[Ted Wojcik]

How about a discussion of some of the challenges in designing a 29er frame. Let's talk about making a frame with an 18" seat tube and using a front dérailleur. When done, I will build the frame and we will have a local 29 fan test it. We'll call it Monkey Butt.

 

[tozovr]

with the 18" ST and a front derailleur the main issue is the operating angles of the actual derailleur right? So the tube either needs to have a crazy angle (steep?) or you need to manipulate it right? In steepening the angle you effectively shorten the Top Tube...then you get Toe overlap issues and possible fork crown interference.

If we call it monkey butt, the front should be brown and the back, Blue.

 

[Ted Wojcik]

Actually, the biggest problem is if we make the chainstays short enough for good climbing/traction, there is an issue with the front dérailleur hitting the rear tire when on the small ring. If the chainstays are long enough to minimize this issue, the wheel base gets long and steering starts to slow down in addition to the decrease in traction. As this discussion goes on, I will present some drawings with exact dimensions as well as recommendation on how we might address these challenges.

 

[tozovr]

I'm cheating...FTW, Darrell and I just chatted about this on the Sinister 29er a few months back

to keep a sub 17" seat tube angle the seat tube got a nice dogleg in it.

I spoke with Chris a week or two ago, sounds like you guys are kicking ass!

RJ

 

[Angus]

Ted,
Great to have you aboard an on RM! I have admired your quality for years.
I am not a frame designer (nor do I play one on TV). But I will be watching this thread to see what develops, as I am an avid 29er fan. Cheers...

 

[MMcG]

I'd say put a little bend in it - get the chainstays to around 17" and find an older Shimano rear derailleur (say an old XT or LX or something - one of the models that Surly used to recommend on the Karate Monkey) and then have at it.

Also now that so many new tires are coming out - design considerations should also include the ability to run as wide a tire as possible should a rider prefer to go that route, but with a design that would allow for ample chainring clearance for at least a two ring set up.

Another thought would be a seat tube to top tube brace on the frame to provide for a slightly more sloping top tube which could provide a little more clearance for the rider.

Just a few thoughts on my end.

 

[MMcG]

I had another thought here.

What about some type of sliding rear dropout setting or slotted dropouts at different chainstay lenghts. So for example, an east coaster or a short chainstay advocate could run the frame in a short chainstay mode, but a west coaster or a fireroad type of guy could lengthen the chainstays a tad for his or her preference? Could this be done via Paragon Sliders or perhaps some type of system like they utilize on the Evil Sovereign?

 

[Ted Wojcik]

This is the dialog I'm looking for. I'm on the way to the shop now, so I will continue this chat later in the day. Let's see what grows out of this.

 

[Stray_cat]

I'd certainly like to see a 29er using a shorter wheel base. Most of the ones I've tired I've though to myself "hey I'm on a big bike." I'd say do what ever you have to do to get those chainstays short.

 

[MMcG]

This is the dialog I'm looking for. I'm on the way to the shop now, so I will continue this chat later in the day. Let's see what grows out of this.

Ted - thanks for starting up this thread. Should make for a real solid conversation here. I made it a sticky so it will stay on top for people to see easily.

All the best,

Mark

 

[Toddre]

This should be interesting to follow... Can't wait to see how it turns out..Maybe it will help me with some tweaking of some frame designs I'm working on for future projects...of course, the frame here is too small again...lol

 

[MMcG]

This should be interesting to follow... Can't wait to see how it turns out..Maybe it will help me with some tweaking of some frame designs I'm working on for future projects...of course, the frame here is too small again...lol

We'll just get you a really Long seatpost!

 

[Possum]

How about a 17.75" chainstay? 73.5deg STA?

When you say 18" seat tube, do you mean "traditional" 18" seat tube (i.e. for a rider that would normally ride an 18" (c-c) frame in a 26" bike)? This would be roughly a "medium" sized frame, with an ETT of 23.75-24"?

