You can probably fit the Thunderburt 2.1, it is just a little over 50 mm. In 50 mm the G One RS is really fast…
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Depends on your priority. Thunder Burt seems to be the fastest, although not great traction and poor puncture resistance. I’ve run it front and back successfully on Texas gravel but won’t at unbound.
I just picked up the Schwalbe g one rx 50mm and mounted it today. Planning on a long gravel ride tomorrow and to use it up front for unbound. In its 40mm version it is fast on BRR. The puncture rating also appears to be pretty good. For a bit less traction but a little more speed, the g one RS (mentioned above) also seems to be a good choice.
If I can gain confidence in its puncture resistance I can see having it be my go-to for rough trails with the thunder Burt being the tire for smoother gravel.
My fork has rated clearance for 50mm and the RX measured at 51mm and looks great. The thunder Burt measured around 53.5? Mm and was on, although I did trim the side knobs a bit.
I bought and mounted a 2.2 race king last week and I could see it potentially rubbing under load, or close to it.
Lastly, the new specialized tracer seems to be promising in 50mm. If they made it in a black, I’d probably be riding it. Same with if they made the pathfinder in a 50mm.
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Well, the degree to which the Aspen ST 170 outperforms its Bicycle Rolling Resistance results is pretty impressive.
Yeah, it’s the 2.25 vs the 2.4 but, jeez.
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Interesting results for those 170tpi Aspens. There’s something about that casing that doesn’t translate well into the BRR drum testing. I did roll down tests before (not even remotely as repeatable as Chung) comparing the 2.4 non ST Aspens against the Super Race Racing Ray/Ralph and got exactly the same results for what should be a 12w difference
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my Pathfinder Pros feel pretty fast
Wow that’s good to hear! Rechecked results many times on these haha.
So, should we question BRR data as it applies to real life? Seems so
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Well yeah.
BRR is fine, just has its limitations… which are more pronounced with larger tires and varying compounds.
I still pay monthly for it.
BRR results are not wrong, but by testing on the steel drum they measure only casing losses. And it’s only one of two variables, that determine total rolling resistance. Total rolling resistance consists of casing losses plus surface impedance losses. To measure surface impedance losses tire needs to be tested on the real road. And for gravel tires impendance losses completely dominates, so casing losses, measured by BRR, are not a good indicator of total rolling resistance.
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but it seems they are a good indicator of total rolling resistance (plot it out and the trend quite closely matches with Chung method testing, with just a few outliers). Why is this the case if impedance losses dominate?
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Casing losses and suspension losses, seem to be too tightly intertwined to conveniently pull them apart but maybe I just haven’t seen the right research on it or know enough about it?
I say that partly because the paved stuff I test on is pretty consistently faster than steel drum, especially for mountain bike tires.
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This is a good article explaining it in detail:
Your tests are probably the most accurate and representative of real world performance, but there’s one point a lot of testers miss: total rolling resistance vs pressure chart is U shaped, and you really need to find this optimal pressure, where crr is lowest. Otherwise the whole testing becomes just a lottery - whether you happened to run this particular tire at the right pressure. And Silca pressure calculator gives too high pressures, especially for narrower tires.
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+1000 on this. I like BRR as a data point, but the pressures (and obviously the surface) are rarely going to align with real world use cases. Again, I’m not throwing rocks at BRR or the validity of their data, just how people tend to assume too much from it. Lots of “slow” tires could be fixed by running appropriate pressures and lots of “fast” tires on the drum at a given pressure could be very slow in the real world using terrain-appropriate pressure.
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In addition to casing losses and impedance losses, there is a third category of rolling resistance loss that many people don’t realise, or think about, but which is relevant to any of us that ride off road. That third rolling resistance source is the energy loss you get from the ground deformation.
Ground deformation losses are independent from both impedance losses and casing losses.
Impedance losses are sometimes often called suspension losses, which I think better describes the mechanism that causes the energy losses. Essentially those impedance losses result from a rider’s flesh and organs jiggling around and absorbing energy, due to bumps that are transmitted through the tire to the rider’s body.
The best way to visualise ground deformation losses is to imagine some extreme cases where very high ground deformation losses occur, for example the situation when you ride though soft sand or soft mud. Those surface deformations are pure plastic deformation, with the front of the tire contact patch deforming the sand/mud, and with zero spring-back of that sand/mud at the back of the contact patch, so no return of that energy. Even if that sand or mud is perfectly smooth, the lack of bumpiness means the casing losses and impedance losses are not significantly different to the losses on a hard surface, yet the resistance is still very high in that sand/mud. On gravel surfaces, the ground deformation and associated losses might rather more subtle, but nevertheless most of us have experienced the speed differences between winter trail and a summer trail conditions whenever there is some underlying dirt and softness to the ground.
I think lower tire pressures might play a role in reducing these ground deformation losses, as well as helping with impendence losses. I think the increased tire footprint at low pressure probably helps. Anybody that has seen the ease with which a fat bike rides across soft sand or snow will know how the large tire footprint helps in those situations, reducing those ground deformation losses.
Practically, what this means for tire testing is that we might need to be careful when comparing tests from one day to another, in case the ground softness changes due to weather conditions and ground moisture content.
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@ndart Nailed it.
Moisture content definitely changes things. For different areas I found different thresholds of soil moisture, where the rolling resistance stays the same once you are dry enough.
By this point I’ve tested enough on all these different areas I can usually predict a day where the rolling resistance will be off by even a small amount. The Delta of wet versus dry rolling resistance also depends on each course.
This is one reason why I think if you really want to do good off road tire testing you better really enjoy riding your bike!
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Sounds like you’ve got things dialled. I think there’s no substitute for experience when it comes to testing, which you’ve got, because that gives you a better handle on the many potential pitfalls of testing. I’ve had lots of those in the past, either strange results or repeat runs that don’t repeat. Most of those dodgy results go unexplained and I just throw the data away, but in doing so it somewhat hides the fact that real world testing, aerodynamic or tire testing, is fraught with difficulties.
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So currently for the top large gravel tires we have the Schwalbe rs/rx and Specialized Tracers with also the Tufo Thundero 48 mm (not quite 50)?
I’m pretty sure I can fit a Race king 2.2 but I do like not worrying about mud ruining my bike (UK based)
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Should we now just call anything 2.2 down to 45s gravel tires? Everything above 2.2 is mtb, and 38-44s all road and below that are road tires?
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Maybe. But there’s a lot of gravel bikes still spec’d with 45 and below. For example the crux comes with 38s. Even the Santa Cruz stigmata which is a “MTBr’s adventure gravel bike” comes with 45. Do any gravel bikes come with larger tires these days?
Seigla comes with 50s. Allied has Race Kings on their bikes in the showroom in the Meteor
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