Tom Z.

Hi. I have a 29" Schwinn Traxion mountain bike, and I'd like to upgrade the crank assembly. It looks like that might mean changing the bottom bracket also.


Does anyone knows what size and type of bottom bracket is on this bike? The crank looks like a BMX three piece. (To my uneducated eye.) Or what crankset would fit, for a 42 tooth 3 gears on the front (for 24 gears)? I don't mind replacing the bottom bracket, if I know what fits, and what tools I need.


I don't know what matches up with what, and the blind investment in tools starts to make this look like a bike shop job. Any advice would be appreciated!


Thanks!

veganbikes

I wouldn't put a dime into that bike, save up the money towards a bike that suits your needs better. If something is broken more will likely be to come and you can go down to your local shop and they will likely tell you to save up towards a decent bike and if you want full suspension you are probably at minimum going to spend $2k.

If you are just starting out I would look at a hardtail with a good air fork at the front if you are mountain biking, if you aren't mountain biking a hybrid will get you in the door at a much lower cost and while the quality at the $600 point isn't great at all it will be miles ahead in certain areas than a Schwinn, Huffy, Magma, or similar bike. They will have frame sizing and some slightly better parts in some areas and will be properly built by a bike shop with support from that brand in the shop should something go awry.

Please understand Schwinn is an old name that existed in the past as quality but they stopped making quality bikes a long time ago after being bought out and their quality has significantly declined. Yes it is designed to look kind of like an old 90s full suspension bike but the parts on it are far from any mark of quality or care put into selection and like most of those bikes you will see a sticker (or should) that says something to the effect of do not ride this bike off road or use it for mountain biking or some such wording. Be careful stay safe and wear your helmet and again save your money towards a bike that will suit you better.

Tom Z.

With all due respect, that wasn't an answer to my question. Instead, it was a multi-paragraph opinion piece on what YOU would do. Which isn't necessarily incorrect, but I needn't justify my reasons for why I want to do it, wrong or not.

If anyone has direct knowledge of the the subject of my questions, I would greatly appreciate the information. If not, please have the good grace to keep your opinions to yourself, and allow others to ask questions and look for knowledgeable information about whatever they may wish.

Best regards.

Arrowana

Your bike has a BSA threaded bottom bracket. Most likely a 68mm shell, but it could be 73mm. Measure the part of the frame that the bottom bracket threads into, and if you get a measurement of 68mm or 73mm, you have your answer. If you get another number, you are probably measuring the wrong part. Most cranksets that would come with a 42t large chainring should fit, unless it has an oversized BB30 spindle. Which bottom bracket you get will depend on the crankset you grab. To do the swap, you will need a crank puller, the correct bottom bracket tools for your current bottom bracket, plus the correct tools to install whatever bottom bracket you are swapping in. The forum won't let you post pictures yet, but if you take some pictures of your bottom bracket and upload them to an album on your profile we might be able to tell you which tools would be needed to remove it.

Trakhak

Looks like a pretty nice bike. The frame's bottom bracket is likely 73 mm wide. The crank is probably what's referred to in the BMX world as the three-piece type. (Guessing, obviously. Looked it up on the Schwinn website, but there seems to be no specific spec info on the Traxion's crank and bottom bracket there.)

Then I looked at comments on the Amazon page for the bike. (68% five-star ratings, so most people seem to be happy with the bike.) Look at the 3-star and lower reviews for feedback from people who encountered problems, because that's where details about the parts get reported. There was one mention of a pedal pulling out, stripping the crank threads - likely happened because the pedal hadn't been tightened enough during assembly - and another about the bottom bracket bearing assembly making noise/falling apart.

The person with the BB problem contacted Schwinn and was sent a replacement bottom bracket. (The wrong one, it turned out.)

The takeaway from that is that you can contact Schwinn and ask your questions about parts compatibility for your Traxion. That guy having been sent the wrong cartridge bottom bracket is irrelevant - what you want are part numbers and - if available - dimensions.

Or else you can bring your Traxion to a bike shop and ask your questions about compatibility. (Maybe think of some tools, tubes, gloves, etc., that you can spend ten or twenty bucks on while you're there as a thank you for providing the specs you're looking for.)

By the way, here's some advice from an ex-bike store manager:

Might be worth considering spending the money to get the bike tuned up, too. One big (and underappreciated) advantage to buying bikes from bike shops is that you get a free tuneup, which can be crucial for the bike's dependability. Parts seat themselves onto other parts, for example, and need to be snugged up to avoid premature wear and failure. You already (probably) saved a bunch of money by buying the Traxion at a big-box store or from Amazon or the equivalent. So it's worth thinking about spending some of what you saved on a tuneup. (February is pretty slow in bike shops, so it's a good time for it.)

