Hello there,
i’m currently trying to get built my very own muni but am having trouble on some of the specs that are desirable for the sport, I’m making my own hub with the help of a local engineer/bike shop owner, but need to urgently know what the ideal width is of inside of crank to inside of crank, this puts limits on the whole hub design. Any help whatsoever would be appreciated,
Mark
Mark,
There’s a really helpful writeup on building custom munis at www.muniac.com that I referred to every now and then when building my muni.
I measured my 3" Nokian Gazzaloddi tyre to be between 71mm and 72mm. I’ve actually only got about 2mm clearance! This was a mistake though. My design specified that the fork legs should be parallel which would’ve allowed for about 6 or 7mm clearance but it wasn’t followed for some reason. Oh well. I’ve learnt from my mistakes…I’d say go for about 10mm clearance because you’re not going to hit your legs on the crown of the frame.
Here are some of the specs of my frame:
Tubing for fork legs - 19mm x 32mm (I think it was crimped from 1" dia. tubing)
Top of crown to centre of hub - 350mm
Spacing of legs at the crown (inside) - 74mm
Spacing of legs at the hub (inside) - 86mm
Bearings - 41mm dia.
Thickness of bit connecting legs - 6mm
Seatpost section - 150mm, accommodates a 22.2mm seatpost…you’ll probably want a bigger diameter.
I think the frame ended up weighing about 900g which is apparently pretty light. The muni is only 6.3kg or something around there.
Hope that helps, custom muni making is good fun and very satisfying. You’ll end up with a one of a kind muni. Here’s a photo of my custom muni…
Andrew
I just realised that link isn’t very helpful. Go to http://www.muniac.com/emuni.htm and go down to “Building a Custom Muni” or whatever it says.
Mark,
If you went to Andrew’s link, that’ my epic novel on my building a muni experience. I am pretty sure I included all specs except the one you are looking for.
The first thing I would do is make sure the hub you build is wider than the tire. Assuming you will be using a 3.0 Gazz, a width similar to a stock Suzue hub is two short. You also need to budget in the side clearance on both sides of the tire. So maybe start out that way.
Also, why not figure out a way to get a commercially available hub and then measure that to begin.
Cromoly can bend when welded.
Be careful, your use of the word, “urgently” scares me. This isn’t something that can be pulled off quickly, IMHO.
Good luck
Rod,
Thanks again for doing that write up, it helped me a lot. I’d forgotten it was yours.
Andrew
thanks
thanks for that info, it has given me a ball park figure from which we can start serious designs. On a different note what saddle would you go for the Myata or the KH velo?
Tyre clearance is important, most designs seem to taper in towards the hub, so that you can have a big fat tyre but without a 3.5 inch wide hub. A straight down design would mean you’d be stuck with a narrower tyre or a much wider hub.
There are some disadvantages to making a 3"+ wide hub, you’ll end up with a larger distance between pedals. Some people like their pedals to be far apart, others don’t. A lot of people use bicycle euro cranks on suzue hubs, which gives a pretty narrow uni. There are a few people who like width and use mtb cranks that flare outwards, but most people seem to have straight cranks.
The current standard muni hubs are KH 56.7mm, profile 65mm, suzue 62mm width, so there’s not much difference between them all. That’s flange to flange width (not distance crank to crank though).
Out of interest, why a custom hub rather than profiles? Won’t it cost at least as much, not have the guarantee and probably not have had as much design and definately not be so well tested, so not be so good?
If you want a good (but simple) frame design, buy yourself a Yuni/Nimbus II frame for not very much at all and look at the way they’ve designed that.
Out of interest, if it’s urgent, why not just buy a cheap frame and make a hub to fit in it first and then try building a better frame later?
Joe