RebekahsZ Posted December 6, 2015 Share Posted December 6, 2015 2016 is going to be all Standing Mile (straight line acceleration/chute/braking) suspension prep for me in order to try to take the car to 200mph by the year 2020. We do not do burnouts and we try to leave the line gently enough to avoid spinning the tires (big, sticky drag radials). Next test and tune session will be the Sept 2016, 3-day event at Wilmington, OH. My goal by the end of the2016 session is to run up to the 175mph range again, but with a rock-solid steering wheel and dry panties thru all phases of the event. Car is a 2500 pound 240z with 225F/250R springs, single adjustable Koni's and coilovers with the typical adjustable components to the stock strut suspension design. There were three handling problems I faced at 174 mph. Increasing toe-in and tire air pressure did not help. 1) Wandering above about 165mph, 2) steering to one side or the other upon braking at 174mph, and 3) scraping of the rigid airdam somewhere along the course when static ground clearance of the airdam is 3" (I would like to lower the car further but the staging lanes are too uneven due to in-ground runway lights and a rough transition from tarmac to concrete). Rather than trying to tackle everything at once, I hope to tackle one issue at a time. I've given all this background to make it easier for the smart guys to offer brief suggestions. Since ride-height affects alignment, I think I want to start be establishing my ride height first so, let's start with issue #3: reducing the amount of suspension compression. So, here's my first question: Should I: Increase spring rate, install bump stops, or both? Consider this a fairly bumpy 1-mile drag race in a car that will need enough traction to put down 600-800 hp. Quote Link to comment Share on other sites More sharing options...
johnc Posted December 6, 2015 Share Posted December 6, 2015 Number 1 is an aero issue. What aero modifications are you allowed? BTW... It's probably unrealistic to assume the car will track perfectly straight and be perfectly stable at speed. Bumps, track surface, and wind will all introduce instability. Number 2 is a tire, bushing, camber change, or track surface/bump issue. Your aero ride heigh change at speed affects front and rear toe. Number 3 is an aero issue. You need a lot more spring rate. That can come front the springs themselves or from progressive rate bump stops. Your issue will be getting the correct shock rebound for the spring rate under aero loading. Quote Link to comment Share on other sites More sharing options...
clarkspeed Posted December 6, 2015 Share Posted December 6, 2015 I agree with stiffer spring rates. At 150mph my 425# front feels real mushy. Which also means you better not have any bump steer. In general, F&R toe in adds stability and doesnt scrub that much speed off. Quote Link to comment Share on other sites More sharing options...
G-E Posted December 7, 2015 Share Posted December 7, 2015 1. definitely aero, either uneven airflow or just too susceptible to crosswind or something, possibly too light on the front wheels? 2. something is moving or twisting under biased load, since it happens in either direction, I'd lean towards the chassis twisting (you use rodend arms/links no?) 3. could be a combination of aero and spring rate, does the car rise and dip sharply between shifts, or oscillate at all? Quote Link to comment Share on other sites More sharing options...
heavy85 Posted December 7, 2015 Share Posted December 7, 2015 What do LSR people do for suspension? Whatever they do thats what I would do. Have you measured bump steer - if not losing 3" of ride height may cause significant toe changes from what you set at static ride height. Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted December 7, 2015 Author Share Posted December 7, 2015 (edited) I should acknowledge that someone else tried to help me, I think it was tube80z, but the conversation got too complex for me. That was in another thread and I will try to edit those suggestions into this thread. Please keep the comments coming, I will digest them as I read them over and over. Please use simple, short words-I'm a simple, short man. Ok-I found Cary's comments in my build thread in the Build Thread forum he suggested that perhaps I could use bump stops and "packers" in an effort to increase spring rate while retaining the soft springs I currently have. I couldn't really understand how the thin packers retain once slid around the strut rod. I will do more investigating in that. Edited December 7, 2015 by RebekahsZ Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted December 7, 2015 Author Share Posted December 7, 2015 Johnc- I can do just about anything to the car forward of the cowl. I can run a full belly pan. I can run a spoiler on front and back, but no wings. The car currently has just a vertical airdam, the equivalent of blocking airflow thru the grill. No rear spoiler(but I have one like Mikelly's for next year). On pass 1, I had a 3" splitter on the airdam and the airdam contacted the ground. I blamed the splitter for pushing the front down. So, I cut the splitter off flush and repaired the gouges. On pass 2, the airdam hit the ground again even without the splitter. Question: does the stock body produce enough downforce to push the car down? I tried to look at the wind tunnel data and I saw lift, not downforce...am I looking at that wrong? After we discuss the aero stuff some, I will come back to the springs/struts. Thanks so much for helping. Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted December 7, 2015 Author Share Posted December 7, 2015 Just watched a really nice YouTube video from FCM (Fat Cat Motorsports) that explained bumpstops and packers simply enough for me to understand. They showed some 200# per inch bumpstops. I wonder if I could just install something like those and adjust them (with packers-thanks Cary) to have zero clearance off the bumpstops, such that I am running essentially ON the bumpstops? Quote Link to comment Share on other sites More sharing options...
