Mikelly Posted June 4, 2003 Share Posted June 4, 2003 So I've been playing with Springs... I have FOUR Eibach 250# 12 inch springs, two QA1 220# 9 inch springs and two QA1 300# 10 inch springs. I've Got two cars with coil overs and adjustable suspensions... One for track use, one for street use... Both will have LARGE brakes... Both using Tokico struts... One adjustable, one non-adjustable. On the street car I swapped out the 250# springs I had up front and swapped in the 9 inch 220# springs... Leaving the 250# 12 inch springs in the back for now... However, I can't get the street car low enough with that setup, and unless I modify the hat, I'll be relegated to swaping shorter springs in the back as well... This is a street car that will have really wide tires under stock fenders... So now Doug and I are playing with springs for the track car and Doug has enlisted the help of his racer buddie's past tips and tricks... We're likely going to use the 250# springs in the rear, with the 300# springs up front... Why you may ask? Brake dive... According to Dougs buddies who spend significant time at the track, Brake dive is and issue, and that is how guys running large brakes are combating this very issue... With 250# springs in the back and 300# springs in the front we'll be able to provide more stability and less un-weighting of the rear of the car under heavy braking... This is VERY important for my particular driving style. When at the track on the ZX9R I'm typically at the end of the braking zone with daylight under my REAR tire just before entering the corners on the end of long straights, as much as 2-4 inches... I really like using my brakes up, and this will hopefully help us retain straightline stability, tractability for positioning entry into the apex, and allow for deeper braking... This is how I do it on the bike, with significant stiffness (Preload) in the front forks (Also using Racetech Gold emulators for tuning the forks) with a moderate amount of preload in the rear, enough so the rear doesn't sag a lot and transfer to much weight back under acceleration, which on a motorcycle equates to lots of wheelies... Back to the car! Anyway, with this setup, I'm contemplating running the non-adjustable tokicos on the track car, as opposed to the adjustable tokicos. Not 100% sure yet, and will have to discuss with Pete, Jamie and Doug... But that is the latest... Comments??? Mike Quote Link to comment Share on other sites More sharing options...
jt1 Posted June 4, 2003 Share Posted June 4, 2003 What kind of bars are you going to run with that, Mike? I've got 250F 275R, adjustables, a 15/16 f bar and no rear bar, and my car's a little tight on entry. I've just added some adjustable bushings to the rear control arms to get some more rear camber and hopefully hook the car a little better off the turns. I'm gonna take it to a fellow racer with a 4 wheel alignment machine and set it up, then try it at the track next Friday. I'm going to see if the rear camber tightens it any more on entry, then I'm gonna add a rear bar, size TBD. Your dealmight work well with a little more than normal rear bar, otherwise I suspect it would be pretty tight. I tried stiffer springs on the front once, and along with more push, the car was real spooky over bumps in the track, just sorta unsettled. No rear bar then either though. Hell, I don't know. Try it out and let us know how it does! John Quote Link to comment Share on other sites More sharing options...
Mikelly Posted June 4, 2003 Author Share Posted June 4, 2003 John, We're gonna run a 1 1/8 front bar and a 5/8th adjustable rear bar. I'm also gonna use straight tube Tie rods with heim joints to get rid of as much bump steer as possible... some fo what you describe might be attributed to the bumpsteer issue, maybe not though. If it doesn't work well, we can swap them around and try 250's up front and 300s in the rear... Goal is to have a MUCH wider selection of springs come spring time, ranging from 200-400# in incriments of 25# increases. Mike Quote Link to comment Share on other sites More sharing options...
jt1 Posted June 4, 2003 Share Posted June 4, 2003 I tried switching my springs, going to 275 F/ 250 R in the hopes softening the rear would help the car hook a little better off the corner. It did, but only slightly; entry push was much worse; the worst thing was the spooky feeling over bumps. It's real hard to describe how the car felt, sort of a whiplash effect on the rear that DID NOT inspire confidence in the driver. It was most noticable going thru the kink at CMP, a flat 100+ mph right hander with a big bump right at the apex. Penalties for spinning out there can be pretty high, so I ditched the spring switch idea. I don't THINK it was a bumpsteer issue, cause the problem wasn't there with the previous setup. I just switched springs and maintained the same ride height and shock settings. I blamed it on the car violating the "flat ride" principle; ie, a higher frequency rear rate than front, so when the car hits a bump the F & R settle at the same time. Sounds good, but in reality I am too ignorant and inexperienced to know if that was what was happening or not. Anyway, it resulted in slower laps and an unhappy driver! John Quote Link to comment Share on other sites More sharing options...
