velotel
12-06-2017, 04:16 PM
I have zero expertise in frame design. I’m just an old guy who’s ridden a good bit and has had the marvelous good fortune to ride on some astonishingly beautiful mountain roads, paved and dirt. But I enjoy thinking about what a fat-tire road bike is. I also asked a few builders what they think a fat-tire road bike is. You’ll find those at the end so if you want some expertise on the subject, jump on down.
My bike is a road bike wearing fat tires with a subtly tweaked geometry to bring its performance on single-tracks and dirt roads up to what I expect of a road bike on pavement, but without compromising its performance on blacktop.
Single-tracks here means relatively smooth trails, the kind trail runners enjoy, and dirt roads means tame enough that four-wheel drive and high clearance aren’t absolutely required. Grades are generally moderate enough so neither super-low gearing for going up nor dropping the seat post for going down is required.
Two biggies to clarify before looking at fat-tire road bikes: what kind of terrain you intend to play on and how fat a tire you’re willing to ride. Plus the future, what is ridden will evolve. Going from a trail or road like that doesn’t interest me to, well damn, I bet I can ride that. That happens, even at age 72!
Fat-tire road bike geometry has to deal with surfaces squirming around under the tires, with rocks, holes, roots, etc trying to knock the front or rear wheel caddywhumpus, with grades steep enough to climb out of the saddle only the surface is loose so you can’t, etc., etc. Always with impeccable handling on pavement where probably the majority of time will be passed.
Note a special bike for gravel/dirt roads and trails isn’t mandatory. Fatter tires aren’t even needed. I used to ride dirt and rock roads with 23 and 25mm tires and never gave it a thought. But having gone to the dark side so to speak, I now say anyone contemplating spending serious time riding dirt with a road bike and who can afford one would be nuts to not get a fat-tire road bike. They’re just way, way more enjoyable to ride off-pavement.
Chainstay length does not define a fat-tire road bike. Most gravel bikes have longer chainstays but it’s not some huge difference. My Stoner Bike’s stays are 16mm longer than my pure road bike’s. 16mm is nothing. Longer chainstays provide clearance for fatter tires, produce a stabler, smoother ride due to the resulting longer wheelbase, add to the rear end’s stiffness by enabling the use of larger diameter tubes with minimal tube bending for tire clearance.
Forget the back end. It’s only along for the ride, the bass setting the beat. The front end is where the action is, the lead guitar soaring in the stars. On blacktop there isn’t much for the front end to do because technical challenges are lacking. Trails and jeep roads are where a bike’s front end dances, following the rider’s eyes, flicking around rocks and roots, chasing the groove in a wonderful ballet of quickness and stability.
This is where frame builders can differ in their solutions. Steep or shallow head angle, more or less offset/trail, long or short stem, long or short top tube, stiff or soft front end, etc., etc. Which means you need to understand your riding style and be able to communicate that to a builder or someone helping you choose a bike. For my fat-tire road bike, Kent knew my riding style from way back and designed it with that in mind. In technical passages I’m in the drops, pressing down on the front end, the connection with the axle so intimate that the wheel seems to dart before I’ve even seen what it’s darting around.
You need weight on the front end to weave lines through rocks and trees, otherwise the steering’s vague. Which means pulling the handlebar closer in. But too much and the front end will be zigging and zagging every time you blink. A lot of fat-tire road bikes have pushed out front centers via a softer head angle, like mine, but again too much and keeping weight on the front end for steerage control in a steep climb can be tricky. Too short a front center means too much toe overlap plus dropping down steep descents can feel like you’re in the front car in a roller coaster going over the top into a monster plunge. A steep head angle with too much rake will make the front end so reactive you’ll forget what a straight line is. Same head angle with too little rake will be super stable at speed but reluctant to dart around obstacles. A shallow head tube angle with not much rake will be forever flopping into turns with the slightest lean of the bike. Etc., etc.
The front end also needs to be designed for when you’re out of the saddle. A grade on dirt will be harder than the same grade on pavement which means climbing out of the saddle more often. But traction will be thin so you’ll need more weight on the back wheel and of coursre standing automatically shifts weight forward. If it’s too steep to climb seated you’ll have to drop into a low crouch over the top bar with the butt floating over the nose of the saddle, the hands in the drops pulling back and that means the frame needs to have the space for you to do that.
Some people like a low bottom bracket, relative to the line between the front and rear wheel hubs. They say low is more stable. Others like it higher. I think mine is relatively high, or it’s higher than my pure road bike’s. I don’t feel any lack of stability and it gives me more pedal clearance which I really like but to be honest, I’ve never given it any thought one way or the other. As usual, no rule, just personal preference.
