I'm thinking about upgrading my shifters and rear deraileurs on my bike. Right now I have a Shimano Alivio rear deraileur, and cheap Shimano brake/shifter combo's. If I put on Deore components will it make a big enough difference to make it worth the $$$.
Good luck with that, IMO that would cost more then its worth but again that's just my opinion. Your only going up one level by going from alivio to deore. I bet properly tuned Alivio setup can be just as good as a deore setup.
That money would be better spent saving for new bike or upgrading something better like the wheelset, maybe better brakes(go to disc if still V), maybe a better shock or even a new crankset/BB.
Or hell just save for repairs. I know I can't get more then 500-700 miles out of my chain and chainrings.
It won't be the money best spent, in my opinion. I have both Alivio and Deore rear mechs on my 2 bikes and can't feel any difference in shifting. Alivio is more massive and heavy, but, from my experience, lasts longer than Deore. Same stands for combo shifters. By the way, shifters, for all I know, are sold in pairs only, right and left one together, which adds to the expense. Replacing cables/housings with new ones will probably give you more improvement for fraction of the cost. Also, if you are experiencing problems with shifting, it would be a good idea to check/straighten the derailleur hanger. You may combine this with some other repairs/purchases at your LBS, so you may even get the work done for free or almost for free, as it takes just couple of minutes. It is possible to do at home as well, but hard to match precision of the device a good LBS keeps for this purpose.
Well, with cheaper bikes, the most glaring issue is that the crank and chainrings are riveted together. This is nigh on worthless, as you can't replace bent chainrings without doing the whole shebang. Usually these setups use BMX style bottom brackets as well.
A more expensive crankset is going to give you more strength per gram of weight (critical as you want your rotating mass as small as possible, but you also want really strong cranks), closer tolerances and just plain better metal. There are a few different BB -> crank interface standards; I'm currently stuck on square taper yet but the cool kids tell me that Isis format cranks and BB are the industry standard.
I run Shimano FC-440 cranksets on my bikes; they're like 40 bucks, are square taper, and come with three chainrings (of which I always remove two) and are standard 104/64mm bolt interface, so that I can easily swap bash rings and chainrings. I'm sure they're not top notch or anything, but I'm Mr. Budget Cyclist, and they are miles beyond the riveted crap that came on my old bikes and feel great; my oldest set is around 800 miles and is as good as new, for what it's worth.
Going from an Alivio to a LX drivetrain is certainly an improvement.... The Alivio is a borderline commuter derailleur.
If your riding consists of mainly groomed multi-use trails and parks, the Alivio & square taper crankset/bottom bracket is fine. If you don't charge hills or rabidly bomb descents, roll with what you've got.
But once your riding steps up, you'll be replacing that OEM drivetrain soon enough. More than likely, if your bike already comes with a square-taper crankset, it'll be hard to find the right ISIS bottom-bracket and cranks. Most square-taper BB shells are pretty small, and standard ISIS bottom-brackets needs be larger due to the different style bearings contained in them. You may have better luck finding an outboard bearing BB.
So go ahead and replace the Alivio with at least a SRAM X7 or ShimanoLX derailleur, along with the matching shifters, cassette & chain. Find quality replacement chainrings to swap out your old crappy ones with. The difference will be quite noticable.
ISIS bottom bracket - notice the 10 spline design, meant to distribute the torque from the cranks over more surface area
Now a 'square taper' bottom bracket. These are the old standard, the shaft is not a perfect square; there is a 2 degree taper from the beginning to the end of the crank mount. This can cause some really stuck-on cranks, as well as tough-to-fix loose crank issues when the taper starts to wear down a bit, but they are more inexpensive.
As for what fits on your bike, I can't dig up a 4300 spec sheet offhand, but I'm sure you can find the bottom bracket dimensions for your bike (most likely, either 68 or 73mm). From that you've got your selection of bottom brackets.
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