diyman25

As u guys can see, with over 1650Lb spring at front and 1400lb at on special revalve endless zeal coilover
With 18x11j. And 280/65/18 A005 slick

When coming out of corner, is clearing on 3 wheels, that is a lot of weight transfer to rear
But kinda da too understeer!!!
Next race is due in 2 week
So no time to revalve, guess I will play with bump stop on the rear to see that will reduce the understeer!!?!

BLUE TII

iTrader: (9)

Yes, generally I see Japanese FDs with GT wing set-up with a higher rear spring rate than front spring rate because of the added downforce.

16K front/18K rear seems like the off the shelf rates for FD on circuit- you obviously needed more spring for your actual slick tires.

If you are happy with the turn in with the 29K up front try raising the rear 25K springs up to 29K and above.

If you feel the car understeers when you turn in fast (doesn't look like it does) you could swap to 25K front 29K rear (but, that is a huge change in balance of the car).

But, I would still try more rear spring than front if you have a GT wing (how much more depends on your front splitter design.)

I would also add a front splitter to try and help balance your rear wing if your rules allow. A 6" splitter won't even get you balanced downforce with even the single element rear wing unless you take some angle out of the rear.

I am only advising on what I see othe FD racers do, not from my own experiences.

diyman25

Yep , the a lot of Japanese car have very high spring rate, I think one reason is their Tarmac is very sticky

Sec most of car u see with higher spring rate is Time attack car, that only run one or two lap only

On my endurance race set up , I can't have that kind of extreme set up

Other in this condion I won't be able to save it back



That why I want to try some bump stop tuning
That don't impact too much on the car's weight transfer

racingdriver

I run 1350 fr, 1300 rr and no real bodyroll problems. I do run full slicks, 330/320 18's and big aero. I had to run mazda motorsports biggest front sway bar to remove the roll in the front.

BLUE TII

iTrader: (9)

As u guys can see, with over 1650Lb spring at front and 1400lb at on special revalve endless zeal coilover
With 18x11j. And 280/65/18 A005 slick

Spring rates?

Do we have a miscommunication?

1650lbin = 29.5kgmm
1400lbin = 25kgmm



Yep , the a lot of Japanese car have very high spring rate, I think one reason is their Tarmac is very sticky

Sec most of car u see with higher spring rate is Time attack car, that only run one or two lap only

On my endurance race set up , I can't have that kind of extreme set up

Other in this condion I won't be able to save it back



Yes, maybe not go with higher rear rate than front then, but bring it closer like "racingdriver's".

24k front/23k rear

diyman25

Just get my special order blade type sway bar:-)
Will see what this do on my race car!!!

One reason I run that high spring rate on front is to prevent tire hitting frame rail on full bump.....

racingdriver

Your car looks really low as well. I run 5 1/4 inch from the ground to the rocker lip behind the front wheel. Any lower will throw off you geometry and actually create roll as you mess up the roll center geometry. Then when you bottom out you get snap over/understeer.

diyman25

Did u cut off frame rail ? What tire diameter of ur set up ?

I have to control the travel by soft bump stop
So far it work ok ......

Valkyrie

Lower ride heights require exponentially higher wheel rates.

You could probably afford to use lower spring rates if you raised the ride height a little.

You can make up for the loss in front downforce by changing the front lip. You could add a flexible rubber skirt or something.

diyman25

That is true to a some point

I was believer of that until I see the R8 cup race car

Stock control location, lower to the ground
And install with 2750LB spring on ftont
On MR car imagine how hevey on the rear

Basicsly the car will told u screw the geometry I will just use tire and power to get fast lap !!!

Valkyrie

Any suspension will work if you don't let it.

Alpine

with the 3 wheeling issue, i'm wondering if it can be helped by one of the following

1. soften the front sway bar
2. front droop travel, maybe your coilover has limited travel in droop and thus picking up the front inside tire?

picking up the front inside is not necessarily a bad thing though, FD can always use some understeer on corner exit imo =)

Alpine

in anycase, please keep us updated with your progress, we could use more race FD discussions around here !

Alpine

thinking about it some more, I think it's very likely your front suspension is lacking droop travel.

here's my logic, assuming your front corner weight is 750 LB, your front spring is 1650 LB/INCH.

The FD front motion ratio is 0.67, so the mechanical leverage is 1.49.
750 LB x 1.49 = 1117 LB of force acting on the shock/spring.

