spring rates for rough tracks, opinions and advice sought Options

[Seabird]

For those who run on Sebring and equivalently rough tracks what is a good starting point for torsion bars and spring rates on a -4 with DOT R type tires and Koni Sports.

I have done a search and see a lot of advice from West Coast drivers. Also spoke to the experts at Elephant (F 23mm R 250#) but again they have limited rough track experience.

Thanks in advance!

[Jetsetsurfshop]

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[SirAndy]

For those who run on Sebring and equivalently rough tracks what is a good starting point for torsion bars and spring rates on a -4 with DOT R type tires and Koni Sports.

I don't know how rough Sebring is (never been there) and thus don't know how that compares to the tracks we have here but i haven't swapped springs in forever.

Playing with the shock adjustment has been enough to deal with different track surfaces.

I guess that probably doesn't help you much ...
(IMG:style_emoticons/default/unsure.gif)

PS: Completely unrelated, but i can't wait to try Thunderhill West (IMG:style_emoticons/default/evilgrin.gif)

[ThePaintedMan]

I would think there are some other variables here that you'd need to include first. HP and weight figures of your car would be toward the top of the list. Also, what other handling items do you have? Swaybars? Have you done any chassis stiffening?

I.e. if you've got a ton of HP, a really stiff rear end may not be the best way to go. Likewise, if you put crazy springs in it and have not done a whole lot of stiffening, then the extra stress from bumps will be less absorbed by the now-hard springs, meaning that stress goes into the chassis.

In my opinion, which is based mostly on what I've learned from seasoned guys like T.C., Sebring is not as rough as everyone makes it out to be. I've driven it in several types of cars now, and until you get into the really low, stiff cars with less total suspension travel, grip isn't as much of a problem as one might think. However, it seems like 250lb springs would put you in the range of way too stiff, unless you're driving a V8 conversion or something with a ton of weight toward the rear. Again, I am by far still very much a novice though, so I'll wait for the big boys to chime in.

My car is a /4 with stock bars in the front, a stock swaybar and stock springs and DOT R tires. At Sebring I never felt like I was every really out of grip or had any problems with the bumps. If anything, I'd like just a little more spring or swaybar in the back to give me a little better turn-in, and produce a little more oversteer. I think 140 or at VERY most, 180 lb springs in the back would do it. I'd leave the front alone.

[nolift914]

I would think there are some other variables here that you'd need to include first. HP and weight figures of your car would be toward the top of the list. Also, what other handling items do you have? Swaybars? Have you done any chassis stiffening?

I.e. if you've got a ton of HP, a really stiff rear end may not be the best way to go. Likewise, if you put crazy springs in it and have not done a whole lot of stiffening, then the extra stress from bumps will be less absorbed by the now-hard springs, meaning that stress goes into the chassis.

In my opinion, which is based mostly on what I've learned from seasoned guys like T.C., Sebring is not as rough as everyone makes it out to be. I've driven it in several types of cars now, and until you get into the really low, stiff cars with less total suspension travel, grip isn't as much of a problem as one might think. However, it seems like 250lb springs would put you in the range of way too stiff, unless you're driving a V8 conversion or something with a ton of weight toward the rear. Again, I am by far still very much a novice though, so I'll wait for the big boys to chime in.

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[Seabird]

Fair enough. Unfortunately I have few answers. I just bought the car last weekend.

added stiffness: A basic cage (SVRA compliant) is welded into a very solid (rustless) chassis.

hp: might be a warmed up motor. 130hp according to PO...

weight: 1750 or there abouts plus 250 on my account.

front sway bar, adjustable welts type

rear sway bar, stock but currently disconnected

I have raced on Nelsons Ledges and have done several DE at Homestead and Sebring. In my e30 with spece30 suspension I don't have a problem with Sebring as a general course. So in my limited experience I kind of agree with you on Sebring, it is not as bad as it might be made out to be. I am just looking for a starting point to work from.

Regards,

Miguel

[SirAndy]

I am just looking for a starting point to work from.

911 front a-arms? If so, i'd start with the smallest 911 torsion bars (19mm? 21mm? dunno) and use 200+ lbs adjustable springs in the rear.

On the big track, running with the rear bar can be beneficial, if the car is set up for it.

