Hi -- with a 26" wheel I am using a 1" roller -- not that great in math -- how does that work out with a 20" wheel -- just a guess --- maybe a 3/4 in. ?? More speed with a 7/8 --- my top speed 23 mph --- my engine 35cc --- my weight 195 lbs.. Happy Riding from - Mountainman
Think of something in a steel roller. Knurled steel works best but that may be a problem unless you have a lathe laying around. One member took his smooth roller and coated it with J. B. Weld mixed with sand. Might do a search and PM him.