XC vs Gravel speed / loop test

The spirit of Grav-lo-cross. No but seriously, cyclocross and gravel go here!

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req110
Posts: 866
Joined: Thu Nov 22, 2018 10:23 am

by req110

Hey guys, out of curiosity i was interested how each bike performs in my hometown forest.

15.6km a 241m ascent

75% unpaved > optimal for gravel
20% XC incl DH > one technical climb and two technical descents with roots and stones (i wouldn't ride through these areas on gravel bike normally)
5% paved/tarmac

Quarq AXS on both bikes. My FTP is 340W @ 75kg.

Same Normalized power, lower average power on gravel... The gravel bike was 108 seconds faster.
Same shoes, XTR pedals on both bikes.
Same day, same weather, muddy in some sections, raining a bit one mtb loop, raining much more on gravel loop.

Both bikes running with tubolight foam inserts. Both bikes clean before start.

https://www.strava.com/activities/6537915051 (mtb)
https://www.strava.com/activities/6538113027 (gravel)

The segment: https://www.strava.com/segments/30816305

Details about bikes here:
Image

Conclusion:

Gravel bike is faster on loop which contains two technical descents and one technical climb you wouldn't dare to visit with gravel bike, indeed it's no joy. On unpaved / softer section the gravel bike flies. Gravel bike was faster while having same NP, but even lower avg power than XC.

I believe that huge contribution to speed is aerodynamic, the mtb cockpit is 74cm (vs 40cm gravel), and 9cm higher from the ground.

My gravel bike geometry and bikefit is like road bike, but little bit smaller drop (6cm vs 8cm), 45mm wheels, so i can imagine if there is guy on expedition steel gravel bike with wide flare handlebars and loose shorts, he would be slower than my MTB.

Gravel bike for me is like road bike offroad.
MTB is about joy... just ride in forest and then riding totally off track discovering deeper forests and riding every possible climb and descent

Any thoughts here? I am considering to perform some other tests like loop on gravel tires vs road tires on same gravel bike.

Image
SW SL8 RTP 56cm @ 9270 / CLX II / CS OSPW / CEMA BB
S Epic 8 L @ XX T-Type / Berg Ratheberg 30 / Quarq / Fox Transfer SL 100mm / 3p

centaur4608
Posts: 33
Joined: Wed Jan 05, 2011 2:20 pm

by centaur4608

Hi, really intersting test ! Thanks for this last.
You're faster on your gravel and you also spend less energy.
I had the possibility to test a Kanzo Fast during the last weekend. On a mix terrain road/xc offroad, it's was really nice. For sure in the downhill section compare to my full suspension Scalpel it's quite more tricky but for the rest it's really good. I did the same section than the week before with my Scalpel and I was faster. +/- 2,7km/h on the average.
Monday I decided to go out with the Kanzo for an road only session, i put more pressure in the tires but the feeling was really not good. The rigidity of the frame, the rolling resistance of the tyres and the fact the bike was a little bit to big for me, kill me literally ... For the last 10km I came back home with offroad line and i drop the pressure and it was really better.

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Marin
Posts: 4035
Joined: Wed Jan 22, 2014 11:48 am
Location: Vienna Austria

by Marin

Very interesting! My guess is that you gain a lot on the gravel whenever you are faster than about 20kph just from aero, and with a 25kpg avg this will be a lot!

Also some gains on most climbs from the lower weight. Also, on the steepest part, your min speed is lower on the gravel bike, but the average speed is quite simliar.

My personal theory is than if start and finish are *at the same elevation*, a gravel bike will ALWAYS be faster. Except maybe for the most extreme cases, i.e. stuff that noone would ride for fun even on an MTB.

jromano89
Posts: 22
Joined: Sat Oct 02, 2021 6:48 pm

by jromano89

Thanks for sharing, this is good data! Do you notice any efficiency difference with the wider cranks on the XC bike? I don't have enough data to be conclusive, but when sustaining high power, my heart rate is consistently higher with a wider q-factor.

yinzerniner
Posts: 206
Joined: Tue Jun 13, 2017 8:54 pm

by yinzerniner

That's an awesome test with lots of valuable measured data and subjective observations. The speed difference is pretty big but as you said the riding style for each bike is differentiated enough that you can make a preferable decision once you know the particulars of a route.

With you data you should be able to construct you're own personal "flow chart" which will provide a guide to bike choice. But either way you win since that's a killer quiver!

