355 ssuspension rebuild - DIY attempt

As FBB said, as the chassis gets stiffer, the car enters the sliding zone easier because more weight is transfered to the outside tires while turning. An infinirely stiff car, cornering at the limit will have no weight on the inside tires. A car with no springs or anti-roll bars will corner with much more weight on the inside tires (assuming one can keep the chassis from rubbing on the road.)

Thus, chasiss (i.e. spring and anti-roll bar) stiffness is trying to find the point where you have not so oversprung the car that the inside tires are still working well, and being so undersprung that the cambers move to much and shed tire grip due to not being upright on the road. Thus, you want as little spring as possible for overall grip, and just enough springs and bars to keep camber changes under control.

I have pictures taken of me driving my F355 at just about exactly 1 Gs of lateral cornering, showing the outside front and rear tires prefectly verticle on the road surface.

 

Got the ride height measured and put the car on the scales. Was actually impressed at how close the corner weights are (this is half tank of gas).

Posting some pictures of the bushings.
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Did you try with your weight in the driver's seat and footwell?
Did you make sure you have flat floor?
Are there slip plates under the scale pads?

 

How do those bushes look......?

How can you tell if they need replacing?

H

 

I have read this thread the whole way and it shows that when you ask a question about the "right" way to set up a car you will get as many answers as there are drivers..even among pros.
If I may add my 2 cents, I would ask you to re-think some things you are planning.

If, as you say, you will keep this a road car at all, do not "double" your spring rates. This is likely to make the car very uncomfortable to use on the road, cause body and chassis flex and things to rattle loose inside. It will also not be very fast on the track. Stiff tends to equal quick response and rapid breakaway. Unless you are are a pro this is not the fast set up. With sedans, like the 355, the chassis geometry is designed to work best if you allow the car to roll a little bit and going "cave man" stiff will only overload the tire and make the car feel very nervous.

Perhaps an increase of 50-100 pounds in spring rate, upgraded shocks, and a set of adjustable sway bars might be the best way to go at first. This will allow you to tune the car to suit what YOU like rather than struggle with something that is not what you want based on another's advice.

There are lots of good people on here who can help you out, just don't get overloaded!

 

The spring rate and the effective rate at the wheel are very different on a 355. Rob at Deltavee has a pretty good tutorial on his site. Working strictly from memory, the effective rate at the wheel is about 1/2 of the actual spring rate in the front end due to the suspension's motion ratio. So doubling the spring rate is not as radical as it sounds on these cars.

 

Doubling the spring rate divided by the motion ratio, still doubles the effective spring rate after the motion ratio--unless the car is lowered quite significantly (which changes the motion ratio.)

 

Mitch is correct! There is not enough travel available to make a significant M/R change on a 355....soft =grip and grip= faster

 

Sorry if I didn't give the right information, I was speaking from memory after talking to Rob. The reality is that I will be using springs chosen by Rob based on my input and dampers rebuilt and valved to match. I will not be changing the anti-sways at this time.

Rob asked for some more data so I will get that tonight and post if here.

 

No, no, and no. I will do the former tonight. I have no control over the floor. Hell, it's tile, so even if the concrete was perfect, the tile is not. The only slip plates I have are the fact that the scales slide on the tile pretty easy.

 

OK, I am lazy. Rob asked for weights before and after taking the roll bars loose, and weights with me in the driver seat. I had pulled the wheels. The thing to do would have been to set up the scales again, put the wheels back on, weigh the car, pull the wheels, disconnect the sways, then put the wheels back on and weigh again.

I had to get the girls from dance, so I just had enough time to yank the sways loose, slap on the wheels and see what I got.

LF 701, RR 896 = 1597
LR 916, RF 683 = 1599

I think someone has done this before!

This is with a half tank of gas and no driver or passenger or any ballast.

 

Then you are wasting your time with scales. 1/8" flooring tiles, ruler, aquarium tubing, bucket, home depot you can level a floor. Slip plates because you are on a twin post lift and have no scale platform to roll car. Slip plates best made of 12" steel plates that are greased. Can use plexiglass with sand in between second. No slip plates = suspension stichon = bad results on scales. Driver's weight in car and 1/2 tank gas is standard when scaling cars. Google corner weighting race cars. Hope that helps!

 

^^^ yes, to get correct readings of your corner weights you must make sure you have no suspension bind. If you are using your hoist to lower the car on the scales you will get suspension bind unless the scales can move freely in and out as the wheel is lowered. (even then you should bounce the car to help the suspension settle) Not a fan of that method... With those scales you should have ramps to role the car on them... and disconnect the sway bar end links (front and rear) to make sure there is no preload skewing your numbers.

You could use 1 ft square tiles to level the floor by putting them under the scales. And a long straight bar with a 5 or 6 ft level to make sure everything is good.

Only then you will get correct, repeatable numbers.

-daniel

 

I disagree. Is this the best way to set up a race car? No. Is it better than having no idea? Yes. C'mon here, this is a road car, with rubber bushings and constantly changing loads (fuel, passenger, luggage, top, wheels, etc). Close IS good enough.

BTW, the top of the scales shows perfectly level left to right.

 

^^^^^^^^^^^^^ YUUUUP ^^^^^^^^^^


You have to settle the car on sliders, without doing that your essentially not calibrating the system.

Wheel alignment 101

 

Jeez, this is a tough crowd!

