Roll centre adjustment - options & benefits?
 

My car's only lowered 30mm but I'm keen to know more about the benefits and importance of roll centre adjustment on this car. Is this something worth looking at and why/why not?

I've heard about the Moonface MF-R Roll Centres for $300 but haven't seen any actual reviews or real world feedback on them. Does anybody have more information on these any whether they're effective?

Other than the Moonface units it seems that there's only the Robispec front control arms as far as roll centre correction goes. A lot pricier at $750 but you get a ton of other adjustment with them besides roll correction (camber, track). I'd be very interested to hear some feedback on those too.

Big thanks to anybody who can shed some light on this. Seems to be grey territory at the moment which is bit weird considering the amount of lowered cars out there & people tracking them etc. :popcorn:

Reference links:

Moonface MF-R Roll Centers - $300
http://www.ft86club.com/forums/showthread.php?t=35337

Robispec front control arms - $750
http://www.ft86club.com/forums/showthread.php?t=31424

You should look into the book Race Car Vehicle Dynamics - the Milliken guys have quite a bit to say about it. They explain what it does, why its important, and its overall affect on the rest of the vehicle's dynamics. I would say that if youre not tracking your car, theres no need to consider roll center adjusters.

If youre interested, Milliken talks about roll center in Chapter 12 - Chassis Set Up. Im sure you can find a pdf copy floating around on the net

Maybe @robispec, @Dave-ROR, or @CSG Mike can chime in

While they're nice for rounding off the car, I'd recommend you get the larger modifications squared away first.

We don't use them on our car. Would we like to have them? Of course! Alas, the ROI of roll correction is small enough that the cost is not justified to us at our level of development, so we don't have them.

This. While RCAs are nice to have, they are far from mandatory.

To put it simply, a lower RC will increase body roll. Raising it back to a stock height will reduce roll. But the amount it changes usually isn't enough to matter.

I hear what you're saying. I do track my car and I've already done the whole coilovers/bushings/alignment/big brake kit routine. I know that I may not need an RCA but I'm the kind of guy who'll go from 20mm to 10mm spacers just to improve my scrub radius.

To me every bit of feel and handling counts, especially on a car like this which doesn't have the power to bury a bad chassis. :)

I'm curious to know what the tangible benefits might be, if any, and whether any of the track rats besides @robispec might have fiddled with roll centres on this car, or have anything to say on the subject.

Interested to see the nonchalance towards RCAs on this car so far. They were one of the must-have chassis mods in the Evo/STI track day world. :iono:

Thanks! :thanks:

This car doesn't suffer from losing camber via compression as badly as the Evo/STI :)

Maybe not (not that I'd know lol) but I'm pretty sure I've heard some mutterings about camber curves in the Suspension and Track & HPDE sections of the forum. :D

Are roll centres really such a non-issue for us? Sorry if I'm being pedantic - just genuinely curious.

It's a bottom-of-the-list thing like strut tower bars. Good to have, but not the bang for the buck that many other mods are. So they should be towards the end of the mod path.

It's one of those things that need not concern anyone who doesnt intend to utilize them. Theres no point in the average joe spending $5000 on coil set ups when shock dynos and finite adjustments dont matter to the end user. In my opinion, a marginal return to the original roll center height will not make a reasonable return on investment since my vehicle will never be in a scenario where something that finite will be taken into consideration.

While we haven't measured the curves, anecdotal evidence would show that it has (for us, at our level of development), a somewhat negligible effect. I CAN feel the difference, but do not think that it hurts the performance of the car enough that the cost is justified with how our car sits now.

You can see the movement of the wheel, and the car's roll here:

[ame="http://www.youtube.com/watch?v=nGBZWkoQO-s"]CSG BRZ Buttonwillow 2:00 lap - YouTube[/ame]

Buddy Club has extended ball joints for the FR-S

Robispec front control arms also come with bump-steerable tie-rod ends. I feel correcting bump steer is perhaps more important than raising the roll center. Also, if you make the suspension stiff enough, you won't need to worry about roll centers, lol...

