Suspension Upgrade Time - Installing QA1 Proma Star Double Adjustable Coilover + Progress Swaybars

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Short Version:

Overall the QA1 Proma Star coilovers for the C5 Corvette and the progress sway bars are solid products that can be dialed in to produce a very balanced handling car other drivers will be envious of. When configured right and with some minor aftermarket parts, these sway bars and coilovers do both work pretty darn good together.

The sway bars are a no brainer, especially given they are some of the more affordable ones out there. Getting the coilovers setup right however is no easy task. The coilovers are unfortunately plagued by incorrect spring rates in the rear, fairly sparse configuration notes, and minimal community adaptation to fill in the blanks. A few design choices are also difficult to work with and can cause headaches when attempting to adjust spacers, sometimes requiring full dissasembly of the entire car!

I currently can endorse the QA1 coilovers with the progress swaybars, mostly now that I've put the time in to figure them out. It's worked out pretty good long term,. I do think QA1 did not do right by consumers witth this right from the getgo, but they are the best priced double adjustable coilovers for the C5 I could find, and with $100 of springs or so you're in business. Add on a lifetime warranty which they've honored twice now... it's pretty safe to proceed with the QA1 coilovers.

My reccomendations for someone considering these:

  • Run 295/35R18 on 10.5" wheels or 315/30R18 on 11" wheels. That's the golden standard for tracking these cars and surely the tires they used when establishing baseline suggested settings. The rotational mass of such a configuration appears to be what QA1 based it's reccomendations on.
  • Order 650lb springs for the rear from the getgo. Eibach makes them in the 2.25" diameter you'll need. If you are not looking to do any track driving, go 450 front and 550 rear, so order a 450lb spring for the front.
  • Run OEM ride height. Yeah, it's tall. It'll handle better though, you'll put down better times AND you'll find life way easier just driving around town.
  • Don't run any spacers/packers they provide. Only add them if you're going to use drop spindles. QA1 should put this in their documentation.
  • Be sure to have an adjustable rear sway bar to help tune the cars balance to your preference. Progress bars work great for me!
  • Get offset rear toe arms to ensure they toe arms don't contact the coilovers. You'll also want slightly larger spacers/plates for the sway bars to ensure extra space for the sway bars from the toe arms, etc etc.

Configuration Notes:

If you happen to wind up with these, here is a Google Docs spreadsheet where I keep all of my notes on adjustments, how it handled, and some other general changes and configurations. These notes aren't perfect, but they help provide substantially better information than what was provided by QA1.

Why I Initially went with QA1 Coilovers

My 4th track day out was a blast, but the upgrade to square 200tw tires was underwhelming. This seemed to be in no small part due to the very worn out 23 year old base model suspension on the C5 Corvette. I experienced a lot of body roll, and with the square setup the entire car seemed to be a bit tail happy yet somehow still had a penchant to understeer. In general, the handling just wasn't as balanced as I was hoping for. Per researching C5 Corvette spring rates and sway bars, the solution seemed to be a more supportive (higher) spring rate along with better balanced sway bars. A lot of folks recommended going with the various corvette models transverse leaf springs and just upgrading the shocks, but it all seemed like money wasted on a half measure to me. This car is about the track more than anything, so it was time to pony up!

Being that it's the future, I'm a bit impatient about products showing up. I searched for coilovers and was seeing lead times of 6-12 weeks. I'm not terribly interested in what feels like loaning people money while they get around to building me my stuff, and so I searched high and low for in stock components. In the end I was able to find QA1 double adjustable coilovers from Summit Racing. I trust QA1, the spring rates all seemed reasonable, and there were a few aspects of the design I liked over other coilover designs I'd seen as well. There are likely some limitaitons, there are possibly some superior products out there, but there's no really exceptional exhaustive review of these products, so with the information I had and my willingness to wait, this seemed like the most reasonable choice. The double adjustability would let me dial my setup in as much as I likely will ever need to, along with bieng able to roll my setup back to being streetable hopefully.

Sway bars were also essential. There were lots of options out there, but the West Coast Corvettes Street/Race sway bars seemed like the best option out there for me. The price was good, especially considering I could get heim joint adjustable end links as part of the deal as well. The diameter and thickness of the materials used were identical to many other brands, and thus I decided to pull the trigger on these in the hopes I would reduce body roll and get some flatter handling around the turns along with hopefully some improved traction.