At this size, I don't see toe overlap being a problem, unless you get into like a 71deg STA, unless your rider has Sasquatch feet.

I see your primary drivers here being a)clearance with the front der and the rear tire and b)sufficient mud clearance for the rear tire while still being able to fit 3 chainrings and not use a 120mm wide bb.

My suggestion would be a 73mm shell, so that you can put the stays a little farther outboard. You're probably still going to have to do some of your own custom bending to get enough clearance for a Rampage and be able to use all 3 rings.

I honestly think the front derailleur location takes a back seat to this issue.

Thoughts?

 

[sportcult]

How about a braze on style front derailler? You could just have a little arm to place it where you need it.

 

[eMcK]

Great thread.

Rather than the 73mm shell, perhaps go with a press-in bering design as used on quite a few road bikes and the new Pivots. This should give plenty of space to get those chainstays wide enough for 2.3's and some mud.

I would give up my front derailer for some really short chainstays, but I would guess to be in the minority there. I like the Wolfhound style split seat tube, but it would seem to preclude the use of a front derailer, although I wonder if an E-type or braze on would work.

What I would like to see other than short chainstays: Longish top tube (~24") slackish head angle (~70) to go with a higher rake fork, and slackish (~71) seat angle. High BB, at least 12", maybe a bit more. Some extra standover would be great also, with either an extended seattube or a small brace, ala 1st gen El Mariachis.

I happened to be looking at a custom 20" wheeled kid's bike today with the Wojcik name on it.

 

[MMcG]

An E-type is a good idea. Is anyone utilizing that type of set up on any custom frames?

The slacker HT angle with the higher rake fork makes sense for rigid, but if one were to use a suspension fork, about the slackest you could go would probably be 71 degrees don't you think?

I'd love to hear thoughts about a seat tube angle as slack as 71 degrees.

 

[Frank Tuesday]

An E-type is a good idea. Is anyone utilizing that type of set up on any custom frames?

The slacker HT angle with the higher rake fork makes sense for rigid, but if one were to use a suspension fork, about the slackest you could go would probably be 71 degrees don't you think?

I'd love to hear thoughts about a seat tube angle as slack as 71 degrees.

This is how I view it, and the idea I designed my geo with.

Set your seat relative to the handlebar position to adjust the correct cockpit length and weight distribution for seated position. Once you have that, choose the BB position that gives you the cockpit size and weight distribution that you want for a standing position. Of course, if you buy into KOPS, this is heresy.

 

[MMcG]

This is how I view it, and the idea I designed my geo with.

Set your seat relative to the handlebar position to adjust the correct cockpit length and weight distribution for seated position. Once you have that, choose the BB position that gives you the cockpit size and weight distribution that you want for a standing position. Of course, if you buy into KOPS, this is heresy.

Frank - perhaps you could throw up a photo or two of your bike to provide some visual examples of this. That would be greatly appreciated.

And Welcome to Ridemonkey!!

Cheers,

Mark

 

[tozovr]

AGreat thread.

Rather than the 73mm shell, perhaps go with a press-in bering design as used on quite a few road bikes and the new Pivots. This should give plenty of space to get those chainstays wide enough for 2.3's and some mud.

I would give up my front derailer for some really short chainstays, but I would guess to be in the minority there. I like the Wolfhound style split seat tube, but it would seem to preclude the use of a front derailer, although I wonder if an E-type or braze on would work.

What I would like to see other than short chainstays: Longish top tube (~24") slackish head angle (~70) to go with a higher rake fork, and slackish (~71) seat angle. High BB, at least 12", maybe a bit more. Some extra standover would be great also, with either an extended seattube or a small brace, ala 1st gen El Mariachis.

I happened to be looking at a custom 20" wheeled kid's bike today with the Wojcik name on it.

