Direction of gravel bikes

[OreoCookie]

@Trix8806

With that in mind, when you start properly designing for that clearance, the bikes quickly lose the ability to ride a road wheel set without looking completely absurd.

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.)

@Power13

I have seen precious little actual testing…and even then, I think there are some big gaps in logic. Take for example Dylan Johnson’s testing - he’ll ride certain sections of a course / route on different tires. Those sections tend to be the rougher / chunkier sections, so it makes sense that bigger tires test faster. What is not done, however, is to test tires across an entire course, where you have a range of surfaces / levels of gravel. Even Dylan noted that his 2.2 tires were probably the wrong choice at BWR NC, because he got dropped on a road section.

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.

@eddiegrinwald

I have a hardtail with 2.4"s and prefer flat bars for terrain that requires that type of tire, but others might prefer drop bars…

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.

@wake

So right now, the fastest tires for gravel are XC tires, […]

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.

[Power13]

@OreoCookie

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

Constant from me….this has been my point all along.

ETA - I typed “no arguments from me” but somehow that autocorrected to “constant”.

[grwoolf]

@OreoCookie

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.

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).

[mcneese.chad]

I am wondering if/when we will hit the same overshoot & correction we saw in the MTB 6Fattie era? MTB’s pushed well beyond 2.2-2.4" norms of the day into the 2.8-3.0" realm with some benefits & plenty of claims. That was good for some, but less than ideal for many and we see relatively few options in that upper range these days.

Wide is great, until it isn’t and I expect this push to wider in gravel will see a similar overstep and mild retreat at some point. As mentioned by @eddiegrinwald above, and me in prior discussions, there is a massive range of what can be called a “mountain bike”. There are many steps between an XC racer to the DH bombers. I expect “gravel” bikes will end up with a similarly wide swath from stuff in the “all-road” area up to drop bar MTB that has existed in various forms for decades.

As a consumer, I welcome a range of options as there is seldom a single option that suits all and sometimes not even a majority. I just worry about the times like this when things are new and unsettled, with an apparent “gold rush” mentality that may push things to extremes that aren’t as wide reaching as other more moderate approaches.

[The_Conductor]

@crandallGA

If anything, the Silca wind tunnel test would indicate that the Race King + 60mm rim combo would be faster at any bicycle-capable speed.

But how many people are running 60 mm deep rims on their gravel bikes? If someone is down the rabbit hole of these optimizations, they’re probably looking at the new Zipp wheels (54 mm) for the 3T Discus (45 / 40 mm).

@The_Conductor

At this rate I’ll be running my Surly Wednesday with 4.3s at Unbound 2026.

And again…

[Teddy_Focaccia]

FWIW Josh Poertner also said the RaceKing on DJ’s rims was unexpectedly aero. Like, much more aero than he would’ve predicted and much more aero than other tires that size. He cautioned that other tires of that size, or Race Kings on other (e.g. wider and/or shallower) rims might not be so unexpectedly superior. The lesson probably shouldn’t be “2.2 RK is super aero” but rather “wheel/tire/tread aerodynamics is very complicated and hard to predict even for experts.”

[KonaSS]

@mcneese.chad

I am wondering if/when we will hit the same overshoot & correction we saw in the MTB 6Fattie era? MTB’s pushed well beyond 2.2-2.4" norms of the day into the 2.8-3.0" realm with some benefits & plenty of claims. That was good for some, but less than ideal for many and we see relatively few options in that upper range these days.

I was thinking the exact same thing. And remember where these bikes/tires showed up first? At the handmade shows. All kinds of specialty and one offs that made it seem like the entire market was going there. Feels just like the point we are at right now with gravel bikes.

I am not arguing that the trend towards larger gravel tires is wrong, but finding the sweetspot will likely take some time.

[OreoCookie]

@grwoolf

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.

I’m also a by-the-numbers guy, and I agree with you.
BRR drum tests do not replicate the different conditions, which are much more varied off-road. Some tires are not made to minimize rolling resistance, but to maximize grip, you wouldn’t decide between a Magic Mary and a Racing Ralph/Racing Ray combo by looking at rolling resistance data.

@grwoolf

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).

