I'm coming from a pair of SST 6 that are about 7 years old, and I just got a new pair of Tour Ultras, and love how they fit, but there is a point I do have to make...
When I was starting with them, I put in the 6 sole, and took a couple of shots. What I found, I hope I can find an answer for.
The actual leather that surrounds the sole you put in (That's the best way I can describe it) is very slippery, and caused my foot to slip a little as I walked. I could see that being problematic if I was using something like a 4 and the sole surrounding it is like a 10.
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Assuming you have a wire brush, brush just that area, lightly, to roughen it up. It will make it more like the #6.
I have the opposite problem, I use the insert sole.The sole material surrounds the inserts and it is stickier than the inserts I use. I have to allow some dirt and dust from the floor to accumulate to make it closer to the insert's level of friction.
"None are so blind as those who will not see."