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I'm going to put heavier springs in my 240z. I have recieved differing opinions on which end of the Z I should place the heavier springs. Since I'm new to racing I do not have a clue. One of the tracks I race on has high speed bumps and the others are fairly smooth. HELP!!!
P.S. Anyone have a 3:7 for sale
Hi Terry,
I've run F/R 400/300 and 350/275 with good results. 1 inch front sway bar, no rear bar
I like it simple but life and racin ain't most of the time, so here's the truth from Katman....couple of months back
"The basic difference between my novice (less than 2 full seasons) setup and what happens later is spring rate (and whatever corresponding shock changes need to happen, obviously). I like to start them out softer rather than stiffer because I believe it helps them reacclimate to the car quicker during the course of a weekend (remember, we're only driving these things once a month or so) so they're up to their potential sooner. Softer is generally less twitchy (which 240Z's have an abundance of to start with) and easier to stay on top of until such time that the gluteus maximus becomes a finely honed and worthy sensing instrument. Plus, off roading is easier on the unibody with soft springs.
My progression on springs goes something like (front/rear) 285/240, 325/275, 350/285, and finally 400/350. The 350/285 and the 400/350 each won an ARRC. For whatever reason the west coast seems to run in the 250/275 neighborhood as I recall. I don't know if that's because the tracks are bumpier or what. Me thinks those running bigger spring in the back than the front are either in the 6 inch ride height neighborhood or aren't really driving that hard. Also, lots of folks run ungodly big sway bars, like 1+ inch front and 3/4-7/8 rear, which really distorts what the springs should really be (personally I don't like how bars wanker the chassis so I prefer to balance with springs and trim with small bars). I've also come to the conclusion, correct or not, that the spring rates you need to achieve comfortable front/rear balance are very sensitive to roll center. The lower the car gets the more the front roll center heads toward China and the more spring we need to overcome the roll leverage that results. Anyway, be prepared to own a good collection of springs. Ride heights at the rocker around 5-1/8 to 5-1/4, cold with driver.
Here's my preference for things not so varied. Rear toe: I believe in the low drag setup, zero or at most 1/32 total toe in. I refuse to correct bad handling at the back by dragging the tires around. At the front I used to like 1/32 to 1/16 in, but to overcome persistent low speed corner entry problems we eventually settled on 1/8 total toe out. If I can get away with less for some tracks I do (again, low drag), and I begin to squeal when I start needing over 3/32 total out to get it to turn in.
Camber for the Hoosiers is in the 2.5-3.5 front and 1.5-2.5 rear neighborhood. I quit being anal about measuring camber because I tune with the pyrometer, for better or worse, and near the end we weren't visiting many different tracks. When properly measured and repeatable (i.e. I never change the camber unless for two sessions in a row I get the same answer), I like about 20 degrees hotter on the inside than the outside (and I won't be too bothered by 25). With the old bias ply's I shot for almost no bias but that's another kettle o' fish.
Sway bars: Like I said, in the SE the tracks are pretty smooth so I can get my balance with spring. If you have lumpy tracks and need more roll control than you can get with the springs because you got potholes to contend with then you're out of my realm of expertise. We ran a front bar equivalent to a 15/16 solid with one end of the end links mounted in poly so it was somewhat adjustable by preloading the poly- so its torsion rate was probably closer to a 3/4 solid. Our bar was something I made along the factory shape but in a 4130 tube (heat treated to a Rc=63), which only wighed a few pounds. Nicest part I ever made. I miss that bar.....
Shocks will eventually be very important. When the overall understeer/oversteer balance is achieved with the springs and bars for sweeping smooth turns, everything else is tuned with shocks (tire longevity, transitional handling differences between high speed and low speed turns, daily changes to the track affecting one end of the car or another, transitional differences between entry and exit, blah blah). I doubt the Illumina's will be enough shock (I'd revalve a Bilstein since the rule change outlawed my real shocks if it was still my problem)if you get over the 250lb/in spring zone. If the average tire temps from each corner vary more than about 20 degrees you may not have enough shock. That's a provocative statement (i.e. most people would blame the difference on the fact that there's more right turns than left, of the spring balance is off, etc.) I'll address later.
Corner weights- put everything on the right side of the car you're allowed to move, including the driver (our seat was offset 1.5 inches to the center from stock). A very good "with driver" distribution with a mid race fuel load would be 648LF, 625RF, 598LR, 580RR. Heck, that's EXTREMELY good for with driver.
