d2create

I have the Sugino RD 48T crank.
I'm slapping it on a frame with 130mm spacing.
This is what sugino says...
"103 Bottom bracket gives 42 mm chainline, matches most track hubs."
Most track hubs are 120mm. So should i get the suggested 103 bb or get a 113mm or something inbetween?

sivat

The hub spacing (120mm) doesn't have anything to do with the chainline since the spacing measures the distance from locknut to locknut and is adjustable, while the chainline of the hub measures from the center of the hub to where the cog will sit. If you are using a track hub with spacers, get the 103mm. If you are using a road hub or mountain bike single speed hub, find out what the chainline of that hub is and adjust the bb accordingly.

ultraman6970

HI...

That crank is not ISo, is JIS to start with, secondly u say that u want to put that thing in a 130 mms frame. The 103 is too narrow for what u want specially in JIS. If you had the sugino 75's that are ISO u might be able to get away with a 103 or even a campy 102 road (thing i have personally tried in my old road bike) but with the RD i doubt it would work.

103 mms is for track frames, we are talking about 120 mms wide frames. And the other thing is that usually japanese track the driver side of the rear end nearby the cranset is thiner (cant remember the name in english of that, sorry) Even in japan some frames are still 110 mms wide in the rear end so u can even put narrower bb axles.

I would go sure putting a 110/112 JIS bb in there if i was you. Just my oppinion...

Thanks.

ps: what kind of bike is? a 29r or a road frame?

d2create

It's a Steelwool Sweet City Limited. Was 120mm but i coldset it to 133mm to fit the SRAM i-Motion 9 hub.



If the RD won't work what would you suggest?

d2create

The SRAM specs say that CL is 48.9mm. So what does that tell me?

tellyho

Not much. I don't know that you're going to be able to solve this via any math at home. It might be trial and error. That said, 48mm chainline is pretty common for geared road bikes. Perhaps Sugino will give you other stats for that crank in a different use.

Theoretically, you've added 6 mm to that original 42 mm chainline, so you could add 12 mm to the spindle length.... I can't say I've had any success with this logic, though. I often have to pop the crank on and adjust the rear spacing and dish to match.

frankstoneline

well, if you need ~49 mm chainline, and a 103 bottom bracket will give you 42mm you need a wider BB by about 14mm unless I'm off (7mm for each side) That would be a 117.
Shimano makes a 118 square taper that should work for you for about 20 bucks. They have em on bens cycle, though you might have to move the chainring from the outside to the inside to make your chainline right.

Edit: some people say with the ring in the outside position RD's give something greater than a 42 mm chainline, so you could also look into the shimano 113 bottom bracket, though its kind of a trial and error thing.

d2create

That's exactly my thinking.
I just didn't know if I was missing something or what.
I knew that the rear spacing/hub CL and the crank CL must have to work together. Just didn't make sense otherwise.

I just ran over to the lbs and picked up a shimano 68x115. That seemed like a good place to start.

sivat

You've got a lot of strange (read: wrong) info in there. His original post didn't say anything about ISO vs JIS, so I'm not sure where you got that. However, as long as they are paired correctly (ISO and ISO, or JIS and JIS), the taper standard won't effect where the cranks sit. You really don't want to mix the standards if you can help it as either way has the possibility of damaging the cranks. (The OP won't need to pay attention to this, since his question has been answered)

Second, I currently have a 103mm, JIS, sugino bb with cranks designed for a 42mm chainline with said bottom bracket, in a 135 spaced frame and I have plenty of room for a 48t chainring. The rear spacing doesn't have anything to do with the length bottom bracket you can run. If you want proof, consider this; The NJS frames that are made with 110mm rear spacing are also designed to run NJS cranks and bottom brackets. Currently, that means either Sugino 75s or Dura Ace, both of which use a 109mm bottom bracket.

dobber

If the 103mm bottom bracket would give you a chainline of 42mm, then you need (49-42)*2+103 to obtain the chainline you want for the SRAM.

So you're be seeking something around 117. Now whether its JIS or ISO, thats a different kettle of fish.

sivat

The only sugino cranks that use ISO are the Sugino 75 track cranks. The XD, RD, messenger and road cranks all use JIS tapers. Shimano doesn't make the UN series cartridge bottom brackets in ISO taper, so that won't be a problem.

d2create

Ok, get this...
I get home (and I should have done this yesterday) I held up the crank so it was flush with the bb shell. Even flush, the chain ring (when mounted outside the spider as it showed up in the box) is too far out to be perfectly in line with the rear sprocket on that i-motion hub. With the 115mm bb i bought today, it puts it wayyy out of line. So it looks like a 103mm is the one i need and even that won't give me a perfectly straight chain line.That rear sprocket is mounted pretty far in towards the center of the wheel... about perfectly in line with the edge of the bb shell. Well... back to the lbs for the exchange...

EDIT: Just did some actual measuring instead of eyeballing and it looks like the 103mm should be just about right.

sivat

Before you take it back, you might want to try mounting the chainring on the inside of the spider.

d2create

Yeah, i thought about that and it would probably work out ok but I'd rather have the ring on the outside because honestly it looks better. lol

d2create

Here it is... 103mm. Nice and straight.

satanas

IME, some Sugino-made cranks work just fine on either ISO or JIS taper spindles; I am thinking of the Ritchey Logic cranks here, in either the 110/74, 110 road or 94/58 varieties. For the same nominal spindle length, switching from ISO to JIS typically moves the cranks out ~1mm, and vice versa; this can be handy to fine tune the chainline and gives more options.

While it's possible to damage tapers with a mismatch, gross problems should be obvious from inspection after sliding the cranks onto the axle.