Does it rub?
We see this question asked and answered every day in online forums with respect to wheel-and-tire packages, especially when it comes to lowered cars.
The answers often provide conflicting information due to varied alignment, ride height, spring rates and coil-over packaging. Having the right combination of parts on your car is only half the battle. Dialing it …
What is the spring rate of your helper springs? Is it actually enough to overcome the shocks rebound control and keep that tire in contact with the ground over bumps/dips when the effective spring rate for the combination main/helper in series is so low when the helper is not locked out?
Bumps stops as suspension, that will never work.
Mmm Tom, don't you race a Formula 500?
(sorry couldn't help it).
I always thought it was better to put helper springs (especially the super-soft ones you can compress with your bare hands, not so much a concern with the thicker/stiffer ones like in this article) on top of the main spring so that the weight of the spring itself isn't pressing on the helper spring, unless the car is in negative Gs which should never happen. I worry that when the shock is fully extended the main spring might compress the helper spring a bit with its own weight and float off its seat.
Also it's relatively easy to make snap-on shims of different thicknesses you can install or remove from your shocks with almost no disassembly, Delrin is a great material for this:
adam525i said:What is the spring rate of your helper springs? Is it actually enough to overcome the shocks rebound control and keep that tire in contact with the ground over bumps/dips when the effective spring rate for the combination main/helper in series is so low when the helper is not locked out?
Dampers are time-based so any amount of spring force will eventually extend the damper. We found that it worked fine over the bump/dips at our local track...which is know for being quite bumpy (I should post a video...you'd be shocked. Oh, look what I just did there :) )
Here's some 411 from Chris at Redshift. We are only running the low rate helpers. He also sent some higher rate helpers which we'll play with at a future time.
Swift is sending the following springs:
H65-060-015 (x2) - these are 1.5k helpers with spring adapters which can be used front or rear.
H65-060-030 (x2) - these are 3k helpers with spring adapters which can be used in front.
Generally helpers/assist springs are either almost no rate or they are 20-30% of the main spring rate and can be engaged while the car is in motion. So, I am sending 4 helpers along with the 203L 5k springs. 2 helpers are 1.5k and would work well in back but can also be used as low rate helpers for the front. The other 2 helpers are 3k and would be a good match for the front. So that gives you some options.
The higher rate helper will engage earlier, but when it does, the combined spring rate plummets (non-linear) and changes how the car feels. So the 3k spring on the front may engage at times depending on swaybar, etc.... and it could help the tire stay in touch with the ground but will do so at the expense of doing it at a lower rate, and the balance of what helper spring rates to use is best done through testing.
GameboyRMH said:Also it's relatively easy to make snap-on shims of different thicknesses you can install or remove from your shocks with almost no disassembly, Delrin is a great material for this:
Yep. Commonly called "packers". And the print version of this story has a follow-on with commercial sourcing for these and other dial-in bits.
In reply to Andy Hollis :
Thanks for the follow up! Very helpful.
I remember about 15~ years ago when working at another exhaust shop, I did some work on a few street cars for a customer that raced (races still) nationally and had a shop that specialized in a specific brand of car (to keep it vague).
He saw my then, first Tercel that was modified and prepped for mild track use as I was doing HPDE stuff then with Nasa. We BSd back and forth a bit and I was still pretty green with suspension tuning. I had ground control sleeves as any sort of real coilover was out of my budget. I mentioned the car really needed more spring rate but I didnt want to over power the struts. He asked about my bump stops (which were essentially nothing) and said something along the lines of "all the race cars, essentially corner on bumpstops, so try tall progressive units and trim from there".
I played along like ok, but in my head I was like yeah right, why would you want to corner on bumpstops. Well about 5 years ago I think it was, I started playing with bumpstops and it became very clear what he said. I just wasnt there (in my head) to understand it yet. Now its a main focus on all of my suspension work, personal and for current customers in my shop.
Timely story bump...I'm in the process of this exact thing now on one of my CRXs.
Big aero adds a whole 'nuther element to this, as high downforce will push the car onto the bump stops now during any significant high speed action.
