Beater79TA

About 7 years ago we started converting our GTA from a daily/drag car to a daily/corner carver. This started as a slow progression as we initially only ran 4 or 5 events a year and, normally, we were the only car in the class at the local event. As the pace of events increased to the current 20+ events a year we run now, the car evolved to keep up with ever improving driver skill and ever improving competition.

Over those years we used first Bilstein and then Koni shocks and struts with an Eibach Pro Kit and later Ground Control weight jacks to help control the suspension in the corners. Along the way we swapped out the LCAs and panhard for UMI Performance rotojoint adjustable pieces to help keep the rear centered as we lowered the car and added power. So when it came time to look at upgrading the shocks and struts again, we took a look at UMI to see if they had anything that fit our budget.

Last summer we had the car at Finch Performance in Nashville to have a chromoly cage installed and some work done on the wheel wells to fit a set of 18x10.5 wheels on all 4 corners. While the car was there, he also installed a set of the UMI single adjustable rear coilovers (p/n 2054-200) for us and swapped out the springs for 400 in/lb units. For those of you unfamiliar with Finch Performance, it is located in Nashville and operated by Brian Finch. Brian has participated in the Optima Ultimate Streetcar Invitational and the events that feed participants into the final, he is one of the driver’s from the TV show R U Faster than a R edneck, a driver for the BFG R U Driver Enough events, and a multi time Baja 1000 winning driver. Brian designs and builds serious cars for serious Pro Touring drivers. This is why we didn’t question it when he exchanged the UMI recommended springs for the 400 in/lb ones. Naturally, the Moser 12 bolt axle configuration used on the car was different from anything used by UMI when writing the instructions and required some tech support from UMI to determine the cause of the initial fitment issue, resolve the issue, and provide details for the updating of the installation instructions. But after removing the lower bracket spacer, everything fit correctly and we started tuning the rear suspension.

The Koni’s and weight jacks we removed for the coilovers had performed well for almost 5 years but driver skill had improved to where we needed better on car tunability for the suspension to get those next bits of speed. And the coilovers delivered. After some adjustments, we managed to shave a half second off our lap times on the LSFest autocross track. Since then, we have learned how to use the rear adjustability to compensate for track conditions allowing us to stay on the throttle harder and run faster instead of lifting to keep the rear planted. We now have a list of settings to compensate for damp, wet, and dry conditions to help keep the rear planted on the track. This was possible with the Koni’s on a much more limited scale but required unbolting the shock from the car to make the adjustment. The UMI/AFCO units are adjustable on car and provide a greater range of settings.

With the rears working so well, we called UMI in Nov 2016 to inquire about matching front struts. This led to a development effort with UMI and AFCO to develop an autocross/roadrace valved front strut that covered a wider range of adjustment than the Koni units currently on the car. After a couple months of R&D and testing on the shock dyno, we received the prototype struts to install on the car and start the tuning process. Again, the specific configuration of the car, resulted in some tech support calls to UMI to make sure I wasn’t doing something wrong and get their advice. The end result is the install requires minor clearancing on the spindles and proper clocking of the lower adjuster **** and then the struts bolt right in. These do require new upper strut mounts to be installed at the same time as the upper shaft of the strut is slightly smaller and does not fit a stock sized upper mount. UMI included these new upper bearings as part of the package to fit in the UMI caster camber plates already installed in the car. After some discussion with the team at UMI, we selected a starting point for the front adjusters and took the car to the races.

The first event with the front struts was the NSRA Tampa event on 3/31 – 4/1. The NSRA event featured a tight autocross course that kept speed down but emphasized acceleration, braking, and turning as well as driver skill. At the end of the weekend, we were in 1st place versus some pre-1975 Pro-Touring cars with significantly more money invested by a margin of almost a half second. In all, the struts performed exceptionally well in controlling the front end of the car on their first outing and we look forward to the next event where the team from UMI will be in attendance to help us continue the learning process of when and what to adjust based on track and tire conditions. These struts do not have a part number in the UMI catalog yet (as of April 12, 2017) as we are still testing the prototype units but should be available if you call and inquire about price and availability.

Based on our results, if you need a set of track valved shocks and struts with more adjustability than Koni and a lower price than the other race tuned options, give UMI a call.

