If I ran the circus: Plus Bikes, Chainline, and Short Chainstays

As the world of mountain bikes gets more and more diverse, things get... more interesting for a framebuilder. I've got a big drawer of obsolete tools and parts that are only 5 years old (need a jig to install an ISCG mount or direct mount front derailleur, anyone? 150x12 through axle dummy? 1 1/8" head tube stock? Didn't think so...) and I'm constantly getting presented with odd new problems to solve.

But hey, interesting times. And all the options out there are just simply awesome for riders. The bad old days of 71/73 and 2.1" tires are long gone (though you can still have that if you want it!)

Because I build a decent number of plus size (ie, ~3" tire) bikes lately, and I have a lot of picky customers who don't want just a big tire slammed into really long chainstays to make it all work, here's the plus-bike wish list, as brought to you by someone who builds them and rides them too.

First off, if you're someone who fits nicely on a 29er, consider that 29+ is really 30.5" diameter, give or take a few mm. If you're close to toe overlap on your 29er, or you really feel like the bike is close to too long/unwieldy - then you should do 27.5+ (about 29" diameter), not 29+. Likewise if you're pretty small, 26+ exists and is a great option (it's basically the same diameter as 27.5, but wider tires). Don't just decide you want fatter tires and automatically upsize your wheels at the same time - that might not be appropriate for you and what you want to do.

The most important thing to do for these bikes (regardless of wheel diameter): wider than normal chainline. Let's assume you won't run a front derailleur. That's a pretty safe assumption these days with 1x giving up to 4.4x1 overdrive - enough for anything that will mostly be ridden on a trail for 95% of riders.

The battle, as always, is fitting the chainstays, tire, and chainring all into the same small area near the BB shell. A quick look at any mountain bike will show you why this is trouble. Every extra millimeter we can squeeze out is worth it's weight in gold, so throw the usual ~50mm chainline out the window.

How? Lots of ways, in order of max tire clearance/short chainstay awesomeness:
1. Boost (ie 148mm hub spacing, ~52mm chainline)! It only gets us 2mm of extra space, but that's not a bad thing. If you do nothing else, you can do a boost rear end/crank.
2. Run your chainring on the outboard position of a triple crank (~56mm chainline) and offset rear dropouts/hub to match. Alternately run a direct-mount chainring flipped over (ala Raceface Cinch) or BB30 ring on GXP crank (SRAM). This helps a ton and also has the sidebenefit of a mostly dishless rear wheel.
3. Run an 83mm BB (~55mm chainline) and matching cranks. There are lots of great options out there now though finding 175mm cranks in XC-ish configuration can be challenging. Offset rear wheel to match. Or build around a 150/157mm through axle rear hub.
4. Run an 83mm BB and offset ring (~60mm chainline). Offset rear end 10mm or so to match or run a 170/177mm fatbike rear end (ala Kevin's low-Q fatbike). My favorite option, this actually gives enough room to run a 4" fatbike tire if you so desire and plenty of space for short, short chainstays with loads of tire clearance.
5. Run a 100mm BB and 170mm rear end. If you're going for a fatbike with plus-tire/summer setup, this is the next step up. Some folks won't like the Q factor, though.

I get a lot of pushback on all of these ideas from people because it seems some folks are really stuck in the "bike should be symmetrical" mindset. Here's the thing: your bike is already not symmetrical. You have a drivetrain on one side, brakes on the other (assuming disc brakes). Your wheels have the spokes coming out of the flanges at dramatically different angles. In some cases your rims are drilled offset to one side...etc. My goal is to make the bike that rides the best for you - and in most cases, having the rear end symmetrical is going to detract from doing that with many of the plus sized tires that are out there. Yes, you'll have to have a dedicated rear wheel for your plus bike that you won't be able to swap around with your other bikes without redishing it. C'est la vie. Wheels are cheap (relatively speaking).

Q factor is another question. If you really want narrow Q, options get limited. But fatbikes have proven (for *most* people) that Q factor isn't as crucial as you might think. Adding 5mm to each side (ie using an 83mm shell instead of 73mm) isn't even noticeable to most riders. You might be the exception, of course, but there's no reason to think you need to worry about it unless you have a preexisting knee problem and you know the Q factor is going to be trouble.

So bottom line: if you want a semi-fat/plus bike, consider letting me go a little nuts to make it awesome. It's going to be weird, yes. But much more fun than a cookie-cutter setup with 45cm chainstays (unless 45cm chainstays is what you need, of course!)

