[{"data":1,"prerenderedAt":408},["ShallowReactive",2],{"article-en-wheel-sizes":3,"articles-en":312},{"id":4,"title":5,"applies_to":6,"author":9,"body":10,"confidence":289,"description":290,"extension":291,"faq":292,"meta":299,"navigation":300,"path":301,"seo":302,"sources":303,"stem":307,"test_bike":308,"topic":309,"updated":310,"__hash__":311},"content_en\u002Fen\u002Fwissen\u002Fwheel-sizes.md","Wheel Sizes and ETRTO for E-Bike Conversions",[7,8],"front","rear","fabio-gentsch",{"type":11,"value":12,"toc":278},"minimark",[13,17,22,34,37,41,161,164,168,174,180,186,190,234,238,246,249,253,265,269,272],[14,15,16],"p",{},"When you buy a motor wheel, what counts is not the inch size but the ETRTO number on the tyre. The second number, for example the 622 in 40-622, is the rim diameter in millimetres. Inch names such as \"28 inch\" are ambiguous and often lead to wrong purchases on conversions.",[18,19,21],"h2",{"id":20},"how-to-read-the-size","How to read the size",[14,23,24,25,29,30,33],{},"On the tyre sidewall there is a marking such as ",[26,27,28],"strong",{},"40-622"," or ",[26,31,32],{},"37-622",". The first number is the tyre width in millimetres, the second the rim diameter. Next to it you usually find inch figures like 28 × 1.60, which help you little. Note the ETRTO number and match it against the motor.",[14,35,36],{},"You can also measure the rim itself: determine the inner diameter at the rim shoulder with a tape measure, but that is less accurate. The tyre marking is more reliable.",[18,38,40],{"id":39},"the-table","The table",[42,43,44,63],"table",{},[45,46,47],"thead",{},[48,49,50,54,57,60],"tr",{},[51,52,53],"th",{},"ETRTO",[51,55,56],{},"Name",[51,58,59],{},"Typical bikes",[51,61,62],{},"Trap",[64,65,66,81,95,108,121,134,148],"tbody",{},[48,67,68,72,75,78],{},[69,70,71],"td",{},"622",[69,73,74],{},"28\", 29\", 700C",[69,76,77],{},"trekking, city, road, 29er MTB",[69,79,80],{},"28\" and 29\" are the same rim",[48,82,83,86,89,92],{},[69,84,85],{},"635",[69,87,88],{},"28\" × 1 ½ (old)",[69,90,91],{},"old Dutch-style bikes",[69,93,94],{},"does not fit 622 kits although both are called \"28\"",[48,96,97,100,103,106],{},[69,98,99],{},"584",[69,101,102],{},"27.5\", 650B",[69,104,105],{},"MTB, gravel",[69,107],{},[48,109,110,113,116,119],{},[69,111,112],{},"559",[69,114,115],{},"26\"",[69,117,118],{},"older MTB, touring bikes",[69,120],{},[48,122,123,126,129,132],{},[69,124,125],{},"507",[69,127,128],{},"24\"",[69,130,131],{},"kids' and youth bikes",[69,133],{},[48,135,136,139,142,145],{},[69,137,138],{},"406",[69,140,141],{},"20\"",[69,143,144],{},"folding bikes, cargo bikes",[69,146,147],{},"do not confuse with 451",[48,149,150,153,156,159],{},[69,151,152],{},"451",[69,154,155],{},"20\" (narrow)",[69,157,158],{},"some folding bikes, BMX race",[69,160],{},[14,162,163],{},"The table is a compilation from our knowledge base. The statement on 635 versus 622 is an assumption that Fabio is still checking.",[18,165,167],{"id":166},"the-traps","The traps",[14,169,170,173],{},[26,171,172],{},"28 inch is not always 28 inch."," Modern trekking and city bikes have 622 mm. Old Dutch-style bikes marked \"28 × 1 ½\" often have 635 mm. Both are called 28 inch, but a kit fits only the right size. So always check the second ETRTO number.",[14,175,176,179],{},[26,177,178],{},"20 inch comes in two sizes."," 406 is the usual 20-inch wheel, 451 the narrow variant. A folding bike kit for 406 does not fit 451. On folding bikes a second look pays off, because both sizes occur.",[14,181,182,185],{},[26,183,184],{},"26, 27.5 and 29 inch:"," 26\" is 559, 27.5\" is 584, 29\" is 622. A mountain bike with \"29 inch\" has the same rim as a trekking bike with \"28 inch\".",[18,187,189],{"id":188},"what-to-check-when-buying","What to check when buying",[191,192,193,200,206,218,228],"ol",{},[194,195,196,199],"li",{},[26,197,198],{},"Read the ETRTO number"," off the tyre.",[194,201,202,205],{},[26,203,204],{},"Order motor and wheel to match"," the ETRTO. Many dealers sell kits as a ready-built wheel, others only the hub for lacing.",[194,207,208,211,212,217],{},[26,209,210],{},"Cross-check spacing and axle",", see ",[213,214,216],"a",{"href":215},"\u002Fen\u002Fknowledge\u002Fhub-spacing","hub spacing",".",[194,219,220,223,224,217],{},[26,221,222],{},"Brake type:"," rim brake or disc? The braking surface must fit, see ",[213,225,227],{"href":226},"\u002Fen\u002Fknowledge\u002Fbrakes","brakes",[194,229,230,233],{},[26,231,232],{},"Tyre width:"," The new tyre must fit in fork and rear triangle.",[18,235,237],{"id":236},"hub-rim-spokes","Hub, rim, spokes",[14,239,240,241,245],{},"Lacing creates a new wheel. Thin spokes and motor weight are a common cause of broken spokes, see ",[213,242,244],{"href":243},"\u002Fen\u002Fknowledge\u002Fcommon-problems","common problems",". If in doubt, let a workshop that does it regularly handle the lacing.",[14,247,248],{},"With kits that come