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Reducing Roll

Discussion in 'Technical Q&A' started by pma1010, Nov 21, 2003.

  1. pma1010

    pma1010 F1 Rookie
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    Poor quality scan of pic from exit of turn 14 at Road America in September. Hard to tell from pic, but I should be well on the gas by this point on the curve so car will be leveling out. Any advice on front ARB sizing?

    Spec: Front ARB is stock (18mm on a 308 B IIRC) and rear is 15 mm, 1mm over stock. Springs stock. Shocks QV. 16 inch wheels with 225F, 245R Kumho v700s.

    Any help appreciated.
    Philip
     
  2. vincenzo

    vincenzo Formula 3
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    Does the car push?
    Rgds,
    Vince
     
  3. pma1010

    pma1010 F1 Rookie
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    Not much as long as you get the front planted. It has taken a lot of advice (thanks Rob S.) and effort to "tune" the set up to reduce understeer.
    Philip
     
  4. vincenzo

    vincenzo Formula 3
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    Unsure of where you want to go with the handling?
    Of course, less front ARB, less push. In general, stiffen the side of the car you want to slide first.

    When you said:
    "Not much (push) as long as you get the front planted."

    Makes me think(?) that your transient handling is literally leaning towards excess of body roll. Meaning: if you 'toss' the car (fast roll transient) it will want to push??

    How does the car respond to 'snap' transients?

    Looking at the front, it would appear that you might benefit from more front camber. The rear looks good.

    Have you measured temps across the tire contact patch after a run?
    What kind of tire pressures are you running?

    Rgds,
    Vince
     
  5. fatbillybob

    fatbillybob F1 World Champ
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    Aug 10, 2002
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    Did you consult with rob on more front spring and stock arb at the rear? Also have you tried solid delrin for the arb bushings? PU and rubber bend.
     
  6. pma1010

    pma1010 F1 Rookie
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    I find transition as experienced through an S-bend for example needs to be handled with care. In the transition between 7 and 8 at Gingerman last year I applied power too early exiting 7, car ploughed into 8, dialed in more steering, spun, 4 flat-spotted tires. "BBQ-ing" was how one wag referred to it!

    My sense is more ARB to cut down roll.

    I have played a lot with tire pressures to even out the inner, middle outer temp readings and to reduce plough. With Yoko AVS's I was running 36F, 32R which felt about right. With the V700 Kumhos, I've tried to keep hot temps to 40 or so, meaning 34F, 34R. With the improved stick, more roll.

    I have talked to Rob about stiffer springs ("yes, it would be better on the track at the cost of comfort on the street" where it sees less use) and lowering (QV London does a 40% stiffer, 1 inch shorter spring) again, lower is better. However, I'd like to do one piece at a time hence the progression to date and now the desire to firm up the stock ARB.

    Camber settings are stock. Any recommendation?
    Thanks all,
    Philip
     
  7. pma1010

    pma1010 F1 Rookie
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    Billy
    Both F, R ARB bushings are delrin on the chassis. Solid links at rear, rubber bushings (stock - new) at the front on the links.
     
  8. mk e

    mk e F1 World Champ

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    If the car is balanced well already, you will need to increase both front and rear antisway bars at the same time to maintain the balance. Changing just one will make that end loose. I’ve been told that 1” front and 7/8” rear in a good set-up, but I have not tried it. My car had the stock bars, but 450/400 front/rear springs and has almost no roll. I’m sure the ride in not as good as it was, but honestly I really didn’t notice the change. It might be because I changed the shocks at the same time, but I find the ride quite acceptable.
     
  9. Mitch Alsup

    Mitch Alsup F1 Veteran

    Nov 4, 2003
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    I dont see any particular pushing going on.

    The car is in the perfect position, except that this position should occur just before the apex. Back the whole turn up (say 30 yards--yes really), early braking, early off braking, initiate steering, and squeeze on the throttle.

    By deep braking you got yourself out of shape for the turn exit.
     
  10. pma1010

    pma1010 F1 Rookie
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    Mitch

    Typically, turn 14 at Road America is a late apex with quite high entry speed (flat out of 12, a right hander, in 3rd, up the rise, set up 13, a left hander, slight lift then flat through the apex under the bridge at 13, hitting the rev limiter on the exit as the car drifts out, into 4th, flat, and into the braking zone in 14, late apex, feed in the power and off you go as the car drifts out to the LH side of the track (where this pic is taken).

