RebekahsZ Posted June 24, 2013 Share Posted June 24, 2013 (edited) I need help learning how to understand how adjustable shocks work and how any changes in adjustment relate to changes in performance. Recommend any books/articles for reading. I don't have a mechanical engineering degree, so try to use simple terms. I am running Illuminas currently and likely will be for the next several years. Best I can read is that increasing the number on the adjuster makes the shock stiffer to both compression and rebound at the same time. I read lots of discussions about compression and rebound, but I don't understand how those independent parameters change the behavior of the car. I use my car in autocross and drag racing and my hope is that I can have one setup for each activity. Any recommendations for initial shock settings are appreciated, but I also hope to understand some of the BASIC concepts. Super technical discussions may go right past me, but I'll try to be thick-skinned if any floggings ensue. Exhibit A is a video from my last trip to the strip. I would like to see weight transfer, causing the rear to squat-and stay down, at least until the first gear change. In the video, you can see the back of the car bouncing up and down. I don't think that is what I want-so how should I adjust my shocks to stop that bouncing? http://youtu.be/iLFARn5i9Ac Edited June 24, 2013 by RebekahsZ Quote Link to comment Share on other sites More sharing options...
SUNNY Z Posted June 24, 2013 Share Posted June 24, 2013 I don't know how much luck you'll have with them only being single adjustable. What setting was that video on? From the looks of things, it needs more compression and less rebound. What spring rates? Quote Link to comment Share on other sites More sharing options...
johnc Posted June 24, 2013 Share Posted June 24, 2013 http://www.theoryinpracticeengineering.com/drift_mag/basic_damper.pdf Quote Link to comment Share on other sites More sharing options...
JMortensen Posted June 24, 2013 Share Posted June 24, 2013 That guy Tim from TIP used to hang around here a bit, and obviously knows his stuff. With Illuminas that's a lot of knowledge you can't use though. IMO in more practical terms what you need is stiffer springs, probably stiff enough that the Illuminas won't work for them. Looks like you're hitting the bumpstops repeatedly. Since your options are so limited, try the Illuminas on all 5 settings and do videos and check time slips to see if that improves things. I suspect springs are probably the right answer. Illuminas have "cross-talk" where the rebound setting affects the bump, but I doubt you're going to get enough bump damping to keep it off the stops. You may get enough rebound to where it doesn't bounce back up as high, but I'd guess that it will still be smacking the stops similarly. There are all kinds of different theories on damping too, so beware that this is a rabbit hole that is deep and wide, if you decide to jump in. The best setting for autox is likely to be completely different than the best drag racing setting, so your choices are either to get really good adjustable shocks or to run some sort of compromise. Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted June 25, 2013 Author Share Posted June 25, 2013 Thanks, gentlemen. Johnc, I read the article and it was just what I needed-basic. The last change I made to my shock adjustment prior to this track outing was dropping from #4 to #2 in back to try to reduce throttle induced snap oversteer at the autocross-and it helped. I don't think I am hitting the bump stops at the drag strip. Rather, I think the spring rate is inadequately opposed my the shock. I'm gonna go to #5 in back and work back down using video to track my changes. Next trip to the track is July 13-I've now got a plan! Quote Link to comment Share on other sites More sharing options...
letitsnow Posted June 25, 2013 Share Posted June 25, 2013 The rear suspension gains camber in bump, right? I'd want to avoid that while drag racing. Lots of drag specific shocks are 90/10 front and 50/50 rear, equal compression and rebound rear and MUCH more compression than rebound in the front. I believe it's trying to get the front to raise, and relying on the rear suspension geometry to influence the rear. Lots of the solid axle cars will use significant anti squat geometry that will actually cause the rear of the car to *rise* as power is applied. If I were doing it, I'd start front at full soft and rear at full hard, then play with launch technique to avoid hitting the tires too hard, adjusting the rear shocks down would come after playing with technique. I'd also set the rear camber to 0 or even slightly positive. Quote Link to comment Share on other sites More sharing options...
socorob Posted June 25, 2013 Share Posted June 25, 2013 this guy has some interesting stuff. He also has a corner balance calculator that may be helpful, http://robrobinette.com/S2000Info.htm Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted June 26, 2013 Author Share Posted June 26, 2013 Thank you socorob! Read it and will try to live it. Quote Link to comment Share on other sites More sharing options...
m1ghtymaxXx Posted June 26, 2013 Share Posted June 26, 2013 Another good resource for suspensions setup: http://farnorthracing.com/autocross_secrets.html Written by an engineer, and probably beyond the scope of the average autocross, but some helpful info none the less. Quote Link to comment Share on other sites More sharing options...
