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308 Corner Weights

Discussion in 'Technical Q&A' started by pma1010, Jul 26, 2004.

  1. pma1010

    pma1010 F1 Rookie

    Jul 21, 2002
    2,559
    Chicago
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    Philip
    I am installing adjustable spring perches on my 77 308 GTB to accomodate some shorter (and higher rate) springs. With the basic set up of the car (driver, half tank gas), has (i) anyone recorded corner weights; (ii) how much variation in ride height (S->S) is "tolerable"/"recommended" and (iii) how much room is there to get closer to "ideal" corner weighting on the cars without causing inappropriate ride height differentials; and last (iv), is the goal as close to even (S->S) and diagonal (LF->RR etc) or does experience suggest setting it up differently for different tracks?
    Thanks,
    Philip
     
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  3. spang308

    spang308 Formula Junior

    Jul 17, 2004
    887
    York, PA
    I'll take a stab at this one. I have lots of experience setting up and testing various race cars and have scaled more cars than I care to remember.

    I would suggest taking ride height measurements before you start anything. Just as a baseline reference. Make sure you are working on a flat and level "pad". Measure from the ground up to reference points on the car at all four corners (rockers). Be careful how much you lower a 308, particularly if you have a euro front spoiler. It already sits very low and is compounded by how far it is in front of the front axel center line. The 308 has a low CG to start with, so don't expect huge gains by dropping it in the weeds. If they suffer anywhere, it's in soft spring rates and factory sway bars that look like pencils. I'm about to do some suspension tuning on my 308, but haven't had time to dive into it, so I can only provide you with theory and not hard numbers.
    1. In a street car, shoot for 25% of the weight to be on each wheel. 50/50 front to rear.
    2. Balance left to right across the front and rear is very important and if achieved will give you balanced cross weights or "diagonals".
    3. When scaling, raising a corner a bit will add weight to that corner as well as it's diagonal. The weight has to come from somewhere and that somewhere is mostly from the opposite side of the axel that was raised.
    4. Ride height is more important to cars which have underbody ground effect such as F1 cars. I wouldn't be crazy concerned with perfectly even ride heights on a street car. Just so it doesn't look lop sided. Try your best to balance the weights and have the ride heights be even from side to side.
    5. Ride height ratio front to rear is generally labeled rake and will have a huge effect on handling. The more rake, the less the car will want to put down power. Less rake will induce understeer. I been to tracks with a lot of abrupt elevation change, i.e. Watkins Glen or Lime Rock, where the car didn't like any rake at all.
    6. One last note. Align after you scale. Raising and lowering the corners will have an effect on camber and toe because of changes in the static settings from which the A-arms will begin their travel through the arc when compressed or unloaded. Also, as you lower the front, the angle of the tie rod arms change, effectively changing their length from point to point. This will effect the toe setting. If you want to really sweat the details, set the tie rod arms to run parallel to the A arms. This will eliminate bump steer caused by tie rods running through a different arc than the A arms.

    Good luck and if you have any questions feel free to e-mail me.

    John
     
  4. jw6513

    jw6513 Karting

    Nov 24, 2003
    50
    Arizona
    Full Name:
    Jim Whitney
    I'm in the middle of making the same changes to my car, and like Spang308 I have experience in corner weighting (FF and FC racing). Here is what I'm doing:

    1. Inflate tires and record pressure
    2. Record ride height (I measured to a fixed point on the chassis at each corner - I also measured from the top of the tire to the wheel arch using a straight edge laid on top of the tire)
    3. Install springs and dampers
    4. Adjust ride height (from referenced heights recorded) I've heard of people going 1" lower, but I think that is too much, and I agree with Stang308 it won't get you that much handling improvement on this car
    5. Adjust corner weights (again agree with Stang308 - do this prior to other alignment adjustments - my experience is that most cars like a little rake (.25" to .5" - but to begin with, keep it the same as it was (lower front and rear equally) - The car is not going to be equal weight left to right (especially with the driver weight in place), so balance the car to get as close to 50/50 weight distribution diagonally (to maintain about the same ride height, lower the heavy corner a little, and raise the light corner a little)

    I hope this helps - I should have mine done in a few weeks.
     
  5. enjoythemusic

    enjoythemusic F1 World Champ

    Apr 20, 2002
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    Steven
    Wow, great info given! Here is what i did:

    New suspension (from Fchat advertiser Nick) and insured i did indeed have better (thicker) sways.

    Redid ALL bushings with the graphite Energy Suspension.

    Spring rates on stock Euro spec 308GTS QV is 178 front and 187 rear, i went with 300 lbs front and 250 lbs rear.

    Lowered the car about 1.5 inches while also releveling her since i never carry the stock spare tire and the front was too high (see picture below)

    Had car height adjusted/corner weighed with 170 lbs in driver's seat. FYI: Right now she is slightly nose heavy (to my surprise!)

    After all was done, had 4 wheel alignment.


