NC Koni Sport, adjust for understeer

NTAXS #6 at TMS last weekend was my first time out with my new suspension setup consisting of Koni Sports and Progress front anti-sway bar. I asked a question on miata.net about it, and managed to convince myself at different points that I needed to soften the front shock adjustments and stiffen the back, or to stiffen the front and soften the back. Or just stiffen the front. Or both. Or soften them both. Arggggghhhh!!!!

Jerrett co-drove with me, so maybe has another perspective, but it seemed like understeer was evident but manageable in the slaloms, hardly noticeable on entry to corners, but massive when accelerating out. I'm sure some of it is my driving; not slowing down enough before the corner, accelerating too hard and too soon... or like Jerrett told me, accelerating in weird places... :) But I think some shock adjustments might help too. There's no oversteer to contend with.

The front shocks are set fairly soft, half way (1 full turn) between softest and firmest settings. The rears are stiffer, at 1/4 turn off of full stiff. Mainly because of something on this page http://www.ncrscca.com/autocross-tuning-tips , I think increasing the front shock stiffness will help. This is the part that seems relevant:

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Vehicle is understeering after the apex

Front rebound dampening force is not enough – make font dampers stiffer.
Or make pre-load equal to zero / add 3 to 5mm of pre-load.
Reduce front ride height by 3 to 5mm.
Rear spring is too soft – add pre-load to rear or change to higher spring rate.

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The only one of those things I can do is make the front dampers stiffer, although other things I've read say that doing so will increase understeer.

Here's the thread over on the other forum: Koni Sports, NC, CS, compensate for understeer?

The bottom line is that I haven't got a clue.

Suggestions?

There was a ton of on-throttle understeer. It would tuck in nicely if I lifted, but I was really having to wait to get back on the gas coming out of a corner and I could not power through sweepers at all.

Your car was squatting down a lot in the back, even when sitting between runs, and I wonder if it was the Koni's jacking down (that's how they "stiffen," by not having much rebound) that caused some of the oversteer. I think you should just try an event with all four corners set to soft and see what happens.

Assuming you want to keep the car "stock" put the largest wheel spacers you can in the front.

Is ER going to have a test and tune event this year?

I set my Flyin Miata coil overs to the recommended setting and left them alone while I learn to drive. However, I am looking forward to a test and tune day so I can experiment a little.

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Originally Posted by Davidss

Assuming you want to keep the car "stock" put the largest wheel spacers you can in the front.

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I want to keep it C-Street legal for next year. I will check the rules, but I think the maximum allowed wheel offset from stock is 7mm. So the wheels would be 14mm further apart total? What does that do? (I'm guessing front tire angle to the pavement is flatter when turning, so better grip?)

Everything I've read (no real experience, yet), states the NC understeers badly. Putting a larger bar on the front just exacerbates that.

I'm considering running stiffer bump stops (with the stock springs), to effectively increase the spring rate somewhat.

I think CS is limited to 60mm bumpstop length.

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Originally Posted by jrj512

Your car was squatting down a lot in the back, even when sitting between runs, and I wonder if it was the Koni's jacking down (that's how they "stiffen," by not having much rebound) that caused some of the oversteer. I think you should just try an event with all four corners set to soft and see what happens.

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I've got a little reverse rake that is there all the time. 14.25 inches on both fronts, measured from center of hub straight up to edge of wheel well, 13.75" on driver side rear, 14.0" on passenger side rear. I looked at the A-arm bushings on the front, and they are slightly twisted. Per threads on miata.net, that can cause the front ride height to be high.

^If the bushings are twisted, it probably wasn't torqued under load. I think.

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Originally Posted by sammm

^If the bushings are twisted, it probably wasn't torqued under load. I think.

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That seems to be the consensus on the pointy forum. I need to ask Wags how he did it.

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Originally Posted by riverman1

Is ER going to have a test and tune event this year?

I set my Flyin Miata coil overs to the recommended setting and left them alone while I learn to drive. However, I am looking forward to a test and tune day so I can experiment a little.

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A test and tune day would be helpful. I might also try setting my front sway bar at the softest setting. Right now, it's on the medium setting (center hole).

