Rennsport Factory



BMW 3 series G20 / G21 – AST and Moton Height and Damping Adjustable Coilover Suspension


AST 5100 / 5200 / 5300 Series

Includes springs

All AST and Moton dampers are monotube in design. Oil and gas are separated which offers a larger oil capacity and main piston when compared to twin tube. This combines to improve response and thermal resistance whilst preventing cavitation (aeration of the oil). Weight of the units is reduced through having less parts and the ability to use aluminium as damper bodies.

Each AST and Moton kit is specified bespoke to the car and driver, with the dampers being rebuildable for years to come this ensures long term ownership. Please note some of the pictures may be generic.

ast 1 way coilover suspension

1 Way

  • Mainly rebound with a smaller amount of compression adjustment on one knob.
  • Most simple to use but a limited range compared to the 2 and 3 way.
moton 2 way coilover suspension

2 Way

  • Offers rebound with compression adjustment both independently via external reservoir.
  • Larger range of adjustment to cater for customer preference, different scenarios or changes to specification.
ast 3 way coilover suspension

3 Way

  • Offers rebound on the rod with high and low speed compression adjustment independent via external reservoir.
  • Largest range of control.
Generally speaking the non inverted design doesn’t lend itself well to motorsport applications without development due to the increased lateral loads on the strut. Even in fast road applications, strut rods will bend. The solution has long been to invert the damper and run the polished outer casing through DU bushes in a strut casing. AST use a 45mm inverted diameter body. By inverting the strut damping performance is more consistent under the larger lateral loads found with hard driving.
The Moton by comparison is an ultra low friction non inverted design but with strength via extra support of the rod throughout its travel. This offers improvements in response due to a larger piston creating the damping forces. This is combined with a reduction in friction and maintenance as the DU bushes are smaller and sealed within the damper submerged in oil.
  • The adjustment system on AST dampers is a rod and needle in the center of the tube, this restricts the amount of oil that bleeds from the rod and in turn how much oil bypasses the piston.
  • Moton is a novel system completely different to AST and most other dampers on the market. Adjustment is done via very small precisely drilled holes which offer a large improvement in accuracy, repeatability and a larger range. The larger range ensures the vehicle specification and in turn spring rates can be changed dramatically without the dampers needing a revalve.
The AST DDP stands for double digressive piston, this changes the way damping forces are created. Both the compression and rebound create a large amount of low speed force. Turn in is sharp whilst the high speed blows off allowing the spring to oscillate over a pot hole or race curb. The only downside is on the road or a rough track, when multiple smaller low speed bumps are involved it could feel what some would describe as choppy. As the Moton is more of a motorsport orientated damper, this kit comes with a piston which creates low speed forces in a similar way as standard.
1 way kits that are designed for OEM top mounts will use rubber bushes on the dampers unless otherwise specified with optional spherical bearing top and bottom mounts. All other kits are supplied with spherical bearing upper and lower mounts where possible. This will be more direct and will improve response by removing the rubber on the damper at the expensive of some increase in noise, vibration and harshness (NVH).
AST offer adjustable drop links as an option for most kits. These are already developed to be the correct length range. As some kits may change the position of the mounting point, these are recommended as we can’t guarantee fitment of other brands.

Every kit comes with a free consultation, we’ll contact you after ordering to get details about the car. Almost any spring and damper length or rate can be supplied. You’re welcome to supply us ratings, or with a quick consultation we can specify them. This ensures you get exactly the kit you need for you and your application – be it a comfortable road going kit, a full race kit or anything between.

Damper Options

AST Inverted 1 Way Adjustable for OEM Top Mounts, AST Inverted 1 Way Adjustable for OEM Top Mounts with 2x DDP, AST 1 Way Adjustable With Spherical Bearing Top Mounts, AST 1 Way Adjustable With Spherical Bearing Top Mounts and 2x DDP, Moton 1 Way Adjustable, AST 2 Way Adjustable Coilover With Spherical Bearing Top Mounts, AST 2 Way Adjustable With Spherical Bearing Top Mounts and 2x DDP, Moton 2 Way Adjustable, AST 3 Way Adjustable Coilover With Spherical Bearing Top Mounts, AST 3 Way Adjustable With Spherical Bearing Top Mounts and 2x DDP, Moton 3 Way Adjustable

Spring Ratings And Damper Valving

Road, Fast Road And Occasional Track, Track And Rough Circuit, Circuit Racing, Tarmac Rally, Drift

Make Model Year
Make Model Year
BMW 3 series G20/G21 2018-
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