Speed roadie vs gravel

52 replies · 6,618 views

Mark_S
144 posts
#1Mar 8, 2021, 2:22 AM
These are my times for a 4 mile, 6% road climb over the past couple of years.

The first grouping of rides is a Specialized Roubaix with 28mm slick tires at around 100psi. The second grouping is a GT Grade with 42mm Resolutes and then 43mm GK-SKs at around 35psi tubeless.

~15% speed difference between the roadie and the gravel bike with most other things being equal, including aerodynamics because it doesn't come into play at this speed.

Are others with a prior road habit having this experience with their gravel bikes, or perhaps better said, with the switch from low volume, high pressure slick tires to high volume, low pressure treaded tires?

This is really just curiosity and entirely about experiences on tarmac - for me there's no going back to a road bike or low volume tires as I love the option to head off road any time I feel like it.
1
Volsung
878 posts
#2Mar 8, 2021, 9:41 AM
The only reasons I keep my road bike is it's a Bianchi and I like the color. It's probably not 15% faster than my carbon gravel bike.
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stu
646 posts
#3Mar 8, 2021, 10:35 AM
If I'm reading the chart correctly the road bike time is around 31 minutes (12.5 Km/hr) and the gravel bike time is around 35 minutes (11 km/hr). The difference would then be 13%. I agree aerodynamics shouldn't be significant at these speeds. But I also suspect at these speeds rolling resistance wouldn't be enough to explain the entire difference. If your road wheels will fit your gravel bike (or if you're willing to swap the tires) I'd be interested to see how the gravel bike performs with the road tires.
1
bearlyfinish
49 posts
#4Mar 8, 2021, 10:37 AM
On my 20 mile loop with 1100' of gain with variable road surfaces, I'm about .5 mph faster on my road bike over a gravel bike with road wheels and 1.5 mph faster over a gravel bike with gravel tires. (17.5 mph avg on the road bike). The difference can be contributed to more relaxed positioning, additional bike weight, and tougher compound tires.

I ride my gravel bike with a road setup on most rides longer than 3 hours and my road bike gets a lot of usage on the trainer.

Also I hope you've learned that 28's at 100 psi is about 40% too high. I realize that data is from 15 months ago, so I'm assuming you learned that lesson. 🙂
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Mark_S
144 posts
#5Mar 8, 2021, 11:06 AM
Yes, I learned it the hard way! Crashed the Roubaix taking a shortcut on a path with deep gravel. Broke my hand and four ribs. Sold the Roubaix and ordered the Grade while convalescing.

I realize all things are not entirely equal apart from the difference in tires. The Grade is geared differently. The (modified) low gearing is 32x40 (=0.8). For the Roubaix it was 34x30 (=1.13). Perhaps the higher cadence is a factor somehow?

Heart rate is about the same in each grouping.
1
Jumbo
123 posts
#6Mar 8, 2021, 11:38 AM
I don't have the exact data, but my rides off-pavement are roughly 13% slower than my rides on pavement, with the same tires (Conti Terra Speed), so right in your ballpark. If I swap to road tires (Conti GP5000) on the same bike, I get about another 4% in speed on pavement (so 17% faster than gravel tires on gravel).
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thumper88
198 posts
#7Mar 8, 2021, 1:14 PM
Weight of the bike may be one factor. Also, 35 psi in the big tires strikes me as far too low for pavement unless it’s really rough.
It’s only a little bit more than I run in those same tires in gravel. But... if the road is smoothish pavement they don’t need to be that pillowy.
we ran an informal time trial series in my town last year and for a roughy 10 mile course I hit a certain time on a Venge Vias, full bunny hands for as much as I could on Conti 5000 with latex tubes, 25mm rear, 23mm front and with deep 64mm wheels.
Then I ran the Diverge on the same course with 700c 41mm deep gravel wheel and a Conti Terraspeed pumped to nearly 60 psi in front and a 650B alloy with a Schwalbe 2.1 G-One Speed liteskin rear, measuring 54mm true and pumped to nearly 50psi.
I hit exactly the same time as the Venue, down to the second.
The wild card is I used aerobats on the gravel bike, and weight didn’t come into play as there were no major climbs. But the diverge frame is pretty draggy aero-wise and I was def in bunny hands most of the Venge run.
Moral though, is there’s no magic to it. Gravel bikes are less aero, put you in less aero positions, are heavier and real gravel tires (not flimsy “supple” slicks with no flat protection) are slower. Except on real gravel.
I figure even pumped up, I gave up maybe 10 watts of RR with the terra speed, which is a pretty light but still mainstream gravel tire...and prob another few watts in aero losses with it, even though it was the narrowest proper, fast gravel tire I could mount.
the G-one probably no loss or negligible loss vs GP5000 but its not something you would use on serious gravel. Just sandy courses, or total hardpack.
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ccand51997
265 posts
#8Mar 8, 2021, 9:05 PMedited
[QUOTE

