The key differences between Mavic's all-mountain Crossmax Quest XL 29in Tire and its XC-specific, non-XL counterpart are the former's improved puncture resistance and grippier rubber compounds. Though it's built for rides leaning more toward trail, the Crossmax Quest XL does feature an additional nylon layer on its casing, giving the rear-specific tire another plate of armor to stand up to enduro abuse.
It also softer center and shoulder compounds, registering a durometer of 50 and 40, respectively, which provides more confident grip on terrain than the standard Crossmax Quest's hardness of 55 and 50. The centerline's modest reduction by five is noticeable, but not nearly as much as the sidewall's reduction of 10, which helps the tires stick to the sides of rocks and roots so you can clean lines without washing out.
The Crossmax Quest XL is rear-specifc; pair it with Mavic's Crossmax Charge XL up front.