Takeaways from installation:

Right off the bat, I would recommend giving yourself two days for this process if you're doing it at home. I blitzed through the coilover assembly process in one day, and as the day progressed onwards I got tired and started making mistakes that in the long run cost me more time. I would even go so far as to give yourself 3 days to install these, with the first day being spent just assembling the coilovers themselves and double checking against the install diagrams they are correct.

Why QA1 or anyone else ships unassembled coilovers is beyond me. Faffing with the snap rings is endlessly annoying, even with my specific set of snap ring tools it was a nuisance. For the price of several thousand dollars it doesn't seem outlandish to assemble these and then ship them. They'd fit in the box all the same as well. One benefit to the manufacturer of shipping them unassembled though is the moment you assemble them you can't return them anymore. Shitty for the end consumer, but protects manufacturers against people just tryig to return perfectly fine products.

One thing I recommend that unfortunately the instructions don't mention is just how much preload to put on the spring on initial install. I went halfway on mine right from the start, which if I recall was roughly 40mm from the preload adjuster to the bottom of the rebound knob. This gave me a pretty decent ride height right from the getgo to adjust. I had to make a few adjustments after the fact, but it was quite reasonable to do so just jacking the car up and squireling my hand up and around the suspension to where I need to reach.

TIP: Regarding the spacers. Knowing exactly how lowered your car is is surprisingly difficult. The correct measurement from the factory is 6" of height from the floor to the factory jack point. Measure how much you're lowered from there. I personally simply removed all the spacers after having problems with understeer from being right on the bump stop. If you want to be really thorough, install a coilover sans springs and then jack it all the way up to see if there's contact at full travel.

To confirm your setup works without spacers, with no tension on the small preload spring and compression set to soft and rebound set to the max, mount your wheels and place a jack under the tire. You should be able to crank up the coilover to max out the suspension travel without transfering hardly any force into the chassis itself (IE: Disrupting stands or quickjacks). You can then tell just how much clearance you have at the bump stop and if your wheel will contact the body. Add spacers if you determine you need them. I believe tire diameter will dictate a lot of how much travel is possible on your vehicle.

This appears to be another area QA1 failed to provide useful documentation.

QA1 Suggestion: Unfortunately, the 3/8" spacer is a pain in the ass to remove, requiring removing the coilover entirely and partial dissassembly. Also, due to the design of the spacers, you can't just skip it and instead utilize the removable spacers. I would recommend QA1 figure out a way to make all spacers removable to ensure that a person does not need to fully remove and partially dissasemble the coilover to remove these particular spacers. Reversing the direction so as the bottom out bumper contacts the shock body first with spacers behind it seems like a reasonable way to make this happen.

Initial Street Impressions:

QA1 initially underwhelmed me with some pretty broad ranges of settings for compression and rebound on installation with zero differentiation for front to rear. This appears to have changed in updated installation instructions. I wound up at the extremes of their recommended settings in the rear, and also setup the adjustments different up front. To me they clearly didn't test this on enough Corvettes to have a solid baseline for a lighter weight wheel/tire combination such as my 275 square setup that I started with.

Speaking of adjusters, these are supposed to have 18 clicks of adjustment, but anything past 10 clicks feels like you're going to break something with the amount of force required to get the click in there. As I have had these more they started to break in and the adjustments became semi reasonable up until 12 clicks now, but out of the box it's just one more areas these coilovers are not as good of a product as they should be.

My street settings on my 275 square setup with the provided 550lb springs wound up 4 front and rear for compression (below their recommended street range) and 7 rebound front. I had to run 11 rebound in the rear, well above their recommended street range. Using a 4/7 combo front and rear, the suspension would hit a bump, compress in the rear, and then rebound quickly, causing the rear to bounce multiple times. The rear would settle again, and come back up yet again, sometimes bouncing a third time. This created a jolting sensation and was quite uncomfortable on the street. No idea why QA1 didn't differentiate the needs of the front and back, but interestingly enough when I went with 315's and 550/650lb springs... this all went away.

Initial Track Impressions:

I hit up the Streets of Willow Springs running clockwise to test out my setup. While the handling itself was a bit underwhelming, I cannot deny that my results were that I shaved six seconds off of my previous lap times.

