Bump stop selection matrix:

• FCM 12mm bump rubber - for cars with 400/300 springs or higher, typically aggressive or race applications. May be slotted and added to shock as a spacer. Standard on FCM coil-over kits, 500f/325r and higher

• FCM 36mm linear - for cars lowered 1/2" or more OR using front springs MORE THAN 250 lb/in. Recommended for low cars with stiff springs. Standard on most FCM coil-over kits (300f/220r - 450f/300r)

• FCM 36mm front/46mm rear - Recommended for moderately stiff lowering springs such as Tein S-tech, Eibach, Racing Beat, H&R or Flyin Miata

• FCM 46mm linear - for cars at stock ride height/stock springs or slightly lowered. Supercedes FCM 54mm and better for street/mild sport applications.

• FCM 54mm - superceded by the FCM 46mm linear. Why? First, the spring rates are within 20 lb/in, which is unnoticeable. Second, the 46mm offers more distance before the bump stop engages, which improves ride quality (as several users of our have found, going from 54/54 to 36/46). Third, if you desire to increase spring rate or reduce ride height, the shorter stop is already present and will integrate better than the longer 54mm. For Stock-class autocross competition, racers desire to increase effective spring rate with a longer bump stops. We want to make it clear what is for competition and what is for comfort

• FCM 58mm high-performance - available in red, white and blue (soft, medium, and hard) densities. For 1990-2008 Miatas used for aggressive driving (on stock springs) or Stock-class autocross to stiffen effective spring rate when stock springs must be retained. Mix densitities front/rear to achieve desired handling balance (usually one step stiffer rear vs. front when using a large front bar). May also be used on Penske/Koni 28-series shocks to prevent tire/fender contact and supplement primary spring rate ala NASCAR/Indycar

• FCM 76mm high-performance - available in red, white and blue (soft, medium, and hard) densities. For 2006+ Miatas, 76 red may be used as a OE replacement bump stops. For custom applications stops may be cut to varying lengths

Shock absorber application guide:

90-97 Miata

• Bilstein R-pkg - original-equipment on the '93LE and '94-97 R-pkg, these are digressive, monotube shocks. Digressive means the forces decrease (or digress) at higher velocities. Digressive forces are important to prevent either rebound or compression forces from upsetting the chassis, either with too much compression (wheel jumps up over bumps) or too much rebound (wheel pulls down over bumps). The factory R-pkg shocks can be used with up to 450/350 lb/in springs as a budget race setup. A coarse revalve from Bilstein (usually only one or two internal shims changed) may be performed at a cost of ~$65 per shock. In the past (pre 2010) we offered revalve services on R-pkg/LE shocks but have discontinued this service due to the time/material needed to update the parts to current standards. See Bilstein HD for more information.
• Background: very strong low-speed rebound damping and very weak low-speed compression
• Usage: Best suited to smooth roads or stiffer springs. Users have paired with springs from 300/220 to 700/325 (Spec Miata rates). Our suggestion is in the range 400/300- 550/350. These truly come alive with an FCM revalve!
• Revalve/rebuild? Can be revalved by Bilstein to achieve your goals. We no longer offer services on R-pkg/93LE shocks due to volume of orders for custom coilover packages using new Bilstein HDs.
• Dyno graph:

• Bilstein HD, 90-97 Miata - aftermarket, German-made, intended for 90-97 Miatas, may be adapted to 99-05 via FCM mounts
• Background: soft low-speed rebound and compression, although rebound increases very quickly. very strong low-speed rebound damping and very weak low-speed compression
• Usage: The valving was designed in Germany for German roads (which are smoother than most in the United States). Best suited to smooth roads or stiffer springs, up to ~450 lb/in front, 350 lb/in rear
• Revalve/rebuild? Can accept a very low-mileage 90-97 Bilstein HD but prefer to start with brand-new. You achieve better performance and longevity if we revalve new HDs whether shock-only or as part of a complete coilover package. Revalve cost is $150 per shock and we shape the entire damping curve based on vehicle + passenger weights, driving style and your typical roads. Bilstein revalves are less refined than what we perform based on our modeling and detailed consulation process
• Dyno graph:

