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D Company departed Nui Dat at 11:00 on 18 August led by Smith. They were accompanied by a three-man New Zealand artillery forward observer party under Captain Maurice Stanley, making up a 108-man company. Already behind schedule and with B Company having been out for longer than expected, Smith wanted to relieve Ford and then follow the VC tracks to continue the pursuit that afternoon.[74][69] Opting for speed, he adopted single file, with 12 Platoon under Second Lieutenant David Sabben in the lead.[75] Despite the heat the company moved at a fast pace, traversing the low scrub, swamp and paddy fields as they closed in on B Company's position.



At 17:02, Smith reported D Company was running low on ammunition and required aerial resupply. With just three magazines carried by each rifleman, they were only lightly equipped prior to the battle. This was a standard load calculated on 1 RAR usage rates which had been enough during previous actions, but it proved insufficient for sustained fighting. Due to the thick vegetation, the ammunition boxes would need to be dropped through the trees, and intending on moving his headquarters behind a low knoll, Smith nominated a point 400 metres (440 yd) west. This position would afford greater protection, while the helicopters would be less likely to attract ground fire. Yet with their casualties now unable to be moved, D Company would have to remain where it was.[99] Townsend passed the ammunition demand to Headquarters 1 ATF. In response, Jackson requested two UH-1B Iroquois from No. 9 Squadron RAAF to deliver it; however, the senior RAAF officer at Nui Dat, Group Captain Peter Raw, was not prepared to risk aircraft hovering at tree-top height in the heavy rain where they would be exposed to ground fire, citing Department of Air regulations. Relations between the Army and RAAF over the use of the helicopters had become increasingly bitter in the preceding months, and were still tenuous despite recent improvements. Jackson requested American assistance, and when the US Army liaison officer responded more favourably, Raw felt no alternative than to accede to the original request, offering to effect the resupply instead.[107] By coincidence, two RAAF Iroquois were available at Nui Dat, having been used for the concert.[108]

3 Troop continued forward in assault formation, moving deeper into the plantation, with improved visibility allowing them to increase speed.[135] By 18:30. B Company was also drawing near on foot, and observed the VC moving around the western flank, likely to escape the APCs. Shortly after, they were accidentally engaged by the APCs and lost one man wounded.[136] After moving a further 200m, the relief force came out of the tree-line and were confronted by groups of 8 to 10 VC moving east, in total about 100 men, believed to be the lead elements of the force that had just been struck, now withdrawing after abandoning its attempt to outflank D Company. The APCs opened fire, engaging their flank with heavy machine-guns. A number were hit while others turned to engage the APCs as it closed with them. A 57 mm RCL then fired on one of the APCs at close range with the round narrowly missing and blowing apart a tree which fell across the vehicle.[137] The crew commander, Corporal John Carter, engaged the anti-armour team from the top of the APC as they reloaded, but his .50 calibre machine-gun jammed as they fired again, and he killed two of them with his Owen gun from just 15 to 20 metres (16 to 22 yd). The second RCL round subsequently detonated against the fallen tree, saving both the vehicle and its occupants. Despite being dazed, Carter killed three more VC soldiers as he scrambled back into the carrier, which was now without communications following the destruction of its aerial. By drawing further fire he allowed the remainder of the troop to advance.[138][139]

Is it time to upgrade or replace your rear derailleur? Do you sit awake at night worrying about what \u2018tooth capacity\u2019 is? Or have you ever simply wanted to know absolutely everything there is to know about buying a rear derailleur or thought which rear derailleur do I need? If so, you\u2019ve come to the right place.\nWhile we certainly don\u2019t recommend you break out this hot derailleur chat at your next social appointment, this is undoubtedly useful information if you\u2019re looking to buy or upgrade a rear derailleur.\nWe must stress that this article only covers rear derailleurs because including front derailleurs would make this guide far too unwieldy. Otherwise, here\u2019s everything you need to know about the rear derailleur.\n\n \nRelated reading\nRoad bike groupsets: everything you need to know\nMountain bike groupsets: everything you need to know\nBest road bikes: how to choose the right one for you\nBest mountain bike: how to choose the right one for you\n\n\n \n Which brand of derailleur should I buy?