Frame design and tire width clearance/capacity

[Duende]

With all these gravel bikes offering room now for 44mm, 50mm or greater... I'm curious to know how these changes to the frame and fork (to accommodate these tire sizes) changes the feel of the ride.


How would the ride vary between 28mm tires on an endurance road bike vs 28mm on a gravel bike with similar geometry, but had a fork and chain stays to allow for an extra wide gravel tire???

Besides looks, does the wider fork and chain stays make a big difference in ride? I'm thinking the different fork alone has to feel different.

Curious!

[spoonrobot]

If it's a production bike the larger tire capacity comes with a massive dose of extra stiffness. The tubes on my gravel bike are slightly larger than on my hardtail mtb, steerer is 1.5", fork is built for off-road riding and so forth. The gravel bike rides extremely harsh on 28s and is pretty much worthless for riding that tire size outside of very smooth, new pavement.

[Duende]

If it's a production bike the larger tire capacity comes with a massive dose of extra stiffness. The tubes on my gravel bike are slightly larger than on my hardtail mtb, steerer is 1.5", fork is built for off-road riding and so forth. The gravel bike rides extremely harsh on 28s and is pretty much worthless for riding that tire size outside of very smooth, new pavement.

Good info! Thanks... so all this talk of swapping out road wheels for gravel wheels doesn’t take into account inherent extra frame stiffness in the gravel frame.

[fignon's barber]

Gravel bikes are great for being able ride in more varied terrain, but to me there really isn't an "all road bike", despite what marketing folks want you to believe. In order to help accommodate the big tires, most have a 70 or 71 degree head tube angle, along with a higher head tube. If you try to ride them in , say, a competitive fast group road ride, you are at a disadvantage IMO.

[prototoast]

Another factor to consider is handling. Everything else equal, a larger tire will steer slower than a smaller one. What size tire your frame was designed around at baseline will affect how it handles with the other. Similarly, the different size tires will put the bottom bracket height at different point. Not many production frames actually adjust for this, but it can matter.

[Mark McM]

Good info! Thanks... so all this talk of swapping out road wheels for gravel wheels doesn’t take into account inherent extra frame stiffness in the gravel frame.

What extra stiffness? Most riders can't really tell any difference in ride compliance between frames (even if they think they can). In blind tests, riders generally do poorly in detecting differences between frames that are supposed to be "harsh" and frames that are supposed to be "compliant".

This topic should probably be added to the thread on topics for Josh's "Marginal Gains" podcast. Here's what Josh had to say about rider's ability to detect frame compliance in an interview published on the Slow Twitch web site (https://www.slowtwitch.com/Tech/Thoughts_on_science_perception_4571.html):

I've participated in numerous blind product studies over the years where we controlled bikes or the wheels (I've done this twice with a bike manufacturer during development work around a pro team, and many times with wheels) with fabric shield tensioned between seat post and stem, flat black rattle can paint on everything, etc. In each of these studies, the entire subject group including pro riders, engineers, and other industry people with LOTS of experience, struggled to find any real differences between any of the bikes, until after the study was de-blinded and everybody (including me) instantly began to try and rationalize it all… This is just human nature, we all do it, and from experience, it is nearly impossible NOT to do it.

One of the major discoveries was that after controlling for seat post (round post shimmed into aero frame so as to not give it away) not a single rider found the aero road bike to be less comfortable, less compliant, etc, than the identically setup 'endurance' or 'roubaix' bike (clearly this leaves room for the aero seat post to be why people feel aero bikes are less compliant..seatposts generally have more effect on bike compliance in the lab than frames do, but that's another story).

[David Tollefson]

If you try to ride them in , say, a competitive fast group road ride, you are at a disadvantage IMO.

Unless that fast group ride is a tight crit course, this is utterly untrue. And even then the disadvantage is minor.

[Duende]

Gravel bikes are great for being able ride in more varied terrain, but to me there really isn't an "all road bike", despite what marketing folks want you to believe. In order to help accommodate the big tires, most have a 70 or 71 degree head tube angle, along with a higher head tube. If you try to ride them in , say, a competitive fast group road ride, you are at a disadvantage IMO.

