KENNBR wrote:
I read the slowtwitch build up, along with a few other articles. But I’m still debating on building my own gravel bike/ buying an old road bike and gravelizing it, also there are several options from cannondale and others just over a grand that could be bought.
Any suggestions, thoughts, or feedback on how to best select a frame?
The big thing is to sort of what you want from a gravel bike. That's going to depend on both you as a rider and what your local gravel is like.
If all your "gravel" is well-groomed velodrome-smooth hardpack dirt, a road bike with 23mm tires at 110PSI might be fine. But if there's a lot of double-track made made from really chunky aggregate, you'll probably want 40s or bigger. If you have lots of mud, you might want some spare clearance even if you aren't planning on using super-wide tires.
Think about what you expect from your drivetrain arrangement. How much steep climbing will you have to deal with? Will the gravel bike see a lot of paved miles, and how sensitive are you to gearing step size? Frames with cylindrical seat tubes usually allow you to mount just about any front derailleur at any height and angle; some frames can't mount front derailleurs at all.
From the late 1980s up until fairly recently, a high fraction of road bikes had very restrictive tire clearance, and are unlikely to make good gravel bikes. Cyclocross bikes from this era are often fine, but if you need a tire wider than the low-30s range, you'll still want to pay attention to the actual clearance.
Many road bikes from the early 1980s and before have fairly healthy tire clearance. Nearly all road bikes had healthy room for at least 30s, and a few can reach the upper 30s without flying too close to the sun. Right around 1980 there was also a beautiful time when the world was heavily dominated by 28.6mm seat tubes and 1" steerers and 68mm BSA bottom bracket shells, resulting in bikes that are still very easy to find compatible parts for today.
There are some caveats, though.
Road frames from back then were spaced narrower at the rear dropouts than today's bikes, so you'll want to re-space the frame if you'll be switching to a modern drivetrain with a freehub.
If you'll be doing a lot of interesting descending, brake choice can get tricky. Cantilevers and dual-pivot centerpulls can be tricky to set up, and their mechanical advantage tends to be low, but decent ones can feel pretty good if you manage a good setup. Single-pivot calipers, however, are usually both weak and spongy. If you want to replace them, you'd have to either modify the frame (tricky) or find a non-recessed-mount brake. There aren't a lot of modern options, although picking up older centerpull calipers on the cheap is definitely an option.
If you need really wide tires, old rigid mountain bikes can be a decent basis for a gravel bike.
The
really early mountain bikes can be pretty convenient to work with, but initially had beach-cruiser-esque geometry. When postured and fit like a road bike, this can make for some moderately esoteric characteristics. Of particular note, the super-long chainstays can make it hard to weight and plant the rear wheel, and the high trail results in a lot of wheel flop, so they're not the most confident or lively bikes on steep climbs. And the difficulty of bringing weight off the front wheel can make them a bit unconfident on super-loose surfaces as well. Not to say that they can't be loads of fun, but... things to be aware of.
Getting more toward the NORBA era circa 1990, MTBs got somewhat more road-bike-shaped (and then later started getting longer and slacker in front again towards today). You could also look into 1990s hybrids, some of them were lively wide-tire 700c all-rounder frames that can take a drop-bar conversion just fine.
If you start with a 26er MTB, tire choices are growing scarcer, but there are still good options for all manner of surfaces. Obviously there are still lots of MTB and beach cruiser tires floating around. If you want a lively fat slick, Panaracer Pasela is a good budget choice, but I usually keep my '84 Stumpjumper fitted with Rat Trap Pass tires.
As always, remember that trying to save money by modifying a cheap bike can sneakily morph into an expensive route if you start getting creative and having too much fun. :)