1st gen push

[glen1]

I have been to a few driving schools with my 1st gen rx7 and it has a small push, or understeer. The car is set up to NASA Pro 7 specs, springs, camber kit, shocks, Toyo tires, posi rear. Any suggestions?

[moto62]

Wow! You have a small bit of understeer in a 1st gen? I wouldn't change anything except trying to make adjustments with tire pressure. Either increase the rear cold starting pressure or decrease the front. Make changes with two lb increments.
Ray

if you have a push in a legal NASA pro7 you have a front brake dragging, massive toe in or a flat tire. all 7's are tail happy....

[Quickshoe]

Congratulations!

You've rid yourself of the nasty oversteer inherent to that car.

Small changes to bring it back towards neutral. I have found that a 2psi differential (changing one end only) is a rather large tuning change. Especially after you've said "okay that's better" and you try two more. Beyond a 4psi split f/r and I'd go back to even and make another change (front bar one hole softer) and start again with small pressure changes.

Off to Grandma's, Happy Easter!!!!!

On edit: When does it push?

Entering a corner?
Mid corner?
Corner exit?
Does it push going both direction?

Okay, now I'm off to Grandma's!


[This message has been edited by Quickshoe (edited April 20, 2003).]

[glen1]

Thanks for the replies. The car pushes as soon as I turn in and get on the gas, not a big push, but just enough to keep me out of trouble, but I would like to get it more neutral. I will try air pressure first, then a little bit of toe out.

[Allen Brown]

Glen,

How tight is your posi? With the oversized clutch plates in my diff, I have a slight understeer. I run a 85 GSL-SE. The car doesn't have turn-in spacers installed.

[wlfpkrcn]

What year is the chassis? I have an 85 that had a big push in Pro7 trim until I relocated the lower trailing arm to pre 83(84?) position (up 19mm)

Eric

[This message has been edited by wlfpkrcn (edited April 21, 2003).]

[glen1]

I am not sure how the posi is set up, I will try to find out. The chassis is a 1983. What do I have to do to relocate the trailing arms?
Glen

[rlekun]

Originally posted by glen1:
I am not sure how the posi is set up, I will try to find out. The chassis is a 1983. What do I have to do to relocate the trailing arms?
Glen

I assume your not running IT, because I beleive that would be illegal:

GCR ITCS D.5.d.8 "No other relocation or reinforcement of any suspension component or mounting point is permitted."

[rlekun]

sorry, double posted




[This message has been edited by rlekun (edited April 24, 2003).]

[Quickshoe]

If there is a dif. in trailing arm mounting location between 79-85 cars, why would it be illegal to relocate them to any position if they are on the same spec line? Assuming that the whole assembly is replaced.

[moto62]

Originally posted by Quickshoe:
If there is a dif. in trailing arm mounting location between 79-85 cars, why would it be illegal to relocate them to any position if they are on the same spec line? Assuming that the whole assembly is replaced.

If you say... drill holes in the bracket on the rear end that the t/a is attached to, to attach the trailing arm in a different location, I would think thats illegal because that would be relocating a mounting point. If you swap rear ends between the different years, then you are changing the complete assembly, regardless of where the control arms are mounted on the different year rear ends, I would think that is legal. Hope this makes sense.
I Ray Man

I stand very corrected, my 7 has a push as well with 1 1/8" of turn in spacers. yesterday at BWRP I was doing the open testing (with all formula cars ne less) and in star mazda turn if I got on the gas too hard at mid turn it would push bad, also would do it in turn 1. I did 300 miles of practice and boy am I sore this morning, learned alot, spun 5 times, 2 of them doing the wild thing out in the dirt at warp nine. I now understand the pucker factor of the talladega turn at BWRP, 100 mph + dirt + vertugo = max pucker factor.

------------------
Daryl Brightwell
ITA RX7 #11
SFR, NORPAC
ITA RX7 #77
CSCC, SOPAC
E/P BOTH SOON

[This message has been edited by 7'sRracing (edited April 25, 2003).]