~15% speed difference between the roadie and the gravel bike with most other things being equal, including aerodynamics because it doesn't come into play at this speed.
[/QUOTE]
Did you ride wattage or was this just perceived exertion? Heart rate is not useless but it is not accurate enough to actually test something. It is pretty easy to pull out some of reasons. The GK SK is about 25 watts per tire so even if you are using an old GP4000 on the road bike then you are still looking at 12-13 watts per tire or nearly 25 watts in rolling resistance.
I doubt it is the weight. You only give up about 1 watt per pound climbing so unless your gravel bike is like 30 pounds (don't laugh, mine is because it is dual-sus with aerobars and 2.2 tires) then you are probably not giving up more than a handful of watts there.

I doubt tire pressure has very much to to with it at all. I've tested pressure differences when climbing hills and found absolutely no difference in speed between 50 psi, about 35 psi, under 20 and 8 when climbing on the road. I've done it on three different occasions and each time I almost could not believe the results. Tire pressure just does not matter. The last one (8 psi) was so bouncy it made me really concentrate on pedalling evenly and I would have been terrified cornering (it was a 2.2 tire), but when I rolled across the line at exactly the same wattage as before at exactly the same time there was not much more to argue. Run the pressure as low as you like without it bottoming out and damaging the rims.
I suspect if you were to get your hands on some old G-One Speeds like were mentioned above, then the difference in speed would dramatically narrow. Those tires are probably only a hair slower than the old GP4000 road tire. Even the Terra Speed would probably give you 10 watts compared to the GKs if you changed both tires.
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Mark_S
144 posts
#9Mar 9, 2021, 12:53 AM
ccand5197 - If you scroll to the OP you'll see the basis of my question - these are sets of the same 6 degree, 4 mile climb over fairly disperse time periods, recorded in my Strava account.

The gravel bike is on the heavy side, and me too (6'4" and 230) I carry repair spares, pump and tools, and typically a generous coating of mud, so the bike does actually weigh around 28 lbs. The road bike would have been about 23. I might have gained a few with time myself (it happens...) The biggest difference I can identify, apart from the tires (the big volume, tread and pressure difference) is the gearing. I climb at much higher cadence on the gravel bike (0.8 lowest gear) than I was able to manage on the road bike (1.13 lowest gear). That's why I mention heart rate - it's roughly the same for both sets of results, as is my perceived effort. I'm still pushing just as hard, just at higher cadence. bikecalculator.com suggests that 10lbs of body and bike weight is worth about one minute.

I can't explain the full 5 minute difference, except for the tires. 42c with tread at 35-40psi is quite different to 28c slick at 80-100psi. My assumption has been that this explains it, but I'm aware that most people don't think the gravel tire effect is so dramatic.

Again, it's really just curiosity - I'm very happy with the gravel bike and won't go back, even if a 10%+ difference in efficiency is typical. I do have a set of 38c GK-SS on order now. I'd rather be a bit faster on road and don't mind having to be a bit more careful on loose surfaces to achieve it. Not expecting a huge difference, though.
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ccand51997
265 posts
#10Mar 9, 2021, 1:37 AM
Mark_S wrote:ccand5197 -
The biggest difference I can identify, apart from the tires (the big volume, tread and pressure difference) is the gearing. I climb at much higher cadence on the gravel bike (0.8 lowest gear) than I was able to manage on the road bike (1.13 lowest gear). bikecalculator.com suggests that 10lbs of body and bike weight is worth about one minute.
I can't explain the full 5 minute difference, except for the tires. 42c with tread at 35-40psi is quite different to 28c slick at 80-100psi. My assumption has been that this explains it, but I'm aware that most people don't think the gravel tire effect is so dramatic.

