Little play on front disc, Normal?
 

I have got this like new Trek 4300 recently. I noticed if you hold the front brakes tightly and try to move the bike forward and backward, there is a little bit of play. It seems like the rotor holds firm but the rim moves a little bit. I removed the front tire and checked the rotor but it appears to be firmly attached to the center with no play. I would say the rim moves about 5mm each way( at the tire end) is this normal?

Sure it's not the headset?

It's not the headset. If I put the bike on a stand, hold the brake with one hand and try to move the tire with the other I see the play. I dont see the rotor move but the rim moves. I inspected the pads which has a little bit of play which I assume is normal.

Ok, looking closely I can see the rotor moves too, seems like the play is from the pads...

the rotor shouldn't be rotating on the hub but a little play in the brake pads is sometimes normal. if your bike came with a front suspension fork i would also check to see if there is any play in the fork. many times a brand new bike will have a bit of play between the upper and lower tubes which is also sometimes normal.

Do you have centerlock rotors?

I have the same play in my brakes (it makes it tough to tell whether your headset is preloaded enough). I have some concerns that the splines will wear in the disc and on the hub because of the play, but I'm not convinced. I considered using tephlon tape to make the fit tighter.

I would not be concerned with A LITTLE (1-2 mm) play between the rotor and hub. This is showing up by rocking the wheel back and forth with the brakes locked - in what riding circumstances would one do this rocking (other than a trackstand) ? When riding and using the brakes, the rotation is all in the same direction and thus the disc will bear against the splines in that same direction- that is why I would not be concerned with splines wearing.

By the way, I never use locking the brakes to test headset preload as any play in the brakes will confuse, as you have duly noted. What I do is lock the wheel between my feet and knees, standing at the front of the bike.

I took the bike to the shop today. After removing the tire and inspection the guy was convinced the play is not from the rotor being loose to the hub. He thinks the play is from the pads. I considered changing the whole caliper setup with a different brand (it is shimano) to get rid of it but the guy says there is nothing to be worried about and I should leave it as is.....