You're talking about spring wedges, like they use in NASCAR?
spring rubbers, yes as in circle track /.NASCAR. not familiar with 'spring wedges' naming but perhaps they are same.
firm below sells multiple widths and durometers for 5-5.5" and 2.5" coilover springs. they will custom make other diameters per your spec.
https://www.acrotechinc.com/automotive-applications/
advantage is you can add or remove them quickly (re NASCAR). disadvatage is even on a pure linear spring, the durometer adds some progression to your target effective rate.
overall though, two very different setups for street and comp can be achieved, with minimal install / setup
edit; now, on the bump spring side, a spring substitutes for a bump stop. Usually the OD is 2" or less and length between 1" to 2.5". Above and below the spring are spring retainers with a hole in the center that threads over the shock shaft.
In my case, I use spring retainers from Slade Shock Technology and.1200# bump springs from Landrum. A small o-ring below the bottom retainer keeps the spring and its retainer sandwich up against the top of the.shock mount. This leaves a 2+ inch gap between the top of the shock body and the bottom retainer. Thus, on the street, the bump springs do not effect ride quality. Keeping them up with the o-ring keeps them silent...no rattles even with a.gap.
https://www.sladeshocktechnology.com/store/p_2193638/bump-spring-retainer-kit
https://landrumspring.com/products/bump-stop-springs/
For autocross, that 2+ inch gap is filled with bump stop packers, or shims which are round disks of delrin with a slot that allows them to snap on to the shock shaft. Filling the gap 'activates' the bump spring.
https://allstarperformance.com/16mm-bump-stop-shim-1-8in-brown-all64325/
Note you can buy them cheaper in bulk from Allstar and other co's
https://www.resuspension.com/bump-stops/packers/packer-16mm-625-125-10p.html
Total install process requires lifting the car to create some droop, place the front rubbers between the coils and.snap in the packers. Maybe 5 mins tops install time per side. Removal is the reverse.
For both front and rear, initial setup requires improvising shock dust boots. I have none in the front and the rears are thin plastic sheeting that can be pushed aside to facilitate packer install.
edit: added some pictures
pic 1; a spring rubber placed on stock GTI.springs. I run two rubbers on each front spring
pic 2: behind the low-rent dust boot, Landrum 1200# bump spring on the rear shock. Spring position is lowered so you can see it.
pic 3: same as pic 2, but bump spring now located at top of the shock shaft, supported by an o-ring. No effect on daily ride with this much clearance.
pic 4: current inventory of bump stop packers, ready for next event
pic 5: bump spring with packers in place. spring is now active and ready for AX.