The reason why I went on about the tires is because, IMO, tires have more to do with the performance of the bike than nearly anything else when aerodynamics are not considered.
New wheels. Almost don't matter.
Better components? Unless your 'old' stuff is worn out and creating friction then new components won't be noticeable.
Weight? Well, it matters but not a huge amount. Drop 5 pounds and you only gain about a minute from the bottom of Alpe D"Huez to the top out of a likely 60-70 minute climb if you are pretty fast. That climb is twice as long and steeper, so five pounds is probably only going to be about 30 sec for your climb. So where is the speed loss or gain? In the tires.
You never mentioned what the 28c tire was so that could be most of it or not. If you were riding a Conti Gatorskin, well, that tire is as slow as an mtb tire with tread. If you rode a solid tire like the GP4000 then that could easily explain the difference. I would seriously look at the Schwalbe G-One Speed in 38mm for the back. I found some on biketiresdirect that still use the OneStar compound. That is about as fast as you can get in a higher volume tire. The fastest of the mostly slick GK tires is going to be giving up 5 watts to a G-One Speed, but they also cost half as much, I suppose.
Oh, and I hope you are riding these tires tubeless. That will gain you another five watts over butyl tubes. Plus they are way more compliant.
You could also try the 42mm Rene Herse tires, but those are REALLY expensive. Well, it looks like a standard Snoqualmie Pass in 44mm is $72 so about what that G-One Speed cost. I've ridden a G-One Speed hard over rocky terrain though, so it will hold up.
I'm not sure I'd run the SS on the front unless my gravel was really tame and did not have ruts. I definitely prefer some serious side knobs on my front tire.
stu
646 posts
#11Mar 9, 2021, 1:54 AM
Mark_S wrote:... The biggest difference I can identify, apart from the tires (the big volume, tread and pressure difference) is the gearing. I climb at much higher cadence on the gravel bike (0.8 lowest gear) than I was able to manage on the road bike (1.13 lowest gear).
FWIW this episode on Global Cycling Network compares different cadences on a climb, in this particular case the rider was faster at a lower cadence.
https://www.youtube.com/watch?v=43ci68I23hA
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Mark_S
144 posts
#12Mar 9, 2021, 2:08 AM
The tires on the road bike were indeed GP4000 in 28c (tubes).

The gravel bike has had the 37c Riddlers it came with, followed by 42c Resolutes and now the 43c Gravel King SKs. The SK has been the best fit for my riding. I'm probably on the road 80% of the time, but I love to mix in a bit of forest road and trail most rides. I'm in Switzerland riding in pretty steep terrain. 8-10% grades are typical. Road descents are fast. Difficult for any tire to meet all these needs.

Yes I do run the gravel tires tubeless. I tend to pump the rear to 40 and the front to 35, and then ride 2-3x (a week) before doing it again because I'm lazy.

You haven't said that climbing at higher cadence with the gravel gearing would cause slower times, perceived effort and heart rate being roughly equal. So I must assume that it doesn't, and that the tires are four out the five minute difference (the other minute going to bike and belly weight).

The 38c SS are on the way already. I have a 10 hour road event in a few months (80 miles and 15k feet) so will bias toward efficiency, and accept that I need to slow down on the off piste bits. I hope to make back a bit of the efficiency loss because my partner for the event is 50 pounds lighter and riding a Cervelo...

I could stick with the SKs and then pop on a set of 32c slicks for the event, but I must say it's reassuring to have burned through three sets of tubeless gravel tires without a single flat...
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Mark_S
144 posts
#13Mar 9, 2021, 2:40 AM
Stu: Thanks a lot for the video. Now it seems that higher cadence may well bring down the power output a bit. On the roadie I was out of the saddle quite a lot (not anymore, except to get blood the flowing to sensitive bits again...)

Perhaps, non-scientifically, weight and cadence are half of the difference, and tires the rest. Interesting. Matches my instincts, although that's not worth much as I'm still a very amateur rider.

Love that he considers a 34 chainring and 28T lowest gear 'spinning' up a 9% grade...
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Noonievut
165 posts
#14Mar 9, 2021, 7:25 AM
@Mark_S

I’m also curious...but where you sold me was your crash on the Roubaix on 28’s on gravel. My analysis would be trying to minimize the risk of that by having a suitable tire for the rough stuff. Sure you can take it easy on the worst sections, allowing for a tire that isn’t meant for single track, but I had to go through that I would focus away from speed. I wish we could measure compliance/comfort/handling etc on our rides (beyond feel and perception).
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Mark_S
144 posts
#15Mar 9, 2021, 7:37 AM
@Noonievut I'm not going less than a ~40mm semi-slick (GK-SS 38-622 in this case). The old Roubaix with the 28s is long gone by now. Great bike but I'm an ex MTB rider that gets bored easily. The current SK 43s really hit the sweet spot for me, but I want to squeek out as much road performance as possible in preparation for a big ride in a few months. I'll likely be back to the SK 43's, or something similar in the long run.
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John Z
174 posts
#16Mar 9, 2021, 9:21 AM
Mark_S wrote: These are my times for a 4 mile, 6% road climb over the past couple of years.

The first grouping of rides is a Specialized Roubaix with 28mm slick tires at around 100psi. The second grouping is a GT Grade with 42mm Resolutes and then 43mm GK-SKs at around 35psi tubeless.

~15% speed difference between the roadie and the gravel bike with most other things being equal, including aerodynamics because it doesn't come into play at this speed.

Are others with a prior road habit having this experience with their gravel bikes, or perhaps better said, with the switch from low volume, high pressure slick tires to high volume, low pressure treaded tires?

