Advice on tuning out understeer

[Zmanco]

Here's the current setup on my 73:

- Tokico red springs

- Tokico Illumina struts

- 1" bump steer spacers in front

- stock rubber bushings all around

- MSA anti roll bars (1" front, 7/8" rear)

- 16 x 7 panasports with 225/50-16 Yoko ES100

- BruteForce LSD

 

At my last 2 track days I've found I have more push (understeer) on 3rd gear sweepers than I would like, especially when I'm on the throttle. Before I installed the LSD I was closer to neutral.

 

There were only 2 second gear turns and the car was very neutral in them with no noticeable push. I had enough torque coming off the turn to begin to get the rear to rotate on its own (with the help of the LSD I'm sure). Also, initial turn-in was while I was off throttle under braking which helped I'm sure. They were a lot of fun

 

I've staggered my tire pressures as much as 6 psi higher in the front which helped a little, but not enough. My Illumina's are set to the softest setting (1) in the front, and 3 in the rear (on a 5 scale).

 

Most of my driving is on the steet, so I don't think I want to go down the camber plate route.

 

I was thinking that I might try changing the front antiroll bar to 7/8" to soften the front to get better grip. Beyond that, I'm pretty much out of ideas.

 

What do you think of the changing the front bar? Should I consider a 3/4" front bar, or is that likely to go too far? I don't want to create a tail-happy devil on the street.

 

Other ideas?

[JMortensen]

You really can't go wrong with adding some more adjustability to the front end. From the looks of it you can basically tune with tire pressure, the adjustable shock, and how tight you have your endlinks. Adding caster and some more negative camber would be my first suggestions, but those aren't really on your list.

 

I'd suggest you loosen up your front end links and tighten down the rears. Drop the front tire pressure until the tire rolls all the way to the edge of the tread. If it rolls onto the sidewall add more pressure.

 

I wouldn't suggest messing with the swaybars yet. I'd see about getting more adjustments available to you first.

[Twoeightnine]

Whats wrong with options?

 

Ask any racer to be disallowed the option to utilize camber, he probably wont race the car. You can set up the camber for forward bite at the track. Have it premarked for the street and slide it back. It only takes a few moments per side. How fast do you want to go?

[wheelman]

TwoEightNine,

My guess is it's a matter of dropping another $700.00 - $800.00 for a coilover/camber plate package which will be put into a car that is mostly driven on the street where they are not needed.

I went through the same argument with myself, I had installed the Tokico springs with their HP struts but then got into Auto-X. The springs are not the best so I decided to bite the bullet and upgrade to adjustable components but it's not a trivial amount of money.

 

As for other things to change that might help with the understeer. When I had those springs on my car the rear had a large amount of negative camber (2 degrees or more) but the front had virtually none. The bumpsteer spacers you have make for even less, you might try removing them just to see how things change. It will make for a small amount of added negative camber at ride height but the lower roll center may not be worth it. The large MSA bars might mean you never noticed the lower roll center but you won't know until you try it.

 

Wheelman

[tube80z]

You don't need camber plates to slot the towers. That would be a cheap option. My guess is the car is losing camber at front and this leads to understeer. Softening the front will not solve this issue and only lead to chasing your tail.

 

Cary

[Zmanco]

I'd suggest you loosen up your front end links and tighten down the rears. Drop the front tire pressure until the tire rolls all the way to the edge of the tread. If it rolls onto the sidewall add more pressure.

Both front and rear end links are quite tight, so I'll try loosening the fronts.

 

I'm a bit confused by your suggestions for changing the tire pressures. It was my understanding that with street tires a little more pressure usually INCREASED grip, at least up to a point. I had read that track tires might behave differently. My own experience, which is only with street tires, has been more pressure increases grip. For this day, I started at 26/24 F/R but soon increased it to 30/24 to help with the push. I had pretty even tire wear across the tread (~100 miles on track) with only a very little feathering on the outside edges of the tread, so figured I wasn't too far off from the optimal pressure.

