New project?

[Terry Johns]

https://forum.miata.net/vb/showthread.php?t=549409

[Reijo]

That link is for the NC.  The ND is quite a bit different (100 kg lighter for one thing).

Ron Bauer has worked with Mazda from the beginning getting a CS setup done and then the STR setup so I would pay attention to what he did but also use his setup info as a starting point since this is still early in setup.  Andy Hollis has an ND as well and is very good at setup so he would be another fellow to follow for setup advice.

Here's the ND autox thread and I notice Ron and Andy are both commenting in there:

https://forum.miata.net/vb/showthread.php?t=590076&page=28

[Stuart]

I'm quite confused Terry, first you say that bumpstops are very important then you tell Stephen that his idea about bumpstops is nonsense.  What he said about the bumpstops is the exact reason they are important as you go from a relatively softly sprung car to an extremely stiffly sprung one in an instant (and in many cases will break the tires loose)

On a side note, when did Chris Harvey win nationals?

[Terry Johns]

My comments were related to a stiffer sway bar, not the bump stops

[PedalFaster]

Somewhat off-topic, but I wonder if what's happening there is that you're hitting your front bump stops, which is in turn "shocking" your tires and causing them to break loose.

Sorry Stephen with all respect that's nonsense LOL

My comments were related to a stiffer sway bar, not the bump stops

Terry, I have two thought exercises for you:

• From first principles: Please think about what the effect is on a loaded tire when the suspension on one corner of a lightly sprung / lightly damped car "slams" into its bump stop. Explain what effect this will have on the car's behavior if it happens to the car's outside front tire at corner entry. Then think about how this behavior would change if the suspension's transition into the bump stop was more gradual. Which behavior will be preferable, and why?
  
  
• Specific to your refutation of my recommendation: Consider that most, if not all, of the fast guys in ND Miatas are following my nonsensical recommendation to run a stiffer front bar:
  
  
  • Julian Garfield, 2nd at 2016 Nationals in CS: Runs a stiffer Karcepts front bar (posted on a "secret" forum, but if you know what I'm talking about, paste the forum URL followed by /showthread.php?56587-ND-Miata-prepped-for-C-Street&p=1845160&viewfull=1#post1845160). Note also the comment at the end of this post: "Julian went almost a second faster than Chris' NC at Wilmington so the Karcepts bar must worked pretty well. "
    
    
  • Tyler Kvetko, 3rd at 2016 Nationals in CS: Runs a stiffer Karcepts front bar
    
    
  • Andy Hollis, multitime national champion: Runs and recommends a stiffer Karcepts front bar
    
    
  • Ron Bauer, multitime national champion: Ran and recommends a stiffer front bar
  
  (I can't find a post by 2016 CS national champion Daniel McCelvey describing his setup, but I'd bet money he's also running a stiffer Karcepts front bar.)
  
  Given all that, apply Occam's Razor while considering which is more likely:
  
  
  • They're all wrong, and the advice that you read on the internet for a different car is coincidentally also the best way to set up an ND Miata, or
    
    
  • The advice that you read on the internet for a different car is not also the correct way to set up an ND Miata.

[Reijo]

Just a quick note here on why you may want to run a stiffer front anti-sway bar even in the front of a FWD car:   As opposed to the track, in autox you want the stiffer and faster reacting front end so you get quicker turn-in response at corner entry which is more helpful (sometimes) than even a balanced car. 

One of the odd-ball characteristics of autox vs. track setup.   

Reijo

[Reijo]

Hmmmm......interesting thoughts on a large FSB and driving style.  It just occurred to me that if you have slight understeer due to a stiff FSB, you might have to alter your driving style to keep weight/traction on the front tires by trail braking until you are ready to exit .... e.g. balance the car with the brake.  That may also mean a slightly (very small) different line to account for the handling characteristics ... or some variation ...

Interesting.

r

[PedalFaster]

Normally a stiffer bar would induce more push, but if it kept the front off of the bump stops, and hitting the stops is really what's inducing the death push currently, then the stiffer setting might still result in a net improvement in front-end grip.

I'm procrastinating here, so let me elaborate on my thinking:

Picture a graph showing the effective spring rate of your springs and sway bar at the wheel:



(This is of course an idealized representation.)

Now picture the equivalent graph for the bump stop:



The bump stop only affects the last part of your suspension travel.

Now add the two:



Note the step function spring rate increase when you hit the bump stop. In reality, the increase would be a little more progressive, but the spring rate would also asymptotically approach infinity as the bump stop reached full compression.

