Reluctance rings
I wanted to find a reluctance ring that would provide the ECU with accurate wheel speeds, and after trying several OEM parts, decided to have a go at making my own. Drawn in Fusion 360, I use a UK based company to laser cut the rings to my design, and they can be seen on several race cars in the British Sprint paddock. Customers include SBD Motorsport, and both cars that won the British Sprint Championship in 2022 and 2023.I can alter the design for any size output cup, and we can discus the number of teeth that you need on each ring.
I can also supply NPN 12 Volt barrel induction sensors, to go with the reluctance rings, and they work at up to 4000 pulses per second (4KHz) switching frequency, and feature a bright internal LED to aid setting up. Prices start from £25 each. For best results, an induction sensor needs to be positioned with a gap between 1mm and 2mm to the reluctance ring tooth.
Switching frequency
How many pulses a second will a 20 tooth ring produce?At 150 mph, using a 13 inch 250/575 rear tyre, a tyre will rotate at 2227rpm, a 20 tooth ring will produce 742 pulses per second, and the car will travel 3.6" per pulse. With an older ECU, where the input frequency may be limited, we can produce a ring with fewer teeth to suit. For example a 12 tooth ring will produce 445 pulses per second at 150 mph, and the car will travel 5.9" per pulse.
| Teeth | Pulses per second |
Distance per pulse |
|---|---|---|
| 12 | 445 | 5.9" |
| 14 | 519 | 5.1" |
| 16 | 593 | 4.4" |
| 18 | 668 | 4.0" |
| 20 | 742 | 3.6" |
Please get in touch for prices and availability. Either contact me through my Facebook page, or send me an email to [email protected]
All reluctance rings are a friction fit over the output cup, and are laser cut from 6mm mild steel, in the UK.
Hewland FTR fit reluctance ring
£40.00
This is the 16-tooth Hewland FTR reluctance ring that I run on my Mygale EcoBoost. Laser cut in the UK from 6mm steel. The design allows a small amount of flex, which allows the rings to be friction fitted over the Hewland FTR output flange.
Each 7mm tall tooth provides a 36mm² surface to the sensor.
Weight: 54 grammes
Hewland FTR ring cover
Available from 2024 This 3D printed PA12 Nylon cover slips over the reluctance ring, and provides a smooth finish leaving a 1mm gap to the speed sensor.
Empire EVO 2 reluctance ring
£40.00
This is a 20-tooth reluctance ring for the Empire Evo 2.
Ford Focus reluctance ring
£40.00
This is a 16-tooth reluctance ring for the Ford Focus.
Force TA reluctance ring
£40.00
This is a 16-tooth reluctance ring for the Force TA
Front wheel trigger disk
£25.00
This is a 16-hole front wheel trigger disk, laser cut from 2mm steel.
70mm OD
6mm mounting hole
Weight: 40.5 grammes
This is a render of the output cup from the Empire Evo2, with the 20 tooth reluctance ring fitted. Drawn in Fusion 360.
Installation
On my car, the FTR reluctance rings are matched with Honeywell GT101 induction sensors, using 3D printed GT101 sensor brackets. The printed bracket uses an aluminium socket head M6x35mm bolt and titanium locknuts, to allow the sensor gap to be easily adjusted. In testing, this setup has proved 100% reliable, with zero speed drop outs, set using a ~2mm tooth gap. Using 16 teeth gives the ECU a high resolution, and the GT101 sensors work well with the 36mm² surface area of the teeth.