For now, I am keeping this spot as the central hub for the tire and aero testing I am doing. It is mostly focused on gravel and MTB setups but I am also working on road / TT oriented bike setups.
The gravel scene in the US (I feel like a moron saying that but hang with me for a minute please…) has lots of folks thinking about their tire choices thanks to numerous pros in the Lifetime GP series very obviously maxing out their tire clearance…and doing quite well with it.
Bottom line here is, I want to have some well defined data (spoiler: I have some of it) for what makes tires fast or not so fast off road …while also addressing the rather obvious aerodynamic or weight factors included in the tire change decision process!
I have been posting most of it on my Instagram as I like it and it is good practice to make it easy to understand with limited content. That is a major goal. The posts blend in some with my other content there, so here they are in one place…
Power to hold 15 mph on Medium Rough Gravel.
So…what does a test day look like with this?
Whatabout really fast and smooth gravel?
It sounds like too much. I get it. Why go so deep into it?
How many folks tell you this stuff like, “I switched to X and got a Strava PR after using Y the time before that!” We all know how to be nice but we all know we got a story there. Of course, there is more basic testing that is better than a straight up story. Usually riding a set course at a set wattage and comparing times. This is fine, and it beats Strava story time, but I have done plenty of that and wanted more defined answers!
I’ve done all kinds of testing over the last 15 years, but my current methods are mainly focused on the Chung Method. If you really want to understand how bikes go fast or slow, the pdf in the link is free to read. Robert has been incredible helpful to me on this project so I cannot thank him enough. For anyone halfway into the pdf… the testing is simple in format but NOT easy to pull off well! This YouTube video from Silca (Aero testing expert explains how to get accurate aero testing at home) has a fantastic interview with Robert Chung reviewing some testing files before the 2024 Unbound 200.
Golden Cheetah’s Aerolab.
This gives the data, when done well, of an actual CRR (coefficient of rolling resistance) and CdA (coefficient of aero drag) which then can play out ALL kinds of riding scenarios, whether on or off road! This means instead of isolated “faster or slower” testing days we have a data set that can be used to model ALL KINDS of “whatabout” riding scenarios…
The Data and the Data Collection Site
For off road tire testing, we of course have the Bicycle Rolling Resistance website, which I pay the small fee for a membership even though much of it is free. I like it. Some think it tells ya everything about what tires are always fastest off road and some think it is dumb because “conditions are always changing”.
Both camps are wrong. THAT is why I am doing this.
After being without a gravel bike for a couple months, I spent lots of time on my MTB with a rigid fork out riding. I was really surprised how fast the bike was everywhere… even on fairly flat and easy gravel tracks, so of course, like any decent cyclist, I headed to Strava! Fortunately, I didn’t stop there!
I wanted to know what the actual rolling resistance of these tires was off road, so….I did it. I am still doing it actually. I probably will be doing it for years. The progress is awesome so far. I am not alone here, the others doing this are small in number but are super helpful so that is encouraging.
I started this project with the goal of taking folks out to field test THEIR setup…. how fast is your setup, for real? That is still happening, and it’s cool, and it works. I realized there was another layer so I kept pushing on the off road testing.
Some fast tires on drum testing remain fast off road and some less so. General trends are pretty clear and some of the wild bike setups from the Lifetime Grand Prix (for real though… what is Dylan Johnson so excited about?) will make more sense soon.
FAQ:
What about tire psi?
It does matter, that is for sure. I am usually testing off road with the rider’s preferred pressure, which also ends up usually VERY close to what the Silca or Wolf Tooth calculators would serve up as a suggestion. The goal is to get a “best case” for each tire, which is fairly easy.
Aren’t wider tires less aero?
Absolutely. The Swiss Side link below in the Resources section goes over this. There seems to be much more possible variation in CRR wattage than aero wattage swapping between different tires.
RESOURCES:
Impact of Wheel Size on Energy Expenditure during Mountain Bike Trail Riding
More Speed, Less Power Offroad Tire Testing
Swiss Side Gravel Tire Width Aero Impact
Tyre Volume and Pressure Effects on Impact Attenuation during Mountain Bike Riding
If you have questions, feedback, or want to compare notes just leave a comment below or email me at johnkarrasch@gmail.com
Testing Grounds