MX5 Budget Coilover Guide

 

Stop Listening to Bad Coilover Recommendations

Stop listening to people who say BCs/Teins/ISCs/Godspeeds/Racelands/[cheap coilover brand name] are good. If you do listen then do so with a grain of salt, a very large grain of salt. Those options have their place in the market but should be seen for what they are. There are better options that keep your wheels on the ground, ride smoother, make your car more comfortable and easy to drive, and represent much better value for money. This post covers some things to consider + bang for buck recommendations.

You might think more expensive = more better. You might not be convinced that anything can beat x brand shiny stance coilovers because x brand is the best, or because so and so uses them and their car gets mad clout. Maybe you just don't know better and your only priority is slamming your car.

If you’re interested in affordable coilovers that actually perform well and represent good value for money then you’re reading the right post. This post covers: the problems with two piece coilovers, a brief overview of DIY Bilsteins, and some other recommendations.

What's Wrong With 2 Piece Coilovers?

Two piece coilovers are coilovers with universal threaded bodies screwed into lower cups. The problems with two piece coilovers are:

• Poor valving: The dampers on cheap two piece coilovers often suck. The shocks and springs don’t move harmoniously, resulting in poor ride quality with frequent knocking & clunking and bobbing & bouncing. Sometimes, the valving is beyond saving by the damper knob on the top of the coilovers which might make the car feel stiffer or softer, but never good. This isn't always the case, some two piece coilovers have good valving, but they're expensive.
• Poorly optimised travel: Travel is poorly optimised on two piece coilovers made of universal shock bodies screwed into lower cups adapted to MX5s. BCs suffer from this, Feals suffer from this, heck Ohlins suffer from this. Thread the shock body all the way into the lower cup, trim the bump stop down to 10mm left and there's still room between the tyre and the arch. You can work around this by buying extended top hats to shorten the effective length of the shock bodies and get the car lower. This allows the wheel to get closer to the arch when fully compressed. To top it all off, if you can get the shock bodies short enough, two piece coilovers have less stroke than one piece coilovers.
• Price: $1500USD is expensive for groceries but about as cheap as it gets for good brand new coilovers. Two piece coilovers with good valving are expensive (e.g. Ohlins), often couple hundred from Xidas expensive. Even lots of coilovers with bad valving are expensive…

Even Ohlins kind of suck... Ohlins out the box are only good for close to stock height street cars. Don't get me wrong, the valving is great, and they are incredibly plush and smooth. However, they don't go low in the rear without sacrificing travel unless extended top hats are installed. Pretty poor form for such expensive coilovers from such a big name in the game. To make them track friendly, you'd need to buy the coilovers, stiffer springs, extended top hats and revalve them to support the new spring rates. At that point, you may as well buy Xidas for less...

What are DIY Bilsteins/Billies?

DIY Billies are MX5 Bilstein shocks (Bilstein B8/B6) converted to height adjustable coilovers. They are a popular choice for MX5s across the world from street cars to race cars. The main advantages they boast are: they are affordable, they're road as well as track friendly, stock valving can support popular standard spring rates up to about 14k/8k (Supermiata recommends no more than 10/6), and they can be revalved to perfectly match & support any spring rate. DIY Billies with stock valving and matching springs can cost a few hundred less than a new set of BCs (if you already own Bilsteins); revalved Billies cost a few hundred more.

Don't let the DIY scare you. The main benefits of preassembled coilovers are that they're conveniently assembled with most/all necessary parts, they're shiny and they haven't been used before. All coilovers need to be disassembled and reassembled to be set up properly anyway so throw away the excuse of not wanting to have to build your own coilovers. To make a set, you'll need:

