Gravel bike tyres are getting wider and wider, with Pirellis inclusion of 55mm widths for its new Cinturato Gravel RH and Cinturato Gravel RM tyres the latest example. The 55mm widths are part of a growing portfolio of tread patterns and widths for Pirellis gravel tyres and are the widest tyres across a range of options for its new RH and RM tyres that also includes 40mm, 45mm and 50mm tyres, as well as a 35mm for the RM. RH signifies Race Hardpack, while RM stands for Race Mixed, indicating the new tyres performance orientation and preferred surfaces. Pirelli says the new tyre models round out its range of made in Italy gravel tyres and that the RH lowers rolling resistance by up to 17% and the RM by up to 20% over Pirelli's equivalent Performance Line tyres. Cinturato Gravel RH tyres The RH tyre's slick central section is designed for speed on firmer surfaces. The Cinturato Gravel RH is designed for gravel races that feature both hard-packed gravel and tarmac sections. It has a slick centre to the tread, with side knobs to handle grip and cornering in off-road sections. Pirelli says the tyre has a squarer cross-section to enhance rolling efficiency and borrows from its XC MTB racing tyres. The 55mm tyres are available in Pirellis HP-Line, which offers black sidewall options with white lettering and and one with yellow Team Edition lettering, as well as tan-sidewall Classic and cream-sidewall Retro versions. Claimed weight is 710g. Between the different width and colour combinations, there are a total of 18 different tyres. Cinturato Gravel RM tyres The Cinturato Gravel RM's more aggressive tread increases grip on mixed surfaces. The Cinturato Gravel RM-Line was previously called the RC and has a more aggressive tread pattern than the RH that Pirelli says still rolls fast, as well as providing grip on a range of surfaces. Theres the same range of sidewall and logo options as for the RH tyres and the 55mm tyre has the same 710g claimed weight as the RH. The RM adds a 35mm width for the lower-spec P-Line tyre, for a total of 19 width/colour/tyre line options. New compound and casing for HP-Line tyres The RM and RH tyres have a new casing and tread rubber compounds. The wider RH and RM tyres come in Pirellis HP-Line, signifying High Performance. This uses a new set of Smart Evo GR rubber compounds and a new ProWall Gravel casing with reinforced sidewalls for control and puncture protection, which together reduce the rolling resistance significantly. Theres also a P-Line, for Performance, although this doesnt include the 55mm option and carries over tech from Pirellis current gravel products such as its SpeedGrip compound and TechWall Gravel casing with bead-to-bead protection. Other gravel tyres already available from Pirelli are the Cinturato H (for hardpack), which we rated for its impressive performance on firm surfaces. There's also the Cinturato M (for mixed) and Cinturato S (for soft terrain). These tyres stop at 50mm maximum width and are also available in 35mm, 40mm and 45mm sizes. Is wider better? Schwalbe launched two 60mm wide tyres last month, but does your frame have room for them? Schwalbe Pirelli launched a 55mm Cinturato Evo road tyre last year and its 55mm gravel tyres join the general gravel tyre inflation thats going on. Last month, Schwalbe added two 60mm-wide options to its G-One range, as well as a new 55mm tyre. It reckons theyre just the thing for ultra-bikepacking and XL gravel races. Of course, you could always fit MTB tyres if you want to go that wide and many gravel racers are now doing so. It predicates having a big-clearance gravel bike, such as the Factor Sarana and Ridley Ignite GTX to fit. We reckon you shouldnt buy a gravel bike that doesn't have at least 50mm tyre clearance if you don't want to become a gravel fossil. Were not so sure about the 'bigger is better' trend though, with Warren setting out why he thinks narrower and lighter may be a better choice if you're not planning to ride Unbound XL next year.