johnc Posted December 7, 2015 Share Posted December 7, 2015 The S30 body by itself generates lift. Adding front take reduces that. Airdams also reduce that. Is your car hitting the ground over a bump or is it dragging from aero downforce? With and aero modifications it's critical to keep the aero platform stable. You want as little downforce as possible while still keeping the car relatively stable at speed. I would go with spring rate over bump stops and use softer shock compression damping to keep the tires on the road. You might also want to check and see if you might have too much shock rebound damping for your existing spring rate. That can cause the car to pack down and loose ride height. Quote Link to comment Share on other sites More sharing options...
tube80z Posted December 7, 2015 Share Posted December 7, 2015 I personally would use shocks with a lot of rebound to pull the car down, just like NASCAR. That will allow less air under the car and help with lowering the drag number. The bumpstops I talked to Keith about were actually linear bump springs. The idea being he could run softer main springs at a higher ride height but when running this event lower the car and use packers to engage the bump spring. This would raise the rate similar to running a higher rate main spring but you don't have the rougher ride when using on the street at normal ride heights. These springs can stack solid or be used in combination with other rubber or poly bumpstops when maxed out from aero load. Cary Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted December 8, 2015 Author Share Posted December 8, 2015 (edited) I don't have a clue as to whether the airdam hit due to downforce or from a bump. I really wish I had put some kind of tell-tale on the strut rods like a sliding o-ring. I also guess I need to mount a camera on a long pole or something to be able to video the ride height changes. My attempt to mount a GoPro by the rear tire with the flare removed was an epic fail-the wind just pushed it out of align. The track, being concrete is pretty rough, but everybody says: "Maxton was worse!" However, by my analysis, the bumps are fairly small amplitude, high frequency, with a couple of fairly big bumps along the way. No real rises to make the car light-the car never felt "light." No long, smooth dips that would make the suspension feel "mushy." Kinda like that hammer feeling like hitting a bridge abutment. But no suspension bottoming-I never coil bound or hit metal on metal. I've done some searching for packers and will continue. I need to find some that are pretty thick-lots of the observable type seem to be thin for super fine-tuning. I will try to add YouTube links later tonight. There's not a lot out there for Landspeed suspension. There's some folklore for Bonneville but nothing really for Wilmington. Some discussion of toe-in and some about bump steer. Most guys run solid rears and a lot run solid front axles to avoid camber changes. "Stability" is an ill-defined, unit-less property that I don't yet understand. They do have spins and crashes. It's so much more fun that one would think! I'm thinking that I will put bumpstops on and use packers to ensure that I'm ON the 200# bumpstops at static ride height. But do I add the bumpstops to 200# springs or 400# springs? Edited December 8, 2015 by RebekahsZ Quote Link to comment Share on other sites More sharing options...
clarkspeed Posted December 8, 2015 Share Posted December 8, 2015 (edited) Bumpstops and packers - the secret sauce for Chumpcar racing. Edited December 8, 2015 by clarkspeed Quote Link to comment Share on other sites More sharing options...
johnc Posted December 8, 2015 Share Posted December 8, 2015 http://www.bloodhoundssc.com/project/car/wheels/suspension/suspension-land-speed-record-car Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted December 9, 2015 Author Share Posted December 9, 2015 (edited) All of today's input reviewed-thanks guys. The thickest insertable packers I have found are 1/8" at Spoedwaymotors.com. Anybody have a source for thicker insertable packers? Oh yeah, for what it's worth, I think I ran with the Koni's set full soft rebound. I figured with a track that was kinda like a washboard I should try to keep the tires on the ground. Edited December 9, 2015 by RebekahsZ Quote Link to comment Share on other sites More sharing options...
260DET Posted December 11, 2015 Share Posted December 11, 2015 3" drop, incredible, never heard of that before. Front springs must be made of wet noodles but it is a good thing to keep the front as close to the deck as possible. The less air going under the car the less aero drag which facilitates more speed and better stability. Pics are useful to see what is actually happening, run some rake too. Quote Link to comment Share on other sites More sharing options...
tube80z Posted December 11, 2015 Share Posted December 11, 2015 Actually I'd argue you don't want rake, perhaps the opposite. Primarily because you're standing the windscreen up, which will add drag. Get the car low but perhaps run the tail down or at least try level and then nose down. Cary Quote Link to comment Share on other sites More sharing options...
JMortensen Posted December 12, 2015 Share Posted December 12, 2015 I dunno. I think I'd want level or rake. Screw the drag, I want the front on the ground. Seen this, Keith? https://youtu.be/D59x_2PyUcc?t=8m7s Quote Link to comment Share on other sites More sharing options...
johnc Posted December 12, 2015 Share Posted December 12, 2015 Rake is used to control center of pressure. Ideally on a LSR car you want the center of pressure behind the CG to make the car aerodynamically under steer at speed (inherently more stable). Adding rake increases downforce (pressure) right at or behind the S30's CG (windshield area). The low pressure area over the roof is reduced slightly also. Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted December 12, 2015 Author Share Posted December 12, 2015 (edited) Second photo shows rake that I arrived at track with. Second photo shows take after raising front 1" and lowering rear 1". Car drove exactly the same in each configuration. Next photos show bumpstops and packers. Edited December 12, 2015 by RebekahsZ Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted December 12, 2015 Author Share Posted December 12, 2015 For straight line, why do I desire downforce? Isn't the absence of lift adequate? If I can just create zero lift, isn't that good enough? Quote Link to comment Share on other sites More sharing options...
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