Numbers such as 90/90-21 and 110/80 R19 tell you much more than which wheel a tyre fits. This guide explains how to read these adventure touring tyre sizes, what each number and letter represents, and how different dimensions suit front and rear wheels. You’ll also know about common Trailhound STR sizes and what to check before selecting replacement tyres for your adventure motorcycle.
Adventure touring can take you from smooth highways to gravel trails in a single ride. Your tyres need to suit both your motorcycle and the terrain it was designed to tackle. But what does a size such as 90 90 21 tyre actually tell you? Those numbers are more useful than they may first appear. Once you know how to read them, comparing adventure bike tyres becomes simpler and you can research replacement options with greater confidence.
A tyre size is more than a set of numbers printed on the sidewall. It tells you the tyre’s width, profile and compatible rim diameter.
Take 90/90-21 as an example:
So, a 90 90 21 tyre has a relatively narrow profile and fits a 21-inch wheel. Such dimensions are commonly associated with adventure motorcycles designed to tackle rougher surfaces.
Tyre markings can also show construction type, load index, speed rating and whether the tyre is tubeless. These details must also match the motorcycle manufacturer’s specifications.
Both sizes are commonly associated with adventure touring, but their dimensions are different.
Size | Width | Aspect Ratio | Rim | Construction |
90/90-21 | 90 mm | 90% | 21 inch | Bias |
110/80 R19 | 110 mm | 80% | 19 inch | Radial |
A 90 90 21 tyre has a taller, narrower profile. A 21-inch front wheel can roll over rocks, ruts and other rough surfaces more easily. Its narrower footprint can also work well through loose dirt and mud.
A 110/80 R19 tyre is 110 mm wide, while its sidewall height is 80% of that width. The letter “R” indicates radial construction. A 19-inch front size can offer a useful balance between road-focused steering, braking performance and touring ability.
Neither size is automatically better. The correct choice depends first on the specification approved for your motorcycle.
Front and rear tyres perform different jobs. The front tyre has a major role in steering and braking feel. The rear tyre must also deal with power transferred from the engine to the road.
This is why many adventure bike tyres use a narrower front and wider rear.
For example, a motorcycle may use a 90 90 21 tyre at the front with a 150/70 R18 at the rear. Another adventure motorcycle may use a 110/80 R19 front with a 150/70 R17 rear.
These combinations are selected as part of the motorcycle’s overall design. Changing tyre dimensions without manufacturer approval can affect steering response, stability, clearance and handling.
Eurogrip’s Trailhound STR range offers sizes for 17-inch to 21-inch adventure touring wheels. It is designed with a 90% road and 10% light-trail orientation.
Some Trailhound STR specifications are:
Position | Size | Rating |
Front | 90/90-21 | 54H TL / 54V TL |
Front | 100/90-19 | 57V TL |
Front | 110/80 R19 | 59V TL |
Front | 120/70 R19 | 60V TL |
Rear | 150/70 R17 | 69V TL |
Rear | 150/70 R18 | 70V TL |
Rear | 170/60 R17 | 72V TL |
Here, “TL” means tubeless. The number before the speed-rating letter is the load index, while letters such as H and V indicate speed categories.
The 90 90 21 tyre option suits motorcycles specified for this front dimension. Wider 150/70 and 170/60 rear options cater to motorcycles designed around greater rear tyre width.
A tyre can look suitable and still be the wrong fitment for your motorcycle. Never select adventure bike tyres simply because their dimensions seem close to your existing tyres.
Before buying, check:
If your motorcycle specifies a 90 90 21 tyre, start your replacement search with that specification. Do not move to a wider or smaller size based only on appearance or assumptions about extra grip.
Adventure touring tyres have a demanding job. They must support predictable handling on long road rides while coping with the surfaces your motorcycle is designed to tackle.
Reading tyre markings makes replacement research much easier. Whether your motorcycle uses a 90 90 21 tyre, a 110/80 R19 or another approved size, always follow the motorcycle manufacturer’s recommended specification.
When it is time for a replacement, you can also consider Eurogrip’s range of two-wheeler tyres. For suitable adventure motorcycles, the Trailhound STR range offers verified adventure touring sizes designed for road touring and light-trail use. Always confirm the correct fitment for your motorcycle before purchase.
Yes, 90/90-21 is commonly used as a front size on adventure motorcycles designed for varied terrain riding.
Its nominal sidewall height is 81 mm because 90% of the 90 mm width equals 81 mm.
Its nominal sidewall height is 88 mm, calculated as 80% of the tyre’s 110 mm section width.
No, they require different rim diameters and should only be fitted according to motorcycle manufacturer specifications.
Sizes such as 150/70 R17 and 150/70 R18 are commonly found on several adventure motorcycle configurations.