<===Something in the 35-40mm range seems to be the "sweet spot" for gravel tire width.
Tires. The question about what tires to use on gravel road events is a constantly asked one and the answers are constantly evolving as to which type of tire and width works best.
This post won't tell you what to use, but hopefully it will help guide you to a choice that is appropriate for you.
<===Sometimes mud defeats any tire choice! (From T.I.V2)
In my experiences on gravel, running events, and riding in them, I would say that a semi-knobby, 700c, 35mm-40mm tire hits the sweet spot for almost any gravel event. Tires that are cyclo-cross based, urban/commuter based, or 29"er based might all fall within these parameters.
Typically these tires are fitted to cross bikes with plenty of tire clearance, or they show up on 29 inch mountain bikes, but whichever type frame they are stuffed into- I've seen anything from Surly Steamrollers to Niner hard tails- this type of tire should cover your bases in terms of having a great balance of speed, comfort, and durability.
<===Riders like Rusty Kay, whose T.I.V2 rig is shown here, sometimes get away with true road racing rubber, but this is rare.
If I had to pick one tire in this category, it would be the Schwalbe Marathon Extreme, or one of those models based upon the Marathon series. I have seen Trans Iowa events won on Marathons, and I have seen many top gravel contenders using those tires. Says something to me!
Now, I've seen skinny tires used as well, but typically the pinch flat ratio goes up with these narrower than 35mm choices and obviously, comfort goes down. Pick yer poison.
In the realm of larger tires, you are generally stuck with 29"er frames, and if that is okay with you, Nanoraptors, Stan's Crow/Raven tires, or WTB's Vulpines are hot treads on gravel. A bigger, wider tire may be seen as slower, but keep in mind that riders of these will typically be fresher in the long haul, and they should theoretically experience fewer pinch flats.
<===I have witnessed "fat bike" tires walk away from other skinnier tired rigs on gravel if the conditions are right.
Yet with all of the "classification" going on here, I have to say that I have witnessed everything from 25mm road slicks in horribly wet conditions to ginormous "fat bike" tired sleds do really well on gravel. Nothing is outside the realm of possibility. So if you are on a limited budget, don't fret. Just get out and ride!
