How To Measure Crank/Chainrings Size BCD
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- Опубліковано 26 сер 2024
- I show how to measure a chainring or crank to be able to replace a chain ring. The main things you need to know are the number of teeth and the BCD (Bolt Center Diameter). Well, and the number of holes. I show what to measure and how to calculate or look up the BCD.
As referenced in the video, this is Sheldon Brown's BCD crib sheet:
www.sheldonbrow...
The multipliers I used to calculate BCD by measuring the distance between adjacent bolt holes are:
3 bolt x 1.155
4 bolt x 1.414
5 bolt x 1.699
6 bolt x 2.000
Some of the most common BCDs:
4 hole: 64mm, 80mm, 104mm, 120mm
5 hole: 74mm, 110mm, 130mm, 135mm
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The Best explanation of BCD meaning and how to measure it. Clear and concise ... Thanks !! 🔥
Always my favorite channel for bike repairs if I don't have the slightest idea what to start with. This is a good channel for both beginners and experienced.
Did my measurements on my5 bolt before watching this video. Long story short, Glad I watched this!!
you are a fricking fountain of info. your friends and neighbours must LOVE you like crazy (especially now !! )
Thank You
Thank you! I've struggled with how to measure centre-to-centre accurately, your tips really helped me understand how to do it.
very good better than the local bike mechanic !
RJ is a cycling treasure. Thanks again brother.
Thanks for the video,..
From: 🇵🇭🇵🇭🇵🇭
Masterful! Thank you!🌱
Good methods!, you can also mark the holes in a flat piece of plywood or cardboard, then measure hole to hole with ruler. As for the caliper you can also switch to the internal jaws and measure hole to hole moving to the right or left edges as you did. But the better measurement probably will be touching the edge of the bold without moving it to the right or left. This way you will have solid touch from bolt to bolt, then subtract half diameter of the bolt to the total distance and presto!
Perfectly explained.
Thank you RJ i had no idea how to measure this thanks so much for your videos.
Thank you, super useful
I like the way How you explain to us this kind of thing, cheers mate!
hey rj, your channel is my go-to-work-info-channel!! love your in depth explanations : ) once again its this channel where i found what i was looking for!
Thank you RJ for sharing knowledge
Super clear explanation! Thank You!
600 Fc 6400.. nice crank RJ. Almost identical to the Dura ace 7600. Very sweet looking crank
Clear and concise instructional, many thanks.
Great explanation, no bullshit, straight to it.
I love all your videos, I learn so much , thanks for passing on the knowledge
If you know the lengths of the lines formed by the segments that will form the largest isosceles triangle on the five bolt chain ring, you can find the diameter of the circle that circumscribes it using the Pythagorean theorem. Simply divide the smallest side by 2, giving you the hypotenuse and one side of a right triangle. Solve for the other side x by subtracting the square of the smallest side from the square of the hypotenuse. The square root of the result is the diameter of the circle.
No, wait what was I thinking, that measurement wouldn't be long enough! If you know the length of three sides of a triangle circumscribed by a circle, you can find the circumference by multiplying the lengths of the three sides abc, then dividing that by the square root of (a+b+c)(b+c-a)(c+a-b)(a+b-c). That gives you the circumference, then you divide that by 3.14 to get the diameter. My mistake, I didn't think about it long enough before I posted!
+John Hanley Or you could just do what I do in the video?
RJ The Bike Guy You could, and I probably would if I was fixing a bike. But, while I was watching the video, I was trying to figure it out using geometry.
Still helpful after 7 years ❤️
Very nice, thank you!
This actually helped me out a lot!
Thanks buddy !!
very useful thank you
Thank you so much!
i love this kind of specific stuff. i hope you are making money from this. you deserve it.
Thanks, I’m changing from a two by to a one by on my mtb
That’s what i’m looking for 😊
Thanks!
thanks RJ this video came in handy as i needed to chainge a chain ring
Great and informative video, question on converting the inner to a smaller chainring on a vintage road bike? I would like to convert from a 52-40 to a 52-28?
Perfect! Thanks, dude! You're a saver!
thank you
So clear and easy to follow. Subbed.
Thanks man!,this is really helpful!😊 i always wanted to make my crank setup onto 1x but i dont know how to measure my crank bcd😂😂 thank you it saves me a lot of money buying again a new crank phew😥
Nice One! I was missing your videos!! Keep on coming!!!!
same
Thank you so much! This video is so helpful.
My man
Thank you. Good stuff.
