Adjustable Brake Bias Proportioning Valve Kit for Mazda MX-5 NA NB

£68.14 inc. VAT

The Adjustable Brake Proportioning Bias Valve Kit allows you to adjust the brake bias on your Mazda MX-5 NA or NB. The non-ABS MX-5 proportioning valves are heavily biased towards the front brakes, meaning they lock up prematurely whilst the rears are doing little work. The stock bias valves were adjusted for the later models. However, on track, it is still easy to lock up the front wheels under heavy braking. So over-worked are the front brakes that in race series where bias valves are not permitted, racers will opt to use a more aggressive compound on the rear brakes than on the front.

We have had brake line adapters made especially for us. These allow any adjustable brake bias proportioning valve with 1/8NPT ports to be fitting to your Mazda MX-5. With a brake bias valve fitted, the brake balance can be adjusted so that the rear brakes are worked as hard as the front. Brake balance can be finely tuned for different tyre compounds and weather conditions, ensuring braking performance is always maximised.

Works with NA and NB1 ABS cars not NB2 ABS


  • Motamec brake bias valve with 1/8NPT ports
  • 1 x M10x1 inverted flare female to M10x1 inverted flare female brass union
  • 2 x M10x1 inverted flare female to 1/8NPT male brass adapter

Additional information

Shipping Weight 0.225 kg
Shipping Dimensions 13 × 6 × 5 cm

Mk1 (89-98), Mk2 (98-05)

Warranty information

Warranties cover defects in materials and workmanship only. Warranty is for replacement of a similar product, repair of the original product or refund of the purchase value only and excludes all labour and incurred charges including towing, fitting, inconvenience, and purchases of other manufacturer's products. The warranty is good for the period stated in the additional info tab from the date of purchase. Mileage warranties are for road use only and proof of mileage is required. Products must be installed by an independent experienced professional mechanic and the suspected defect must be present at the outset. The warranty does not cover damage caused by incorrect installation, failure to comply with the maintenance requirements of the vehicle, processing or otherwise changing the product, ordinary wear and tear, or any other external influences. Warranties are invalid if the product is used for racing, rallying, drifting, track days or any other form of motorsport or competition. Please refer to the manufacturer's own warranty documentation for more information.

Making a warranty claim

Proof of purchase receipt showing the date of purchase, proof of mileage at installation, proof of current mileage and invoice of the work undertaken by an independent experienced professional mechanic must be supplied along with the returned products for a warranty claim to be considered. If your vehicle needs to be used whilst your warranty claim is considered replacement parts from the same manufacturer should be purchased through BOFI Racing. In the event of a successful warranty claim, we will refund the card that was originally used to purchase the replacement parts, in full or in part depending on the nature of the claim. BOFI Racing reserves the right to make full or partial compensation at its sole discretion depending on the condition and mileage use of the returned suspect parts. For example, if you have used the part for several thousand miles before a defect is noticed, only partial compensation may be offered.

Make Model Year
Mazda MX-5 I (NA) 1989 - 1998
Mazda MX-5 II (NB) 1998 - 2005