Bicycle Mechanics - Disk Brake Help

On my bike ( Giant Boudler SE 07 ) I cant get disk brakes on the back, because there are no disk brake tabs on the frame, but I can get disk brakes on the front fork. So is it worth it to just have front disk brakes? Is just having front disk brakes going to be good?

Your front brake gives you the most effective braking of the two. Though roughly 60% of your weight is supported by the rear wheel and therefore it would seem to have the edge, as you brake and the bike slows down your body weight is shifted forward increasing weight on the front. And the rear wheel tends to lift when braking making it even less effective. So to directly answer your question if you can only have one disc brake, the front is where you will get the most benefit. And IMO the type of biking you do may make it more or less of a benefit. Of course using them in combination is necessary for maximum braking control and there are times when in a panic you can over use the front brake and become airborne, I've done that and even though there is a momentary thrill of weightlessness you get over the euphoria quickly. Used properly in conjuction with the rear brakes, front disks are good. And I believe there may be some sort of way to fit disks on the rear without the standard mounting boss. I'm sure someone will chime in if that's the case.

Are you having a problem with the front brake? If not why replace it?
If you ride in the wet a bunch, do long downhills with lots of braking, or remove the front wheel a bunch and have a hard time releasing the rims brakes, then a disk brake is worth it.

There are some kits that allow a rear brake on a bike without tabs. They usually require a special hub that has a carrier built into it and a torque arm going up to the brake boss. $$

If you want to make an upgrade to your Boulder that will be a good investment, buy a freehub/cassette rear wheel. The Boulder SE comes with a freewheel hub and this is the only weak point on the bike. If you ride it offroad and weight more than a hundred pounds, you will bend or break the axle. The freehub wheel is a worthy upgrade.

By the time you replace the back wheel for a freehub style and do the front to get disc brakes if you add up the costs you'll find that you're better off to just sell the Boulder and buy a slightly upscale model that comes with discs.

I'm all for minor upgrades but when you start doing the big stuff like this it's best to just stop and admit that you've got the wrong bike and it's time for an overall upgrade. Otherwise you end up with an investment that would have gotten you a model or two upscale and it's still "just" a Boulder and you won't get your money back later. Bin 'dere, got the shirt...... It cost me mucho bucks.

Thanks for your advice. So yeah I think im going to get some front disk brakes. Do you know the differnece betwene bb5's and bb7's. Should I kick in the extra 15$ or wat ev it is?

So how much would that cost to get the thing that would let me have a rear disk brake?

if you are doing the adjusting yourself, get the BB7's. They are incredibly easy to adjust as the pads wear.