Name: Specialized Hillbilly Grid Gravity 2BR T9 27.5" MTB Tyre
Brand: Specialized

This Hillbilly MTB tire likes it raw. Gravity-focused, excelling in steep, slippery, loose, and wet conditions in the continental north, the all-new Hillbilly is designed specifically to find traction in shifty natural terrain and bring confidence and control to the unpredictable wild.

The new mountain bike tire tread pattern features an aggressive tread with deep center knobs and high-volume shoulder blocks to bite through loose soil when cornering. Block-in-block transition knobs reinforce the tire structure, aid traction, and lower rolling resistance, from plowing deep loam to railing rock slabs and charging over slippery roots.

Specialized’s exclusive Sticky Fast T9 rubber compound elevates the Hillbilly’s traction, enabling it to stick everywhere, even in the greasiest conditions. In addition to its ability to grip in slippery situations, our T9 compound is formulated to bring just the right amount of damping to the backwoods party, reducing tire bounce and deflection to enhance stability and control in challenging conditions.

This tubeless-ready trail tire is available in either GRID Trail or GRID Gravity casing, covering trail, all-mountain, enduro, and downhill. GRID Trail’s bead-to-bead protection and stability make it an excellent choice for aggressive riding in rough conditions. GRID Gravity is a burly, two-ply construction designed for durability and puncture protection in extreme conditions, offering incredible strength and exceptional tire stability when loaded hard into corners and compressed into jump faces. Just add sealant as the Hillbilly is a 2Bliss ready clincher for easy mounting and inflation with or without tubes.

Large Block-in-block shoulder knobs for supported cornering.
Spike center knobs to dig in and find traction over loose terrain.
High-damping GRIPTON® T9 compound reduces terrain-induced chatter, rebounds slowly, and has extreme grip in all conditions.
GRID Gravity 2-ply casing construction is ideal for Enduro, Park, and Downhill riding.
GRID Gravity 27.5x2.4", psi 25-50, approximate weight 1240g.

Occasionally, without notice, manufacturers change product design and/or specifications.

Tyre Size Guide

Whether you are replacing a worn out tyre or want a performance upgrade, it is essential that you choose a tyre that is compatible with your bicycle as well as your riding style.

To find out which size tyre you will need have a look at the sizing information on your existing tyre. You can find this information on the side wall of the tyres, either in coloured print or embossed in the rubber itself. Both rim diameter and tyre width are shown in the size info.

Road bike tyre sizing

Slim 700c road bike tyres on a Merida road bike — 700 x 23c

A standard 700c road bike rim with a 23mm tyre width.

MTB tyre sizing

Knobbly wide mountain bike tyres on a rocky trail — 27.5 x 2.3

A 27.5” mountain bike rim with a 2.3” tyre width.

You will notice that road bike tyres tend to me measured in metric units while mountain bike tyres use imperial units.

What Size Tyre Do I Need?

Ypu need to knnow your wheel size and tyre width when chosing a replacement tyre for your bike

Wheel Size

Tyres are made to fit specific wheel sizes, so you need to know what size the wheel on your bike is.

The easiest way to do this is by looking at the tyres on your bike. On the sidewall you'll see a combination of digits such as:

700 x 28c (road bike wheel) or 27.5 x 2.4 (mountain bike wheel)

It’s the first figure that shows the diameter of the wheel or the wheel size.

The next figure is tyre width which is the other measurement you need to know.

Tyre Width

Inner tubes are designed to fit a range of tyre widths, so the next thing you need to know is the width of your tyre.

This is shown in the second number that’s printed on the side of the tyre.

700 x 28c (road bike wheel) or 27.5 x 2.4 (mountain bike wheel)

When choosing an inner tube you need one with a width range that covers your tyre width as well as exactly matching the size of the wheel. See the tables below for examples.

Note: Sometimes metric sizes are shown as c instead of mm. This is just a different way of saying the same thing. A 25c tyre is the same width as a 25mm tyre.

Traditional and ETRTO sizing

Sometimes the sizing info is listed in two different ways; the traditional sizing method shown above and ETRTO sizing which lists the tyre width first and the rim diameter second. The rim diameter size is measured differently with ETRTO, for example:

23-622

This is a standard 700c road bike rim with a 23mm tyre width, which is the same size as 700 x 23c.

We recommend that you use the traditional sizing method wherever possible as most tyres that we stock use this system.

Traditional and ETRTO tyre size tables

If you are unsure which tyre size you need you can use our handy comparison table to find the correct size tyre

Road bike tyre sizes

ETRTO Number	Dimension
700c road bike wheels
18-622	700 x 18C
23-622	700 x 23C
25-622	700 x 25C
28-622	700 x 28C
32-622	700 x 32C
37-622	700 x 35C
47-622	700 x 47C

MTB tyre sizes

ETRTO Number	Dimension
26" mountain bike wheels
50-559	26 x 1.9
54-559	26 x 2.1
55-559	26 x 2.2
58-559	26 x 2.35
27.5" (650b) mountain bike wheels
50-584	27.5 x 1.95
54-584	27.5 x 2.1
57-584	27.5 x 2.25
29" mountain bike wheels
50-622	29 x 2.0
54-622	29 x 2.1
55-622	29 x 2.2

What are the different types of bike tyres

While road, mountain and hybrid tyres have their own specific differences there are some features that are common to all tyres.

Clincher tyres - most bike tyres have a bead which hooks onto the rim to keep the tyre in place. Traditionally this bead is made from wire which is tough but heavy. Premium tyres use a folding Kevlar bead which is equally as strong as wire but is much lighter weight.
Tubeless tyres - while regular clincher tyres require an inner tube to keep them inflated tubeless or tubeless ready tyres form an airtight seal with a compatible rim so you don’t need an inner tube. These are most commonly found on mountain bikes as they can be run at lower pressures without risking punctures.
Tubular tyres - These are specialist road bike tyres that have the tube built into the tyre and are then glued onto a compatible rim.

Frequently Asked Questions

What size tyre do I need for my bike?

Look at the side wall of your tyre for any printed numbers indicating the size and width.

How do I know my bike wheel size?

The easiest way is to look at the side of your tyre. The size and width are printed on the tyre.

How do I choose a bike tyre?

Once the compatible size is known, choose an appropriate tread for the conditions you ride in.

Can I fit wider Tyres on my bike?

Look at your fork and frame where the tyre passes through, measure any available clearance to gauge what width tyre will fit.

Is a 28 inch tire the same as 700c?

700c wheels have a diameter of 622mm. While most 28 inch tyres are for a 622mm wheel, some are not. Check the ETRO number on the sidewall to confirm.

Specialized Hillbilly Grid Gravity 2BR T9 27.5" MTB Tyre