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Crank Arm Clearance ?

May 30, 2007
130
0
Central California
Alright, so I just picked up a pair of sexy white profile cranks for my Eastern Thunderbird. Before ordering them, I called Eastern and confirmed the proper spindle length - 5 3/4". I measured the old Eastern spindle, which came out to 6" - but I didn't think that was going to be an accurate comparison seeing as how insertion depth into crank arm is unlikely to be the same between the 2 cranksets.

So I install the cranks last night, and (1) - The washers provided with the Profile BB aren't enough, which isn't a huge deal, I've got spare washers. (2) - I'm left with around 4mm of clearance between the crank arms and the chainstays.

The obvious answer is to ride it to see whether the clearance is acceptable, which I'll do tonight. In the meantime, How much clearance do you have between your crank arms and chainstays? Better yet, anybody out there with a Thunderbird or Night Train with Profiles? How long is your spindle?

Thanks in advance if you make it through my long-winded post...
 
i think most people that run profiles on an MTB use the 6" spindle, i know i do on all 3 pairs. i wouldn't use a smaller one, there wouldn't be much insertion overlap(well, i did once and i rounded out the spindle and crank arm interface in no time)...
 
Last edited:
May 30, 2007
130
0
Central California
i think most people that run profiles on an MTB use the 6.5" spindle, i know i do on all 3 pairs. i wouldn't use a smaller one, there wouldn't be much insertion overlap(well, i did once and i rounded out the spindle and crank arm interface in no time)...
The crank arms are at maximum insertion :brows: - as in the installation tool is bottomed out on both sides, so no issue with interface damage. Also, being a bmx (spanish) bb, i'd be running a ton of spacers... An additional 3/4" worth with a 6.5" spindle.
 
hmmm... never ran a set on a spanish bb. besides spacer amount is irrelevant anyway. you need as many as it takes to clear the chainstays, even if it's 1.5" of spacers. the space reqiured is also depending on the inherent flex of your frames material. on a frame i have that is made of OX Platinum steel i have a clearance of about 2mm's that does not ever rub. on a 4130 frame i have, i need about 3.5mm's to prevent rubbing...
 
May 30, 2007
130
0
Central California
hmmm... never ran a set on a spanish bb. besides spacer amount is irrelevant anyway. you need as many as it takes to clear the chainstays, even if it's 1.5" of spacers. the space reqiured is also depending on the inherent flex of your frames material. on a frame i have that is made of OX Platinum steel i have a clearance of about 2mm's that does not ever rub. on a 4130 frame i have, i need about 3.5mm's to prevent rubbing...
Very true... I'll see how they do tonight. I appreciate the reply.
 

Cru Jones

Turbo Monkey
Sep 2, 2006
3,025
2
Hell Track
Any clearance is enough clearance. I have Wombolts on my 2six (fixed spindle length) and have it setup where the chainwheel just barely grazes the frame.
 

Mr Tiles

I'm a beer snob
Nov 10, 2003
3,469
0
L-town ya'll
yep, I run that same spacer kit posted above on my twenty - it's got wide stays. I have about 1.5mm clearance (crank arm to stay) on each side and it's buttah...
 

Stoked

Turbo Monkey
Nov 28, 2004
1,809
1
LI, NY
yes those cone spacers are nice. i run them with a 5.5 spindle and profiles and I don't need any additional spacers.
 

ThePriceSeliger

Mushhead
Mar 31, 2004
4,860
0
Denver, Colorado
i think most people that run profiles on an MTB use the 6.5" spindle, i know i do on all 3 pairs. i wouldn't use a smaller one, there wouldn't be much insertion overlap(well, i did once and i rounded out the spindle and crank arm interface in no time)...
Just for the record, Profile's longest spindle is 6 inchs. I run a 6 inch spindle on my MTB, and I don't really beleive they have a longer 48 splined one.
 

cmc

Turbo Monkey
Nov 17, 2006
2,052
6
austin
i also use a 6" on a MOB with bmx Profiles.

but they do make longer ones (at least on the MTB cranks):


http://www.profileracing.com/products_mtb.php
MTB Cranksets

• Uses our legendary Race Crank arms for superior strength and stiffness.

• All Race Crank color and size options available.

• BB spindle options: Solid CrMo, Hollow CrMo, Titanium, 5.75", 6", 6.25", and 6.875"

• BB spacer width options: 68, 73, 83, 100mm

• Spider options: 104/68 four arm, 94/58 or 110/74 five arm
 
May 30, 2007
130
0
Central California
Turns out the 5.75" spindle is just fine for the Thunderbird as far as chainstay clearance goes - but sucks if you have the stock hub and like a straight chainline. A 6" spindle would have made it even worse, it's pretty much unrideable as it is.

Now I have an excuse to buy a Tree splined sprocket, though. :biggrin:
 

DirtBag

Monkey
Feb 1, 2006
648
0
The Profile 6.875" Spindle is really for MTB use that also (usually) has 2 rings or a bash guard that requires the extra length.

Most BMX/MTB have a small shell (american, mid, spanish or 68/73) that a 5.75" or 6" will be fine for. Then you have to space it accordingly to both match the chainstays and space out the chainring.

With the Tree splined you can have spacers in between the cranks and chainring to get the right chainline if needed. But the original question of how much space between the cranks and chainstays are really dependant on crank and frame flex.

I run Profile race with 6" Ti spindle and a Tree splined on my Mob. It lined up perfectly for chainline, chainring position about 2mm away from the CS and my cranks are about 4mm away from the CS I would guess. In all cases the cranks and chainring don't hit the frame. It took a while to dial in, but it is perfect.

I run one of the cone spacers on the non-drive with a couple of extra spacers. On the drive side, due to the fat Tree, I run one spacer inside of the Tree (against the BB) and no other spacers. Crank is right against the Tree.