Shimano has launched its new road pedal and cleat system, SPD-SLR. The system offers lower weight, lower pedal/cleat stack height, easier engagement and added lateral adjustability relative to the long-running SPD-SL system.The new pedals will be available at Dura-Ace and Ultegra spec levels, and there are new red, blue and yellow cleats with similar degrees of float to the current ones, although the new cleats arent compatible with SPD-SL pedals.There are new shoes at the S-Phyre RC9 and RC8 spec levels, designed to complement the new pedals and cleats. Shimano states SPD-SLR pedals are compatible with its current SPD-SL road cycling shoe range, although it says its new shoes will help realise the full performance benefits of the new system. Shimano says maximum gains come from its new pedals, cleats and shoes working as a system. Theres also a new grey cleat, which is claimed to be compatible with most non-Shimano SPD-SL shoes and offers the same float as the yellow cleat, although without the reduced stack height of the other new cleats.Shimano says the new SPD-SLR system lowers the stack height for the pedals plus cleats by 2.3mm. It also enables easier clipping in with a wider catch area for the cleat and a reduced engagement angle of 10.5o versus 15.5o for SPD-SL. The lower stack height is claimed to increase foot stability, and improve power transfer and control of the bike. Shimano's new SPD-SLR cleats have a different shape from its previous cleats and greater lateral adjustment. Along with the redesigned pedals, the new cleats have a different shape. Theyre lighter because they fix to the base of the shoes without the washers that were needed with SPD-SL. Shimano claims the weight of the cleat plus hardware has been reduced from 71g to 55g. It has added extra markings to help you align the cleats more easily.The 6o of float for the yellow cleats, 2o for the blue cleats and zero for the red cleats is the same as for the SPD-SL cleats. The new cleats offer greater side-to-side adjustability though, so it's easier to alter your stance width. They can also be used with cleat spacers. The new Dura-Ace and Ultegra pedals are superficially similar to their predecessors, but Shimano says they offer a lower engagement angle and easier catchment. As with the SPD-SL system pedals, the new Dura-Ace PD-R9300 pedals have their inner bearing positioned to the side of the pedals top surface, while the Ultegra PD-R8200 pedals have it placed under the pedal platform.This slightly raises the stack height above the pedal axis for Ultegra, to 13.3mm, and reduces pedal stiffness by 11%, Shimano claims. Dura-Aces fancier bearings are also claimed to reduce rotational resistance for the new Dura-Ace pedals by 53% relative to the new Ultegra pedals.Both pedals are made of injection-moulded carbon composite and include steel contact surfaces to reduce pedal wear, as with Shimano's older SPD-SL pedals. The new Dura-Ace pedals weigh a claimed 227g a set and the Ultegra pedals 1g more.Old SPD-SL Dura-Ace and Ultegra pedals were available in two spindle lengths, and the same 4mm-longer option will be available with the new pedals.New shoes to match Shimano has also refreshed its S-Phyre shoes. Along with the new pedals and cleats, Shimano has launched updated shoes. It says the new SH-RC901 S-Phyre shoes are lighter than their predecessors and provide greater cleat adjustability. They have a new Dynalast 2.0 fit that's claimed to reduce foot fatigue.In addition, theres a carbon fibre heel cup for increased foot stability and a new upper design, closed by two Boa Li2 dials, that is claimed to wrap more closely round the foot, increase stability, and improve fit and pedalling efficiency. Theres increased ventilation too. The RC8 shoes have also had an update. Similar features are carried over into the lower-priced SH-RC810 shoes, which also include two Boa Li2 dials and share the new Dynalast 2.0 fit. Shimano points to the hollow-channel carbon sole, which aids ventilation and helps drain water from the shoes in the rain.What are the low-stack-height alternatives?Its not only Shimano that has persisted with a similar pedal design for years, but recently two new pedal systems have stirred up what has been one of the least progressive aspects of bike design. Here are three low-stack alternatives.Wahoo Speedplay Wahoo Speedplay's stack height can be as low as 8mm with the right shoes. Ashley Quinlan / Our Media Among established brands, Wahoo Speedplay offers the lowest stack height of 8.5mm for a shoe with four bolt drillings, but three-bolt shoes require an adapter plate between the shoe and the Speedplay cleat, increasing the stack height to 11mm.Shimano hasnt provided a stack height for SPD-SLR, but based on the 14.6mm stack height for old Dura-Ace pedals, the claimed 2.3mm reduction would bring this down to 12.3mm still higher than Speedplay, even with an adapter plate.Ekoi PW8 Ekoi's pedals are very light because there are no moving parts, but require a shoe with a compatible sole. Warren Rossiter / OurMedia Ekois PW8 pedal system has a much larger shoe contact area than competitors and the pedals weigh only 105g each, because they have no moving parts, just a replaceable tongue at the rear that engages with the shoes cleat.The system requires a specific Ekoi shoe though, which incorporates the anchor points for the pedals. The cleats come in front and rear parts that bolt to these, resulting in an 8mm stack height.When Warren tested the system, he was won over by the stability of the large platform and ease of clipping in and out. He was less enamoured of the Ekoi PW8 C12 shoes, though or at least their elevated price. Theyre comfortable and fit well, although their weight isnt market-leading at their price.There are cheaper alternatives available from Ekoi now though and, as is typical of the brand, all PW8-compatible shoes are heavily discounted on its site.Q36.5/SRM Q36.5 claims its system increases pedalling efficiency, but it costs 1,000. Q36.5 Q36.5 collaborated with German power meter maker SRM to develop the X-Power Direct pedal system (without a power meter) that it says lowers stack height by over 6mm relative to mainstream systems. It doesnt state an actual stack-height value, but this probably betters Shimanos new SPD-SLR.As with Ekois system, the X-Power Direct pedals only work with specific shoes, in this case Q36.5s Unique Pro 4.0 model.The system is even more expensive than Ekois, with a 500 price tag for the SRM pedals and the same again for the shoes.Why lower stack height? A lower stack height works in opposition to the need to raise the saddle when using shorter cranks. SRAM Q36.5 performed an analysis of the effect of stack height and claims three principal advantages.First, the foot is closer to the centre of pedal rotation, which it claims increases the effective area of force transmission. As with Shimano, it claims this increases foot stability and improves power transfer. It also claims a lower stack height reduces shear forces through the shoes sole.Second, the riders centre of gravity is lower, which enables them to get more aero. This is only going to be by a few millimetres though.Third, Q36.5 suggests, with the trend for shorter cranks, the riders saddle needs to be raised, which in turn raises their centre of gravity. This is counteracted by the lower stack height.It concludes that the further the riders foot is from the centre of force generation, the more shear forces occur, resulting in a greater loss of power. The optimum, it states, would be a pedal system with zero stack or even a -5mm stack.These changes are tiny though and were not convinced they make a significant difference for most riders. Moreover, weve been told by a major pedal brand that its studies dont confirm that small reductions in stack height result in a material increase in pedalling efficiency.