I rode this on 44mm slicks yesterday:
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Will you be solo? I ask because GKās throw a lot of grit in the face of the person behind you. No big deal if youāre solo.
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Iāve been very happy with Continental Terra Speed in 40mm (and bicyclerollingresistance give them a good score) - theyāre particularly good on the dusty, rocky fireroads and trails I ride the most and donāt feel draggy on the road.
Butā¦ if youāre looking to save time over 320km of road/cyclepath then have you considered going the other way? If you put something like a 26mm Pirelli Cinturato Velo tyre on, then you get less rolling resistance, 100g less weight per wheel and better aerodynamics.
I use my gravel bike as a road bike too - last week I went from 40mm Terra Speeds (on stock alloy wheels) to 26mm Cinturato Velos (on a slightly deeper and lighter alloy wheelset) and dropped a few minutes for about the same power output on my normal 20km commute. Those kind of savings would really make a difference over 320km!
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More often than not Iām solo so I should be ok there.
I was thinking of that but Iād want tubeless and about 30mm which would mean I couldnāt use them on the roadie after the event since 28mm are tight with rim brakes and needs tubes. If my roadie was a bit newer thatād be the best option.
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Iād pretty much decided on the Panaracer until @timb34 threw another idea in the mix!
Iāve narrowed it down to the above tyres. Rolling resistance has the Contis at 40mm as much faster but to get the 40s theyāre a good Ā£15 more per wheel so looking at the wider option which I think would still be pretty nippy and hopefully not slower than my existing wheels (which considering the 40mm is about 4W faster it should be).
There is also the GK at 43mm and Ā£38 but that doesnāt have tan sidewalls and Iām a sucker for tan walls - makes me think of the original Panarace Smoke/Dart.
Such a great tire combo from back in the day!!
Sorry, replied to wrong messageā¦
77kg here with Diverge Comp Carbon (9.5kg ready to ride) and I run 2.4 bar front and 2.5 bar rear!
Might be on high side but pretty fast gravel here + lots of bike paths etc.
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Looking at the info sheet for my wheels (h son hydra rims) it would seem that their 25mm internal width puts them designed for ~35mm tyres. I can either find a seller for the 35 contis or size up to 38mm panaracer (or 35mm).
Which reduces the question down to how wide is too wide for the rims?
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Iāve run donnelly strada ush 700x40 at last years dry rasputitsa no issues and just ran the same tire unfortunately at State 9s Pavement ends race april 1 with sleet and crazy sandy roads. Ran the Ultradynamico Cava 700x42 for overland last year. Ill also run gravel king slicks in 700x38. For the most part I think in NE if you have proper pressure your can get away with very little tread. If your looking early season mud I would reccomend some of the reneherse full knob options. If its dry you should be fine with just file treads at low psi rest of the time.
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25mm rims will take a lot bigger than 35mm tires. Iāve ridden 2.4ā MTB tires on 25mm rims. This wasnāt ideal - 30mm rims work better for 2.4ā tires - but it was certainly rideable.
For size ranges of gravel tires - 35mm to 50mm - 25mm rims will work fine. Other things will change somewhat like aero characteristics and bike handling, and of course you need the frame clearance for bigger tires. But youāll still be able to ride your bike just fine.
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Sure it would be fine just thinking about performance!
Although some of the tractor tyres I used back in the day on 26inch wheels were massive on narrow rims! So really should have thought of that.
Possibly worth a look:
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Iāve had couple sets of GK SK, Power Gravel and Terra Speed, all 35ās. In this size theyāre all very good for 25 id rim. You can check out tech specs from https://www.bicyclerollingresistance.com/.
IMHO Power Gravel is the best racing tyre overall it you forget how bad it is to wrestle on to your wheels, itās quite bad actually from that point. Very durable frame. Fast and super nice handling and grip.
Terra Speed is probably fastest from these, but it was a bit disappointing for me how narrowish optimal tyre pressure it needs at least for my riding style and surfaces. Itās lightning fast for fine sandy roads. Very thin sidewalls against cuts. Wears out so fast, at least back tyre.
Gravel King SK is very good tyre overall. Itās slowest from these three, but all these are very fast tyres. Itās very good tyre to put on, seals nicely.
I only have 40ās for Terra Trail for rocky trails and spiked winter tyres. I go Power Gravel 40ās next, probably what Iām looking for for my ultimate tyre.
I got a pair of IRC Bokken Double Cross 42mm for half price as part of my not so half price Unbound Entry. going to give them a try on the Sea Otter Gravel Course this weekend.
This doesnāt quite add up, are you sure everything else is similar, namely traffic/wind?
According to BRR, Cinturato 26mm run 19.9W at 80psi and 17.5W at 100psi. Terraspeeds 40mm run 16W at 42psi and 15.6W at 54psi. Even at 33psi they only run 18.6W. Saving a few minutes on a 20km commute would be quite the improvement for any tire/wheel combo.
Albeit I havenāt anything to compare them to, I like the WTB Raddlers on my bike. I replaced the rear one ataround 3,000miles after putting a hole in it with a tyre worm prong that I thought might fail in future, on hindsight the tread was good and I could still be using it but Ive retired it to the spares and fitted another Raddler.
First gravel races of the year for me the last 2 weekends. Good mix of chunky gravel, sand, tarmac, washboard, etc. I ran 42ās for the first time, s-works pathfinders on zipp 303 FC rims (25mm internal, so measure about 45mm). 32psi rear, 30 front @ ~175lbs. Early season races always feel great with the weather, but I really liked the 42ās and lower pressure. Just felt fast rolling, even on pavement. It took me a while to hunt down the pathfinders (and I paid full price), but Iām pretty happy with them.
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Likely a half pound as well.
I couldnāt quite believe it either, so Iāve been back over the last 2 months of commuting. If I exclude the rides where I had a strong headwind or was trying hard, then the effect isnāt as big as I thought - average speed goes from just under 19 km/h to around 20 km/h - which gives about a 3 minute saving . So overall time over the 21km route drops from 1h06 to 1h03 (table of rides below)
This is with the same clothes, backpack, position and helmet.
I think that the speed change is about 10W ? (really not sure about thisā¦ if anyone wants to correct me) If BRR is right about the Cinturatos saving around 1 or 2W, then thereās still about 8W saved somewhere else. 2 or 3W for the wheel and tyre aero advantage? Maybe 2 or 3W lost in the hubs? (the Terra Speeds are on a pretty low end wheelset and I havenāt checked the bearings for a while)
Date speed time av power
5/4 20.2 1.03 140
(31/3 17.1 1h13 141 headwind)
28/3 19.8 1h04 140
(20/3 21.4 0h58 160 not recovery)
3/3 19.5 1h04 143
1/3 18.5 1h08 140
6/1 18.9 1h06 140
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Cinturatos are slower rolling actually, unless you run them at 100psi and Terraspeeds at 33psi! Makes your results even more interesting! 
Not knowing your pressure, it seems Cinturatos will run you 2-4W slower, so youāre making up even bigger gains elsewhere which is awesome!