TEDSgrad

iTrader: (4)

Great write up. Thank you.
What rear sway bar do you have?
Do you experience any brake wheel hop with that spring rate (what TA used?)?
Have you changed any RC's?

Thanks again.

Beater79TA

The rear sway bar is the factory WS6 24mm bar. We haven't noticed any wheel hop with that spring rate using a full length transmission mounted adjustable TA (also a UMI part). Use of the rears with that spring rate covers multiple road course and autocross days. I will be looking for wheel hop issues when I get the rear brakes properly set with an adjustable prop valve and newer brakes. With stock rear brakes, I'm not sure they grab enough to induce wheel hop. If we start to see wheel hop that can't be dialed out with shock adjustment, I'll look at reducing the spring rate as these are significantly higher rates than recommended by UMI/Strano for the rear coilovers.

With the car being lowered, the RC has changed but I haven't done the engineering to determine how much. But the change in ride height should impact the RC. I will get more serious about this when/if we move from a panhard based rear to a Watts link based unit. I'm still getting into the math/science based side of this as we work on moving the car to the next level of competition.

TEDSgrad

iTrader: (4)

I have heard of people going up to #600 in rear - with a no man's land in between. Usually with softer front, though. DSE runs 950 fr and 275 rear; I'm 850 fr and 250 rear (RideTech HQ 6110) with 19mm.

Front RC will drop the same rate; the rear will not drop as much. This will increase the roll angle inclination.

If you like to read, here are some stickies to go through (top 3). You have to sift out what doesn't apply, but there's plenty to digest: http://www.lateral-g.net/forums/forumdisplay.php4?f=38

Will you be coming north to Road America for Optima?

Beater79TA

We're currently running 950 fr weight jacks with the 400 rear coilovers with the 36mm front and 24mm rear bars. Seems to be working good so far. Tuning the suspension will start all over again mid year when I update the rear brakes and the prop valve to get the rear brakes more involved in stopping the car.

I'll take a look at the thread on lat-g. There is a lot of good information on that site but you are correct about having to sift it out at times.

We ran some of the USCA events in 2015. 2016 we didn't make any of them and 2017 doesn't have any of them lining up for us as to where their event is and where the car is at that point in the year. For example, the NOLA USCA event is April 22, which is the same weekend we are running at Atlanta Motorspeedway at the Summit Motorama event. The remaining schedule for the first half of the year has us at:

1. Summit Motorama in Atlanta April 21-23
2. FM3 Cars and Cones April 23 - 29
3. NSRA Knoxville TN May 5 - 7
4. Midwest Musclecar Putnam Park / Terre Haute IN May 19 - 20
5. NSRA Springfield MO May 26 - 28

Then the car goes back west to run Laguna Seca in late June before coming back east at the end of July for the fall series including:

1. NSRA Louisville August 4 - 6
2. UMI Open House in Philipsburg, PA August 11 - 12
3. Holley LSFest Sept 8 - 10
4. FBody Nationals Memphis Sept 15 - 17 (not 100% on this one yet)
5. Cruisin the Smokies Pigeon Forge TN Sept 22 - 24 (tentative dates for the event)
6. Cruisin the Coast Biloxi MS Oct 1 - 6

Then back west where we might hit an autocross or two in SoCal and 1 or 2 road course days a month in Phoenix before we start the 2018 national tour again. In all, I think we have about 22 weekends at the track this year in 10 states. Plus day jobs.

UMI Sales

Thanks Tom! Love the write-up.

For roll center adjustment we have the UMI Watts on deck. We'll talk more about that at Atlanta and beyond. We are currently plotting the front end geometry and will be making some k-member adjustments soon (or maybe not - depending on the results).

ramey

KITT1983

iTrader: (3)

link please

Beater79TA

The rears are listed here: http://umiperformance.com/catalog/in...oducts_id=1005

For the fronts, you will need to call them. Those are not in the catalog yet.

UMI Sales

For specifics on the UMI Afco fronts (or any other UMI products) you can call me direct at 814-376-6000 or ramey@umiperformance.com.

Always happy to help.

later

ramey

Arctic White 91 RS

Outstanding review, thank you for sharing.