• FCM custom Bilstein - based on brand-new aftermarket Bilstein HD shocks (for 90-05 Miatas). 2006+ Miatas we can use either new aftermarket Bilstein HD or an OE "crimp top" (non-serviceable) Bilstein that we can have converted to a serviceable unit. These shocks may be supplied individually or built into a coilover. For 2006+ Miatas and 2004+ RX8s, the factory shock mounts are re-used but new MCU bushings are provided. Valving is tailored to the customer's needs. A thorough phone interview is performed to determine optimal ride heights, spring rates, recommended front and/or rear sway bar, and alignment settings. No two customers are the same and one-size does not fit all
• Background: Based on the proven Bilstein monotube design. Our complete coil-over kits carry a MONEY-BACK GUARANTEE
• Usage: Can be built to any specs for any application, from street to autocross to high-speed road racing. May include single-adjustable (double-acting rebound/compression), double-adjustable (independent rebound/compression), with external reservoir
• Revalve/rebuild? Yes. Can easily accommodate +/- 100 lb/in change in spring rate before any revalving is needed.
• Dyno graph: specific to each customer's needs. Dyno curves are only provided with adjustable shocks to show full range.

• Bilstein HD, 06+ MX-5 Miata, 04+ RX-8
• Background: decent amounts of bump and rebound at mid and high-speed but overdamped at low-speed. A firmer ride than is needed but decent choice for tighter handling than stock or with mild lowering springs. Not recommended for coilovers without an FCM revalve.
• Usage: The valving was designed in America so the profiles are less harsh than the 90-97 Bilstein HDs.
• Revalve/rebuild? Can accept a very low-mileage 06+ MX5 or 04+ RX-8 Bilstein HDs but prefer to start with brand-new. You achieve better performance and longevity if we revalve new HDs whether shock-only or as part of a complete coilover package. Revalve cost is $150 per shock and we shape the entire damping curve based on vehicle + passenger weights, driving style and your typical roads. Bilstein revalves are less refined than what we perform based on our modeling and detailed consulation process
• Dyno graph:

• Flyin' Miata AFCO - aftermarket, American-made twin-tube, digressive character
• Background: Twin tube double-adjustable shock designed for Flyin' Miata by AFCO. Be careful not to confuse claims of 'winning history' (usually on monotube suspension) with the lower-cost FM twin-tube product.
• Usage: Road, track, autocross, rally
• Revalve/rebuild? Yes
• Dyno graph:
• Comments: UPDATE: 1/6/2010 - We've received several complaints of users of the FM AFCO system who could not find a comfortable damping setting, even if the springs were softened. Once those Miata owners installed FCM custom coilovers, they were amazed at the ride quality and grip improvement. One former AFCO owner's review of his new FCM suspension had two words - 'HOLY SH*T!"
  
  NOTE: the original the Flyin' Miata page for the AFCO suspension had some incorrect and misleading comments about shocks and still claims twin-tubes can be equal to monotube 'when properly implemented.' Click here for our critique of their marketing efforts.

• JIC Magic FLT-A1 - aftermarket, Japanese-made monotube, digressive character
• Background: Very strong low-speed rebound, also fairly strong low-speed compression. Double-acting thru-rod bleed adjuster (low-speed rebound and bump together). Can work well for smoother lots and track but very harsh riding on the street, even on full soft
• Usage: Track, autocross on smoother lots, drift
• Revalve/rebuild? Yes
• Dyno graph:

• HKS Hipermax - aftermarket, Japanese-made monotube, linear valving
• Background: One of the nicer monotube shocks, though very strong rebound damping and somewhat soft compression. A good track or potential drift setup
• Usage: Track and competition mostly, has a very firm ride quality.
• Revalve/rebuild? Yes.
• Dyno graph:

• KYB GR2 - aftermarket, Japanese-made, twin-tube digressive shock. Non-adjustable.
• Background: not having measured one, we can only comment on user reports and marketing. It seems to be geared as a stock replacement.
• Usage: Stock springs only, not intended for lowering springs or performance applications.
• Revalve/rebuild? Not serviceable.
• Dyno graph: None

• KYB AGX - aftermarket, Japanese-made, twin-tube digressive shock with a single double-acting (rebound/compression) low-speed bleed knob
• Background: rebound is 3x stronger than compression throughout the shocks operating range. This causes jacking down and a rough ride over bumpy roads, though not as much as Bilstein R-pkg or HD.
• Usage: The damping is not very strong and our calculations indicate a maximum front spring of ~230 lb/in. These paired with stock springs or Tein S-tech would be the best compromise. Note that ride quality will be less than Koni Sport (on softer settings), Tokico Illumina (also on softer settings), or an FCM-valved Bilstein.
• Revalve/rebuild? Not serviceable.
• Dyno graph:

