Putting Bmx Cranks On A Trials Bike

[rupintart]

I spaced my rear cog by putting the wheel on, using no cassette spacers, then backpedalling it till it stopped moving.

After it floated to it's position, I added the spacers, and job done.

I can't say the same for BMX cranks. Not to mention most BMX cranks just hammer on and hammer off, kind of archaic.

Who hammers on BMX cranks? They all use pinch bolts to pull the crank arm onto the spindle. To take them off, you need the tool that you do have to hammer (it basically just pushes the crankarm off the axle) to get it off.

You do it the same way with BMX cranks, except you have the ability to space them out closer or farther to the bike for both clearance and chain line. I think it's coincidence that the 5.75in axle fits PERFECTLY with the amount of spacers I had to put on my BB and it just clearing the yoke.

So as you can see, if I didn't have those spacers, the axle would be too long and the crank arms could shift around. And if the axle were the shorter one, the cranks wouldn't clear the yoke. And if I were to put those spacers on the short axle, there wouldn't be 100% spline interface.

Also, as you can see, it gives you pretty much infinite adjustability for my chainline.

[Borgschulze]

Most every BMX has to have the spindle hammered into the BB, and the spindle hammered out to get the crank arm off.

Your weight argument still fails though?

What BMX cranks are lighter than what trials cranks?

Edited February 10, 2010 by Borgschulze

[Sponge]

Semi-hijacking, but somewhat relevant to anyone wishing to use BMX cranks:

I'm curious... Do you know of any sure-fire method that's fairly simple that allows you to have a perfectly even crank interface on the spindle? That is to say, since BMX spindles float, is there any way aside from trial-and-error to get perfectly even interface on both sides?

[Mark W]

The reason most BMX cranks break is 1 of two things:

1. They're OLD. Meaning can you realistically expect a set of cranks that are 5+ years old, that have surface rust from them being grinded on daily, and them being used for dirt jumps, really expect to hold up much longer? I don't really ride ANYTHING hat's more than 5 years old, lifetime warranty or not, even if it looks to be in good shape. You know what they've been through and how you ride. be smart in knowing that things fail. Just because your chain works and looks fine, would you continue riding on it after 1 year of daily use? No, you'd be a little more smart about it and replace it before it injures you. Too bad most people are too cheap when it comes to the same kind of thinking when it's over $10 and just a chain.

2. They're not installed correctly. Most people ride them loose, or don't properly prep the surfaces (loctite or grease) and it results in failure.

Haha, what? Almost all the first version of Fly cranks broke because of the way they wrapped the pedal boss at the end of their flat plate on their crank arm. They rectified that for the V2. A fairly large amount of Odyssey Wombolt cranks broke because the boss where the wedge cluster fits in was made too thin so it broke pretty easily, in that it split around the end of the arm. They said that that was installation error, but that's a load of bollocks. They thickened that up for the V2 anyway. Shadow's cranks broke in a very similar way to Fly's cranks because they shared a very similar design. KHE's Hindenbergs broke because where they'd fixed the axle, they did a shit job of it. Most of the DK cranks I've seen broken seemed to generally go nearer the spindle boss, but a few did seem to peel off their pedal bosses. The only cranks that really are pretty bombproof are the Primos, and they're slightly prone to cracking where the pinchbolts are just from the aluminium getting warped when they're overtightened.

Most 'new' cranks from the past few years have all broken because the designs have been generally pretty wank, and have been made to have them very light. I don't really get how so many companies managed to produce so many cranks that were so bad, but I guess the race to try and beat competitors had a part in it. Regardless, I'd massively disagree with that part of your post. Oh, and 'riding them loose' won't 'break' them, it'll just mean that they'll develop wobble faster if you're riding non-pinch bolt cranks.

When I was talking about spline interface, yes, I was talking about nearly bottoming out the crankbolts on the spindle. The only way you can do that, is the crank arm is COMPLETELY on the axle. With the axle being able to "float" back and forth between both arms, most people don't have the axle centered on both arms, let alone interfacing 100% with the crank arm. Most of the time, the spindle for the application is too short (usually due to spacing), and like only 30-50% of the axle is interfacing with the crankarm and usually interfacing more on one side than the other. i.e. they didn't take the time to even it out when installing it.