Mess with Texas...

Or just pose your bike in front of some giant accordion type structure...

Thanks to Jon for the picture!  Geometry and geekout here.

Edit: Got a couple folks asking about the sweet Nox wheels. Yes, I sell them. Yes, you can get custom colored decals (costs a few extra bucks). Rims alone are $375 each in any model/size/width. Whole wheels obviously will vary tremendously, drop me a line if you need a price quote.

Oh, what the heck... one more

Sarah's (not my Sarah) new 29x4" bike. Featuring BB wrench counterweight and no shock bushings yet! It's friday...

No decals either? Walt's not even trying...

Pretty normal modern XC geometry, dropper post compatibility, and remote lockouts and adjustable travel out the wazoo. Sooner or later I gotta modernize my own stuff, my own FS bike looks pretty darn obsolete these days.

This thing would fit me pretty well if the seat tube and head tube were both 2" longer

When the weird turn pro...

With apologies to Hunter S.  Sam is pretty small in stature. 4'10", to be exact. She wanted a bike that could, as much as possible, do it all (ie XC, trail/enduro, maybe even huck?)

If you go more compact, the seatstays hit the collar!

Even with 26" wheels, 100mm travel was pushing standover too high for comfort... until we went old school (props to Cannondale) and threw the usual front triangle configuration out the window. We also got one of the excellent new Syntace Flatforce stems (*excellent* for folks struggling with handlebar height) Result? Plenty of standover, 100+mm travel, and an appropriate geometry for someone on the short side.

415mm chainstays. Eat your hearts out, tall people.

Here's the print:

Flatforce stem gets the bars level, not shown here.

Gal's Slack/Short/Long FS bike... done!

Well, it still needs cable guides. But mostly done.

Really squeezing to get everything to fit with those short stays!

DBinline is hot hot hot - 140mm travel here.

And, of course, the geometry (with magic invisible rear end). No sag shown here. Gal also has a fun 29+ hardtail I built for him a few years back.

Short rear end, slack, long travel... sound familiar? 

Walt finishes something!

It's been an epic week of tonsillectomy chaos (along with: teaching a framebuilding class, selling a house, possibly buying a house, our usual daycare shutting down...) I am finally back at the bench and finished up a couple of frames that have taken *way* too long.

I'll post up just one for now. John's short-stay 29er.

And of course, geometry info, now presented in a nice easy drawing instead of voluminous text. It's got some offset at the dropouts to allow a decent sized tire along with a 34t chainring running at 55mm chainline, and all the usual bells and whistles (but no front derailleur). 

72.5cm effective toptube...

Not much to give it context here, but this is going to be one BIG bike...29+ is a godsend for those really big folks out there! Upward curved toptube? Standover's not a problem when you have a 94cm saddle height and ~40" inseam!

Just to get the bars high enough, this will use a 150mm travel MRP stage fork!

Joe's Geometry Jamboree

By popular (ok, one person) request!

Executive summary: short and semi-slack racey bike for attacking the twisties in TX.

New bandsaw says, "I am not impressed"

-69.5 HTA and 90mm trail, designed for a Niner carbon rigid fork or 80-100mm travel suspension

-60.5cm ETT, 66.9cm front center, 107.8cm wheelbase. 

-42cm chainstays, plenty of room for a 2.3 and a 34t oval chainring (lotsa runout on those bad boys - I had to have Joe send me the crank and ring to double check clearances)

-295mm BB height. Just a smidge on the low side if you were running suspension but with a rigid fork you can go a hair lower and Joe likes low.

-Curved seat tube for tire clearance. Joe took it easy on me and let me use straight tubes for the rest of the front end. 

-Built for a nice normal 27.2 post and using nice skinny-ish 35mm/28.6mm down and toptubes for a steel-is-real ride with a little give. Joe is not a huge dude either, so fat tubes were never on the radar.

-Paragon rockers for SS fun if needed, plus chainstay length adjustability.

Looks like the car's going to go over backwards...

Couple pictures from John

Short-stay (though he's running the wheel slammed...back?) 29er, baby!

Bar ends are so 1995

I like DT cable routing on these curved-toptube bikes

Ken - done

Flowers coming up?

There is a lot to talk about with this frame - super long front center/slack/low aggro geometry for big-ish 27.5 wheels (up to 27.5x3!), 148 spacing with some offset (!), supertherm pipes all around, etc, etc.

