I have just discovered that Avon make 21" Speedmaster tyres for the front wheel. Has anyone tried them? I was going to buy a 21" Roadrider but now I have to make the choice. I have a RoadRider on the rear.
I have a 21" Speedmaster on my 1933 500 TTR Rudge and a 21" race compound RoadRider on my 1938 500 Rudge Special race bike. For looks, especially for the TTR, I think the Speedmaster is best, but having said that I will probably replace it with a RoadRider when I change the rear 19" Dunlop to a RoadRider.
In my opinion the ribbed tyres are fine until they encounter road surface imperfections that are just off of the tyre centre line and then they tend to be drawn towards it, so grooves, where they are preparing the road for resurfacing, or tar over banding on the edge of repair patches, are always interesting, as in the days when narrow wheels dropped into tramlines.