This is really just curiosity and entirely about experiences on tarmac - for me there's no going back to a road bike or low volume tires as I love the option to head off road any time I feel like it.

The real test would be to find a similar, climb on dirt/gravel to compare those numbers, or any moderately long gravel climb to perform one. A test over gravel/rolling terrain would be even better. I have such a course, but dismembered my road bike and sold or gave away the parts.
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ccand51997
265 posts
#17Mar 9, 2021, 1:17 PM
Mark_S wrote:The tires on the road bike were indeed GP4000 in 28c (tubes).
Re: Then I'm pretty sure that is the biggest culprit. The WTB tires you mentioned are not terribly slow but compared to a GP4000 you are probably talking about at least 10 watts per tire. With the GKs tubeless vs the GPs with butyl it is not quite as much, but it is still a large difference.

I'm in Switzerland riding in pretty steep terrain. 8-10% grades are typical. Road descents are fast. Difficult for any tire to meet all these needs.
Re: I think you understand that no tire can meet every need nor can one bike. It sounds like you might be a good candidate for two wheelsets for your gravel bike. I can promise you that if you had a second set of wheels running GP5000s, tubeless or with latex tubes, your times on the road would drop considerably. Those are really fast tires and I really like the 32mm version in tubeless. The fastest version of the GK (not slick but herringbone tread) was equal to the Terra Speed in rr, but still still a good 10 watts per tire slower than modern road tubeless tires (I keep using the GP5000 but there are a couple of other companies that are making good tires as well. I just think the GP5 represents the best all-around value). The second set of road wheels does not need to be anything special. Unless they are deep carbon rims that provide an aero benefit, then anything that is solid that will mount up the second set of tires will do. It is an old myth that weight in your wheels matters more than any other weight. It does not. (I can provide the math if you like).

You haven't said that climbing at higher cadence with the gravel gearing would cause slower times, perceived effort and heart rate being roughly equal. So I must assume that it doesn't, and that the tires are four out the five minute difference (the other minute going to bike and belly weight).
Re: Cadence. It is so individual that I think it is hard to say that would make a difference. It could make you faster if you are spinning a more appropriate gear.

I could stick with the SKs and then pop on a set of 32c slicks for the event, but I must say it's reassuring to have burned through three sets of tubeless gravel tires without a single flat...
Re: Flats. I've never had a flat in all the miles I've used my GP5000 tubeless. It has been a really solid tire. Weight weenies hated that tire when it first came out because the 32mm tubeless version is 360 grams, but that tire is tough and probably overengineered. Even if you just had a rear wheel with the GP5000 that you swapped out you would pick up a lot of climbing speed.
I'm jealous of you European riders. I finally made it back to France after 25 years in 2019 and had a great 17 day trip riding the Alpes and Pyrennees.
Mark_S
144 posts
#18Mar 9, 2021, 2:10 PM
I'm unlikely to go with two sets of wheels, being a bit too lazy to bother. This is all really just curiosity more than frustration, as I typically ride alone and 'against myself' rather than others.

Doing an event with a partner is out of the ordinary. If I don't pick up my speed enough while training I'll get a set of the GP5000 in 32c and install them tubeless on my existing rims. Appreciate the suggestion.

Thanks to all who have offered their views and experience. I'm satisfied that tires do probably explain most of the efficiency loss, with lower gearing and a bit more bike weight being lesser factors. Good excuse to try different tires...

I'll be sticking with the gravel geometry and gearing, though.
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chas
1,305 posts
#19Mar 10, 2021, 3:33 PMedited
I've gotten some great data, as I ride weekly with a group of ~20 people who are as strong as me. flat road speeds are 20-30mph

I found that my 32mm Conti 4-season and gravel tires were pretty close to each other (40mm Schwalbe G-one, Maxis rambler). The Gravel would lose in a sprint, but otherwise they were pretty comparable.

I did find a HUGE difference switching to 32mm GP5000 tires though. It was the difference between worrying about being dropped, to leading sprints off the front. At 30mph drafting, rolling resistance is a huge benefit. The GP5000 have less than 1/2 the rolling resistance of the 4-season or excellent good gravel tire.
They are something like 15% faster when riding solo and in a group ride, they lowered my heart rate by about 10BPM as I recall. That is big if you are riding competitively.

Interestingly the 48mm GK-SK (650b) were incredibly slow (and loud) compared to the tires above - yep, slow enough that they couldn't keep up with the pack at all (30mph road).
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stu
646 posts
#20Mar 10, 2021, 5:07 PM
chas wrote:... I did find a HUGE difference switching to 32mm GP5000 tires though.
I've asked Conti about offering the GP5000 in larger sizes - I think they'd have a real winner. So far no reply. 🙁
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