I recently spend many hours researching wheels and tires for my mountain bike. This may be not big news for many of you but I was blown away by research done on off road rolling resistance.

It's not specific to off-road. Even on decent asphalt, it's possible to pump a tire too stiff, such that transmission of road buzz through the bike+rider wastes rolling energy and reduces performance. That's a big part of why the pro peloton has trended to wider tires over the past decade.

Maybe the dropbars would be nice for aero riding and more hold positions.

That's the big thing. It takes effort to maintain a powerful+aero posture with a typical mountain bike fit. It's totally possible to do gravel rides on an MTB, but it's usually not the most optimal machine, unless the "gravel" ride is weirdly technical.

 

Narrower crank q-factor might be more efficient to some riders. Their wheels generally have less drag since their hub bearings and axles are smaller. They have more drivetrain efficiency due to their bigger chainring. The increased challenge of riding CX can make the ride feel more fulfilling.

HTupolev mentioned posture/positioning, which is a big one too.

 

drop bars on modern mtb’s is no bueno

geometry issues, shifting cost/issues, brake issues... can all be overcome but by then you may as well get a gravel/cx bike

I’ve ridden and own both. Most of the time for gravel rides I grab the cx bike. It’s faster by a lot for most of what you’re talking about. However, on super rough roads and/or super long stuff with rough sections (hillybilly roubaix type racing) I prefer the ht mtb.

 

drop bars on modern mtb's is no bueno

geometry issues, shifting cost/issues, brake issues... can all be overcome but by then you may as well get a gravel/cx bike

I've ridden and own both. Most of the time for gravel rides I grab the cx bike. It's faster by a lot for most of what you're talking about. However, on super rough roads and/or super long stuff with rough sections (hillybilly roubaix type racing) I prefer the ht mtb.

This. By the time you convert to drop bars with a more efficient drivetrain, might as well get a cx bike that's already meant to do that.

 

Dropbars on a MTB works very well. Just make sure you measure everything carefully (very carefully) to get a proper fit.

I used my road bike as a reference (which fits me perfectly) and matched it up with my monstercross setup. I have done several 65+ mile gravel rides on it and it's very comfy!

The biggest issue was the front end and fork selection. Axle to crown was a key measurement. I tried to match the AC of the original suspension fork because I didn't want to alter head tube and seat tube angles too much. I'm very pleased with the outcome.

The bike has clearance for all kinds of tires! Currently running 40mm gravel kings and it has room for much bigger. I like having so many tire options.

 

Dropbars on a MTB works very well. Just make sure you measure everything carefully (very carefully) to get a proper fit.

It CAN work very well. However, like I said there is a LOT to consider since most drop bar stuff is not directly compatible with MTB stuff. It just depends on budget and what you are willing to give up.

 

Follow-up:

 

Thanks for the replies. They make gravel/CX frames that allow up to 45cc tires. That would probably the most ideal to run dropbars with widest rims/tires possible.

Something like this. DonnyBrook - OX Platinum All-Road

 

or this one KONA BIKES | ROAD | SUTRA | Sutra LTD

 

If you're really wanting wide there is this https://salsacycles.com/bikes/fargo/2017_fargo_ti_frameset

or a bit more traditional but still mtb wide https://salsacycles.com/bikes/cutthroat/2018_cutthroat_force_1

or closer to cx/gravel but still plenty of clearance
https://salsacycles.com/bikes/warbird/2018_warbird_carbon_ultegra

 

that Fargo Ti is beautiful... but that price !

 

Are there any mtb HT frames that allow big chainrings? Could be a start to begin to compare CX vs rigid.

 

define"big".

 

SRAM CX1 chainrings come in 38t to 46t.

SRAM Eagle chainrings come in 30t to 38t.

Having trouble finding any that allow more than 36t. Open One+, Air9 RDO, SIR 9...

Andy Blair said he's going to race 38t on his Epic HT: » Bike Check: 7.8kg Specialized S-Works Epic Hardtail

The bike came stock with a 34t chain ring but I will race on a 38t. That's the beauty of the huge range of SRAM Eagle, a 38 will give me a smaller gear than using a 32 on XX1 (which was as small as I ever rode) but a taller gear at the other end that can be nice on fireroad sections on marathons, especially if there is a tailwind and you need to put someone under pressure.

