corner entry push

[coyled]

I have had a slow turn in/ corner entry push for quite a while. Its worse at low speeds and not as bad at high speeds. Once I roll into the throttle, the car rotates but does not really turn. Low speed turns, back to back, a little better turn in would help. I have tried toe out up to 3/8ths, no help. I have thought about going down in spring rate in front or up in back. But, a guy in phoenix that has set up a very fast hi-tech, told me to go up in front spring rate. Roger Kraus told me the same thing. They both said that the narrow front track on the cobra causes the front end to tip over versus the rear, causeing the corner entry push. Finich line is running like a 600 pound front and 450 pound rear and I am just the opposite. Sound counter intuitive to me, but any comments before I spend money on springs to figure this out? Scott

[RACER X #99]

Scott go the Roger Krause site and check out the oversteer/ understeer correction sheet.

RD

[Junket]

Coyled I belive they a correct what you might try if you can find a large SAFE patch of asphalt & run in circles get your buddy to video tape the aspect of the car rolling over or not & what the front wheels are doing.This is typical of a high HP to weight car.
Good luck Ken

[John Hannaford]

Scott,

Going from 450 to 650 on my fronts decreased entry push. You're right that it's counterintuitive, but it seems that the gains from improved geometry (better camber control, reduced dive, reduced transient time) outweighed the increased front weight transfer. I'm not going to claim that the car was balanced at that point - this was just the first step on a suspension makeover - but it did help the entry push.

[coyled]

John, did the car turn in quicker once you changed the springs? I am not as concerned with the push at high speeds or in longer corners as I can control the mid corner and exit push with the throttle. Its just the initial turn in push that I really want to fix. Scott

[RACER X #99]

Scott,
You may want to consider a 10" wide front tire if you are running the 8" fronts. Don Durner has the 10's on his ERA and his seems to turn in pretty good considering the slightly heavier BB he runs.
Perhaps he will post and give you his opinion.

RD

[John Hannaford]

Yes, much quicker. Had to add more power to balance it mid-turn and exit until I did the rest, but that's obviously no problem for you. Chews up the tires faster, but what else are they good for anyway? Another guy that runs with me tried one click stiffer on bump on his Konis, figuring that it was a transient problem, and he said that helped.

[David Borden]

John,

What kind of camber/caster are you running?

There is curve... 450 is too low in the front... going over 600's will start to make the car push again... but may feel more stable at speed and lower lap times.

I just went through this exercise on the spec racer. Give me a ring if you want to talk.

David

[Bob In Ct]

Hey Coyled:
Here are the rules for understeer/oversteer

To reduce understeer
use softer springs in the front
use stiffer springs in the back
use softer sway bar in the front
use stiffer sway bar in the back
use softer shock in the front
use stiffer shock in the back


If the push is happening under braking, bias the brakes toward the back more. The stiffer shocks in the back (softer in the front)will have no effect once the car reaches an equilibrium. The shocks have their effect during transition.

The Cobra tends to push because most have bigger tires in the back which are also farther apart. Playing with Toe-in or out will have little or no effect. A bigger tire up front would also help.

Also keep in mind that when leaving a turn a little power tends to give understeer (push) while a lot of power tends to give oversteer (loose). The rules for correcting problems on road courses are different than on ovals.

Bob

[John Hannaford]

David,

I'm very well sorted out thanks. (I still think you should come to Bay Bottom to see how well!) I'm just relating to Scott what happened back when I started sorting it out. I'm at the same specs as I reported for Shannonville. I don't mind publishing them here, but perhaps after the regional series wraps up this month. I really want that bowling trophy!

Bob,

The standard rules are fine and everyone knows them, or should. But they assume a lot, and when you make an adjustment and the damn car just doesn't do what it's supposed to, well you get to play "special cases". The base FFR front end for example follows the curve David mentioned. Add rate from 450 to about 650 and entry push decreases, keep going and it starts increasing again. It's following the rules of race car physics, just not the simplified version.

[a427sc]

Scott

I would agree with stiffining up the front some. Try tightening up the anti-roll bar first, as it is easier (at least on mine).
And there is the rub. What spring rates Dave B and John H run won't be necessarily right for your Hi-Tech, although the idea is correct. You need to figure out your wheel rates. It's what your tires feel, filtered through all the intricacies of your suspension. Shock angle, distance from tire center etc. Then you can get a true relationship between front and rear. My original Jag ran 2 springs per side @ 525# each,1050 effectively. The front was 400#. But the ratio f/r worked out to 2/3.
The oval guys around here run stiff front, soft rear, claim that the rear will set under acel, and rise under decel, holding the front alignment more accurately. Just the oposite of the road racers I have spoken to.
10" tires, well, I got an FE and it gets a might heavy under braking/turning and just balls up the 8" stuff. 12" in back. But on a cold day, it takes forever to get any heat in them, just can't lean on them hard enough without sliding all over first. And try to find tires in these sizes with a softer compound.

