Shortening your cranks

[philipshaw]

Correct.

Thanks again

 

[surlyrides]

I was really happy to see this thread as I have been continually irked by the length of the cranks on my altitude power play...

Reading the op's first post, The question that comes to my mind is, can't I just take my existing rf crank arms to a machine shop to be drilled and tapped down to 150mm? This wouldn't require purchasing any new parts. Am I missing something? I have the C70 altitude.

Thanks in advance!

 

[A06]

I was really happy to see this thread as I have been continually irked by the length of the cranks on my altitude power play...

Reading the op's first post, The question that comes to my mind is, can't I just take my existing rf crank arms to a machine shop to be drilled and tapped down to 150mm? This wouldn't require purchasing any new parts. Am I missing something? I have the C70 altitude.

Thanks in advance!

That was literally in the very first post of the thread.

Yes you can machine them depending on which crank arms you have, Atlas have enough material to go to 155mm from the stock length but I think 150 will be risky. If you want 150mm you would need to start with 165's.

Thats the route I'm going as its an incremental process. 165's are a welcome improvement for sure but eventually I'll probably go to 155-150 but to be honest I'm stalling to see if RM or RF come up with a better solution in which case I'd sell the 165's to fund the purchase of hopefully a shorter drop in option.

 

[surlyrides]

That was literally in the very first post of the thread.

Yes you can machine them depending on which crank arms you have, Atlas have enough material to go to 155mm from the stock length but I think 150 will be risky. If you want 150mm you would need to start with 165's.

Thats the route I'm going as its an incremental process. 165's are a welcome improvement for sure but eventually I'll probably go to 155-150 but to be honest I'm stalling to see if RM or RF come up with a better solution in which case I'd sell the 165's to fund the purchase of hopefully a shorter drop in option.

Thank you. The first post discusses switching crank arms rather than machining the stock crank arms. My question was specifically about the stock crank arms without purchasing new crank arms or any other parts.

I think that the answer to my question is " yes " ... But if anyone wants to chime in on using the stock crank arms without replacing any parts and just machining the existing ones shorter, that's what I'm curious about specifically.

 

[S13]

It doesnt matter if the cranks are new or came on your bike pre-installed. What matters is which type it is. The more expensive Atlas or Turbine cranks can be drilled down, the cheaper Ride cranks cannot.

 

[KAMTHETANK]

Any recommendations for where to get cranks drilled and shortened and what I should expect to pay?

 

[KAMTHETANK]

Over the past weeks ive been gathering information on how to shorten the cranks on Rocky Mountain Powerplay bikes. I hope this info helps some of you with this quite complicated task.

So in order to get shorter cranks than the stock 170's (or if you are lucky the 165) there are a couple of solutions, both involve getting either a RaceFace Atlas or Turbine crank set.

So to start with you either have one of 2 situations:
1. You already have the bigger 30mm axle cranks installed on your bike (probably Turbine)
2. You have the smaller 24mm axle Ride cranks


The solution for situation 1 is simplest. Buy a set of Atlas cranks in your preferred length. Shortest you can go is 165mm. If you buy the longer 175mm you can drill them down to 155. You can also drill Turbine cranks shorter, if you prefer that route. 170 to 150 is possible and 175 to 155 as well. Turbine is sold out everywhere so might not be the easiest option. Turbine does not come shorter than 170.
After you get your new and optionally machined cranks, fit them with the original spindle that came with your bike. It should be a RF149 spindle (149mm end-to-end spindle length). Also fit the original clutch spider assembly with the 30mm locking ring. Install on bike and you are done!

Now situation 2 is more complicated, because you dont have the parts to use the 30mm cranks, and re-drilling the original Ride cranks is not recommended due to the internal structure. So the only option is to first install a 30mm bottom bracket (for example a BB92 Double Row CINCH 30mm with 92mm shell width). Then you need to buy the correct length 30mm spindle. Rocky Mountain advises the RF149 (149mm end-to-end spindle length), and that is what most people seem to use. You can buy these spindle kits at several web shops. You also need to contact RM or you local RM dealer to get a hold of the 30mm locking ring for the spider clutch. For the remainder, the same applies as for solution nr 1; get a set of Atlas (or Turbine) cranks, optionally drill them to desired length, fit cranks with the new correct sized spindle, install original clutch spider with new 30mm locking ring, and you are good to go.

