For what's it worth, between reading up on other people's setups and doing quite a bit of my own research lately, I've found that the magic # is .325" for variance in widths...I've seen other people go wider/narrower in both directions..deck to axle and vice versa...but for me that seems to be the magic #. I've gone as narrow as an 8.375 deck on 8.75" axles (Indy 159s) and it worked well I thought...I've not gone past .25" in the other direction but I've seen others do it with success...so .325" seems to be it....