Gravel and mtb tires…what is fastest and why?

Welcome! This is home base for the Chung Method tire testing I am doing. You are probably here for the juicy stuff… so I won’t keep you waiting! The table below shows the latest Crr values across all tested surfaces. I have some testing gaps, as you can see. I need to get the Race Kings out again for Cat 1 and 3 gravel, also need the Aspens out for cat 1 track. I actually did the 700 x 40 Caracal Races on the rough gravel (Cat 3) track but it was so tough to ride a “regular line” I didn’t think it made sense to include them in that column. I also will not try this again with a tire obviously too small for the test track. This was my intuition, but it’s better to have it proven than make an assumption!

More Cat 3 testing soon.

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

Payson McElveen’s Allied Mule prototype

I am gathering data on what tires are fast or not so fast off road …while also addressing the related aerodynamic and weight factors! Weight and aero differences are factored into the “Power to hold 15 mph” column in the photo below. This uses tested CRR values to calculate exact power to hold a speed. I know it sounds backwards but with known coefficients, this is WAY more accurate than attempting to go out and ride an exactly flat course over and over. Steve Gribble’s website, The Computational Cyclist, is a fantastic spot to visualize changes from what might at first seem like trivial differences in CdA or Crr values.

Many riders don’t do ALL of their riding on one certain type of gravel,,, it varies, and often has a good bit of pavement mixed in. Mixed surface rides bring their own questions, such as how much power one might need depending on the ratio of gravel to pavement. The photos below illustrate this scenario for riders at midpack amateur speeds as well as those closer to pro level speeds. The actual Instagram post on these photos is with the other IG posts a bit further down the page!

The Cat 1, Cat 2, and Cat 3 gravel classifications I am using are adapted from those included in Silca’s TIre Calculator and VERY similar to their photos. You will notice Cat 4 Gravel is very rough…I have messed with this a little and the CRR values drift into the .0200 sort of range, which is very close to mountain bike tracks.


I have been posting most of the testing on my Instagram … it is important to me that this is easy to understand. This stuff gets confusing FAST. If you use IG at all, definitely stay in touch with it there, I throw a good bit of things out on Stories before they are ready for a real post. The posts blend in some with my other content there, so I am also keeping them here:

Power to hold 15 mph on Medium Rough Gravel.


So…what does a test day look like with this?


The Delta Tells The Tale!



CRR varies by surface.



Whatabout really fast and smooth gravel?



Schwalbe Thunder Burt Super Ground 29 x 2.1 update



Into the Gnar… Cat 3 (Rough) Gravel testing


Off Road Tire Testing: Mixed Surface Scenario.

Spring Classics Edition - Cobblestone vs Gravel CRR Values

Hutchinson Caracal Race Cat 1 Comparison


Testing the “Fastest Gravel Tire Available” on 3 gravel tracks

Hunt Limitless 40 Gravel Aero wheel testing

Mixed Surface Comparison of Thunder Burt 29 x 2.1 and Caracal Race 700x40

I’ve done all kinds of testing over the last 15 years, but my current methods are mainly focused on the Chung Method. 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. Dr. Chung was recently on the Performance Process podcast with Ronan Mc Laughlin. Check it out on Spotify here. The full version is available for Escape Collective members.


Ronan was also kind enough to host me on the Performance Process podcast to talk about my tire testing…recorded right after the episode with Dr. Chung himself. Check it out free on Spotify here… all Escape Collective members have access to the full episode along with an incredibly thorough article that brings together my testing with Ronan’s insight: Real-world testing hints that MTB tires are faster on all gravel.

If the testing still sounds like black magic. I get it. As a contrast, think about this…How many folks tell you this stuff like,  “I switched to X and got a Strava PR after using Y the time before that!” That’s interesting, but ya can’t do much with it. A vs B basic field testing has a place in the mix, and that is how I did mine before learning this way.



Peyote Cat 1 Test

Chung testing (aka Virtual Elevation) can provide an actual CRR (coefficient of rolling resistance) and CdA (coefficient of aero drag) which then can help model ALL kinds of riding scenarios, whether on or off road! The Race King vs Terra Speed scenario at the start of this is a good example. See the FAQ at the bottom for more talk about coefficients, which can be somewhat mysterious.

Cat 1 Gravel. EASY.

Cat 2 Gravel. Medium

For 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”. It has its place of value, for sure. The indoor drum data and my outdoor testing has been a potent combo so far, as you can start to see the info we have all wanted:

Cat 1 to Cat 2 Breakpoint

Cat 2 to Cat 3 Breakpoint

Interesting, right? Some fast tires on drum testing remain fast off road and some less so. General trends are appearing and some of the wild bike setups from the Lifetime Grand Prix (for real though… what is Dylan Johnson so excited about?) are starting to make more sense. I don’t have all the answers, but I have a few, so I will keep testing.

