# chainring clearance modeling



## afwalker (Apr 26, 2012)

Hope this hasn't been posted recently, I did search, send a link and kill this then:
Question: I can get the tires to fit inside the chainstays now that I got my JMan 3 a BB tower mod to hold a puck the size of the tire to tell me tire clearance, 
BUT, I'm still guessing on chainring clearance. I draw it out on paper with chainrings and the BB, WHERE can I get info on the distance the ring is from the edge 
of the BB? Say I use Chris King BB, are other BB's the same width? Can this help spacing? 
What about all the different cranks? Are the rings the same distance from the BB edge?
I think I saw someone with an adapter to the Anvil BB bolt that uses a crank with ring to guage spacing. 
Where do I find the diameter of the chainrings also?
Thanks in advance
andy walker
still a noob, 6 bikes so far, only just starting to know enough that I'm surprised the first bikes work ok!


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## pvd (Jan 4, 2006)

Measure.


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## briderdt (Dec 14, 2012)

I had to do this just this week... Found Q-factor for the cranks I'm using, measured the arm thickness, but when it came to the 'rings, I had to measure the location on a bike. SUCKED!

I'm in the middle of trying to lay out the chainrings for a "road" MTB with FSA Gossamer cranks/MegaExo BB, 50/36 'rings, 26x2" tires, and 425mm chainstays... It's gonna be interesting.


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## Clockwork Bikes (Jun 17, 2006)

I made this a while back and found it helpful. 7/8 Stays with Clearance | Flickr - Photo Sharing!

Use the center plane of the bike for your base measurement, not the BB. Shimano publishes this data on all their cranks.

Look back in the Groovy blog a bit for Rody's method.

-Joel


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## Rody (Sep 10, 2005)

Look here for answers the the universe...

Groovy Cycleworks 330-988-0537: How to lay out a rear end...old school style

rody


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## afwalker (Apr 26, 2012)

Thanks for the help!
I also tried using bikecad pro for layout:







and it looks like I could do a direct mount 2x10 modeling a 36 and 30 chainrings, This is using the new Deda 29r chainstays.
After the build out, it's not so good. Pretty much looks like a single chainring with spacers will be what it works. I was trying to use the Knards for a snow bike= Snard, so it was going to be super tight on both sides, I'm just thinking is there a better way to not be surprised when I put the actual crank on and say "crap, not again!"
I realize this is pushing the design limits, most of the time it doesn't matter. 
cheers
andy walker


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## afwalker (Apr 26, 2012)

ahha grasshopper! I begin to see Thanks both Joel and Rody, I was needing a more physical way of visualizing the room. And needing that Shimano spec.
cheers
andy walker


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## TrailMaker (Sep 16, 2007)

Hey;

I asked the same question once. I got the same answers. I took the safest route and measured, ala PVD. Nothing like having the bits right in hand with your calipers and rules to feel all the variables at play. A full scale drawing follows. I build a virtual bike right on the screen with everything at full scale, including BB spacers even.


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## febikes (Jan 28, 2011)

+1 on measure and CAD work.

I also like having a layout reference.


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## Meriwether (Jul 26, 2007)

TrailMaker said:


> Hey;
> 
> I asked the same question once. I got the same answers. I took the safest route and measured, ala PVD. Nothing like having the bits right in hand with your calipers and rules to feel all the variables at play. A full scale drawing follows. I build a virtual bike right on the screen with everything at full scale, including BB spacers even.


Hey TM, what's that you're using to draw that out in the computer? I'm looking for a way myself to get a printout like that and futz with angles and numbers. Without paying for autocad or etc is there an open source option? Sketchup maybe?


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## Meriwether (Jul 26, 2007)

afwalker said:


> Thanks for the help!
> I also tried using bikecad pro for layout:
> View attachment 778203
> 
> ...


Andy, 
This also happened to me using bikecad. It can be done in bikecad but it's an indirect method...one can't put in the specs from Shimano or SRAM directly into the crankset dialog box (i asked if i was missing something and i wasn't). You can futz with the inputs and get a good estimate but it's not as good as hand drawing or using a CAD software.