• Koni Sport (also Koni Yellow) - aftermarket, Dutch-made, twin-tube digressive shock with a single double-acting (rebound/compression) low-speed bleed knob
• Background: designed as a stock-replacement, this shock works quite well with a stock spring except for having insufficient mid- and high-speed compression to prevent jacking. On stiffer rebound settings the shock is often used to 'control' stiffer springs. However, the control being exerted is only in the rebound direction so the result is jacking down, creating a loss of grip, unpredictable handling in the wet and reduced ride comfort. We used these shocks for 10 years and they served us well until we discovered monotube technology via Bilsteins and haven't looked back.
• Usage: For touring and sporty driving, we find 300 lb/in front, 220 lb/in rear springs is a good complement to the Koni damping. Higher rates are typically used for STS2, CSP and more dedicated track cars.
• Revalve/rebuild? At an authorized Koni center (no, we do not revalve Konis).
• Dyno graph:

• Koni DA (double-adjustable) - aftermarket, Dutch-made, twin-tube digressive shock
• Background: based on the Koni Sport (or Yellow), a screwdriver-activated rotary knob/adjuster is installed on the foot valve to control compression separately from rebound.
• Usage: Often used for autocross or road race to gain finer control on vehicle dynamics via the independent double-adjustment. Capable of generating copious amounts of rebound force but a delay in the onset of compression force is noticeable. The three sets we've seen were degassed and had audible foaming during operation which makes the shock behave inconsistently and causes faster internal wear.
• Revalve/rebuild? At an authorized Koni center (no, we do not revalve Konis).
• Dyno graph:

• Koni Race (same as revalved/shortened Koni Yellow) - aftermarket, Dutch-made, twin-tube digressive shock with a preload adjuster affecting the rebound damping.
• Background: the softest settings is nearly the same as Koni Sport. Extremely strong rebound, shown to cause extreme jacking down. Not recommended for rough roads or where ride quality and ultimate grip are desired.
• Usage: Minimum spring rates of 500 lb/in front, 300 lb/in rear from our best estimation.
• Revalve/rebuild? At an authorized Koni center (no, we do not revalve Konis).
• Dyno graph:

• Ohlins PCV - aftermarket, Japanese-made, monotube shock
• Background: No longer sold
• Usage:
• Revalve/rebuild?
• Dyno graph:

• Ohlins DFV - aftermarket, Japanese-made, monotube shock
• Background:
• Usage: With 450/336 lb/in (8/6 kg/mm) spring rates, this is a very firm setup for street use. We prefer the damping to Tein Flex, Koni, or any other twin tube, along with the early 90-97 JIC, but find it has too much rebound damping. Shock travel in the rear is very limited.
• Revalve/rebuild? Yes, a 1 year service interval is recommended (from our recollection)
• Dyno graph:

• Tein Basic - aftermarket, Japanese-made, twin-tube shock/adjustable perch/fixed damping
• Background: A good quality twin-tube but not a good long-term investment for an enthusiast
• Usage: With 392/336 lb/in (7/6 kg/mm) spring rate, it is a firm setup for daily driving. The damping quality is poor overall, underdamped for the spring rates.
• Revalve/rebuild? Yes
• Dyno graph:

• Tein SS - aftermarket, Japanese-made, twin-tube shock/adjustable perch/adjustable damping and shock body length
• Background: better damping than the Basic but still overdamped in rebound, underdamped in compression
• Usage: Uses 392/336 lb/in spring rates standard, adjustable damping and height.
• Revalve/rebuild? Yes
• Dyno graph:

• Tein Flex - aftermarket, Japanese-made, twin-tube shock/adjustable perch/adjustable damping and shock body length
• Background: a Tein SS with adjustable body-length. In principle, this feature is nice to have but it steals droop travel and can cause inside rear wheelspin in certain situations. The rebound is strongly overdamped, mid- to high-speed compression is underdamped
• Usage:
• Revalve/rebuild? Yes
• Dyno graph:

• Tokico Illumina - aftermarket, Japanese-made, twin-tube digressive shock with a thru-rod double-acting bleed adjuster affecting rebound and compression simultaneously
• Background: The Illumina has stock-like damping at the softer settings and since compression increases with rebound, it is able to prevent jacking down at higher settings. A downside is that since it is a twin-tube, there is a practical limit to how much compression can be generated via piston valve without causing hysteresis (non-ideal response).
• Usage: Stock springs on softer settings (e.g. 2f/1r) up to 450/300 springs (Ground Control/Illumina coil-over kit).
• Revalve/rebuild? No
• Dyno graph: