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Rear toe our - pros&cons

Discussion in 'Technical Q&A' started by Corsa, Apr 9, 2005.

  1. Corsa

    Corsa Karting

    Nov 1, 2003
    109
    Stockholm
    Full Name:
    Peter
    It is not that usual to run rear toe out but some do.

    Do anyone know what to gain and lose with rear toe out compared to the moretraditional rear toe in?

    The car is a 328 GTB with Öhlins shocks, very stiff springs etc.

    Ciao
    Peter
     
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  3. fatbillybob

    fatbillybob F1 World Champ
    Consultant Owner

    Aug 10, 2002
    19,992
    socal
    My tip is keep it Ferrari OEM stock. Rear toe can really play games with you. The wrong changes can even make your car dangerous. It is very important that the left and right rear toe be the same relative to chassis centerline unless you are on a track try to correct for specific turns. The weight is like 60/40 bias to the rear. That makes for inherent snap oversteer ala the 911 Porsche. Rear Toe-in helps tame the at the limit oversteer and helps steady the car in high speed straight lines. To further complicate issues the rubber bushings move all over the place and your toe changes in bad ways when you drive. So factory Toe in helps correct for toe changes while in motion. Ferrari has reasons for its "streetcar" suspension settings. Finally, all suspension settings must be taken as a package. One setting effects another so if you go too far astray you need to understand what effect that will have on the suspension "package".
     
  4. carl888

    carl888 F1 Rookie
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    Oct 31, 2003
    4,462
    Melbourne, Australia
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    Carl Jones
    Peter,

    I know of no rear engined vehicle (Or front for that matter) that has a toe out alignment specification for the rear axle. If you are racing a 328 then you could follow what I set up on my 308 GTB as a start with sticky tyres. please note, an alignment like this really makes mince meat of your tyres if you are driving on the highway for any length of time. As for the pros and cons, well, there are no pros for toe out on anything at the rear, simple as that. Toe in increases grip at the rear at the expense of tyre wear. On the track when I did my big tyre and suspension test a few year back the fastest time I did was with the following settings:

    front:
    camber -3.0 degrees.
    caster 6.0 dgrees
    toe 2mm overall toe OUT.

    rear
    camber -2.30 minutes
    toe 7mm overall toe IN.

    Can you tell me what alignment machine you are using? The reason is that when toe is measured in mm as opposed to degrees some machines assume a 14" wheel and some assume a 28" wheel (From where the toe is measured). In other words, you could be double, or half the figure you want to be at depending on the machine. Added to the confusion, some machines measure toe in as a positive value (+) and others measure toe in as a negative value (-)......it's important to know because most people don't.

    The standard Ferrari alignment (On any Ferrari) is quite conservative at the front. The reason is that Ferrari want you to fly off the road front first so it makes them difficult to be sued for any handling issues. An agressive front alignment is where you pick up 80% of the extra speed, the other 20% comes from the extra toe at the rear.

    BTW, I saw that you were wanting to put the 225/245 section tyres on your car. You are wasting your money, stick with the 205/225 combination, see my other post about that. The 032R is an excellent tyre, very progressive in its breakaway and lots of grip. Also consider the Dunlop D-02J, Pirelli P-Zero C and the Bridgestone RE55S, probably the best of the lot, but I have not tested it on a 308/328. Of course, the fastest time you'll set will be on a Hoosier but they are severly compromised for the street and any hint of dampness. Good luck.
     
  5. pma1010

    pma1010 F1 Rookie

    Jul 21, 2002
    2,559
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    Philip
    Great advice here. As others have said, race shops have told me the key with mid engined car stability is maintaining rear toe in when the bushings are under violent flex. If you set it with too little rear toe you'll run toe out under hard cornering and things can get "interesting" waay too quickly. Not fun.

    Two questions to Carl:
    - what difference did you find from the greater amount of caster at the front (and if for "dynamic camber" why this rather than running 3 1/2 to 4 degrees negative camber at the front)?
    - Toe out will make turn in very sharp. Did you find it made the car "darty" and if so, did you find the sharpness of turn in overwhelmed the feeling of wandering (instability) in your lap times.

    Philip
    P.S., I run 3.5 - 4 neg camber at front, no toe 4 deg caster; 2.5 degrees camber at the rear and stock toe.
    Oh, one more: any rec on a slick?
     
  6. Dcup

    Dcup F1 Veteran

    Jan 3, 2005
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    Claude Balls
    i have a 348 ts and my rear toe appears to be slightly out, is this normal in a 348 ??
     
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  8. pma1010

    pma1010 F1 Rookie

    Jul 21, 2002
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    John
    Suggest you check your OM. I can't imagine (i) it is normal and (ii) it is something you'd want.
     
  9. Dcup

    Dcup F1 Veteran

    Jan 3, 2005
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    Claude Balls
    will do, thanks phil..
     
  10. fatbillybob

    fatbillybob F1 World Champ
    Consultant Owner

    Aug 10, 2002
    19,992
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    WOW! that is radical negative on the front to me. It is amazing what works on some cars. I have heard some guys running -7 on the rear or 360C on fast sweeper T8/9 at WSIR. I don't know how they can get this with out ecentric bushings. My guy can't get me that much negative. In my solid bushed 348 during my experimentation I can barely get -3.5 on the rear and -2.5 at the front and keep the nuts on the A-arms. Phil...describe your at limit handling when you run your settings? What springs are you running over stock and are you using stock rubber bushings or poly U, stock rollbars? I have never seen tail heavy cars run more front negative than back
     
  11. pma1010

    pma1010 F1 Rookie

    Jul 21, 2002
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    Philip
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    Alignment rec was from QV London (who've won the Maranello race series multiple times). To get to this we put the rear control arm forks on the front and made up new ones for the rear.