One point to remark is that you can also buy Atlas cranks in so called "83mm" variation. On the Raceface website this shows as "Spindle Size 151". These cranks come with the 151mm RF151DH spindle already attached to it. Now im not sure these will fit the bike, but the difference is only 2mm compared to the recommended RF149 spindle, so perhaps minor enough that you can adjust the free play with free play adjustment ring, or perhaps a spacer. This would save you the hassle to buy a separate spindle kit for another 100 bucks.

This document from Race Face provides you with information on the available spindle sizes.
Note that it says:
• Spindles with suffix “BM” or “DH” (eg.RF136DH) are compatible with SixC and Atlas cranks only
• Spindles without “BM” or “DH” suffix (eg. RF134) are compatible with Next R, Next SL and Turbine cranks only

So according to the document the Atlas crank should not be compatible with the RF149 spindle, but is compatible with the RF151DH spindle. However on the facebook group Norman mentions he has successfully used the RF149 spindle with his drilled Atlas cranks without any problems.

Atlas cranks drilled from 175 to 155 by Norman:

Turbine cranks drilled from 170 to 150 by Andy:

According to Andy, drilling 175 Turbine to 155 is also possible.

So there you have it. I have not verified any of these solutions, so i cannot guarantee the information provided here is correct. But hopefully it helps you get started.

Where'd you get this done?!

 

[S13]

Where'd you get this done?!

Be more specific?

 

[KAMTHETANK]

Be more specific?

Where did you get your cranks shortened and redrilled?

 

[S13]

Where did you get your cranks shortened and redrilled?

I didnt. Did you even read the post?

 

[KAMTHETANK]

Yeah I read the thread. The first post has pictures of cranks that have been drilled and shortened. I'm trying to get some help on resources for this.

 

[S13]

Well like i said in the original post, these are from Norman and Andy on the facebook group. Maybe they can point you in the right direction.

 

[A06]

Yeah I read the thread. The first post has pictures of cranks that have been drilled and shortened. I'm trying to get some help on resources for this.

Short Bicycle Cranks

 

[Kayne]

I had the Atlas cranks installed on my 2019 Instinct. Just bought a new 2024 and had asked the dealer to swap cranks for me but they didn’t seem to think they would fit and since I had the old bike sold I didn’t have time to argue. Asked RM if Atlas cranks would fit but haven’t heard back. It’s been over a week now. Can’t see why RM would change the width of the frame at the bottom bracket but wanted to check before I order new cranks. Anybody with a 2024 changed cranks yet or any idea if bikes are the same?

 

[philbwy]

My LBS just ordered me some hope cranks in 155mm that will work with the instinct powerplay. This will require changing the bottom bracket and using Hope chain rings. All of this will cost about 550 USD . I guess these just became available today. Blue is currently the only color available. All the other colors list availability as TBD. good thing my bikes blue.

 

[S13]

My LBS just ordered me some hope cranks in 155mm that will work with the instinct powerplay. This will require changing the bottom bracket and using Hope chain rings. All of this will cost about 550 USD . I guess these just became available today. Blue is currently the only color available. All the other colors list availability as TBD. good thing my bikes blue.

So the Hope cranks have a cinch interface for mounting the spider clutch? I doubt it since this is race face specific.
Or do you have a different solution for the spider clutch?

 

[philbwy]

So the Hope cranks have a cinch interface for mounting the spider clutch? I doubt it since this is race face specific.
Or do you have a different solution for the spider clutch?

I'll let you know what their solution was after it is installed. According to LBS these are listed as compatible with RM Powerplay and they are dealing directly with Hope. I am letting them do the install so if for some reason it doesn't work I'm not out anything

 

[Bad Mechanic]

I'll let you know what their solution was after it is installed. According to LBS these are listed as compatible with RM Powerplay and they are dealing directly with Hope. I am letting them do the install so if for some reason it doesn't work I'm not out anything

I don't think your bike shop realizes there's a one way bearing in the crank spider.

 

[Astro66]

Got myself measured up using the old skinny box between the legs measurement, and it recommended 155mm cranks. I really wanted to stick with Shimano cranks on my EP6 motor so I got the 160mm.

Took it for a ride up some technical climbs, and it nearly reduced rock strikes to zero, compared with the 170mm cranks. Very, very happy.

Also added double sided pedals, so I can go flats or clipless. This also worked really well, so I can go the shops in normal shoes, and lend the Ebike to my analogue buddies when they get tired.

With clipless

With flats

 

[Bad Mechanic]

Got myself measured up using the old skinny box between the legs measurement, and it recommended 155mm cranks. I really wanted to stick with Shimano cranks on my EP6 motor so I got the 160mm.