This is basically what I'm trying to get to the truth about. I'm just not convinced that throwing 28mm tires on my gravel bike will provide anywhere near the same feel as a road bike... and my Gravel bike's geometry is not too far off from a road bike.

My road bike just has a springy-ness and acceleration that is just not as present on my gravel bike. Guess I really just have to do some A/B comparisons.

[dddd]

This is basically what I'm trying to get to the truth about. I'm just not convinced that throwing 28mm tires on my gravel bike will provide anywhere near the same feel as a road bike... and my Gravel bike's geometry is not too far off from a road bike.

My road bike just has a springy-ness and acceleration that is just not as present on my gravel bike. Guess I really just have to do some A/B comparisons.

You might be able to pin down much of the perceived difference just by looking at the two bike's chainstay lengths and steering head angle.

Also, if the fit parameters are at all different on each bike, that also affects road manners.

I'm just happy that my road-going (for now) Fuji cyclocross bike is happy to hold a line in the corners without any perceived extra effort, using the Mavic Allroad 33mm-wide wheel/tire setup I just bought.

Another concern about bikes made for wider tires is that at some point the chainline gets altered as the chainstay length, tire clearance and frame structure requirements each take their toll on available space.

[fignon's barber]

Unless that fast group ride is a tight crit course, this is utterly untrue. And even then the disadvantage is minor.


You're absolutely wrong.

[spoonrobot]

What extra stiffness? Most riders can't really tell any difference in ride compliance between frames (even if they think they can). In blind tests, riders generally do poorly in detecting differences between frames that are supposed to be "harsh" and frames that are supposed to be "compliant".

This topic should probably be added to the thread on topics for Josh's "Marginal Gains" podcast. Here's what Josh had to say about rider's ability to detect frame compliance in an interview published on the Slow Twitch web site (https://www.slowtwitch.com/Tech/Thoughts_on_science_perception_4571.html):

That's a great article, from 2014. It showcases one of the worst trends to come from modern bicycle journalism. Discrediting the perception of the individual rider. Some of us are trained observers and understand how to evaluate reality in specific ways. However, even the most recreational of riders can figure out which bike hurts more to ride over rough pavement or gravel.

Those tests Poertner is referring to are almost entirely based around road bikes on pavement. Differences offroad are much more obvious and extreme.

I doubt he was doing any blind testing on a frame with a 1 1/8" steerer compared to another with a 1 1/2" steerer with requisite forks and headtubes.

Or one frame with a 50x50mm box aluminum downtube and another with a 9/7/9 31.8mm steel downtube.

Or a 65mm rake steel fork compared to a 45mm rake carbon fork.

There's a lot of stuff in the gravel world right now that wasn't around 5+ years ago. Gravel bikes really took off in 2016 and the few seasons since then have seen manufacturers move towards components and designs that are obviously geared towards durability at the expense of ride quality.

[Mark McM]

Those tests Poertner is referring to are almost entirely based around road bikes on pavement. Differences offroad are much more obvious and extreme.

Quite the opposite is likely to be the case. Pavement roads tend to have high pressure tires with little compliance. Even so, the tire compliance is much greater than frame compliance, rendering frame compliance nearly moot. Offroad bikes tend to have fatter, lower pressure, more compliant tires. This greater tire compliance makes the frame compliance even less significant by comparison.

I doubt he was doing any blind testing on a frame with a 1 1/8" steerer compared to another with a 1 1/2" steerer with requisite forks and headtubes.

Or one frame with a 50x50mm box aluminum downtube and another with a 9/7/9 31.8mm steel downtube.

Or a 65mm rake steel fork compared to a 45mm rake carbon fork.

There's a lot of stuff in the gravel world right now that wasn't around 5+ years ago. Gravel bikes really took off in 2016 and the few seasons since then have seen manufacturers move towards components and designs that are obviously geared towards durability at the expense of ride quality.

You're missing the point. Compared to the compliance in the other parts of the system (tires, saddle, seatpost, handlebars, etc) are so much larger than the compliance in the frame, the compliance in the frame doesn't matter much. If frame compliance is next to nothing, then if you doubled the compliance, it would still be next to nothing. (And that's why the blind test riders couldn't tell the difference between the uber-stiff aero bikes, and the oh-so-comfy endurance bikes.)