    Given the car's attitude, I may have early apexed it, but I seem to recall that I am well into the throttle by this point, unwinding the steering on the exit. I interpret your point to mean: more throttle would have leveled out the car more/dialed in a bit more throttle steering and required less steering input/led to less roll at this point on the track. I suspect you are right. I'd still like to reduce body roll to promote a tighter feel and more confidence.

    Thanks for the input.
    Philip
     
  11. Mitch Alsup

    Mitch Alsup F1 Veteran

    Nov 4, 2003
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    Stiffening up a suspension actually sheds absolute grip, trading grip for control as one transitions from slip to slide. Basically, you want the suspension to be as soft as possible without allowing the chassis to touch the road surface and and be as soft as possible without loosing control of the tire camber and toe. Your car shown no issue with being overly cambered in the supplied picture. So, I cant see that reducing roll would help all that much.

    In the following picture notice my F355 has a similar amount of chassis roll in a 180 degree speed-not-important turn at TWS. In addition, I used to have a more agressive deep braking, late apexing driving style that I ended up provoking the car into an attitude where I did not like the feedback the car was giving me. By being more gentle in braking and setting up the turn earlier (but not entering the turn earlier) I ended up working with the car and being a lot faster. The trick to high speed turns it to only worry about the part of the turn from apex on out. If you have to brake 50 yards early; so be it!, just get it set up so that when you initiate steering input, that you can immediately and progressively apply power and such that you are at full power at or before apex. After you get the apex right 20 times in a row, then work on decreasing the braking distance and initiation point.

    Slow in -- fast out!
     
  12. Mitch Alsup

    Mitch Alsup F1 Veteran

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    Now, this picture shown my car in a similar position as yours (T3 TWS long course). I blew this turn! In early, in too fast, can't get on power <yada...>
     
  13. Mitch Alsup

    Mitch Alsup F1 Veteran

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    This god damned software is so ****ing slow that it make me cry!
     
  14. Mitch Alsup

    Mitch Alsup F1 Veteran

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    And where are the stupid pictures--I give up, this new site is not worth crap.
     
  15. pma1010

    pma1010 F1 Rookie
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    Mitch
    Thanks for comments. Love to see pics if you have success un upload or email,
    Philip
     
  16. mk e

    mk e F1 World Champ

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    Mitch, I had the same problem. 1 pic per post, click attach, then when it comes back, click done. It got me a couple times too.
     
  17. jmillard308

    jmillard308 F1 Veteran
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    Philip
    Attached pic shows similar characteritics to yours - similar setup but I am running neg camber front & rear, max front castor, Hoosiers and standard rear bar.
    Since I gave it some camber, the issues you describe went away :)
     
  18. rexrcr

    rexrcr Formula 3

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    Sounds like you found the (or a) reason for the push (power on too early).
    Tire temperature data, and the feel of balance and grip, will determine camber. If you have the temperature information for the tires you currently run, and they show even temps across the face, you don't have enough camber. For a radial, shoot for a linear temperature gradient with no more than 30 degF difference, hotter on the inner, coolest on the outer. For example: 200 inner, 190 center, 180 outer.

    If it's (inner, center, outer) 200, 200, 180: drop pressure 3 psi
    If it's 190, 195, 190: add 1 deg camber fist before pressure adjustment (which you may not anyway)
    If it's 180, 180, 180: add 1 to 2 deg camber

    Some drivers like even temperatures, and can actually cut faster laps this way. I've found in this case it's because the tire will work at larger slip angles in spite of it's construction, and the driver benefits due to more feedback at the limit. This is ultimately a slower set-up, and a more sensitive driver will have more grip with proper alignment.

    Increasing castor can help you feel the tire's self-centering torque a bit better, and helps add dynamic camber.

    Bottom line in suspension development: Making the tires work efficiently while effectively communicating with the driver is a huge challenge (which is why I've been doing this so long). Gathering data on geometry and chassis characteristics takes a lot of the iterative guessing out of the equation, though iteration and effective testing remain key to success.

    Philip, if camber remains to be sorted, that's the next item to address.

    Larger front ARB probably will yield positive results. Shifting roll couple distribution forward helps tremendously with otherwise stock suspension on Ferrari mid engine chassis. But one thing at a time.