 

I suspect going even lower in the front would make the push worse. Did I misunderstand your suggestion?

[Zmanco]

You can set up the camber for forward bite at the track. Have it premarked for the street and slide it back. It only takes a few moments per side. How fast do you want to go?

I've read many of threads on this site that discuss adding adjustability to camber, but don't want to cut up this particular car as it's pretty clean. Some day perhaps I will do a track car and not worry about it.

[Zmanco]

When I had those springs on my car the rear had a large amount of negative camber (2 degrees or more) but the front had virtually none. The bumpsteer spacers you have make for even less, you might try removing them just to see how things change. It will make for a small amount of added negative camber at ride height but the lower roll center may not be worth it. The large MSA bars might mean you never noticed the lower roll center but you won't know until you try it.

 

Wheelman

When I first installed the springs/struts, I did not have the bump steer spacers. But driving on the street around bumpy turns wasn't fun, so I added them. I never had a chance to take it to the track without them, so don't know how much difference it might have made.

 

BTW, my rear has almost no negative camber (I think it was a few tenths last time I had it on the alignment rack).

 

Thanks for the suggestions everyone. This is a mostly street-driven car so I know I'm going to have to make comprimises at the track. I think loosening the end links up front is a cheap and easy experiment to try.

[wheelman]

Zmanco,

What behavior did you see going around bumpy corners?

How is the behavior different now?

If my understanding is correct those "bumpsteer" spacers do nothing to actually correct bumpsteer but they do raise the roll center.

 

Edit: How much did the Tokico springs lower your car? Mine dropped about 2" on the front and 1.5" on the rear.

 

Wheelman

[JMortensen]

Just to clarify, bumpsteer is usually most extreme at the ends of the suspension travel. A bumpsteer spacer does raise roll center, but it also moves the bumpsteer to a part of the suspension travel where it is not so extreme.

[johnc]

At my last 2 track days I've found I have more push (understeer) on 3rd gear sweepers than I would like, especially when I'm on the throttle. Before I installed the LSD I was closer to neutral.

 

Before you installed the LSD you were power limited in medium speed corners. Too much throttle and the inside rear tire spins limiting weight transfer off the front tires and keeping the car somewhat neutral (actually, not understeering much). With the LSD you can get apply more power, which transfers more weight to the rear, reducing grip in the front and increasing understeer. Power on understeer is typical with a slightly modified 240Z.

 

I'm never been a fan of playing with anti-roll bar end links as a tuning tool. Until you start making spring and shock changes to control the rate of weight transfer your best bet is to change your driving style. Brake more on corner entry, trial brake to get the car rotating, apex late, and then squeeze on the power as you unwind the steering. Basically drive it as if its a FWD car. This will give the front tires a better chance to work with you.

 

Also, be very careful about snap oversteer. The way your car is setup now if you're experiencing a lot of corner exit understeer, have a lot of steering cranked in, and for some reason lift off the gas, the weight transfer forward will increase front grip while decreasing rear grip. The car may very well spin as a result.

[Zmanco]

Wheelman,

Without the bump spacers, going around a bumpy corner had the steering wheel moving all around in my hands as the tires went up and down. It seems like the force I needed to exert on the wheel to keep it turned would change over the bumps causing me to over/under correct and hence I couldn't keep the wheel in one position.

 

Adding the bump spacers made it better, but didn't eliminate it.

 

It is my understanding that the spacers are really only there to get the steering geometry back to (or pretty close to) stock with regard to bump steer. I doubt it changes the roll center very much.

 

As for the drop, I was so excited to get started installing the springs that I forgot to measure my ride height before. I would guess it only dropped me about 1" in front, less in the rear - definitely not 2". But I don't know if the springs I took off were stock. I think the original owner had put a Mulholland package on many years ago.

[DHale_510]

You really have two choices; Engineer the car or drive the car. Since you don't want to spend money engineering it, just drive it.