I can only run a 1x on my Knard bike too. Surly only sells their Krampus that way even though they have a spiffy yoke. A Surly O.D crankset may help it get two up front but man the chainline will suck! I think longer chainstays, an 83 shell, &/or dimpling both sides of the chainstay is needed for future Snards. 
Or maybe Paragon will start selling that yoke seen on a couple bikes at NAHBS...?

Best post-chainstay mess up solution is to go old school - square taper or ISIS with longer spindles and easier to adjust chainline. The bike is already going to be a tank with such heavy wheels...

It's a freaking fun bike btw, get er built up!


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## 18bikes (Jan 15, 2007)

It was me that modified an Anvil jig to take a shimano crank. We had an old XTR crank hanging around so I used the shimano information given above to machine a new cap that positioned the crank correctly for a conventional 22/32/44 set up. The XTR crank is a slightly bigger chainrings (24/?/?) than this which helps to make sure I've got enough room. It obviously only works for the set up intended (ie not 2x or unusual cranks) although it can be used for normal 1x set ups.

Here it is:

New BB tower cap by 18bikes, on Flickr

Here it is in use:

Chainstays 4 by 18bikes, on Flickr
(singlespeed frame so no inner ring mounted)

And recently I've had to make an adapter for the adapter so I can check the crank arm clearance on the Pinion gearbox frame I've been working on recently (the pinion has quite straiight arms and a long axle (effectively)

Doobry by 18bikes, on Flickr

I also made adapters to hold a cassette and disc on the dummy axle so I can check everything in the jig

Cassette mount by 18bikes, on Flickr

Obviously none of these are a substitute for doing the ground work when designing the frame, but they are handy as a physical check before something gets welded

Matt


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## afwalker (Apr 26, 2012)

Great work 18bikes! I think that would be super helpful. Your adapter , BB tower cap, did you model it after a certain bb bracket, any spacers accounted for? Thoughts on design?
I'll make one for a CK bb and no spacers I would guess, on the shimano spec.
TM, full scale, wow! I'm also curious as to which program you're using.
Whit, thanks for the post mess up tips, I can't wait to ride it!
I cannot find rabbit holes, so blunt 35s for me. I didn't want to buy built up wheels.
cheers
andy walker


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## afwalker (Apr 26, 2012)

Looks like I need 5mm more, hard to see inside the crank, but it's not seated. Maybe try dimpling but will probably do 1x10. Joel's direct mount FD braze-on is sweet! Just on the top of the pic. Even if I don't use it Only have 2.0 tire in there, the knard has 3.75" at 14.25" from axle with sliders in. 125mm to outside chainstays so even a small Q crank works, just the chainrings.
cheers
andy walker


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## TrailMaker (Sep 16, 2007)

Hey;

I don't have any CAD stuff. I'm using good old CORELDraw. I don't know if that is smart or cool or what, but it's what I've got and it seems to work for me. I messed with Sketchup a bit, but did not find it particularly intuitive. I'm not smart enough or good enough with numbers to do it all in my head and have it work. I'm better with a pile of parts and going from there. Doing these drawings is really helpful in visualizing where I will be going and what I will end up with, especially since I seem to be most interested in concept stuff. I feel it allows me to make (most of?) my mistakes on the screen, not in steel! I also happen to have a 30" Graphtec plotter, so I can do full size drawings of anything I feel I need. I always do one for stays, and that is also how I matched the radii of the tubes for the Kurvy Kroozer.


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## RCP FAB (Jun 15, 2011)

Here's a link the the SRAM specs, if anyone needs it. http://www.sram.com/sites/default/files/x0_x9_x7_x5_frame_fit_specs_gen_000000002876_-_rev_b.pdf


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## golden boy (Oct 29, 2008)

Subscribing to thread....great question, Andy! I'm using SolidWorks for frame design and I have been putting off modeling cranks/chainrings. This thread will help.