My theory is that, if you're hitting the bump stop while already at the limit of your tires' traction, the resulting step function in wheel rate is causing the tires to break loose. This theory's consistent with the behavior that we observed, where the car would turn in and transition great, but halfway through steady-state corners it would settle into an unrecoverable death push.

If you add a stiffer sway bar, the step will become smaller, and thus the transition into the bump stop would be less likely to shock the tires into breaking traction:



The greater roll stiffness would also decrease the chance that you'd hit the bump stop in the first place.

Of course, by stiffening the bar you'd be increasing the wheel rate before you hit the bump stop, which, all else being equal, would increase push in that condition.

To get around that, perhaps you could leave the front bar as-is and instead use a softer bump stop:



This would reduce the magnitude of the step without increasing the wheel rate when you're not riding the stop.

Please note this is all a theory based on two runs in your car. It ignores, among other things, camber gain or loss in roll. I'm not offering a prescriptive solution like Terry is; I'm just suggesting that you try adjusting your bar and/or your bump stops at an event to see if that helps.

[PedalFaster]

Two more thoughts:

Stiffening your front shocks would also reduce the rate (but not the ultimate amount) of roll, thus potentially decreasing the magnitude of any "shock" resulting from hitting the stops.

...but stiffening your front shocks could also cause your car to jack down and ride its bump stops.

Confused yet? If not, I can keep going.

[MurrayPeterson]

Thanks guys!

I'll be trying a stiffer FSB setting at the next event(s).  The turn in response is superb, so a stiffer bar setting won't hurt too much, even if it forces me to be gentler on initial turn in.  Bump stops aren't something I am willing (or able) to play with right now.

I hadn't though about shock settings with respect to roll rate and hitting bump stops.  I do know that Andy Hollis runs his front shocks at full stiff, which I never did try on Sunday.  Something else to test

I am also going to try playing with tire pressures, especially in the front.  I know that RE-71Rs were quite insensitive to pressure on the S2000, but that doesn't mean it will be the same on the Miata.

[Reijo]

Personally I like setting the tires pressures at the optimum all around and then use shocks, alignments etc. to "tune" the handling .... Why wear the tires unnaturally.

I know some people ran really high pressures in some stock FWD's some years ago as a desperation measure to get them to rotate but I think that was the exception ... but then again I haven't played with the setup on a FWD in a very long time.  Or not much.

R

[MurrayPeterson]

I agree with you Reijo, and have no intention of using tire pressures to reduce grip anywhere.  Instead, I was thinking that if my tire pressures were "off", then I could be losing grip in mid-corner.

[Reijo]

I agree with you Reijo, and have no intention of using tire pressures to reduce grip anywhere.  Instead, I was thinking that if my tire pressures were "off", then I could be losing grip in mid-corner.

Yes, good point.  Of course, as we discussed before, this weekend is not "really" ideal for setting up a car anyway due to the cold temps and consequent lack of grip.  However, you still need a setup for cold temps that we get but then also for the concrete and heat of Lincoln.

Who said setting up a stock/street car was easy, eh?   hahahaha

R

[MurrayPeterson]

I got spoiled by driving the same car for 10 years -- all of the setup work had been long done.

Next event, I'll probably just boost the FSB up to full stiff (no small changes here), and then twiddle the shocks to see if I can find a good balance.  Fort Macleod has only the single sweeper, so I'll probably have to run that set up for the next YYC event as well.

BTW, Sunday's course was superb for setting up a new car!

[PedalFaster]

Did some more research.

Sorry Stephen with all respect that's nonsense LOL

My comments were related to a stiffer sway bar, not the bump stops

I can't find a post by 2016 CS national champion Daniel McCelvey describing his setup, but I'd bet money he's also running a stiffer Karcepts front bar.

McKelvey doesn't post much, but from another forum:

I would not run the car without some kind of front swaybar upgrade. The shocks will help but reducing the amount of terminal roll is very important in getting this chassis working.

Unfortunately he doesn't elaborate on why he feels that's the case.

/showthread.php?56587-ND-Miata-prepped-for-C-Street&p=1832142&viewfull=1#post1832142

Note also that, in the link above, Kvetko (3rd at Nationals) mentions that he's running his bar at a setting that's more than four times stiffer than the stock bar per http://www.karcepts.com/shop/product.php?id_product=125.

Last but not least,

Chris Harvey. US National winner.

Harvey is undeniably a great driver, but for the record I searched the SCCA rule book (which lists all past championship winners in the back), and his name isn't there.