    Remember, you don't want to lose the balance you've worked hard to achieve, just increase overall grip.

    And finally, as Jon stated, sometimes a driver must "wait" to go fast.


    Best regards,

    Rob Schermerhorn


    BTW, December European Car has an well-written (with data) piece on driver style comparison between F1 driver Justin Wilson, and the author, Alistair Weaver, who considers himself a relatively experienced club-level racer.
     
  19. Schatten

    Schatten F1 World Champ
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    thanks for the tips on the temp readings Rob. It's always been my understanding about keeping equal readings straight across. I'll definately have to look at a linear increase way of looking at them.
     
  20. rexrcr

    rexrcr Formula 3

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    Equal temperatures across the face of the tire is for traditional bias ply tires. Yes, modern racing 'radial' ply tires are built on a bias too, not nearly as much as the older technology though.

    Of course, if a manufacture's engineer tells you different, listen. OTOH, tire engineer advice tends toward the conservative, especially with pressure.
     
  21. pma1010

    pma1010 F1 Rookie
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    Can you post comparative alignment (camber) specs for your car?

    Here are mine after a 4 wheel alignment last March (along with factory specs in parens listed in my manual in minutes, converted to decimal for easy comparison):

    LF: 0 camber (-0.16 to -0.5); 4 degrees caster (4); 1.8mm toe
    RF: -0.1 degrees camber; 3.8 degrees caster; 1.3mm toe (equating to 3.1mm total versus factory spec of 1 to 3 mm total)
    Set back -0.15 degrees
    LR: -1.6 degrees camber (factory -1.08 to -1.4); 2.2mm toe
    RF: - 1.5 degrees camber; 2.1 mm toe (so total toe is 4.3 mm versus factory spec of 3 to 4mm).

    The specs were done with the recommended weighting in the car etc.

    Rob and John, it sounds like you are both recommending more negative camber, particularly at the front. Can you provide guidance on how much?

    Rob, I am within the factory specs on caster (4 degrees) given the precision of adjustment on the shims. I note that the 288 chassis was set to run 5 degrees 10 minutes of caster. Any recommendation or leave as is for now?

    I am trying to track down someone that will fabricate a custom front sway bar - my estimate is to increase the front to 22 or 23mm which will preserve a similar F, R ratio with an 18mm rear bar as I experience today on my 15mm rear bar.

    I will do some tire temp logging next season to work on pressures.
    Thanks all,
    Philip
     
  22. Mitch Alsup

    Mitch Alsup F1 Veteran

    Nov 4, 2003
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    You want a linear increase in temperature because the outside of the tires (close wheel vehicles) has a high speed blast of cooling air that the insides of the tire does not. Therefore, if the work being done by the contact patch is evenly distributed, the outside gets more cooling and a natural gradient develops.

    If your suspension is not setup right, a pyrometer is your friend! But get it set right before throwing parts at the issue.
     
  23. rexrcr

    rexrcr Formula 3

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    Temperature, pressure and seat-of-the-pants feel will be your guide.
    I do tend to run more castor. A lot more of a 'feel' in setting this specification. You'll notice this not only in the 'weight' of the steering, but also in the transient corner-entry phase. Try to see if the 308 will give you 5 deg or more. Make certain each side is very close.
    If you supply all the specifications for your bars, including motion ratio, I can run some numbers for you so you can compare knowing the actual contribution to wheel rate, rather than estimate relationships "if this is to that, as A is to B, then 3 is to 4, as cat is to dog".

    • Bar length in torsion
    • Diameter
    • Lever arm length, center of bar to center of drop link mount
    • If hollow, tube thickness
    • Distance from control arm inner pivot to ball joint, center-to-center
    • Distance from control arm inner pivot to drop link mount, center-to-center

    Data from both old and new rear bars, and stock front bar. This is just a small window of a larger chunk suspension information that would provide the 'big picture' of what's going on dynamically. It will allow a more scientific prediction. It's an input/ output thing.


    Best regards,

    Rob Schermerhorn
     
  24. pma1010

    pma1010 F1 Rookie
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    Let me see what specs I can pull up when I am back in town. Thanks.
    BTW, going to come to the FCA track event next year? Looks like May or June with possibly a second event.
    Philip
     

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