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## afwalker (Apr 26, 2012)

RCP FAB nice link, that's all the good info right there.
Now for shimano spec, all I can find for XT deore dyna sys 2x10 is
http://www.shimano.com/media/techdo...FC/EV-FC-M785-3165A_v1_m56577569830800932.pdf and http://www.shimano.com/media/techdo...SI-5MZ0A-001-00-Eng_v1_m56577569830746328.pdf

Where is the numbers on shimano? Did I miss it? 
I can measure mine, but it won't be that accurate I wouldn't think. It'd nice to nail it, instead of guessing. Especially if it's really tight, like bigger tires.
thanks all
andy walker


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## Meriwether (Jul 26, 2007)

> Where is the numbers on shimano? Did I miss it?
> I can measure mine, but it won't be that accurate I wouldn't think. It'd nice to nail it, instead of guessing. Especially if it's really tight, like bigger tires.
> thanks all
> andy walker


PVD's Wiki:
Shimano Framebuilder Info - Pvdwiki


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## afwalker (Apr 26, 2012)

Sweet! Now it's all in one place. Excellent learning experience for me, thanks everyone!
cheers
andy walker


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## 18bikes (Jan 15, 2007)

afwalker said:


> Great work 18bikes! I think that would be super helpful. Your adapter , BB tower cap, did you model it after a certain bb bracket, any spacers accounted for? Thoughts on design?
> I'll make one for a CK bb and no spacers I would guess, on the shimano spec.


I used the data on PVD's wiki, which is based on the crank being istalled correctly (so for a mountain bike bb on a 73 shell, 1 drive side spacer) so that the chainline is correct. This means If I want to use it on a 68mm shell I would have to put an extra spacer between the shell and the cap, but I don't really build with 68mm so it's not a problem. I just designed it all around the chainset I had in hand so it's not worth me giving any dimensions, just make it work for what you have and the most commen set up you will use it for


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## afwalker (Apr 26, 2012)

18bikes sounds good. I'll make a spacer for my FC-M785 xt deore dyna sys 2x10, It's probably the same as a M985, I will try measuring on an installed bike, but unless someone has access to newer Shimano specs... (please link, make this thread all complete )
Joel, now your measuring device makes sense, for an anvil jig with bb centering post, I can do some similar dohickies now that the numbers mean something







cheers
andy walker


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## afwalker (Apr 26, 2012)

Doh! Won't work on Hollowtech II cranks! duh.
back to Joel's idea.
cheers
andy walker


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## afwalker (Apr 26, 2012)

I may try modeling 22/34 chainrings based on this thread:
http://forums.mtbr.com/shimano/shimano-xt-fc-m785-crankset-38x26t-24t-possible-769119.html
cheers
aw


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## 18bikes (Jan 15, 2007)

I'd suggest just finding any old triple crank (preferably isis or octalink so you don't have to make a square end for your adapter) and using that. It doesn't really matter what it is, if you can get to our shop I'm sure I have something in the scrap bin I can give you, most shops probably do


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## afwalker (Apr 26, 2012)

I'll check my Lbs for a triple, something round, and get at least a good visual. If not, I shoot a pm
cheers
andy walker


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## afwalker (Apr 26, 2012)

What a fun project! Got an octalink2 triple, just a 22 on there now, I'm good to go. Thanks everyone for the great input, learned a lot.
cheers
andy walker


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## RCP FAB (Jun 15, 2011)

Andy,

Could you upload some bigger pictures, looks like a sweet set up.


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## afwalker (Apr 26, 2012)

Thanks RCP FAB 
Small pics to not overload mtb.com's servers, originals at
Flickr: afwalker's Photostream
2" Al, turned down to 1.5" 33.74mm goes inside BB, 13mm width is what I measured the CK BB cup + 1 2.5mm spacer to be. The crank was my go/nogo measure.
cheers
andy walker


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## RCP FAB (Jun 15, 2011)

Nice!


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## unterhausen (Sep 28, 2008)

you inspired me to raid the used cranks down at the bike shop. All I could find was an ISIS, which is not as good, but I'm pretty sure I can get it to work.


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## afwalker (Apr 26, 2012)

Just turn the spindle holder down til it just takes the ISIS without too much wiggle and it's good to go Licensing fees go to 18bikes!
cheers
andy walker


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## 18bikes (Jan 15, 2007)

The crank I use is an Octalink, I personally think it is easier to make work with an OCtalink or ISIs crank, just do the calcs so the chainrings end up in the right place.

Please send all licensing monies to my Nigerian bank account, then I will forward detailed plans of the part....


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