I did my first autocross this past weekend and encountered what I believe to be the front end "pushing" through turns. I didn't have any issues during the AM session, but it was very apparent during the PM session.

Problem Description:

As I was entering some of the very sharp curves on the course I was turning the wheel and the front end was continuing to go straight ahead. This ocurred both on and off the brakes. At the last moment the car would snap around the corner with tire chrip coming from the rear. There was some fine gravel in the parking lot the course was on, but I'm not sure it's fair to blame this on that issue.

My Set Up:

Bridgestone RE71R - 205/50/15; 28 PSI cold. Front outside shoulders are very worn from where I drove a couple hundred miles without an alignment when I finished the build (I'm a dumba$$). THe wear was on the inside, I had the tires remounted to move it to the outside. Tires have a total of 1800 street (mostly Dragon runs) and autocross miles.

Konig Dekagram Wheels, 15x8, ET 25

DIY Bilstein Coilovers - Bilstein B6 Dampers, QA1 Springs (550F, 350R), Advanced Autosport coilover sleeves, poly isolators, delrin washers, FCM bumpstops. Maruha extended tophats rear, NB tophats front.

Racing Beat solid 15/16" front sway bar w/ AWR mounts (mine were torn out). OEM rear sway bar (11MM?) Got is used from Treasure Coast, not sure of year. Advanced Autosport adjustable end links.

New balljoints and tie rods.

Poly bushings EVERYWHERE (control arms, diff, engine mounts, steering rack) w/ SADfab bearings. Steering rack spacers installed (raises rack to reduce bumpsteer).

V8R frame rails

Porterfield R4S Brake Pads w/ stock rotors and calipers.

Ride hieght is 4.5" inches at the pinch weld, front and rear. 1.8* front camber, 1.6* rear camber; no toe front or rear. Alignment shop could not get it to the Supermiata "dual duty" specs.

I suspect that this is a driver problem, not a car problem, but I'm open to any input you can share. THANKS!

 

Looking at your parts list I would think dial back the rear camber so that there is a better split between front and rear camber. I think ideal is somewhere around half a degree split. If you want more front camber I think your next step is getting the extended lower ball joints and bringing out the front camber some more. I also think you need a bit more suspension rake front to rear. I'd look to raise the rear suspension about a quarter of an inch.

 

I think your swaybar setup is the issue. The spring rates themselves have a good front/rear ratio for a miata, but the RB swaybar setup in the front coupled with a stock rear bar is going to make the car push.

Also, my car really starting rotating a lot better after I put a tiny bit of forward rake in the rideheight. Somewhere between 1/8 and 1/4" should do it.

 

Thanks for the feedback guys.

andym- extended lower ball joints are definitely part of the plan. Not sure I canever get camber the way I want it without them.

Fireindc - what do you recommend for a rear sway bar? Is the problem that the OEM unit is too soft? All the research I've done suggested no rear sway bar or stock was best for autocross.

 

It is hard to know if the issue is a setup push or a driver induced push.

That said, I would agree with the need for more front camber and 1/4" rake. You could also stand to add a slight amount of toe out in the front. Something like 1/16"

 

TNTUBA - I'm willing to bet that I'm as much of the problem as the car is (if not more). If you've got advice on those issues, I'm all ears. Thanks!

BTW - I noticed you're in Chattanooga. Do you run with CRSCCA or the Atlanta group?

 

If it were a course that worked the front tires especially hard they could have been overheated if it was a hot day. Personally I end up with a little less tire pressure in the rear vs the front but that won't help your issue. Did you check pressures when they were hot?

 

I think TNTUBA touched on a good point about this being driver related, considering this was your first time Autox'ing.

I know my first year i didn't have the best setup nor good alignment but still managed to learn driving dynamics and being fast. Certainly fix your alignment and follow the supermiata alignment spec for dual duty to start out with. Moving forward instead of trying to dial your car in. Work on dialing the driver in, there is no way of knowing if its the car setup or driver when starting out, so I suggest focusing on the driving aspect at least for the first season.

Usually when someone is experiencing push/understeer, it means you're coming in too hot over driving the capabilities of the front tires to do their job, you want to scrub speed sooner in the area where understeer is occurring. Get a feel for how the car is rotating and find the limits of traction and expirement.

 

Rake. Just add rear ride height in two turn increments until the car balances out.

 

[QUOTE=Andifer;1583764

Usually when someone is experiencing push/understeer, it means you're coming in too hot over driving the capabilities of the front tires to do their job, you want to scrub speed sooner in the area where understeer is occurring.[/QUOTE]

Pretty confident that this is the problem, LOL. I need to do some "driver mods". I will be raising the car slightly and putting in some rake as advised, but my primary focus will be learning to drive the car properly. The next event is on 11/15 and I'm going to really focus on getting to the correct speed for each corner; as opposed to braking, sliding, and maxing steering inputs at the same time. I was fortuante enough to see some video of a few of my runs and it was obvious that I was going into the corners where I was "pushing" way too fast. Slow is smooth, smooth is fast; LOL.

