For those guessing the wattage penalty of gravel vs aero bike....

[mtechnica]

I’m pretty sure I’ve said exactly this on this forum before and had a whole bunch of people argue with me.

[Pastashop]

I’m an engineer / scientist, and I do study designs and all sorts of comparisons and calculations for a living, much more sophisticated than what goes on here, and still I don’t understand the usage cases being compared here. Is the choice between riding fat tires vs. skinny tires on smooth paved roads, or fat vs. skinny tires on bumpy gravel? I don’t think those are realistic dilemmas for performance oriented cyclists. The lack of on-road data makes it hard to know what things will look like in the real world:
“Off-road rolling resistance and 'roll-over resistance' data will be published in an update to this report at a later date. -Stay tuned”

Meh.

[zmudshark]

I wish I could still ride and cared about watts.

[hoj]

Given my anecdotal experience comparing my rides on my aero road bike vs my gravel bike, I don't think there's anything too surprising by the data presented in the link -- my gravel bike certainly feels a lot slower on the road with slick 38c tires compared to an aero bike.

I get that tunnel time is expensive and there are only so many combinations they can test, but I really wish they would have dug a little deeper into the effects of tire width by using the Caledonia for both the road tire (25c) vs gravel tire (40c) comparisons. How much of an effect is there if you simply swap between a 25c and a 40c tire, all else being equal?

The reason I'm curious about that is because I (as well as many other people I know) bought a gravel bike in the first place not only for it's versatility in where I can go with wide tires, but also because I can ride the bike with 28-32mm tires out on the road if I so choose and get a "pretty-close-to-road-bike" feel.

I would imagine that the profile of a 28mm tire on an aero carbon rim has significantly less aero drag (and rolling resistance?) than a 40mm tire on that same rim, given that the 40mm tire "balloons" well outside of the rim width... am I totally off base on that assumption?

[jake_m]

Originally Posted by Pastashop

I’m an engineer / scientist, and I do study designs and all sorts of comparisons and calculations for a living, much more sophisticated than what goes on here, and still I don’t understand the usage cases being compared here. Is the choice between riding fat tires vs. skinny tires on smooth paved roads, or fat vs. skinny tires on bumpy gravel? I don’t think those are realistic dilemmas for performance oriented cyclists. The lack of on-road data makes it hard to know what things will look like in the real world:
“Off-road rolling resistance and 'roll-over resistance' data will be published in an update to this report at a later date. -Stay tuned”

Meh.

Thanks for saying this, I don’t have as much experience as others on here but I’m having trouble figuring out where the lost watts in this study are going. I’m all for deep section wheels for aero benefit, but if anything, it’s comforting for me to see evidence that tire width and knobs are only worth a few watts. 5W of aero benefit has to be worth less than comfort and not slipping out and hitting my head on a rock, right?

[unterhausen]

I'm a little bit slower on my gravel bike, but not much. I think a lot of these differences get wiped out when you put a rider on the bike so that's why they show the numbers without a rider.

[drewskey]

The biggest source of aero drag, or any drag for that matter, was purposively omitted…

“Actually, the entire system of a gravel bike would have an amplified aero drag penalty due to the more upright and typically higher rider position. So in order to make a clean comparison of the effect of the bike equipment alone, here we publish the bike aero drag only (without rider).”

But I guess any field of observations have to start somewhere!

[phishrabbi]

I have dialed in precisely the same fit on my "gravel" bike and on my "road" bike. So no difference there.

I have two sets of wheels for the gravel bike, one with 38mm stellacooms, and the other with 32mm gp5k tr.

I wish I could quantify the difference between the 32mm contis and the 25mm contis on my road bike.

[mtechnica]

To be fair that cervelo with those wheels and tires is faster than 99+% of bikes and possibly any bike on this forum as far as I know, including my tarmac SL7 with the same tires and 40mm wheels. A round tube road bike with exposed cables, shallow high spike count wheels, and mediocre tires, very well might be closer to the gravel bike than that cervelo.

[Likes2ridefar]

Originally Posted by drewskey

The biggest source of aero drag, or any drag for that matter, was purposively omitted…

“Actually, the entire system of a gravel bike would have an amplified aero drag penalty due to the more upright and typically higher rider position. So in order to make a clean comparison of the effect of the bike equipment alone, here we publish the bike aero drag only (without rider).”

But I guess any field of observations have to start somewhere!

My fit is exactly the same on a gravel bike compared to road bikes..drop, stem length,etc.

[spoonrobot]

This is an excellent test because of the tire choice and settings allow direct comp to Bicycle Rolling Resistance testing. They're cagey about where the RR data actually comes from - is it a smooth drum or actual riding with PM?

Rolling resistance data is representative of on-road riding in order to make a direct comparison.

Gotta be a drum, assuming it's a regular smooth drum. This seems to overstate the RR of the gravel tires, compared to the BRR diamond plate drum.

BRR has the GP5000 25 @6.9bar with 10.7w at 28.8km/h
BRR has the Terra Speed TR 40 @3.1bar with 19.2w at 28.8km/h

So 17w cost for the gravel tires.

I would think that on fresh, super smooth pavement, the knobbie cost could approach 40w with decreasing relative power cost as the road got rougher until the gravel tire has lower rolling resistance than the road tire.

[Gummee]

Originally Posted by phishrabbi

I have dialed in precisely the same fit on my "gravel" bike and on my "road" bike. So no difference there.

I have two sets of wheels for the gravel bike, one with 38mm stellacooms, and the other with 32mm gp5k tr.

I wish I could quantify the difference between the 32mm contis and the 25mm contis on my road bike.

I don't have the exact same fit between the road and CX bikes, but I'm close. I've got 40c knobbies on one CX bike. I've got 32c GP5K TL tires on the other. Well... right now it's 32c GP4Seasons for the winter.

The 32c GP5Ks are on 30mm carbon wheels. The 32c GP4Seasons are on DT Swiss 411s with more spokes so the winter wheels are going to be slightly slower regardless

I'm fastest on the aero road bike with the 45mm wheels and 25s, but not much faster than the CX bike with the 32s. The 32s ride nicer on the chopped up pavement around the DC area.

I don't think the observations in the OP are necessarily what I experience, but they could be for some people

M

[Likes2ridefar]

It’s not what I experience either but I have nothing to really base it on or proof…

I’m currently on 2.1” teravail rutlands 650b which are basically fast rolling mountain bike tires and they are barely slower in any condition going off average speed compared to many times on the same routes with tires ranging anywhere from 700x30 to the current largest volume I’ve used. And sometimes they are faster….smoking all my times on trails with better traction and even beat a few paved sections I rode frequently.

[muttley]

How about a "Gravel bike" with road wheels???? I ask because I no longer have a true "Road" bike, just a road wheelset (Conti 5K TL 32) that I mount on my Cervelo Aspero when I do dedicated road rides.

[phishrabbi]

Originally Posted by muttley

How about a "Gravel bike" with road wheels???? I ask because I no longer have a true "Road" bike, just a road wheelset (Conti 5K TL 32) that I mount on my Cervelo Aspero when I do dedicated road rides.

I'd love to see a comparison between the Aspero and the r5 with the same fit and the same wheelset.