Don

[coyled]

Guys, thanks for all the comments. My alignment specs are 1/16 out, 4.5 castor, -1.5 camber and in back 1/16 in, -1.0 camber. I may try some 550s or 600's up front. If the car turns in better and does not push much more mid corner, I would be stoked. I have read all the basic stuff on what to do tuneing wise. When I have gone down in front tire preasure and up in rear tire preasure it gets worse. As it is, I have been running 20 cold in back which puts me around 29 to 31 when hot. I have cooked the goodyears and am going to a harder compound in backas per Roger Kraus. The fronts are fine, start them at 22 and wind up at 28, not much wear in front. Now I'm thinking about going down in tire preasure in back and up in front a little. Besides all this, the driver needs more help than anything else. Scott

[coyled]

Anybody know what there actual wheel rates are? I was at 135 front(plus sway bar, don't know how to figure that), and 180 rear. I went from 450's to 600's in front and from 600's to 700's in the rear which give me a new front wheel rate of 180 plus the sway bar(?) and rear wheel rate of 335. The cobra is much more responsive and turns in way better, almost feels like it wants to oversteer a bit now. The ride is stiffer but still not harsh. I am on the bfg street tires so I won't know for sure until next weekend at the track on the goodyears. Just curious what you all are running as far as wheel rates? suggestions? scott

[John Hannaford]

Scott,

240 total front, 295 total rear, measured directly at the wheel. But, this probably doesn't mean much for you since the rest of our setups are different. Do you have access to a skidpad (or big empty parking lot) so you could find your basic neutral balance point and then have a point to adjust from? This did a world of good for me - cut a lot of guessing out of the setup process. Kind of like dyno tuning for the chassis.

[coyled]

My old rear wheel rate was 285 not 180 as stated in my previous post. scott

[Tom T.]

On my car, going to a stiffer (and bigger o.d.) sway bar and stiffer shocks increased push, which is what I wanted. Softening the rear shock settings (4 Aldan coilovers on Jag irs) increased oversteer/decreased push.

TT

[a427sc]

Scott, a little dumb math. Your old setup, 135/285=.47. New setup 180/335=.54. The ratio f/r old and new is pretty close, but you have stopped the roll over with higher rates, holding the front alignment, sounds good. My ERA is 189/282=.67, stiffer front, softer rear balance. The result of a large lump under the hood. Might still go a little stiffer in the rear if tweaking out the balance with the bars and shock valving doesn't get it. Now those FFR's, 240/285=.84! But it works for them, compensating for the spec suspension and shocks they have to run with no (?) bars. Quite the mystery, isn't it.

Don

[Tom T.]

I'd like to clarify that I was referring to the front suspension in the first sentence of my post above.

TT

[John Hannaford]

Don,

You're right that the leading edge of the FFR Spec racers seems to be moving toward significantly more rear weight transfer, which is counter-intuitive since they've largely gone to equal tire sizes on all corners. You'd think that we were giving up some useable grip at the rear.

The Cobras that I've heard numbers for seem to mostly run with fairly high front roll resistance distribution percentages (other way from your numbers - calculated by F/(F+R) ... and I just noticed what the variables spell - not a pun, I swear!) of about .6 to .7. This is the kind of balance that you used to see on the live axle Trans-Am cars of the glory days or on passenger cars, and seems to be used by guys who need or want to use a lot of trail brake and throttle to balance, or by those who are more concerned with getting the power down on corner exit.

My theory is that because the FFR spec cars are restricted to stock 5.0 engines, they are finding that they have to set up their cars to focus more on corner speeds than on excess traction for launching out of the corners. The looser setups are working very well for autocross too, as you would expect.

David Borden's two cars are an example of this, I think. His spec racer seems to run better lap times with a lower FRRD of about .48 as compared to the best setup on his supercharged non-spec car that runs better lap times with a little more push. I think that car is around .55 FRRD (Going from memory here, David might confirm this.) I think his 500 hp car benefits more from the extra corner exit traction of a slightly softer rear than it loses from the slightly lower corner speeds.

Based on the admittedly small sample of three Cobras (Superformance, Classics and FFR) I've tried in what their owners claimed were race setups, I think there is a tendency to run them tight. From a safety viewpoint this is probably a good thing since we're all just running for fun! Hell on the tires though.

[coyled]

John, are you saying that the front wheel rates are way higher than the rear? Does your calculation include sway bars?Your f/(f+r) calculation? To get to .6 or .7, you would have a 600 pound front wheel rate and a 400 pound rear wheel rate=.6 . Is this right or am I missing something? scott