socorob Posted June 26, 2013 Share Posted June 26, 2013 www.drivingfast.net has some basic driving theory to go along with this. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted June 26, 2013 Share Posted June 26, 2013 I don't think I am hitting the bump stops at the drag strip. Rather, I think the spring rate is inadequately opposed my the shock. If you jump on the back bumper would it bounce like in the video? You have a relatively consistent amount of weight transfer happening here. You're not jumping on the gas and off the gas to make it bounce, and it doesn't seem to be related to wheel hop based on what I saw. So if you put a load on the back, and the problem really is underdamping, it should be repeatable. Another solution you could try to improve the bounce would be a better bump stop. Most people with Z's run the poly Energy Suspension bumpstops which are very hard and bouncy. Better bumpstops are much softer and less progressive in their effective spring rate. As to the Far North Racing site, I am a devotee and have quoted it here probably 20+ times, but his calculator for shock valving doesn't work correctly, or if it does, they espouse what in my view is extremely underdamped shocks. I tried to use it to come up with ideal damping rates for my Miata and it was just grossly wrong. Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted June 26, 2013 Author Share Posted June 26, 2013 Cool. I don't think I'm on the bump stops, in fact, I need to add some bump stops as my crappy "drifting" extra calipers were hitting the floor pans last time I tried to lower an inch. Those extra calipers are coming off soon-that was a boondoggle gone bad. The bump stops I have are clearly too short to be doing anything. I'm pretty sure it is under damped, so I'll try to repeat all this when I go to the strip on July 13th. I'm hoping to go to a double adjustable shock in a couple of years, just too many projects that are higher priority right now. I will look at the Far North stuff, but I have to be honest, I'm a surgeon (basically a parts swapper), not an engineer-if it gets too technical mechanically, I'm gonna be overwhelmed. For now, I'm gonna do some trial and error testing with what I have learned so far from all the cool contributors that have responded. I gotta keep it simple. At least I have learned what is meant by rebound and compression-before this thread those were just abstract words that I've heard thrown around but really didn't understand-I get it now! Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted June 27, 2013 Author Share Posted June 27, 2013 Oh yeah-no bumper- it was too rusty-pitched it years ago. I tried jumping in trunk but I keep hitting my head on the hatch! Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted June 27, 2013 Author Share Posted June 27, 2013 Just found johnc's suspension FAQ. Good stuff. Quote Link to comment Share on other sites More sharing options...
letitsnow Posted June 27, 2013 Share Posted June 27, 2013 As to the Far North Racing site, I am a devotee and have quoted it here probably 20+ times, but his calculator for shock valving doesn't work correctly, or if it does, they espouse what in my view is extremely underdamped shocks. I tried to use it to come up with ideal damping rates for my Miata and it was just grossly wrong. I wrote my own in excel and the results were close and reasonable in my opinion, unless his has broken in the past couple months. 65% of critical is a relatively easy calculation to make. As an example, my unrevalved bilstein p30-0032's with 200lb springs and the (incorrect) assumption of 25% of 2700lbs on a wheel are damped at 75% of critical in rebound. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted June 27, 2013 Share Posted June 27, 2013 I'd love to see that spreadsheet. Would you upload it here, or email to me at mortensenjone at gmail dot com? Quote Link to comment Share on other sites More sharing options...
letitsnow Posted June 27, 2013 Share Posted June 27, 2013 (edited) This spreadsheet is just a basic calculator of ride freqency and damping ratio. It cannot account for motion ratio, it was originally a quick sanity check for my Z, with the assumption that the motion ratio was close enough to 1. I have a more advanced spreadsheet that can calculate ARB's for given roll rates and springs etc, however I need to go over a lot of the math in it as I think there are some errors. I'm not ready to post it publicly at this point, but I'd be willing to send it to you after I take a look at a few things. I zipped it because hybridz won't allow .xlsx files to be uploaded directly. Edit: Just realized I labeled ride frequency as rad/s in the spreadsheet, it's actually in Hz. It's fixed now. Damping Calcs.zip Edited June 27, 2013 by letitsnow Quote Link to comment Share on other sites More sharing options...
JMortensen Posted June 27, 2013 Share Posted June 27, 2013 Your formula and the DG spreadsheet are not coming up with the same result when I try them. I don't want to derail Keith's thread, but if you don't mind I'd like to continue in PMs. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.