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Some great suspension tuning info- Thanks Carroll Smith RIP

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    Some great suspension tuning info- Thanks Carroll Smith RIP



    Too much spring: overall
    • Harsh and choppy ride
    • Much unprovoked sliding
    • Car will not put power down on corner exit – excessive wheel-spin

    Relatively too much spring: front
    • Understeer – although the car may initially point in well
    • Front breaks loose over bumps in corners
    • Front tyres lock while braking over bumps

    Relatively too much spring: rear
    • Oversteer immediately on application of power
    • Excessive wheel-spin

    Too little spring: overall
    • Car contacts the track a lot
    • Floating ride with excess vertical chassis movement, pitch and roll
    • Sloppy and inconsistent response
    • Car slow to take a set – may take more than one

    Relatively too little spring: rear
    • Excessive squat on acceleration accompanied by excessive rear negative camber, leading to oversteer and poor power down characteristics
    • Tendency to fall over on outside rear tyre and ‘flop’ into oversteer and wheel-spin


    Too much anti-roll bar: overall
    • Car will be very sudden in response and will have little feel
    • Car will tend to slide or skate rather than taking a set – especially in slow and medium speed corners
    • Car may dart over one wheel or diagonal bumps

    Relatively too much anti-roll bar: front
    • Corner entry understeer which usually becomes progressively worse as the driver tries to tighten the corner radius.

    Relatively too much anti-roll bar: rear
    • If the imbalance is extreme can cause corner entry oversteer
    • Corner exit oversteer. Car won’t put down power but goes directly to oversteer due to inside wheel-spin
    • Excessive sliding on corner exit
    • Car has a violent reaction to major bumps and may be upset by ‘FIA’ kerbs

    Too little anti-roll bar: overall
    • Car is lazy in response, generally sloppy
    • Car is reluctant to change direction in chicane and esses

    Relatively too little anti-roll bar: front
    • Car ‘falls over’ onto outside tyre on corner entry and then washes out into understeer
    • Car is lazy in direction changes

    Relatively too little anti-roll: rear
    • My own opinion is that on most road courses a rear anti-roll bar is a bad thing. Anti-roll bars transfer lateral load from the unladen tyre to the laden tyre – exactly what we don’t want at the rear. I would much rather use enough spring to support the rear of the car. The exception comes when there are ‘washboard ripples’ at corner exits, as on street circuits and poorly paved road circuits.


    Too much shock: overall
    • A very sudden car with harsh ride qualities, much sliding and wheel patter
    • Car will not absorb road surface irregularities but crashes over them

    Too much rebound force
    • Wheels do not return quickly to road surface after displacement. Inside wheel in a corner may be pulled off the road by the damper while still loaded
    • Car may ‘jack down’ over bumps or in long corners causing a loss of tyre compliance. Car does not power down well at exit of corners when road surface is not extremely smooth

    Too much bump force: general
    • Harsh reaction to road surface irregularities.
    • Car slides rather than sticking
    • Car doesn’t put power down well - driving wheels hop.

    Too much low piston speed bump force
    • Car’s reaction to steering input too sudden
    • Car’s reaction to lateral and longitudinal load transfer too harsh

    Too much high piston speed bump force
    • Car’s reaction to minor road surface irregularities too harsh – tyres hop over ‘chatter bumps’ and ripples in braking areas and corner exits.

    Too little shock: overall
    • Car floats a lot (the Cadillac ride syndrome) and oscillates after bumps
    • Car dives and squats a lot
    • Car rolls quickly in response to lateral acceleration and may tend to ‘fall over’ onto the outside front tyre during corner entry and outside rear tyre on corner exit.
    • Car is generally sloppy and unresponsive

    Too little rebound force: overall
    • Car floats – oscillates after bumps (the Cadillac ride syndrome)

    Too little bump force: overall
    • Initial turn in reaction soft and sloppy
    • Excessive and quick roll, dive and squat

    Too little low piston speed bump force
    • Car is generally imprecise and sloppy in response to lateral (and, to a lesser extent longitudinal) accelerations and to driver steering inputs

    Too little high piston speed bump force
    • Suspension may bottom over the largest bumps on the track resulting in momentary loss of tyre contact and excessive instantaneous loads on suspension and chassis

    Dead shock on one corner
    • A dead shock is surprisingly difficult for a driver to identify and/or isolate
    • At the rear, that car will ‘fall over’ onto the outside tyre and oversteer in one direction only
    • At the front, the car will ‘fall over’ onto the outside tyre on corner entry and then understeer.


