Baum DBM Ti Gravel Bike Drop Bars the Mountain Like It’s Hot - Bikerumor
Some brands are catching on. However, this is a really boutique brand.
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I think the Baum is the inevitable “next phase” for rowdier gravel bikes. It mates a MTB rear end with a gravel front, so the geometry isn’t all wonky and you have to resort to weird stem / HB setups.
Whether that idea becomes the standard for gravel remains to be seen, though. The CR size may continue to be a limiter. 44t is sufficient for many, but not for the top tier guys.
On relatively smooth surfaces, at some speed the aero penalty of fat tires outweighs any crr benefit. You can only make a big toroidal thing like a tire so aero by adding material to the rim, and of course that brings a weight penalty. I’d speculate that even a magical “zero crr” 2.2” tire would not be faster than a modern 28mm at WT race speeds.
I think the point of the move to fatter tires for gravel is that testing crr in real-world conditions is hard, and eveyrone underestimated how much drag comes from rollover vs. factors like aerodynamics and weight. But at some combo of speed and roughness those lines cross. Trackies still run tiny, crazy-high pressure tires.
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Rodeo Labs is here
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To these points, I’d just like to add:
- Tire compound seems to affect measured rolling resistance the most of all the factors (casing, compound, tread, sidewall protection).
- The two fastest-rolling compounds for non-road tires (I.e., larger than 35mm and not slick tread) seem to be Continental’s Black Chili and Schwalbe’s Super Ground Addix Speed.
- Those compounds are only available on certain sized MTB tires (Schwalbe is 27.5 x 2.1, 29 x 2.1, and maybe 29 x 2.35? Continental is 27.5 x 2.2 and 29 x 2.2 I think?)
- So right now, the fastest tires for gravel are XC tires, not because of XC tires, but of the products the tire manufacturers choose to produce.
Separately, note that Challenge’s Pro HTLR seems to roll pretty fast too. But they only have the getaway up to a 45 or 45, and the slick Strada Bianca up to either 40 or 45 as well.
All I wanted to add was that some of this has to do with what the manufacturers are choosing to make right now.
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The wind tunnel testing DJ did with Josh Poertner shows this is not true in all cases. The 2.2 Race Kings with 60mm deep rims were faster than every other combination, and had the same aero drag as the 45mm tires. Except the Race Kings have less crr.
So in this test case the larger tire had both a crr and aerodynamic benefit. Which produced another test result in that DJ had his best finish at Unbound 200. Not in placing terms (he got 9th in 2018 0:55 back) but in both overall time and relative time to the winner - 10th 0:05 back.
Ignoring that you originally offered evidence of someone else’s anecdote (DJ didn’t prefer his 2.2 Race Kings at BWR because he was dropped on the pavement), the fact that many racers are riding faster on MTB tires isn’t anecdotal evidence. I’m not saying I’m faster on MTB tires. We can look at race results and see if X racers are on XC tires and their overall times are faster than when they were on gravel tires, this is strong evidence to indicate those XC tires are faster than gravel tires, at this time.
This would be a review of the available data from professional racing, not an anecdote. There were 4 racers in the top 10 and unbound on XC tires. 3 out of the 4 had raced Unbound previously and each had a significantly better time, and relative result, than they had in the past - when they were riding gravel tires.
As I mentioned earlier, the body of evidence that certain XC tires are faster than most, if not all, gravel tires, is as large and robust as the body of evidence that certain 28-32mm road tires are faster than most if not all 23-25mm tires. We can pick and choose what we believe and what we feel is applicable but there is enough evidence to make a decision.
This thread, which you have many posts in as well, contains many tests which show results in favor of specific XC tires: Is a MTB tire the fastest and best tire for Gravel racing?
Torsten Frank’s model and testing provides stronger evidence than anything I’ve ever seen for the current road tire understanding. Of course, Bicycle Rolling Resistance is an accepted laboratory testing suite as well.