Here's another interview with Josh Poertner (http://nyvelocity.com/articles/interviews/josh-poertner/), explaining the (non-significance) of frame compliance.

[Pegoready]

The extra space needed to fit bigger tires doesn't inherently change the road handling with say 700 x 28 tires. Space is just space and the frame's geometry accounts for the added fork's axle-to-crown span. However, these things come into play:

Wider tire clearance usually means longer chainstays by at least 2 cm, sometimes up to 4 cm.

Gravel bikes also err towards slacker head tube angle and longer rake front ends. Why? Probably to avoid toe overlap, with big tires and fenders and the bigger steering sweep characteristic of gravel riding at slow speeds.

So your chainstays will be longer and you won't get that 73° head tube angle, maybe more like 71-72° with a 50 mm + fork rake. Both combine to create a wheel base that is at least 4 cm longer than an equivalent road bike. That's where you will feel the difference.

[Mzilliox]

That's a great article, from 2014. It showcases one of the worst trends to come from modern bicycle journalism. Discrediting the perception of the individual rider. Some of us are trained observers and understand how to evaluate reality in specific ways. However, even the most recreational of riders can figure out which bike hurts more to ride over rough pavement or gravel.

Those tests Poertner is referring to are almost entirely based around road bikes on pavement. Differences offroad are much more obvious and extreme.

I doubt he was doing any blind testing on a frame with a 1 1/8" steerer compared to another with a 1 1/2" steerer with requisite forks and headtubes.

Or one frame with a 50x50mm box aluminum downtube and another with a 9/7/9 31.8mm steel downtube.

Or a 65mm rake steel fork compared to a 45mm rake carbon fork.

There's a lot of stuff in the gravel world right now that wasn't around 5+ years ago. Gravel bikes really took off in 2016 and the few seasons since then have seen manufacturers move towards components and designs that are obviously geared towards durability at the expense of ride quality.

completely with you on this one. Some folks have learned how to pay attention... but i got tired of people using words and not experiences, so i did my own testing last year and again this winter.
I put the exact same wheels and tires (shamals w 28mm compass) on 3 different bikes and rode them on my 1 mile gravel drive.

My aluminum Zanc is easily the most harsh ride, same wheels.
my steel goodrich is something in the middle, not as much shaking as the aluminum, but not as smooth as my
Jeff lyon skinny tubes steel, or my
heretic titanium which feels the best on gravel roads.
Forks are enve 2.0 on the alu and goodrich, steel on the lyon, and whiskey on the heretic.
28mm compass tires at 70 psi

there is most certainly a difference in all of these frames, and i most certainly can perceive them.

Could most? that i cant answer, but thats not the real point we are getting at

[Black Dog]

This is basically what I'm trying to get to the truth about. I'm just not convinced that throwing 28mm tires on my gravel bike will provide anywhere near the same feel as a road bike... and my Gravel bike's geometry is not too far off from a road bike.

My road bike just has a springy-ness and acceleration that is just not as present on my gravel bike. Guess I really just have to do some A/B comparisons.

Do some blind testing and you will find out. Back and forth testing, even with the same wheels, which is essential, will still be hampered by expectation bias. There really is no actual research that shows that among the types of bikes that we are riding there is a positive relationship between stiffness and acceleration. We do, as humans often confuse the feed back we get from a bike as speed or acceleration differences. Stiffness is much more of a marketing factor, since it can be quantified along side with mass, drag, and price. Frame flex is assumed to be lost energy and again the jury is certainly not delivered a verdict on the validity of that claim. It is really an untested assumption AFAIK.

[jtbadge]

My "gravel bike" is less stiff than either of my road bikes, even with skinny slick tires. Whoulda thunk?

It also has a much longer wheelbase, which can slows handling on pavement. Might also make it feel like its more work to climb - even though it's lighter than my MX Leader!

[Heisenberg]

Quite the opposite is likely to be the case. Pavement roads tend to have high pressure tires with little compliance. Even so, the tire compliance is much greater than frame compliance, rendering frame compliance nearly moot. Offroad bikes tend to have fatter, lower pressure, more compliant tires. This greater tire compliance makes the frame compliance even less significant by comparison.



