The kegler mod is documented here -
https://www.inoanorton.com/docs/swingarm.pdf
You can buy nice clamps from NYC Norton or make your own from clamps from McMaster Carr. (which I cant do cuz they wont ship overseas)
All the modern tires recommend a wider rim than a WM2 for anything bigger than a 90/90. If you have the ability, I would suggest moving up to at least WM3, especially for the rear.
| Tire Size | Brand | Minimum Rim | Ideal Rim | Maximum Rim |
| 90/90 | Michelin | 1.85" (WM2) | 1.85" (WM2) | 2.15" (WM3) |
| Avon | 1.85" (WM2) | 1.85" (WM2) | 2.50" (WM4) |
| Bridgestone | 1.85" (WM2) | 1.85" (WM2) | 2.15" (WM3) |
| 100/90 | Michelin | 2.15" (WM3) | 2.15" (WM3) | 2.50" (WM4) |
| Avon | 2.15" (WM3) | 2.15" (WM3) | 2.75" |
| Bridgestone | 2.15" (WM3) | 2.15" (WM3) | 2.50" (WM4) |
| 4.00 x 18 | Michelin | 2.15" (WM3) | 2.50" (WM4) | 3.00" |
| Avon | 2.15" (WM3) | 2.50" (WM4) | 3.00" |
| Bridgestone | 2.15" (WM3) | 2.50" (WM4) | 3.00" |
As far as a Radial MC goes, I spent a lot of time researching what to do with mine. A lot of that was questioning via AI and picking thru the errors to get to a point where I was confident in the recommendation.
The Brembo RCS 15 is where I ended up, and that is a nice unit as it comes with a clip in microswitch for the brake light, which is super useful. It is perfect match for the four pot Brembo P4 30/34 caliper I have with the CNW kit, which used a PS13 Brembo axial MC. Brembo specifically designs and officially lists the 15RCS master cylinder to be paired directly with one 4-piston caliper (a single 4-pot configuration) to hit the performance target.
For your Dunstall setup, the universal formula for determining the correct radial master cylinder size the Total Hydraulic Area Ratio Formula. To achieve the ideal "sweet spot" for motorcycle brake modulation and safety, you aim for a target hydraulic surface area ratio between 23:1 and 27:1.
I just did a quick analysis (you should check 'my' work for yourself):
Step 1: The Core Formula
The mathematical relationship is calculated as:
Hydraulic Ratio = Total Working Caliper Piston Area/Master Cylinder Piston Area
Because a dual Dunstall kit features two opposing-piston calipers, you calculate the area of one side of the pistons per caliper, multiplied by two calipers (meaning you calculate the area of 4 pistons total).
Piston Area = 3.1416 x (Piston Diameter / 2)^2
Step 2: Plugging in the Dunstall Twin-Disc Math
The vintage Dunstall dual-disc caliper uses (4) 1.5-inch (38.1 mm) pistons.
Total Caliper Area = 4 x 3.1416 x (38.1 / 2)^2
Total Caliper Area = 4 x 3.1416 x (19.05)^2
Total Caliper Area = 4 x 1,140.09
Total Caliper Area = 4,560.36 mm2
Step 3: Finding Your Perfect Radial Master Cylinder
Using the target 27:1 performance sweet spot standard for classic motorcycle vintage racing applications
Target MC Area = Total Caliper Area / 27
Target MC Area = 4,560.36 / 27
Target MC Area = 168.90 mm2
Step 4. Check the 15mm Radial Master Cylinder Area:
15mm MC Area = 3.1416 x (15 / 2)^2
15mm MC Area = 3.1416 x (7.5)^2
15mm MC Area = 176.71 mm2
Final Ratio = 4,560.36 / 176.71 = 25.80:1
The Verdict
The exact correct size radial master cylinder for a dual-disc Dunstall setup is a 15 mm radial master cylinder (such as the
Brembo 15RCS). It matches the unique, large-volume requirements of those four classic 38mm Dunstall pistons perfectly.
A note - you will want to use SS brake lines, whether you get a radial MC or not. You would also need a reservoir kit with the RCS, as they don't come with one. It mounts directly to the MC.
