Roll Center Adjusters

[Gold28]

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 RCA´s 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 isn´t 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.

[WDE_BDY]

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

[TheToyman75]

Bump for an awesome thread.

[TheToyman75]

Now where is everyone buying these things from. I want to get some for my RA28

[jeffro ra28]

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

[Duk]

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.

[TheToyman75]

All the pics work fine for me

[SilverRA23]

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.

[Duk]

All the pics work fine for me

But you can't have body roll without steering lock applied.

[Gold28]

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.

[WDE_BDY]

Now where is everyone buying these things from. I want to get some for my RA28

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

[sillycar chick]

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

[Gold28]

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

[takai]

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.

[Rcubed]

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]]