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Originally Posted by 865

I want to keep it C-Street legal for next year. I will check the rules, but I think the maximum allowed wheel offset from stock is 7mm. So the wheels would be 14mm further apart total? What does that do? (I'm guessing front tire angle to the pavement is flatter when turning, so better grip?)

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It will reduce the understeer, particularly under power.

What is your rear toe?

^---- According to the printout, left rear is .06 degrees, right rear is .10 degrees. Total toe is .16 degrees.

225/45R17 is 25 inch diameter, so total toe would be .14 inches? That's around 1/16th per side, average, but really 1/38th on the left, 1/23rd on the right. Weird that he didn't get it even.

It's positive, so is that toe out?

I was on a set of new Koni's but on a ND. The cars are not the same. After the morning runs I asked around and everyone was saying how their cars where not handling well. I made the front softer and the car pushed more. So forget the first 4 runs unless you got the tires good and hot.

The afternoon session was better and more consistent.

Generally, the idea of setting up a car at the bus lot is a waste of time unless that is the only place you autocross. The setting don't apply to anywhere else.

The MSR package ran the Koni full stiff on the NC. Then they removed the adjusters so you could not change it. Not saying that is the best setting, just giving you a ball park setting. MSR had big front and rear bars "stock". I think the front was 27mm but it has been some time since looked that up.

The NC is sensitive to rake. 1/2 inch difference transforms the car. How do you get 1/2 inch of rake on a stock class car. :) Ask David. It can be done.

^--- The Progress front bar is 28.5mm OD. Very heavy gusseted brackets, so the effect is supposed to be greater, per the GWR site.

My rear bar is the OEM stock 12mm bar that comes with the suspension package.

As for rake, front should NOT be higher than the rear, right? If anything, lower front is better? (I'm higher in the front right now.)

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Originally Posted by Davidss

Assuming you want to keep the car "stock" put the largest wheel spacers you can in the front.

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I checked the rules for Street class. Plus or minus 7mm offset is allowed. I haven't found 7mm spacers anywhere. I can get 5mm from Moss Miata.

Ebay is the best place to buy spacers. You can get a 1/4" for $10 shipped.

Go take a single lug nut off your car. Put a mark on the end of it and then reinstall and torque it making a not of exactly how many turns it takes. From there I can tell you how large of a spacer you can use before you need extended studs.

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Originally Posted by riverman1

Is ER going to have a test and tune event this year?

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Maybe Dec 3 or 17. I don't want to make any promises.

I have some 5mm spacers for your car you can try. But I don't think you will notice any "big" difference. I will bring them to the SCCA event if you want to give them a try. I think you will get much more from working with toe and rake since you have the large front bar and small rear. Also working the shock adjusters. In another thread you said you were using up the front tire edges. It sounds like you have a ways to go. Even the F1 and NASCAR crews of professionals have a hard time getting it right on a race weekend. Keep things in perspective try some extreme settings too. Think someone said something about the bump stops. That is an item to look at also. FatCat Motorsports has some but there are some places that sell similar things cheaper. They don't cost that much to begin with.

I think I would solve the positive rake problem first.

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Originally Posted by Davidss

Go take a single lug nut off your car. Put a mark on the end of it and then reinstall and torque it making a not of exactly how many turns it takes. From there I can tell you how large of a spacer you can use before you need extended studs.

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11 and 1/8th turns.

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Originally Posted by general default

I have some 5mm spacers for your car you can try. But I don't think you will notice any "big" difference. I will bring them to the SCCA event if you want to give them a try.

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Thank you, yes, I'd like to try them if they'll fit without extended studs. 5mm is about 1/5th of an inch. David said he could determine how large a spacer I could use based on the number of turns to torque down a lug nut, which turned out to be 11 and 1/8th turns.

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Originally Posted by general default

I think you will get much more from working with toe and rake since you have the large front bar and small rear. Also working the shock adjusters. In another thread you said you were using up the front tire edges. It sounds like you have a ways to go. Even the F1 and NASCAR crews of professionals have a hard time getting it right on a race weekend. Keep things in perspective try some extreme settings too. Think someone said something about the bump stops. That is an item to look at also. FatCat Motorsports has some but there are some places that sell similar things cheaper. They don't cost that much to begin with.