    I run 400 lb springs at front, 350 at rear. 1 inch ARB front. 7/8 rear. Flex bushings on the a-arms, but new. Will go solid/urethane next time. Rear a-arms parallel, 1 1/4 inches rake. A032R and will try slicks this year.

    Car handles v well - Burt Levy did a nice write up in an issue of Classic Sports Car after he drove it and I drove him at Gingerman. It is v stable, has been understeering a bit at medium speed tracks under accel (springs) but very responsive to steering at high speed. I found it was stable through the kink at RA at say 102 but very (too) responsive to the steering at 105. QV recommended a fatter front ARB (specs above). Clearly it has reached the point where a different set up is needed for different tracks.
    Hope some of this is useful.
    Philip
     
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  13. Llenroc

    Llenroc F1 Rookie
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    Jun 9, 2004
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    Vern
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    you may already know this but there are longer (best way to describe them)forks for your lower a-arms. In the 355 challenge parts book the no. is 164755. I assume these would fit your 348. My min. setting is -1.8 and max would be way out there. Just a thought for you.
     
  14. Corsa

    Corsa Karting

    Nov 1, 2003
    109
    Stockholm
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    Peter
    Thanks all.

    I have run with toe out earlier just for the fun of it and for better turn in. Now with even stiffer springs, R-compound tires etc which gives less margins I am afraid that the fun part might end quickly and thing can be very expensive and dangerous. The car is fairly stable on track but on bad roads it sometimes gets interesting at turn in but never at exits.

    However, I want the car to have a small amount of oversteering in the turn in and neutral slight understeering in the exits. I dont want to lose the turn in properties at that I have now and I dont want the car to be dangerous either. Extreme tire wear is also a bad thing and dont really have to since I am not racing the car. Not easy.
     
  15. fatbillybob

    fatbillybob F1 World Champ
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    Aug 10, 2002
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    Phill,

    Very interesting setup you have. I would love to drive it. Have you thought about more front spring? I'm kind of a simpleton and get confused wihen I play with ARB's because they cross talk to the otherside. Or is the reason for the heavy ARB is because you want the cross talk since the 308 body is a wet noodle and heavy springs just deform the shock mount area? I think there is more to be had in my 348 once I truss up the chassis. Then I can go to heavier springs ala 355.
     
  16. fatbillybob

    fatbillybob F1 World Champ
    Consultant Owner

    Aug 10, 2002
    19,992
    socal
    Vern,

    Thanks for the info. I was not aware of the 355 different lower control arms. I am happy with my -3ish rear -2.ish front at this time. I think that severely negative is a mask for other bad things in the suspension. If you need huge neg in your suspension I would think that would mean your set-up can't keep tires flat. There is sidewall deflection where negative camber helps but basically as I understand suspensions it is all about the total set-up package. I'm also lazy sicne I cut my own bushings I would just cut eccentric ones to get the camber I want if I wanted even more negative or I would heimjoint the a-arms which would be superior to the longer 355 arms and cheaper too. But thanks for the info.
     
  17. ferrarifixer

    ferrarifixer F1 Veteran
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    Jul 22, 2003
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    Melbourne
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    Phil Hughes
    Longer control arms also helps raise the roll centre slightly (to a point), and reduces camber and toe changes which make the 348 such a twitchy beast.

    The 355 also has terrible rear geometry when run at low ride heights, but it is better than a 348 once lowered. 360 is no better, with very short upper control arms making for major dynamic geometry changes, only some of which is useful.

    Toe out on the rear is really only useful in exceptional circumstances... basically if you drive on a go-kart like track with no straights whatsoever, it may be beneficial... but the far better way to tune the car is with adjustable shocks, springs and anti roll bars.

    Rear toe out on the road could quite literally kill you, as any sudden twitch from loss of concentration could send you into a spin.
     
  18. Corsa

    Corsa Karting

    Nov 1, 2003
    109
    Stockholm
    Full Name:
    Peter
    Thanks Carl.
    Could you describe how your 308 behaved in turn in and exits with that setting. I suppose that the quite aggresive front set up made the car to turn in quite good with a very stable rear end. Can you remember what ARB, spring rate and tires was used on that car?

    Ciao
    Peter
     
  19. carl888

    carl888 F1 Rookie
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    Oct 31, 2003
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    Carl Jones
    #16 carl888, Apr 19, 2005
    Last edited by a moderator: Sep 7, 2017
    Hi Peter,

    Yes, it's pretty pointy, no problem to set up in a nice drift either. I've never flown off the track forward if that's what you mean! The tyres I tested with those settings were:

    Michelin XWX
    Bridgestone RE71R
    Yokohama A-008Rs
    Yokohama 032R
    Dunlop D-01J
    Dunlop D-02J
    Pirelli P-Zero Giallo Asimmetrico/Direzionale

    Suspension was stock but was completely rebuilt with new inner and outer bushes, dampers rebuilt with increased compression and rebound and lowered 25mm at the front and 15mm at the rear. Note, it's pretty difficult to get more than -1 degree of -ve camber at the front without extended lower wishbone forks (See picture).
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