Same with the handlebar height. Typical pure road bikes have what I consider crazy low handlebars relative to the saddle height. The flat on my road bike’s bar isn’t far off level with the saddle. The Stoner Bike’s is even closer to level. Again personal preference but I think for off-pavement and on technically demanding trails and dirt roads, the higher position enables shifting weight front and back and keeping your eyes on the trail ahead easier. Also makes riding in the drops super comfortable and ideally the default position. That’s the power position for driving the bike through rough sections.
Lots of parameters to play with to achieve a fat-tire road bike that works for you. Which is why in my opinion they were made for custom builders. Production frames are designed around common denominators someone decided will work for most people. If you fit that criteria, excellent. But riding rocky roads and trails has technical skill requirements that paved riding doesn’t even know exists plus the whole genre of gravel bikes has so many nuances that factory sizing won’t necessarily answer for everyone. Happily there are some production companies providing a wide choice in sizing and design, Moots for one. It was a long week of riding a Moots Routt in Colorado that convinced me a by-design fat-tire road bike totally outperforms a standard road bike on dirt and trails.
Given all this performance criteria, a custom build can be super attractive with the ability to meet any and all needs. Like forks. Apparently off-the-shelf forks for fat-tire road bikes, from Enve for example, are available with only one fork rake, so a front end has to be built around that fork’s rake. A builder who does his own forks could build a frame with a custom fork to provide exactly the handling characteristics desired. I don’t think too many builders do this. Building forks is apparently a pain and expensive. Forks used to be as much the domain of the builder as the frame itself but carbon forks pretty much killed that. Not that people are apparently complaining. My Stoner Bike’s got an Enve CX carbon fork and I’m definitely not complaining.
Which brings up the front end stiffness argument. Some claim the old bikes with their thin steel tubing and steel fork with curved blades serve up a superior smooth ride in rough conditions. Others go the opposite route with an oversized head tube and fat fork blades with a fat, tapered steerer tube, resulting in a stiff front end that refuses to be knocked about by ruts and holes and rocks. Personal preference again. I went with a stiff front end and I’ve never ridden a smoother riding bike in the rough. Bottom line is the suspension is generated by the tires, not the tubing. I also have to admit to not having ridden an old style steel frame in longer than I can remember.
Then there’s this evolution to way fat tires, like the Moots Baxter. My son rides one and loves it. Apparently more and more gravel riders are going fatter and fatter. Gravel bikes or drop bar mountain bikes, the distinction becomes blurred. Which is again why I refer to my bike as a fat-tire road bike because that’s what it is, a road bike wearing fatter tires.
As an aside, I don’t think putting drop bars on an old style rigid mountain bike is going to produce the equivalent of a fat-tire road bike. I rode some mountain bikes back in the 80’s with the WTB flared drop bar and while I loved the drop bar position, they never felt quite right. I think because the frame’s sweet spot for the rider’s mass over the bike was designed for a flat bar and that sweet spot isn’t the same for drop bars.
You also might want to keep in mind that whatever gravel bike you buy today could be considered archaic in a couple of years. I’m sure people are working on suspension forks for gravel bikes and that will be followed by full suspension. I have no idea what those will be called. They also don’t interest me.
I love my Stoner Bike’s simplicity, no shocks, no disc brakes, no electric shifting. Just a straight up road bike tweaked to kick ass off-pavement. Super reactive when needed, super stable at the same time, modestly fat but light tires but skinny enough to keep me knowing I’m riding a road bike, goes everywhere I want to go with more grace than me. Places where I’d need fatter tires and lower gearing I ignore. I’m a dinosaur.
For myself fat-tire road bikes are the coolest thing to come along in cycling since mountain bikes. The world of road cycling’s been beautifully expanded and in my case passion for riding thoroughly rejuvenated. Plus, and this is kind of easy to forget at times, they’re awesome just as pure ol’ road bikes, or at least mine is. That was something I insisted on in my conversations with Kent for the bike. The 35mm tires running relatively soft soak up the asphalt’s bumps and ridges, cling like crazy in turns, and just feel friggin fast. And when the blacktop stops and the road doesn’t, neither does my bike.
I can also guarantee that the currently perceived limits of where these bikes can go are in the process of being blown away. I saw that happening with my son and his riding buddies and even more so in videos of riders on gravel bikes riding insanely well in totally insane locations. Which means that everything I’ve said about these bikes is coming from someone who is already off the back in what’s happening in the world of fat-tired road bikes. As in, you’re just going to have to go out and discover all this for yourself. But believe me, you’ll love it.