You're missing the point. Compared to the compliance in the other parts of the system (tires, saddle, seatpost, handlebars, etc) are so much larger than the compliance in the frame, the compliance in the frame doesn't matter much. If frame compliance is next to nothing, then if you doubled the compliance, it would still be next to nothing. (And that's why the blind test riders couldn't tell the difference between the uber-stiff aero bikes, and the oh-so-comfy endurance bikes.)

Here's another interview with Josh Poertner (http://nyvelocity.com/articles/interviews/josh-poertner/), explaining the (non-significance) of frame compliance.

mate, i, don't disagree with you about tires drastically affecting ride quality, but i really question the hemorrhoidal approach you take. everything does not boil down to what's "on paper", and few people have bothered to input all the variables/inputs that come with bike design into cut/dry formulas.

i've ridden a ****pile of custom bikes - a lot. more than most cycling journos. more than damn near anyone alive. and i know my way around a bike design or two*. and i can say unequivocally that you are dead wrong. in short: do you actually ride much, or just regurgitate the limited scope that some numbers present on the sheet/screen? yes, frame material/design GREATLY affect the way a bike rides. to boil it down to tire and contact point choice is a load of ****ing bull****. i get that you like to dig into banality on forums that bore most normal humans to tears, but does any of it actually matter when all inputs are considered? bike design is holistic as ****, and to declare specific portions of it irrelevant is obtuse at best, even if you are an engineer (IN WHICH CASE I WOULD LOVE TO HARNESS YOUR POWERS FOR GOOD AND WE SHOULD TALK MORE).

*i am no ****ing materials engineer. but i know a thing or two about geometry and know how to break bikes by merit of effort.

fin.

ALEX. i think you work near i in the mission. let's grab lunch and chat. i'd love to talk, given i helped you with your gravel bike.

[Duende]

ALEX. i think you work near i in the mission. let's grab lunch and chat. i'd love to talk, given i helped you with your gravel bike.

Hey Nate!

That would be great! Don’t get me wrong... I’m still loving the bike. Just was curious to learn more about this stuff.

I’ll PM you

[Mark McM]

mate, i, don't disagree with you about tires drastically affecting ride quality, but i really question the hemorrhoidal approach you take. everything does not boil down to what's "on paper", and few people have bothered to input all the variables/inputs that come with bike design into cut/dry formulas.

i've ridden a ****pile of custom bikes - a lot. more than most cycling journos. more than damn near anyone alive. and i know my way around a bike design or two*. and i can say unequivocally that you are dead wrong. in short: do you actually ride much, or just regurgitate the limited scope that some numbers present on the sheet/screen? yes, frame material/design GREATLY affect the way a bike rides. to boil it down to tire and contact point choice is a load of ****ing bull****. i get that you like to dig into banality on forums that bore most normal humans to tears, but does any of it actually matter when all inputs are considered? bike design is holistic as ****, and to declare specific portions of it irrelevant is obtuse at best, even if you are an engineer (IN WHICH CASE I WOULD LOVE TO HARNESS YOUR POWERS FOR GOOD AND WE SHOULD TALK MORE).

*i am no ****ing materials engineer. but i know a thing or two about geometry and know how to break bikes by merit of effort.

fin.

ALEX. i think you work near i in the mission. let's grab lunch and chat. i'd love to talk, given i helped you with your gravel bike.

Me thinks thou dost protest too much. It sounds like you have a lot invested in your ability to detect subtle nuances between frames. Perhaps that is shading your perception.

No, I'm not boiling this down to what's on paper. I'm merely getting down to the question of "how do we know that we actually know what we think we know?". We can't avoid the fact that some of how we experience the world is based on actual physical phenomenon, and some is based on what we are expecting to experience. That's were blind testing comes in. By hiding the identity of a thing to be experienced, It eliminates (or attempts to eliminate) sub-conscious pre-conceptions.

As an example, take the example of Stradivarius violins. Everyone knows that these instruments created by the old master violin maker have a certain quality that can't be duplicated today. People have debated why that should be - is it the wood? Is it the glues? Is it the shaping of the material that only the master could do? No one is sure why, but everyone can hear the difference. Or at least, they can if they know they are listening to a Stradivarius. It turns out, when professional violists play in a blind test (https://www.newscientist.com/article/dn25371-pro-violinists-fail-to-spot-stradivarius-in-blind-test/), they actually can't tell the difference between Stradivarius violins and modern violins.

