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Thread: Roll Center Adjusters

  1. #1
    Celica Pilot Conversion King Gold28's Avatar
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    Default Roll Center Adjusters

    I used to have this stuff up on my web page a few years ago, but since moving to Spain, I lost my webspace and hence the page is no longer.

    Anyhoo Rod (AKA- TheToyman75) was asking about RCAs for his RA28 and I though I would dig it out and put it up here as a more permanent record for you guys.

    Anyhoo, here it is, just my measurements and observations of an RA28 that I once had. Basically a study of what does the RCAīs do for the car. I hope it helps you guys understand a little more about the consequences of playing with suspension components may have. If something isnīt clear, let me know and I will try and explain it a little better.






    Roll Centre Adjusters.

    When I bought the RA28, it already had MA61 Supra struts, lower control arms and steering arms fitted. I guess this was to utilize the bigger ventilated supra brakes and to satisfy the engineer signing off the engine conversion.

    The strut inclination in a MA61 is a little more than that of a RA28. Consequently when these struts were fitted, it increased the positive camber on the front wheels. To fix this the front was lowered about 2 inches, pushing the base of the strut out and a pair of eccentric nuts installed in the cross-member to adjust the camber. On the surface this seemed to be the right fix as it resulted in a neat 0.5 degrees negative camber. Unfortunately lowering the front by this much has some adverse affects on the suspension geometry resulting in a very awkward feeling through chicanes and tight corners.

    Being an engineer I tend to spend more time analyzing a problem than actually fixing it. So consequently the first thing I did was to grab my ruler and measure up the suspension geometry and find out what was actually going wrong.

    The process of finding the roll centre is relatively straight forward and is covered in many suspension books and also on the internet. I recommend the following books for anyone wanting to learn more about vehicle suspension systems.

    Race and Rally Car Source Book - Allan Staniforth

    Tune to Win - Carroll Smith

    Anyhow back to it, here is the suspension geometry of my car as I received it. Note that the blue lines are a representation of the chassis, the black lines are the suspension components and the grey lines are the wheels/tyres. The red lines are my working to locate the instantaneous roll centre of each side and the final roll centre of the front suspension. I have shown 4 cases, representing static height level, 25mm bump level, static height 5° roll and finally 25mm bump and 5° roll. This should account for most of the crucial configurations.

    Suspension Geometry as Received

    Figure 1 - Static Ride Height



    Figure 2 - 25mm Level Bump



    Figure 3 - Static Ride Height + 5° Roll



    Figure 4 - 25mm Level Bump + 5° Roll





    Suspension Geometry Including 25mm Roll Centre Adjusters

    Figure 5 - Static Ride Height



    Figure 6 - 25mm Level Bump



    Figure 7 - Static Ride Height + 5° Roll



    Figure 8 - 25mm Level Bump + 5° Roll





    Interesting things to note:

    The RCA's gave +0.55° roll - not good but fixable.

    Without the RCA's fitted, the roll centre moves around a lot. note the difference between Figures 3 and 4 and imagine going through a corner. First hard under brakes then cornering hard, the roll centre shoots out low and to one side. Then ease off the brakes and the roll centre moves to the other side and up a long way, kind'a awkward isn't it. Compare this to Figures 7 and 8 and you can see that the suspension has much better control over the roll centre.

    Note in the first 4 figures that the roll centre is pretty much on the ground. Imagine the centre of gravity of the car being somewhere around the gear stick height. Thus the body inertia has a moment arm of say 60cm. Now look at Figures 5-8, the roll centre has moved up about 6cm, reducing the moment arm to 54cm. Thus I have gained a (1-54/60)x100% = 10% increase in roll stiffness without touching the springs.

  2. #2
    Car Butcher Carport Converter WDE_BDY's Avatar
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    Default Re: Roll Center Adjusters

    Just out of interest, T3 did make RCA's for the MA61 for $80US. Can't find them on their website at the moment but were definitely sold by their NZ distributor so may pay to ask them if they still have them.
    http://www.technotoytuning.com/produ...p?vehicleid=25

    Callum

  3. #3
    Toymods Vice President Chief Engine Builder TheToyman75's Avatar
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    Default Re: Roll Center Adjusters

    Bump for an awesome thread.
    1971 2T-B Celica TA22 ST.
    1973 2T-G Celica TA22, aka "The Unicorn".
    1975 2T-G Celica TA27 GT
    1976 2T-G Celica TA23, aka "The Colonel".
    1985 3F Auto FJ62 Landcruiser
    1989 7M-GTE MA70 Supra, aka "The Poopra"

    History: Rods Classic Celica Sampler thread.

  4. #4
    Toymods Vice President Chief Engine Builder TheToyman75's Avatar
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    Default Re: Roll Center Adjusters

    Now where is everyone buying these things from. I want to get some for my RA28
    1971 2T-B Celica TA22 ST.
    1973 2T-G Celica TA22, aka "The Unicorn".
    1975 2T-G Celica TA27 GT
    1976 2T-G Celica TA23, aka "The Colonel".
    1985 3F Auto FJ62 Landcruiser
    1989 7M-GTE MA70 Supra, aka "The Poopra"

    History: Rods Classic Celica Sampler thread.

  5. #5
    ......... Carport Converter jeffro ra28's Avatar
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    Default Re: Roll Center Adjusters

    The pics are dead for me, would be interested to see the actual results tho.