Cat 3 Gravel. The Gnar.

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. Finding the “magic” tire pressure has more to do with getting the right feel and handling.

I tested this recently for anyone who REALLY needs to see it!

Wait, so you rode all those at exactly 15 mph? I see that column there….

NO! Notice that column says calculated… I tested to get CRR on gravel and used that value with an average gravel bike with rider CdA value and calculated the wattage required. This gets an exact wattage for easy comparison of the whole picture!

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. Tom Anhalt has blog posts on this HERE and HERE as well. I have tested this, and my findings are in line with Swiss Side and Tom, as well as some of the wind tunnel data I have seen from Silverstone in the UK.

Why all the decimal places?!

It is the nature of the beast with this kind of data…presenting it as direct CRR values avoids any confusion of whether the value is one or two tires….it is the same either way as a coefficient! CRR values for each surface also easily give us the ability to calculate wattage at different speeds and gradients to simulate racing or riding scenarios. The same is true of CdA values. These numbers seem quite small but create serious changes in the power it takes to make a bike move.

What power meter are you using?

For most tests, I am using Favero Assioma MX 2 Pro dual sided pedals. I calibrate them before each test after riding around some. I like them. Some tests are done with other rider’s bikes and a different power meter but with careful course selection, even the single sided power meters are enough to get pretty good results!

Are you testing on pavement, too?

Yep. All the time. The values I have gotten are so close to the BRR drum data that I am just using the BRR test data (Extra Low in each case) in the columns to keep things simple. Remember on the BRR website they give CRR values in addition to the wattage values…they just aren’t quite as in your face. I mainly use pavement tests now to pull apart CdA from CRR to make the gravel analysis in Aerolab easier later on.

What outdoor temperature are you testing at?

It varies but a loose target is 68° F / 20°. Anything off this is scaled to ensure consistency. We have generally mild weather here, which makes this easier.

But, my old tires felt faster. Are you saying to ignore that?

Yes.



RESOURCES:

Reliability of the virtual elevation method to evaluate rolling resistance of different mountain bike cross-country tyres

Comparison of tyre rolling resistance for different mountain bike tyre diameters and surface conditions



Torsten Franks blog

Bicycle rolling resistance under winter conditions



Impact of Wheel Size on Energy Expenditure during Mountain Bike Trail Riding



More Speed, Less Power Offroad Tire Testing

Performance differences when using 26 inch and 29 inch wheel bikes - Swiss National Team

Simulation of transient rolling resistance of bicycle tyres at various ambient temperatures



Swiss Side Gravel Tire Width Aero Impact



Influence of wheel rim width on rolling resistance and off-road speed in cross-country mountain biking



Evaluation of aerodynamic and rolling resistances in mountain-bike field conditions. Journal of Sports Sciences



Tyre Volume and Pressure Effects on Impact Attenuation during Mountain Bike Riding



Air Density Calculator



If you have questions, feedback, or want to compare notes just leave a comment below or email me at johnkarrasch@gmail.com

Skyway epic 2022

I have done the 60 mile version of Skyway Epic numerous times, with the most recent (2017) leaving me fairly disappointed. That year saw me dropping from the 100 mile to the 60 a week before the race due to a heat exhaustion scare during my last long ride. I rode the 60 at a pace I could have done the 100 in and finished knowing I could have done more. Not good. A halfway effort feels bad, even if you place well! I had to wait five years for redemption and get a good shot at the 100 ish distance. 


“Ish” is a phrase you will hear often around Skyway…because it is true. 60 and 100 mile distances are offered, but rarely right on the money. I think the 60 usually ends up a 68 and I ended up with 110 miles right on the money with a calibrated wheel speed sensor this year. It is part of the mind game to get this race done. 


After a couple years of barely riding any, I got back rolling consistently summer of 2021. My looming goal was Skyway 100, so everything revolved around that. I even ordered a badass race bike for it, a Trek Supercaliber! After multiple delays  I lost confidence I would have it for the race. Around the time of this realization, I lucked into Lee Neal’s old Vassago Jabberwocky singlespeed. A couple rides later, I committed fully: Skyway 100 in full idiot mode on a rigid singlespeed. I had fallen hard for the bike and as often happens, love isn’t very rational. I wrote a race prep plan for myself and whoever else wanted to buy it, then stuck to it best I could. I’ll detail this in a later post as it is a bit different than some others I have seen! As far as my bike goes, it is a bit odd so I’ll detail it briefly:

  • steel Vassago Jabberwocky frame

  • Niner carbon fork

  • Chris King headset

  • Shimano XT brakes

  • Shimano M520 pedals

  • M952 XTR cranks and BB

  • KMC X11 chain and Wolf Tooth cog

  • 32x20 gear

  • Chris King hubs with Stan’s Arch rear rim and Race Face ARC 30 front built by me.

