Race Engine Forum UK

Hi All,

I'm after some professional opinions on Roll Center Adjusters.

I'm not sure how "common" the knowledge of these things are, so for those that don't know, they're effectively "spacer blocks" that are mounted between the hub and the ball joint. On lowered cars they are used to return the lower arm back to a more "normal" position.

So I guess what I'm asking you all is, have you ever used them? Can you see a benefit to them? Recommended for or against?

Many thanks
Anthony
- hoping to soon have my car back!

You mean something like that, the aluminium block between strut and lower thingi?

have you ever used them? Can you see a benefit to them? Recommended for or against?

used: no, dont have my car lowered that much
benefit: yes, you move the roll center where the OEM placed it
recommended: yes for heavy lowered car, IF designed properly and fixed with correct spec bolts.
take care for rim clearance and to adjust both front and rear, check toe afterwards,
would be interessting to exchange during trackday to see if notable differences occur.

What's it all about? On the scetch you can see what happens during lowering the car (lowering heigth indicated with red rectanguar):
due to the geometries, the roll center lowers further than the center of gravity CG.
The distance between RC and CG is the lever along the centrifugal forces make the car roll during cornering.
Longer lever --> car rolls stronger --> handling may become odd, especially if the setup between front and rear would change.
Typically the rear RC sits higher than the front one, making the roll axis of the car tilted towards the front.

hope that helps
Thomas

Thanks for your reply Thomas. Yes those are the sort of things that I'm looking at. I've seen some information about the RCA's in the past and they do seem like a good idea. My car is heavily lowered compared to stock ride height. I would fit with high tensile bolts, the last thing I want is to have them shearing on me.

Typically the rear RC sits higher than the front one, making the roll axis of the car tilted towards the front.

Does that mean that the rear RCA would need to be larger than the front? Or should they be made the same size? Would you say it is a better idea to wait till I have the car back so I can measure specifically how big the RCAs should be to lower the Control Arms back to the stock location?

Thanks,
Ant

Hi Ant

Does that mean that the rear RCA would need to be larger than the front?

No, your OEM already designed an roll axis inclination and I would try to stick to it.

Or should they be made the same size?

Yes, if your lowering is the same front and rear.

Would you say it is a better idea to wait till I have the car back so I can measure specifically how big the RCAs should be to lower the Control Arms back to the stock location?

Definitely yes, you may also find that the space within your rims limit the possible height of the RCA.
Also check that all control arms / steering arms are free with the suspension fully expanded (rebound).

And when you have your car back you can make pictures of the situation,
which makes it better to judge
and more interessting/educational to read.

Thomas

Then I shall do that. When I get the car back I will get some pictures up and resurrect this post. Thanks again for your input so far!

Ant

Hi,
at our company we've designed a car, called the Unikat. It's a "tool" for engineers to understand suspensions and to feel the difference between two settings.
With this car we have the possibility to change things like wheelbase, camber, caster, bumpsteer, motion ratio between wheel/damper, antiroll bar, etc. in very short time. Some parameter online, during driving.

Within a diploma thesis we lowered the roll center (on the front) in steps of 10mm and kept c.g. all the time on the same height, which isn't the normal case as Thomas pointed already. I didn't feel a large difference in rolling until we largely increased the distance between c.g. and roll center from 105mm to 175mm. Before that the only objective thing I recognized was the improved effectiveness of the anti roll bar. But when we lowered the roll center under the road (distance of 210mm), the car was rolling like a ship in squally sea.
The theory says that it's just a linearity between c.g. and roll axis distance, in practice I cannot agree.

So the only thing is to try out, even it's possible that the car handling will improve. Because of antiroll bar improvement.

Christoph

Many thanks Christoph! The car looks great and would appear to have a host of knowledge thrown into it.

I will bare your comments in mind.

Ant

Hi Christoph

So the only thing is to try out

fully agree, best combined with a systematic approach.

your unikat vehicle looks very interesting indeed.
I would love to see some larger pictures and read some details.
May be worth to put in a new thread.

Thomas

Hi,

I have a powerpoint-presentation of the unikat, but the file is 4,5 Mb and I have no webspace.
I can upload it at rapidshare or send it per mail to somebody who can put it online.

Christoph

Christoph, email me and I will host it for you.

Anthony

Ok, Idecided to start looking at this again - not that I've got the car back but figured that tracking down parts I need would be a good idea.

I've been looking around at various designs and keep noticing that some have a sort of locating "collar" on the bolt holes like in the image below.



I can't think what these are called though. Does anyone know? And know of a supplier?

The only place I've seen these before was when I removed the head from my engine.

Thanks,
Ant

they are called centering sleeves or fitting sleeves, available with a slit or without.
Main pupose is locating, but they also take some shear load, if both counteparts are properly designed.
You can get them in a professional nut+bolt shop or seach the internet (example Hedtmann).

Thomas

Thanks Thomas. The internet is my main source of information and parts as I work in an office so will be having a look for these today now I know the name.

Thanks again,
Ant