Blind testing in a variety of areas has shown that even experts are often not as perceptive and discerning as they think they are, whether it is music, wine tasting (https://www.theguardian.com/lifeandstyle/2013/jun/23/wine-tasting-junk-science-analysis), or bicycles. I believe that you believe that you can easily tell the difference between different frames. But how do you know?

[NHAero]

I mostly agree with what Mark McM has written. My basis is the frame deflection testing we did in 1973-74 at MIT during the aluminum bike frame project. Obviously we didn't test carbon frames :-)
What we measured was that in the vertical plane, frames of all types, those "known" to be super stiff and those known to be noodles, deflected very small amounts. The rear in particular is a tetrahedron, about as stiff of a structure as we know how to make. On the other hand, forks, particularly the beautiful thin tubed curved steel forks we love to look at, deflected plenty.

And tires more so. And long seatposts (I think I can see the flex on my friend's long Lynskey Ti post when we are out MTB'ing.)

One of our observations was that frame size affected perceived stiffness due to geometry. A 51 cm frame with little seatpost showing puts the rider's butt not much more than halfway between the two wheel contact patches. A 65 cm frame like my friend's Legnano put his butt darn close to right above the rear wheel. Who do you think feels that 1/2" bump in the road more?
Longer stays and slacker angles certainly will make the gravel bike handle differently than a pure road bike. But as to stiffness in the vertical plane, I still need to be convinced.

[Butch]

Having gotten to design, build and ride test mules at Moots over the years I think it really comes down to priorities in the ride and the ability to run a variety of tires. As has been pointed out there are changes to geometry to limit toe overlap and to make room for bigger tires in the rear that can effect the feel of the bike.

What defines a "gravel" bike is left to interpretation and the need for a certain size tire. I would like to point out that if you just look at the forks for road caliper, road disc and cross disc the designs and carbon layups make for very different ride in order to meet CEN and ISO specs. Early in the development of road disc we saw failures from a very well trusted brand of fork because of poor manufacturing. As we developed both road and cross disc forks it became clear they needed to be very beefy to meet safety specs which can translate to a very stiff fork that weighs 35% more than a rim brake fork. Again this effects the feel of the bike.

With geometry we discovered if you have the correct bb height and are willing to sacrifice toe overlap you can get a bike that feels good on the road and the gravel and can still hold a 40mm tire. Yes chainstay length and stack height are compromised relative to a skinny tire road bike so there is a little lack of pure climbing and sprinting, but overall the bike can feel very good on the road.

I believe fit, steering geometry and tubing make the bike feel best when they are appropriate for the rider and the intended use. Also never underestimate tire design and pressure when judging the ride of any bike. Bigger tires must be run at lower pressures to get the most out of them whether it is a 25, 28 or 40.

I think Cycling Tips review of the Routt RSL and Bike Radar's review of the same bike picked up on what we tried to achieve from a bike that holds a 40mm tires. Obviously I am biased but when I rode the first proto of that bike it taught me what could be achieved with combining design, material and fit to get a bike that felt right for the job. Not the same as a lightweight race bike, but really good "do everything" bike. Two sets of wheels make for great versatility.

[BikeNY]

With all these gravel bikes offering room now for 44mm, 50mm or greater... I'm curious to know how these changes to the frame and fork (to accommodate these tire sizes) changes the feel of the ride.


How would the ride vary between 28mm tires on an endurance road bike vs 28mm on a gravel bike with similar geometry, but had a fork and chain stays to allow for an extra wide gravel tire???

Besides looks, does the wider fork and chain stays make a big difference in ride? I'm thinking the different fork alone has to feel different.

Curious!

It's really impossible to answer that question. It comes down to what the bikes designer does to make room for the bigger tires, and every designer will do it a bit differently. Some may beef up the tubeset because of rougher terrain, things like that. If you have 2 frames with the exact same geometry, but one only fit 28mm tires and the other fit 40mm tires, they would likely ride exactly the same with a 28mm tire.

Any difference in feel will mostly come down to geometry changes that are often designed into gravel frames like slacker HTA, longer chainstays, etc.