Looking at the NISMO suspension, it seems to me (a novice) the only part of the suspension the "cures" the understeer are the stabalizer bars...I dont know how shocks/springs would do this. So would installing the NISMO bars help reduce understeer? I don want to commit to the whole NISMO setup yet if ever).

Also, while understeer may be less fun, it deffinately is safer, will VDCs till keep everything in check(it should just re-asuring myself). Sure I turn it off ocasionaly to have fun, but most of the time, espesially in the wet, I keep it on.

 

I just remembered that increasing the rear sping rate with also reduce understeer. My bad.

What i want to do is lessen he understeer slightly without changing the character of the car. I dont have enough confidence in myself to drive a perfectly neutral and sensative car as I have never driven at the track and have not spent alot of time dricing at the limit. I fear that I may tap the brakes to late into a turn to slow mself down and end up on the side of the road...ever since my experience swerving off the road to avoid a deer in the middle of a blind turn, I have been very scared of it happeneing again. Call it trauma.

 

Well, I think you have your own answers already

In general: Yes, stiffer springs reduce body roll, hence understeer. Anti-roll bar, as its name implies, helps reduce body roll as well. A package that combines the two is the ideal setup and coil-overs with anti-rolls bars make the most sense.

However, my understanding from messages is that you have not yet been to the track yet with your car. If that is the case, you really should not be worried or loose sleep over "understeer." All cars under and oversteer depending on the corner and driving style. The Z, currently, has no understeer at all during regular street driving; you would be hard pressed to feel it, unless you are significantly over the speed, at license loosing levels

My suggestion to you is to first tackle things like auto-x if you have an interest, find out about the car, your abilities, and see if the car really understeers for you. Then think about such upgrades.

However, if you want to really get this thing called "understeer" off your mind, then the short answer is yes, the anti-roll bar will help reduce it, but I would suggest going with the full Nismo S-tune suspension setup, which runs around $1800 to 2000 I believe.

Good luck.

 

I guess what Im asking is: The Z feels to get slightly more slugish as the tires load up. I mean the steering wheel will get heavier and the car will feel like less light on its feet. The car will hold it line but it takes more effort and it doesnt feel like it wants you to take it where its going. Again, Im not complaining, and the only other rear wheel drive car I have spent considerable time with was a 330ci which didnt exibit this, although the BMW's steering wheel is overboosted and vauge so that could be it.

Is this understeer or is that just the natural process? I have rarely felt the car go much wider of its intended line, but i just wish the car would invite tossable curves more.

 

I've been reading a suspension theory/application book I picked up and thought I'd pass on some info on generally how to reduce understeer.

1. Increase weight transfer at rear by increasing rear roll stiffness.
2. Reduce weight transfer on the front by reducing front roll stiffness.
3. Reduce front toe-in.
4. Increase down-force on front tires.
5. Reduce down-force on rear tires.
6. Use wider front tires.

I probably should just say that suspension tuning or adjustment optimally shouldn't be done ad hoc since it's kinda hit and miss that way... but since you were looking for some ways to reduce the understeer I thought I'd just post the tips up.

 

If you really want to see what understeer is, go to a large empty parking lot (if you can find one) and start driving in a circle. Gradually increase the speed and what you will find (at least in my experiences at AutoX's) is that the front tires will start squealing and pretty soon the car will not stay on the same circle. Im not sure how easy it will be to notice without cones, but I can definitely tell on the AutoX or the track. When it gets really bad, you can try letting off on the gas, turning sharper, giving it more gas, and nothing seems to make the car hook up. Basically you just slow down until the front tires grab and then try to gas out of the corner.

Anyhow, I only noticed the understeer once on the street. It really wasn't until I went to an AutoX or Track that I really started to find it freqently. I also haven't tried different techniques to try and change the character of the car (like turning later and sharper and giving the car more gas, or anything like that).

-D'oh!

 

Understeer is when the front end is trying to leave the turn, so to compensate the driver turns into the curve to drive the car along the turn. This type of handling is found on most cars since it's more intuitive for the driver to turn into a curve rather than away like in oversteer.

Oversteer you'll feel your rear slipping out of the turn. The proper compensation is to turn away from the curve to keep the rear from slipping.

In any case, once you break free (i.e. start skidding) from oversteer or understeer condition, you need to reduce power to let the tires get grip again.

Also performance tires have more grip, but they are not as forgiving in giving feedback about when they are about to lose grip. Normal tires are more forgiving and usually the driver will have time to reduce power before going into a slide.

 

The proper way to handle oversteer depends on what caused the oversteer in the first place. If you get power oversteer (throttling out of a turn at a higher rate than the rear wheels can accept,) then you definitely want to back off of the throttle to allow the rears to grip.

However, in a trailing throttle situation (coming off of the gas/getting on the brakes too hard ) entering a turn, you've transferred too much weight forward. Here, the rear will start to swing around because there's not enough weight holding it to the road, and you want to get back on the gas in order to move some of the weight towards the rear of the car to allow it to grip better.

Gary

 

Thanks Gary.

Out of curiosity is that a Formula V car as your avatar?

 

brad - you thought the 330 had vague steering?? I'm surprised to hear that but I've only driven the M3 and its steering was awesome. No dead window, pretty linear. It felt more better (to me anyway) than my sister's Z in the +- 45 degree window.

all the tips nwind listed serve to increase traction to the front end of the vehicle. I'd go with the smaller sta bar in the front instead of the bigger rear to keep overall traction high. increasing roll stiffness in the rear means the outside rear tire looses traction earlier. of course, spring rates are the first things you'd tune, then the sta bars, but that option isn't possible without switching everything out. just remember that all this understeer that's mentioned are *at the limit handling* on closed tracks. You shouldn't feel any of this on public roads, even when you're at 8/10's.

the skidpad test that d'oh suggests is always fun. you'll feel the front end plow no matter what steering input you give it. then let off the throttle or gently apply the brakes and you'll feel the front bite in again.

