Bicycle Mechanics - 3 part cank vs single

i got a 3 part crank on a new freestyle, and i'm not really impressed. i was wondering about swapping it over to a regular single crank, less bulk, and i think it will reduce a little weight

I think the bottom bracket bearing sizes of the 3 piece and single cranks are incompatible so you cant make the change.

i got a 3 part crank on a new freestyle, and i'm not really impressed. i was wondering about swapping it over to a regular single crank, less bulk, and i think it will reduce a little weight

What kind of 3 piece crank do you have? Frankly, I can't imagine ANY weight saving from shifting to a one piece crank. One piece cranks are HEAVY!

If your frame has a 2" dia. bottom bracket (like many BMX frames do), you can put a one-piece in there. I'm not sure how much less bulky a one-piece will be.

Surprisingly, a one-piece may actually be a bit lighter than some of the three-piece cranks for the BMX market, which are forged solid chro-mo. There are also aluminum (lightest) and fabricated chro-mo three-piece cranks (generally lighter than one-piece and three-piece forged chro-mo but heavier than aluminum).

Most one piece cranks weigh more than all 3-piece cranks except forged chromoly 3-piece cranks. Almost all one piece cranks are also significantly weaker and much more 'flexy' then 3-piece cranks.

BMX bikes typically have two styles of bottom bracket: Euro (new) or American (old) The majority of BMX bikes still use American bottom brackets so odds are you can switch it. But, what is it that doesn't impress you about your bottom cranks - maybe you just need to tune them up instead of replacing them.

Some tri-flow and a little maintenace can do wonders for the quality of 3-piece cranks.

My Haro 3-piece cranks (flatland 165mm) were making all kinds of noise when I first put them on. About a week later I was going nuts, took the crank arms off, sprayed some teflon lubricant on the bearings, and I haven't heard a noise from them since. That was over TWO YEARS ago - and they have been running strong this entire time.

Going from 3-piece to 1-piece is almost never the way to go, but maybe you have some really shady 3-piece cranks... In which case, I still wouldn't recommend going to 1-piece unless you are in immenent threat of hurting yourself. There are several very high quality 3-piece cranks, especially the Profile cranks. Check www.danscomp.com for other crank pricing.

The danscomp website is interesting in that they seem to publish weights for their parts. Perhaps surprisingly, one-piece cranks don't fare as poorly as one might think when compared to three piece chromoly cranks. Their Poverty one-piece chromoly crank weighs in at 35.2 oz. Top even out the picture, I'll add the bottom bracket set, another 10.3 oz. for a total of 45.5 oz, complete crank set.

Comparable three piece cranksets (two crank arms plus bottom bracket) range from 77 oz. to 38.6 oz. generally priced from low to high. As it turns out, while it's certainly possible to get a three piece chromoly crankset that weighs less than a one piece, according to the numbers published by Danscomp, you'll pay at least ten times the price for the privledge. And all three piece cranksets were more expensive than a one piece.

On to durability. Anyone capable of destroying a one piece chromoly crank such as the one sole by danscomp, will almost certainly be capable of destroying some three piece chromoly BMX cranks. Particularly low end ones where the weak link is the spindle or high end ones where strength is sacrificed for weight.

Thing is, you can lay waste to three one-piece cranks (how ever long that may take) before you equal the price of the cheapest chromoly three piece, which you may be able to waste just as well. And you can lay waste to as many as fourteen one-piece cranks before you equal the price of the most expensive chromoly three piece listed.

Ultimately, the OP will have to weigh all considerations. "Light, cheap, strong - pick any two..." The axiom applies.

It actually is slightly deeper than that...

1-piece cranks bend very quickly for street riders (and even for me as I flatland). This happens in under 1-2 months, while not one set of 3-piece cranks has ever caused me problems.

But, bending wasn't my big issue, the big issue is that the bottom brackets for BMX tend to be downwards from crappy. So, every other day I was tightening, or adjusting the bottom bracket, and at least twice a year I was pulling it apart to clean everything out and regreasing it.

I haven't touched my bottom bracket for any maintenance on my 3-piece cranks for about 2 years now. That is extra (precious) hours I get to ride my bike instead of fix it. Definitely a huge plus with 3-piece.

3-piece cranks aren't just 'a little' stronger than 1-piece. They are much, much stronger, and the spindle isn't usually what gets hosed, but the arms themselves from a harsh landing and the arm breaking off at the spindle joint. The spindle often survives.

