2019 SCCA RunOffs Virginia International Raceway Virginia ©2019 Rupert Berrington Action Photography

Engineering Tip #7: Spec Miata – Baseline Setup 9 (Updated)

For those who have a Spec Miata, you’ll want to ensure you baseline setup is ready to go before heading to the track. If you’re working with a shop to prepare your car, you’ll still want to read through this guideline so you understand what they’re doing to it and what kind of minor adjustments you’ll want to make once you’re at the track. This is by no means a complete how-to guide, but it gives you an overview of what you need to achieve before your Spec Miata is properly set up.

Spec Miata setup steps:
1. Set ride height
2. Set corner weight
3. Double-check ride height
4. Set caster then camber
5. Check corner weight again
6. Check ride height again
7. Set alignment/toe

Tips before starting setup:
-Have the driver in the car or use weights if you’re doing the setup yourself.
-Fuel there are two main ways to approach this. One is put enough gas in the tank to simulate how much you’ll have at the mid-point of a race. This gives you a broader setup window, as well as a more strategic setup for the mid-to–late part of the race. Another is to run the bare min (base weight) to be as close to min weight at the end of the race, min fuel requirement is usually 1 gallon in a Spec Miata.
-Try to use one setup pad for everything to ensure uniformity.
-Have tire pressures set to what they will be when hot, generally 36-38 psi, refence the tire manufactures recommendations.
-Disconnect the sway bars before setup, and do not reconnect them until setup is complete. This will avoid putting any preload on them as a result of the adjustment process.
-Lock the steering wheel centered before you make any adjustments. (Vice grips on the steering shaft and a ratchet strap work well.)

1: Ride Height:
You can measure your ride height from the pinch weld to the floor. The pinch welds are in each of the four corners, about an inch from each wheel. Note pinch welds on cars can vary to do many reasons some of the most common are crash damage or damage from lifting the car with a jack. Ride height can also be measured from the spring perch to the center of the lower shock mounting bolt as this is an accurate method for both NA/NB chassis and less likely to be damaged.

Your ideal baseline ride height will vary depending on a few components on your car. Most Spec Miatas now run the 99-05 NB OEM top hats for mounting the shocks with the Penske or Bilstein shocks.

Penske Spec Miata Info

90-05 with 99 top hats only.
Set ride height from the spring perch to the center line of the lower shock bolt to the following
Front – 10 1/8”
Rear – 6 1/8”

Bilstein shocks and Fat Cat-style bump stops

‘89-‘93 1.6 Miata: Set ride height to 5” all the way around with stock top hats, and 4 7/8” all the way around for fat cat and NB top hats.
‘94-‘95 1.8 / ‘96-‘97 1.8 Miata: Set ride height to 5 1/8” all the way around for stock top hats, and 5” all the way around for fat cats and NB top hats.
‘99-‘05 NB 1.8 Miata: Set ride height to 4 5/8” in the front and 4 ¾” in the rear.

2. Corner Weights
Your next step is to dial in your cross weight. Because each tire will be sitting on an independent scale, you’ll be able to see how your car’s weight is distributed between the four tires. The scale software will tell you your cross weight, which adds the left rear and right front weights and presents it as a percentage of the total weight.

Your goal should be a cross weight of about 50.5% of the total weight of the car: this is a good starting point, then you’ll fine-tune the cross weight at the track. Changing the cross weight affects how the car turns, so you’ll want to make adjustments according to the characteristics of each track where you race.

Because you modify cross weight by adjusting the shock height, you’ll want to double-check your ride height after this step. You might need to do a little back-and-forth tuning to get just the right combination of height and corner weight percentage. Have patience!

3. Caster and Camber
Max out your front caster first when you’re doing your setup and alignment. For setting up your camber, you want the front at -3 to -3.4, and the rear at -2.5 to -2.8. Aim for a 0.5 difference between the front and rear. (Spec Miata is now allowing the use of, offset camber bushings and/or extended lower ball joints that let you fine-tune the camber even more.) In addition to front and rear, camber will also vary from left to right. On a clockwise track, the left side should be on the higher side of the camber range, with the right side on the lower side. A track with an even split of left and right corners, like Daytona, will be even on both sides. Remember, camber can also affect the right height slightly and corner weight, so you’ll need to check both after setting camber. When it comes to setup double and triple checking everything is a good practice.

4. Sway Bars
Once you have the above points set, you’re ready to reconnect the sway bars. The reason you don’t want to do your setup with them connected is that you might inadvertently put pressure, or preload, on them. You should never have preload in the sway bars: they shouldn’t engage until you’re in the turn.

The front sway bar on the NA Miata has two holes. It is usually run on the full soft setting, which are the holes closest to the end. (The front sway bar on the 99 NB Miata has only one hole.)

The rear sway bar has three holes for all models. Most drivers opt to use the middle hole, but you can adjust to your preference. You can opt to go full stiff (hole furthest from the end) or full soft (hole closest to the end), or you can change up one of the two sides instead of both. This is another factor that you’ll change depending not just on the track, but also weather conditions.

5. Alignment
Baseline toe should be set to 1/32” toe out on each side of the front wheels, and 0 to 1/32’ toe in on the rear wheels. You’ll wind up adjusting this according to your preference.

When you’re on the brakes and compressing the front, the wheels want to toe in, so by having them set for toe out you’ll get better response. Also, when you turn, having the wheel toed out gives you more contact area for a better turn-in. Keep in mind, though, that cars will be more responsive on the steering wheel with 1/32” of toe out, but going over that number can make the car TOO responsive!

Some of the more experienced drivers looking to maximize straight-line speed run their wheels at zero toe on the rear even though it may compromise rear stability (they work to manage this tradeoff). Others, however, prefer to toe in a little bit to keep the rear of the car more stable, even if it is hypothetically the slower setup (though, it may be faster for these drivers due to consistency/stability in the rear). Fewer drivers choose a little bit of toe out to help overcome understeer (we more often see this in SM racers who came from karting). Setup, including toe, is really about personal preference.