BSP 240Z Solo2 - Set up help request

[260DET]

Concerning ride height, the actual height itself won't indicate whether or not the roll centers are out, that is a function of the suspension geometry. Particularly the relationship between the inner and outer control arm pivot point heights. The rule of thumb is that if the arms are slightly lower at the outside at the static ride height the roll centers should be somewhere near OK.

Even better, using small diameter wheels and low profile tyres is one simple way to lower the ride height that does not affect suspension geometry at all. Its a pity that tyre choice in the smaller diameters is so limited.

The lower the ride height the better for grip (and less frontal area), providing the correct suspension geometry is maintained.

Concerning anti-roll bars, they should be as light as possible because they transfer load to the outside wheels in a corner, particularly relevant at the rear for getting power down. Its better to use heavier springs than heavier bars for that reason.

[gnosez]

I agree re: smaller tires but the supply is quite limited and for those of us with toyo 4X4 brakes they would fit if you use 14-inch wheels. As to higher springs rates, I too agree this is a better way to go but wonder if that is true for autocross activities as opposed to track usage.

[CTR98]

The rule of thumb is that if the arms are slightly lower at the outside at the static ride height the roll centers should be somewhere near OK.

I thought about that when I started but somehow ended up with the arms higher on the outside.

OK, from the advice given here I have raised the car some more and will be getting an alignment next Thursday, mainly to check the castor and increase the negative camber. Is there a consensus on the degree of castor?

Thanks!

[260DET]

Caster on mine was brought back from ~5 degrees to 3.5, same as camber. But this could have been required because the extra caster was gained by moving the front Xmember forward, not really a good idea in retrospect.

The best single turn in improvement with mine was to go toe out at the front. I suspect that the Z may benefit from more Ackermann but to get that would involve a fair bit of front end modification.

Interested to hear how it turns out, each car is a bit different, particularly when body stiffness is considered.

[tube80z]

For let's start from the beginning:

4) car set-up as per John Coffey:

Camber - 3 degrees neg front and 2.5 neg rear

Caster - 6-8 in front (you can decrease camber if you have more caster)

General rule of thumb is one half KPI (steering axis inclination). When running this much caster you also need to check to make sure you don't have too much caster trail (mechanical trail). You'd like to have around half an inch. Also try to have no more than 20 percent of tread width as scrub.

Toe - 1/4 to 3/8 out in front and 1/16 to 1/8 in in the rear

For tight track try rear toe out.

Ride Height - 4.5 to 5 inches at the rocker

Springs - 225 to 250 front and 275 to 200 rear

400 all the way around. You'll need proper shocks to make this work. Helps to quicken transition times and keep suspension gemoetry for going all over the place.

Sway bars - 1-ich front and 5/8 rear

15/16 front max -- both need to be adjustable and connect to the strut, not the control arm. Sway bar should be in a low friction mount, which is not poly or other form of pinch block. Ideally at least one is driver adjustable for when you need to make the last minute tweak between runs.

Offset bushing - yes

Will be needed for street prepared but should be avoided in other classes.

Poly - yes

Never. Poly has too much friction. These need to be low friction pieces to help with mechanical grip.

Good advice on notes deleted. A tire pyrometer is good to indicate wear but not a lot more. But tire pressures are more accurate on how the tires are used. You should work on a setup that gives you an even rise in pressures. This is where good notes and understanding what you need for a hot tire pressure is important. You can switch to nitrogren to help eliminate the effects of water vapor in the tires.

To adjust chassis balance you can change the rake. Rule of thumb is two turns of the spring collar to start. If the effect is too much try one turn. You lower the end that isn't sticking. Make sure you keep the arms near lever and don't end up too low. The car should be corner weighted. Make the front level and the front weights as close as you can and live with what you get in the rear. Move as much weight down and towards the back as you can but not behind the rear wheels.

Remember you need to make ride height changes to compensate for weather conditions to keep a balanced chassis.

Also consider using shims for camber/caster plate alignment. These allow rapid known changes and/or allow you to get the car put back together without having to do a major alignment.

Before an event always know all your settings. Keep notes of any changes that you make at an event. And at the end of an event do a setdown. This last step is important and few people do it.