    Too much tyre pressure
    • Harsh ride, excessive wheel patter, sliding and wheel-spin
    • High temperature reading and wear at the centre of the tyre

    Too little tyre pressure
    • Soft and mushy response
    • Reduced footprint area and reduced traction
    • High temperatures with a dip in the centre of the tread

    Front tyres ‘going off’
    • Gradually increasing understeer – Enter corners slower, get on power earlier with less steering lock

    Rear tyres ‘going off’
    • Gradually increasing power on oversteer – Try to carry more speed through corner and be later and more gradual with power application


    Limited slip differential wearing out
    • Initial symptoms are decreased power on understeer or increased power on oversteer and inside wheel spin. The car might be easier to drive, but it will be slow
    • When wear becomes extreme, stability under hard acceleration from low speed will diminish and things will not be pleasant at all

    Excessive cam or ramp angle on coast side plate (clutch pack) limited slip differential
    • Corner entry, mid-phase and corner exit understeer. Incurable with geometry changes or rates – must change differential ramps. In 1998, virtually everyone is running 0/0 or 80/80 ramps.


    Excessive front scrub radius (steering offset)
    • Excessive steering effort accompanied by imprecise and inconsistent ‘feel’ and feedback

    Excessive roll centre lateral envelope: front or rear
    • Non-linear response and feel to steering input and lateral ‘G’ (side force) generation

    Rear roll centre too low (or front r/c relatively too high)
    • Roll axis too far out of parallel with mass centroid axis, leading to non-linear generation of lateral load transfer and chassis roll as well as the generation of excessive front jacking force.
    • Tendency will be towards understeer

    Rear roll centre too high (or front r/c relatively too low)
    • Opposite of above, tending towards excessive jacking at the rear and oversteer

    Front track width too narrow relative to rear
    • Car tends to ‘trip over its front feet’ during slow and medium speed corner entry, evidenced by lots of understeer (remember trying to turn your tricycle?)
    • Crutch is to increase front ride rate and roll resistance and increase the camber curves in the direction of more negative camber in bump (usually by raising the front roll centre)
    HTH :D


    HTHtoo :D


      That shit is fantastic, Muz.

      Right now I'm eating scrambled egg. With a comb! Out of a shoe!


        I just looked for an email from a bloke and found it- I'd forgotten it completely!

        It really is awesome. The basis of it is open wheel cars from the eighties which is what Carroll was doing as a race engineer, however, the gist of it is true for all motorsport cars.

        Glad you enjoyed it!


          Thanks Muz.
          10.83 @ 125

          Quickest stock exhaust manifold stud 2JZ in Aus.

          Originally posted by cracka
          Some conclusions empirically were that a large protruding ridge like a prolapsed arsehole around the runner was largely beneficial.


            lol, I think I paid $30 for a book that had all that in it. Its got lots more too, worth buying...only trouble is I cant remember which one it was!


              Nice, thanks Muz. Gotta book another tuning day now, try some of these changes!



                "engineer in your pocket"?
                I don't care a damn for your loyalty when you think I am right; when I really want it most is when you think I am wrong.
                Sir John Monash


                  Where does one find Carroll Smiths books? Amazon?
                  Originally posted by Bender
                  Yeah, well I'm gonna build my own lunar space lander!
                  With blackjack aaaaannd Hookers! Actually, forget the space lander, and the blackjack.
                  Originally posted by JamesB
                  What do you get if you cross a negro with a chinese?

                  ... A car thief that can't drive.


                    Originally posted by FaTs
                    Where does one find Carroll Smiths books? Amazon?

                    Um, when it starts working again ...

                    You can safely buy everything Smith has ever written and learn a lot from it.




                      Boxed set for the win- $100 US plus shipping for every book he wrote.

                      Jsut noticed the sae released a compilation he was working on when he passed away, photocopies of 15 sae papers on chassis and suspension design. $100 just for that! They're acting like it's a 'tribute' to him. Wankers...


                        yep, tech bookshop in vic has it...not worth the money IMHO
                        I don't care a damn for your loyalty when you think I am right; when I really want it most is when you think I am wrong.
                        Sir John Monash


                          I can only add a 'me too' for the recommendations on his tune to win, engineer to win, drive to win and screw to win (which is possibly 'actually' listed as the book on fasteners )

                          Drive to win is probably the most amusing (though the humour is likely subtle and mild for most people's tastes, I liked it) and for 95% of us if we were only allowed one of his books, tune to win would be the one. there's absolutely bugger all in it that is 'dated'. Perhaps a little about tyre and shock absorbers, but it's very obvious as to where things have headed, and how to still be able to optimally apply everything he discusses in a modern context. Absolutely brilliant.
                          John McKenzie

                          Science flies people to the moon.
                          Religion flies people into buildings.


                            Originally posted by bigmuz


                            Boxed set for the win- $100 US plus shipping for every book he wrote.

                            Jsut noticed the sae released a compilation he was working on when he passed away, photocopies of 15 sae papers on chassis and suspension design. $100 just for that! They're acting like it's a 'tribute' to him. Wankers...
                            That is where I got mine from.
                            Are you optimistic or pessimistic about the end of the world?


                              Thanks for your time and effort Muz.