Yup. I found Racing Ralphs/Racing Rays really fast on- and off-road, with comparable performance to Maxxis Treadlites when it comes to rolling resistance on smooth terrain while being more versatile.

There are other factors that are really important off-road, too. For example, I have tried Maxis tires and I found them much worse than the equivalent Schwalbe tires when it comes to braking performance. Then there is taste in tires: some tires (e. g. Maxxis TreadLite or Schwalbe Thunderburt) are squarish while Schwalbe’s Racing Ralph/Racing Rays are round tires. I prefer round tires while others evidently prefer squarish tires. If you are a good bike handler, you might opt for a faster tire, that is sketchier on technical terrain.

@grwoolf

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.

Yup, I think there is no alternative to testing tires out on the trails. I don’t think you can design a synthetic test that takes all situations into account. I really makes sense to experiment, taking personal taste, terrain and conditions into account. That’s one of the fun bits of gravel racing as there exists no universal right or wrong answer. You can tell from some of the tire reviews on the usual websites, which can be quite polarized.

The same applies to wind tunnel testing, which can inform your choices to some degree, but the results should always be taken with a grain of salt. (In the real world you don’t have laminar flow, with the possible exception of a velodrome.)

@grwoolf

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).

Yeah, absolutely. If I participated to beat a time I set myself, I would likely opt for beefier, slower tires, run inserts, etc. Because nothing would suck more than DNFing because I flatted half-way through the race.

@KonaSS

At the handmade shows. All kinds of specialty and one offs that made it seem like the entire market was going there. Feels just like the point we are at right now with gravel bikes.

Yes, and this was decided out in the real world by people riding and figuring out what was fastest. The end result was that moderately wider tires are fastest (2.25” —> 2.4”) in most conditions. I reckon this might be the end result for most people in the gravel market, too. It is just that we don’t know what that optimum is for most people in most conditions. That’s why I think it is important to have bikes that can accommodate very wide tires so that people can try.

[OreoCookie]

@mcneese.chad

As a consumer, I welcome a range of options as there is seldom a single option that suits all and sometimes not even a majority.

Fortunately, unlike new suspension designs and such, added tire clearance has few negatives (added weight, slight compromises when it comes to clearance or geometry?), so I don’t mind. It opens doors and closes none as far as I can tell.

[BillyWaldman]

So it seems like this is a battle between rolling resistance and aero drag. Are we forgetting that significant gains are made from big tires on long descents? In the mountains i dont care about drag, but railing downhills is the big benefit for me

[mcneese.chad]

Maybe, but seems to me that beyond the tire clearance aspect, the related geo changes are things I personally dislike. Most relevant is the long Front Center that seems a solution for toe overlap, and stability that comes from slack head tube, longer Reach or a mix of both.

Again, it’s MTB focused and something I never want for a drop bar bike. But I understand others like and accept I am probably in a minority.

[crandallGA]

It’s a complex problem that requires a lot of different things discussed simultaneously, conversation happened upon these two yesterday. Aero drag essentially doesn’t matter at all once potential suspension losses pass a relatively low threshold. The same reason 23s have lower rolling resistance on perfect velodrome surfaces but will have much higher rolling resistance even on smooth pavement.

[crandallGA]

@Teddy_Focaccia

FWIW Josh Poertner also said the RaceKing on DJ’s rims was unexpectedly aero.

That’s because 2.2 tires on 60mm deep rims with 21mm internal width has rarely, if ever, been tested in such a manner. The model assumptions for aerodynamics have repeatedly shown that they rarely carry forward on specific instances. The more wind tunnel data that has been acquired as rim widths and tire width combinations have become more varied has reduced the applicability of the rule of 105 for instance.

The aerodynamics of XC tires, and tires with relatively large knobs in general, relevant to gravel does not have a deep experimental base.

[Bones]

@crandallGA

. The same reason 23s have lower rolling resistance on perfect velodrome surfaces but will have much higher rolling resistance even on smooth pavement.

Wait, is this actually true? I thought Josh Poetner’s position on this was, assuming a given tire had the same construction, it all comes down to casing tension, regardless of tire width. So, if I had a 23mm GP5000 vs. a 28mm GP5000 on average pavement, you would just have to change the pressure of each tire to achieve the same casing tension and then the CRR would be the same.

