MikeSSS wrote:What is soft gum?
Rubber, nylon of any other plastics, are measured for hardness and this "gum" density has a number and a letter. 60A is the most common tire gum for bicycles, and the type of gum is usually written (small) on the sidewall as Nylon, Latex, etc... Tires are made as soft as 40, from 50 down it is called soft gum and it is wearing much faster. 60 and up is called hard gum. Some tires are made with hard gum with the sole and knobs in soft gum, called double compound. You can also see some triple compound on highly specialized tires. The softer the gum, the better the traction and adherence, and the shorter the life expectancy.
Liquid in a tire does slow it down, especially in both acceleration and braking. That is why adding slime is not good for performance. If you do, it should be little of it. 4 Oz is a good compromise in a +2 in. tire, enough to stop a leak but not too much performance loss.
MikeSSS wrote:...details about them and tell us how they ride.
My bikes are specific builds. The street bike is very fast, above 70 Mph and beats any other vehicle on the city streets in handling, braking and acceleration. It is low and very sticky to the pavement. Don't be fooled by the high front on the picture, the fork is set to sag half of its travel when I am on the bike. It does handle its top speed so comfortably that it could be doubled and it is common for me to leave the handlebar and coast at 35 Mph. It is built on a Session 10 frame.
The dirt bike is much slower, higher, heavier. It does ride very fast for a single track MTB trail though. It is jump-able up to 3ft and I find it is its only downside for I would like higher. Mid drives can jump better, but can't keep up with my speed in the mountain. It is very robust, usually crashes without any damage. It is built on a Santa Cruz V 10 Mk 1 frame.