  6. #6
    Non qualified Domestic Engineer
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    Default Re: Roll Center Adjusters

    Cool stuff!
    If you are able to show the negative camber gain from the caster angle, the amount of posative camber the outside tyre adopts wouldn't looks as dramatic/be more realistic to what is happening.
    Quote Originally Posted by oldcorollas
    except for a very few exceptions
    "Don't worry what people think, they don't do it very often."

    Daily: Glorified Taxi (F6 Typhoon). Out Of Action: Twin-charged Adub. Ongoing Nightmare: Over re-engineered (not) Alfa Romeo 75.

  7. #7
    Toymods Vice President Chief Engine Builder TheToyman75's Avatar
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    Default Re: Roll Center Adjusters

    All the pics work fine for me
    1971 2T-B Celica TA22 ST.
    1973 2T-G Celica TA22, aka "The Unicorn".
    1975 2T-G Celica TA27 GT
    1976 2T-G Celica TA23, aka "The Colonel".
    1985 3F Auto FJ62 Landcruiser
    1989 7M-GTE MA70 Supra, aka "The Poopra"

    History: Rods Classic Celica Sampler thread.

  8. #8
    I am crap as a Conversion King SilverRA23's Avatar
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    Default Re: Roll Center Adjusters

    I bought mine from whiteline probably three or four years ago.

    AJPS in South Australia do them for the corolla brigade.. so he should be able to help you out in some form.
    Now - RA23-WRX
    Gone-KE10-KE15-KE35-TA22-AE71-Charade-AE82-MS47-KE15-AE95-MX32
    Need club rego or a CAMS licence in VIC? Join TCCAV www.tccav.org.au

  9. #9
    Non qualified Domestic Engineer
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    Default Re: Roll Center Adjusters

    Quote Originally Posted by TheToyman75 View Post
    All the pics work fine for me
    But you can't have body roll without steering lock applied.
    Quote Originally Posted by oldcorollas
    except for a very few exceptions
    "Don't worry what people think, they don't do it very often."

    Daily: Glorified Taxi (F6 Typhoon). Out Of Action: Twin-charged Adub. Ongoing Nightmare: Over re-engineered (not) Alfa Romeo 75.

  10. #10
    Celica Pilot Conversion King Gold28's Avatar
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    Default Re: Roll Center Adjusters

    I'll see if I still have the pics somewhere and repost.

    Plonka, the amount of steering angle in most corners is very little and would only make for a small contribution to the camber angle. I could include it but it adds another variable for little gain in the understanding of what the roll center is and why lowering the car stuff it up.

    Incedently I haven't used Autocad for about 5 years or so now and don't have access to a PC wih it installed anymore so updatign the pics could be a little difficult.

  11. #11
    Car Butcher Carport Converter WDE_BDY's Avatar
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    Default Re: Roll Center Adjusters

    Quote Originally Posted by TheToyman75 View Post
    Now where is everyone buying these things from. I want to get some for my RA28
    Quote Originally Posted by WDE_BDY View Post
    Just out of interest, T3 did make RCA's for the MA61 for $80US. Can't find them on their website at the moment but were definitely sold by their NZ distributor so may pay to ask them if they still have them.
    http://www.technotoytuning.com/produ...p?vehicleid=25

    Callum
    T3 will have them, just a matter of confirming bolt spacing with them. Depending what struts and steering arms you have will dictate what model to order. My KE70 with TT132 struts is running AE86 RCA's.

    Callum

  12. #12
    Purple is the new black! Automotive Encyclopaedia sillycar chick's Avatar
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    Default Re: Roll Center Adjusters

    Anthony if you send me the .dwg file I can convert them to jpegs for you.
    I'll PM you my email address if you like
    51LII - 1972 TA22 Celica | Morpheous Metallic | 4AGE 20v Silvertop | Razorback ECU | W58
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    Quote Originally Posted by TheToyman75 View Post
    There is not much hotter than a Freshly painted Celica, Unless its the reflection of a freshly painted Celica on a freshly painted Celica

  13. #13
    Celica Pilot Conversion King Gold28's Avatar
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    Default Re: Roll Center Adjusters

    I don't even know if I still have the .dwg file. I'll see it is floating around on the home pc.

  14. #14
    Gary Motorsport Inc. Too Much Toyota takai's Avatar
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    Default Re: Roll Center Adjusters

    Quote Originally Posted by TheToyman75 View Post
    Now where is everyone buying these things from. I want to get some for my RA28
    I bought my sets from T3. Very reasonably priced, and good quality.

    Definately have MA61, and MX83 gear, as well as the AE86 stuff.

    With the other brands make sure they are dowelled for both the bolt holes and the balljoint recess. Ive seen many which arnt dowelled for either.
    -Chris | Garage takai - Breaking cars since 1998
    Sparky - AE86 IPRA Racer | RZN149 Hilux - Parts and Car Hauler
    I never saw a wild thing sorry for itself. A small bird will drop frozen dead from a bough without ever having felt sorry for itself. - D.H.Lawrence

  15. #15
    Hung like planet Pluto... Backyard Mechanic Rcubed's Avatar
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    Default Re: Roll Center Adjusters

    got the T3 ones too. US$80 + postage. they are on the website - they just aren't obvious.
    i ended just sending Gabe an email telling him what i wanted [[email protected]]

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