Tire Management at SCOTT-SRAM

At SCOTT-SRAM, tires are one of the most sensitive topics for the team. Nino Schurter has always been very picky about his tire set-up. In the run up to the Rio Olympic Games, we spent a lot of time researching and testing along with the Swiss federation. We found the right combination of tire size and rim width giving the tire stability, compliance and the right shape for rolling resistance and traction. Now with all that experience, we’d like to give you some basics plus a tutorial in how to set-up and maintain tubeless tires on your mountain bike.

The Carcass

The carcass is the body of the tire. The side walls and the layer underneath the tread are often made with Kevlar or steel threads measured in threads per inch (TPI). The higher the number the more supple and lighter the tire. The lower, the more side wall and tread protection for very demanding conditions. The choice is weight and compliance against puncture risk and performance of the tire. Normal tires have between 60 TPI and 120 TPI. We have a special tire using 170 TPI for the SCOTT SRAM team. There are also different construction methods on how the rubber is layered between side walls and the top of the tire giving smooth transition and a clean look.

Rubber Compound

“Normal” tires are generally composed of just one compound whereas more expensive race tires can have up to three, combining a faster rolling rubber compound in the center and softer compounds towards the edges giving more traction in corners. In wet conditions softer compounds in the whole tread give the rider better traction on slippery rocks and roots while harder compounds will help on asphalt and hard packed fire roads.

What is Tubeless?

Many trail riders are still not aware of the benefits of a tubeless system - a combination of tire, rim, tape, a special valve and a fluid sealant allowing you to do away with the inner tube. The benefits are huge, lower pressures giving more traction and less rolling resistance, and puncture protection from thorns, small cuts or pinch flats from the inner tube getting trapped between the rim, rocks or roots. We have completely done away with tubes for racing, training and all general trail riding in our team.

Tire and Rim Dimensions

Rim widths and tire widths are getting wider across all MTB disciplines. This allows for more stability and more air volume with lower pressures, giving more traction and less air loss. We use an internal rim width of 25mm or more which is wide enough for our tires without adding too much weight in a critical place. This combination also has an important effect on the shape of the tire giving the center ridge some height putting the fast central compound to work on the straights but then a slight lean and the edge with its softer compound kicks in ready for the turns.

Tire Pressure

This is one of the most important improvements with zero financial cost. I think 80% of the riders are riding with the wrong pressure. Some people think that more pressure equals less rolling resistance when it’s the opposite. This is very dependent on rider weight and how aggressively you ride. A good starting point is 1.5 bar in the front and 1.6 in the rear. Test and alter the pressure to suit your weight and riding style.

Check your pressure by pressing down with all your strength, you shouldn’t be able to press half way through to the tire. If you nearly break your thumb you have too much pressure for a tubeless system. Hot conditions or cold winters can have an affect so adjust accordingly.

How to Make Wheels Tubeless: Part 1

First clean the inside of the rim with alcohol letting it dry so the glue on the rim tape will adhere to the rim. Make sure you have the correct width of rim tape. I start 10cm to one side of the valve hole, go 1 full lap and 10cm past the valve before making a clean cut. Make sure to really press the tape on to the rim to seal the spoke holes. A good tip is to make the small hole for the valve using a sharp pointed tool. I heat it up with a lighter so that it melts and doesn’t split the tape. If your tire is new and feels greasy on the inside clean it first, this helps the sealant adhere to any micro holes. Place the valve in and hand tighten.

How to Make Wheels Tubeless: Part 2

Put the tire on starting opposite to the valve. Just before you get to the valve rotate the wheel 90 degrees and pour in the fluid before popping the tire completely on. 80 to 100ml for average tires 2 to 2.25 inches in width, more for larger volumes and maybe slightly less if you check fluid levels regularly. Inflate the tire. If using a floor pump, take the valve core out so that the air goes in quickly. Inflate until both sides seat into the bead, you should hear a “ping.” Spin the wheel to make sure it’s fully seated.

Once it’s sealed pop the valve core in and tighten with a valve key and repressure. I never go over 2 bars. Bounce the wheel on the ground while rotating after each bounce to shake the fluid around until it’s sealed.

How to Fix a Flat Tire

Firstly, stop riding immediately. Find the puncture site and put it to the bottom, shake side to side letting the fluid do its work. If the hole is too big there are repair kits you can use it. We use the Sahmurai sword - a bar end mounted, pre-loaded, worm and needle. You push it through the hole then draw it back to block it and then release the tool leaving the worm to seal the hole. If it’s a bigger rip you will have to put a tube in. Remove the valve and one side of the tire leaving the fluid in there. If it’s a long rip and the tube would just burst then you have to be creative. A patch, a plastic note or even a gel wrapper. If it’s a very long cut you can place zip ties through the tread looping over the rim to keep it all in place.

Maintenance of the Tubeless System

Many riders think it’s a complicated and messy job but it’s quite easy. Let the wheel stand for a few minutes then lift and shake it side to side with the fluid in the bottom of the tire, listen to and feel it washing side to side. This way you can recognize when you need to top up the fluid after a month or so. After say 2 to 3 months, listen and feel for little balls rolling around signifying when it’s done its job and has become solid. In this instance remove the tire, check, clean and reseal. Check the rim tape for damage or lifting from the rim. I change the valve core regularly, if you don’t change it at least clean the core so you can get air in and out easily and get an accurate pressure reading.