My bike is a road bike wearing fat tires with a subtly tweaked geometry to bring its performance on single-tracks and dirt roads up to what I expect of a road bike on pavement, but without compromising its performance on blacktop.
Single-tracks here means relatively smooth trails, the kind trail runners enjoy, and dirt roads means tame enough that four-wheel drive and high clearance aren’t absolutely required. Grades are generally moderate enough so neither super-low gearing for going up nor dropping the seat post for going down is required.
Two biggies to clarify before looking at fat-tire road bikes: what kind of terrain you intend to play on and how fat a tire you’re willing to ride. Plus the future, what is ridden will evolve. Going from a trail or road like that doesn’t interest me to, well damn, I bet I can ride that. That happens, even at age 72!
Fat-tire road bike geometry has to deal with surfaces squirming around under the tires, with rocks, holes, roots, etc trying to knock the front or rear wheel caddywhumpus, with grades steep enough to climb out of the saddle only the surface is loose so you can’t, etc., etc. Always with impeccable handling on pavement where probably the majority of time will be passed.
Note a special bike for gravel/dirt roads and trails isn’t mandatory. Fatter tires aren’t even needed. I used to ride dirt and rock roads with 23 and 25mm tires and never gave it a thought. But having gone to the dark side so to speak, I now say anyone contemplating spending serious time riding dirt with a road bike and who can afford one would be nuts to not get a fat-tire road bike. They’re just way, way more enjoyable to ride off-pavement.
Chainstay length does not define a fat-tire road bike. Most gravel bikes have longer chainstays but it’s not some huge difference. My Stoner Bike’s stays are 16mm longer than my pure road bike’s. 16mm is nothing. Longer chainstays provide clearance for fatter tires, produce a stabler, smoother ride due to the resulting longer wheelbase, add to the rear end’s stiffness by enabling the use of larger diameter tubes with minimal tube bending for tire clearance.
Forget the back end. It’s only along for the ride, the bass setting the beat. The front end is where the action is, the lead guitar soaring in the stars. On blacktop there isn’t much for the front end to do because technical challenges are lacking. Trails and jeep roads are where a bike’s front end dances, following the rider’s eyes, flicking around rocks and roots, chasing the groove in a wonderful ballet of quickness and stability.
This is where frame builders can differ in their solutions. Steep or shallow head angle, more or less offset/trail, long or short stem, long or short top tube, stiff or soft front end, etc., etc. Which means you need to understand your riding style and be able to communicate that to a builder or someone helping you choose a bike. For my fat-tire road bike, Kent knew my riding style from way back and designed it with that in mind. In technical passages I’m in the drops, pressing down on the front end, the connection with the axle so intimate that the wheel seems to dart before I’ve even seen what it’s darting around.
You need weight on the front end to weave lines through rocks and trees, otherwise the steering’s vague. Which means pulling the handlebar closer in. But too much and the front end will be zigging and zagging every time you blink. A lot of fat-tire road bikes have pushed out front centers via a softer head angle, like mine, but again too much and keeping weight on the front end for steerage control in a steep climb can be tricky. Too short a front center means too much toe overlap plus dropping down steep descents can feel like you’re in the front car in a roller coaster going over the top into a monster plunge. A steep head angle with too much rake will make the front end so reactive you’ll forget what a straight line is. Same head angle with too little rake will be super stable at speed but reluctant to dart around obstacles. A shallow head tube angle with not much rake will be forever flopping into turns with the slightest lean of the bike. Etc., etc.
The front end also needs to be designed for when you’re out of the saddle. A grade on dirt will be harder than the same grade on pavement which means climbing out of the saddle more often. But traction will be thin so you’ll need more weight on the back wheel and of coursre standing automatically shifts weight forward. If it’s too steep to climb seated you’ll have to drop into a low crouch over the top bar with the butt floating over the nose of the saddle, the hands in the drops pulling back and that means the frame needs to have the space for you to do that.
Some people like a low bottom bracket, relative to the line between the front and rear wheel hubs. They say low is more stable. Others like it higher. I think mine is relatively high, or it’s higher than my pure road bike’s. I don’t feel any lack of stability and it gives me more pedal clearance which I really like but to be honest, I’ve never given it any thought one way or the other. As usual, no rule, just personal preference.