    Soon the front will be a touch lighter than she is now due to new Brembo SLOTTED front brake system. Also, am changing the rims from Etoile 16-inch 7 front and 8 rear to nbew Kinesis K27 17-inch 8/9. These changes will mean she will need to be reweighed and perhaps a new alignment due to lightening the front a bit (Brembo brakes). As you can tell, am carefully looking at the UNSPRUNG weight and also ROTATIONAL MASS.

    Hope this helps, though many people here are better versed. Just trying to share the path taken here.
     
  6. Ricambi America

    Ricambi America F1 World Champ
    Sponsor Owner

    Steven -

    After all these many months of improvements, I'm anxious to hear some track-time impressions of your new set-up!!! Any dates fixed on the calendar yet?

    -Daniel
     
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  8. chrismorse

    chrismorse Formula 3

    Feb 16, 2004
    2,149
    way north california
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    chris morse
    Jim & Spang,

    Where did you get your scales?? How Much? Does anyone rent them?

    Proceedurally, would it be adviseable to start by setting one end of the car on blocks, without wheels at the desired final ride height, so one could adjust the other end without having to chase one's tail? This business of jacking the car up, taking off the wheel, cranking it up a couple of turns, putting the wheel back on , lowering the car, taking mesurements, jacking up the car taking off the wheel etc. etc. is tiresome. It occurred to me that cranking up the right front also slightly raised the left and compressed the left rear. This of course changes all the weights as well - hence my speculation that it might be quicker to start with one end at the desired height. Does this make any sense?

    What is an acceptable variance in corner weight numbers 30-40 pounds.

    Ditto ride height variance?? Even with the sway bars disconnected and the shocks cranked to full soft, the bushings, (even the graphite/poly ones) still are a bit sticky.

    On a related note, has anyone plotted the camber curves/height change and figured out a way to reduce the bump steer - or is it even a problem with the 308.

    ???????,
    chris
     
  9. jmillard308

    jmillard308 F1 Veteran
    Silver Subscribed Owner

    May 29, 2003
    5,931
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    John Millard
    Steve
    What was the reasoning behind the new front/rear spring balance?
    Best
    JM
     
  10. enjoythemusic

    enjoythemusic F1 World Champ

    Apr 20, 2002
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    Steven

    Was said to be a "known good" by others who have done this. Still, debating going 400 lbs front and 350 lbs rear (with physically shorter springs to accomplish proper ride height). Guess for those who just do "normally spirited driving" the 300 front 250 rear would be good enough.

    As she has settled in all is good so far, but i can see during VERY hard braking the front still dips too much (for my liking) and fear the new front brakes will really test things here. When i hear the LOUD crack and see the front deep Euro air damn in pieces after a hard braking event i guess that will signal upgrading the springs. Right now she has a good 3.75 inches of front clearance. Fairly sane for street driving IMHO.
     
  11. enjoythemusic

    enjoythemusic F1 World Champ

    Apr 20, 2002
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    Steven
    No solid dates yet. Am planning for 2005 really. Have realized there is MUCH work to be done :( No need to rush things, would rather test, test, change, test, change, test. Still, stop on by and i'll gladly give you a ride in her.
     
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  13. pma1010

    pma1010 F1 Rookie

    Jul 21, 2002
    2,559
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    Philip
    John and others, thanks for the input. One more set of data points from Mike @ QV London (who had my [3rd set of] springs custom wound for me). His rec from years of setting up 308s and running in the current Ferrari Classic (UK) series:
    - half tank of gas; driver weight in car; disconnect [adj] sway bar end links.
    - set about 25 - 30 mm (so an inch, axle to axle) of rake, front lower than rear
    - set corner weights to s->s and d->d are about equal (+/- 30 lbs).
    - all above at tire pressures equal to track hot (35 - 36)
    - start with a-arms approximately parallel to ground, be prepared for fronts to go "up" as viewed to the wheel from chassis

    Will increase bump steer. Rod ends and shimming can reduce if too bad.

    Setting corner weights in this way can make the body alignment look pretty "off". It's used mainly on the track. Live with it!

    On other stuff raised here, my experience: f/r bias valve on the brakes helps and is cheap (but not a substitute for better brakes); the euro spoiler becomes toast after some heavy braking and off track excursions/taking the car off the trailer too cavalierly. QV London's 308s in the FC series run with the shallow spoiler.

    Philip
     
  14. enjoythemusic

    enjoythemusic F1 World Champ

    Apr 20, 2002
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    Philip, thanks for the info. Agreed about better brakes and will see if i "need" a biasing valve versus trying different brake pad compounds. And yes, the deep front Euro air dam is going to be toast sooner rather than later :(
     
  15. Sophia

    Sophia Formula Junior

    Aug 17, 2003
    298
    Dash Point/Federal W
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    Peter Barbin
    I'm curious too, as I've just done the front springs alone with thus far favorable "GT" use results. Here's what I've done for my US 308:

    http://ferrarichat.com/forum/showthread.php?t=25666

    PeterB.
     