 

No problem. I love talking about this stuff!

My avatar is a Formula 1 car from 1967. It's the Eagle-Weslake T1G that Dan Gurney drove to victory in the 1967 Belgian Grand Prix at Spa-Francorchamps. That car is still considered by many (myself included) to be the most beautiful F1 car ever.

Gary

 

Oh ok. I thought i kinda looked like a Vee but the tires looked a bit too fat and the body look longer. It was a long shot guess. :P

That is a nice car though. Wow the body style/rules have changed a lot.

 

Its my brothers 330ci. Its a 2001 and I beleive that BMW offered an optional fix to de-bost the steering. Its kinda nice wen your feeling really lazy and start to drive with one hand at around 7 o-clock

But it definately isnt as precise as the Zs, and the 330 is much less sure in the tight twisties...kinda like telling the car to steer instead of steering it yourself.

 

Brad - many have given pretty good information. Unfortunately, when you read all of them back to back they seem to conflict with one another, when in reality, they are all pretty accurate. Granted I am not expert in suspension and car handling setup, but as many of us have some experince. So, I will not get in to it even more and confuse you further.

I currently have a '02 330Ci, and I can tell you that car understeers much more heavily than the Z and you can easily find that out on the street. One of the best upgrades for the 330Ci, in my opinion, is a stiffer anti-roll bar. This allows for less roll in front and rear and does not worse the ride quality.

Any how, what you are describing does not totally sound like you are experiencing understeer, since the car does go the way you want it to. The steering of the Z is better weighted than that of the bimmer. The Bimmer's is very precise but also significantly overboosted (hopefully be fixed with the "Active Steering" soon coming). The steering, I think lost a lot of communication to the driver, when they went from e36 to e46 models, but that's just me.

Please do not take the wrong way as I have no intention of it, but I believe, based on your description, the best upgrade you can do to improve the handling and you enjoyment is to attend DE events. I just got the impression that the somewhat difficult steering experience you had is more related to how you think of taking a turn vs. how you actually take it. Please take this as a constructive critism, I do not intend anything other.

Good luck.

 

Hey man, not at all. I like the heavier stering of the Z, I just wish it felt a little lighter on its feet I guess.

I really want to attend a good racing school, but there are none in my area.

 

Delaware should not be that bad. Deleware BMWCCAand Porche Club of America (Deleware PCA) both have chapters in your area. Both of them provide very good driver education events with very professional instructors, relatively cost-effective (~$350 for two full days) and you get a lot of track and class time. The side discussions are also extremely fun and useful.

Both clubs welcome non-members, the participation fee is increased a tad; and it would also give you the opportunity to see various other marques and their drivers. I would highly recommend them, the season just started

Good luck.

 

Brad,

A lot of interesting commentary here...My expectations are that the stab bars alone will not cure understeer on the Z. Based on my brief experience autoXing the Z, I believe it understeers because the front shocks are underdamped. Think of it this way...you are driving really quickly towards a sharp left had turn. You squeeze the brakes on hard. Now what happens? The weight of the car starts to shift forward over the front wheels...now your weight is over the front, and you start to turn the wheel left. Now the weight shifts over to the right side of the car, on to the outside right front wheel. If that shock/spring can support the load, the spring and shock will compress and push back (rebound). The front of the car would then settle over that wheel, but some of that weight will be redistributed back to the left front side of the car, and the front end will begin to turn to the left. If the shock is underdamped and the spring is too soft, the spring and shock will compress, but not 'push back' enough to make the car turn. The weight of the car will just continue to keep plowing out towards that front right corner, because it will not be deflected adequately. I think this is the problem with the Z. That's why when you turn in sharply, the weight pushes through the outside front corner, and the car will just plow on unless you get on the gas to kick the rear end around and redistribute weight to the back end. A well matched shock/spring combo (like the S tune kit apparently) will support the car better after that weight shift to the outside corner. The anti-roll bars or (anti-swaybars) help control the distribution of the weight to the corners. With a stiffer bar up front, that weight shift to the front right corner in this example will not be as severe as with a softer one. They work in harmony...as do tire pressures, etc. That's why suspension tuning is a PITA, and the more moving parts you have, the harder it is to figure out what's going on and how to fix it. If you don't know a ton about suspension tuning, and you just want to enjoy the car, keep it simple. On street tires, try running a front tire pressure that is about 4-5psi higher than in the back. Maybe run something like 37 front and 33 rear. I only did two autoX's last year, but I found a world of difference on the stock tires when I ran 39psi F and 34 R. This will stiffen up the sidewall on the front and help it turn in better. The next step could be to even out your tire widths F and R. Run a 245 F 245 R or something like that...that will help as well. If you go with a shock/spring combo or full coilover, make sure it was designed well and tested, not just some generic thrown together setup. A mismatched spring and shock will destroy the handling. Watch a riced-out civic bounce down the highway on 'lowering' springs some time. The shocks cannot control the motion of the springs, and the shocks are rendered virtually useless...the car just bounces on the springs. (as a side note, all of the complaints of a bumpy/bouncy highway ride in the Z is another indication that the shocks are underdamped for the springs). Good luck, and remember to keep it simple!

 

It's been posted before but here it is again. JRitt talks about transient understeer, I was talking about steady-state understeer.

http://www.wtrscca.org/tech.htm