John is right on. You made changes to the car and now need to learn to drive it as a new car. Driving it out of instead of stuffing it into the turns is lots of fun. Betcha that it is both more fun and faster once you adjust to it.

[JMortensen]

Both front and rear end links are quite tight, so I'll try loosening the fronts.

 

I'm a bit confused by your suggestions for changing the tire pressures. It was my understanding that with street tires a little more pressure usually INCREASED grip, at least up to a point. I had read that track tires might behave differently. My own experience, which is only with street tires, has been more pressure increases grip. For this day, I started at 26/24 F/R but soon increased it to 30/24 to help with the push. I had pretty even tire wear across the tread (~100 miles on track) with only a very little feathering on the outside edges of the tread, so figured I wasn't too far off from the optimal pressure.

 

I suspect going even lower in the front would make the push worse. Did I misunderstand your suggestion?

I missed this earlier, sorry.

 

With stockish suspension, often times increasing tire pressure will help traction because the tire is rolling over on the sidewall. It has been my experience with street tires, DOT tires, and slicks, that you want to run the minimum pressure you possibly can and keep that tire from rolling onto the sidewall. In your case that might be 40 lbs or more, since you don't have enough negative camber in the front. But when you can get some negative camber going then you can really drop the tire pressure down.

 

The more changes I make to my suspension the lower the air pressure gets and the faster the car goes.

[evildky]

first thing turn the shocks to full hard in the rear! if your still pushing I'd add air to the rear

[proxlamus©]

Daniel do you have illumina's on your Z?

 

what setting to do you have on the fronts and rears if you do?!

[Zmanco]

Ryan, yes I do have Illuminas. I checked last night and it turns out I had them set on 1 (softest) Front and 2 Rear. I had thought it was 3 on the rears but I was mistaken.

 

I did turn it up to 4 in the rear which makes the ride much 'jigglier" (if that's a word), but there's no place on public roads where I can see how it affects understeer in 3rd gear sweepers

[Zmanco]

John is right on. You made changes to the car and now need to learn to drive it as a new car. Driving it out of instead of stuffing it into the turns is lots of fun. Betcha that it is both more fun and faster once you adjust to it.

I tried adjusting my braking points and line, but the understeer was still an issue. For example, at the end of the straight there is a sweeper that is more than 180 degrees around. The entrance is gradual and I was coming into it around 65 mph. It's like a big carousel, and the push was tough coming out. In fact I found that I was roughly equal to the stock 350zs on the track that day in acceleration, braking, but through the carousel, I just watched them pull away. Too much push

[GrommitZ]

How about using adjustable camber bushings(<$100)? According to Jon's FAQ, they'll get you 1 degree more negative, but require toe adjustments everytime you change the bushing offset. Also, maybe your car will get more neutral as your PowerBrute breaks in. How are you taking the sweeper? Where's your turn in point and apex. When do you roll onto the throttle. I'm not too experienced to give advice here, but was wondering how you were taking the turn?

[Zmanco]

GrommitZ, I'm actually beginning to rethink my original decision not to change camber. I'm thinking that maybe this kit from MSA would make sense.

 

http://www.thezstore.com/page/TZS/CTGY/PSDC08

 

Does anyone know how easy it is to change camber on this? Do you have to pull the strut assembly out to adjust, or can it be done on the car? The MSA site is silent about this.

 

With regard to your question about where the apex was on that turn, the concensus from the group was about 140 degrees around (my very poor estimate from my memory). The point is that it was very late. The turn probably has a radius of at least 100 feet. No matter where you apex, the turn is so long that you have to be on the throttle at least part way for much of the turn. The powerbrute seems to lock up without a lot of throttle, which in this case works to my disadvantage.

 

Here is the track map at PMI. I've been talking about turn 1.

http://www.putfile.com/pic.php?img=5201258

 

And my LSD is definitely broken in