I think I would solve the positive rake problem first.

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Yes, seems like it's going to be a combination of little things. I've got the 58mm FCM stops in the front (red stripe, soft) and 58mm FCM in the rear (white, medium). Those are what GWR recommended for the Koni Sports.

7mm would be the largest you could run safely.

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Originally Posted by general default

Think someone said something about the bump stops. That is an item to look at also. FatCat Motorsports has some but there are some places that sell similar things cheaper. They don't cost that much to begin with.

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Kenny, any examples/sources of other bumpstops besides FCM?

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Originally Posted by Davidss

7mm would be the largest you could run safely.

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Thank you, David.

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Originally Posted by sammm

Kenny, any examples/sources of other bumpstops besides FCM?

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RE Suspension has some that look exactly like the FCM stops, and they are the same size (listed as 2.27 inches). They have the red (soft) and white (medium) in that size. I don't know if they are actually identical. But they are only about $1.50 less than the FCM stops when you buy them individually from GWR. Don't buy the sets of four from GWR. Those sets are priced much higher than the cost of four individual stops.

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Originally Posted by sammm

Kenny, any examples/sources of other bumpstops besides FCM?

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Jason McDaniel once posted some cheap alternatives in another thread.

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Originally Posted by general default

Generally, the idea of setting up a car at the bus lot is a waste of time unless that is the only place you autocross. The setting don't apply to anywhere else .

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The front is under steering because the front has less grip than the rear. The car needs weight transfer to the front entering a corner in order to "bite". It looks like the rear of the car is sitting quite a bit lower therefore making the front even lighter. Combining the rear biased rake , stiffer front roll stiffness , and previously mentioned driving style errors equals for a ton of understeer at the bus lot . I like my car much stiffer in the rear at TMS to help the front turn in, mainly via higher rear to front tire pressures .

Soften the front or stiffen rear via shocks ,bars, and tire pressures. Be more aggressive on braking in order to transfer some weight forward.
Remember your mantra Skip; slow in fast out

I think this is what I was thinking about. I don't have any bookmark pages to support the claim.
I used the FCM on the RX8 and it helped.

Skip, it looks like you got the parts to the puzzle. Now you have to get it all to work together to make it picture perfect.
The parallel thread you have going http://forum.miata.net/vb/showthread.php?t=623584
might give you some ideas also.

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Originally Posted by jrj512

Jason McDaniel once posted some cheap alternatives in another thread.

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Negative rake is a huge problem in this scenario. There are other things to look at once that is corrected, but I'd wager that correcting the rake will change the car completely, as KB mentioned. I found that my NC liked about 1/2" forward rake, but it was an STR car, so that might be too much for a Street car.

Its worth mentioning that NC's are prone to understeer when compared to other Miata generations, no matter how they are setup. I found it was mainly an issue of trying to turn-in while still braking, so you want to finish straight line braking before turn in. Your situation sounds like the front wheels are lacking grip when accelerating out of corners, so a different situation.

Again, fix the rake first, as everything else will change too once that is addressed.

Getting the rake fixed does seem to be the critical first step. Wags is expecting me after I get off work, so hopefully I can get that squared away today.

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Originally Posted by 865

Wags is expecting me after I get off work, so hopefully I can get that squared away today.

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You're in good hands.

Loosening and re-tightening the control arm and shock bolts with the wheels fully laden eliminated the reverse rake. There was an audible sound when one of the twisted bushings untwisted itself. The front is now about an eighth to a quarter inch lower than the rear. Thanks to Wags for that.

It eliminated the severe understeer problem. Understeer was noticeably reduced in the slaloms and in the on-throttle turns during yesterday's SCCA event. Steering felt much closer to neutral, but yesterday's course didn't have enough in the way of fast on-throttle sweepers to be conclusive. I'm going to leave the shock rebound settings alone until I get a better feel for how the car behaves during the final few events of the year. As it stands right now, it's very drivable, and handling is much improved over stock.

I am going to mount the wheel spacers that KB lent me to see if I can detect any further improvements.

Many thanks to all of you for your help.

Good news!