Guest gprix1 Posted June 4, 2003 Share Posted June 4, 2003 I'm also gonna use straight tube Tie rods with heim joints to get rid of as much bump steer as possible Me interested in this More info please EDIT: Found it: http://www.hybridz.org/phpBB2/viewtopic.php?t=21824&highlight=tie+rods When my care gets completed I was planning on strying a range of springs myself so I am very interested in how this turns out for you. Please keep up updated. - Rick Quote Link to comment Share on other sites More sharing options...
TimZ Posted June 4, 2003 Share Posted June 4, 2003 I'm also gonna use straight tube Tie rods with heim joints to get rid of as much bump steer as possible... Be very careful to be sure that the heim joints do not bind at any point in your suspension travel if you do this. Unless your front suspension has radically different geometry than mine (unlikely), a straight tie rod end will not put the middle of the heim joint's travel anywhere near the middle of the suspension's travel. I had to put a bend in the tie rods to allow the proper orientation of the heim joints and keep them from binding. Quote Link to comment Share on other sites More sharing options...
ZROSSA Posted June 4, 2003 Share Posted June 4, 2003 If brake dive is a issiue here is a idea that I have been tossing about for a while. Some single seater run single spring or 3 spring set ups to combat this. They are useing push rods of coarse which makes it easyer. I think that we could get away with it buy welding a strong bracket to the center of the anti roll bar. You would need to make a mount for a third spring for this to work on, or a flexable bumb rubber. It would work as normal in turns but when you brake the bar would rotate and bring the "spring " into action and giving more dive resistance. The other option is to put a little anti dive in your suspension. In one of Carol Smiths books he said that every "Heavy Race Car" should have some anti dive. To do this you would need to lower the front, chassis side of the control arm relative to the rear one. Douglas Quote Link to comment Share on other sites More sharing options...
TimZ Posted June 4, 2003 Share Posted June 4, 2003 In one of Carol Smiths books he said that every "Heavy Race Car" should have some anti dive. To do this you would need to lower the front' date=' chassis side of the control arm relative to the rear one. Douglas[/quote'] Ummm - what rear one? Quote Link to comment Share on other sites More sharing options...
Guest gprix1 Posted June 4, 2003 Share Posted June 4, 2003 The third spring was created for extremely high-downforce cars such as the open wheel variety. Don't know if the idea would work well for solving brake dive but it's an interesting idea that's got my wheels turning. How about a pressure switch in the brake system that only activates some anti-dive system at X amount of line pressure. It would have to be based on pressure levels you get in straight line braking so it would not activate for light braking situations such as settling the front or pivoting. That way it would not upset the car during cornering. The '86 GSXR 1100 had something like this where the switch that turned on the taillight also activated a seleniod on the front forks and increased compression dampening during braking. I think a better solution would be based on line pressure so it is only activated during heavy braking. Quote Link to comment Share on other sites More sharing options...
TimZ Posted June 4, 2003 Share Posted June 4, 2003 Okay, I have to ask... what problem are you trying to solve by limiting brake dive? I think I saw something about not unloading the rear suspension during braking. You do realize that increasing the front spring stiffness will increase forward weight transfer, not decrease it, right? Quote Link to comment Share on other sites More sharing options...
Mikelly Posted June 5, 2003 Author Share Posted June 5, 2003 Tim, I'm not following you here... It should Resist the forward load. Acting as a lever, The vehicle should be less inclined to roll forward with stiffer springs, preloaded in the suspension... You lost me... Am I missing something? I know when Doug talked to a couple of his ITS/ SCCA track buddies who ahd campaigned Zs successfully for some time, they had log books that showed that they did this to combat this type of issue at certain tracks... This isn't going to be a be all end all, we're just looking to experiment with it on the track car to get some measurables... Also, I'd like to get some input from you, and source your materials used on your tubular tie rods... Mike Quote Link to comment Share on other sites More sharing options...
Synlubes Posted June 5, 2003 Share Posted June 5, 2003 The set up mentioned here was recommended by and parts came from Ground Control and used their "advanced Design" ajustable struts. It was on a 71 240 ITS car (using 280 front and rear strut housings) (setting track records and winning races / east coast)(with a Very good driver of course). The car had logs from six years of racing, trying many different configuations and this (out of all) seemed to work well. Now, is it the only setup to go with ? Of course not ! It`s just a good starting point . When people who know talk, I listen ! I also helped crew this car, so that doesn`t hurt either. Just food for thought ! Quote Link to comment Share on other sites More sharing options...
Guest Thurem Posted June 5, 2003 Share Posted June 5, 2003 Stiffer springs will keep the front end from diving, thus keeping the CofG up high, thus transferring more weight to the front end. Some brakedive is not bad unless you run out of suspension and a bump will bottom you out and loose traction. On bikes front end dive gives you quicker turn in. Anyways just my 2 cents. Thure Quote Link to comment Share on other sites More sharing options...