This was really helpfull, thank you
nice... now i can order my chainring... kihkih tqiu
this is really a good one RJ.... got to find out if i had to replace my chainrings on the crankset... once i asked somebody on local forum...they said there just fine... how to be shore...any kind of mesaurement?
Where can I get a standard chart for matching the crank arms to the correct chainring bcd
Hi RJ Any Advice On Replacing A New Crank 4 A Dawes 701 Discovery What Would B The Best 1 4 The Replacement Many Thanks M. England.
RJ, This seems the best place I've found to suggest a topic...
Have you or could you address choosing correct/ideal chainring bolt size? Especially for a 3-ring spider conversion to a single narrow-wide. for instance I am currently working w/a setup w/a combined depth of 7mm...👍🏼
You could measure the diameter using the calibrater.
Do you have to match the same number of teeth as well?
What I learned from this video, my chain ring size doesn’t exist and the one in front of me is the only one in existence
Hi RJ... how you measure for new chainring bolts. Whole length or just the thread length? Thank again.
😃absolute great videos.
Do I need a chainring guard? Where one can find one for a bolt circle of 120mm? I can only see 104mm!
For the 5 bolt, measure any radius, multiply by 2.
Theoretically. But it's not that easy to get a precise measurement of the radius on one of these. And if you are off by a few millimeters, now you are doubling your error. That is why it is done this way.
Greatness
Tq sir
Thank you
Do you have a link for that sheet?
Hey RJ, love the videos.
I have the 4 bolt crank on the left in my spare parts bin, but have been unable to find any information on it, could you tell me the make/model if possible?
Thank you
Ok now i know everything thanks mate
I am looking to replace Shimano 42t SG 130mm BCD chainring (middle chainring). Its hard to find that part and it looks more cost effective to replace whole crank. Its for a 3x7 Shimano rx100. Any suggestions since you are the GUY out there in UA-cam? Thanks
I love it i subscribed to you ages ago, but this video I just found while googling^^
thanks very helpful!
This was helpful
Awesome clear explanation. Largest chainring specs 4 bolt, 48t, 120mm adjacent bcd, 160mm diameter bcd. Looking for a chainring guard. Any thoughts?
Leave it off.
I have a five bolt Shimano Claris Octalink double chainring crankset with a BCD of 110 mm. So would I be able to use a 53 or 52 teeth outer chainring which are compatible with 10 speed drive train and has a BCD of 110 mm with a 34 teeth inner chainring in my 8 speed Claris drive train
My FC-M952-5 & FC-M730 both are: 110mm.
Where do you find the web site you mentioned thank
I found it Rj thx
Is there anybody who know what is the BCD of Sugino Impel csslll. I just want to make sure before I buy online. Thanks
Great vid! Now here’s my question how do I remove the bolt holes? I wanted to clean out the cassette but couldn’t get in deep enough and don’t know what tool to use. There were no marks to use a flat head or anything like that. Help please!
I don't know what you are asking. Chainrings? Or are you off topic on cassettes? "Remove bolt holes"?
Maybe the chainrings are bolted?
what if my crankset is asymmetrical 4 bolt ?🤔🧐
Why isn't this stamped on chainring. I'm finding a bunch of different digits on mine
You are like the bob ross of bicycles.
Where did the multipliers come from? The ones to calculate BCD. Another Sheldon Brown sheet?
+minidini10 Sheldon Brown and also in my Barnett's Manual.
Mr. RJ, I was planning to put 10 speed chainring on an 8 speed crank. I currently have a claris r2000 crankset and I was planning to put tiagra 4700 chainrings on it so that i wont have to buy the whole 4700 crankset. Both has a 4 bolt design and same 110 pcd.Do you think this will work without compromising my front shifting? Thanks
Should be fine.
is hi temp grease OK to grease parts on bikes
+bikeman C I only use hi temp grease in drum brakes on the brake shoes. Hi Temp grease is much thicker and sticky. I wouldn't use it in applications other than hi temp. The movement will be much stiffer.
it is possible to fit a 110 bcd chainring on a 130 bcd crank??
No.
I see RJ already responded but that was covered in the video .
👍
For chainrings with an odd number of bolt holes, couldn't you measure the radius (center to bolt hole) and multiply by two?
Try it.
@@RJTheBikeGuy , yep works.
Numbers work out the same as in the chart at 4:50. Chart gets numbers from geometry and trig.
Formula is 1 / sin (180/n) where n = the number of bolts.
