Chainset/chainstay clearance?

[hulsroy]

Hi

When drawing up frames how do you decide how much clearance is needed and where to put the stays?

I am building a montercx-frame using Zona MTB stays and 68 bsa bb. I want to use my 110bcd FSA S LK Light cranks but can not find cad files or drawings online, so I can't really figure out how to draw out the stays.
Is there a standard way of drawing this? I have an exact drawing of the stay shape from Ceeway and I have made a 3d drawing of these.

I want maximum clearance for tyres, but I fear making the stays to wide to fit my chainset.

The picture shows my fear. Mtb chainstays + 68 bb from an old Kona and not enough clearance.

14864658006_f8db81d985_c.jpg

How do you go about this? Is there some obvious measurments og rules I am not aware of? Thanks.

[steve garro]

Dude…..
Why not put a chainring on that and measure the tolerances?

Then write it on the wall for posterity.
For example XT crank w/ a triple if you are < 91mm @ 48mmfrom BB shell all is good. IMG_3697.JPG


- Garro.

[David Tollefson]

Install those cranks in phase, measure the Q, and put that on your drawing. Not rocket surgery.

[Rody]

Holsroy,

Here is everything you need to know to begin the process...

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

Take some time and read it then check back here if you have any questions.

rody

[Will Neide]

Is that photo a picture of your actual build? I like to draw the rear ends out on paper first. Looks like you could have put a nice little S-bend in for for better arm clearance without affecting tire clearance.

[afwalker]

Probably need a dimple for the cranks to clear.
bikecad.ca does draw this out pretty well. Spend some time entering all correct numbers for crank thickness, length, chainstay diameter etc. It's a powerful program and worth the money I'd say.
You can spend time doing a full scale drawing, it will be as accurate as you make it.
Steve has also pointed out that you may well have a clearance issue with you chainrings, go ahead and put one on and do this frame with actual components.
This is a link to a similar thread elsewhere, some good info there on drawing a full size, and making an adapter for chainring checking: chainring clearance modeling
cheers
andy walker

[afwalker]

Opps, couple replies all around the same time, I reposted Rody's link inside that thread since it was so good:)
Thanks
andy

[steve garro]

Probably need a dimple for the cranks to clear.

Steve has also pointed out that you may well have a clearance issue with you chainrings, go ahead and put one on and do this frame with actual components.

Dimples for the crank to clear is a ghetto fix - it has almost 68mm of tire clearance, it's just botched for that crank - sad but true…….you should have sacrificed a few mm's of tire clearance for the cranks to clear, simple as that.

Yes the ring is going to hit there as well as the cranks.

You have a link to your biz but you aren't familiar with basic layout?

For the record, yes I am grumpy, sore & crusty today.
- Garro.

[David Tollefson]

Dimples for the crank to clear is a ghetto fix...

Maybe better to witch out a nice subtle s-bend... [/sarc]

[hulsroy]

Hi all,

I appreciate you taking your time to answer my questions.

1. I didn’t make the bb/chainstay junction in the picture in my first post. I cut it off an old mtb frame. I just used it for showing you my concerns / testing out the different crank options I have at my workshop. I am not using this for a bike.

2. I am using Zona MTB s-bend chain- and seat stays.

3. I ended up making my own method measuring the chain set. I wanted you to tell me how you do this. This is how I did it:

Attachment 71193

Picture is for illustration purposes only.

It is not 100% accurate, but good enough to design the frame geometry.

I am trying to get a 50c tyre to fit using a 68mm bb and 420mm stays.

Attachment 71194

@Garro: Building a tumblr website and posting pictures of your work, in 2014, is very easy. Getting your head around bicycle geometry, not wasting money on cutting your precious steel to wrong lengths etc, is hard work. I am not a pro. I do not claim to be a pro. But I am very proud of my/our work and I put an honor in sharing my/our process and bicycle experiences through my/our website. Yes you are grumpy ;-)

[Rody]

"It is not 100% accurate, but good enough to design the frame geometry."


Holsroy,

What we are trying to communicate is the importance of being 100% accurate in your layout prior to fabrication. You must use a method that clearly illustrates the physical proportions of all components relative to each other to prevent wasting time and materials.

Please keep in mind that regardless of the raw materials used, manipulation of the tubing will likely be required to fit the anticipated design criteria. Seldom are "off the shelf" materials a perfect fit. Having a layout process that helps to determine fit and required fabrication is a necessity for a professional.

Good enough is not sufficient for designing vehicles that are encumbered with the responsibility of life safety.

rody

[Amaro Bikes]

I won't be as polite as Rody, but basically what they're trying to made any of us newbies to understand is that much earlier than starting a tumblr/flickr/instagram/facebook/wtf website where to offer our products to final customers, we should have the very basic knowledges on how to build an absolutely proof and reliable product, based on long time workbench experience and frames under the belt. So if someone asks some basic questions while offering their custom building services on an open basis, it kinds of surprises them and they try to make clear something should be done (get experience) before getting the full package (offering framebuilding services)

Of course, it can be taken as some kind of grumpy attack or similars, and no one likes to be told when they're doing something wrong (me included a lot!), but nothing as far as reality than this view. Consider the thought that those guys have been building bikes for decades and have more frames under their belts than any of us could build in three consecutive lifes, so if they're not keeping their world incapsulated and they share some simple advices and knowledge with any of us, for free, in their spare time, is because they have to love a ton al this framebuilding thing and trying to help other people with less experience. And that's a gift we should thank and appreciate, as the other option would be a forum competely empty of real knowledge and experienced lessons where any possible source of knowledge would be the usual "I've read" "I've seen" "I know a friend" or "As a PhD level fitter". Damn! this would be a real nightmare! :o

[hulsroy]

I see what you are saying. In my drawings and general work I try to be precise.
I understand that there is a difference in being a pro and building for yourself.
I feel that I am honest in my responses to peoples requests and I turn down builds I feel we can not manage or build safely.
That being said I can see that the statement on our site make the impression that we can build anything custom. I have never thought of it that way and I will change the words to something more humble and precise. I also realize that being a pro builder, that have build thousands of bikes, it must be annoying and frustrating when people (hobby framebuilders) pretend to be something that they are not. We have felt that there was a demand for knowing more about the bikes we build and for people to get in contact with us and since it was easy for us to build a site we did.

I really just wanted to know if there was a smart way to measure and draw chainstay/chainset clearence, but ended up learning something more valuable. Thank you.

It seem like the pictures I added do not work. So I will try again.

[hulsroy]

chainline.jpg
Skærmbillede 2014-08-13 kl. 12.35.15.png

[David Tollefson]

Seems that crimping the CS's for tire clearance is the answer.

[hulsroy]

Thank you. I will consider that.

[edoz]

If clearance is a concern, consider using a 73mm bottom bracket shell. An extra 2.5mm on each side doesn't sound like much, but it sure as hell beats 0.0mm.

[Will Neide]

If clearance is a concern, consider using a 73mm bottom bracket shell. An extra 2.5mm on each side doesn't sound like much, but it sure as hell beats 0.0mm.

I think he's building around a particular road crank, so not really an option here.

[afwalker]

bikecad pro
read over the page on the auxillary page for stays:
Stays (Displaying Auxiliary View) | www.bikecad.ca
cheers
andy

[hulsroy]

Thank you Andy. I currently use Rhino for modulating 3d, but it might be worth the money going for bike cad.