The term is hysteresis. (You can see it here starting at 5:04, inside a car tire)
Roughness is commonly known as impedance: https://silca.cc/blogs/silca/part-4b-rolling-resistance-and-impedance
The model that supports wider tires on rougher surfaces cannot have an arbitrary limit. A 2.2 Race King may be significantly slower than a 28 GP5000 on smooth pavement, but that’s not the comparison. The comparison is the 2.2 Race King v. the above average gravel tire. In this comparison it’s not clear, and much data seems to indicate the Race King will be at least as fast on pavement and much faster on gravel and unpaved surfaces.
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Exactly, this really comes down to market segmentation. I’ve got a Giant Revolt that’s one of my favorite bikes ever. It fits me perfectly, takes up to 2.1" tires, and is just an amazingly all around capable bike. Easily the most versatile bike I’ve ever owned.
That said, I still want something that’ll take a big-ass mountain bike tire for some of the rowdier, chunkier gravel rides where I live in Vermont. There’s a lot of really fun Class IV riding (basically 90’s mountain biking), that you can connect with nice stretches of gravel. I can do something like a 40-50 mile ride with as many miles of Class IV as I want right out of my front door, and I wouldn’t want to do it on a hardtail MTB because the vast majority of it is still on gravel and dirt roads, with the occasional stretch of pavement.
So there are clearly two different market segments here: one that’s more of an all-road style that could max out at 45-50c tires with closer to conventional road geometry that could be fast on pretty much any road you want throw it, be it paved, dirt, or fire road, and the other than can take even fatter tires (2.2 - 2.4 XC tires) and slacker geometry, that’s fast enough on pavement but also totally capable on some real off-road riding.
I think Trek tried to do this with their new Checkpoint and Checkmate, but things are moving so quickly they’re both under-tired for their targeted purpose. If the Checkpoint could take 2.25" or bigger, and the Checkmate could take 50c, they’d be perfect. Although it really does seem like over the long haul even pure race bikes will need to be able to take up to 2.2" tires, so maybe it’ll be big tires more with road geometry or huge with slacker geo? I’m glad I’m not the one who has to design these things.
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I’d just push the industry to make bigger Boost chanrings or to make them all compatible with each other. You’re gaining space where it’s most important this way – at the BB.
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You can only do that if you isolate the result from all other factors except the tires. At best, you currently have correlation, not causation. Which goes back to my original point - we don’t really have any hard testing data. We have some flawed conclusions through extrapolation of limited data.
And just to be clear - I am not arguing against wider tires. I’m simply disputing the notion that it is now a given conclusion that XC tires are the fastest option. They may well be, but saying “oh, these guys ride them so they are therefore the fastest option” is not conclusive proof.
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That thing makes me want to stop shopping for a MTB…
My gravel bike is still on 35s so I’m not here for the tire fitment discussion…
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Addix Speed is the rubber compound, Super Race/Super Ground/Etc are the construction types.
Otherwise, this model doesn’t seem to be true. Super Race and Super Ground tires use the same rubber compound but different casing construction and the Super Race tires consistently test 10-20% slower than Super Ground.
The comparison tests BRR has performed seem to indicate each part of the tire type and construction is important with perhaps overall thickness the most important. Most likely because constructing a very thin tire requires high TPI with thin threads.
The Gravel King test where the thicker tire tests relatively slower than the thinner tires seems to be a good contrast to the GP5000 test where the tires are much closer in thickness and test much closer in crr.
I’ll be honest and say I don’t know enough about Boost spacing to have a take on it. It came about after my time in the industry and well after I stopped riding MTB’s. Living in the Chicago area will do that. 
The biggest challenge would simply be getting the industry to move gravel bikes to another frame spec “standard”. Or maybe Boost is just used for rowdier frame designs…probably a lot of ways to peel that onion.
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We do have hard data; there are R Chung tests in the thread I linked, there are laboratory grade tests from BRR, there is real life data from professional racers. There is wind tunnel data from Silca. Torsten Frank has created a comprehensive model that can be applied to tires and courses to help determine where an XC tire would probably be a faster choice, or not.
We have testing from ndart: More Speed, Less Power: Rolling resistance testing
What hard data would you like to see?