Thanks again for the feedback guys. As always, you've given me some good advice.

 

Big front sway bar. Adjustable is nice, easy to soften. Or adjustable on the rear and stiffen.

 

That raises another question for me. I just remembered that an adjustable sway bar came with the car when I bought it. It's a little rusty and I'm not sure of the brand, but it absolutely has 3 points of adjustment. Would it be too stiff for my Racing Beat solid front sway bar? I don't want to throw the imbalance back in the other direction (though a little loose in the back might be fun, LOL).

Is it worth a try or should I just learn to drive the set up I have before making more changes? I'm leaning towards leaving it alone and getting better at driving first.

EDIT: I just measured the adjustable rear bar I have; it's 16MM. From what I've read here that's going to be WAY too stiff. Guess I answered my own question. LOL

 

Personally, if not already on the softest setting, I'd adjust the front bar to be softer and see if that helps the handling balance. However, the #1 thing would be to add a touch of rake to your ride height, it should take you no time to do this and will transform the way the car handles.

As far as your handling issues being related to your driving habits, that is certainly possible - but I doubt it. I've been in a miata that pushed and It was obvious the first corner. That same car with more rear ride height rotated like a miata should. On the street you could probably never tell.

 

I run a racing beat big hollow up front and disconnected in the rear. It gives the car a good neutral feel to it allowing for me to charge at cones, especially in the wet. Though I do plan to upgrade to small fortune racing sway bar but now I am focusing more on track stuff than autox after almost four years of it.

 

So in the edit above I mentioned measuring the mystery rear sway bar. While I was at it, I also remeasured my pinch weld heights. I'm at 4.5" in the front at 4.75" in the back. I guess I already have some rake; which means most of this comes down to getting better at driving. I do plan to raise it slightly to 5" front and 5.25" rear as I think I may be a little low for my spring choice (550F, 350R).based on some of the comments above (and some reading I've done here). I don't want to up the spring rate on the B6 dampers, so I'll live with what I have for now. If I get more serious about autocross (and much better at driving) maybe I'll spring for some Xidas.

 

I found extended lower ball joints fixed my understeer quickly since it allowed more front camber, I have -3 and its crazy how little it will understeer. Rake like others have said is another fix. Id say the easiest thing especially for auto cross is disconnecting the rear sway bar in between run groups or if you can changing the stiffness of the front as well. Feeling the change made me a better driver since it allowed me to see what was me and what was the suspension. One last thing is in autocross people have a tendency to make sharp movements with the steering wheel, being smooth in autocross is difficult to do since there are lots of tight turns but it makes a huge difference.

 

So I wanted to post some follow up on this. In preparation for my next autocross on 11/15 I decided to try simulating different size sway bars on Forza Motorsport on my X Box One (I'm a giant child and this is probably a dumb idea). Anyway, before I could try out any sway bar combinations I decided to turn down some of the "assist" functions. One of those was ABS. As soon as I ran my first lap on the "simulator" without ABS, the car refused to turn while I was on the brakes. This was the EXACT behavior I witnessed at my last autocross event.

In other words, those of you that suggested "driver mods" instead of car mods were spot on. I need to work on adjusting my braking points so I can be off the brakes when I'm trying to steer.

Though this is an embarrassing story I thought I'd share to further the point that seat time is always worth more than modifications.

 

Forza is a arcade game, if you want a sim racing experience get a PC and do Assetto Corsa or iRacing, it can be good training for real life.. it's not a 1 to 1 simulation but it does help quit a bit.

 

I don't disagree, but turning the ABS feature on an off allowed me to duplicate the behavior. My only point was that I need to get better at driving.

 

About your comment that the front tires are more worn, its possible those are heat cycled out as well. Meaning they won't have the grip level as a tire that isn't heat cycled out. Maybe you can rotate the tires to the rear? RE-71r tend to drop off once they get past their working life of heat cycle (usually over 120 or so autox runs from new). When brand new, they also take a few heat cycles to be fast. Often times, they are understeery for the first couple events, and then are good until they heat cycle out. In my experience, even if I drove my RE-71r tires on a long trip (500 miles), they still needed an autox event before they "came up to speed" for me.

I'm late to this post, but it could be helpful to see video of your runs to determine if your inputs are contributing to the understeer or not. It could be a setup change, but it might also be driver input related.

As far as "being off the brakes when trying to steer", my experience at autocross shows that trailbraking is a skill that helps for not only autox, but track driving as well. Once I learned that skill in autox, it was a game changer for me. It's extremely good skill to have for almost any car setup, but even more so in a car that is tough to get rotation in.