Bottom bracket replacement on rockhopper 2005 model
 

Hello all. I'm fairly new to bike maintenance so looking for help. I have been reading / youtubing quite a bit but haven't been able to find the answer to the following question:

Can a 2005 Rockhopper frame handle a BB30 / PF30 bottom bracket?

Background:
I purchased this 2005 rockhopper and added a 11/36 10-speed cassette to it. I am having issues with the chain tension when switching to the two LARGEST or two SMALLEST sprockets. I wanted to switch the front crankset to a 2-sprocket setup anyway so I figured now would be a good time to do it - and hopefully it would solve my chain tension issues.

I am able to get one of these at a very reasonable price:
SRAM X7 2X10 GXP Crankset
It comes with a bottom bracket that says "BB30 / PF-30"

The specs I found for the 2005 rockhopper are:
CRANKSET
Truvativ 5-D, forged alloy, capless bolts
CHAINRINGS
42t Cr-Mo x 32t heat-treated Cr-Mo x 22t heat-treated Cr-Mo, replaceable
BOTTOM BRACKET
Truvativ, 68x118mm, square taper, sealed cartridge bearing with double crank stops
PEDALS
Alloy body, alloy cage, toe clips and straps

So, can it be done? Or am I stuck with using "Square-Taper" bottom brackets?

You're not stuck with square taper, but you're stuck with one of the many types of bottom bracket that'll install into an English-threaded 68 mm bottom bracket shell. Press-fit bottom bracket types like BB30 and PF30 will not fit your bike.

So there are no adapters or anything that will allow BB30 or PF30?

Why do you want to drink the Kool Aid?

huh? Not sure what you mean.

Unless you want to hire some custom frame builder to cut away the BB Shell and weld in another one,

Screw in an external Bearing set and buy the crank that goes with it .. thats almost as bad..

OR Go Buy A New Bike..

Ok, so back to my original problem with the chain tension. Am I able to replace the chainrings on the existing crankset that I have - rather than replace the whole thing? Is it possible to switch it to a two-gear setup instead 3?

One of the problems I notices with the chain tension was that angle between the large chainring on the front - to the large ring on the rear became magnified because of how far the rear derailleur cage was pulled forward. So I was hoping that a two-ring setup with the chainrings more centered up front might help the issue.

There are adapters to go the other way, fitting threaded bottom brackets to BB30/PF30 frames, but you can't physically fit a BB30/PF30 bottom bracket and crankset to an English-threaded bottom bracket shell. They're both 68 mm wide, but BB30/PF30 requires larger bearings than you can fit into a threaded bottom bracket shell. And you can't mount bearings outboard, or the shell plus bearings would be too wide for the spindle of a BB30 crankset.

There are LOTS of bottom bracket and crankset choices for English-threaded bottom bracket shells, though. It's been the most common standard for decades, only losing market share to other bottom bracket types in the last few years.

If the problem with chain tension started happening when you replaced the cassette, it's possible you installed a cassette that exceeds the take-up capacity of your rear derailleur. You need your chain to be a certain length to reach your big chainring + big cog combo. When you shift to the small+small combo, there's going to be slack in the chain, which is taken up by the derailleur cage swinging back. The greater the gearing differential between the big+big combo and small+small combo, the bigger the difference in required chain length, the more slack there'll be in the small+small combo, and the longer the derailleur's cage needs to be.

If that's the case, the easiest fix is to swap your rear derailleur for one with a longer cage. Without knowing specifically what derailleur you're using, I can't give you more specific advice. The other easy fix is to replace your cassette with one that doesn't exceed your derailleur's wrap capacity. Replacing your crankset or chainrings could fix your "chain tension problem" by reducing the difference between your big+big and small+small combos, but there are a lot more variables and potentially more expense involved: crankset, chainrings, and/or shifters, even. And you'll possibly lose some gear range, too.

If you're still interested in swapping chinrings, the answer to your question about whether it's possible is "possibly". It depends on what kind of crankset you currently have. Most better cranksets have chainrings that can be unbolted. Lower-end ones have non-replaceable chainrings. If your chainrings are removable, you can certainly remove one and/or replace them. If you go to a double, whether by going to a new crankset or removing a ring, you may have front shifter & derailleur considerations to take into account.

Oh, and going back to chain length and derailleur capacity for a moment... You mentioned the derailleur being pulled so far forward. Did you swap your chain for a longer one when you installed a bigger cassette? Your current one might be shorter than ideal.

Square taper BB's have done a great job for decades. Many of these so called "upgrades" are more problematic than what you currently have.

Which model Rockhopper do you have? There are 4 versions listed here-
BikePedia

Your current ring & cogs require a RDER with a 45T chain wrap capacity. Without knowing what RDER you have (why I ask which model and assuming it's the original RDER) I am VERY suspect your RDER has more than 43T if that.
Sizing a chain to safely fit on Big:Big is probably going to result in noticeable chain sag when on Low:Low.

Did you change the shifters when you put on your 10 speed cassette? 8 speed shifters AREN'T going to work with a 10 speed cassette.

EDIT- Is this your RDER?
http://www.disraeligears.co.uk/Site/...39_SGS%29.html

IF it is, you only have a 38T chain wrap capacity.