Marin
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Joined: Wed Jan 22, 2014 11:48 am
Location: Vienna Austria

by Marin

Comparison says it all

Image

JMeinholdt
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Location: Topeka, KS

by JMeinholdt

I think it's pretty much safe to assume that the only time a gravel bike is going to be slower than an XC (or any other MTB) is in places that you're going to be walking the gravel bike because it's unrideable when the MTB can ride it.
Wilier Cento10AIR - SRAM Force AXS - Road/race
3T Exploro - SRAM Rival AXS XPLR - Gravel
Wilier Sestiere - Shimano Tiagra - Commuter

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req110
Posts: 866
Joined: Thu Nov 22, 2018 10:23 am

by req110

Right. Now I am sad that I haven't used the HRM, it would bring some interesting data as well. But I am not wearing that in general.

Wider qfactor of mtb is interesting point I am going to focus probably.
SW SL8 RTP 56cm @ 9270 / CLX II / CS OSPW / CEMA BB
S Epic 8 L @ XX T-Type / Berg Ratheberg 30 / Quarq / Fox Transfer SL 100mm / 3p

yinzerniner
Posts: 206
Joined: Tue Jun 13, 2017 8:54 pm

by yinzerniner

JMeinholdt wrote:
Thu Jan 20, 2022 7:15 pm
I think it's pretty much safe to assume that the only time a gravel bike is going to be slower than an XC (or any other MTB) is in places that you're going to be walking the gravel bike because it's unrideable when the MTB can ride it.
Not necessarily true - if the loop has lots of roots, mud, sand, etc the wider tires and suspension will surely be faster than a gravel bike you can ride but have to guide very carefully. This comparison vid from GCN shows such an example - while the MTB trail is certainly "rideable" with the gravel bike it's SO much faster on the MTB. It would still be fun on the gravel bike to explore, but you're flying on a modern MTB on those types of conditions.
https://youtu.be/PvYFzKjdGmU?t=1191

Think they're conclusion still holds up, that as long as the path is smooth you're always faster on the gravel bike. Introduce rocks and roots then the MTB is the way to go.

urostasa
Posts: 9
Joined: Wed Dec 29, 2021 8:55 am

by urostasa

I plan to do a similar test with a gravel bike this year. I will compare gravel bikes on gravel wheels and road bikes on aero wheels. The road will have 30% of the plane, the rest will be a hill with an average slope of 8-9%.

RyanH
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by RyanH

I think with how NP works it's more appropriate to use average power on a loop like that which puts the comparison even more in favor of the gravel bike since your average power on the MTB was over 10% higher.

With that being said, why do you think there was more variability in power on the gravel bike than the MTB?

req110
Posts: 866
Joined: Thu Nov 22, 2018 10:23 am

by req110

ad NP vs. AVG > this was my first test and i though that it would be easier to get the same NP rather than AVG power, because there were some sections where you can't pedal with gravel bike, especially over roots. These sections are much in favor of XC bike, where you are pedalling all the time.
SW SL8 RTP 56cm @ 9270 / CLX II / CS OSPW / CEMA BB
S Epic 8 L @ XX T-Type / Berg Ratheberg 30 / Quarq / Fox Transfer SL 100mm / 3p

Hexsense
Posts: 3269
Joined: Wed Dec 30, 2015 12:41 am
Location: USA

by Hexsense

Nicely done.
Your effort surely is useful for a lot of people.

I have to interpolate the data a bit to make sense for myself.
Specifically, I use the same 400mm bar width on my gravel bike but 710mm bar on MTB. That'd narrow the gap down.
I can only do 3.5 W/kg rather than your 4.5 W/kg, that'd narrow the gap down as I'd go nowhere as fast.
Knobby gravel tire (Conti Terra Speed) and race MTB tire (Wolfpack MTB Speed) would narrow the gap down as well.
Regardless, your time gap is just so big that I think I gravel bike still win significantly anyway.

Mirco
Posts: 142
Joined: Thu Jul 12, 2018 7:09 pm

by Mirco

It isnˋt rocketscience saying road bikes are faster than CX bikes, CX bikes are faster than gravel bikes and gravel bikes are faster than MTB.

Marin
Posts: 4035
Joined: Wed Jan 22, 2014 11:48 am
Location: Vienna Austria

by Marin

Mirco wrote:
Wed Feb 02, 2022 7:16 am
It isnˋt rocketscience saying road bikes are faster than CX bikes, CX bikes are faster than gravel bikes and gravel bikes are faster than MTB.
Really? So XC Worlds were just ridden on MTBs because UCI demands it

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