\n\n \n \n \n \n \n\n \n Dura-Ace 9100 is Shimano\u2019s top-flight road groupset.\u00a0\n \n Matthew Loveridge \/ Immediate Media\n \n\n\n \n \n \n\n \n Red eTap AXS takes SRAM\u2019s top-slot on the road.\u00a0\n \n Tom Wragg\n \n\n\n \n \n \n\n \n And, finally, Record EPS 12 is Campagnolo\u2019s premium road groupset.\u00a0\n \n Immediate Media\n \n\n\n \n \n\n\n\nWhich rear derailleur do I need? Shimano, SRAM and Campagnolo are the three main players in the drivetrain market. \nMicroshift, Box, Rotor, FSA and others all also make groupset components, but it would be beyond the scope of this article to cover all of these.\u00a0\nAs a general rule of thumb, it\u2019s best not to mix and match drivetrain components from different brands. While things such as cranks, chains and cassettes are mostly inter-compatible between brands, generally speaking, shifters and derailleurs aren\u2019t.\nIn brief, Shimano, SRAM and Campagnolo all use different cable pull ratios (the amount that a derailleur moves for every millimetre of cable pulled through by the shifter), and mixing parts will result in very poor shifting.\u00a0\n\n Generally speaking, road and mountain bike groupset components will not work with each other. Various\nHowever, it\u2019s more complicated than that. Mountain bike groupsets and road groupsets, even when they\u2019re from the same brand, typically use different cable pull ratios.\n Ratios may also change as the number of gears changes, and there may even be pull ratio differences between different generations of the same gear model.\u00a0\nThere are, of course, exceptions, and there are lots of bodged, Sramshimpagnolo mashups that can be cajoled into working, but for the sake of simplicity, we suggest you stick to the same brand as your shifters when buying a rear derailleur.\nHow many gears does my bike have?\n\n To work out how many \u2018gears\u2019 your bike has, count the number of sprockets on your cassette. Jack Luke \/ Immediate Media\nOnce you\u2019ve settled on the brand, you must now determine the number of gears that your groupset has.\nIf you are replacing an existing derailleur on a bike, simply count the number of cogs on your cassette and you\u2019re good to go.\nIf your drivetrain\u2019s speed is an unknown quantity, you can count the number of steps that your shifter runs through and add \u2018one\u2019 to determine the number of gears your drivetrain has.\nHow to replace a bike cassette\nDerailleur compatibility explained\n\n Compatability across Shimano\u2019s road and mountain bike groupsets is a little bit complicated. Steve Behr \/ Immediate Media\nAs a general rule of thumb, you shouldn\u2019t mix and match groupset parts of different generations or mix mountain bike and road components, but there are a few exceptions. Below, we have broken down compatibility by manufacturer.\nFor clarity, the following information is applicable to both derailleurs and shifters.\nShimano derailleur compatibility\nMost 8- and 9-speed Shimano mountain bike and road kit is inter-compatible because they both use the same cable pull ratio. This means that you can use an 8 -or 9-speed mountain bike derailleur with road shifters or vice versa.\u00a0\nThe only exception is pre-1997 9-speed Dura-Ace gearing, which won\u2019t play nicely with anything because it uses a totally different cable pull ratio.\u00a0\nAlthough it initially doesn\u2019t appear to be the case, the situation is a bit more clear with the newest generation of both Shimano road and mountain bike components. Bear with us\u2026\n\n \nShimano road bike derailleur compatibility\nAll 11-speed Shimano road components are inter-compatible \u2013 you could for example use a Dura-Ace 9100 derailleur with a pair of 105 7000 shifters\nShimano\u2019s 11-speed GRX gravel groupsets are also cross-compatible\nAll 10-speed road components (except Tiagra 4700 and 10-speed GRX gravel, see below) are inter-compatible \u2013 you could for example use an old Ultegra 6700 derailleur with old 105 5700 shifters\nCurrent 9-speed road components are backwards compatible with older 9-speed road and mountain bike components, excluding the aforementioned exception\n\n\n \n The only exceptions to the above rules are Tiagra 4700 (and the associated RS405 hydraulic shifters) and GRX400 gravel mechs, which use the same cable pull ratio as current generation 11-speed road kit.\u00a0\nThis means you could, for example, use an 11-speed derailleur with 10-speed Tiagra 4700 shifters.