Looking for big crank.

[dogman dan]

Anybody know where a large front chainring crank for a mtb might be found, or a roadbike crank that has enough clearance to fit a MTB? Of course it must be cheap too! I don't want a $200 crank on a $40 bike. :lol: :lol:

I'm thinking to the future when I might buy a bike for real money, if it can fit a 52 tooth crank, or has one. At the speed I ride now, 24mph on the flats, I can peadle it up to about 27mph with my current 48 tooth crank. But next summer I'd like to go to a 48v battery and then would be back to barely able to peadle as fast as the motor goes. I don't want to go to a hardtail, since my route has some really big bumps where the water channels cross the bike path. I keep looking for a crank on used bikes, but the road bikes don't have the offset to clear the rear frame tubes on the MTB. The biggest MTB crank I have seen so far is a 48 tooth.

 

[deecanio]

Hi Dogman,

i fitted this weekend a shimano road crankset consisting of 30/42/52t to my kona stinky MTB.
The crankset i chose had a 9/16" hole for the pedals and was the square taper variety?
I was worried that the 52t wouldn't fit without bashing the frame and sure enough the 52t caught the frame when fully tightened, however i have a 110mm wide square taper BB and i have just ordered a 127mm BB which will give me and extra 8.5mm either side which is plenty.
i paid £40 for the crankset but it was MUCH cheaper than buying custom chainrings - i use my shimano deore shifter that came with the bike and it works beautifully - or it would do if i hadn't spaced out the 52t to pass the frame so i could set up, cant quite get "3rd" yet but once i get the wider BB im sure it will be sweet, could post some pics later if you want to see?


Cheers,

D

 

[docnjoj]

U should be able to find a 52 tooth chainwheel on an old bike at Goodwill or the dump. I found a Peugot frame and pedals at the dump and drilled to fit my chainring. Works fine!
otherDoc

 

[dogman dan]

Been there, done that, but the older bikes have a real straight crank arm that hits the frame, or the chainring hits, one or the other. A wider bottom bracket though, I hadn't even considered that. Should work like a charm. I thought It would be easy to find a mountain crank with a 52 tooth, but aparently not.

 

[deecanio]

Hi dogman,

i went through the same hassle but only found mtb up to 48t max, if you choose a roadset crank you can find 53t easily.
I now have a pretty standard shimano road set and it will fit perfect once i get the wider bottom bracket, i will post on gear changing once the bb arrives as i had to space the 52t sprocket out by 4/5 mm to clear the frame so cant test the final gearchange yet, to be clear there was no problem with the other two chainrings (30/42t) they fit right in where the mtb 22/32 used to fit, and 1st/2nd select with no problems at all 8)
The new crank arms aren't straight, they bend out to avoid the frame - not by much maybe a 10mm swerve?
my left side crank passes my frame by about 1mm (i would think it would hit under the right pressure). However this is with a current bottom bracket length of 110mm.
I should have a 127mm in the post anyday which will give me an extra 8.5mm either side - this will make the left arm clear the frame by 9.5mm and the 52t chainring will clear the frame by roughly 4.5mm, should be plenty.
Bear in mind that this alters the chainline some, but being as i need to space my rear freewheel anyway it should be all good.
Also bear in mind when you go for the roadset the size of the pedal tapping or you may have to get new pedals........ erm thats about it really...... oh you need to know what type your bb is eg. square taper/isis whatever and you'll need to know what size - most are 68mm or 73mm wide by anywhere from 107mm - 127mm long.
As long as you know what you have and how far out you want to come it's as easy as pie to change (you may need a crankarm extractor and a bb tool of some sort too).
Have a look at these and see if you like anything..................... http://www.chainreactioncycles.com/Categories.aspx?CategoryID=577
weird you should post this just as im doing it

Cheers,


D

 

[dogman dan]

Internet esp. When I was young, it worked better, and would occasionally pick up the phone before it rang. My bike is a cheapie mongoose so I may be sol for any type of upgrades, much like the forks with the cheese 1" headsets. Of course I'll upgrade to a better bike in a heartbeat as long as the garage sale sellers price is under 50 bucks. I looked at some bb's last night on the net and got thouroughly confused as to how to figure out what I have in the first place. But it looks like the solution to my problem for sure. The other way to skin this cat would be a slower motor, but I don't see myself liking that. Today I had a real hard tailwind coming home and I actually did some peadling at 33 mph, but it must have looked like I was on crack. with my current 48 tooth crank, I can peadle pretty comfy at 27 mph, but If I bite on a 48v Ping next year, I will have to get a bigger crank, or a slower motor. I was kinda suprised that DH bikes don't have huge cranks, but I guess mostly they don't peadle at all.