Where things fall apart, is when the surface is so rough, and you have to air down the smaller tire a lot to achieve the optimal casing tension that you run the risk of flatting.

[crandallGA]

Increased casing tension means increased suspension losses (impedance), even on smooth pavement. The point at which one overtakes the other would be specific to that tire and surface.

The lowest rolling resistance is immediately before impedance losses begin, but this can never be known in the real world where there is surface variety at all time, so a given tire pressure model is predicated on the logic from it’s creator and their opinions and dataset.

If you equalize the casing tension of a 23mm and 28mm GP5000 the perfect rolling resistance will be the same but the larger tire will be more susceptible to punctures and will already be into impedance losses in the real world.

You can model this yourself to see how the theoretical structure asserts itself, using the BRR GP5000 comparison test and the Silca pressure calculator with the BRR test load (94lbs a wheel):

Continental Grand Prix 5000 23, 25, 28, 32 mm Comparison

SILCA Professional Tire Pressure Calculator

[Bones]

I believe we are saying the same thing - a larger tire of the same construction does not have better CRR if equalize the casing tension. The problem is you can only go so low on pressure, hence why larger tires become a better option as the terrain becomes rougher.

[grwoolf]

@Bones

The problem is you can only go so low on pressure, hence why larger tires become a better option as the terrain becomes rougher.

I think this point is core to the tire discussion. All else being equal, if you can get to an ideal tire pressure on a smaller tire without too much risk of pinch flat, you should opt for the smaller tire. There are courses that I’m fine running 38’s with pressure in the mid 20’s and there are courses where I’d want 47’s (or bigger) if running pressure that low.

But figuring out the ideal pressure is where it really gets hard in my opinion. The commonly used tire pressure charts can be good tools to get some feel for the relationship between tire size, pressure, and surface, but it’s a swag at best with limited surface options (and highly subjective). Even if someone comes out with a calculator that can do a decent job for a single consistent surface, most courses are going to vary dramatically by segment. You almost need something like best bike split that looks at the entire course and does some magic math balancing surface vs. resistance vs. flat protection, etc… And it also depends on the skills of the rider (avoiding flats is probably 90% rider and 10% luck). It’s a really complex problem. I’ve raced gravel/dirt on 28’s and I’ve raced on 2.2’s, both options were great on certain parts of the course and terrible on others.

[Bones]

@grwoolf

All else being equal, if you can get to an ideal tire pressure on a smaller tire without too much risk of pinch flat, you should opt for the smaller tire. There are courses that I’m fine running 38’s with pressure in the mid 20’s and there are courses where I’d want 47’s (or bigger) if running pressure that low.

This has always been my approach riding all formats of bikes. I take the smaller tire, all things equal, if I can get the pressure I need without risk of flatting dominating my decision. As you said, this can get quite complex once you throw in a bunch of variables, but it’s a great starting point for the decision making process. I guess what bugs me from the “wider is better crowd”, is that wider being better isn’t always the case!

There is no way a low CRR 2.2 mtb tire is always faster on my gravel/pavement routes, compared to say a low crr gravel tire in the 40mm range. The gravel just isn’t rough enough and there is too much pavement to connect roads to balance things out. This is where everyone’s situation is different. I’m certainly not disputing a fast 2.2 mtb tire isn’t the best option for a lot of the lifetime races we have been seeing - it just doesn’t carry over to every other terrain and rider out there.

[drwelby]

I know we all love anecdata so in the latest Bonk Bros podcast DJ says the Maxxis riders were testing tires and found the Aspen rolled faster than the Reaver on pavement.

No real details, but certainly will add fuel to the fire.

[drwelby]

@mcneese.chad

I am wondering if/when we will hit the same overshoot & correction we saw in the MTB 6Fattie era? MTB’s pushed well beyond 2.2-2.4" norms of the day into the 2.8-3.0" realm with some benefits & plenty of claims. That was good for some, but less than ideal for many and we see relatively few options in that upper range these days.

Tires are a huge investment and since big tires won’t fit in existing frames you need buy-in from manufacturers to hit your minimums. It’s hard to get adoption when it means buyers have to upgrade their frames at the same time. That’s why you’ll see flexstems outsell gravel suspension forks 10 to 1.