Took it for a ride up some technical climbs, and it nearly reduced rock strikes to zero, compared with the 170mm cranks. Very, very happy.

Also added double sided pedals, so I can go flats or clipless. This also worked really well, so I can go the shops in normal shoes, and lend the Ebike to my analogue buddies when they get tired.

With clipless
View attachment 141163
With flats
View attachment 141164

FYI, this thread is for Rocky Mountain bikes, which us the Dyname motor, and not a Shimano motor. The cranks are not interchangable.

 

[Donnyboy66]

An update on availability of shorter cranks from North Shore Billet (Talon Crankset - Rocky Mountain Powerplay). Bought the 155 cranks and so far only the rare pedal/crank strike doing goofy stuff. If you can stomach the cost, the reduction in pedal/ crank strikes is huge!

For those concerned about leverage from very short cranks, I am just under 6 feet tall and it is fine.

Note: Some Powerplays came with 24mm spindles. Had to go with 30mm bottom bracket (not in the box) to match the new 30mm spindle in the box. Larger lock ring is in the box. See installation guide in link provided above.

 

[Bad Mechanic]

I converted to 165mm Atlas cranks and it's been better, but even is the default Ride4 position I'm still getting pedal strikes too often. So I've picked up a set of 175mm Atlas cranks and will shorten them to 155mm and give that a try. It'll be my first time shortening cranks, but it shouldn't be all that difficult with my benchtop mill. The hardest part will be cutting off the extra length of crank and making it look good.

If I end up not liking the 155mm cranks, I'll post them up for sale here.

 

[EzRyder]

My LBS just ordered me some hope cranks in 155mm that will work with the instinct powerplay. This will require changing the bottom bracket and using Hope chain rings. All of this will cost about 550 USD . I guess these just became available today. Blue is currently the only color available. All the other colors list availability as TBD. good thing my bikes blue.

Did this solution work? Hope crank would look great with my V4's on my Altitude

 

[Bad Mechanic]

Finished machining the 175mm Atlas cranks to 155mm and installed them on my bike this evening. Hopefully I can get out for a ride this weekend and put them through their paces.

 

[philbwy]

As suspected the hope cranks didn't work even though the people at hope kept insisting they were compatible. but it didnt cost anything to try. so now I'm on the waiting list with North Shore Billet.

 

[skewered]

Great thread everyone! I have a found a used set of 175 Aeffect Rs locally which I could machine myself down to 155mm. My A70 has 170 Aeffects on it now. Are Aeffect spindles removable or permanently attached to one crank? If they are removable It seems like I could just use my original spindle with the newly machined crank arms. If they are not removable what do I need to check regarding the spindle specs on the used set? Used set I am considering shown below. I do not yet know the spindle specs. Thanks.

 

[Bad Mechanic]

Great thread everyone! I have a found a used set of 175 Aeffect Rs locally which I could machine myself down to 155mm. My A70 has 170 Aeffects on it now. Are Aeffect spindles removable or permanently attached to one crank? If they are removable It seems like I could just use my original spindle with the newly machined crank arms. If they are not removable what do I need to check regarding the spindle specs on the used set? Used set I am considering shown below. I do not yet know the spindle specs. Thanks.

View attachment 143675

I'm pretty sure the spindle is permanently attached to the left crankarm, and from looking at the picture I can tell it's too short. You need the ~150mm long spindle, which are only available for the Atlas and Turbine cranksets.

 

[Bad Mechanic]

I rode the 155mm cranks for the first time this weekend. While I need to fiddle with my seat height a bit now, it was AMAZING not having any peddle strikes!

 

[skewered]

I'm pretty sure the spindle is permanently attached to the left crankarm, and from looking at the picture I can tell it's too short. You need the ~150mm long spindle, which are only available for the Atlas and Turbine cranksets.

Thanks BM. I see now that the those options are presented specifically because they can be used with a variety of spindle lengths.

 

[Astro66]

Got myself measured up using the old skinny box between the legs measurement, and it recommended 155mm cranks. I really wanted to stick with Shimano cranks on my EP6 motor so I got the 160mm.

I rode the 155mm cranks for the first time this weekend. While I need to fiddle with my seat height a bit now, it was AMAZING not having any peddle strikes!

Not a Rocky Mountain, but just a comment on shortening cranks. I have gone further, and put 150mm cranks on my EMTB. It's not just the rock strikes, it's the ability to pedal later and earlier, in and out of corners. It's has incredibly increased my ability in technical terrain.

Game changing modification.