Guest gprix1 Posted June 5, 2003 Share Posted June 5, 2003 The set up mentioned here was recommended by and parts came from Ground Control and used their "advanced Design" ajustable struts.It was on a 71 240 ITS car (using 280 front and rear strut housings) <snip> is it the only setup to go with ? Of course not ! It`s just a good starting point . You've got my attention, I just don't know what setup you are referring to besides the fact that it used GC Advanced Design struts, what springs and sway bar(s) were used for this ITS car you speak of? Are you referring to one of the setups in the previous posts (there are several being discussed)? Enquiry minds want to know. Quote Link to comment Share on other sites More sharing options...
260DET Posted June 5, 2003 Share Posted June 5, 2003 My road/track car has 250 front 300 rear springs, big brakes, and does not suffer from excessive nose dive under heavy braking. Sometimes I think that excessive nosedive can be brought about by too much brake bias onto the front brakes, but that is only a guess. On the other hand, there is another road/track car around here with heavier springs on the front than the back, around 300 to 250 I think, and he seems happy with that. But those who use their cars only for the track and use wide slicks usually have much heavier springs. Around 500 is common. Quote Link to comment Share on other sites More sharing options...
jeromio Posted June 5, 2003 Share Posted June 5, 2003 What TimZ says does make some sense. By stiffening the front, you'll be working your tires alot harder. I dunno - I know nothing about suspensions. You should check out http://forums.corner-carvers.com/search.php?s= - the suspenion board there has lots of in-depth information. Also, there's a particular thread someplace near the top (has like 500 replies) titled something like Check out this setup for a 66 Mustang. Lots of detailed tech on suspension and vehicle dynamics. Very learny. (Just a warning though, be sure to search before you post - they really like to crucify new people there. You'll probably find plenty in the archives though) Quote Link to comment Share on other sites More sharing options...
Mikelly Posted June 5, 2003 Author Share Posted June 5, 2003 Jeromio, It makes sense that the tires would get more abuse from loading them. And Thure, I understand what you're talking about with brake dive on bikes, But I'm pretty sure that (Based on some dicsussions I've had with others) that this could well be a possible solution, sometimes and at some tracks... I don't plan to run this car at one track only. I hope to get out to several different courses... Mike Quote Link to comment Share on other sites More sharing options...
TimZ Posted June 5, 2003 Share Posted June 5, 2003 Okay... I was having trouble making a consistent explanation of my theory, so I decided to dig a little deeper. As a result, I'm changing my story a little. (at least I admitted it ) In general, changing the spring rate in the front should have no effect on front/rear weight transfer during braking, except from the resulting relative change in the cg height during braking as thurem pointed out. Weight transfer is a function of weight, wheelbase and cg position. So, while increasing the spring rate in the front won't appreciably increase forward weight transfer, it won't decrease it, either. So if you are having problems with the rear end unloading under braking, you should probably look for another solution. Possibly add anti-lift geometry in the rear? This is what BMW does - they let the front end dive a fair amount, but they also have the rear suspension setup to squat a bit under hard braking. The result is a feeling of the entire car 'hunkering down' under hard braking. Quote Link to comment Share on other sites More sharing options...
pparaska Posted June 6, 2003 Share Posted June 6, 2003 Tim, I agree with your theory - in part. But I think that if you consider the dynamics of what's going on, the stiffer spring (and attendent shock/setting) will create a tendency to break away sooner. Just a brain fart... Were's that John Coffey guy when you need him? Quote Link to comment Share on other sites More sharing options...
johnc Posted June 6, 2003 Share Posted June 6, 2003 Checking in Sir! The only reason I can think of to use spring rate to control longitudinal weight transfer under braking is to maintain some bump travel in the front suspension. Certain race tracks may dictate this if the braking zone for the most important corners on the circuit are bumpy. That's probably why the East Coast ITS racers recommend an increased front spring rate for SOME tracks. Hard on the front bumps stops under braking makes hitting any kind of bump a guarantee of front wheel lockup and a pair of nice flat spots. Designing in some additional anti-dive into the 240Z suspension would be nice but as long as you're not shortening the effective TC rod length the built in anti-dive should be enough. I would focus more on transient response control (shocks) before I would start compromising the balance of the car to fix a braking issue. Another, simpler solution would be to adapt your driving style to the vehicle. I know a lot of experts (including Carrol Smith) recommend adjusting the vehicle to suit the driver, but most folks forget that their point of view is from Formula Ford where damn near everything on the vehicle is adjustable. Us sedan racers don't have half the adjustments the open wheel guys do. BTW... Did you folks know that Carroll Smith died of Pancreatic Cancer back on May 16th? Quote Link to comment Share on other sites More sharing options...
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