[{"data":1,"prerenderedAt":373},["ShallowReactive",2],{"article-en-torque-arm":3,"articles-en":277},{"id":4,"title":5,"applies_to":6,"author":9,"body":10,"confidence":255,"description":256,"extension":257,"faq":258,"meta":265,"navigation":266,"path":267,"seo":268,"sources":269,"stem":272,"test_bike":273,"topic":274,"updated":275,"__hash__":276},"content_en\u002Fen\u002Fwissen\u002Ftorque-arm.md","Torque Arm: When You Need One",[7,8],"front","rear","fabio-gentsch",{"type":11,"value":12,"toc":244},"minimark",[13,17,22,25,34,38,97,100,104,107,114,118,165,172,176,203,210,214,224,231,235,238],[14,15,16],"p",{},"A torque arm stops the axle of a hub motor from turning in the dropout. With aluminium dropouts and with front motors it is always sensible. Without one, the motor's torque can let the axle walk in the dropout, and that is a real safety risk.",[18,19,21],"h2",{"id":20},"what-the-arm-does","What the arm does",[14,23,24],{},"A hub motor turns the wheel by pushing against the axle. The axle takes the full reaction torque. Normally the flat-milled axle holds in the dropout, but only if the flats fit cleanly and the material is strong enough. The arm takes part of this force through a second fixing on the frame or fork.",[14,26,27,28,33],{},"Hub motor axles are usually 10 mm, sometimes 12 mm thick, and flattened. More on axles is under ",[29,30,32],"a",{"href":31},"\u002Fen\u002Fknowledge\u002Fhub-spacing","hub spacing",".",[18,35,37],{"id":36},"when-it-is-needed","When it is needed",[39,40,41,54],"table",{},[42,43,44],"thead",{},[45,46,47,51],"tr",{},[48,49,50],"th",{},"Situation",[48,52,53],{},"Arm?",[55,56,57,66,73,81,89],"tbody",{},[45,58,59,63],{},[60,61,62],"td",{},"Front motor",[60,64,65],{},"always",[45,67,68,71],{},[60,69,70],{},"Aluminium dropouts",[60,72,65],{},[45,74,75,78],{},[60,76,77],{},"Steel dropouts, rear, weak motor",[60,79,80],{},"recommended",[45,82,83,86],{},[60,84,85],{},"Widened or worn dropouts",[60,87,88],{},"mandatory, or replace the dropout",[45,90,91,94],{},[60,92,93],{},"Mid-drive",[60,95,96],{},"no, different system",[14,98,99],{},"The assessment comes from experience and is an assumption Fabio is still checking.",[18,101,103],{"id":102},"why-the-front-is-especially-touchy","Why the front is especially touchy",[14,105,106],{},"The front fork has open dropouts pointing downwards. If the axle turns and slips out there, the front wheel can drop out. That happens at the handlebars, not the rear, and the consequences are accordingly serious. That is why many dealers add retaining washers on front motors in addition to the arm. Ask whether your kit includes some.",[14,108,109,110,33],{},"On carbon forks or very light aluminium forks a front motor is not recommended anyway, see ",[29,111,113],{"href":112},"\u002Fen\u002Fknowledge\u002Fmotor-types","motor types compared",[18,115,117],{"id":116},"fitting-step-by-step","Fitting step by step",[119,120,121,129,135,141,147,153,159],"ol",{},[122,123,124,128],"li",{},[125,126,127],"strong",{},"Check the axle."," The flats must sit cleanly in the dropouts. Do not widen tight dropouts if you do not know what you are doing.",[122,130,131,134],{},[125,132,133],{},"Choose an arm."," It has to suit axle thickness and frame. Many kits include one, otherwise universal arms exist.",[122,136,137,140],{},[125,138,139],{},"Slide on the arm."," It sits outside or inside the axle depending on the model and is secured with nut and toothed washer.",[122,142,143,146],{},[125,144,145],{},"Fix it to the frame."," With the clamp on the fork or chainstay. It must not touch the brake area or the cables.",[122,148,149,152],{},[125,150,151],{},"Tighten nuts to torque."," With a torque wrench to the manufacturer's value. Check the figure in the kit's manual.",[122,154,155,158],{},[125,156,157],{},"Route the cable cleanly."," The motor cable must not be under tension or chafe on the arm.",[122,160,161,164],{},[125,162,163],{},"Test ride and recheck."," After the first kilometres, retighten all bolts.",[14,166,167,168,33],{},"Which tools you need for this are under ",[29,169,171],{"href":170},"\u002Fen\u002Fknowledge\u002Ftools","tools",[18,173,175],{"id":174},"risks-and-typical-mistakes","Risks and typical