My overall takeaway though was that the car had MASSIVE understeer now. Calling the understeer I had "push" wasn't even accurate, as it was more often than not just straight up PLOWING into turns. While controllable-ish and workable, I know I was leaving a lot of time on the table. I would later determine the understeers was caused by being on the "bump stops" during heavy braking and corner entry. As the "bump stops" are solid plastic, you contactt them, your spring rate goes pretty much infinite, and you just plow forward.

BIg improvements to my handling came most notably though coming into turn 10 and into the entry of turn 11 running CW at SOW. This turn/transition is notoriously taxing on suspension, and a lot of folks spin here when pushing aggresively. I could carry notably more speed through there with significantly improved feel and without much concern or fear of losing traction. This both incresaed the amount of fun I could have there along with let me maximize the the speed potential of that back straight away.

Spring rate adjustments, Ongoing Track Impressions and different settings for 305s on 18x11 wheels:

After speaking with a gentleman over at Eaton Motorsports in the Corvette Track Facebook group about how much understeer I had, we sourced up a set of 600lb and 650lb springs for the rear of the C5. I then first installed the 650lb springs in the rear, and went with the softest setting on my rear sway bar to see just how the setup felt.

At the same time, I also upgraded my wheels and tires to Apex SM10 ET57 18x11 wheels with 305/35R18 Federal 595RS-RR tires. I figured why not throw more grip at the equation, along with wanting to run improved clearance wheels to allow for a big brake installation.

Welp, it turns out adding the wheels and tires really changed things up. The larger wheels and tires weighed a bunch more of course, and the suspension settings I had no longer applied. Given these are the wheel size and roughly the tire size Spec Corvette calls for, I'm not exactly pushing the limits of what these coilovers should be expected to handle. With some suspension adjusting, time spent familiarizing myself with the car, and sway bar adjustments with this spring rate I was able to acheive a pretty balanced car. Grip was still lacking at times, due to not yet having figured out the coilover "bump stops" as I would later discover.

One thing I did notice is that going further up in my settings, up even into the QA1 settings reccomendations, the car did start to feel notably more planted and handle better. QA1 perhaps provided a spec range for a particular wheel and tire weight such as what Spec Corvette runs, and did not provide adjustment considerations for lighter versus heavier weight wheel/tire combinations. Another area QA1 did not document.

Other Discoveries about these Coilovers confirming these aren't correct from the manufacturer:

While trying to configure these for optimum track handling, I met a fellow from MSI Motorsports and was talking with him about the QA1 coilovers. He had the following to say:

"I'm actually the person that back in 2001, designed and sold version 1.0 of QA1 Coil overs for C5 and newer corvettes. In 2008 when the car business slowed way down, I gave them my design for brackets and suggested spring rates, but because they didn't make 2.25" id coil springs back then, the whole product got modded (Version 2.0), got crappy reviews and got mothballed. In the past couple years, they began making 2.25" springs and resurrected the product in version 3.0, however it is only available in a twin knob adjustable format. For the street we used to run 450# front springs and 550# rears, for track use and most auto-x we used 550# front and 650# rear. They were 50% less expensive that the Eibach coil-over set up and less than half the price of Penske. Back then there weren't a lot of alternatives."

Some important takeaways from all that: the correct spring rates were actually 550/650, which has been what I've found to actually work for a balanced handling Corvette! QA1 however sells these with 550lb square, and they only have a 700lb 2.25" ID option available that can be put in the rear. QA1 yet again did not seem to know their own product nor paid attention to the person who developed it for them.

Also, doing more research on what the industry runs for spring rates, I've started to notice a pattern. Nearly everyone runes 550/650 or similar. Spec Corvette runs 550 squared, but everyone in spec corvette states they wish they rear was stiffer. While some folks vary their rates, some even going softer in the front, nearly everyone runs a stiffer spring in the rear. This is due to the geometry in the rear providing more leverage and consuming more shock stroke for the same amount of wheel travel, requiring a stiffer spring.

A Lesson in Spacers and Handling

While cruising various facebook groups, I was reading a story shared by a Miata racer who had lots of issues with intense understeer, and it wasn't until he realized they were on the bump stops that they were able to fix the issue. Reflecting on my setup, I thought perhaps this could relate to me. Believing myself to have only lowered the car 1", I had put the suggested amount of spacers in. Doing further research on the car and OEM measurements at jack points, I discovered the car came with 6" of height at the jack points. I was at 4". Needless to say, I was actually 2" lower, but with taller tires as at the time I had switched to my 305/35R18 tires. I settled on removing all of the spacers except the 3/8" hard spacer, and instantly traction improved.