This is an interesting topic.

I don't think anyone has had the confidence to admit that MAYBE single piece "Ashtabula" cranks might be as good as or better than the three piece cranks.

I have been working on bikes for many years and often wondered what the big advantage is for the three piece cranks. OK, you can get aluminum crank arms and hardened spindles - but is that really such a big deal?

I have heard of some guys breaking their single piece cranks on cheap bikes, but by the same token, I have stripped aluminum crank arms as well.

Considering the special tools needed to remove and maintain three-piece cranks, I haven't seen a really convincing argument of their advantages over single piece cranks.

Considering the special tools needed to remove and maintain three-piece cranks, I haven't seen a really convincing argument of their advantages over single piece cranks.


special tools? what special tools? i've got some three-piece BMX cranks i'm using on a chopper project, and it looks like all i need to install them is a wrench and a couple of allen keys...

j-

special tools? what special tools? i've got some three-piece BMX cranks i'm using on a chopper project, and it looks like all i need to install them is a wrench and a couple of allen keys...

j-

You usually need a crank puller to get the crank arms off the spindles. This is not a tool that average Joe Dad has in his tool box.

some 3 piece cranks dont need a crank puller.... they have a small cut straight through to the hole where the arm attaches to the spindle and there is a bolt going from one side to the other to tighten the gap... go to www.danscomp.com and look at some of the 3 piece cranks on there ... youll get what im talking about.

some 3 piece cranks dont need a crank puller.... they have a small cut straight through to the hole where the arm attaches to the spindle and there is a bolt going from one side to the other to tighten the gap... go to www.danscomp.com and look at some of the 3 piece cranks on there ... youll get what im talking about.

Yes, I see what you mean. Very interesting. As you may have noticed, however, these are not the norm for three piece cranks. Most still need crank pullers.

Ah well.

There's no doubt that decent one piece cranks are really a great idea for things like commuter/workbikes. One thing I always thought was really goofy were the steel cottered three piece cranks of old workhorses such as Raleigh. Sure they were durable, but they were no lighter or stronger than forged one piece cranks, such as the types found on old Schwinns. And they were even harder to work on than alloy three piece cranks, those cotters being almost impossible to remove.

Three piece cranks with a pinch bolt seem to be a relatively recent BMX innovation requiring no crank puller. However, I'm not sure I would trust a aluminum crank with a pinch bolt design (most seem to be chromoly).

Interesting about the BB quality mentioned. I've never found BB quality on a one piece crank to be a issue. Except for some very low end bikes with those cheap Wald BB sets, which almost appeared to never have been greased at all. In fact, I've found generic YST and the prettier "sealed" Odyssey one piece BBs to be perfectly functional and cheap. I think Tange and a few others still make one piece BBs with sealed cartridge bearings.

Yes, I see what you mean. Very interesting. As you may have noticed, however, these are not the norm for three piece cranks. Most still need crank pullers.

Ah well.

you're talking about road/mtb cranks. we're talking about BMX cranks here.

j-

3-piece cranks aren't just 'a little' stronger than 1-piece. They are much, much stronger, and the spindle isn't usually what gets hosed, but the arms themselves from a harsh landing and the arm breaking off at the spindle joint. The spindle often survives.
i agree with you, i ride street and bent many one piece cranks, but when i got my three piece i havent had a problem even when i do crack arm slides, sproket stalls, and landing huge airs. three piece are worth the extra money and easy to maintain.

As far as 'special tools' goes, most riders (BMX) who don't have a crank arm puller, use a block of wood and a hammer to knock the crank arm off from the opposite side.

For that matter, Profile cranks ship with a crank arm removal tool with the cranks.

Freestyle BMX riders have this weird thing, you see, they often don't care how much some stuff weighs, or how easy it is to work on... They want it to be durable. If they torque the cranks down a little tighter so they don't spin on them randomly in the air, they want the cranks to not be all jerky or need to be regreased every month. They just want to ride.

That was my reason to switch to 3-piece for sure. After 5+ years with 1-piece cranks I wanted to see what sealed bearings were like and found that not only were the sealed bearings nicer, but I never, ever, had to work on my cranks again. No, not as important as a good frame, fork, and most of all wheels - but nice if the budget allows.