I'm sporting 71.5° head Tube angle with the 73° ST...24" TT and the 17.5" seat Tube (center of BB to top of ST). 73mm wide BB shell and no way in hades to run a big ring. 12.75" BB height

This was based on quite a few rides on different stuff available and most importantly, what Darrell, Frank and I wanted out of a 29er here in the depths of New England. This was a very specific thing for us, hence no provisons for a big ring etc.

We didn't really worry about mass market appeal, just our vision. It works awesome for us, but I know there are folks out there who would hate my bike.

 

[MMcG]

I'm sporting 71.5° head Tube angle with the 73° ST...24" TT and the 17.5" seat Tube (center of BB to top of ST). 73mm wide BB shell and no way in hades to run a big ring. 12.75" BB height

This was based on quite a few rides on different stuff available and most importantly, what Darrell, Frank and I wanted out of a 29er here in the depths of New England. This was a very specific thing for us, hence no provisons for a big ring etc.

We didn't really worry about mass market appeal, just our vision. It works awesome for us, but I know there are folks out there who would hate my bike.

I took a parking lot spin on D's Simon Bar last night. Holy Crap - that's one helluva nice bike that Simon Bar! You guys done good!

 

[tozovr]

I took a parking lot spin on D's Simon Bar last night. Holy Crap - that's one helluva nice bike that Simon Bar! You guys done good!

You should try one without the gonky H-bars...and gears

Pretty stoked Darrells fork turned out breaking in very nicely.

 

[MMcG]

You should try one without the gonky H-bars...and gears

Pretty stoked Darrells fork turned out breaking in very nicely.

I loved those Gonky H-Bars. And his fork was very nice!

 

[eMcK]

An E-type is a good idea. Is anyone utilizing that type of set up on any custom frames?

The slacker HT angle with the higher rake fork makes sense for rigid, but if one were to use a suspension fork, about the slackest you could go would probably be 71 degrees don't you think?

I'd love to hear thoughts about a seat tube angle as slack as 71 degrees.

Some of the newer 29" forks on the market have a bit higher rake, the Fisher OE Fox F29 comes to mind, along with the Minute and the Maverick, although I'd have to sit down and do some figuring to see what the trail would be with a slacker head angle.

The slack seat tube with a longish top tube, paired with a shorter stem would get my weight further back over the rear of the bike, helpful to get the front wheel up and over things, and to stay more centered on the bike on steep downhills.

 

[MMcG]

Some of the newer 29" forks on the market have a bit higher rake, the Fisher OE Fox F29 comes to mind, along with the Minute and the Maverick, although I'd have to sit down and do some figuring to see what the trail would be with a slacker head angle.

The slack seat tube with a longish top tube, paired with a shorter stem would get my weight further back over the rear of the bike, helpful to get the front wheel up and over things, and to stay more centered on the bike on steep downhills.

I think the Maverick is 47.3mm of offset and one of the Manitous might be 48mm.

Thanks for the reply. might that slack of a seat tube angle cause you to "loop out" a bit on climbs? Whattya think?

 

[Ted Wojcik]

I'm sorry about the delay in posting here, but I have to make bikes during the day and the computer is kept at home to keep the shop's environment from eating it.
This is going to generate a long discussion. Let me lay out some ground rules. (really there are no rules, but we do have limitations) Every frame/bike builder has restrictions, his stock list, that is the available tubing, drop-outs, braze-ons, and other needed fittings, and available components. I would like to use readily available parts. If we start designing a frame to use proprietary components, there will be a time when the project will be obsolete. Lets think on the long term. You will find out how challenging designing a bike to suit a large assortment of riders can be. I don't want the identity of the bike to be lost in compromises, but it needs to be as universal in appeal as possible. I'm going to build this frame with steel because the stock list is so big and I am committed to that material. We will talk about why as we go forward.
We need to decide on the components and fork. I will tweak the geometry and weight distribution as the build progresses, after all, 25 years of frame design shouldn't go to waste. We will find there are ways of making the bike handle the way we want without a predetermined trail number. We will use a ratio called stability index that includes fork offset, head angle, wheel diameter and mass, and center of gravity placement. Because fork offset is provided by the fork manufacture, we are constrained in geometry. I will set the head angle last. Let's select the component group and fork first.

