The Adventure Component arm set is CNC machined from billet 7075-T6 aluminum alloy. The right arm is a two piece design, and we can't get over how similar the arm set is to those being sold as GT Aluminum arms, (there are also similarities to the T-Gear arm set). They share very similar styling, bends and material thicknesses as well as near identical spiders, The AC model has an additional set of inner chainring holes so a 20 tooth steel inner using a 56mm BCD can be mounted.
The AC crank arms are cleanly machined with angled faces and "hogged out" (milled away) triangular areas both the front and rear of the arm. The arm is 34.5mm wide at the pedal spindle, narrows to 1" (25.4mm) at 2" from the bottom and remains at the 1" width until 5" from the arm top, where it gradually widens to become 1.60" (40.65mm) on the left arm and 2" (50.4mm) at the B/B spindle. The arm is 1/2" (12.70mm) thick at the pedal spindle, where it remains until 5" from the top where it gradually thickens to 61" (15.6mm). Both arms at the B/B spindle have a 26.0mm thickness to support the spindle in the arm. Cleanly milled away triangles in the front and rear faces of the arm reducing the wall thickness to 1/8" (3.18mm).
The spider is made of machined aluminum plate with a 4.71mm thickness, reduced to 3.6mm where the mid and outer chainrings bolt to it. The spider has three sets of holes, the outermost has a 110mm bolt center diameter pattern, the middle hole is drilled and tapped for the inner bolt sets at 74mm and at 56mm. This third inner set allows the rider to use a 20 tooth SR/Suntour (or equivalent) Micro Drive inner. When used with a 28 tooth rear it creates a .7 to 1 gear ratio for an ultra low "Granny" gear. The spider is bolted to the arm using four steel cap bolts with 4mm hex fittings. The 5mm by .8mm bolts have a 10mm length, (these are what many frame builders include to hold the water bottle cage into frame braze-ons) and have the head recessed slightly into the back of the spider. We've mentioned that two piece construction of drive arms sometimes leads to a "creaking" noise under load. This noise is from dissimilar stress loads on different parts of the arm and spider in use. Under load the spider shifts and the movement of the metal against each other and back again is what creates the "creaking." The classic solution is to grease the spider and arm where they are joined and the sides of B/B spindle prior to installation. AC actually greases the spider and arm before bolting them together, and we haven't noticed another crank maker do so. Because the AC crank uses a separate spider bolted the right arm changing the bolt pattern used is as simple as changing the spider. AC makes a Hyper-C (58mm/94mm) spider that can be purchased separately. The AC crankset can also be purchased with any of these spiders on it.
We found the Adventure Components Mountain cranks had a Bike-Pro Q measurement of 151mm. The AC Mountain arm set comes as right arm with spider, left arm, and five aluminum inner fixing bolt spacers. Chainrings, the outer fixing bolts and nuts, the inner fixing bolts, and crank arm dust caps will be needed separately. They are made in two lengths, 175mm, or 177.5mm and come anodized in Blue, Black, Green, Ti Grey, High Polished (un-anodized), Lavender, Red, Silver (clear). The weight of a 175mm AC Mountain crank arm set is 478.5 grams, the spacers add 3 grams. Made in USA, specify length and color. $ Price in Catalog