For 5 bots, 1 / sin (180/5) = 1 /sin 36 ~= 1 / .588 ~= 1.7
How to identify an air spring suspension and a coil spring suspension?What do they have?
+Yap Wei Cheng Look up the specs/and details for your shocks and see what they are.
+RJ The Bike Guy What i mean is do coil spring suspension have reboun or they do not have?
I am not understanding your question.
R.I.P Sheldon
weard my compact roadbike crankset has 130mm
Hi, if i have my chainring too wasted, is it possible to turn it around so i can use the other "face" of the chainring? on a SS bike (sory for my english)
Not really. The chain ring is still worn out.
@@RJTheBikeGuy thanks. So on a worn chainring (wave shape on tooth) its not worthy put a new chain, right?
@@lorensmashing It's not just the tooth shape. The gaps between the teeth are wider.
Or measure from hole to center and x2 = diameter.
I gotta get a paper to understand the hole to hole math formula. I don't get that one.
Okay, measure from the center of this!
www.amazon.com/exec/obidos/ASIN/B004YWGV4E/ref=nosim/youtube25-20
AH!
Pitch circle diameter actually.
I think I may slow down with my bike build and maybe learn before I do.
Getting too excited I'm ordering wrong size parts including a chainring! Lol! I know better too. I'm auto mechanic by trade. Derp!
You are a fucking hero
thanks, this helped me know that i got the wrong size for the cranks, my day is ruined 😭😭😭
great video RJ im doing a bike mechanic course in april and your videos are helping me a lot would it be possible to do a video on how to tell what headset i have and how to measure the bike to find the headset size i need and how to buy use the info gathered to buy headsets and bearings would really appreciate it as would a lot of cyclist on my cycling group on facebook keep up the good work RJ
+Jonathan Farrelly I am not quite sure what you are asking for? What headset? Threaded vs threadless? 1" vs 1 1/8"? Brand? I am not sure what you mean by what headset? On older bikes, it wasn't that hard. Many new bikes have really funky headsets and tapered forks, and lots of variations that I haven't even messed with yet.
I have a semi integrated threadless fsa headset on one bike and a fully integrated threadless headset on another bike the both 1 1/8 " I was wondering what do I need to measure on the bike to know what size I need and type
Enjoy: www.canecreek.com/resources/products/headsets/technical-specifications/headset-identification-and-specification-guide.pdf
+RJ The Bike Guy thanks RJ really appreciate that
do u ride them
can u use a ruler to measure crank
+bikeman C If you can lay it flat and get an accurate measurement.
+RJ The Bike Guy OK an can u do it any other way to
+RJ The Bike Guy do u now where I can buy spoke renches
Amazon, ebay, the local bike shop, about a hundred places online.
+RJ The Bike Guy OK I'll have to buy some
All you need is the tables.
76 x 1.699=129.189 therefore my bcd is 130mm?
Most likely. 128mm is possible, but that is pretty obscure.
do ride bmx bikes
+bikeman C Nope. I ride road bikes, mountain bikes, tri-bikes, gravel bikes. But not BMX.
Mine have 10 1/2 cm what bcd is it??
The steps are in video
Ohhh ok
next time leave print out on long enough for screen shot. Called filmography:)
What print? The cribsheet? There is a link in the description.
For 5 bolts measure the Radios - from bolt hole to the middle of the crank, then double that and you get the Diameter :)
Due to center of the crank not being on the same plane as the ring, it would be guessing about where the middle is. Not very accurate. And if the ring is not mounted to a crank?
No! The ratio for 5 pins is 1.7013... and not 1.699. In general, the ratio of the diameter of a circle that circumscribes a regular polygon with N sides to the length of the side of the polygon is 1/sin(180/N). So for 5 sides this is 1/sin(36) = 1.7013016167... This is 7th grade school math, not rocket science.
When it comes to bicycles best not to argue with THE Sheldon Brown, Hambini nor RJ. In addition did you compare the number you are suggesting to the number RJ referenced from THE Sheldon Brown? Use both numbers and multiply by appropriate measurement and I bet you get the same bcd after rounding out . Yeah but .whatever difference is nothing to squabble over. 🤦🏽♂️
Literally ‘yeah but’ .102 of a difference. Mm are small brother. We are not talking about rocket science we’re talking about bicycles that do not space travel and the relative measurements are microscopic compared to rocket science and for example landing on the moon type measurements where you could get excited over your .102 objection.
Furthermore what RJ suggested turns out more accurate than your number. I’m sticking with RJ, Sheldon and Hambini.