After that, quick and dirty:
Set the ride height, corner balance and use the front sway bar for fine tuning.
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[dlestep]

Before you go down that road, you may want to consider reducing the un-sprung
weight, first.
The reduction of unsprung weight would allow the suspension to react quicker to
compression and extension. Then control it with sufficient torsion and shocks,
not necessarily a requirement, but nice if they are adjustible.
In choice of torsion bar diameters, moderation is the word.
There is a point when one can "over-bar" a car and then the body becomes the
suspension, which you don't want.
Listening to everyone's idea of the best setup is like listening to a hundred
individual conversations, all of which, on the most part contradict each other.
I pick stereos with my ears, and couches with my ass.
I enjoy a car when belted, my body is one with the car, my hands, arms and feet
dictate my cars' immediate response, with predictable confidence.
Only then can I really press the envelope with consistancy.
Running above mechanical failures, is addictive and expensive.
It will always feel three steps forward, two steps back.
And then, it all comes together. What a ride. Position, who cares.

[ThePaintedMan]

Manuel,
I agree with what's been said previously. Suspension is one of those things were we can all approach it differently and get similar results. In your case, it might be worth driving the car once at Sebring so you can feel for yourself what you need. No sense in spending money on "upgrades" yet if you haven't taken the car out and flogged it yourself (IMG:style_emoticons/default/smile.gif)

The 914 suspension stock is pretty damn responsive, especially for being 40 years old. With your previous experience you should have a good feel for what you think the car will need to go faster/be more responsive. Having the rear swaybay is a big plus in your situation, because it'll give you a chance to run a session or two with it disconnected. Then if you think you need a little more oversteer, you can connect it. The Konis are an added benefit as well. If at the end of the weekend you have some solid notes of things you'd like to improve, you could probably report back here and people can give you an idea of things to try to give you the biggest bang for your buck. My vote is to run it like it is and see how you like it! (IMG:style_emoticons/default/beerchug.gif)

[Matt Romanowski]

What elephant told you is probably a decent. In my stock bodied car with around 160 HP, I ran 21mm T-bars, 19mm swaybar, and 180lb springs at Sebring and it was pretty good. What I listed is a very solid starting point for a fairly low car. You can go 23mm t bars, 21mm sway, and 250lb springs, but it will be pretty stiff. That will let you run real low with minimal suspension movement, but it's tougher to feel what the car is doing.

19mm torsion bars are way too soft. You will be on the front bump rubbers all the time.

[brilliantrot]

By the time you factor in the reaction in the A-arm, 24mm front torsions work out to around a 230 lb/in wheel rate. 23mm/#250 rear with a softish front bar and no rear sounds about right to me.

[Jetsetsurfshop]

Manuel,
I agree with what's been said previously. Suspension is one of those things were we can all approach it differently and get similar results. In your case, it might be worth driving the car once at Sebring so you can feel for yourself what you need. No sense in spending money on "upgrades" yet if you haven't taken the car out and flogged it yourself (IMG:style_emoticons/default/smile.gif)

The 914 suspension stock is pretty damn responsive, especially for being 40 years old. With your previous experience you should have a good feel for what you think the car will need to go faster/be more responsive. Having the rear swaybay is a big plus in your situation, because it'll give you a chance to run a session or two with it disconnected. Then if you think you need a little more oversteer, you can connect it. The Konis are an added benefit as well. If at the end of the weekend you have some solid notes of things you'd like to improve, you could probably report back here and people can give you an idea of things to try to give you the biggest bang for your buck. My vote is to run it like it is and see how you like it! (IMG:style_emoticons/default/beerchug.gif)

I agree with running it as is. My car in stock form was a blast. You can change things, little by little, and dial her in.
Something else to mention. One of my Sebring instructors in TT softened up his Corvette suspension and shaved two seconds off his already fast time. Food for thought.... (IMG:style_emoticons/default/driving.gif)

[dlestep]

