Skip to product information
1 of 5


AST 4250 Monotube Coilover Struts and Shocks BMW E46 E46 M3

Regular price $2,900.00 USD
Regular price Sale price $2,900.00 USD
AST 4250 Monotube Coilover Struts and Shocks BMW E46 and E46 M3  


The venerable 4000 Series damper stands as AST's entry level, adjustable damper. Using the same internal technology found in the 5000 Series competition sets, the 4000 Series creates near-budget level single adjustable and double adjustable dampers for the track and amateur road racing market.

Key Features

  • Monotube dampers that use 22mm shafts for struts and 14mm shafts for shocks
  • Nitrogen charged to 175 psi for 22mm shaft shocks and 265 psi for 14mm shaft shocks
  • Utilizes AST's Load Bearing Piston (LBP) for all strut designs (AST is the only coilover in this price range to use this feature)
  • Steel bodied struts and shocks all use European KTL coating which is stronger and more weather resistant than powder coat or wet paint found on most shocks
  • Utilizes design principles required for grueling TUV testing including withstanding 1 million cycles with 1100 pounds of side load on the strut
  • Available as Rebound-only adjustable (4100) or Rebound and Compression adjustable (4200)
  • Fully rebuildable and revalvable
  • Shortened appropriately for lowered performance cars
  • The 4000 series have been tested at events including SCCA Nationals, NASA Nationals, 25 Hours of Thunderhill and Grand Am races
  • Valved for a comfortable, agressive street ride that performs great at the track

Parts Included:

  • 2 Front AST 4200 Double Adjustable (12 adj. Rebound on Top, 12 adj. Compression on Bottom) Monotube Struts
  • 2 Rear AST 4200 Double Adjustable (12 adj. Rebound on Top, 12 adj. Compression on Bottom) Monotube Shocks
  • AST Front Spring Perches for 60mm springs and your OEM upper strut mounts (removed when bought with camber plates)
  • AST Tool Kit

Also note: the rear shock is made to work with a spring in the OEM location (coilover rear shock conversion kits are optional on BMW 4200s, please call).

The Design

AST coilovers are monotube, high pressure nitrogen shock absorbers. Why do you care? Most other products on the market are twin tube designs that are not pressurized, or only have 1-2 atmospheres of nitrogen inside a little bag. Monotube shocks offer the biggest pistons for more control and the high nitrogen gas pressurization in monotubes (8-12 atmospheres) means the oil will never cavitate around the piston. This is particularly important in environments where the vehicle makes rapid changes in direction like during an autocross or while road racing because a monotube shock will continue to provide consistent damping force and performance. Monotubes also allow for a wider damping range and can more easily provide a better ride with stiffer spring rates - we usually start with 3X the stock rates and often go to 6-7X the stock spring rates, even on street driven cars. This is the same technology used on $7,000-10,000 shocks packaged here in a competitively priced kit.

Custom Valving

AST-USA is setup to offer custom valving services to its customers, including dyno services on their Roehrig 2VS shock dyno; they can even rate your old springs if you are curious (fees apply). There's no need to find a third party company to get your custom valving applied - Just send them back to us and we will work with AST to get your shocks revalved to your exact specifications.


CAMBER PLATES : We highly recommend AST camber plates be used with AST strut kits, but the shocks can be used with the OEM upper strut mount for racers on an extreme budget and/or where class rules do not allow an upper camber plate (such as SCCA Stock Class). Easily adjust camber track side with camber/caster plates. Over-sized spherical bearings are designed to withstand the rigors of street and track abuse. All components are plated for maximum corrosion resistance and long life. Ordering this option includes the associated upper spring perches made to work with these plates, 60mm springs and AST struts.


REAR SHOCK MOUNTS : Optional Rear Shock Mounts include AST-USA Spherical design or Heavy Duty rubber E46 M3 style. We recommend the spherical RSMs for most users that see any competition use, such as autocross or track events. If the car is a daily driven vehicle only and/or the user is worried about bad roads and any additional NVH transmitted through a rear spherical mount, then choose the HD rubber style instead. Our HD rubber RSMs will be machined to fit the 12mm rear pins on the current 4100s and the 4150s at no additional charge. The advantage to spherical RSMs is their ability to transmit reactions to shock forces instantly and direct - something that shows up on a shock dyno plot.


RSM REINFORCEMENT KIT : Many BMW models are prone to cracks near the rear, upper shock mount bolt holes from both street/track use with higher cornering loads (and higher damper forces) as well as normal street use over extended time periods. Bolt these steel reinforcement plates on top of the rear shock tower sheet metal to strengthen this known weak area and prevent these cracks. Can be used with OEM style rubber RSMs or spherical RSMs. Can be bolted or welded in place. To install just place above the shock tower, underneath the RSM top nuts, as shown below - takes mere minutes to install.


SPRING RATES : While AST-USA provides you with the shocks only, Lang Racing Develoment offers the unique option for racers to pick their own front and rear spring rates at a reduced cost. These options will included new Hypercoil or Swift springs depending on the rates you request, AST rear ride height adjusters, and nylon rear spring alignment platforms. We know that every application is different so we let you tell us what rates you need, or just select "custom" and we can discuss with you your specific spring needs and find the best solution for you.


HELPER SPRINGS : We have found that certain applications benefit greatly from helper springs. When lowering the rear of an E46 the shock travel is usually longer than the short spring required in the stock location which can sometimes make the spring fall out when jacking up the car. A nightmare when the car needs to be serviced or even when changing a tire. To solve this we use a helper spring which keeps the spring in location when uncompressed but acts as a flat spacer when compressed, allowing the linear spring to do all the work. This can also be beneficial on a coil over shock that has a lot of travel like in rally applications.
  • 2 Front 60mm Coilover Springs, 150mm (6") Long
  • 2 Rear 60mm Coilover Springs, 140mm (5.5") Long
  • Optional helper springs for front, rear, or both.
  • AST Rear Ride Height Adjusters
  • 2 Rear Spring Alignment Platforms