A 240Z can be a handful for a novice. The back end loves to dance around under braking, and most of the time stomping on the gas when you don't want to will save you. Rotsa Ruck."
[quote]Originally posted by terry:
[B]I'm going to put heavier springs in my 240z.
[This message has been edited by dspillrat (edited June 15, 2004).]
Gee, thanx for hanging on to that, David.
One word of caution- when this "East Coast" setup fails to hook up, it usually manifests itself as a push in slow corners. To some degree shock valving and driver technique can aid the turn in phase of the corner. At some tracks with more of a collection of slower turns (below 60mph) you may need to start adding rear spring or reducing the front. This may be where the "east coast" bias (400F/350R) vs. "west coast" bias (250F/275R) comes from. Different kinds of tracks. The 240Z appears to be sensitive to that.
Best of luck.
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katman
The tracks I run do have some slow corners, ie, 2nd gear. Would that influence putting the heavier spring rates from front to back?
Yes, but what spring rates are we talking about? Is this an ITS car or something else? What other mods? WHich tires?
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katman
I'm looking for your insight and guidence on what spring rates to run. Also tire recomdations for an its car. Also would like to talk about why heavier springs go on front or back end of the car.
terry
Katman:
I've read your various posts regarding setup and some of your recommendations(switched from WC to EC setup last season). Regarding your shock recommendations, are the Bilsteins you recommend the same front and rear? I believe these are non adjustable, are they suitable for a variety of tracks with the revalving?. I'm still running Iluminas and am thinking of upgrading.
DC
The Bilsteins I've recommended are the same front and rear (P30-0032 revalved 300/100) and were what they settled on for the ERadatz Motorsports/Kemp Heumann/Grayson Upchurch EP 240Z that always seems to finish second at the RunOffs. That car eventually got ShockTek RR Adjustables from another ITS driver also screwed by the RR ban in IT (but I digress with malice), with the same 2nd place result.
I like Bilsteins in general because of their inverted design, and the fact that they are rebuildable and revalvable for about half of what Koni wants. The Ground Control AD adjustable has not worked for another competitor who's opinion and development skills I trust (another RR ban casualty no longer running). A loooong time ago we ran Illumina's up to about 240 lb/in spring rates but couldn't get them to last.
Novices won't usually know the difference between any old shock and what the car really needs. My experience has been that when the overall balance and setup of the car is good, a skilled driver can turn a lap just as fast with a shock that might not be well matched as a lap with the "optimum" shock. But it will scare him. At this point most drivers figure they're giving the car all they have (and in fact they are) and that's that. It's the engineer who decides "maybe there's some more speed to be had in the shocks". For us the right shock resulted in more consistent tire temps from corner to corner, much lower tire wear (like, it paid for the shocks), more consistent lap times, better margin against tire lockup under braking, and earlier "hard" throttle application on corner exit. Biggest problem in IT is the amount of money and talent it would take to find the right shock within the current rules. Tough row to hoe.
From track to track, and even corner to corner, adjustables can help with transitional handling problems. However, overall understeer/oversteer balance is the first thing you have to get right at any track, and that we still do with bars and springs. Get the high speed corners right first. Slow corner handling problems can usually be overcome by a change in driver technique, and they aren't that important to begin with. A car will accelerate better and lose less ground from a bad 40mph turn than it will from a bad 100mph turn.
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katman
Thanks Katman.
Terry... I have a 3.70 locked R200 for sale
DC
Thanks for the info. still would like to know why there is a difference on which end to place the heavier springs.
I think I have to run a R180 on a 240
Thanks again
Terry
Weight transfer. More spring = more weight transferred. Theoretically, more weight transerred = less grip (two equally loaded tires have more lateral grip than one tire with twice as much load, because F=uN is not linear for a car tire), however, things like camber thrust and geometry change with suspension deflection affect each tire's available grip in conjunction with the vertical load. Weight transfer therefore affects the relationship between over and understeer. So, you eventually arrive at a combination of spring rates that preserves the contact patch as much as possible by reducing roll without skating across road imperfections, and that gives you the weight transfer necessary at each end to balance the car wrt understeer or oversteer for a steady state corner.Quote:
Originally posted by terry:
Thanks for the info. still would like to know why there is a difference on which end to place the heavier springs.
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katman