There was an interesting discussion on a Mini Facebook group recently in regards to some of the adjustable Hi-Lo trumpets being sold for the classic Mini and their suitability for rubber cones. The discussion was based around the dimensions and lack of a radius machined into the alloy Hi-Los. As it turns out, the popular style of Hi-Lo's that I purchased a long time ago are made for specifically for coil springs, not the traditional rubber cones.
Compared to the factory trumpets with a rolled edge, these alloy Hi-Los are a slightly larger diameter and have a flat mating face (no radius machined) for use with coil springs. Here is a comparison pic of the alloy Hi-Lo's vs a factory trumpet (taken from the online discussion) :
The requirement for a radius is thus - when the rubber cone compresses against the curved lip on the factory trumpet, the radius shape makes the suspension progressive, essentially providing a rising spring rate. The more the rubber cone compresses, the larger area of the trumpet that is in contact with the cone rubber which equates to a higher spring rate. So a small diameter and sharp-radius will achieve a hydrolastic suspension (read : soft) type ride; A standard diameter and radius for a standard ride (depending on the cones you use - standard/red dot); A larger diameter and radius for a stiffer ride (eg. racing)
There are a few places in Australia that sell Hi-Los with a radius already machined onto them and it would of course be preferable to purchase the correct ones, but since I'd already purchased a set and I have a lathe it wasn't a big deal to modify mine.
The first modification I made was to drill a series of holes around the outer edge of the Hi-Los so that when adjusting the suspension height via the main bolt that goes through the trumpet (whilst fitted in the car), I can insert a rod into the hole to keep the trumpet from rotating. The holes are 6mm diameter and approx 30mm deep. Note that I've previously had the Hi-Los anodised in a black colour, whereas they are normally supplied as a raw aluminium colour
I then machined down the diameter from approx 88mm to 82mm (same as the factory trumpet).
Then I formed the radius to be close to the factory trumpet, using a lathe tool that a fellow Mini guy gave me after he machined his Hi-Lo's.
With the diameter reduced and radius machined into the Hi-Los, the spring rate will be closer to a factory set up.
Before :
After :
Compared to the factory trumpets with a rolled edge, these alloy Hi-Los are a slightly larger diameter and have a flat mating face (no radius machined) for use with coil springs. Here is a comparison pic of the alloy Hi-Lo's vs a factory trumpet (taken from the online discussion) :
The requirement for a radius is thus - when the rubber cone compresses against the curved lip on the factory trumpet, the radius shape makes the suspension progressive, essentially providing a rising spring rate. The more the rubber cone compresses, the larger area of the trumpet that is in contact with the cone rubber which equates to a higher spring rate. So a small diameter and sharp-radius will achieve a hydrolastic suspension (read : soft) type ride; A standard diameter and radius for a standard ride (depending on the cones you use - standard/red dot); A larger diameter and radius for a stiffer ride (eg. racing)
There are a few places in Australia that sell Hi-Los with a radius already machined onto them and it would of course be preferable to purchase the correct ones, but since I'd already purchased a set and I have a lathe it wasn't a big deal to modify mine.
The first modification I made was to drill a series of holes around the outer edge of the Hi-Los so that when adjusting the suspension height via the main bolt that goes through the trumpet (whilst fitted in the car), I can insert a rod into the hole to keep the trumpet from rotating. The holes are 6mm diameter and approx 30mm deep. Note that I've previously had the Hi-Los anodised in a black colour, whereas they are normally supplied as a raw aluminium colour
I then machined down the diameter from approx 88mm to 82mm (same as the factory trumpet).
Then I formed the radius to be close to the factory trumpet, using a lathe tool that a fellow Mini guy gave me after he machined his Hi-Lo's.
With the diameter reduced and radius machined into the Hi-Los, the spring rate will be closer to a factory set up.
Before :
After :
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