All of this seems to me like saying that if your torque wrench is not accurate to within 0.1 lbs/inch, then you just shouldn't use it at all.

I am not applying for a job with an F1 team here. For sure I am introducing more error than a dedicated race-setup shop will. But in my experience (which is limited but not zero) there is enough stored energy in the rubber bushings that the best setup on earth will simply have you chasing your tail.

And BTW, this has nothing to do with alignment, only ride height.

I also have some saying they wouldn't change the 15 year old bushings...

 

Were just beating on you

Buy honestly chances are your pretty close if you bounced the car a few times on the scales


Back in the day when the 928 came out there were tones of alignment issues at the rear and protocol needed to be followed exactly along with a torque wrench on the wheels to stop it from shimming so I have that burned into me at an early age to get it correct from the get go.

Tools dont make a technician procedure does

 

Change them, I am doing mine over the winter I have them all rebuilt on a second set of arms ready to go. I am using the soft ones as its a daily driver rag top flexible flyer. LOL

 

I am optimistic that the bushings will be the biggest improvement.

What about tie rod ends? Mine feel tight and look good, but I don't know how to know when to change them.

BTW, your avatar makes me want a beer.

 

If the tie rod ends are tight and clean I would leave them

Just move them around and check them really well like you would and elbow LOL
You dont want any binding or looseness

I have new ones to install but will compare them side by side before I decide to put them in when the cars apart

Then my job is done LOL

 

Agreed, so let's do the easy math using round numbers. Factory front dynamic spring rate is around 425lbs/inch as I recall, so doubling it to 850lbs/inch takes the effective rate @ wheel from about 212 to 425lbs/inch. Since Jay (the OP) tracks his car, I don't see these numbers being radically out of proportion especially if he's going to get Deltavee to revalve the shocks at the same time. Challenge spring rates were far higher, right?

So maybe 850lbs/inch is a little too high, but if we took Apex97's lower end of the spectrum and moved up just 50lbs/inch to 475lbs/inch, that is not going to make much difference for track driving. Maybe the real sweet spot for him to start at is somewhere in between.

My original point is that Rob at Deltavee would be a good guy to give a starting recommendation and it appears that is where Jay is getting his setup from. If I have posted the wrong dynamic front spring rate (definition: average spring rate from static ride height to bump) then someone please jump in and correct me.
Thanks!

Also, someone should nudge JM3 (also named Jay) and ask him to jump into this thread. He deals with these questions every day. "3000 lb car, 2:1 motion ratio, driving at XYZ track -- what spring rates should I run?"

 

If I recall correctly the Challenge cars had 900-1050 pound front springs, so this choice is almost are hard as a challenge car.

Depending on application this might be a fine choice.

As someone who has driven my F355 45K miles.....one those long trips the stock F355 suspension is just a little hard, on track days, the stock suspension is well damped but significantly underspring. Verdict, not bad for a street car not bad for a track car.

As the application gets closer to a pure track car on racing rubber the spring rate will tend toward challenge car spring rates. Granted. So lets defnie a spring rate continum with the lower bound set at the factory spring rates, and the other at challeng spring rates.

In this model, you have chosen 80% of the spring rates difference between stock and challenge.

What I am suggesting is that if there remains any significant desire to do long trips inthe car, you night be happier with 30%-50% of the difference in spring rates. This corresponds to 600-odd spring rates.

The counter argument is that if you go 80% to challenge spring rates, why not go the rest of the way?

So why did you choose 80% over (say) 60% or 100%?

 

I am not heavily invested in the suspension math for this car, and got to hit the sack now, but Deltavee's website (Tech Articles link) says Challenge front springs were 2200 lbs/in. I read somewhere else that they were 1600lbs/inch, so let's find someone with a spring rate tester who can get the exact number.

 

The parts diagram shows two different Challenge spring options. For the front I understand they are 2200 lb/in and 1800 lb/in, with the stiffer one more commonly used. I also seem to recall hearing of a third front option for rain.

The standard front spring rate is 185 lb/in according to Rob. That would make the 2200 challenge rate 12 times higher. In that context, doubling the rate doesn't seem extreme.

All this applies to the front, which in my estimation is way too soft in stock form, even for highway driving (lane changes are horrible). Someone more eloquent called it a waterbed in another thread.

As to the rear, I've only heard of the lower of the two Challenge options, which is 700 lb/in. This compares to 260 lb/in standard, again according to Rob. So it appears the rear doesn't need nearly as much stiffening as the front. That is why earlier in this thread I questioned the OP's plan of increasing the rear rates by the same percentage as the front.

Does anyone know the Fiorano Handling Pack spring rates? They appear to be for the front only, so it stands to reason that they take the Challenge approach of making the front stiffer than the rear, while being oriented for street driving.

 

Can someone check with Rob if the 180lb/inch front factory spring rate is the initial rate or the dynamic rate? That seems too soft to be the dynamic rate for a 3000 pound car with roughly a 2:1 motion ratio in the front suspension.

The initial rate (measured on the tester from free height to static ride height) is usually much softer so that the spring remains fully seated in the shock assembly at full droop.

Also, those of you who maintain setup books for your track or race driven F355s can help move this thread from theory to real world by posting your corner weights, ride heights, tire sizes, spring rates, damper selection, and track data (lap times, segment times, etc.) This is usually standard operating procedure in the club racing world to maintain a setup book for every track you run at, and at different ambient temperatures. Thanks.