If you've ever rode on 3 piece BMX cranks, you'd know exactly what I was talking about. The axle isn't stationary like it is on a mtb, once the bearings are in, you can slide the axle back and forth.

For your information, I have "ridden on 3 piece BMX cranks" in that I've been riding BMX for a good few years now, and also do a fair bit of news info for a few websites and help out with stuff for Ride magazine. I'm not just some clueless trials rider, if you thought that.

Semi-hijacking, but somewhat relevant to anyone wishing to use BMX cranks:

I'm curious... Do you know of any sure-fire method that's fairly simple that allows you to have a perfectly even crank interface on the spindle? That is to say, since BMX spindles float, is there any way aside from trial-and-error to get perfectly even interface on both sides?

It's not really that hard to try and even it out in any case, it takes a few seconds to do so I don't really get why you'd need to try and find some other way of doing it? Having a slightly off-centred spindle isn't really the end of the world either - my first set of Profiles got a pretty meaty dent around the lip of the spindle boss from pedal grinds which meant that I couldn't undo the crank bolt because the edge of my flushbolts got warped into the dent on the crank arm itself. As a result of that, when I changed sprockets, BBs, etc., it meant that I couldn't even it out and my cranks have been fine. The only real issue you'd get is that they might develop wobble slightly faster, but again, if you keep them tight then you shouldn't have that problem. The spindle boss is basically the strongest part of your entire crank, so again it doesn't really get affected too much by your spindle not being evened out. I don't think I've ever seen a crank break along the spindle in a way that'd suggest that it was from that, in any case.

Who hammers on BMX cranks? They all use pinch bolts to pull the crank arm onto the spindle.

What? The pinch bolts are the single or dual bolts on the end of a pinch-bolt set of cranks that you tighten after tightening the main spindle bolt, not an installation tool.

[monkeyseemonkeydo]

What? The pinch bolts are the single or dual bolts on the end of a pinch-bolt set of cranks that you tighten after tightening the main spindle bolt, not an installation tool.

I think he meant that because they use pinchbolts, with the bolts loose in theory the tolerances should be such that the crank arm will smoothly slide onto the BB axle without too much drama... In theory.

[Mark W]

There's approx. notmuch% of BMX cranks that are worth running that currently use them though, so if you're trying to base an arguement on a very minor percentage of overall users, then, well...

[rupintart]

Most every BMX has to have the spindle hammered into the BB, and the spindle hammered out to get the crank arm off.

Your weight argument still fails though?

What BMX cranks are lighter than what trials cranks?

I have NEVER needed a hammer to install the axle into BMX bb bearings. If you loosely fit one arm onto the spindle, you have enough surface area to just push them through.

Lets also let it be clear that we're comparing a steel crankset to an AL on (the trials cranks). If you want to compare AL BMX cranks to trials cranks, you'll find that the BMX cranks in most cases ARE lighter.

But generally speaking, as for BMX cranks lighter than trials cranks, everything being FFW makes it a little harder to compare, but I pointed out the weight of burns compared to BMX cranks in an earlier post. Not really lighter, but I pointed out that the BMX cranks aren't nearly as heavy as people are making them out to be. A couple months back BrettM showed that you can build a lighter drivetrain set-up with Burns and a King, than FFW when he switched back from a FFW drivetrain. Seems a bit more fair to compare it in that regard as a drivetrain as a whole because you're able to factor in your freewheel weight, and if it's not FFW, people will say "well, I have to add in the weight of a freewheel when you don't". So as a whole, I think Brett pointed out it was something like 500-600 grams lighter going King/Burns. When I was thinking of converting from BMX cranks to Burns, I was only going to save a pound. So respectively speaking, the drivetrain as a whole, is on par if not lighter in the weight department.

As far as which I would go with, obviously I went the BMX route and decided that the weight savings of Burns wasn't worth it to me. Don't get me wrong, I would LOVE a set, but the value isn't there for me.

Same goes for going with a FFW crank that just has a fixed cog on it. The hassle of worrying about stripping out threads, and having to buy a nice BB just wasn't worth the value for me. That and it's a widely known fact that ISIS isn't nearly as stiff as a BMX or two piece crank/BB design.

