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 @eddie 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.
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).
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.”
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.
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.
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.
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.)
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.
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.
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.
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
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.
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.
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.
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.
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):
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.
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.
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.
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.
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.
The R Chung testing in the MTB tire thread shows similar results with other XC/Gravel tire comps.
The issue is that hysteresis losses are at a different scale from suspension losses. A wider tire may lose 5-7w by virtue of it’s width rolling along on pavement or smooth dirt, but a narrower tire will lose multiple times that from suspension loses on anything else due to it’s own width.
It’s much less likely a given racer can determine the best pressure for the fastest 38mm tires as opposed to the fastest 2.1/2.2 tires, because of the massive differences in losses from each type of rolling resistance. If you have to air down to extreme low pressures to limit suspension losses, hysteresis losses will necessarily increase.
It’s easy to fall into the “horses for courses” idea but the relative differences are of such different power, there’s a stronger argument to be made that the fastest 2.1/2.2 XC tires are a better general choice than the fastest 38-42mm gravel tires.
At least for right now, as I mentioned earlier. Gravel tires appear to be getting faster. The new Hutchinson Caracal Race is the fastest tire BRR has tested so far in the gravel class that has any sort of knob feature. In addition the new logo Specialized Pathfinder Pro appears to be an updated model that is slightly faster than the older Pre-2024 models.
Sure, there is short-term and long-term progression at play here, just like the MTB evolution WRT to stuff like suspension as well as tires & frames (26" > 29" > 650b > 32"? and then all the width growth for each one of those along the way.)
But I am talking more about the fact that we often see pendulum swings in these trends where there’s a point that too much becomes TOO MUCH. Suspension travel, tires, etc. have followed that trend to a degree or two and I fully expect to see something like that here. For the life of me I can’t see how a 2.?" tire on non-extreme gravel will be faster than something in the 40mm range, but that’s where science and data hopefully come in to clear the confusion & assumptions.
Either way I sit on the sidelines as I already found what I want so it’s just entertainment for me now.
DJ is always saying Pete (IRC also wicked slow) or Maxxis sponsored riders besides Keegan would be doing better if they weren’t tied to those grave tires.
and then all the width growth for each one of those along the way.)