Getting the balance right between stiffer springs, helpers/tenders, and bump stops to maximize mechanical grip while providing appropriate "platform" for the aero to work properly is a bit of a black art. Plus keeping it balanced both at low speed and high.
I feel another GRM how-to story in the making...
Andy Hollis said:I feel another GRM how-to story in the making...
"How we added 3rd elements to control the aero on our project CRX."
Article comes out on April 1st and "project CRX" is an IndyCar or GTP.
How about something to diagnose what this car is doing mid-corner with the tire chirping. I suspect it's not enough roll/too much rebound not letting the car transfer weight to the outside tires, but I have no experience with test and tune.
I'm sure you'll recognize the track, Andy.
I've often swiss-cheesed long bumpstops to make the contact more progressive. I'm still riding the bumpstops on hard turns or hard bumps, but it's less "upsetting" to the chassis.
In reply to racerfink :
I'd think the only factors that could cause a cyclic suspension movement like that would be a damping issue or aerodynamic porpoising.
Mind you the shocks being unable to keep up with the spring rate of the bump stops, or the movement of big squishy bushings being undamped could also be categorized as damping issues...
racerfink said:How about something to diagnose what this car is doing mid-corner with the tire chirping. I suspect it's not enough roll/too much rebound not letting the car transfer weight to the outside tires, but I have no experience with test and tune.
I'm sure you'll recognize the track, Andy.
Could be any number of things, but dampers is where I'd focus first. Try some sweeps to see if the problem gets worse/better with various large adjustments. That should at least give a direction for improvements.
You are basically going slightly over the limit as you encounter the bumps, causing the skreeches.
Could also be bottoming into bumpstops.
And ignore anything happening on the new pavement at T6-7...the new stuff will skreech a lot until it gets more use & sun.
Speaking of bump stops does anyone with gm experience know of a good replacement for the discontinued zq8 bump stop 15956547? There are Dorman & multiple Chinese replicas online that have the same shape, but material is unknown. As they are a popular upgrade for multiple gm chassis I was hoping someone had experience & suggestions
In reply to Caperix :
I'm not sure about those tall ZQ8 bump stops, but my GMT800 Suburban 2500 uses similar progressive front stops that you may be able to adapt. There are two versions - one that is black rubber, one that is the yellow foam. I'm not sure which models got what. The rear bump stops are also really tall foam cones, you might be able to use those and trim down the cone a bit.
Another good source of progressive bump stops is the rear suspension of the GMT800 Tahoe and Suburban 1500. Similar foam cone, but much shorter. I use them whenever I'm building something with a drop kit or C notch that has those crappy polyurethane pucks supplied.
In reply to racerfink :
That mid-corner hopping thing - my Caprice used to do that even at autocross speeds. The front shocks are spindle mount and it ended up being that the rubber mounts on the spindle had given up, so the shock had some free play before it started to do any damping. That translated to probably half an inch or more of undamped travel. I couldn't really feel it from the driver's seat, but the tires would jump up and down a bit and make that "scree-ree-ree-ree-ree-ree" sound when cornering.
I ended up adapting a pillow ball upper mount from something else, I think they came from RideTech. Zero slop damping mounts made more of a difference on that car than testing different off the shelf shocks ever did.
In reply to gearheadE30 :
Some of it is tire sidewall spring rate, too, which is by nature undamped. When I set my suspension to full stiff, it will bounce like that but it's dependent on which tires I have and what the pressures are. Lower pressure boing less.
What I would like to know is, what happened to all of the through bolt bumpstops for those of us with solid axles? Only a couple years ago, I had tons of choices for length and durometer, now it seems like only Energy Suspension makes one, one size, two different colors but apparently same durometer.
The PO cut my cars original rear bumpstops and the effect is very non progressive. I'd like something more elastomeric/foam type and with some length so it acts more like a progressive spring than a solid puck. (Really, I'd like hydraulic bumpstops, to add additional damping to the bump and no increased spring rate to overload the shock rebound rate, but that would require lots of rules-bending fabrication)
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