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I say again: On relatively smooth surfaces, at some speed the aero penalty of fat tires outweighs any crr benefit. The test they did didn’t find that speed (32kph is pretty slow relative to WT-level racing, and they didn’t test a real road setup.)
Nothing against fatter tires for gravel, but you seem to be suggesting the world tour would benefit from running 2.2” tires, and I don’t think that’s correct.
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This assumption is not supported by available evidence. The fluid model of aerodynamics would not indicate a wider body would create more aerodynamic drag relative to it’s drag at lower speeds, purely because of it’s width. If anything, the Silca wind tunnel test would indicate that the Race King + 60mm rim combo would be faster at any bicycle-capable speed. We know that crr increases as speed increases and increases relative to the initial crr. So the above average gravel tire would have a higher increase in crr, as well as higher relative aerodynamic drag compared to the fastest XC tires.
I am not making this claim either, as I addressed below:
I have already outlined what I see to be the flaws in the available data.
We can conclude our discussion at this point.
I think this is putting too much emphasis on looks. What looks good/natural is in no small part dictated by what you are used to. @Teddy_Focaccia already posted a picture of the Lotus track bike, which also sports a very unusual look.
Form should follow function, and if the aim is to allow for massive clearance, then you must design the fork and frame accordingly.
To give you another example: to a lot of roadies, a traditional road bike has rim brakes and they find them more aesthetically pleasing. I am a recovering mountain biker without proper MTB terrain nearby, and all of my mountain bikes have had disc brakes for close to 2 decades now. Only very cheap mountain bikes still came with rim brakes. So bikes with rim brakes initially look cheap to me even though that’s patently false with road bikes. 
(I’m aware of my aesthetic bias, of course.)
Proper testing is very hard as there are more factors than reducing rolling resistance at play. It is really a balance of rolling resistance, grip, durability and suitability for the terrain. So it makes sense that different races might call for very different tire choices.
I reckon there are also cases where the tire choice is personal preference or equivocal, i. e. the time you save on one segment/type of terrain balances out the time you save on another. Or riders simply make the wrong choice.
This will be interesting, especially for non-UCI races where you could put drop bars on your mountain bike. I personally prefer flat bars overall, my next commuter will be a gravel bike with flat bars, but I am aware that I could likely go faster with drop bars.
I can see a future where for the XC marathon side at least, the bar type is down to personal choice of the athlete.
I thought the fastest gravel tire was Schwalbenschwanz G-One RS, which gets close to the rolling resistance of a slick. Bummer that it only comes with a tan wall, but I’ll try them as soon as my spare set of tires have reached their EOL.
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Constant from me….this has been my point all along.
ETA - I typed “no arguments from me” but somehow that autocorrected to “constant”.
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Yeah, I’m generally a numbers guy, but the stuff I see in many of these tests doesn’t line up with my personal experience. In particular, I don’t find the BRR drum test data to translate to real world. BRR would indicate a big (over 10 watt) difference between a 2.2 Race King and a 2.25 aspen on rolling resistance at 25psi (and they show the delta and watts going up as PSI goes down). All I have to do is look at my strava segment history at Leadville (where I have double digit rides on each segment on each tire) to see that the tires have very similar efficiency. The data shows very little difference on road, gravel, or trails. I’m not saying the race king doesn’t roll faster in some cases, but it’s not anywhere near 10 watts per tire (it would be impossible to miss that in the segment data). And I while I don’t believe BRR is claiming their drum test is a 1:1 proxy for real-world performance, a lot of people seem to take it that way. I think BRR is a good data point, but testing on the road/trail is always preferred in my opinion (despite the challenges of controlling variables). If you do enough testing with the same setup and control what you can control, at some point the variables statistically start to cancel each other out and you can formulate an informed opinion.
And it still requires some critical thinking to make tire selections even if you have decent real-world data. If I was going to race Unbound Gravel in solo TT mode and just wanted the fastest tire based on surface mix, that would likely be a different tire selection vs. a race where I plan to race with the lead group (where the chunky sections are critical and would dictate tire choice even if those tires weren’t optimized for 90% of the course).
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