[wlfpkrcn]

I had to drill the front location point up 19mm on the lower trailing arm. It is legal in Pro7. Wouldn't that fall under the update and backdate rule. You would be backdating to an earlier mounting location or does that only work for parts? I have read the IT rule book, but not to the extent to know the rules that intimately.

E

[moto62]

Originally posted by wlfpkrcn:
I had to drill the front location point up 19mm on the lower trailing arm. It is legal in Pro7. Wouldn't that fall under the update and backdate rule. You would be backdating to an earlier mounting location or does that only work for parts?


The rule goes something like this: Any updated/backdatedcomponents shall be sustituted as a complete assembly.....
Not sure about the pro7 rules but in IT, changing the pick up point of the lower control arm would be a no no.
Ray

[dickita15]

whether or not this is a legal update or you have to change tubs, does anyone have a good handle on what his change does to the handeling. i thought the change on the stock car improved the geometry so why go back to the old spec.
dick

[Allen Brown]

I believe the the old spec is better once the car has been lowered close to or at IT spec min. Still not ideal when lowered this much, but better.

I am far from being an expert in suspension set-up. It was mentioned that turn-in spacers are installed. Has a trilink system been installed? If so or even if not, give Jim Susko (sp?) at G-Force Engineering. His in depth knowledge of the 1st gen suspension should be able to assist in trying to solve some of your handling woes.

[wlfpkrcn]

The change to the car was drastic. It went from a pushing pig to having to dial out all the adjustments I had tried to get oversteer before moving the links. I did not think it would have the effects it did. I know it changes pinion angle. I'm not sure of the other effects it had when cornering

E

[wlfpkrcn]

I believe they changed the mounting point when they started building the SE. Maybe Mazda had a handling problem with it in stock trim, and that's how/why they changed it

E

[wlfpkrcn]

I did some research and here is what I came up with. By moving the link up I increased anti-squat. Increasing anti-squat reduces roll understeer. Therefore curing my push.

So does anybody race a 84-85 chassis in IT? Since adding a panhard rod lowers the roll center on the rear end. I assume this would also reduce roll understeer. Can anyone confirm this?

E

[Tak]

I run an 84 chassis with a panhard rod and turn in spacers. I seem to have the only ITA Rx-7 in the SFR that pushes (not bad, but enough). The real problem is that tire pressures become critical. If I'm off by more than 1 PSI, the push comes on hard and my times drop 1+ sec per lap.
As for relocating the holes, the GCR says traction bars are free. Do our upper axle links qualify as traction bars?

Tak
#29 ITA SFR

[lateapex911]

Tak-


To comment on your thoughts, but in reverse order.....
It sounds as though you are running the upper links. The story goes that the rear end, when lowered to the ride heights we run, goes into a binding situation. (This is a twofold issue, from what I understand ...the links and the watts link both contribute. The axle gets twisted as it gets lowered) Take a look sometime and you'll see that the upper and lower link follow different arcs. The upper links are effectively eliminated in certain scenarios, and the upper location is provided by a new third link, and is considered a traction control device under the ITCS rules. The smae rules allow any material (air, even) as a bushing, so while the upper links are retained, they are located with extrememly soft materials, which really means that they are just along for the ride.

The third link is designed to provide the proper geometry.

If you were talking about retaining the upper links, the free bushing rule would allow you to create a bushing that would allow you to alter the length and/or angle of the link, as long as the link was not modified in any way. I imagine you could do this with machined delrin/aluminum casettes, among other similar solutions.

To directly answer your question about the top links being considered traction devices, I don't believe so.

Also, can you describe your push? High speed? Low speed?, On throttle roll off? Mid corner? On throttle pick up? Corner exit?



------------------
Jake Gulick
CarriageHouse Motorsports
ITA 57 RX-7
New England Region
[email protected]

[lateapex911]

Sorry-double post....

------------------
Jake Gulick
CarriageHouse Motorsports
ITA 57 RX-7
New England Region
[email protected]

[This message has been edited by lateapex911 (edited May 16, 2003).]