Haha, what? Almost all the first version of Fly cranks broke because of the way they wrapped the pedal boss at the end of their flat plate on their crank arm. They rectified that for the V2. A fairly large amount of Odyssey Wombolt cranks broke because the boss where the wedge cluster fits in was made too thin so it broke pretty easily, in that it split around the end of the arm. They said that that was installation error, but that's a load of bollocks. They thickened that up for the V2 anyway. Shadow's cranks broke in a very similar way to Fly's cranks because they shared a very similar design. KHE's Hindenbergs broke because where they'd fixed the axle, they did a shit job of it. Most of the DK cranks I've seen broken seemed to generally go nearer the spindle boss, but a few did seem to peel off their pedal bosses. The only cranks that really are pretty bombproof are the Primos, and they're slightly prone to cracking where the pinchbolts are just from the aluminium getting warped when they're overtightened.

Most 'new' cranks from the past few years have all broken because the designs have been generally pretty wank, and have been made to have them very light. I don't really get how so many companies managed to produce so many cranks that were so bad, but I guess the race to try and beat competitors had a part in it. Regardless, I'd massively disagree with that part of your post. Oh, and 'riding them loose' won't 'break' them, it'll just mean that they'll develop wobble faster if you're riding non-pinch bolt cranks.

And look at those, those are all two piece designs that you even stated earlier are shit. Looking at all those failures, aren't all those cranks exposed to grinding and/or DJing? Not to mention the stress distro of riding a bike with small wheels and high PSI. Couple that with an unsmooth rider and you have one set of cranks that's pretty abused.

For your information, I have "ridden on 3 piece BMX cranks" in that I've been riding BMX for a good few years now, and also do a fair bit of news info for a few websites and help out with stuff for Ride magazine. I'm not just some clueless trials rider, if you thought that.

My apologies if it appeared that way. In your posts, maybe because of the way I was typing things, made it appear as if you haven't or haven't installed a set.

It's not really that hard to try and even it out in any case, it takes a few seconds to do so I don't really get why you'd need to try and find some other way of doing it? Having a slightly off-centred spindle isn't really the end of the world either - my first set of Profiles got a pretty meaty dent around the lip of the spindle boss from pedal grinds which meant that I couldn't undo the crank bolt because the edge of my flushbolts got warped into the dent on the crank arm itself. As a result of that, when I changed sprockets, BBs, etc., it meant that I couldn't even it out and my cranks have been fine. The only real issue you'd get is that they might develop wobble slightly faster, but again, if you keep them tight then you shouldn't have that problem. The spindle boss is basically the strongest part of your entire crank, so again it doesn't really get affected too much by your spindle not being evened out. I don't think I've ever seen a crank break along the spindle in a way that'd suggest that it was from that, in any case.

Look at that, you have to keep them tight. That's also the point of having them even, they're far less susceptible to loosening because of there being more load on one side than the other. And you can't tell me riding them even slightly loose doesn't put any more additional stress onto the cranks. They're now receiving yaw loads in additional to whatever they were seeing previously. Most every broken profile I've seen had a wobbley crankarm, you can't call that coincidence.

What? The pinch bolts are the single or dual bolts on the end of a pinch-bolt set of cranks that you tighten after tightening the main spindle bolt, not an installation tool.

I was referring to the only time needing the installation tool and needing a hammer to install cranks was when taking a crank arm off, or checking to see if my spindle was even.

In the end, we can go back and forth all day on whatever. The BMX cranks on my trials bike has worked out fine. I haven't had any hassles, failures or problems. And they may not work on a pure trials bike due to the crazy wide yokes, but I got it to work on my Inspired (which is a "trials bike") and have been loving it since day one. And wasn't this the point of the thread? On whether they'd fit or not? And at the end of the day, all that matters is that you're happy with your set-up, not that X set-up hasn't worked for X person. If it's worked for you, and you're enjoying it, that's all that matters right?

Edited February 10, 2010 by rupintart

[Mark W]

So as a whole, I think Brett pointed out it was something like 500-600 grams lighter going King/Burns. When I was thinking of converting from BMX cranks to Burns, I was only going to save a pound. So respectively speaking, the drivetrain as a whole, is on par if not lighter in the weight department.

Wasn't your whole point before that it was lighter, and now you're saying that they're half a kilo heavier?