(Chances are you won't run into the bike shop guy who delivered his usual knee-jerk "your bike is worthless" diatribe earlier in this thread. Most bike store employees are at least somewhat more circumspect in rendering their opinions.)

veganbikes

Trying to give good advice...no good deed goes unpunished. I didn't stop you from asking your question nor did I end your pursuit for information as you are claiming. Because this is a public online forum people are allowed to have discussions that is the whole point of the forum that is why many of us have joined (some prefer to use this as a more complicated search engine).

If you don't like what I have said you can move on as well or ignore it, it is your money and if you want to spend it on something not worth the time or effort for some reason that is your prerogative but not having info on it which is why a lot of people will buy full suspension objects from big box stores and online retailers who are not bike shops. Then they find all the of the issues as they go to ride it and want to start dumping money towards it instead of cutting their loses and getting the bike that makes sense for their riding. If you want to put money towards it again your money you do you I simply provided useful info about the item and items like it. Some people just want to replace something just to replace it and in a context like this I cannot in good conscience recommend that hence my post.

I have known enough people who start off wanting the money pit and then they lower deeper and try to climb out angrily as if you did something wrong even though in the cases I am thinking of everyone had the cost already and knew what was going to happen and already approved it.

grumpus

But you can hear the disappointment when they say "So you bought one of those?" I don't think he actually said "worthless", just not worth spending money on an upgrade. It's a $600 full-bounce Amazon special, not great for on- or off-road riding, probably fine for fire roads but heavy and not the best handling machine. A couple of my bikes started out the same sort of level, but hardtails that I've put rigid forks and better parts on (mostly cheap used eBay stuff) so lighter and better handling, nicer to ride. The usual "you'd do better to buy a good used bike than one of those" advice is fine if you're an experienced mechanic, but not so helpful for the average entry-level bike buyer.
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veganbikes

I didn't say worthless at all, in fact if you read my post you could see what I wrote Trakhak Maybe you aren't good at reading or just dislike me for some silly reason because you dislike honesty or something else silly. I don't know.

I stated you should not put money towards the bike and explained what the bike was and what the brand means but never said worthless or was exceptionally negative in fact I gave useful advice for starting out. I know I didn't faun over the bike as you did Trak but that doesn't mean what you thought it meant in that I somehow said something I didn't say.


There will always be bottom feeders I guess and if that is your thing, that is your thing. However the problem is you think that nobody should ever dare provide a useful opinion coming from experience and anything that isn't positive towards the bike must be extreme negativity automatically which simply isn't true and you should know that. Plus you should note that this is an online forum and not real life I don't change my honesty in real life but it is actual talking and not text on page so there is emotion and facial expressions which you miss.

andrewclaus

The issue of chainline hasn't been mentioned yet. When you replace a crank or BB, or both, you need to reproduce the existing distance from the centerline of the bike to the crank cogs. See Sheldon Brown for standards. (If you miss by enough, the front derailleur won't shift its full range.) Putting a new or different crank on an existing BB is especially hard, and often requires several tries to get it right. That can be expensive if you don't have a bin of parts to pick from.

Duragrouch

To original poster (OP):

Your bike most probably has a "square taper" (most probably JIS, Japanese Industrial Standard, I think that is the most common taper) bottom bracket, either individual parts (axle, bearings, cups), or is a "cartridge". Either one requires special tools to remove or replace, though not terribly expensive ones. Does the bottom bracket axle feel at all loose (moving the crank arms laterally, or trying to spin and move the spindle alone)? If so, it should be replaced. If not, you may be able to leave in place.

If you are replacing the crank with a *similar* one (i.e., single chainring for single chainring, three chainrings ("triple") for another triple), you can probably use the same bottom bracket length. If a change in that, you may need a different length bottom bracket. "Chainline" matters, that being how far the middle of the chainring(s) is from the center of the bike, to have best average of chain alignment with the gears (cogs) on the back wheel. But most square taper triples, doubles, will be similar chainline.

If going to larger or smaller chainrings, you may need to adjust the height of the front derailleur on the frame.

You can find low cost cranks on Amazon, if you know what you are looking for, how many teeth on the chainring(s), and whether you want steel or aluminum chainrings, etc. Read reviews before ordering parts, those are often helpful.

Another issue with cranks is "Q-factor", this is how far the pedals are apart laterally; Generally, "road" cranks have straighter crank arms and a lower Q-factor, mountain cranks have more bent arms and a wider Q-factor for the crank arms to clear the frame tubes (chainstays).

Going to bigger crank gears (chainrings) means you may need a longer chain. Smaller chainrings may need to shorten the chain.

If you need to replace the bottom bracket if loose, it's still quite easy to get a replacement cartridge (square taper), however you may want to consider a different system; I converted to a "hollowtech II" style crank (copy of originally a shimano design); The bottom bracket axle is hollow, strong and light, and as a unit with the right crank arm. The bearings, instead of inside the bottom bracket shell (tube), are "external", closer to the crank arms, and thus larger and more durable. I have NOT seen this design in a triple crank, only doubles and singles.