  • Maxxis Rekon 2.6 front / Ikon 2.2 rear w Orange Seal

  • Basic alloy cockpit parts

  • ESI grips

Vassago Jabberwocky

As I rolled down towards the start of the race, it certainly felt colder than 40 degrees. The wind blasted me and it felt good to be cold somehow. Adrenaline was high and it was time to race. I saw lots of familiar faces and any pre race nerves I had were gone from just enjoying where I was. Brian Toone rolled in from his 7 hour commute from home, got his number fixed in a frenzy, and it was go time. Skyway 100 had begun!

For those unfamiliar, here is a brief rundown of the Skyway 100 course: It starts at the Sylaward trail system near Lake Howard in Sylacauga with about 10 miles of fast twisty singletrack, then turns out some rolling gravel hills towards the real meat and taters: the Skyway Motorway. Around mile 20, the major climbing starts up towards Bull Gap and heads all the way out to the road climb up to Mt. Cheaha. You return the same way and eventually end up with 110 miles and 12-13K climbing. It sounds simple enough, but it is, to put it simply, unrelenting in its challenges. 


My plan was to hang back at the start to ride easy in the singletrack so my legs wouldn’t feel dead from going hard in the cold. {Narrator: He did not in fact ride easy} I ran an easy ish gear this year (32 x 20) and got spit further out back than I wanted and had to really push on the road climb to get into the singletrack conga line mid pack. Oof. I ended up riding harder than desired the first 5 miles due to kinda being stuck in line. If you stop it can be almost impossible to get back in. My hands ended up being WAY colder than expected and I was a bit concerned I would crash through here because of it. I rode with Lee Neal and Brent Marshall and let them go once we got to Wiregrass. Jason Shearer rolled up in the Explorer and asked how I was feeling. I started whining then realized maybe just faking it til I felt good would work. Nick Butler, also on a SS, rode with me most of the way to Bull’s Gap where I saw Brent packing up to leave. Well, well…not that far ahead. Oh yea!


My legs were smashed from the hard initial effort in the cold. Or maybe my whole body. Everything just felt like hell and I didn’t want to ride. Knees hurt, quads hurt, my ab muscles cramped a few times. I was in a state and didn’t want to ride 90 more miles. Dammit! Brent seemed pretty upbeat so I pretended to feel the same the next 30 miles or so. I rode conservatively downhill, so I didn’t get too beat up by the rigid front fork. I realized during my pre ride, this would be critical to finishing. I had another Brent sighting at the 60 mile turnaround aid, and didn’t waste time filling bottles! Not long after leaving that spot, I saw him fixing his chain trail side but figured he would make quick work of it, which he did. Around mile 48, I popped out on the pavement at Adam’s Gap and made a resolution heading up to Cheaha: Don’t. Fucking. Walk. Brian Toone was pushing hard up Adam’s Gap with a commute from home also in his legs at this point, which was super motivating! 


Walking is part of singlespeed racing, but having to do it on a paved road just feels pitiful so I stayed on the bike and had a really strong climb all the way to the top of Cheaha. I was able to count riders coming back from the 100 mile turnaround and was probably midpack overall and 4th Singlespeed. I knew the chances of me catching Chad Brandon, John Schwab, or Lee Neal this particular day was about that of me beating the mid 90s Chicago Bulls in a pickup game. Nobody, absolutely nobody, shows up for Skyway 100 with one gear that’s a slouch. You finish last place SS, and it would still be a victory! 


I saw Jake Huggart, Hunter Cole, and Matt Ithraburn at the top of Cheaha and was jealous of their cohesive group. I made quick work of the aid station and did my best to catch them on the way back. I also saw my other singlespeed friends, Brent and Nick, grinding up Cheaha as I was descending. A bit too close for comfort with 54 miles to go. I had some things on my side at this point. My nutrition and hydration was dialed. 250 calories per hour of Uncrustables, Payday bars, gels, aid station Cokes, and potato burritos. Eat real food? I say eat it all! I stuck with Nuun for hydration and abided by my own advice at aid stations…no weird shit!

Something also kinda got together with my legs and mind here. I no longer wanted to quit and the chase was on. My descent energy conservation worked and I was able to really start ripping on the downhills headed back without worry of some kind of total arm and hand failure! I rode back and forth with a couple guys headed back…Chris and Jason I think? In my opinion, the hardest part of Skyway is the gravel climbs headed back in towards Bull’s Gap. They are steep and loose and it always seems to be sunny. Once on Skyway, Jeep traffic started picking up, but most were pretty easy to share the trail with. I only got yelled at once but kept my cool. I made a decision to leave my light behind at the 60 mile turnaround aid station to give myself some extra motivation to get back. 


