etc), things like pinion angle, IC, etc, will change more gradually (quieter) than they would with shorter links. This one is double interesting, if you consider the fact that they get away with a short PHB, which implies that the vertical movement is small, then the above mentioned aspects won't change much either. Hmmm... One note, the longer the bars, especially if they are skewed in any direction, the more resistance to bending you need, hence the large-ish tube diameter on the lower links.

Mark (Tigman), I'd LOVE to see the front suspension geometry of that car, it would be cool to compare to another T/A setup that I have seen. My guess: long control arms (front view), modest camber gain (as a result), and very "quiet" roll center migration.

Mark

David Pozzi
09-18-2004, 07:58 PM
here is a front suspension view, this is a Camaro but looks the same as the rocketsports ft suspension. Note it's in full droop up on stands.
David

boodlefoof
09-18-2004, 08:13 PM
Hey PTAddict (or anyone else for that matter),

You mentioned Art Morrisson's 4-bar setup with the upper bars angling in. I've heard of this referred to as a "triangulated four bar." I was recently talking to a guy who said that a setup with the top bars being angled gives too high a roll center... and that if instead the bottom bars are angled in, this is much better.

Just curious if anyone has thoughts?

dennis68
09-18-2004, 09:03 PM
Look up "Satchell link" in google. Also can be found at c-c.com or in Herb Adams book "Chassis Engineering". Good set-up, very little packaging problems, low RRCH, and not much to build (just the 4 links and brackets).

ballistic69
11-08-2004, 07:20 AM
:usa:

David Pozzi
03-18-2005, 05:35 PM
I wanted to post this pic a while back but my scanner was out of whack.

It was taken looking through the driver's side rear quarter window.

This is a vintage race 69 Camaro, I was told this car was built by a College somewhere near Penske's race team. They wanted to try a three link suspension. I don't recall how this setup worked for the present owner, not much was said about it to me or I would have remembered it.

MrQuick
03-18-2005, 05:48 PM
Wow thats a cool shot, looks like the inside of a slot machine. Hey David, how was the tire seminar? What do you think the length of that upper link was? guestimate? 24" maybe?? thank you

David Pozzi
03-18-2005, 08:07 PM
Well the seminar covered mostly what was in his book, there were a lot of generalities but each tire has specific needs that may be different from mfr to mfr, so no great revelations. Certainly it was worth the ten bucks I spent for the day, but I'd rather hear from a savvy crew chief type than an engineer.

Those lower links look to be very high, should have taken some picks of the rear axle brackets, but they look level and must hit the housing pretty high near the tube or just below it. The lower front brackets don't look very well braced. I'd guess the links are 24" to 28". I wouldn't copy this one but it's interesting.

USAZR1
03-19-2005, 04:50 PM
How practical would one of these esoteric chassis set-ups be on a car that spends 98% of its time on the street?

David Pozzi
03-19-2005, 08:22 PM
If the car were on the street most of the time and didn't have extreme horsepower, I don't think you wouldn't need any fancy rear suspension.

boodlefoof
03-20-2005, 10:53 AM
Great to see this post come back up!

Yes, I did look into the Satchell link and now I'm interested in building one!

So, one of the main points of this thread (as I read it) is the focus on the length of the control arms and the effect that has on geometry changes through suspension travel... I imagine that the longer the bars the better (Except that you need stronger bars the longer you go).

My question... well, a couple questions.

First, on a Satchell link type suspension, the length of the lower arms is limited because of the angle towards center... at some point they intersect. Is it better to maintain a roughly 45* angle on the lower bars, or to reduce the angle to have longer bars? Of course, reducing the angle might reduce lateral stability and require a panhard.

Second, that three link picture above appears to have the arms (upper and lower) angling towards one another... i.e., they aren't parallel. I've seen other 4-bar and Satchell setups that have the lower bars angling up as well... shouldn't they be parallel?

Finally, anybody know of an easy to use suspension design program that will model the Satchell link?

Sorry for so many questions. Once I find a new project car (hopefully by this summer), you'll be seeing more questions! It is going to be wild!

David Pozzi
03-20-2005, 11:19 AM
The lower arms in my photo of the 69 Camaro are level. The photo was taken on an angle so it's a little hard to tell. The arms are pretty close to the same length which isn't really good. Just remember, this suspension was built in 69 by a school, it isn't an example of the best way to do it.

boodlefoof
03-21-2005, 02:58 PM
I see. Does the same rule apply to a 4 link type setup then? That the arms shouldn't be the same length? It seems like most that I see have nearly equal length arms. I'm not sure if this is just for convenience of packaging.

z28tt
04-25-2005, 06:21 AM
It didn't seem clear in the posts above, but the TransAm car I crewed for has a Watt's link, rather than a panhard bar. It's sometimes hard to see the other bar, depending on packaging. This has short links going to the center of the rear, with a pivot/180 deg bellcrank, then to the other side. Bellcrank pivots to allow suspension movement, but its laterally centered. Page 623 in Milliken for a simple picture...

Andris Skulte
www.skulte.com
'89 Camaro T56 DFI Twin Turbo

David Pozzi
04-25-2005, 01:32 PM
I would not do a Satchell link, they are prone to binding.
I'd look at Three link setups.

PAI Racing
04-27-2005, 09:31 AM
David,

The "College built car" is the University of Pittsburgh '69 Camaro T/A car. The Penske guys had a hand in the car, from what I heard. In Donahue's book and in subsequent interviews with VanValkenburgh (who was one of the GM engineers when Penske was running the Camaros) I understood that they tried a variety of different rear suspensions in testing. I'd guess that the Pitt car's 3 link is either one of those test set ups, or potentially that it was a band-aid when the car was running in IMSA or TransAm in the early to mid '70s.

Here's a link to some info on that car: http://historictransam.com/Drivers/JohnMiller.htm