Why different rubber for backhand?

A lot of it depends on style.  Some people like a faster rubber with a harder sponge  on the FH side  to generate speed and spin; then they use a slower rubber on the BH side for blocking and control that has a softer sponge.  Not a lot of people have super powerful BH shots and just look for control. 

FH and BH rubbers sometimes vary extremely. There are many top players who play with smooth rubber on FH and short pips-out on their BH.

Main reason: quick fast attack from FH, no need for pushes and/or superexact placement or defense there. On BH, however, they employ pips to maximize control and counter the effects of the opponent's spin - so they just quickly push or block the ball in the needed direction therefore controlling the next opponent's move or preparing their own attack.

With two smooth rubbers it could be the same reason. Or altogether different because it is very individual. Let's take myself as an example:

On FH I need some control because I am not an all-out looper/attacker, I need more preparation and my footwork is not the greatest (to quickly run to the left and execute fast precise FH topspin is usually beyond me). So my FH rubber needs to be a) good enough in the short game; b) but fast and spinny enough for the looping. You can counteract the other guy's spin easier than on BH because generally you have more time for that on FH; therefore you can allow a wider range of rubbers, and you can take them soft as well (which will help with spin and placement). Examples: 729 Cream MRS, Dawei Inspirit, Sriver FX.

On BH I need less reaction to the opponent's spin because I often quickly block or counterdrive from left - that affects the type of rubbers I am willing to put on the BH. Usually I am much more picky when choosing my BH rubbers because at least 70% of my hits are done with that side. Also I often employ fast almost-no-spin hit-thru counterattack - that means I shouldn't use thick, very soft rubbers, especially if I am using less than OFF+ blade. In addition I require a bit less of a control rating on BH because my BH technique is better than FH, therefore I can compensate for the rubber being less controllable (but usually the rubbers I use have high enough control rating anyway). Examples: JUIC Shenron, Sriver L/EL, DHS H3 42 deg 2.0

I mostly use the same rubber on both sides.

hymm wrote: The top male chinese pros use a tacky rubber on the forehand and a grippy rubber on the backhand.  The tacky rubber produces more spin than a grippy rubber and this allows more control when playing forehands close to the table.  The tackiness also slows the ball down a bit.  On the forehand this isn't a problem because on the forehand side most men have more power than needed to hit winners.  On the backhand side this isn't as true.  The backhand is a much less powerful (speedy) stroke, so a grippy rubber is used. It might also be that the mechanics of the backhand stroke lends itself more to mechanical looping vs brush looping, but I don't know enough to be able to say this conclusively.

I think you've got a point there - during FH topspin it is much easier to develop faster speed of the racket because of a) original position of the hand with respect to the ball; b) extra time allowed to execute the stroke. Therefore power is there and so it mainly matters whether the ball will be carried by the stroke at all, hence preference for tackiness. On the BH, direct mechanical contact with the ball is required (also you have less time) therefore high tackiness would only slow you down during not-so-fast topspin.

I have Tackifire on both sides.

Thanks for all your feedback. It seems like my set up is not optimal for my style. Originally a j-pen user now learning c-pen. I'm getting comfortable with forehand loop and learning to generate more speed using the big arm. As for backhand, it used to be not much, just blocking, but now I'm learning RPB and starting to hit decent loop against backspin and can attack slow balls, but can not sustain fast rallies. I hope to attack from mainly from my forehand side, but to able to attack from the backhand side, hopefully near future.

My blade is Avalox 550, Mark V AD on forehand and AVX Sterco on backhand. When I first started I had no clue and the club owner recommended Avalox 550/Mark V AD on both sides. After a while, I thought I'd try Sterco on my forehand, but I had hard time keeping the ball in and so I use it on backhand instead. Since I'm still learning I didn't want to disturb my setup so I kept it the same way, but now I'm thinking I should switch. Any opinions?