It's funny to me that the Ride posts a mini. gearing ratio needed of 39/25 or 27 since most bikes, if they have a double, will have 39/25 or 27 (and yes I know they could also have 23 or 21). A triple chainring system will have not only the 39 as the middle ring, but a 30 or smaller (as the small ring) as well. If you have a triple and a rear cassette of 25 or 27 (the number of teeth on the largest cassette in back) then that's fairly low granny gear.

So I wonder, - will the ride directors check and see if someone shows up with a 39/23 and if so, will that person be tossed out? Ride here in California usually just post the gradient and then it's up to the rider to decide if they are able to climb it. I know in some states, say Texas, when riding around in
the country, you can run across some short but very steep little hills like with a 30% gradient. Without a granny, I would have to walk the hill.