kerikstri wrote:
So my W/kg at my threshold is about 4.8 W/kg (I was a bit over 400 W for a 20 minute test at 78kg a couple of weeks ago), so I'm a pretty strong rider. And in terms of the gravel I will be riding, I'm located in Vancouver, BC and have heard we have the entire spectrum
I haven't ridden gravel in BC, but if it's anything like the Seattle area, it's definitely very variable. Most of the gravel is forest roads in the foothills, often very steep, that get surfaced with whatever is convenient, and quite literally: the gravel road networks are dotted with little quarries where they blast and crush the required aggregate for the roads.
On low-maintenance roads which will handle logging trucks and drainage is a concern, sometimes the aggregate gets extremely large; depending on compaction and weathering, these roads can vary from "actually pretty smooth" if they're freshly-compacted, to "like riding on rough cobblestones" if the hardpack that they're compacted into has weathered around the chunks, to "can a truck please smash this down already LOL WTF":
Actually, it gets even worse than that. Recently I rode a road that was semi-compacted by the vehicles building the road. It was sort of like the above, but with deceptive ruts and scattered chunk piles. I was only on it for a few minutes, but I nearly crashed several times from the front wheel contemplating whether it wanted to fold out from under me. I know a guy who
did crash on it recently, and destroyed a tire in the process. It'll be a good road when it's complete and compacted, it's got fun gradients and good scenery.
Most roads are better-quality than that kind of stuff, even when they're double-track.
The high-usage roads made from finer aggregate can sometimes be velodrome-smooth:
But thanks to the damp regional weather, they're highly prone to developing potholes, especially in low-gradient spots. And, severe washboarding also happens in places.
I'd avoid erring low on tire clearance. Most people I ride gravel with have their bike's clearance close to maxed out; I've got a bit of spare room in mine, but I've already got 2.1" tires on there and I'm trying to keep the fender clearance safe.
Sometimes people do okay on tires in the ~33mm ballpark, but it depends on the setup and the road. I've seen people ride fast skinny CX tires just fine for most of a ride, and then we'll hit a stretch where they suddenly burn through all the spare tubes in the group in just a few miles.
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I'm hoping to build up the bike to be able to tackle it all. So I guess that would kinda answer my own question then... I may as well just build it up with the 2x drivetrain so it is never going to be the limiting factor for me being able to ride everything.
The gradients can definitely be significant around here. A lot of climbs average 10-12% for a mile or two.
The bottom gear on my gravel bike is 19", achieved with a 24T chainring and 32T big cog. That's
mostly adequate, although some stretches still make me go "ow":
The view at the top was AMAZING, though.
I can't agree with dangle's point that ultra-low gearing is "walking speed", though. 3mph might be gentle walking speed unencumbered on flat ground, but it's not gentle walking speed dragging a bike up 20% chunky double-track. When the gearing allows it and the terrain isn't too technical to ride, riding is nearly always better than walking.
That being said. At 4.8W/kg, you are a monster. A hill that I can handle smoothly with a 19" gear, you could probably manage similarly well if your lowest gear is somewhere around 1:1.
That also being said. 2x isn't about getting a super-low low-end. You can get a super-low gear on 1x just fine; just use a tiny chainring and a cassette with a huge cog. The caveat is what kind of spacing you can get over what kind of range, since you have fewer total ratios to work with.
If the bike is a "do everything" machine and you still want it to have good attitude on paved road riding, you might want 2x to keep the gear spacing and top-end reasonable.
My gravel bike gets a fair amount of use on paved roads and even in road pacelines, so I like having multiple chainrings so that I can manage good spacing through the road cruising range and a 113" top gear. Or I'm just making excuses for the fact that my gravel bike is a drop-bar converted old MTB and it just happened to have a triple crank on it when I got it, haha. But I
am able to squeeze about 18 unique useful ratios out of the 3x8 without the shifting getting wildly esoteric.
I can't speak to chain drop risk on GRX. My drivetrain is pretty bouncy*, and used to be capable of dropping chains on rough terrain even when I wasn't shifting, so it's got a Dog Fang chain catcher on it now. No chain-drop issues on gravel since I installed that.
*Rear derailleur is Alivio RD-T4000. It has no clutch/damper, and applies pretty low chain tension on its super-long arm.