Simply put, a single layer of material on the inside of thetyre’s carcass.
All the materials used in a tyre are about performance – abalance of grip, flexibility and durability. It may surprise you to hear thatthe ideal mix of rubber is actually porous, so will slowly leak air. In thepast, this was overcome by fitting a tube with a completely different rubbermix that would contain the air much better and have little effect on theoverall performance of the tyre.
The biggest issue with this design is that if it’s subjected toa puncture, the tube will lose all of its air suddenly, which would havetypically escaped rapidly through the spoke heads on the wheel. Rapid deflationof a tyre on any vehicle is not good, particularly when travelling at speed.
Created predominantly with safety in mind, the tubeless tyre wasdesigned by taking a section of tube material and making a single continuouslayer on the inside of the tyre carcass, and also saving weight.
Of course, a tubeless tyre can still be punctured, but theoffending object usually stays stuck in the tread and the tyre deflates slowly,giving the rider an opportunity to slow down. At the same time, cast wheelsmean spokes are no longer needed, so the entire unit has become sealed.
Now, instead of manufacturing both tubed and tubeless tyres inthe same size, most companies only make tubeless, and recommend that tubes canbe fitted if required. The disadvantage to this is that it adds additionalweight to the total wheel assembly, which can lead to more heat generation,which ultimately means faster tyre wear.
If a tyre states that it is ‘tube type’, then it will have notubeless liner, so it will not hold air and therefore must be fitted with aninner tube.