Same with the handlebar height. Typical pure road bikes have what I consider crazy low handlebars relative to the saddle height. The flat on my road bike’s bar isn’t far off level with the saddle. The Stoner Bike’s is even closer to level. Again personal preference but I think for off-pavement and on technically demanding trails and dirt roads, the higher position enables shifting weight front and back and keeping your eyes on the trail ahead easier. Also makes riding in the drops super comfortable and ideally the default position. That’s the power position for driving the bike through rough sections.
Lots of parameters to play with to achieve a fat-tire road bike that works for you. Which is why in my opinion they were made for custom builders. Production frames are designed around common denominators someone decided will work for most people. If you fit that criteria, excellent. But riding rocky roads and trails has technical skill requirements that paved riding doesn’t even know exists plus the whole genre of gravel bikes has so many nuances that factory sizing won’t necessarily answer for everyone. Happily there are some production companies providing a wide choice in sizing and design, Moots for one. It was a long week of riding a Moots Routt in Colorado that convinced me a by-design fat-tire road bike totally outperforms a standard road bike on dirt and trails.
Given all this performance criteria, a custom build can be super attractive with the ability to meet any and all needs. Like forks. Apparently off-the-shelf forks for fat-tire road bikes, from Enve for example, are available with only one fork rake, so a front end has to be built around that fork’s rake. A builder who does his own forks could build a frame with a custom fork to provide exactly the handling characteristics desired. I don’t think too many builders do this. Building forks is apparently a pain and expensive. Forks used to be as much the domain of the builder as the frame itself but carbon forks pretty much killed that. Not that people are apparently complaining. My Stoner Bike’s got an Enve CX carbon fork and I’m definitely not complaining.
Which brings up the front end stiffness argument. Some claim the old bikes with their thin steel tubing and steel fork with curved blades serve up a superior smooth ride in rough conditions. Others go the opposite route with an oversized head tube and fat fork blades with a fat, tapered steerer tube, resulting in a stiff front end that refuses to be knocked about by ruts and holes and rocks. Personal preference again. I went with a stiff front end and I’ve never ridden a smoother riding bike in the rough. Bottom line is the suspension is generated by the tires, not the tubing. I also have to admit to not having ridden an old style steel frame in longer than I can remember.
Then there’s this evolution to way fat tires, like the Moots Baxter. My son rides one and loves it. Apparently more and more gravel riders are going fatter and fatter. Gravel bikes or drop bar mountain bikes, the distinction becomes blurred. Which is again why I refer to my bike as a fat-tire road bike because that’s what it is, a road bike wearing fatter tires.
As an aside, I don’t think putting drop bars on an old style rigid mountain bike is going to produce the equivalent of a fat-tire road bike. I rode some mountain bikes back in the 80’s with the WTB flared drop bar and while I loved the drop bar position, they never felt quite right. I think because the frame’s sweet spot for the rider’s mass over the bike was designed for a flat bar and that sweet spot isn’t the same for drop bars.
You also might want to keep in mind that whatever gravel bike you buy today could be considered archaic in a couple of years. I’m sure people are working on suspension forks for gravel bikes and that will be followed by full suspension. I have no idea what those will be called. They also don’t interest me.
I love my Stoner Bike’s simplicity, no shocks, no disc brakes, no electric shifting. Just a straight up road bike tweaked to kick ass off-pavement. Super reactive when needed, super stable at the same time, modestly fat but light tires but skinny enough to keep me knowing I’m riding a road bike, goes everywhere I want to go with more grace than me. Places where I’d need fatter tires and lower gearing I ignore. I’m a dinosaur.
For myself fat-tire road bikes are the coolest thing to come along in cycling since mountain bikes. The world of road cycling’s been beautifully expanded and in my case passion for riding thoroughly rejuvenated. Plus, and this is kind of easy to forget at times, they’re awesome just as pure ol’ road bikes, or at least mine is. That was something I insisted on in my conversations with Kent for the bike. The 35mm tires running relatively soft soak up the asphalt’s bumps and ridges, cling like crazy in turns, and just feel friggin fast. And when the blacktop stops and the road doesn’t, neither does my bike.
I can also guarantee that the currently perceived limits of where these bikes can go are in the process of being blown away. I saw that happening with my son and his riding buddies and even more so in videos of riders on gravel bikes riding insanely well in totally insane locations. Which means that everything I’ve said about these bikes is coming from someone who is already off the back in what’s happening in the world of fat-tired road bikes. As in, you’re just going to have to go out and discover all this for yourself. But believe me, you’ll love it.