Three link suspension used in TA race cars

[David Pozzi]

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]

Sounds like an awesome time checking out all the badass cars!

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

[PTAddict]

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]

david i love reading your posts, i have learned alot, but whats this no pics
???

[David Pozzi]

here is a side view of Tommy Drisi's TA car.

[David Pozzi]

here is the upper link with adjuster, pretty neat system!

[nancejd]

I love how the axle is between the upper and lower frame rails in the car!

[CoryM]

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]

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]

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]

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]

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]

here is a side view of Tommy Drisi's TA car.

Hmmmmm.... Looks familar....

[CoryM]

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]

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]

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]

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?fo...action=product


Kevin

[Marcus SC&C]

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]

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]

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