• Set of Bilstein shocks:
• B8, B6, Hard S, HD, MSM. Any of these will do but B8 is preferred. New shocks are purchasable from RockAuto or anywhere else that sells them.
• Top mount solution:
• OEM NB front top hats.
• 4 sets of OEM replacement rubber bushings - KYB SM5139 from RockAuto. Consider 2*M10 washer on each shock under the bottom bushing if the OEM replacement washer interferes with springs.
• Note: 5XRacing sells a kit but don't come with extended top hats to maximise rear travel.
• Extended top hats - rears are a must to maximise travel.
• Pair of Maruha extended rear top hats. Alternative: FlyinMiata/RoadsterSport extended travel rear shock mounts.
• Sleeves & collars:
• 2 pairs of Allstar ALL64143.
• Spring isolators (optional):
• Energy Suspension 9.6103G.
• Springs:
• Swift/Hyperco/Eibach/BC 6" front and 7" rear 2.5" springs.
• 9k/6k for street down to 120mm pinch weld height, 12k/7k for 200TW and casual track use, 14k/8k for more serious track car. Consider revalving to support stiffer springs.
• Bump stops:
• Integra Speedthane bump stops.
• Optional:
• It's fine for your springs to sit loose when the wheels are at full droop. But if this bothers you, buy:
• 4 * 2.5" tender coil sliders.
• 4 * Hyperco helper spring CS100.
• If you want to be super extra, QA1 Torrington thrust bearings so your springs spin smoothly.

See how to assemble here: https://www.clubroadster.net/threads/budget-bilstein-ballers.198881/, https://www.miataturbo.net/suspension-brakes-drivetrain-49/better-bilstein-ebay-coilover-thread-78451/

See how to set up the Bilsteins at the bottom of this article.

I'm now running Whitener revalved Bilsteins with 1000/600 spring rates. I’ve used Ohlins R&T DFV, BC DS, Tein Flex, Yellowspeed coilovers and now race built Billies on the MX5 platform. If MX5s came with race spring rates from factory, this is how I imagine it’d feel. These coilovers are quiet, smooth, controlled, well contained, and always tight and firm, stiff but not hard. Compared to the others, they don't skip, knock, clunk, bounce or bob. Dare I say with softer spring rates, this might be more comfortable than a brand new Mazda 3.

Revalved Billies are a budget alternative to Xidas that are a bit less hardcore and lower maintenance for only a touch more than a set of BCs. Even stock valved Billies would outperform many two piece coilovers. Combined with their durability, it’s really hard to beat the performance/$.

949Racing Tecna & MeisterR

It would be remiss not to address other high value for money options that exist in the current market.

For $1475, you could buy Tecnas with sport springs. They're a bit more expensive than DIY Bilsteins but they're the easy button. They have good valving to match the springs, they have all the travel you need, you don't have to separately source all the pieces, they're one piece shocks, and they're made by 949Racing/Supermiata who developed the gold standard value for money motorsport coilovers for the MX5 platform (Xidas). These are the peak performance affordable street coilovers. Revalved Bilsteins cost about the same as fully optioned Tecnas, and are raceable.

Emilio Cervantes from 949Racing is of the opinion that MeisterR Zeta CRDs fall somewhere between DIY Bilsteins and Tecnas in outright performance (https://forum.miata.net/vb/showthread.php?p=10767118 post #2). MeisterRs don't quite hit peak performance or peak value for money but are still a valid option to consider if you have a hard budget or have trouble accessing better options (Tecnas/revalved Bilsteins). Their setup instructions are a bit confused like most 2 piece coilover manuals but that doesn't detract from the actual performance of the shocks. While they are claimed to have lots of stroke, users have identified that part of it is dummy stroke, i.e., it has less stroke than claimed. Jerrick from MeisterR (business owner) is transparent and doesn't claim for these coilovers to outperform everything on the market.

The way I see it, if you can save up for MeisterRs then you can save up a bit more for Tecnas or revalved Billies.

What Should You Buy?

Is there ever a time where it’s okay to buy two piece coilovers? Sure, it’s your money. Just know the pros and cons. If it’s cheap, the ride quality is probably awful. If the valving is good, it’s probably expensive and still suffers from poorly optimised travel.

Proper Coilover Setup (TLDR) (The long version: https://minifdmx5.blogspot.com/2023/06/coilover-setup-guide-your-coilovers.html)

To properly set up your coilovers:

• Install the shocks with springs removed
• Jack the lower control arm up
• Adjust shock body length/bump stop length so that the shocks bottom out right before the wheels touch anything
• Reinstall shocks with springs installed
• Adjust ride height by the spring perches