Suggestion to QA1: Add a note to your findings that intense understeer can be caused by the suspension contacting the spacers early.

A blown Coilover, and Good Customer Service

Unfortunately, at my next track weekend I would only enjoy a short period of enjoyments as one of my coilovers quickly demonstrated itself to be blown. With the rear passenger side coilover blown, I couldn't accelerate out of turns at all without getting intense wheel hop.

Investigating the issue (and a few other theories before hand) it turns out that the coilover shock body had come unthreaded from the mounting bracket just enough that the O-ring keeping the oil in was no longer perfectly sealing. This meant that over a bump the shock body would burp oil out. Hit enough bumps, and hey now there's not enough oil to provide any damping.

I cannot say for certain this was the fault of QA1. I did take my Corvette to get an alignment before this track weekend, and when dropping it off I told the gentleman at the alignment shop (a seasoned fellow in doing track alignments) that I was able to adjust the coilovers by hand. When I went to pick it up, he noted out loud he was unable to turn it by hand. As the gentleman was older with a few health issues, I just attributed it to those factors and ignored it. In hindsight though, his hammering may have been because he didn't remove the set screw and so he was loosening the shock body at the same time as he was adjusting the spring. That said, maybe he legitimately did things right and it was off from the factory. I'll never know.

QA1 though was pretty good. I called in the week before thanksgiving, aka black friday. QA1 was swamped but a fellow got all my info and proceeded to work internally to get me a new coilover. He was able to confirm they'd send me a new one. About 8 or 9 days later, it arrived at my door and was good to go. I checked it was snug with a pipe wrench and installed it. All good to go.

One area of Concern: Removing a blown shock SUCKS. The correct way to both install and remove these is to go all the way soft on compression, all the way stiff on rebound, remove all spring preload and then compress the shock. This will allow you to sneak the coilover out. However, when you've got a blown coilover, there is no rebound damping, so you can't compress the coilover for removal. Prepare to pry and possibly cut the damn thing out and have to remove everything else in the vicinty while you're at it to get it out.

I don't know if other manufacturers products are better about this, but do know this is one weakness of the QA1 design.

Results of Having The Coilovers Configured Entirely Correctly at the Track

So after a lot of trial and error, I'm finally onto something I think. No blown coilover, some settings I know work through experimentation and documentation, spacers are set correctly and tested... there shouldn't be anything keeping these from being the best possible coilovers that they can be. This in turn yielded an amazing feeling car that delivered very balanced handling and feel! I let a few instructors and other folks I know with race experience try the car out, and they all commented on how balanced and easy to control the car was.

As I switched to 315/30R18 tires, I also got further improvements as the rotational mass was reduced (305/35/R18 weighing notably more than 315/30R18) and I had some additional mechanical grip. Further improvements were additionally made to handling when I returned my car to near stock ride height. Returning to the OEM intended suspensiong geometry yielded significant felt improvements. I do wish the car was lower, but the correct way to do that is with drop spindles, not at the coilover or leaf springs.

Current Overall impressions: I can and do comfortably endorse QA1 coilovers with an aftermarket rear spring for the C5 corvette... but it's not a glowing endorsement.

My current takeaway with these is that I can just barely suggest them. They do work, they do the job, but the directions were lacking significantly, so utilizing these will take some experimentation. Fortuantely for you, I've got pretty good notes and information on them so you may find it a much quicker process.

UPDATE: Since I got this article I received anew coilover to to replace a blown one. The directions quality has improve drastically, but is still lacking a bit.

I am underwhelmed by the entire lack of feedback from anybody in the Corvette facebook groups (track + modified groups) I'm in. I posted up that I've got these coilovers and what are people using for settings... and I got crickets. Nobody is running these and therefore there is very little community knowledge to fill in the gaps in the install directions.

QA1, if you want these to take off, you need to support these more. Get them out to racers, get them out to autocrossers, collect their findings and update your documentation. Adjust your spring rate offerings or partner with Eibach to offer additional spring rates. 

Presuming these can be sorted all the way out though, they are a solid option for the price. Double adjustable coilovers aren't that common, and at this price point, even less so. Being able to order these from Summit Racing and having these at your door in 2-3 days, nobody else can compete with that. QA1, you've got an advantage, you could conquer this part of the market, WHY ARE YOU SQUANDERING IT!

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