And look at those, those are all two piece designs that you even stated earlier are shit. Looking at all those failures, aren't all those cranks exposed to grinding and/or DJing? Not to mention the stress distro of riding a bike with small wheels and high PSI. Couple that with an unsmooth rider and you have one set of cranks that's pretty abused.

Firstly, no, a lot of those sets weren't "exposed to grinding and/or DJing". I saw quite a few warranty sets of Wombolts and Fly cranks, and they were all in really good condition, but most manufacturers these days are trying too hard to err on the side of lightweight rather than strength. With the Fly and Shadow cranks, they're not 2-piece cranks in that the spindle is independent of the crank arms, you're simply only able to install them from one side. Effectively, they're 3-piece, but awkward. A lot of other manufacturers attempts at Profile clones haven't worked out too well - the only really successful 3-piece cranks that I've seen are the WTP Royal cranks which have a reasonably good reputation, and fairly low failure rate.

Regarding your second point, I really, really can't imagine that 'small wheels and high PSI' are going to have much impact at all on your cranks. A large amount of the force from them are going to be distributed by the tyre itself flexing slightly, the spokes flexing, the rim flexing, forks and frame flexing and so on. The impact they'd have on cranks breaking would be neligible, and that factor would also be fairly consistent throughout all BMX bikes.

So, in general, I wouldn't say it was 'small wheels/high PSI' or 'abused cranks' that are causing all these failures, it's just shit design which even the manufacturers themselves have acknowledged by releasing newer models of their previously weak cranks.

Look at that, you have to keep them tight. That's also the point of having them even, they're far less susceptible to loosening because of there being more load on one side than the other. And you can't tell me riding them even slightly loose doesn't put any more additional stress onto the cranks. They're now receiving yaw loads in additional to whatever they were seeing previously. Most every broken profile I've seen had a wobbley crankarm, you can't call that coincidence.

Your cranks would have to be amazingly loose for them to be succeptible to a yaw load - bearing in mind your weight is going to be pressing down on the cranks at all times, they don't really get much of a chance to wobble when you're actually using them, so the fact they're loose would be more likely to just slightly warp the actual splines/boss itself rather than breaking the cranks. Regarding keeping them tight, that's the same for every pair of cranks. Mine aren't especially even, yet I hardly ever have to tighten my cranks up. When they were really new, for the first ride or two they came loose but I tightened them up whenever they were loose and I haven't had to mess around with them for a while. Because I'm running a spline-drive sprocket, my setup would show up signs of looseness far sooner than people running 'normal' setups, yet I don't have any issue with that, despite not having this "100% spindle interface".

I was referring to the only time needing the installation tool and needing a hammer to install cranks was when taking a crank arm off, or checking to see if my spindle was even.

And I was refering to the fact that pinch bolts aren't an installation tool...

[eskimo]

UKBikeCo Revolution frames had a lifetime warranty,

You could of picked a better example, those were for the bin as soon as they were released

If you were interested OBM, i had full faith in my DK Socials until they got worn out. I probably used them for about a year. Good price and sensible weight compared to the rest of the 48spliner cranks at the time.

Can't be bothered to jump into the argument, but i'm gonna agree with everyone who recommends just buying trials or mtb cranks. The price of bmx euro bbs are expensive, well so are high range ISIS, but you can get decent ISIS ones cheap. You can get second hand ISIS cranks, bash and sprocket for £50 too.

Also bearing in mind 23t bmx sprockets don't tend to be very robust. And 22t often require micro drive compatible cranks which you may not have?

[rupintart]

If you look at my first post, I never said they were LIGHTER, I said that BMX cranks aren't nearly as heavy as people made them out to be:

http://www.trials-forum.co.uk/index.php?showtopic=147950&view=findpost&p=2078922

As for the small wheels and high pressure thing, it's simple physics that a smaller wheel with rock hard tires is going to be more abusive on the rest of the parts than a large tire and low psi. The impact forces are dissipated through the lower pressure and the larger wheels. You don't think that has an adverse affect on anything and is all negligible? Look at what a difference of 10psi does on your wrist when riding your BMX. Think about what 50+ psi and a loss of 6 inches in diameter does to parts. Jump off a 6 foot high ledge on a BMX bike with 100psi tires, then jump off the same ledge on your MTB at 50psi. You can't tell me there isn't a difference in impact forces to your body.