mistakes",[177,178,179,185,191,197],"ul",{},[122,180,181,184],{},[125,182,183],{},"Nuts too loose:"," The axle walks. A drop of thread locker helps if the manufacturer allows it.",[122,186,187,190],{},[125,188,189],{},"Clamp too tight:"," It can dent an aluminium tube. Tighten with feel.",[122,192,193,196],{},[125,194,195],{},"Arm in the wrong place:"," It has to catch the direction of rotation, not just sit there.",[122,198,199,202],{},[125,200,201],{},"Worn-out dropouts:"," Replace the frame or fork if they are widened.",[14,204,205,206,33],{},"A turned axle is among the common problems, see ",[29,207,209],{"href":208},"\u002Fen\u002Fknowledge\u002Fcommon-problems","common problems",[18,211,213],{"id":212},"if-it-does-not-fit","If it does not fit",[14,215,216,217,223],{},"If you cannot find an arm that suits your bike, or the dropouts are too soft, that is a reason to move to a mid-drive or to leave the conversion. Honestly: an arm is no stopgap for an unsuitable bike. That workshops refuse conversions often has to do with exactly these questions (",[29,218,222],{"href":219,"rel":220},"https:\u002F\u002Ffahrrad-xxl.at\u002Fblog\u002Fe-bike-umbausatz",[221],"nofollow","Fahrrad XXL",").",[14,225,226,227,33],{},"You find the whole process in the ",[29,228,230],{"href":229},"\u002Fen\u002Fknowledge\u002Fconvert-bike-to-ebike","conversion overview",[18,232,234],{"id":233},"how-reliable-is-this","How reliable is this?",[14,236,237],{},"Statements on hub motor standards partly come from the source named; the rule on torque arms with aluminium dropouts and front motors, the fitting advice and the risks are experience or assumptions that Fabio is still checking.",[14,239,240],{},[29,241,243],{"href":242},"\u002Fen\u002Fconfigurator","Does a conversion fit your bike?",{"title":245,"searchDepth":246,"depth":246,"links":247},"",2,[248,249,250,251,252,253,254],{"id":20,"depth":246,"text":21},{"id":36,"depth":246,"text":37},{"id":102,"depth":246,"text":103},{"id":116,"depth":246,"text":117},{"id":174,"depth":246,"text":175},{"id":212,"depth":246,"text":213},{"id":233,"depth":246,"text":234},"assumption","Why the axle of a hub motor turns in the dropout, when you need a torque arm and how to fit it.","md",[259,262],{"q":260,"a":261},"Do I need a torque arm?","Always with front motors and with aluminium dropouts. With sturdy steel dropouts and low power you may get away without, but with an arm you are on the safe side.",{"q":263,"a":264},"What happens without one?","The axle can turn in the dropout, widen it and in the worst case let the wheel come loose or tear off the cable.",{},true,"\u002Fen\u002Fwissen\u002Ftorque-arm",{"title":5,"description":256},[270],{"title":271,"url":219},"Fahrrad XXL: e-bike conversion kit (German)","en\u002Fwissen\u002Ftorque-arm",null,"drehmomentstuetze","2026-11-09","QCZWsn0gmgg-pVihszJj4S7M-UPW6KoF2rDq32d3vjU",[278,285,291,297,303,309,315,321,327,333,340,346,352,359,365,367],{"path":279,"title":280,"description":281,"topic":282,"applies_to":283,"confidence":255,"updated":275,"author":9},"\u002Fen\u002Fwissen\u002Fbattery","E-Bike Battery for a Conversion: Position, Space, Range","Where the battery fits on a converted bike, how to measure the space, what branded cells bring, real-world range and how to dispose of it.","akku",[284],"all",{"path":286,"title":287,"description":288,"topic":289,"applies_to":290,"confidence":255,"updated":275,"author":9},"\u002Fen\u002Fwissen\u002Fbrakes","Brakes for an E-Bike Conversion: What You Need","Rim or disc, cut-off levers and sensors: which brakes are enough for a 250 W pedelec and when an upgrade is needed.","bremsen",[284],{"path":292,"title":293,"description":294,"topic":295,"applies_to":296,"confidence":255,"updated":275,"author":9},"\u002Fen\u002Fwissen\u002Fcoaster-brake","Coaster Brake and E-Bike Conversion: What Works","A coaster brake is the most common deal-breaker. Which motors work, where coaster-brake variants exist and when to leave it.","ruecktrittbremse",[284],{"path":298,"title":299,"description":300,"topic":301,"applies_to":302,"confidence":255,"updated":275,"author":9},"\u002Fen\u002Fwissen\u002Fcommon-problems","Common Problems After an E-Bike Conversion","Axle spinning, broken spokes, motor cutting out, jerky starts, fast chain wear: causes and fixes