  16. jw6513

    jw6513 Karting

    Nov 24, 2003
    50
    Arizona
    Full Name:
    Jim Whitney
    There are many sources for scales. I'd check Pegasus or another racing supply company such as Racer Parts Wholesale, but a set of scales and a platform is going to be expensive....over $2,000. I suggest contacting a local race shop, and renting time on theirs, or have them do it. As far as doing one end at a time....I think you are out of luck there. The key is getting the car balanced diagonally, and you need all four corners to do that. Also, remember to disconnect the sway bars (one end of each) while you are doing the corner weighting. When you reconnect the bars, do it with the car still on the scales (perfectly level) If they have to be bound to get them on, then they need to be bent to eliminate any preloading. On a race car that is easy because you have adjustable rod ends. We won't be so lucky.
     
  17. enjoythemusic

    enjoythemusic F1 World Champ

    Apr 20, 2002
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    Peter,

    Nice job and glad it turned out well :)

    My apologies but... there is much more to the equation than just springs in the case of the 308 here. New dual adjustable shocks and also new Energy Suspension graphite bushings were also done. Frankly, the Koni shocks leave much to be desired and have truly adjustable shocks allow for many variables.

    Simple examples are:

    1. A good modestly firm setting for street

    2. Different setting for ultra smooth ride

    3. Yet another super stiff for road driving fun

    i have 'found' an in between setting for ease of use. Adjusting the front shocks means i need to use my jack so... Basically, i set the fronts to medium-firm for rebound and compression, yet the rears are set for medium rebound. The rear COMPRESSION i can adjust very easily and therefore can make the ride relatively smooth when on a date, yet easily firm it up for more aggressive driving. While this in between setting is really not necessarily optimized for anything in particular, it gives a middle ground of sorts and provides some versatility without leaning too much towards any one area.

    If you lived close by i'd gladly make some suspension adjustments so you could feel the variables in different settings of the compression and the rebound. The difference IS NOT subtle.

    PS: the new shocks also allow the height to be fully adjustable. This is an asset for those who want to corner weigh/balance their car. Add to this the fact that the new springs use industry standard size so any spring is good to go and you DO NOT need a spring compresser to install it. See Fchat sponsor's website http://www.nicksforzaferrari.com/forzaferrariwebsite1005.htm
     
  18. spang308

    spang308 Formula Junior

    Jul 17, 2004
    887
    York, PA
    Good point Jim. It was late when I was typing my reply last night and I failed to mention how critical it is to disconnect the sway bars. One link on each axel is sufficient. If you want to be precise, make up some drop links using rod ends and a threaded coupler. This will allow you to hook up the bars with zero preload when finished.
    As far as scales go, Longacre makes a good set up for around $1200. If you have a level shop floor you can skip the set up pad. A 6' or 8' carpenters level will come in handy. Set up the scales and shim the pads from underneath to arrive at a level plane. Lay the level across the scales and check side to side, front to back, and diagonally. It has served me well in the past. If you don't want to dump a pile of money on scales, borrow some like Jim said. If you have access to a set, somebody would probably be happy to loan them to you for a couple of green backs. I drove for teams who owned scales and set up pads, so I always had access to some. Lucky me I guess. :)
    pma1010, good advise from what I can tell. The rake number sounds a little strong, but I haven't done any set up and testing with my 308 so I can't say for certain. These cars may like that much. Being mid engined with natural weight bias to the rear would back up that theory.

    Glad there are some that are daring to make the 308 what it could have/should have been all along. Good luck to you all.
    This site is awesome isn't it???

    John
     
  19. fatbillybob

    fatbillybob F1 World Champ
    Consultant Owner

    Aug 10, 2002
    19,024
    socal
    Rob needs scales. Lets convince him to buy Fchat scales and we will rent them from him on an asneeded basis.
     
  20. fatbillybob

    fatbillybob F1 World Champ
    Consultant Owner

    Aug 10, 2002
    19,024
    socal
    I always start with the tires and wheels I'm going to run and the factory ride heights. I then lower the car to where i want with the motion ratios per WSM. Then disconnect sway bars and scale the car with the classic 50/50 diagonal. This keep the factory intended rake alone but lowers the car. After you drive th car on the track you can chnge parameters like rake for oversteer understeer braking stability etc....
     
  21. enjoythemusic

    enjoythemusic F1 World Champ

    Apr 20, 2002
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    Steven
    In theory, yet last time we weighted the Euro spec 308 here it was a touch front heavy(!). We were scratching our heads. Once the new Brembo front brakes and rims/tires are on her i want to see what the scales say as i also removed the crap sstock seats for Sparcos.

    Amen my friend. The 308 really seems to have MUCH life in her provided time/parts/funds. Am very impressed at how well the 308 here is doing so far. But to be frank, she is underpowered yet that can be 'fixed' too. Also wondering what a lighter clutch/flywheel will do. The stock unit must weigh a ton (proverbial speaking) as i can feel how damn heavy it is.
     
  22. chrismorse

    chrismorse Formula 3

    Feb 16, 2004
    2,149
    way north california
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    chris morse
    I would definitely second that motion.

    I'm sure there are a whole list of tools, some expensive, some not that could be rented, with a realistic deposite, to chat members.

    This would also be a minor book keeping effort and likely involve waiting lists.

    sure sounds good.

    chris
     

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