I will do several posts on these topics, though, because they all deserve more attention than I can give them right now.

Blooming?!?! Spring, you're here too early.

So, basic geometry:
-67 HTA (assuming quite a bit of sag) with a 140mm fork, 770mm front center.
-72.5 effective STA and 66cm effective toptube
-41.5cm (actual, 41cm effective) chainstay length that can adjust out to 43.5 with the rockers. Clearance for up to 27.5x3" tires
-Around 30cm bb height with a rider onboard
-For a 31.6 dropper post (external routing, Ken wanted the rock-solid reliability of a Gravitydropper over some of the blingier but less durable options)
-148x12 spacing, offset 2mm to the driveside (more on that later)
-Supertherm tubes and a ton of beef but "only" 5.8# with all hardware

Now available: Curved tubes for framebuilders

I've spent quite a while figuring out a reasonable technique for making nice curved tubes with butted tubing and I've had a reasonable amount of luck (after ruining plenty of fine American steel in the process of learning what not to do). If these items are popular I may offer some other options that I commonly use (curved 31.8mm seat tube for 27.2 post, curved 34.9 seat tube for 31.6 dropper post, curved 31.8 supertherm top/down tube, 19mm twin toptube/seatstays?)

Without further ado:

Please note: All bent tubes will exhibit some minor ovalization. It is up to the end user/builder to determine appropriate diameter/butting and miter/cope/join appropriately. There is no visible ripple/flaw at butts/butt transitions (transition from bent/straight on seat tubes is visible). Butts marked for builder's convenience on request.

28.6mm diameter 9/6 single butted seat tube. 650mm total length, 75mm butt. Bottom 250mm is curved 10mm (approximately 1750mm radius). Appropriate for short-chainstay frame designs and will take a 27.2 seatpost. REQUIRES a sleeve or lug at toptube/seatstay cluster. 4130 cromoly. Bent/straight transition is visually obvious and overenthusiastic insertion of a too-long seatpost can damage this tube. Builder must adjust seat angle for desired saddle positioning. $60

-28.6mm diameter 9/6/9 double butted x 600mm. Butts are 100mm at each end. Curved 25mm over total 600mm length (approximately 1750mm radius). Appropriate for toptubes with curve oriented either up or down. 4130 cromoly.  Butt transitions are NOT visible after bending. $70

-31.8mm diameter 9/6/9 double butted x 600mm. 90mm butts at each end. Curved 25mm over total 600mm length  (approximately 1750mm radius). Appropriate for toptubes oriented either up or down, or for light-duty downtube. 4130 cromoly. Butt transitions are NOT visible after bending. $70

-Custom tube bending. Want something unusual? I can bend most sizes of commonly used bike frame tubing, both straightgauge and butted. Heat treated material will cost considerably more, but yes, I can do it. Contact me for a quote.

The Curry-Sixer - Complete!

Thanks to Mark for the photo. Back to work on Monday!

Before bombarding me with emailed questions, please read the 36er FAQ.

Aaaand... we're out.

And just in time. Ugh. It's supposed to be 114 in St. George this weekend!

For those who are curious, this week was devoted to fulfilling my promise of a wedding tandem to Redcoat and Smoyle, who got married a little over a year ago. Logistics (they live in Switzerland) and inertia kept it from happening until now, but I'm finally (almost) done. Yes, it's coupled to fit in an S&S case.

Bungee cords are crucial when figuring out where to put the couplers to fit into a case...

Note that I will only sell tandems to WW frame owners (ie repeat customers) and UT locals. I am FAR from a tandem expert and in many cases talking to Santana or Davinci is a better plan but I am pretty happy with how this one came out and I'd be comfortable selling you one if you're interested. Cost for a frame will be around $3000 but will depend on details so please call or email for a quote.

I'll try to get one more photo tonight of the finished frame.

We'll be back from VT on the 8th of July, don't expect quick (or any) replies to email/phone until then.

Pictures from Minh

Minh says: "shamefully, that's a gold chain to match the kashima". Details and geekery here.

Minh's garage is a bit cleaner than mine.

At least the tires are dirty.

Totally Unbiased Review: Stupidmobile

First off, just to make sure we're clear - the manufacturer of this bicycle made me do something like 10 hours of work, for no pay, just so I could ride it. The company made me pay for all the parts as well as powdercoating the frame and didn't even give me an employee discount. Apparently if I break it, I have to fix it myself.