with a ready-laced wheel you have to trust that the dealer used a suitable rim. Check the ETRTO in the product description and ask if unsure.",[18,250,252],{"id":251},"what-this-means-for-motor-types","What this means for motor types",[14,254,255,256,260,261,217],{},"Front and rear hub motors need the right ETRTO size, while the mid-drive does not depend on it. If your bike has an unusual size, a mid-drive is often the more relaxed solution, see ",[213,257,259],{"href":258},"\u002Fen\u002Fknowledge\u002Fmotor-types","motor types compared"," and ",[213,262,264],{"href":263},"\u002Fen\u002Fknowledge\u002Fmeasure-bottom-bracket","measure your bottom bracket",[18,266,268],{"id":267},"how-reliable-is-this","How reliable is this?",[14,270,271],{},"The ETRTO numbers and names are standard values; the statements on fit and traps (especially 635 versus 622) are based on experience. Fabio is still checking the table.",[14,273,274],{},[213,275,277],{"href":276},"\u002Fen\u002Fconfigurator","Does a conversion fit your bike?",{"title":279,"searchDepth":280,"depth":280,"links":281},"",2,[282,283,284,285,286,287,288],{"id":20,"depth":280,"text":21},{"id":39,"depth":280,"text":40},{"id":166,"depth":280,"text":167},{"id":188,"depth":280,"text":189},{"id":236,"depth":280,"text":237},{"id":251,"depth":280,"text":252},{"id":267,"depth":280,"text":268},"assumption","Inches are unreliable, ETRTO is not: how to read wheel size off the tyre and avoid the 635\u002F622 and 406\u002F451 traps.","md",[293,296],{"q":294,"a":295},"Where do I find the ETRTO marking?","On the tyre sidewall, for example 40-622. The second number is the rim diameter in millimetres.",{"q":297,"a":298},"Are 28 inch and 29 inch the same rim?","Yes, both have a 622 mm rim diameter. 700C is the same size too.",{},true,"\u002Fen\u002Fwissen\u002Fwheel-sizes",{"title":5,"description":290},[304],{"title":305,"url":306},"Fahrrad XXL: e-bike conversion kit (German)","https:\u002F\u002Ffahrrad-xxl.at\u002Fblog\u002Fe-bike-umbausatz","en\u002Fwissen\u002Fwheel-sizes",null,"laufradgroessen","2026-11-09","hJ1lMiQvrVbQQJPW5AHjo0NxtuOBUOdQ2ukTxRFYqw4",[313,320,326,332,338,344,350,356,362,368,375,381,387,394,400,406],{"path":314,"title":315,"description":316,"topic":317,"applies_to":318,"confidence":289,"updated":310,"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",[319],"all",{"path":321,"title":322,"description":323,"topic":324,"applies_to":325,"confidence":289,"updated":310,"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",[319],{"path":327,"title":328,"description":329,"topic":330,"applies_to":331,"confidence":289,"updated":310,"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",[319],{"path":333,"title":334,"description":335,"topic":336,"applies_to":337,"confidence":289,"updated":310,"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",[319],{"path":339,"title":340,"description":341,"topic":342,"applies_to":343,"confidence":289,"updated":310,"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",[319],{"path":345,"title":346,"description":347,"topic":348,"applies_to":349,"confidence":289,"updated":310,"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",[319],{"path":351,"title":352,"description":353,"topic":354,"applies_to":355,"confidence":289,"updated":310,"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",[319],{"path":357,"title":358,"description":359,"topic":360,"applies_to":361,"confidence":289,"updated":310,"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",[319],{"path":363,"title":364,"description":365,"topic":366,"applies_to":367,"confidence":289,"updated":310,"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":369,"title":370,"description":371,"topic":372,"applies_to":373,"confidence":289,"updated":310,"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",[374],"mid",{"path":376,"title":377,"description":378,"topic":379,"applies_to":380,"confidence":289,"updated":310,"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",[374,7,8],{"path":382,"title":383,"description":384,"topic":385,"applies_to":386,"confidence":289,"updated":310,"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",[319],{"path":388,"title":389,"description":390,"topic":391,"applies_to":392,"confidence":393,"updated":310,"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",[319],"source",{"path":395,"title":396,"description":397,"topic":398,"applies_to":399,"confidence":289,"updated":310,"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",[319],{"path":401,"title":402,"description":403,"topic":404,"applies_to":405,"confidence":289,"updated":310,"author":9},"\u002Fen\u002Fwissen\u002Ftorque-arm","Torque Arm: When You Need One","Why the axle of a hub motor turns in the dropout, when you need a torque arm and how to fit it.","drehmomentstuetze",[7,8],{"path":301,"title":5,"description":290,"topic":309,"applies_to":407,"confidence":289,"updated":310,"author":9},[7,8],1794254701765]