 

[pinkshirtphotos]

sliding vertical dropouts with the disc mount built into them would be really cool.

 

[Possum]

I vote Reba fork and XT components. Nice, durable, reliable, fairly affordable. Also fairly standard. No goofy H-bars or any other "specialty" type items.

I think everyone is going to learn a good deal on this. I know I learned a lot when I built my frame. Producing the drawing was an education in and of itself, in terms of learning how much changing one aspect changes several others. Then actually putting the frame into the jig and getting it all to work was another level of education.

 

[Psychic_Pimp]

This promises to be a fun discussion, indeed.

I had another thought here.

What about some type of sliding rear dropout setting or slotted dropouts at different chainstay lenghts. So for example, an east coaster or a short chainstay advocate could run the frame in a short chainstay mode, but a west coaster or a fireroad type of guy could lengthen the chainstays a tad for his or her preference? Could this be done via Paragon Sliders or perhaps some type of system like they utilize on the Evil Sovereign?

Another option to make a frameset more versatile is what Frank the Welder has done with the Simon Bar and others. Interchangeable dropouts could be used so that one could run a track end or vertical drops. Different sizes of vertical drops could also be machined. That way the same frame could be configured geared with longer or shorter chain stays so it could be set up as a fire road bomber or rock crawler without messing with sliders or slots.

 

[tozovr]

I agree about building the bike for across th eboard acceptability. I think every single person here has an idea about what makes a perfect 29er for themselves....unfortunately that bike might be a nightmare for someone else.

I was lucky to work with Frank, as many have been to work with Ted...to find someone who can translate what you dig, into angles and dimensions. I can tell you what I like and don't like about certain bikes, but can not articulate that in number at times. Since the Simon bar, that has changed quite a bit. So instead of maybe tossing out things like "short stays" or steep HA, maybe just talk about what you have and why it rocks or sucks for you and where you ride?

lastly, I don't think the current reba platform is a good basis as it will undoubtedly change to the next gen of offset...I pray it does anyhow LOL. They'd be crazy to keep it at 38mm. Maybe the manitou or th enew Fox...not so much the Maverick DUC32 (as much as I LOVE mine)-it's just too uncommon.

 

[Ted Wojcik]

I understand that Fox has made the first of their 29er forks OEM only. I will try to pry one out of their hands for this project. I'll let you know as soon as I talk to the rep. I think XT is a good idea as well as Paragon slider drop outs.

 

[pinkshirtphotos]

ted, you can order the new fox 29er fork from bti i think.

 

[Ted Wojcik]

Unless things have changed recently, Fox does not sell through distributors. I have an OEM account with FOX, but I was told they had an exclusive deal with Fisher for the first of the 29" forks for 1 year. I could be wrong, but I will check tomorrow.

 

[ByStickel]

One nice solution to clearance issues is elevated chainstays. Sure, they look old-fashioned, but they allow for easy tire clearance. Biggest issues for a 29er happen at the tire/chainring/fr. der. junction. Most , but clearly not all, of those problems are solved by e-stays.

Front derailleurs stink, especially on 29ers. Since we're talking east coast here (crossing myself), I'd love to see a 2x9 20/32 crankset, sans bashguard, with the rings pushed out as far as possible without increasing Q.

Using an old-school bottom swing front der (non-universal pull) will gain you a few precious millimeters, but where are you going to find them? Unfortunately, top-swings would allow for lower, stiffer chainstay location on an elevated bike.

Ted, will you let me in on your beadless welding secret? Pretty please? I'll be up in the neighborhood this coming week and could bring my trusty Huntsman and some turkey leftovers...