 

As a road-bike geometry enthusiast (because they're more comfortable) I think gravel bikes are better in every respect except one - and unfortunately it's a big exception - and that is they use skinnier higher pressure tires. Not only are the tires skinny and higher pressure, but they are also just as heavy and often heavier than 2.1" tubeless Schwalbes. Also the road-style rims are heavier because they have to be sturdier with small high pressure tires. They won't work as well tubeless either which is significant issue in places where you expect to get punctures on almost every ride, as in the Southwest. Bikes should be designed around the best tire for an application - the tire with the best weight, grip, and tubeless ability. Slightly-bigger-than-a-cx tire doesn't cut it, that's an idiotic, nonsensical design consideration.

I built up a drop-bar vintage mtb bike with 2.1 tubeless tires which I love although the steel frame is very heavy.

 

The Timber Spork

The Timber Spork works really well everywhere I've tried it. Converted to drop bar 29er mountain bike with remote lock out Lefty - something of a greater Slate.

Apologies for the upside down photo - this site doesn't play nice with Apple products

 

I also really like my converted kona mtb. The main hassle I had with it was finding a way of using a triple chain ring with brifters. Other than that very easy conversion. Whether you'd be better buying a proper gravel bike depends almost entirely on how much cash you've got to spare and what parts you have lying around.

 

I have been debating the same thing: add a rigid fork and smoother tires to a MTB or buy a CX/Gravel bike.

 

It's been a couple of months since I posted that. I'm putting money aside to buy a CX/Gravel bike.

 

FIFY :thumbsup:

 

Thinking about the same thing. Buying a hardtail with boost wheels and rigid fork, which I can change to a suspension fork whenever I need it. Or maybe just go directly for a gravel with enough clearance for 48/50 tyres...

How thin can be my tyres if I have 23-25 inner rims?

Enviado desde mi ONE A2003 mediante Tapatalk

 

I prefer my modified hardtail mtb for gravel purely because of the ability to run 2.35" Schwalbe big Apples. They seem to me to be a good allround tyre that doesn't hold you back on the road and is ok on most offroad surfaces if the pressure is low enough for the tyre to conform to the surface.

What I like about CX bikes is their more horizontal toptubes which are more comfortable when you shoulder the bike.

 

The main advantage of a gravel bike is the frame geometry if you prefer a road bike riding position with drop bars. Mountain bikes have waaaaay too long top tubes to use with drop bars. Consider that mtb handlebars sweep 50mm or more backwards from the stem while road-style drop bars sweep forward about 80mm from the stem. That means you can only use mtb or road handlebars on bikes specifically designed for those handlebars. They're not interchangeable. People try to do it but it doesn't generally work very well.

One advantage of mtbs over gravel bikes, aside from their better lower-pressure tires which work better tubeless, is their rims can weigh less because they aren't required to be as strong for tires with more cushion. Smaller higher pressure tires require stronger rims which weigh more. There's no weight or performance advantage to skinny 40mm tires on a gravel bike unless you're going to be riding on pavement a lot.

 

One advantage of mtbs over gravel bikes, aside from their better lower-pressure tires which work better tubeless, is their rims can weigh less because they aren't required to be as strong for tires with more cushion. Smaller higher pressure tires require stronger rims which weigh more. There's no weight or performance advantage to skinny 40mm tires on a gravel bike unless you're going to be riding on pavement a lot.

My strong tubeless gravel rims weigh 440f/450r. They are also much more aero than a MTB rim which makes more of a difference than mere weight at higher speeds.

There certainly is a weight and performance advantage to skinny tires off road, especially on mixed surface rides.

My experience is quite different than what you have claimed.

 

I ride geared and single speed MTB's everywhere and often do fast pace (15-16 mph average over 2-3 hours) urban assault rides.

Recently picked up a Soma Wolverine CX/gravel bike to click off the 35+ mile round trip bike commute faster than on an MTB. It has TLR rims and I setup 1.8" small knobbies on it that can be inflated up to 60 psi. I have no trouble churning at a 20+ mph pace on this setup...

 

I ride geared and single speed MTB's everywhere and often do fast pace (15-16 mph average over 2-3 hours) urban assault rides.

Recently picked up a Soma Wolverine CX/gravel bike to click off the 35+ mile round trip bike commute faster than on an MTB. It has TLR rims and I setup 1.8" small knobbies on it that can be inflated up to 60 psi. I have no trouble churning at a 20+ mph pace on this setup...

This. I love my Wolverine! I have 700x42 Resolutes on mine - mini knobs for hook up, and high ridge in the center for pavement. Low and long geo for long rides and plenty of room for stretching out. Smooth steel to absorb road/trail chatter. And I spec'd to my own fancy for less than a lot of comparable bikes would have cost as a complete.

