XM 421

Australian Mountain Bike - - Speakers’ Corner -

With the XM 421 hav­ing many of the same traits and char­ac­ter­is­tics of its 5mm wider peer XM 481, was it to be ex­pected that we would sim­ply dis­cover the same re­sults, but sim­ply be able to ap­pre­ci­ate its slightly lighter pack­age?


With the XM 421 be­ing al­most iden­ti­cal to the XM 481, ex­cept hav­ing a 5mm nar­rower in­ter­nal and ex­ter­nal width, we set it up with our base­line fig­ures and hit the trails. Af­ter sev­eral runs down our two Stromlo For­est Park trails we could feel that mod­i­fi­ca­tions were re­quired – quite sim­ply, there wasn’t enough grip pro­vided un­der the base­line set­tings. Mov­ing out onto the Flow Track at Thredbo we also moved our XM 421 air pres­sures to match the sweet spot air pres­sure of the XM 481, re­duc­ing them to 25psi rear and 22psi front. Right away we were off to a much bet­ter start with im­proved per­for­mance un­til sud­denly… BANG ! A mas­sive burp­ing off the rear tyre in one of the tight berms in the fi­nal me­tres of the track. Af­ter this and a few more small changes per run, sim­i­lar to the XM 481 30psi rear and 27psi front did not de­liver any en­joy­able rides, how­ever, by our 8th turn again down the Flow Track, we set­tled on the base­line rear air pres­sure of 27psi but main­tained 22psi in the front. While this did feel a lit­tle un­bal­anced at times when de­scend­ing at high speeds, drop­ping to lower pres­sures again would not be an op­tion. Un­der lower pres­sures, such as re­duc­ing the rear tyre to 25psi we ex­pe­ri­enced the same burp­ing that had oc­curred when rid­ing at Stromlo For­est Park us­ing the XR 361. Our test­ing of the XM 421 when paired with a 27.5x2.4” tyre proved that the 25mm in­ter­nal rim was not par­tic­u­larly durable, nor did it per­form as strongly as its 30mm in­ter­nal width peer the XM 481. How­ever, this is cer­tainly not a deal breaker. Per­haps us­ing the XM 421 with a 27.5x2.3” tyre might de­liver the sta­bil­ity and grip at lower pres­sures, but this could po­ten­tially also of­fer a rougher ride – it’s all about com­pro­mise. Note:

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