Quad Tyre Guide

This guide aims to help you understand your quad bike tyre's size, load carrying capacity, maximum speed and tread pattern.

Imperial Quad Tyre Sizes - 20x11.00-9, 25x8.00-12. 25x10.00R12

Most quad bike and atv tyres are marked up with this type of size marking, and fortunately it's pretty easy to understand. The first number tells us the tyres total height in inches. The middle number tells us the tyres width in inches, and the final number tells us the rim diameter (hole in the middle of the quad tyre) in inches. so, a 25x10.00-12 is 25 inches tall, 10 inches wide and has a 12 inch hole in its centre. The numbers given for height and width are approximate, and manufacturers are allowed to vary these slightly as long as they stay within agreed limits so it doesn't affect your machines handling or gearing ratios. Also worth noting is that before the final number you will see either an 'R' or '-' symbol. The dash '-' symbol tells you its crossply cronstruction whilst an 'R' means its of Radial construction. Radial is newer and has more benefits (see below section crossply vs radial quad bike tyres).

Metric Quad Tyre Sizes - 145/70-10, 185/88-12, 205/80R12

Some manufacturers now use the more modern metric quad tyre size markings. With these the first number tells us the width of the tyre in millimetres. The second number after the '/' is a percentage figure, which when applied to the first width figure will tell us the tyres sidewall section height. The last number is the rim diameter in inches (the hole in the middle of the tyre). So a 145/70-10 quad tyre is 145mm wide, has a sidewall section that is 70% of 145mm = 102mm, and has a 10 inch hole in its centre. To work out the tyres total height (if needed) you would add two sidewall height sections to the rim diameter so (102 mm  x 2) + 10 inches = 18 inches or 458mm. Again these measurements of quad bike tyre width and height are approximate and vary between manufacturers but will always be within tolerances to ensure your vehicle isn't affected.

Converting Imperial & Metric - 165/70-10 to 18.5x6.50-10, or 185/88-12 to 25x8.00-12

Sometimes a metric size is very close to an equivalent imperial size, and so either of the two sizes can be used. If this is the case the tyre would normally have both sizes written on the quad tyres sidewall, or the vehicles user manual will indicate both sizes that can be used. If you want to do a sanity check then use the above guide to work out each sizes width, height and rim diameter and check that they are very similar. Usually quad tyre width or heights can vary by upto 5% and still be safe to use, but always check with you machinery dealer before purchasing to confirm this.

Quad Bike Tyre Construction - Radial vs Crossply

Radial construction is newer and offers more benefits for high speed or road going vehicles. As most quad bike and ATVs don't travel on the road, or at high speed they are still made using the older crossply construction method because it is cheaper and easier to manufacturer. If you do find you have a radial quad tyre currently fitted (it will have 'R' not a '-' before the last number in its size marking) then it usually means your quad tyre is more flexible, will grip the road better, will handle heat build up better, and thus wear longer and also reduce fuel consumption and give a more comfortable ride as it handles bumps with more grace. You should generally as a rule stick with what you currently have, but for the most part swapping from the older crossply tyre to the more modern radial version should have little downside other than a higher price tag. Swapping from radial to the older crossply however isn't advised as you could loose vital handling capabilities and the crossply quad tyre may not be able to be run at the higher speeds that the radial quad tyre could. You should also ensure you never mix construction on the same axle of a vehicle. 

Ply Rating / Load Rating / Speed Index

Modern radial quad tyres will all have 2 numbers on them followed by a single letter. This is the tyres load and speed index and tells you the maximum weight a tyre can carry at a set maximum speed. For example you may see '46J'. The table below can be used to look up what that first number means the quad tyre can carry in Kilograms. The letter can also be looked up the table below that one so you can see the tyres maximum speed. so 46J means the tyre can carry 170kg at 62 MPH.

Older crossply quad tyres don't have these markings sadly, but may have a 'Ply Rating' on the tyre instead. The ply rating is a reference to the quad tyres carrying capacity, and you should look for the same ply rating or higher when replacing your tyres. There isn't a table which can be used to find out exactly what the ply rating means, instead you need to look at a manufacturers technical document, but as long as you don't go to a lower ply rating you will be okay when buying a replacement. Common ply ratings for quad tyres are 2 ply, 4 ply & 6 ply. They may be written as 2PR, 4PR, 6PR on your quad tyre. Crossply tyre also do not have a speed index letter on them like modern radial quad bike tyres, so again you need to look at the manufacturers technical sheets. 

As an aside, it is worth knowing that American manufacturers sometimes don't use a ply rating, but will list a 'load range'. The table above shows how to convert a load range into a ply rating, for example quad bike tyre with a load range of C is equal to a 6 ply quad bike tyre in terms of weight carrying capacity.

Quad Bike Tyre Tread Patterns

Quad bike tyre tread patterns are usually not too dissimilar between manufacturers. For those requiring traction in mud, dirt and rock the quad tyre treads will have large and deep block or lugs, to help bite into the ground and achieve grip. The bigger and deeper these lugs the more traction you normally get. The spacing and size of the lugs can affect how easily the tyre self cleans (removes dirt and mud as it spins), how well it handles sideways slippage (on hillsides for example), and how it copes with obstables like rocks as they impact the tyre on both the tread and  tyre sidewalls. 

For quad bike tyres designed for road use the tread is often non aggressive so as much contact can be made with the road as possible to aid handling. They will resemble a car tyre more than a quad tyre, with grooves to displace water being their main tread feature.