But to me, the difference between a gravel and rigid/hardtail MTB is geometry and riding position. Shorter top tube for drop bars, longer stem, and more weight over the front wheel. Steeper headtube for more nimble handling, lower headtube for more aggressive riding position, lower bottom bracket for stability, higher top tube, and reduced tire clearance to fit just what is needed and nothing more. It is much easier to get aero on a gravel bike with drops than a suspension ready/equipped bike with flat bars.

Someone above mentioned smaller axles for smaller bearings for less resistance, but that isn't the case. Smaller axle and smaller bearings make more resistance. But, smaller 12mm front axle for road/gravel because less weight and less need for the stiffness provided by 15mm axles. Rear axle is the same 12mm.

 

I just bought/built a 3T Exploro, billed as an aero go anywhere bike. Optimized for 20mph. (https://www.3t.bike/en/3t-bikes/new-exploro-flatmount-20.html)

Bought it after trying to gravel mod my Epic HT, for a few reasons. The HT (I put 45mm tires on) riding position wasn't comfortable on a 50 mile ride where it was 50% flat gravel/tarmac. With the Exploro I can put 700x23 as well as 650b and up to 2.1 mtb tires...currently have 650bx47mm on there. I can load it up with travel bags or svelt it down to a 16 lb road racer. Currently building a second wheelset to do that for when I want to tag along with my roadie buds. It suits the kind of riding I like these days: longer mixed surface.

 

There is a lot of talk about aerodynamics here and elsewhere, but I'm guessing none of you have any data on the matter other than generalizations from the internet. I see tons of people on gravel and cx bikes that are more upright than my position on my rigid xc hardtail. Presumably, based on our assumptions on aerodynamics, my hardtail should be better. Add a frame bag and a crosswind, and any bike will be terrible. Also, there are many options for increasing hand positions on a hardtail. Bar ends, inner bar ends, Jones bars, etc. I'm more comfortable on flat bars than drop bars, and I can use grips that absorb more shock than bar tape on drop bars, even double wrapped. For the record, I am equal parts roadie and mtber, so I'm not speaking from a mtb bias. I have spent much more time on road bikes over the years than mtbs.

Many areas of the country have steep, rough descents that are much more comfortable on a hardtail. Someone mentioned Hilly Billy Roubaix. I've done this race on a mtb, and often the winner is on a mtb. When you are crawling up the climbs, aerodynamics do not play any role, but on the rough descents, the control of a hardtail is very helpful.

Lastly, in areas like KS and OK where the mud is beyond sticky, the extra clearance on a hardtail is a major advantage.

Oh, and there are plenty of people that do well in races on a hardtail. Andrea Wilson won her age group at DK, and was third overall in the women's category. Pretty sure she was able to keep up with tons of people on gravel and cx bikes. All of this is to say that the advantages of a gravel bike are not as clear as people claim. I have no problem with people buying and riding gravel bikes. I also like them. I just think they are too often touted as being faster, more efficient, etc. than a hardtail, and I'm not convinced that is true. All the youtube comparisons I see are worthless too because they compare hardtails with a suspension fork, 780mm bars, and mtb tires to gravel/cx bikes with narrower tires designed for the terrain being ridden. It's an unfair comparison.

 

There is a lot of talk about aerodynamics here and elsewhere, but I'm guessing none of you have any data on the matter other than generalizations from the internet.

Bad guess.

"My strong tubeless gravel rims weigh 440f/450r. They are also much more aero than a MTB rim which makes more of a difference than mere weight at higher speeds."

https://enve.com/journal/reducing-tradeoffs-the-ses-4-5/

 

That is one component viewed in isolation. It was not tested on your bike, with you pedaling the bike. If you have a gravel bike with those rims, but your position on the bike is less aero than mine, it's irrelevant. I'm speaking of systems and riders, not a single component. Nobody on the forum has been in a wind tunnel with their bike, in their riding position. People make broad statements about such and such a bike being more aero than a hardtail, but my point is that there are a multitude of factors that affect aerodynamics, so it is not possible to make such claims based on a component mfg's claims on the internet. Simply buying a "more aero" bike, does not guarantee that you are more aero than the next guy, regardless of the type of bike.

 

That is one component viewed in isolation.

So?

You guessed "none of you have any data on the matter other than generalizations from the internet."

I do have data, provided above.

Again, a bad guess on your part.

 

You are ignoring the larger context of the discussion, i.e. people saying a gravel bike is faster than a hardtail because it is more aero. This is a common claim, and my contention is that the people making the claim have no data. If you think being a pedant, and isolating one variable counters my claim, enjoy your victory.

 

Says the guy with no data. Awesome.