I rode back and forth with a group of Katie Bolton, Bo Bozeman, and some others back and forth towards Bull’s Gap. I had more mud and water on my glasses than optimal but also didn’t want to stop and mess with them. I ended up setting a PR on the Bull’s Gap descent. I guess if you can’t see much, it is also tough to overthink your lines. Point and shoot! I still figured anything was possible here with about 20 miles to go. Brent seemed to be riding well, and I know him well enough to know he wouldn’t just sit up and spin to the finish. What I didn’t want was a Hardwick type catch to happen. You know if you have been there. They stalk you for a while, then make a low key catch with 5-10 miles to go. It hurts, but is so well calculated, it feels like fate. 


One of the most common failure points at Skyway is the last 10 miles of singletrack and I was determined to not implode here. I caught a few 60 milers on the way back in on Wiregrass and got my head in the game for the last 10-12 miles. I ate half a Payday and took a caffeine gel during the first mile of singletrack with my main goal to keep focused and ride smoothly. It is also important to stay realistic about the distance. I knew I had to ride 110 miles and it would NOT magically get shorter. I somehow felt really good the last few miles and was able to enjoy the trails and push hard! Jason changed up the last little bit of singletrack this year giving a cool run into the finish that makes pretty much everyone look like a badass…which if you made it that far, you are! I don’t know if I have EVER been more proud to finish a race than this one. I finished around 11 hours and Brent never caught me. The back and forth really made for a great time out there and I enjoyed myself once I got in the zone. It only took 50 miles to start feeling okay! This was also the longest race I have done since 2012. So pumped! I am not really back to great shape but well on my way. 


Melissa was waiting for me at the finish, which was awesome. The whole finish line vibe is one of the best parts of Skyway. Everyone is stoked for each other, and I think the level of community involvement here is what leads to high finisher rates for a very hard race. I stuck around for a while to see other finishers come in, including Kellye Carlisle, who I have coached for months leading up to this race. This is the hardest race she has ever done and she finished! Patrick Wigley and his crew all had good races, which I was really glad to see. Finishing this on the Vassago was also special. That was the bike Lee Neal rode when we first started racing together long ago and I feel like I brought it what it deserved. Everything worked great on it all day long. Brent also rode his old Vassago, which was pretty cool. After the race, I already had next year on my mind…have fun and go faster! This probably means I’m a lunatic, but I have a feeling I’m not the only one planning a return. See y’all next year! 


There is no way to properly thank Jason, Wendi, and everyone else that helps out with this race. Pete Foret (Cajun Sherpa LLC) washed my bike for me post race, after his 100 mile DNF, and had everyone’s back as usual! All the volunteers killed it out there. Josh Waldrop even put up with me putting him in charge of filling my muddy bottles out there, haha. You guys rock, all of ya!

Skyway ePic 2021

A few shots from one of my favorite races.

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Not a bad sleep spot.

Not a bad sleep spot.

Come on. Get yer wolf shirts.

Come on. Get yer wolf shirts.

Pete Foret, y’all. That food was BOMB

Pete Foret, y’all. That food was BOMB

Bull’s Gap with Chad Joiner and Bruce.

Bull’s Gap with Chad Joiner and Bruce.

…Bruce. All good. All crazy.

…Bruce. All good. All crazy.

The views suck. Don’t come here.

The views suck. Don’t come here.

Brian Toone. I only take pics of him to update Kristine at this point…

Brian Toone. I only take pics of him to update Kristine at this point…

23 miles in.

23 miles in.

1st Singlespeed through. Grinding.

1st Singlespeed through. Grinding.

Up Up Up

Up Up Up

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Bull’s Gap headed out!

Bull’s Gap headed out!

Fat Joe reunion. He got it done!

Fat Joe reunion. He got it done!

Sam Porter recharge.

Sam Porter recharge.

Florida Women smashes course.

Florida Women smashes course.

The best our marketing department has…

The best our marketing department has…

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All downhill from here

All downhill from here

Katie “this bike is fine” Curtis “no really I’m good” Bolton

Katie “this bike is fine” Curtis “no really I’m good” Bolton

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Gently Rolling Hills

Gently Rolling Hills

Mary Morrow Davis

Mary Morrow Davis

Bulls Gap station. 1:30 PM.

Bulls Gap station. 1:30 PM.

Toone commute vibes

Toone commute vibes

Mad props to Chad Soner on these.

Mad props to Chad Soner on these.

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