This is a really great example to help us in our thinking about set-up.  It’s a practical demonstration of what results we might expect with a coilover shock and spring upgrade.

The supercharger does a great job of equalizing straight-line performance – 0-60 and standing ¼ times near the same for both cars.

In the video, we are told what suspension upgrades and set up have been done to the Mazda.  So we are able to assess the results and have a view about how good the set-up is. 

Can the Supercharged Mazda MX5 Miata Beat the Porsche Boxster?

Well, not in the Video.  It was 2 1/2 seconds slower around the track, even though compared to the standard car, the modified car gained over 7.5 seconds per lap.  But there are a few clues in the video, as to where the Mazda could improve.  Maybe improve enough to beat the Boxster.

Handling of the Supercharged Mazda - Grip and Balance

Comparing the handling before the mods and after, the handling of the Mazda is remarkably improved.  Of course, the drivers love the acceleration from the extra power.  But Owen, driving the car on the hot lap, get's quite excited about the extra grip available to him.

The biggest single factor in creating the extra grip is the spring rates. And it is clear that the spring rates chosen, are doing a pretty good job.

We know the spring rates fitted to the MeisterR coilovers are:
Front: 10 Kg/mm (560 lbs/in), 119 CPM
Rear: 6 Kg/mm (335 lbs/in), 112 CPM
(Spring frequencies have been calculated for the Mazda in our Weight Transfer Worksheet™.)

The spring frequencies, shown above in "Cycles per Minute" (CPM), are a good compromise for a road car where you want to use it for the occasional track day - what we might consider a good Targa bitumen rally set up.  Still well short of circuit racing stiffness, though.  Note that these front springs are about 3 times stiffer than standard!

As explained in our video training, Suspension Tuning 101, we know that this extra spring stiffness has created heaps of extra grip. Other factors in the set up have less contribution.

• There are no particular shock settings that will influence the result that much.  In general terms, you need sufficient shock to control unwanted chassis movement.  Too much shock will hurt grip.  Also, in general, you do not soften the shocks up for the road - there is no significant gain in ride.  (It’s not like the mechanic said in the video.)  That said, if the bump setting is particularly stiff, you can feel the extra harshness in a car like this Mazda with stiff front springs.

• The final details of wheel alignment settings - caster, camber, toe - again, will not influence the result that much.

• Of course, you need the best tyres you can afford. But good tyres without the suspension spring stiffness will not deliver the grip you need.
(Just to be clear, weak shocks and or bad wheel alignment, are going to make the car slow.)

Balance

Grip and Balance – That’s What Handling Is All About...

Did you see that the Mazda has got too much oversteer?  This will greatly affect speed of the car through the corners.  If the balance was improved, maybe the car can be 2 1/2 seconds a lap quicker. Hard to say without more testing.

If this had been a test session to improve the car, first thing would be to bring the car in and remove a link off the rear sway bar (to de-activate it).

If that is not enough, then as a stop-gap measure, you could try playing with a tyre pressure split of at least 4 psi to start. Increase rear pressure, reduce front pressure.  We expect/hope that the higher pressure tyres at the rear will build slip angles faster, and therefore reduce or eliminate the corner entry oversteer.

Possible cause of the oversteer is insufficient travel in the rear suspension before contacting the bump stops in roll.  For NA and NB MX5s,  there is not enough travel in the rear suspension.  When contacting the bump stops, the sudden increase in roll stiffness causes oversteer.

When the rear suspension is being assembled, it is most important to check travel and when the bump stops come into play.  Remove the coil spring and put the shock back in the car.  Jack the hub up to ride height, and see what you've got.  You'll probably find you can't lower the car as much as you want.

If suspension travel is OK, it's possible the rear shocks are too stiff, slowing down the roll generation at the rear compared to the front.  Try turning down the rear shocks (softer).  Sometimes coilovers are delivered too stiff, and cannot be softened sufficiently on the adjusters.

A major improvement to the car would be to add properly sized anti-roll bars.  As per our training in Suspension Tuning 101 and 102.  This will give us more stiffness at the tyre contact patch in roll, and therefore increase grip, without having to go stiffer in the springs.

Let's look at the feedback from Owen, the Driver....

Brakes: He says early on in the lap, that the brakes are not nearly as good as the Porsche, so maybe there is some significant time to be gained with better brakes. Without more information, it is hard to say.

Grip: He is so impressed with the extra grip and the traction he gets that he is not truly noticing the affect the oversteer is having on his overall pace.  He is running some of the corners in a higher gear, instead of changing down. (In the Porsche he does change down.) 

I think he is using the higher gear in response to the oversteer - he has more control under brakes, without the need to change down, and his throttle control is better (to control the oversteer) on corner exit. If the car balance was OK, I suspect he would change down, same as he does in the Porsche. The change point is 7,200 RPM, so there is plenty of RPM left to accelerate off the turn in a lower gear.

Balance: He recognizes the oversteer is there. He says at one of the tighter corners "Little bit of oversteer on entry, little bit of oversteer mid corner"... and we see oversteer on some of the corner exits.  For quickest lap times, we want to drive the car as straight as possible - any oversteer will lose time. 

Summary:

The mid corner steady state oversteer in the car is obvious. (Not to be confused with driver induced oversteer on corner entry and corner exit).  The car is very nervous and unstable.  To get the best performance from the supercharged Mazda, we would have to address the oversteer. The people responsible for this comparison test seem to be unaware of the extra handling performance for the supercharged Mazda that they are leaving on the table.