Bastards.

Sorry about all the shadows. 

So I decided to name it "Stupidmobile". Why? Well, mostly because this bike has the most ridiculously short chainstays you've ever heard of (40 cm, or 394cm if measured horizontally). A 2.1" 29er tire only has 15mm of clearance to the BB shell itself. There's not much way to go a whole lot shorter and for someone who has a 36" inseam, the whole idea of chainstays this short is... well, stupid. Right?

Well, not so fast. My first ride (around the block, in the rain) had me pretty worried - so much so that I pulled out the angle finder to check things over, because it seemed MUCH too twitchy for a bike with a 69 degree head tube angle. After confirming things were right, a little cogitation solved the mystery: I had been riding exclusively on the cargo bike (7' wheelbase!) all winter. Any "normal" single bike was going to feel weird.

Nevertheless, I was still nervous last week when the trails dried out enough to get some real rides in. I set out to find out just how stupid Stupidmobile actually was by riding a number of variations on our local (literally a 10 minute ride from the door) trail system. The Shoreline trail is mostly bench cut singletrack on steep, semi-rocky (limestone) soil. It occasionally wanders up a drainage (the Dry Creek section is a classic) or a mountain (Mt. Van Cott is a fun way to cough up a lung) and it features what might be the most fun section of singletrack in Utah - the Bobsled (yes, it's really berms the whole way, yes, those guys are jerks for riding it when it's muddy). Long story short, it's got most of your types of XC terrain to test frame geometry.

I have to admit that at first, I wasn't riding the bike very well. I was oversteering everything due to the super short wheelbase - the bike steers much quicker than you'd expect from something with a 69 degree head tube angle and coming from an FS bike (my main ride in 2012) with almost an extra 1.5" of wheelbase, it was a bit of a shock. If you leave your butt in the saddle over any kind of rough terrain the tucked-under rear wheel will let you know in a hurry by attempting to eject you. I managed to not crash up the Dry Creek climb and figured I'd take it easy on the Bobsled. Unfortunately, I was with my buddy Paz Ortiz who is not only the only non-douche realtor I know in SLC but also a really badass descender and enduro/SuperD racer. He and I always duke it out on the descents so I ended up riding way faster than I should have.

Man, that rear tire is close to that bottom bracket. 

The results were stunningly awesome. Stupidmobile's short wheelbase let me rip through the berms and the slack front end made things manageable on the rougher and straighter stuff (though to be fair I think a longer bike would be better on the rough/fast/straight sections). I've got experience with this type of geometry and in fact I've been riding similar bikes for years - but I figured there would be diminishing returns under 42cm or so of chainstay length and 42" wheelbase (at least for me). I was wrong. The bike is probably not *faster* on most terrain but it's not slower than a longer bike either and it's super, duper fun for trails where jumping, flying, and general silliness are your goal. Would you be faster in a race? Probably not - the bike is pretty unforgiving of mistakes and a poorly executed bunnyhop that comes up short over a log or rock is going to result in an ass-over-teakettle disaster. I don't even want to imagine how hard it would be to keep things under control after a few hard climbing efforts with your whole body exhausted and your brain on autopilot. It would be bad.

But for rides under 2 hours, or short races, or anything where the goal is fun and not playing chicken with your lactate threshold? Awesome. I love it, I don't regret a thing. I'd recommend it to customers, even, with a few caveats (see the bullet points below).

Awesome stuff:

-Very "intuitive" and hip/lean steering action. If body english is your preferred steering method, this is the kind of bike for you. If you like to jump over/wheelie over/roll up the berm to the side of obstacles, this geometry will help you do it.

-Great climbing traction whether standing or sitting. Man, there's a lot of weight on that rear wheel.

-It's very easy to unweight the front wheel (shocking, I know) for getting up over obstacles whether you're going uphill or down.

-Just plain fun. But then again, it's a mountain bike. Pretty much all mountain bikes are fun unless you're a seriously grouchy individual.

Not much creativity from the Waltworks photography div. on display here.

Not so awesome:

-Mistakes will be punished severely. If you come up short on that jump over the little rocky section your dentist will be getting another mistress and/or boat, probably. Kidding aside, this is a terrible geometry for riding where you'll be trying to go fast when you're not fresh and alert. You need to be on the gas and be paying attention to your lines because the bike won't bail you out of a lot of mistakes that a longer one would.

