Sunday, September 2, 2012

Suspension Testing: Spec:Race Atom & Lotus Street Nitrons

We tested and conducted suspension development on both the Lotus Elise and Spec:Race Atom last week at Spring Mountain.  We had a new street suspension from Nitron that needed a proper track test and also recruited Dave T. to help dial in the SRA's suspension.  After four days of testing and tweaking, we achieved good results.

Nitron Street Series for Lotus Elise/Exige:
We have been working with Nitron to develop an affordable alternative to a stock Lotus suspension.  Typically most OE shocks are showing wear by 40k miles.  The degradation happens slowly, so most people don't notice that their shocks are worn out.  These Nitrons feature valving that is fixed.  The adjusters shown in this picture will not be on the final parts.  A key feature of these shocks is that they have a threaded body which allow for ride height adjustment and corner balancing.  The stock shocks do not allow any adjustment.

We installed the test set of shocks on a normally aspirated Elise with stock rims and Toyo R888 tires.  We set the ride height to a stockish 135-140mm.  I drove the car on Spring Mountain's 2.2mile config and rode up every bump and curb that I could.  I put 277 track miles on the car and set a fast lap of 1min 58s with dozens of laps under 2min.  A fast time is about 2min on this configuration.  Overall the suspension performed beautifully.  It was compliant and delivered great grip.  Yes, it sways, pitches and squats more than a Nitron NTR series but it is designed as a street shock that may see occasional track use.  We will now place it onto a street car and run through some street testing to confirm that it works properly on the street as well.

Spec:Race Atom Suspension Tuning:
West coast tracks can be quite bumpy and a real challenge for stiffly sprung cars.  Previous track testing that I conducted with our SRA showed that it is very stiffly sprung.  The SRA features double adjustable coil-overs with a bell crank and pushrod suspension.  The car comes stock with 400# front and 500# rear springs.  I spent one weekend at Spring Mtn with the car, comparing it to an Atom3 with the Bilstein adjustable shocks.  The Atom3 was far more compliant through bumps that would fully upset the SRA.  I called the factory and they suggested I test the softer springs they had sent with the car.

I asked our Ride & Handling expert, Dave Thilenius to help us set up the SRA.  We decided to test spring rates on Saturday and then vary rebound and compression on Sunday.  Rebound and compression settings were left alone as we first tested the following rates:

  1. Baseline: Front 400# & Rear 500#
  2. Front 400# & Rear 300#
  3. Front 300# & Rear 400#
Carlos swapped the springs and reset the ride height to stock for each configuration.  The pushrod on the SRA sets ride height - which is much easier than on a Lotus.  We ran 1 warm up lap, 2 hot laps and 1 warm down for each configuration.  We then ran the car on the skid pad in both Clockwise and Counter Clockwise directions.    The SRA comes with Race Technologies data logger, dash and video.  We downloaded the data after each session to see what the data revealed.  Dave also took notes after each session to record his impressions.  Watch the video below to hear some of his comments from one test session.

The skid pad became the test that best determined the balance of the car.  It was clear that the first and third spring config were the best balanced.  The second config. delivered a car that understeered more than the others - the softer spring kept the rear planted!  The skid pad lap times were also the quickest in the third set-up.  Actual lap times were close but we ultimately used Dave's qualitative comments to select the third (Front 300# & Rear 400#) spring config.  This set up managed to soak up the bumps better than the first and delivered a neutral car.  Dave did suggest that the second config. would be the most comfortable to drive for beginners.

On Sunday, we began to vary the Rebound and Compression settings.  The QA1 shocks that come standard on the SRA feature 18 clicks of adjustment for each variable.    Again we downloaded data and recorded comments to evaluate the handling.  We tested ten different settings.  Dave ended up running lap times that were significantly quicker than on Saturday.

I tested the SRA at the end of the day - I couldn't let Dave have all the fun!  I'm at least as fast as the average Atom driver so felt my opinion would be relevant for most.  The car was much better than the original with plenty of grip through the bumps.  It was more compliant but remained stiff.  Unlike with the original set-up, I was able to climb the curbs with confidence.  Ultimately, we landed on settings for the SRA that I think are better suited for bumpier tracks.  Great job Dave and Carlos for wrenching!

The Atom will always be a 'loose' car, especially when compared with other cars - like a Lotus.  The SRA has no wings so remains a car that relies solely on mechanical grip.  The rear bias and power-to-weight ratio make it a car that is even closer to a formula car.  This is not a beginners track car nor one for the faint-of-heart.  Even with our tuning, you need to keep a high level of focus to go quickly. I suspect this is one of the reasons why the Atom delivers excitement in spades...this car is not for wimps!


alex tuter said...

Really- very important and helpful ideas about suspension testing ...........thanks for sharing

suspension systems

All about 4wheels said...
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