Handling issues

[johnc]

The lightweight setback position of the v6 made standard "known" suspension setups for the S30 inappropriate, and took a bit of pure trial and error.

 

 

Actually, that's a good point. If your weight distribution is more rear biased then a staggered setup makes more sense, but there needs to be a significant difference in front to rear balance. On my 48F/52R 240Z I ran a square setup with great results.

 

Also, comparing what OEMs deliver to what might be an optimal track setup is incorrect. Having some experience with the Honda S2000 it should be noted that it responds very well to a square setup. The current thinking is to run a square wheel and tire combo (245s for the AP1 and 255s for the AP2 cars) with a larger front anti-roll bar. Bob Endicott's AP2 S2K runs 255s all around. Same is true for RX8s and Jason Isley's car ran 245s all around. And my own 2006 350Z respounded very well to a square 245 or 285 setup.

[tube80z]

Actually, that's a good point. If your weight distribution is more rear biased then a staggered setup makes more sense, but there needs to be a significant difference in front to rear balance. On my 48F/52R 240Z I ran a square setup with great results.

 

I had a similar weight distribution on my 240Z when I ran the FA tires and that makes it very out of square. What I found was that I could tune the car to allow for extra cornering grip and still take a lot of throttle. This proved to be quicker than running the car square with four front tires. I was never able to get four rears to clear everything to see if that was faster. I'm not saying that one is better than the other but I think driving style plays a lot into this too.

 

Also, comparing what OEMs deliver to what might be an optimal track setup is incorrect.

 

But if you look at a number of racing cars there are a lot that run staggered setups that don't necessarily have rear bias. But then again there's the acura LMP1 car that got a lot quicker by going square. Definitely something that will need to be tested this next year.

 

Cary

[JMortensen]

Agreed. I'm actually going to try a square setup, but not because I don't believe a staggered setup can be made to work. My impression is the more power you're putting down the more sense the staggered setup makes, because what you're really getting out of it is the ability to accelerate out of a corner with more throttle. That advantage might be more apparent at an autox than it is at a road course.

[johnc]

I had a similar weight distribution on my 240Z when I ran the FA tires and that makes it very out of square. What I found was that I could tune the car to allow for extra cornering grip and still take a lot of throttle. This proved to be quicker than running the car square with four front tires. I was never able to get four rears to clear everything to see if that was faster. I'm not saying that one is better than the other but I think driving style plays a lot into this too.

 

But if you look at a number of racing cars there are a lot that run staggered setups that don't necessarily have rear bias. But then again there's the acura LMP1 car that got a lot quicker by going square. Definitely something that will need to be tested this next year.

 

Cary

 

Let's see if I can confuse this a little more

 

Another issue we're skirting is aero and center of pressure effects from downforce. As the car goes faster, downforce increases, and the center of pressure tends to move towards the back. This generally occurs because cars can generate more downforce from rear aero then from front. This forces an increase in rear tire carrying capacity, which leads to a staggered setup that's less then ideal at low speeds. The more a car relies on aero grip the more likely it will understeer when it has to rely on mechanical grip.

[tube80z]

I did observe tire pressure under two heavy sessions. The track is a right hand dominant so left side tire pressures were obviously higher. After tires pressures recorded The car came in hot with an increase as follows ; LF +8 RF +5 LR +4 RR +3 PSI.

 

Looking at your pressures shows me that you're working the front end much harder than the rear, which you would see as understeer. Ideally the front and rear will build pressure at a very similar rate if the setup is balanced. As a first step I'd go stiffer on the rear springs and add some rake. More camber won't hurt but the pressure rise should stay about the same. If/when you get a pyrometer and average temps you should see a similar trend.

 

Hope this helps,

C

[EMWHYR0HEN]

So in hopes of decreasing push and getting the rear tires to work more efficiently I've reinstalled the rear sway bar, extended the front track by 1.5 inches, decreased front spring rates 25 lbs, increased rear spring rates 25 lbs, raised the rear ride height and lowered the front. What I really need to do is get my car on some scales so I know what im working with. In the mean time I'll be adjusting my corner weights according to tire temps and ride height.

 

I have a pyrometer on my Craftsman digital multimeter with a tiny probe attchment. I tested it today and it seems fairly accurate. I'm wondering if this will be good enough to take surface tire temps or would I want something I can poke into the tire thread beneath the surface. Should I not even bother and get a laser type? any thoughts on this?

Edited November 12, 2010 by EMWHYR0HEN

[JMortensen]

I asked about those multimeter probes and was told they take too long to get a reading. How long does yours take? You really need to get tire temps as quickly as possible when you get the car off the track.

 

As far as your mods, it's best to do one thing at a time whenever possible. It'll be interesting to see how that works out though.

[EMWHYR0HEN]

It takes readings quickly. I had an ice cube next to a stove burner and it instantly read 300+ down to 31 degrees F. The only thing is that I cant really probe, or poke a tire with it. Basiacally I can only read surface temp.

 

I was a little concerned that I might have gone overboard and done too much. I'll report back with results.

[tube80z]

It takes readings quickly. I had an ice cube next to a stove burner and it instantly read 300+ down to 31 degrees F. The only thing is that I cant really probe, or poke a tire with it. Basiacally I can only read surface temp.