 

[dogman dan]

Sure enough I am SOL for doing anything different on this frame. It appears that I allready have a 125 mm spindle. I suppose i could get out the hammer and anvil and start reshaping the swing arm on it. But it won't be the first time, had to do that to the forks to get a hub on the front. :lol:

 

[lepton]

There are some useful links in this thread: http://www.endless-sphere.com/forums/viewtopic.php?f=11&t=1173

 

[Ypedal]

You want a " Bink Crank " .. wait a moment.. i'll go find my boss !!!

 

[deecanio]

Hi,

well you won't get much wider than 125mm unfortunately - are you running a cluster at the rear? what teeth?
you could look into alternative chainring? maybe swap the 48 for a 53t ?
do you have any pics of the drivetrain at all?


Cheers,

D

 

[swbluto]

I have a 42-tooth crank. At 48V, needless to say, it needs replacing. I think I'll follow this thread to see where it goes.

 

[dogman dan]

I have the typical box store cheap bike setup. I comes with a 14 tooth smallest ring on the 7 speed freewheel, and a 44 tooth front crank. finding a 48 tooth was sorta a problem, but some bikes have em, and I got one for 10 bucks at a garage sale. Bikes nashbar has an inexpensive one that is a 48 tooth. Finding the bigger than 48 tooth MTB crank is another issue. I'm sure they are out there, but not at 50 bucks. No way am I putting a 200 buck crank on a 40 buck bike. But if a good bike with full suspension is out there that comes with a big crank, I might spend money eventually.

Right now I had hopes of finding it at some obscure site that dismantles and sells off parts from warranty returned bikes or something. comfort bikes often come with cranks that have the bend to allow the peadle to clear the frame, but I haven't seen one with much bigger than a 44 tooth crank. Fitting a road crank chaniring to a MTB crank seems impossible since the chainring bolts are in totally different positions on roadbikes and MTB's. Local bikeshops have been unhelpfull, most of them see me as a heritic of some kind for having a motor. I may just end up grinding the teeth off a MTB chainring and welding on a road crank, but my welding leaves something to be desired for sure. Front shifting i don't care about, the deraliur is long gone. I can hand shift to a small ring if I break down.

 

[dogman dan]

Looking at Ebay road cranks, I found one with a pic that looks like it might work, or would with a hardtail maybe. Some of the Ebay auctions have a better pic than the online catalogs of regular retailers. This one looks like the crank arms have some curve to them, but whether the chainring clears, who knows? At 59 bucks the price is right. It would sure be nice, on my commute, the first 6 miles to work are downhill, and on the way to work, a few more mph would be cool. Speed limit on that road is 35 mph so a 52 would be just right.

Oh well, the seller says it likey won't fit. If I put the swingarm in a vise, i know I can get a bit more clearance, but the trouble with roadbikes is they are so areo oriented that they would never allow something to stick out more than they have to. So even that may not work. Looks like I'll be fabricating a road chainring onto a MTB crank somehow. When I solve it I'll start a new thread. I could easily go hardtail but I like some spring on the wheel so I don't make tacos out of rims. I do ride hard.

 

[pschmatz]

I bought this cheap road crank 52/42 (http://www.niagaracycle.com/product_info.php?products_id=10585), for my Schwinn Mesa MTB, and I did not have enough clearance on this bike (odd shape of frame). I could have filed away pieces of the swing arm, but decided against it.

In the end I settled for a MTB crank (48T) and a rear 8-speed freewheel with 11T (from ebike.ca). This works well with my 408 48V setup (26"). you can cruise comfortably at ~26Mph with a low cadence.

Peter

 

[dogman dan]

Yep a smaller rear freewheel would work too, but the 26" rear wheels with a 14 tooth freewheel are piling up around here as I keep buying 10 buck bikes for some other part. It's been kinda nice to just grab one and run it till it flats, or whatever and grab another. Right now I am pretty comfy with a 48 tooth and my WE brushed allowing me to add about 3 mph to the motors top speed. Any more would be work, but on the downhill leg of my ride, 35 mph would be sweet. Who knows what the future may hold, a few good scares and my wifes new 150cc scooter could be my ride. Me, if I don't get a good scare once in a while, I'll go looking.

 

[dogman dan]

oops post :lol: