I'm wanting to buy some sinister wheels for my street bob wondering what size to get. I'm going to go up one inch in the back 18 (stock 17). My two choices for the front are 18" and 21"(stock 19). What would be better in your all's opinion for handling? I'm think the 18.

 

21X3.5 and 18X5.5 looks pretty sweet on a street bob.

 

if you go 18 in. on front, it will fit fine but will have an extra 1/2 in. of fender gap. if you go 21 in. you will need to get fender adapters to lift it to the proper position. me, i would go 21 and move fender.

 

Formula 1 runs 13"
A lot of the GT3 cars run 18"

When's the last time you saw a sport bike with a 21"?

Food for thought...

 

18x5.5 and 21x3.5 here and no need to move the fender at all, its close but doesn't touch

 

That looks good, I'll have a tough time deciding which I end up with.

 

This right here should answer your question in regards to what would handle better...

 

True enough.

 

Loving that 21x3.5, looks real good.

 

Just to throw in here...16's front and back... handles great.