 

I was a little concerned that I might have gone overboard and done too much. I'll report back with results.

 

Well we won't accuse you of not trying a few changes For tire temps you really need to get down in the rubber. I measured surface temps and they often were cooler and closer together than down in the rubber. As Jon mentioned the key is getting to them quickly after you've been loading the tires up.

[Dan Baldwin]

Initial turn in is okay. I can get it pointed where I want after braking. It's after I turn in where the car starts to understeer, and pushes outward. I tried giving some throttle mid corner to try and induce oversteer and it doesn't seem to help much. All that does is push the car along further, or slide the rear out too much. The car is very predictable where you can pretty much catch any under/oversteer as it happens.

 

Dunno how much power you're making, but generally "giving some throttle mid corner" induces understeer, not oversteer. If you wanted to tighten your line, in most cases you'd want to lift or feather the throttle to point the car.

 

You have to get most of your turning done early in the corner so that as you apply throttle and your arc widens due to unloading the fronts and increasing speed, you asymptotically approach the edge of the track at track-out.

 

The car may indeed be understeery, but it sounds to me like you might be turning in too early, at least for the current setup of the car. If the car turns in fine initially, but runs wide later in the corner, you hafta get more of your cornering/turning done earlier.

[260DET]

Some interesting comments being made here, as usually happens when race suspension issues are raised. Some of the 'correct in theory' comments may work in isolation but as Neil Roberts says 'everything depends on everything else' which seems to particularly apply to suspension tuning where usually changing one setting will have secondary consequences, some of which will not be welcome and may even add to the problem in other ways. Might add that over the years this forum has stimulated my interest in suspension dynamics even if I don't necessarily accept everything as written here as being the best or most complete solution to the problem at hand.

[Sideways]

Again have to agree with what was said before. Id set it all back to how it was before, and just change things one at a time instead of going all out and doing it all at once. You wont know how much of an impact each individual change is making, ya know?

[johnc]

Might add that over the years this forum has stimulated my interest in suspension dynamics even if I don't necessarily accept everything as written here as being the best or most complete solution to the problem at hand.

 

Suspension setup is all about compromise. There are many different ways of setting up a suspension because there are many ways to work that compromise. We can argue based on theory, personal experience, or tea leaves which is the "best", but the ultimate objective measure is lap times and finishing position in the race. There are thousand of examples of driver's winning a race in an "ill handling" car and other driver's losing a race in an "outstanding handling" car (the story of my racing career).

[EMWHYR0HEN]

For tire temps you really need to get down in the rubber.

 

Probe type pyrometer seems to be preferred when taking tire temps.

 

 

The car may indeed be understeery, but it sounds to me like you might be turning in too early, at least for the current setup of the car. If the car turns in fine initially, but runs wide later in the corner, you hafta get more of your cornering/turning done earlier.

 

I tried late apexing but that didn't seem to help. The problem was that the rear end could not rotate quick enough. I could have been satisfied with that setup but, It just didn't feel right with the track layout and my driving style.

[EMWHYR0HEN]

Played around with a few things today with good results. It's getting close to feeling neutral which is what i'm shooting for. I'm sure with a few more track days I'll be able dial things in a lot closer However, not all the changes are considered good. The car is a little trickier to exit a corner and requires better modulation of throttle. Just as Johnc mentioned suspension tuning is all about compromise. I'm hoping setup the car to corner as neutral as possible and then finding alternative ways to get the car to hook up exiting a turn.

 

I might add that I installed droop limiters and played with that for a little bit. The ride is harsh with them on over bumps but, It does keep the car flatter through a turn. Right now i'm setup with 1'' less of droop all around. I'm considering extending it a little more on the rear. It seems kind of 'jumpy' during accel and bumps.

 

Also, in light of all this I picked up Chassis Engineering by Herb Adams. Great little book regarding information on high performance handling. Mainly practical principals with less theory. The kind of stuff that makes you fall in love with this sport all over again.

[johnc]

Please read: http://forums.hybridz.org/index.php/topic/96471-low-and-high-speed-balance/

[tube80z]

I might add that I installed droop limiters and played with that for a little bit. The ride is harsh with them on over bumps but, It does keep the car flatter through a turn. Right now i'm setup with 1'' less of droop all around. I'm considering extending it a little more on the rear. It seems kind of 'jumpy' during accel and bumps.

 

When you mention 1 inch of droop is that total or how much you reduced it by? On 550 Pound springs my car had a little less than 1 inch compression. In the rear I typically set the limiter so that I can slide a 0.040 feeler gauge between the spring and seat (like adjusting valves). In the front I was running around 5/8 to 3/4 total droop. On a really smooth track sometimes less and if really bumpy setup the same as the rear. I didn't have any of the jerkiness you describe.

 

I'm guessing with your softer springs you need more droop in the rear. Try the procedure above for the rear and I think you'll find it helps. We accidentally eliminated droop from a friends car in and it behaved very similar to what you're seeing. So that's my long winded way of saying I think you're on the right track.

 

Cary

[EMWHYR0HEN]

I worded that poorly didn't I?

 

I reduced my total droop by 1'' on all four corners. That's a great idea with the feeler gauge and adjusting the rear suspension. I'll have to give that a try.