can i use bigger rotors?

More info would have helped. I had to Google Gary Fischer Cobia to find out that it has a RockShox Tora Race Solo Air 29 fork on it then I had to Google that to find out that the maximum recommended rotor size is 210mm.

Having said all that, there is no reason that you can't do it nor any reason that you shouldn't do it. The 203mm front rotor will give you a lot more braking power but it may be overkill, depending on your weight.

thanks, pcc! yeah, i didn't know it went by the fork- if i knew that i would have given more specs. i'm 240+ so i can use the extra breaking power thanks, man!

one more quick question. would it be worth my while to go 203mm front and rear? is the only reason not to because of overkill? thanks again, guys!

It's your call. I'd try 203/185 but going with 203/203 costs the same and will give you more power on the rear brake. Also, going with a 203 in the rear will increase the possibility of the rear wheel locking up when you don't want it to due to the massive stopping power available.

thanks, pcc! i see your point- i'll probably go with both 203s. i'm a bigger guy so it definitely won't hurt. thanks again!