Your body isn't a perfect machine. The load isn't Aalways pressing straight down on cranks. Your legs aren't on a track and only pressing down. You can't say that there aren't ANY yaw loads on your cranks when pressing down. If that were the case, your cranks would never work loose because there's never any side loads on it. The very nature of pedaling and keeping balance is more than enough of an example of your cranks seeing yaw loads. The amount is obviously varied depending on what's doing on.

Having 100% spline interface is just more secure and the maximum amount of surface area is on my crank arms. It would be stupid to say that not having 100% interface, and having it, there isn't a bit of difference. I never said it was the end all of crank problems, it just significantly minimizes everything from going wrong and I have no problems on mine, and every person I've seen that has has not had problems. Not to say that it can't, but I have never seen it happen.

In the end, I can tell you my crank arms are on 100% and in two years of ownership haven't EVER had the need to tighten them after installation. I have had ZERO problems with them in the two years of ownership, they have seen dirt jumps, and the abuse of a 230lb friend both on DJs and urban. Never once have come loose or have problems. I think I can safely say that those cranks have been exposed to more than enough abuse to show that they're more than reliable and those things speak volumes for their quality. Which is more than I can say for Dengs stuff. I don't care if X person says theirs keeps coming loose or can't stay tight. I didn't install it and it's not mine, so I can't say the same as that person. FOR ME, they've worked out perfectly.

[Mark W]

Trialtech isis arms are 510. After you add a bash and a sprocket, you're sitting around the same weight and not NEARLY as strong. And that's with a standard a crmo axle in the BMX cranks. Don't forget you can also get a Ti axle for the BMX cranks.

If you run Middleburns, you're gonna be slightly heavier than the Trial Tech crank arms, and it puts you toughly in the same weight as BMX cranks.

Seemed like the implication was there that if you run a Ti spindle your setup would be lighter, after saying that "they're around the same weight", which later turned out to be 500-600g heavier...

If you look at my first post, I never said they were LIGHTER, I said that BMX cranks aren't nearly as heavy as people made them out to be:

No, you said they're about the same weight with a regular spindle, but you could make them lighter with a Ti spindle...

As for the small wheels and high pressure thing, it's simple physics that a smaller wheel with rock hard tires is going to be more abusive on the rest of the parts than a large tire and low psi. The impact forces are dissipated through the lower pressure and the larger wheels. You don't think that has an adverse affect on anything and is all negligible? Look at what a difference of 10psi does on your wrist when riding your BMX. Think about what 50+ psi and a loss of 6 inches in diameter does to parts. Jump off a 6 foot high ledge on a BMX bike with 100psi tires, then jump off the same ledge on your MTB at 50psi. You can't tell me there isn't a difference in impact forces to your body.

Who even runs 100psi on a BMX for street for a start, but what I was saying was that I don't see your tyre pressure as being much of a problem in terms of how long your cranks are going to last.

Your body isn't a perfect machine. The load isn't Aalways pressing straight down on cranks. Your legs aren't on a track and only pressing down. You can't say that there aren't ANY yaw loads on your cranks when pressing down. If that were the case, your cranks would never work loose because there's never any side loads on it. The very nature of pedaling and keeping balance is more than enough of an example of your cranks seeing yaw loads. The amount is obviously varied depending on what's doing on.

I meant that if your cranks had a bit of wobble then normally because your weight is going to be on your pedals at the end of your cranks, it should mean your cranks are held down against the spindle simply because even if your weight's not going directly down, your cranks aren't just going to flap around on your spindle because the weight of you going through them, in any way, is going to be keeping them pressed against the top of the spindle. It's obviously not a good thing to do though...

Having 100% spline interface is just more secure and the maximum amount of surface area is on my crank arms. It would be stupid to say that not having 100% interface, and having it, there isn't a bit of difference. I never said it was the end all of crank problems, it just significantly minimizes everything from going wrong and I have no problems on mine, and every person I've seen that has has not had problems. Not to say that it can't, but I have never seen it happen.

I said I didn't think there was much difference, simply because I've never seen a crank fail from not being 'balanced', and I haven't had a single problem myself.

[willdudeXD]

lol, my thread has turned into one big argument :X lol

i cant do it anyways cuz icant afford the new sprocket and euro bb