The DC2 Castor Thread

[milkman]

Anyone running a caster/castor kit in their DC2's?

Haven't had much luck in tracking down kits for my DC2R. Seems like Whiteline are the only company to make a kit. Am I missing something here..

http://www.turbowholesale.com/catalo...DC-p-7540.html

My car currently has 0 toe and -1 camber according Doug Heaseman. He suggested I add some positive castor to provide better steering feedback when cornering and kerb understeer. So I'm curious.. anyone done this?

[tinkerbell]

yeah, he is right = more castor is always a good thing!

but, to increase castor in DC2 you just swap the upper control arms...

easy as pie

and free

[tinkerbell]

some good info in post #19 in this thread:

http://forum.clubitr.com.au/showthre...ghlight=castor

NB - he saus "like night and day"

[tinkerbell]

more background on Castor here:

http://www.whiteline.com.au/faqsusp01.htm#Caster – What is it and why

[freakygeek]

yeah, he is right = more castor is always a good thing!

but, to increase castor in DC2 you just swap the upper control arms...

easy as pie

and free

And creates awful bumpsteer in your suspension geometry.

Many others have done this and found the negative effects far outweigh the positives.


Quoted from http://honda-tech.com/zerothread?id=2333432

This is most certainly not a myth. Be prepared to switch the UCA back almost immediately. It is a waste of time and effort. I wasted a couple years with unnerving bumpsteer before I realized it was due to this swap. There was a thread where somebody did the measurements, but it looks to be gone.

It's too bad that the bumpsteer created by swapping the UCA actually creates a very tail happy car, it probably wouldn't be so bad if it generated understeer.

By swapping the control arms, you gain caster but by tilting the spindle back you lower the location point where the steering arm mounts to. Because the steering arm is now at a different angle, the line of action is moved upward and no longer aligns with the instantaneous center of upper and lower control arms. Because the line of action is moved upward, this means that the steering arm effectively becomes 'longer' than it was before, and causes toe-in during bump. This toe-in is sudden and upsets the car tremendously during cornering. And what do you think happens with sudden toe-in during bump? It happens that it ends up pitch the rear end around...my god I had this happen so many times during the autocross (especially in the rain).

I am so glad I figured out that it was this mod that caused the bump steer issues. That was like the biggest lesson I learned about cars and suspension. Bump steer is very very bad. And Honda did a ton of work making sure the EG6-DC2 chassis has almost none of it from the factory.

[ChargeR]

I agree with freakygeek. Unless you are absolutely sure that you are not going to mess up your suspension geometry by making changes leave it alone. Exactly how much castor does this swap net you anyway? Unless it is significant amount the level of camber gain at the outside wheel at the levels of steering lock encountered on track will be negligible. It will give you nice outside wheel negative camber when parking though .

You guys with double wishbone front suspension have plenty enough camber gain under compression anyway. Spare a thought for your macpherson strut blessed DC5 brothers .

[freakygeek]

I found the thread where the guy did the measurements on an EG chassis. (essentially identical to DC2 chassis)

6.35mm of toe change with 2" of suspension compression.... !!!!! And in the wrong direction... causing nasty twitchy handling.

http://honda-tech.com/zerothread?id=1082319

with upper control arms swapped left to right:

1" bump showed a toe change of ~.13"
2" bump showed a toe change of ~.25"
1" droop showwed a toe change of ~-.20"

with upper control arms in stock configuration:

1" bump showed negligible toe change
2" bump showed negligible toe change
1" droop showed a toe change of ~-.1"

some other interesting things i noticed were that track gets nearly .25" narrower from static to full bump and swapping the control arms affects static toe by roughly .75". that last part is important. if you remember that you can do back to back testing of both configurations and be able to quickly re-zero toe by remembering to just turn the rod ends 6 flats on each side. from stock to swapped the toe change is positive, from swapped to stock the toe change is negative.

the final thing i noticed is that having the arms in stock configuration gives you another 1/4" of bump travel before the arm hits the tower. needless to say, you won't find swapped control arms on my car.

[tinkerbell]

FYI - neither of the DC2's i have driven with UCA swap have had bump steer issues.

can you describe what yours felt like after you tried teh UCA swap freakygeek?

[freakygeek]

FYI - neither of the DC2's i have driven with UCA swap have had bump steer issues.

can you describe what yours felt like after you tried teh UCA swap freakygeek?

I was all geared up to do the UCA swap then I found the toe-change data.

I decided that it wasn't worth the effort to swap them and then swap them back again after seeing that information. Clearly the effects of toe-in on bump are detrimental, so I don't see the need to do my own tests on this. I'm confident it would make the car less enjoyable to drive and introduce unusual mid corner handling characteristics, not to mention poor tyre wear.

[tinkerbell]

hmmm, maybe on a stock car it is not a good idea, if you want the car to feel stock.

just so you know - i did not notice any bump steer "issues" with the 2 cars i have driven set up like this, but that is not to say you couldn't measure it.

also - both cars were set up to be aggressive, with lowered suspension and agressive toe settings...

i am fairly certain the other changes to the suspension (lowered & agressive align) set-up contributed more to tyre wear than UCA swap ever could...


maybe milkman can talk to heasmans about the UCA swap - as both ways of changing castor on DC2 lead to increased bumpsteer...

[freakygeek]

hmmm, maybe on a stock car it is not a good idea, if you want the car to feel stock.

just so you know - i did not notice any bump steer "issues" with the 2 cars i have driven set up like this, but that is not to say you couldn't measure it.

also - both cars were set up to be aggressive, with lowered suspension and agressive toe settings...

i am fairly certain the other changes to the suspension (lowered & agressive align) set-up contributed more to tyre wear than UCA swap ever could...


maybe milkman can talk to heasmans about the UCA swap - as both ways of changing castor on DC2 lead to increased bumpsteer...

I understand that the cars may be running aggressive alignment but surely you can understand that you don't want ANY dynamic toe change with suspension compression / droop if possible...

I think you would find that if you swapped them back that your car would feel more confident in corners, especially those with choppy surfaces. (ie. old wakefield)

[tinkerbell]

yep, understand that any/all BS is "unwanted"...

but if you want more castor, you have to compromise...

i am just providing this thread with a practical perspective, and whilst i agree with the maths (i.e. move a control arm you change geometry), i feel that the emphasis placed on it (oh, you ruin your handling y0!) might be excessive...

be nice if there were more folks who have tried it and changed back - who could describe how/why they didn't like it...

[freakygeek]

yep, understand that any/all BS is "unwanted"...

but if you want more castor, you have to compromise...

i am just providing this thread with a practical perspective, and whilst i agree with the maths (i.e. move a control arm you change geometry), i feel that the emphasis placed on it (oh, you ruin your handling y0!) might be excessive...

be nice if there were more folks who have tried it and changed back - who could describe how/why they didn't like it...

I don't think compromising bump steer so dramatically for a few measly degrees of caster is advisable. Basically what I am saying is that I don't think it's a sensible compromise. If you have a problem with off center steering weight and automatic centering of the steering I suggest looking at other issues before making this change to your suspension.

After making this modification you will still have nowhere NEAR the caster a factory VE commodore / merc / BMW has.

[tinkerbell]

I don't think compromising bump steer so dramatically for a few measly degrees of caster is advisable.

if it is in fact really that "dramatic"?

i am pulling out my sussy next week, so will take measurements to confirm the extent to which a lowered DC2 is affected...

[freakygeek]

Are the benefits of that small amount of caster dramatic? lol