\n\n \nShimano mountain bike derailleur compatibility\nAll 12-speed Shimano mountain bike components are inter-compatible \u2013 you could for example use an SLX M7120 derailleur with an XTR M9100 trigger shifter\nAll 11-speed Shimano mountain bike components are inter-compatible \u2013 you could, for example, use a XTR M9000 derailleur with a pair of SLX M7000 shifters\nAll 10-speed Shimano mountain bike components are also inter-compatible \u2013 you could, for example, use an old 10-speed XTR M986 rear derailleur with new Deore M610 shifters\nCurrent 9-speed Shimano mountain bike components are compatible with older 9-speed road and mountain bike components, excluding the aforementioned exception\n\n\n \n Just for clarity, current generation (10-, 11- and 12-speed) Shimano road and mountain bike components are not inter-compatible with each other because they use different cable pull ratios. For example, you couldn\u2019t use a set of road shifters with a mountain bike rear derailleur.\nIt bears mentioning that cable pull converters from brands such as JTek, and Lindarets\/Wolf Tooth Components do exist and will allow you to mess about with your drivetrain configuration to your heart\u2019s content.\nSRAM derailleur compatibility\n\n SRAM\u2019s latest 12-speed GX mountain bike rear derailleur. Russell Burton \/ MBUK magazine\nThe situation is a little more clear with SRAM and we\u2019ve summarised the main points below.\n\n \nSRAM road and mountain bike rear derailleur\u00a0 compatibility\u00a0\n7-, 8- and 9-speed SRAM components are all inter-compatible, regardless of whether they are road or mountain bike parts\n10-speed SRAM components are inter-compatible, regardless of whether they are road or mountain bike parts \u2013 for example you could run road shifters with a mountain bike rear derailleur\n10- and 11-speed SRAM mountain bike components are not inter-compatible\n10- and 11-speed SRAM road components are inter-compatible \u2013 meaning you could run a 10-speed SRAM Red rear derailleur with a pair of SRAM 22 shifters\n12-speed SRAM components are not backwards compatible with 11-speed. The exception is eTap batteries, which work with all 12-speed AXS and 11-speed components\n\n\n \n SRAM has also been at the forefront of the push to ever-wider gear ranges and its newer rear derailleurs are designed to handle wider range cassettes. So it\u2019s important to consider whether a replacement mech can handle all the cassette sprocket sizes that you might want to run.\nFor clarity, despite visual similarities, SRAM\u2019s Force 1 11-speed groupsets are not compatible with 11-speed mountain bike components because they each use different cable pull ratios (though it will work with 10-speed road shifters).\nCampagnolo derailleur compatibility\n\n Campagnolo\u2019s entry-level Centaur groupset. Russell Burton \/ Immediate Media\nIn un-typically Campagnolo fashion, cross-compatibility between different generations of groupsets is fairly easy to understand because there are no mountain bike groupsets (yes, we know it made Euclid and a host of other off-road bits way back) to contend with.\u00a0\nBut as is typical of Campag, there\u2019s the odd flourish of awkwardness.\n\n \nCampagnolo rear derailleur compatibility\u00a0\nAll 8- and 9-speed Campagnolo groupsets before mid-2001 used the same pull ratio and are compatible with each other. This generation of parts is often referred to as \u2018Campy old\u2019\nAfter mid-2001, Campagnolo started using a revised pull ratio for its newer 9-speed kit, and these and all 10-speed (and 11-speed) groupsets from this period are inter-compatible \u2013 for example, you could run an Athena derailleur with Record shifters\n\n\n \n \n Campagnolo has introduced many changes to its groupsets, resulting in reduced compatibility between generations. So boxed letters (indicating the ranges) will aid you in identifying if your parts are compatible. Campagnolo\nBut now things get more complicated (or simple, depending on which way you look at it) with slight tweaks to all of Campagnolo\u2019s groupsets resulting in reduced inter-compatibility between groupsets.\nIn short, these changes have affected most of its drivetrain parts (different width bottom bracket cups result in altered chainlines, different cable pull ratios, and so on) and compatible parts are marked by a letter surrounded by a square box \u2013 simply put, if all of your components have the same stamped letter on them, they\u2019ll work together. \nCampagnolo provides a much more thorough description of the changes here and we highly recommend you read through this guide carefully before committing to any new parts from the Italian marque.\nThere are also differences in the pull ratios used between different groupsets: the Ergopower shifters used by mechanical Super Record, Record and Chorus 11-speed are not compatible with Potenza, which itself is incompatible with both Ergopower and Centaur Power-Shift systems.\nElectronic groupset compatibility\n\n They certainly aren\u2019t the norm, but electronic groupsets are getting more popular each year. Jack Luke \/ Immediate Media\nIf your bike has an electronic groupset, or if you\u2019re thinking about upgrading to electronic shifting, you\u2019ll need to keep within one brand because the makers\u2019 groupsets use different systems.