In response to running [as is], at least do the following first:
Replace: Street worn front discs, pads, rubber brake lines, front bearings,
rod ends, and ball joints. Bleed system, lower first, then upper on each caliper.
Double check vent clearance on rear calipers.
Replace shorter lug bolts with the longer ones and check lug torque, twice.
Check: fuel lines and replace all rubber, including the steering shaft rubber disc,
and check steering shaft u-joints and shaft bushing.
Replace: exhaust and intake gaskets.
Move all fuel filters forward and not in trunks or engine bay.
Check: transaxle fluid, CVs and boots, output shaft seal, shift rod input seal.
Replace: pivot and throw-out bearing, and clutch disc.
Replace: shifter bushings, and shift rod coupler (safety wire bolt).
Replace: front engine mounts on crossmember and new outboard bolts.
Replace: Clutch cable and throttle cable.
Reset chamber on all four corners and align.
Now everything has been checked and controls are on equal terms.
You have a base-line to operate from.
Use check lists, do not rely on memory.
~
I have probably missed alot of little stuff, but after these things are completed,
your confidence level will be higher.

[Seabird]

Thanks everyone for your input! A lot of good points made.

Dave, thanks for the beingins of a check list. Check lists are goood (IMG:style_emoticons/default/idea.gif)

This car has been sitting for a long time and needs plenty of catching up on maintenance. If it had been in regular service before I bought it I may have thought about doing less to get it ready for the track. I am not interested in showing up to the track and have to end the weekend early because the shocks are blown out or a bit of dried rubber failed. Going through and getting the safety equipment, drive train and suspension sorted is just the cost of tracking a car in my book.

Yes it becomes a slippery slope, one I have slid down before! It costs a little money but I like where it ends up. A well sorted car that provides enjoyable weekends on the tarmac (IMG:style_emoticons/default/driving.gif) instead of in the pits (IMG:style_emoticons/default/smash.gif)

A lot of Florida folks on this forum, that's cool! I hope to see you all at the track!

Happy turkey day everyone!

Miguel

[ThePaintedMan]

There are indeed a few of us here. Where are you located? A few of us are in the Tampa Bay area. I'm in St. Petersburg myself. It'd be fun to meet up with you at some point and check out the ride!

Happy Turkey Day! (IMG:style_emoticons/default/beerchug.gif)

[brant]

23mm is too large/stiff

[Seabird]

There are indeed a few of us here. Where are you located? A few of us are in the Tampa Bay area. I'm in St. Petersburg myself. It'd be fun to meet up with you at some point and check out the ride!

Happy Turkey Day! (IMG:style_emoticons/default/beerchug.gif)

I am down in Hollywood, between Ft. Lauderdale and Miami. I will be doing another year with NASA before making the move to SVRA or what ever other vintage group that will take me and the 914. If you do go to a NASA event lets get together.

Regards,

Miguel

[brant]

I'd recommend pulling the svra (or which ever club) rules now. Read them through and base anything you do for nasa on hose rules so that option isn't in conflict in the future

I'm the porsche eligibility chairman for our vintage club. I see lots of cars built for other clubs, and the car owners get really frustrated when modifications they have made without reading the rules are in conflict

[Seabird]

I'd recommend pulling the svra (or which ever club) rules now. Read them through and base anything you do for nasa on hose rules so that option isn't in conflict in the future

I'm the porsche eligibility chairman for our vintage club. I see lots of cars built for other clubs, and the car owners get really frustrated when modifications they have made without reading the rules are in conflict

10-4 all ready have done that (IMG:style_emoticons/default/biggrin.gif) and that is the plan. I see a lot a of 914-6 on the timing sheets hardly ever a 914-4. I am assuming these are mostly replica cars? Are the -4s at that much of a disadvantage out on the track?

Thanks Brant.

[r_towle]

I'd recommend pulling the svra (or which ever club) rules now. Read them through and base anything you do for nasa on hose rules so that option isn't in conflict in the future

I'm the porsche eligibility chairman for our vintage club. I see lots of cars built for other clubs, and the car owners get really frustrated when modifications they have made without reading the rules are in conflict

10-4 all ready have done that (IMG:style_emoticons/default/biggrin.gif) and that is the plan. I see a lot a of 914-6 on the timing sheets hardly ever a 914-4. I am assuming these are mostly replica cars? Are the -4s at that much of a disadvantage out on the track?

Thanks Brant.

In vintage racing you are competitive, in SCCA racing you have to deal with miatas a which seem to have better power to weight ratios in stock form.

Rich