I think so much of what tire is suitable for someone depends on where they live and the riding surface of gravel roads, trails, etc. That said, I don't know many (any?) people who ride 'gravel' where I do, so I figured if I give you a vague sense of my conditions and riding intentions and I'll get something in terms of recommendations...and something is better than nothing 😆
Conditions - I live in Southwest Ontario ( hour outside Toronto) Canada. - Within riding distance from my house are two long rail trails. One is 10k away from home, the other 25k. These are in very good condition with true crushed gravel surfaces. I've been on them with my road bike and 25mm tires, and while it's do-able, though comfort is very important to me (more on that below). There are other rail trails within a 30-60 minute drive, some of which have gravel roads intersecting with them, so a lot of fun exploring to do (this summer I hope). - The gravel roads close by are usually on a base of smooth crushed gravel (tiny particle, and fine on a road bike if you avoid the crap), but there are small to large pot holes, and stones up to marble size that seem tossed about. And the odd washboard thrown in that can usually be avoided if no cars around. There are not many of these roads, however, so always some paved mixed in. The climbs and descents are short and not very steep. - I have a small community mixed-surface trail two minutes from my house that I would ride at least once a week (so much fun), it is a crushed surface like the rail trails, but also has dirt, sections with a few rocks/roots, wooden boardwalk, and many, short steep climbs and descents (it's what got me started with gravel bike thinking)
Riding and my Stable of Bikes (all two of them) - I have a road bike that rides like a dream and anytime I'm planning to ride spring/summer/fall just on paved surfaces, it will be on the road bike - I've had gravel bikes in the past, didn't own one last year, and I have a new one this year (200k on it so far). It's carbon, GRX group, has 700 wheels and I have 40mm Touareg on there (tubeless) at the moment. Frame can handle up to 42mm easily. - The gravel bike will also be my winter bike, though I ride only when the roads are safe (no snow/ice). I'm good with cold though, so I plan to ride it as often as I can in winter (getting sick of Zwift). - I love the idea of a 50-80k mixed surface ride to break up my usual routine of road riding. On a typical 80k ride from home, I would pretty much be on paved roads 50% of the time, and then 50% split between rail trail and gravel roads.
Tire choice - The Touareg have only seen roads so far, when pumped to 50ish they roll fine and I have no complaints. I do wonder how much paved surface they can take before the tread dies away. - So that has me thinking, once these are done (first I see how they handle the gravel riding in my area) should I go with a lighter tread tire (maybe smooth strip down the centre) so that they last longer and handle the pavement better (figure I'll spend 50% of my riding on these tires on pavement, as they're used either in the winter on roads, or in the other seasons on mixed surface, with some dedicated gravel rides mixed in)? - Comfort is important and I don't like harsh ride on my privates, so any tires on this bike will be set up tubeless
I went through the tire finder on this site but looking at 40mm (or thereabouts) the database seemed out of date...I thought there is more out there to choose from.
I had 650x47 GKSK on a previous bike. I liked them as an overall tire. I realize my Touareg are 700x40, but they feel similar or a bit faster on paved.
I may try the GK SS one day though.
I forget about that site, so thanks for the reminder.
You may be fine with slicks. Tread patterns only help when the size of the surface texture is smaller than the spacing between the tread blocks. That applies to soft dirt, mud, sand, and snow but not to pavement, hard dirt, or gravel bigger than a few mm. In mud tires with closely-spaced blocks (G-One, Terra Speed, GravelKing SK) will clog up and become very heavy slicks.
I've been happy with Soma Shikoros. They're very comfortable, roll well, handle well, and seem durable. Much like a GravelKing slick but sturdier. Only the 48 mm size is marked tubeless compatible. I've used them in 48 mm and 42 mm, both with tubes. I think the 42 mm is actually a little more comfortable, dunno why other than it is quite a bit lighter. If tubes really bother you look at the Schwalbe Aerothan SV17E (only 61 g).
If you never get punctures you might consider the lighter Soma Supple Vitesse and Rene Herse slicks.
I am using the GK SK 43-622 right now and am very happy with it for my mixed surface, slightly road-biased riding. I think you could try either the SK or SS but I'd suggest you try the SK first, since you have a road bike to use too. Try it in the 43 and it will give you the comfort you want. It's very good on dry dirt and gravel and as good you're going to get on the road for that category of tire. Your road bike might end up a bit lonely.