[Tak]

Jake-
Just to clarify, I run a panhard bar, not the stock watt's link.
The (mild to moderate) understeer comes after turn in, as power is rolled on. In a long sweeper (say turn 2 at Thunder Hill, CA, ~180 degree, 90 mph) the push begins about 1/3 of the way around. Rolling on throttle makes it worse, jabbing the throttle brings the tail out (too much). Very light brake dragging with throttle on usually solves the problem--just a lot pedal dancing! Doesn't seem to matter what speed, it does the same thing at Laguna turn 2 (~180 degrees, 45 mph)

If you would like to get more detailed, drop me a line ([email protected]).

Tachi (aka Tak)
# 29 ITA SFR SCCA

[dickita15]

tak
what do you have for a rear. limit slip, welded ect..

[Tak]

I have a limited slip in good working order. No wheel spin or chatter exiting slow corners. A little wheel spin if I hop a curb.

Puzzling aint it?

Tak

[Quickshoe]

Originally posted by Tak:
...the push begins about 1/3 of the way around. Rolling on throttle makes it worse, jabbing the throttle brings the tail out (too much)...

Tak,

My chassis set-up skills/knowledge are good, but not great. Having limitations in knowledge and budget have forced me to learn to drive cars with certain 'quirks'.

Obviously a car that is balanced in all types of corners under all conditions would be ideal. However, since that is very unlikely. My theory is to get a car that is close and predictable. The rest will have to be made up with my technique.

This is sincere advice, not some smartass answer, my apologies if it comes across that way.

If rolling the throttle on makes the push worse and jabbing the throttle makes it loose then you need to find the sweet spot somewhere between rolling and jabbing http://Forums.ImprovedTouring.com/it/wink.gif.

Many times every car on the grid will be less than 'perfect'. The biggest difference will be what each driver does with what he has to work with.

Best of luck! Seat time and a longer throttle throw can make this easier.

[lateapex911]

Tak

Does your Panhard rod have adjustable height? If so, this will have an effect. testing should reveal a new personality.

------------------
Jake Gulick
CarriageHouse Motorsports
ITA 57 RX-7
New England Region
[email protected]

[glen1]

Hey everyone, lots of good replies and questions to my original post. I will be running the hpde at Sears this Sunday with Nasa. What are some quick and easy fixes for the understeer? I will try some toe-out and differant tire pressures, maybe 30# in front, 34# rear? What say you?

[Quickshoe]

I'd try an additional 2# split in tire pressure towards the rear. This would be the quickest fix. 30/34 would be okay if you are currently running 30/32.

What happens if you soften the front bar one hole?

Does it have this same behavior when turning right and left? Turn 2 at Laguna is a left hander, not certain about the other corner you were talking about.

[wlfpkrcn]

Glen1
How did Sunday go at Sears. Did you enjoy the "Chute"? Did the car handle ok?

E

I got rid of my push by dropping the nose 3/4", dont know what ill do when I camber the rear end a pinch, it'll probly be pushing again.

[Speed Raycer]

Originally posted by 7'sRracing:
dont know what ill do when I camber the rear end a pinch, it'll probly be pushing again.

Uh oh... get ready for the rules nerds onslaught!!! http://Forums.ImprovedTouring.com/it/biggrin.gif

Seriously though, everyone should check the camber on their rear housings. Our replacement housing (after a crash) had positive caster on both ends and some toe out on the drivers side.



------------------
Scott
It's not what you build...
it's how you build it
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[glen1]

Sunday's Infineon event went well. The car had less push, ran 30psi front, 34psi rear. The chute is great, very narrow opening between the berms on entering, but you can run on the inside berm, it will make the car hop, the no-no's on the outside berm don't do much for the handling, but you can run on them and not get into trouble. It's downhill so you pick up speed, a very late apex on the turn at the end of the chute (7?), great place to do a little power slide. Lots of fun, but not as challenging as the standard course.