\u00a0\nApart from first-generation Dura-Ace Di2, which uses a different wiring harness, newer Shimano electronic groupsets \u2013 both road, MTB and GRX \u2013 have inter-compatible wiring and electronics. \nSo, if you smash up your \u00a3550 Dura-Ace Di2 R9150 rear mech (ouch), you can replace it with a \u00a3250 Ultegra Di2 R8050 derailleur. Note that while the mechs will work, chainlines do differ between GRX, Shimano\u2019s road groupsets and its mountain bike groupsets.\u00a0\nSRAM\u2019s latest 12-speed eTap AXS road and MTB groupsets can be used together, setting up the option for \u2018mullet builds\u2019, which pairs up road shifters with an Eagle AXS rear mech and a 10-50 cassette, for an ultra-wide gravel bike build.\u00a0\nThat was great until SRAM introduced its Force AXS Wide groupset. Bridging the gap between road-going AXS groupsets and mullet builds, it offers a lower bottom gear for road and a good range for gravel riding with cassettes up to 36 teeth, but does this by altering the drivetrain alignment.\u00a0\nThis means there\u2019s a new rear mech designed to handle 10-36-tooth cassettes. The original eTap AXS Red and Force rear mechs are only rated up to 33-tooth cassettes. The older 11-speed Red eTap shifters and rear mech aren\u2019t compatible with 12-speed eTap AXS.\n\n Campagnolo\u2019s Super Record EPS electronic groupset is now onto its fourth generation. Matthew Loveridge \/ Immediate Media\nCampagnolo\u2019s Super Record EPS electronic groupset is on version four now and has gone 12-speed. Again, it\u2019s a system unto itself, with its own electronics to communicate between the shifters and the rear mech. \nPlus, parts for the disc brake and rim brake systems don\u2019t work together properly. There\u2019s also no backward compatibility with older 11-speed EPS or forward compatibility to upgrade from 11-speed to 12-speed.\nThe good news is that there\u2019s some reverse compatibility between version three 11-speed EPS components and older generations.\nWhat cage length derailleur should I buy?\nNow that we\u2019ve determined the speed, brand and compatibility of your derailleur, you must now determine the cage length that your drivetrain requires: long, short or medium cage.\nThe length of your derailleur\u2019s cage defines the range, or spread, of gears you can have on your bike \u2013 the longer the cage, the more slack in the chain the derailleur can take up.\nFor the sake of simplicity, we have included a quick guide below, but if you\u2019re in any doubt read on to see how we come to these conclusions.\nDerailleur cage length quick guide\nThere are two common situations where there may be a large range, or spread, of gears on your bike; when using a super-wide range cassette (e.g. 10-42t or larger) or when there is a large difference between chainring sizes (e.g. when using a triple chainset). In these circumstances, you will require a long cage derailleur.\nIf you are running a 1x drivetrain with a regular-sized cassette (i.e. 11-36t or smaller) or some 2x mountain bike drivetrains with a similarly sized cassette, you may want to use a medium cage derailleur.\nIf you have a traditional road double-drivetrain with a regular cassette (i.e. 11-28t or smaller), you can use a short cage derailleur.\u00a0\n\n Downhill-specific groupsets use exceptionally short derailleur cages. Alex Evans\nSome downhill-specific drivetrains also use short cage derailleurs (e.g. Shimano, Saint and SRAM X01 DH).\u00a0\nYou will notice that there are lots of ifs and buts in this guide and that\u2019s because there are too many variables to give a conclusive answer in any situation.\nDerailleur tooth capacity explained\nTo get a definitive answer, you must refer to the \u2018tooth capacity\u2019 of your derailleur. You can work out the required tooth capacity of your bike by calculating the following:\n\n \nHow to calculate tooth capacity\n(largest cog \u2013 smallest cog) \uff0b (largest chainring \u2013 smallest chainring) = Required capacity\nSo, for a modern, double chainring road bike drivetrain we would have something like:\n(32 \u2013 11) \uff0b (52 \u2013 36) = 37t capacity\u00a0\nFor the sake of example, let\u2019s assume you are looking at a Shimano road derailleur here.\nThe total capacity of a SS (short cage) Shimano derailleur is 35t and 39t for a GS (medium cage) derailleur. As such, in this circumstance, you would require a medium cage derailleur.\u00a0\n\n\n \n It bears mentioning that the quoted capacity of derailleurs tends to be pretty conservative and, in practical terms, you could almost certainly get away with using a short length cage derailleur in this circumstance, so long as you avoided extreme (e.g. big and big) gear combinations.\nClutch derailleurs explained\n\n Clutch-equipped rear derailleurs were once the sole preserve of mountain bike offerings, but are now seen on both gravel and road groupsets from Shimano and SRAM. Matthew Loveridge \/ Immediate


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