If you're using the same size tires all around keep notes on how hard they were used and rotate to keep the use as close to the same as you can. Do all chassis etup work on old tires. New tires will mask a lot of the changes until you have killed them. By doing all this you'll end up having a car that is kinder to its tires.

Test, test, test, and have lots of fun.

Hope this helps,

Cary

[Steve Parmley]

O.K. I get some of this, but how is ride height related to chassis balance with a weather change? Also what is a setdown? I have attached a picture of Vic Sias' swaybar to strut attachment. Do you just weld a bolt to your strut tube?

[tube80z]

For the sway bar you can weld a mount to the strut tube (should be fairly wide) to distribute the load. Another way that works well is to build a special collar that is on the spring perch. I'll see if I can dig up a picture.

Ride height divided by air density ratio is more or less a constant. I use this relationship to change the ride height as the temperature/humidity/barometric pressure change (I have a small weather station with me when I race). In reality I only make changes for large swings. Where I race there often changes in track temp of 40 degrees from morning to afternoon. If you were racing a ground effects car you live or die by this (think about this when you watch F1 this weekend).

If you don't like doing this you can use my second trick. That's to only practice when the conditions are similar to when you'll typically race. I do this a lot of the time and watch my competitors chase their tales for a lot of the day. Then they find a demon setup and are really fast. When we race the conditions are often not close and they wonder what happened.

Another item that isn't well understood is that to see the effect of a spring change you need to adjust ride height. If you don't then you have changed more than one variable. Here's the key:

wheel rate =(motion ratio)^2*spring rate

wheel rate (at the contact patch) (WRc)=(wheel rate)*(tire spring rate)/(wheel rate + tire spring rate) or WRc=1/WR + 1/TR

Ratio 1 = WRc/Corner Sprung Mass

WRc/ground clearance is a constant

This gives you a formula for the ride height change you need to make when you change springs.

Along these same lines are a few more formulas called magic ratios. These can be used to look at any setup and make another that works similar that has different sway bars and springs.

Here are what I'd recommend for records at each race.

1. setup sheet. This is all the car settings before the race.

2. Run sheet. Use this to record lap times and variables while you are running. I have one of these for each run and use it to watch tire pressure rise, temps, etc. I also make notes about how the car worked and what I'd like to try next.

3. Setdown sheet. This is used to record all the settings after you have completed a race. As you make changes during a run or if something has changed that you didn't know about you find it here.

4. Tire record sheet. I keep track of each tire and how much use it has. After every three events I flip them on the wheels to maximize life.

And if you run bias ply tires (slicks) you need to keep records of tire circumference. Bias ply tires grow as they are ran. You'll need to adjust ride height to compensate for this. I also get the car off the tires when I bring it in from a run and scrape the crap from them while they are still hot.

So you're probably thinking I'm totally full of crap by now. But if you have ever driven your car one day, didn't really pay attention to the weather conditions, etc. and it worked perfectly. Then another day, which you would swear is similar, and the car drives like crap. These are some things you can try to keep the car working well.

Good setups are the product of hard work done in a systematic manner over time. Don't expect to master this in a season, let alone a few races. Good record keeping of setups, changes, and variables at the track will help you make the car fast and help you make changes when it is not.

Cary

[Steve Parmley]

Well, attention to such detail makes you Ross Brawn and Michael Schumacher combined. Weather in the California central valley ranges from effin' hot to Iraqui hot. Low on the humidity.

I am still happy if I remembered to properly torque all the lugnuts. You have inspired me though and I am doing alot more reading on suspension and set up. Spreading the load around the strut for the swaybar mount should not be hard to design but if you have any pictures that would help.

[tube80z]

You don't have to do all this but starting to do more and more really helps. If you only do two things I'd say keeping track of track temperature and your pressure rise are the most critical. Even if you don't want to do anything else you can make meaningful changes playing with those two.

I race in White City, Oregon. It was used to train troops for desert warfare in WWII and is only fit for insects in the summer. So I know what you mean about heat, but at least it is a dry heat.

As far as ride height changes,etc. if you keep good notes about weather conditions (like ambient and track temps) it can help when you find that magic sweet spot. You can always make the change at home when you think you know what the condidtions will be when you run. Or if they are almost always the same then you don't have much to worry about.

At the end of the day this is just autox.

