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Gravel Bike Standards Guide: Buying a New Bike Made Easy





Gravel Bike Buyer’s Guide

Gravel Bike Buyer’s Guide

1. TL;DR – what kind of gravel bike to buy

If you’re only buying one drop bar bike, a gravel bike is the way to go. It’s as versatile as a bike gets, able to run skinny tires and keep up on group road rides, or fit up to 29×2.1″ mountain bike tires and hit the trails. And everything in between, from dirt roads to bikepacking, gravel bikes open up opportunities. In this guide, we’ll explain the terminology and latest standards so you know what to look for and why it matters. If you want to future-proof your investment in a new bike, this is your Gravel Bike Buyer’s Guide!

TABLE OF CONTENTS

1. TL;DR – what kind of gravel bike to buy
2. Hub Axle Standards
3. Bottom Bracket & Crank Standards
4. Number of Chainrings and Cogs
5. Gear Shifting Methods
6. Brake Types and Trends
7. Wheels & Tires
8. Freehub Standards
9. Cockpit Standards and Trends
10. Suspension
11. Fork Standards
12. Frame Geometry

2. Hub Axle Standards

By the time “gravel bikes” were officially a thing, so was the 12×142 rear thru axle. So, even if you’re buying used, it’s highly likely that’s what you’ll get. Don’t buy a “gravel” bike with a quick-release skewer holding the wheels in place. Not only are those less stiff and secure, you’ll also have a really hard time finding any good wheels that work with them anymore. Early gravel bikes borrowed the 15×100 mountain bike thru axle standard, before every mountain bike fork went to the wider 15×110 Boost standard. Then road bikes settled on the sleeker 12×100 thru axle, and gravel bikes adopted that, too. There is a wider 12×110 “Road Boost” standard used by a few bikes, but the vast majority use the 12×100 standard. Which refers to 12mm diameter by 100mm hub shell length. So, the axle will actually be longer than 100mm, because it has to go through (and thread into) the dropouts, too. The exact size will vary by bike and fork brand, but the numbers you need to know are:

Front: 12×100
Rear: 12×142

If you’re buying a new bike, 99.9% chance that’s what you’re getting. And if you need to replace a thru axle, look at the specs etched onto the original, because the actual length and thread pitch will vary and you’ll need to get the same exact specs for it to work with your bike. Then just call Robert Axle Project because they make replacements for everything. Or just take it to your local bike shop.

But aren’t there different thru-axle types?

Yes, there are “tooled” and those with a lever. Tooled thru axles simply mean you need an allen wrench to remove the axle, which adds time, but saves weight and looks sleeker. Tool-free axles use a QR-style lever, which gives you a lever to spin and thread the axle into place, then you clamp it down to secure it. Technically, these are more secure because they’re applying tension against the threads, making it harder for the axle to come loose, but they add a bit of weight and stick out from the bike and fork. DT Swiss makes a thread-in thru axle with a lever -some models have a removable lever- giving you a blend of benefits.

Will a thru-axle bike fit on my indoor trainer or bike rack?

Now that most bikes have disc brakes, most direct-drive indoor trainers come with adapters for thru axles. And most fork-mount bike racks have options for all the different axle types. Just order what you need.

3. Bottom Bracket & Crank Standards

Ever the source of controversy, bottom brackets come in a lot of different types, each with its pros and cons. They include:

BSA Threaded
T47
Square Taper
PressFit
BB30
DUB
GXP

…and within PressFit, there are various types. This section is provided as a top level pros/cons explanation so you know what you’re getting, but the reality is you’re probably not deciding which bike to buy (or not buy) based on which type of BB it has. Most gravel bikes have a 68mm wide bottom bracket shell, but most bottom bracket manufacturers (and your local bike shop) will also be able to tell you which size you need if you tell them which bike you have.

DUB and GXP

These two aren’t really BB standards, they’re crank spindle standards, but require a matching BB to work, and both are SRAM-specific standards. DUB refers to a ~29mm spindle diameter (versus the very well established “BB30” cranks that use a 30mm spindle), and GXP is a tapered spindle that goes from 24mm to 22mm in diameter. While DUB’s allowance for ever-so-slightly larger bearing sizes may be of DUB-ious benefit, GXP did make setup slightly easier…however, it’s essentially discontinued, so you’re unlikely to find a gravel bike with it. If you get a bike with a modern SRAM crankset, it will have a DUB spindle, and you’ll just need to make sure any bottom bracket upgrade is DUB compatible. Because of SRAM’s prevalence, you’ll have no problem finding options.

BSA Threaded

BSA is what most “bike shop bikes” (as in, not cheapos from big box stores) have used for years. It has two sides that thread into the frame, ensuring good crank spindle alignment, simple installation, and decent durability. This makes…



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