PS: fox forks are currently available through retailers, in the retail-offset (not G2). O.E. accounts will have access after 1 year.

 

[tozovr]

I understand that Fox has made the first of their 29er forks OEM only. I will try to pry one out of their hands for this project. I'll let you know as soon as I talk to the rep. I think XT is a good idea as well as Paragon slider drop outs.

Ted, They'll sell you one of the Non-OE forks (44mm offset as oppose dto 46 IIRC?) but Gary Fisher has the lockdown on the G2 offset until '08 sometime. You or Chris can likely EP a normal one though.

RJ

 

[sportcult]

An E-type would be cool so you could just take it off if you want to run 1x9 or single (as I would). It would complement the versatility of the slider dropouts.

 

[Ted Wojcik]

The problem with dérailleur clearance is that the tail end of the cage hits big tires with short chainstays when on the small ring. When standing and cranking hard, there is enough tire deflection that it will require more that a millimeter or two clearance. Do we limit tire size or compromise chainline? The new cranks from Shimano kinda' prevent screwing with chainline, but offer great stiffness. Because 29" wheels have such a big rollout, we could live with a 20 tooth small ring and a 2X9, but we are leaving the realm of off the shelf parts. Elevated chainstays still won't increase the tire to cage issue. I'm going to do some precise measurements and a drawing and we can see how much room we have and work with that. It will be a few days before I can post the drawing because of some software issues. I had a bad virus that required reformatting my 'puter, so I can't convert my CAD files to a postable format right now. I will try to straighten that out over the weekend

 

[MMcG]

My vote would be for a Fox F29er fork - that fork is getting great reviews and it has a 44mm offset (the non Fisher OEM one) which is a great middle ground for a 29er frame. Perhaps Mike B. could help out with some Stan's wheelset for this. He's a RM regular and works for Stan's.

Perhaps we could get Brian HCM to offer up some Hope bits for the build as well (headset, seatpost collar, skewers)

I think the frame should be done up in the Signature Red, White and black or perhaps a Ridemonkey themed paint scheme (with some type of light to dark green fade scheme to it).

I could go on and on I guess.

I still wonder if there isn't a way to find pile of New Old STock Shimano front derailleurs that could get the job done. I had one on a small Karate monkey and ran my wheel all the way forward in the drops with an Exiwolf tire and had plenty of tire clearance. I knew I shoulda kept that front derailleur!

This thread kicks ass! Let's keep it going folks!

 

[MMcG]

One nice solution to clearance issues is elevated chainstays. Sure, they look old-fashioned, but they allow for easy tire clearance. Biggest issues for a 29er happen at the tire/chainring/fr. der. junction. Most , but clearly not all, of those problems are solved by e-stays.

Front derailleurs stink, especially on 29ers. Since we're talking east coast here (crossing myself), I'd love to see a 2x9 20/32 crankset, sans bashguard, with the rings pushed out as far as possible without increasing Q.

Using an old-school bottom swing front der (non-universal pull) will gain you a few precious millimeters, but where are you going to find them? Unfortunately, top-swings would allow for lower, stiffer chainstay location on an elevated bike.

Ted, will you let me in on your beadless welding secret? Pretty please? I'll be up in the neighborhood this coming week and could bring my trusty Huntsman and some turkey leftovers...

PS: fox forks are currently available through retailers, in the retail-offset (not G2). O.E. accounts will have access after 1 year.

Steve - welcome to the Monkey!!! Stoked to have you hear and contributing to this thread.

Cheers,

Mark

 

[BikeGeek]

This thread kicks ass! Let's keep it going folks!

Interesting reading so far. I don't know enough about frame geometry to participate, but I'm looking forward to seeing where this goes.

 

[Ted Wojcik]

Hi Steve! If I taught you how to weld like that, what would set my frames apart from the rest. LOL. Practice, man, practice. I'm leaving for Ct. Tuesday to eat the bird, but I should be back Friday. Give the shop a call if you want to stop by.