Cary "who was hoping for a Rory Byne :-)"

[260DET]

Has anyone any thoughts on what tyre pressure should rise by from cold up to when they reach their usual operating temperature?

For example, last time mine were checked they rose on average from 28 psi to 36 on a warm to hot day. Which seems a bit excessive to me, 5-6psi rise would be better?

[jmortensen]

Richard, you could run nitrogen instead of air in the tires. That would make the pressure change smaller. I had a boss who ran ITSS who did that. He brought a big cylinder of nitrogen to the track, and he used it to run his impact gun and other tools also.

The faster I go the more the pressure increases, and the lower I find I want the total pressure. Started out at ~33 cold to get to 35 hot with BFG R1's back in the day, now I'm running 28/26 hot on slicks. I usually start with 24/23, then bleed off pressure in between runs or work groups, and I have to bleed of a lot of air...

I've got this theory, maybe Cary or others can verify. The more heat you can put into the tire the better (within reason of course but I haven't overheated a tire yet) and the less air pressure you start with the hotter the tire will run. So as I continue on, I find myself running less pressure, and more negative camber and still getting good temps across the tire.

Another way of saying it: Used to be I didn't have the required camber and I had to jack the pressure up to keep the the temps good across the tire. Now with more negative camber I can drop the pressures, maintain good temps across the tire, and it sticks a hell of a lot better.

It's a bit counterintuitive to me, but that's what's been happening with me since I started running R tires, and a couple friends' experiences seem to back me up.

[tube80z]

Richard, you could run nitrogen instead of air in the tires. That would make the pressure change smaller. I had a boss who ran ITSS who did that. He brought a big cylinder of nitrogen to the track, and he used it to run his impact gun and other tools also.

One of the largest performance increases for me this past year was moving to nitrogen. Why I like it is that I can use the ideal gas law to determine my starting pressure for a given ambient temp and a target hot pressure. I made a chart in excel and printed it off for use on race day.

To see if nitrogen would help use the ideal gas law to determine what your pressure rise should be. If you're much higher than this, which I'm guessing 260DET may be then you can benefit from nitrogen. To get your tires onto nitrogen you need to purge them of air before. Smith has a procedure and a lot of tire shops are moving over to it.

For slicks I have found I lose less pressure over night on nitorgen and it is not reactive. I spend a lot of time taking care of my tires and this is one step.

It also comes in useful to run air tools as well. I need help to run my car and nothing works better than to offer "air" and the use of an impact gun on race day. Once you've bought the cylinder and regulator it doens't cost that much to use nitrogen. It was also very handy when I had a flat on the trailer on the way to a race. Someone stopped to help me out and I pulled out the impact and went to work and they just kinda watched dumbfounded.

I've got this theory, maybe Cary or others can verify. The more heat you can put into the tire the better (within reason of course but I haven't overheated a tire yet) and the less air pressure you start with the hotter the tire will run. So as I continue on, I find myself running less pressure, and more negative camber and still getting good temps across the tire.

Another way of saying it: Used to be I didn't have the required camber and I had to jack the pressure up to keep the the temps good across the tire. Now with more negative camber I can drop the pressures, maintain good temps across the tire, and it sticks a hell of a lot better.

I don't have any magic info here but I've seen the same thing. I do know a tire has a rate that varies with camber and pressure and this probably has something to do with it. I stumbled across this last year when I had tires that had given up on me. I tried lowering the pressure to overheat them and soon found more performance. Up to that point I was floundering trying to figure out how the car went from really good to really poor. See -- I'm no expert :-)

I can't say that they run any hotter this way, at least from taking temps but they do provide more grip and work better. This may be something to do with spring rate. I do think they heat up quicker at least from how they work. I'm running Hoosier tires in R25A and R35 compounds. If you plot lateral acceleration to tire temp you'll find that slicks have a couple of operating windows with a noticeble dip in the middle. I'm guessing that lower pressures may help you cross this window more quickly, which is especially important in autox and hillclimb type events.

To get more heat into the tire you can raise the RC, the car, increase toes, and play with pressure and camber. Pressure and camber are the two items I spend a lot of time messing with between runs once I get the car balanced. The key is to always get the car balanced and see an even pressure rise before you start tweaking too many things. Otherwise you'll soon be chasing your tail.

Cary