-Unless your technique is very good or you run a very low bar position, it's hard to keep the front wheel down on some steep climbs. The lack of weight on the front wheel and general high trail number mean that this bike does want to wander on slow technical climbing - those who really enjoy that type of stuff may want an adjustable travel fork or a bit different geometry. It's not unmanageable but it's also far from a perfect climbing bike.

-This frame requires a zero-dish (hub offset to the driveside by 5mm) rear wheel and you can *only* run an outboard position (~56mm chainline) ring. That means no crank mounted bashguard (ISCG can be done, though) and no front derailleur. XX1 cranks are a no-go. A Rohloff hub could work reasonably well as they use a 54mm chainline if you are a planetary gears kind of person.
EDIT: Actually, with a 28t MRP bling ring running at 51mm chainline, XX1 will work. In theory you could avoid the offset rear end here.

-Even with the whole rear end moved outboard to line up with the ring the chainline is not especially good in the highest or lowest gear. The stays are so short that the angle just gets extreme. I've had good luck running 9 out of 10 cogs on a 10 speed cassette, which is plenty for me, but those who want a full range will not be happy with the drivetrain performance. Singlespeeders will have no problems. EDIT: With a 28t Bling Ring, chainline is much better and I get full use of all 10/11 gears.

-Tire clearance is somewhat limited - a 2.3 will fit fine but anything bigger is a tight squeeze. Adding 5mm to the chainstays or using an 83mm BB shell (which brings another set of issues that I won't go into now) would take care of this.

So bottom line: I love this bike. I like it even better than my previous short-stay setup from a few years ago and for the right rider (ie more interested in having fun on 2 hour rides than absolute speed or 24 hour solo sufferfests) I think this sort of geometry is a great fit.

I should also note that the new Paragon Polydrops (which Mark asked me to test prototypes of with this frame) are working great after probably 15 hours of riding and I'm happy to build with them (no extra charge) for anyone who is interested. They are probably not the ideal dropout for this bike due to their length (makes it hard to use the second bend on s-bend chainstays to get any heel clearance) but they offer some cool flexibility in terms of bike setup and I have had zero problems with them thus far. Most riders may prefer the low mount or classic DR2010 (or sliders for the singlespeed crowd) but that's a decision that's complex enough that I'm not going to go into it here.

Don

Don's mostly a singlespeeder and he's got a SS I built for him 7 or 8 years ago, but he wanted a geared bike with a suspension fork for longer, rougher rides. Or maybe he just got old and lame like me and figured out gears and suspension can make up for creaky knees and wrists a little.

In any case, it's a big bike for a tall fellow, built to handle everything the Wasatch can throw at him. Geometry:
-69.5 HTA, 73 (effective) STA
-For a 100mm travel tapered steerer fork
-65.5cm effective toptube, 71.3cm front center (yeah, that's long!), 93mm trail
-43cm chainstays, clearance for a 2.4" tire, no front derailleur
-Curves (toptube, seat tube, stays) for tire clearance and fun.
-32.5cm/12.8" BB height (Don uses 180mm cranks and doesn't like to hit his pedals on stuff)
-Supertherm front end mostly with Deda chainstays and trusty Paragon DR2010 dropouts. Frame weight is about 2300g.

So basically, a bike built for all-around XC adventure, on the stable side for long days in the saddle and rough terrain. Should be a blast!

Nick, this picture is for you - big as a garden gate, as you like to say!

Thursday afternoon quick rant: you can't manual

I hear constantly about how this or that bike doesn't "manual" easily enough. Often I hear this from obvious freds or 50 pound overweight retired dentists online.

Folks, this is a manual. It means you get up on your rear wheel and balance there, without pedaling, and roll along. It's not a wheelie, it's not just lifting your front wheel for a second to get it over a dip or a rock in the trail. Almost no mountain bikers can do it (including most pros), and it's not even a particularly useful skill for most people for trail riding. It's a skill that often coincides with being a really good bike handler and it's occasionally useful, but if you're skilled enough to do a real manual, you can basically do one on ANY bike.

So if you want to complain that a bike doesn't manual well, I'll be happy to listen provided you go grab your trials bike or BMX and manual that for me. Otherwise, you can't manual because you can't manual, no matter what bike you're on, and furthermore, manualing won't really help you on the trail, so don't worry about it.


Yours truly, 36 year old fred who can't really manual Walt