The counterpoint is that if you get the rolls centers right, you can run a softer suspension and (especially) softer sway/anti-roll bars while still keeping body movement and weight transfer under control

Wish we could get @robispec in here to say a few words :)

I used to have this idea of how to improve the handling of the brz without sacrificing any ride comfort. Lower the car 3 inches like Robispec has but keep the stock spring rates. Use his top mounts to retain suspension travel and his control arms to correct roll center and bump steer.

This would hugely reduce the distance between roll center and center of gravity. I wonder how big of a difference it would be compared to a stock car. it'll probably be my project when my stock shocks wear out. I'm not too sure about going over ramps though.

IIRC, @robispec has been slowly increasing spring rates. While ride quality does suffer with higher spring rates like the ones we use (10/12k and 12/15k), on-track performance is increased.

The video I posted above is on 10k/12k.

Guess this hpthread had kind of run its course...roll centres not a priority for this car.

Thanks to everyone for chiming in.

Now...what about bump steer correction options? :)

racerx or robispec both can make bump steer correction toe links...

Coming from an S2k... I use bumpsteer to my advantage.

Tell me more :popcorn:

Holy spitballs! Just watched that vid. Aside from the lack of body roll it seems you've got some really sweet chassis balance + driving style synergy happening there. I love how you're able to throw it around BW like that, tail occasionally coming out now and then, and just keeps charging.

Great, fun looking setup!

Could you please elaborate on this.

How badly you need to correct this is also going to depend on how much you lowered the car... Robispec's car is 3"+ lower, I don't think most people spending much time on a track are anywhere near that much lower? I could be wrong, but I seem to remember most people staying in the 1.5-2" range.

In the video, at 0:53, you can see the rear come out. Unwanted bumpsteer.

at 1:21, I miss my mark (the apex), and try to force the car to turn more, which results in the rear coming out. The intention was to get the car to rotate a tad more by using the bump in the apex.

At 1:32, I use the bumpsteer to induce extra rotation in the car, so I can carry more speed.

Just a few of the more obvious examples :)

But... Isn't that rear bump steer, not front that causes/allows you to do those? Or is it a changing Ackerman angle that changes the rotation point. Or am I just lost?

Thanks.

bump

steer
@stockysnail :D

What's with the necro bump?

Stocky and I were questioning the merits of roll center/bump steer correction kits. It stuck in my head so I went back and searched.

I already suspected as much - that a few cm drop wouldn't wreak havoc on the platform.

Do you have a take on it?

My car has been dropped only 20mm. I have nothing to compare it to so I have no take (or give) on this.

Well, that's almost 2cm. I don't really notice any bump steer driving other's lowered ones. Do you feel anything?

This was the thread I was talking about with you a couple weeks back. Great read.

Lowered on RCEs. Don't feel anything. Sidenote: installed Perrin Steering Rack lockdown. Amazing little mod. I will be doing most all the little bushing type mods now for a fully "positive" experience. Like a GT3 BRZ haha.

Almost?! By definition that is 2cm.

My car is lowered 2cm in the front aswell. I don't notice any ill effects from bump steer. The whiteline kit might add some steering responce, but that's certainly not lacking either. Are you still on stock springs?

That's not how it works.

Yeah. This is a solid thread.

Same same, eventually, maybe... :D

Bumpsteer correction is only 1 part of the Whiteline kit, and probably the less obvious one from the driver's seat. The roll center correction is subtle as well, but the series of plots that RBbugBITme made a while back show that the front end geometry could use some help when lowered. It's still a little difficult to "feel" on this platform especially with firmer springs.

On an EVO with lowering springs it was pretty easily felt.

- Andrew

I'm thinking first I should spend the money on a lap timer so I can tell the difference if I ever get good enough.

:D