Since your spring rate is 1650LB/INCH, 1117/1650 = 0.67 the front will only compress 0.67inch with the car on the ground.

Assuming the spring has no preload, and spring has no tender spring, you will only have 0.67inch of droop travel !

I think the best solution is to add helper spring, in order to have more droop travel.

diyman25

My Endless zeal shock have very limit stroke

As the motion ratio, I think by switch to 18x11j ET 18 wheel from stock
That will afect the motion ratio

BLUE TII

iTrader: (9)

As the motion ratio, I think by switch to 18x11j ET 18 wheel from stock
That will afect the motion ratio

Well...
Motion Ratio is just the ratio of how much the wheel moves vertically in bump compared to how far the suspension compresses the shock.

Wheel offset won't affect it, but moving lower shock mounting position on the lower arm would.

Wheel Rate is the actual force at the tire contact patch that must be exerted to displace the spring (so, like spring rate at the contact patch).

Suspension Frequency is where the wheel and tire mass comes into affect with the Motion Ratio.

Suspension Frequency doesn't really matter in a race car except for to mitigate driver fatigue (it is a comfort thing) and you don't want the chassis resulting front and rear natural frequencies coincide so you end up with a critical coupled condition (rear tire cycling at exact same frequency as front after a bump so entire car bounces instead of pitches).

But really... you have dampers and race car dampers do not tend toward under damped like street car dampers in the name of comfort- so Suspension Frequency matters even less.

BLUE TII

iTrader: (9)

Front tire is being picked up because-

The rear spring rate is much lower relative to the front spring rate.

The car is overly lowered without proper Roll Center Correction.

The car has more rear aero downforce than front (which is exaggerated once the rear does roll and front downforce decreases).

^^ overly lowered car without correcting the Roll Center causes a longer Roll Couple (difference between Center of Mass of car and the Roll Center of the suspension.
Therefore the mass of the car causes more roll through the lever arm of the Roll Couple than it would if the car was actually at a higher ride height- so you need a higher spring rate/stiffer roll bars (or correct the suspension Roll Centers).

*Would the car be faster if you raised it?*
Not necessarily.
You may lose some front aero effect raising (depends on front splitter design). You may increase aerodynamic drag (depends on how good the FD underbody aero is).
Maybe it is better to lock the suspension down so it doesn't work and keep the car low.

*The car would be easier to drive raised up with a lower front spring rate (rear is already lower)- which seems to be a priority for your endurance racing.*

*Or... correct suspension Roll Centers if rules allowed.
Front is easy, I think you are on your own for the rear on the FD though (which seems to be the root of the current problem you would like to address).*

BLUE TII

iTrader: (9)

You want to add a longer softer bumpstop I assume.

This is the same thing as raising the rear spring rate except that it won't affect initial suspension movements (so small inputs at low speed when your rear aero isn't working).

Problem I see is at high speed with the rear aero you will be driving on the bumpstop. I would rather drive on a more precise and linear coil spring at high speed to make the car more settled.

Alpine

thanks for the tip, can you elaborate on why this is happening? Since the CG also move down as you lower the car together with the roll center.
I'm just wondering what happens to the suspension geometry pass this point?

Valkyrie

You would do well to find out the ride height the car was originally campaigned at. Do you have any documentation or data from the original owners?

They spent a lot of money testing and tuning it, so you would do well to copy whatever setup they used as a baseline. I would recommend using whatever setup they used for Tsukuba, since the tracks are seem to be fairly similar in size and speed ranges.

They might have jacked the height up to make it easier to ship to Taiwan. They probably would have had to just because of how low the front aero is, unless they shipped it with the bumper in the hatch or something.

diyman25

From my driving experience few of endurance race car

Grand am ST Bmw Z4 , NC miata

And this ST3 RX7

For production base race cAr,
Most of team will lower the car to the miniment ridehigh and use widest tire they can this of course throw up the roll center and bump steer

So u can say CG&tire > is more importabrt then geometry or suspension design

Valkyrie

Yeah, probably.



I think this is an ST3 car, too.

They're using side skirts so they don't have to slam it to get the aero down low, though.

diyman25

As u can see, this is how low this car use to be

I even rise up the ridehigh about .5cm
Inorder to have more shock traveling with 280/650/18

Alpine

Came across this picture today , I guess even the best in the business gets inside front lift !

Valkyrie

Nothing on an F1 car is done by accident...except the accidents.

I think F1 cars of that era had monoshocks, which don't roll.