Just as a FYI, that crankset, SRAM X7 2x10 GXP Crankset 2011, does not use a BB30 / PF30 bottom bracket.
Not sure why you think it comes with one.
Page says External GXP bottom bracket with Gutter Seal Technology. That should fit your Rockhopper.
A GXP crank cannot use a BB30 or PF30 BB without adapters.

There's no way to say this gently: that gear combination is a bad idea and all the advice offered in response just makes it worse. You have a gear selection problem, not a chain tension problem. Your bike has multiple gears just so you can avoid big-big and small-small.

I did swap a new derailleur: Shimano Deore M615 Shadow Plus Rear Der
as well as a new 10-speed shifter and 10-speed chain. When trying to size the chain, it would either be too tight for the large cogs or too slack for the small ones. I tried a couple of different lengths in the process and probably need to get a new chain now because some of the chainlinks are a bit tight now from the adding/removing of links - but that is a seperate problem.

As fat as the BB30 bottom bracket, I was not planning to purchase the one in the link, I am able to get almost new cranks (exact same model) with a different bottom bracket for $50 - hence the interest in using them. Attached is a pic of it:

I do realize that I can use other gears but the bike is actually for one of my kids so I can't be assured they won't use those combinations and if they try the large/large cog combo, I think it might damage the rear derailleur.

Maybe I can just adjust the front derailleur so that it is limited to two cogs instead of three? I'll hve to try it out.

I think the bike has the original crankset:Truvativ 5-D, forged alloy, capless bolts

How do you tell if they are removable?

You learn what a Typical chainring bolt set looks like. google will help.

As I mentioned, you have exceeded the chain wrap capacity of that RDER!
It has a capacity of 43T.
Your gearing needs a wrap of 45T.
(50-30) + 36-11) = 45

Until you get that through your skull........

ouch! I get it, though still not sure exactly why you used the "50-30" numbers. My front chainrings are 42 / 32 / 22. So wouldn't I use (42-22) + (36-11)? I know it still comes out to the same number but just curious. And just to be sure, the new cranks I want are 39 / 26 so: (39-26) + (36-11) =38. So I would be safe with my current RDER - correct?

I want to thank everyone who has respoonded - this has been both very helpful and informative. I have a few more questions, if anyone is still trudging through this thread :)

Can you guys give me some reccomendations on what type of BB will fit my bike AND those sram x7 cranks I linked in the 1st post?

Also, I'm mostly interested in durability / longevity for the bike so any reccomendations on a brand / model of BB would be appreciated. The budget would be ~$40.

Would I need any extra tools? I have standard garage tools bpus this set: Nashbar Essential Tool Kit

Thanks again

That rear mech is set up to run a single ring up front, why not go that route? Then you don't have to worry about cross chaining, lose a little weight and complexity and it looks good.

You want a ring that looks like this, note how the teeth are cut.

http://img1.qbp.com/6SPsvm45/p350x350m/CR5245-02.jpg

I Guess I had the BB 30 in my mind, but you are correct that it's the same chain wrap.
Reducing your chain wrap by 2T will get in in the range of the RDER. Going to the 39-26 will give you a little extra margin to play with, without having to size your chain "EXACTLY" right. (consider that sometimes you are stuck with the odd 1/2-3/4" extra length because things just work out that way)
There have been 24-34-42T triples manufactured, but trying to find one WHEN you need it....

This is what you need

Sram/Truvativ Team GXP Bottom Bracket > Components > Drivetrain, Brakes and Pedals > Bottom Brackets | Jenson USA

To the crank you linked to or the crank you said you are buying?
A 30mm spindle crank cannot be used on your Rockhopper. The linked crank will work with a GXP BB like the one ColonelSanders shows.

Just do this. Your kid doesn't need 30 speeds, I promise. You can do this by turning in the high limit screw on the front derailer.

Or put a less radical cassette on there. Your kid surely doesn't need a 22/36 combo either.

The more I think about it, the more I am leaning this way. I considered the 1x sprocket on the front (suggested by Frank Cannon) but there is a decent amount of road riding with this bike and I don't think 1x would provide big enough gears.

So I saw the link from ColonelSanders (thanks!) which brings up another question on crank / BB compatibility:

Was looking at BB's and saw this: Shimano XT-SLX BB70 Hollowtech II Bottom Bracket
I *think* this will fit in my bike - PLEASE confirm someone..
but it doesn't look like those SRAM crank arms will fit - correct?

Just trying to look up info and it llooks like SRAM cranks / BB's are incompatible with Shimano? I'm not necessarily trying to solve this Rockhopper issue at the moment just trying to learn and figure out what my options are - I have a couple other bikes that may need fixing up :)

Well all the bikes stores who sell these bottom brackets say when questioned, that you can't use a GXP bottom bracket on a Shimano crank and you can't use a Shimano BSA bottom bracket(which the BB70 Hollowtech II bottom bracket is an example of) with SRAM cranks.

Correct - Shimano BB's will not work with GXP cranks - or other way around.
Trail Tire TV: Sram's GXP Bottom Bracket, how it differs from others