from everyday conversions.","haeufige-probleme",[284],{"path":304,"title":305,"description":306,"topic":307,"applies_to":308,"confidence":255,"updated":275,"author":9},"\u002Fen\u002Fwissen\u002Fconvert-bike-to-ebike","Convert a Bike to an E-Bike: Overview and Steps","What a conversion costs, which motor fits, what the law says and when you should buy a used e-bike instead. An honest overview from the workshop.","fahrrad-zum-e-bike-umbauen",[284],{"path":310,"title":311,"description":312,"topic":313,"applies_to":314,"confidence":255,"updated":275,"author":9},"\u002Fen\u002Fwissen\u002Fcosts","What Does an E-Bike Conversion Really Cost?","Cost items at a glance: kit EUR 400 to 1,700, brakes, tools, small parts. Plus the comparison with used and new (about EUR 2,500) and the cost calculator.","kosten",[284],{"path":316,"title":317,"description":318,"topic":319,"applies_to":320,"confidence":255,"updated":275,"author":9},"\u002Fen\u002Fwissen\u002Fframe-and-weight","Frame and Weight: Which Bike Suits a Conversion","Steel and aluminium are usually fine, carbon is not. Plus the magnet test, total weight, warranty and the wear parts to replace before converting.","rahmen-und-gewicht",[284],{"path":322,"title":323,"description":324,"topic":325,"applies_to":326,"confidence":255,"updated":275,"author":9},"\u002Fen\u002Fwissen\u002Fglossary","E-Bike Conversion Glossary: Terms Explained","Rated power, volts, watt-hours, newton metres, PAS, torque sensor, Higo and Julet, controller and display: the glossary for e-bike conversions.","begriffe",[284],{"path":328,"title":329,"description":330,"topic":331,"applies_to":332,"confidence":255,"updated":275,"author":9},"\u002Fen\u002Fwissen\u002Fhub-spacing","Hub Spacing and Axles for an E-Bike Conversion","How to measure hub spacing, quick release versus thru-axle, spreading 130 to 135 mm on steel frames and what to watch with dropouts.","einbaubreite",[7,8],{"path":334,"title":335,"description":336,"topic":337,"applies_to":338,"confidence":255,"updated":275,"author":9},"\u002Fen\u002Fwissen\u002Fmeasure-bottom-bracket","Measure Your Bottom Bracket for a Mid-Drive","How to measure shell width and bore of your bottom bracket and tell BSA 68\u002F73, Pressfit and BB30 apart. Step by step for a mid-drive motor.","tretlager-messen",[339],"mid",{"path":341,"title":342,"description":343,"topic":344,"applies_to":345,"confidence":255,"updated":275,"author":9},"\u002Fen\u002Fwissen\u002Fmid-drive-vs-hub-motor","Mid-Drive or Hub Motor: What Suits You?","Ride feel, hills, gears, installation and cost compared, with a clear guide to when a mid-drive and when a front or rear hub motor makes sense.","mittelmotor-oder-nabenmotor",[339,7,8],{"path":347,"title":348,"description":349,"topic":350,"applies_to":351,"confidence":255,"updated":275,"author":9},"\u002Fen\u002Fwissen\u002Fmotor-types","E-Bike Conversion Motor Types Compared","Front, rear and mid-drive motors, friction rollers and seat-tube motors compared: feel, installation, cost and which bikes suit which.","motorarten",[284],{"path":353,"title":354,"description":355,"topic":356,"applies_to":357,"confidence":358,"updated":275,"author":9},"\u002Fen\u002Fwissen\u002Fpedelec-law","Pedelec Law: 250 W, 25 km\u002Fh and Walking Assist","What a conversion may do legally: 250 W rated power, assist only while pedalling up to 25 km\u002Fh, walking assist up to 6 km\u002Fh and what lies beyond.","pedelec-recht",[284],"source",{"path":360,"title":361,"description":362,"topic":363,"applies_to":364,"confidence":255,"updated":275,"author":9},"\u002Fen\u002Fwissen\u002Ftools","Tools for an E-Bike Conversion: The List","Which tools you need for front, rear and mid-drive conversions and what kits usually lack, above all the lockring tool.","werkzeug",[284],{"path":267,"title":5,"description":256,"topic":274,"applies_to":366,"confidence":255,"updated":275,"author":9},[7,8],{"path":368,"title":369,"description":370,"topic":371,"applies_to":372,"confidence":255,"updated":275,"author":9},"\u002Fen\u002Fwissen\u002Fwheel-sizes","Wheel Sizes and ETRTO for E-Bike Conversions","Inches are unreliable, ETRTO is not: how to read wheel size off the tyre and avoid the 635\u002F622 and 406\u002F451 traps.","laufradgroessen",[7,8],1794247507198]