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Derailleur Alignment, Gear Cables & Cheap Power Meters | GCN Tech Clinic

Derailleur Alignment, Gear Cables & Cheap Power Meters | GCN Tech Clinic

(whooshing) – Welcome back to another
episode of the GCN Tech Clinic, where I aim to help and solve
your bike related problems. So if you’ve got one, leave it for me down there in the comments section and I’ll do my very best to help answer it in an upcoming episode. With no further ado, let’s crack on with the first question this week. And it comes in from Theo Hernandez. Their question is, “Can
you use break cable housing for a shifter cable?” As Theo is all out of shifter housing and needs a little piece to go in between the rear derailleur and
chain stay cable stop, about six inches. “Would such a short length compress enough to make my 7-speed indexed
shifting unreliable?” Theo, do not do that, my friend. The reason being is that the outer cables are created differently. In that a break cable is made of a spiral-bound bit of outer, which the indicator then runs through. Whereas a gear outer
cable, has its length done well, in one long line, if you like. So it’s made of many, many
strands and they can’t compress. Whereas that spiral one on a brake, can compress, giving you well, a slight bit of modulation I
guess, if you lock up a brake. But it’s not going to give
you like an ABS style feel. But yeah, the purpose behind
the gear cables being made in that way, is they don’t compress because your gear cables have to be really, really
exact in their tensioning. So stick with some outer gear cable, if you want to have perfect gear shifting. And next up a question from Luis Sanchez, “I was wondering if we will
ever see budget power meters, ones you can simply glue onto your cranks, or something of that sort for us peasants who don’t want to drop
hundreds on a new crank?” Right, Luis, possibly, there have already been a
couple of examples of this. The Watteam Powerbeat
and also the iQsquare. Their first product was a
bit of equipment basically that went in between the pedal and also the crank kind
of screwed into the thread and then you put the pedal in on there. Although, now I’ve
looked on their websites, neither of them are
currently shipping anymore. But keep your eyes peeled, this sort of thing does
pop up on Kickstarter and Indiegogo, that sort of thing, but right now, there is nothing in production that I’m aware of. Next up is zurjon23, who
says they love the Tech show, which is brilliant. Their problem is though,
recently their rear mech fell off and it got caught on the wheels and bent the derailleur hanger. Now zurjon says they tried to straighten the derailleur hanger and
installed a new rear mech as well. The problem is, it seems
that they can’t index the rear mech properly anymore. Ooh, zurjon, right then, that rear derailleur hanger
alignment is absolutely crucial. Doing it by eye is really not good enough, which I reckon you’ve probably done there. What you are going to need is a derailleur hanger alignment tool. So, when you fasten that
on, you can actually line up in a few different
places on the back wheel to make sure it is in the correct place. So, laterally adjusted as
well as vertically adjusted. It’s amazing what a few
degrees out of place can actually make when it
comes to your gear indexing. Along with that, I would
get some new gear inner and outer cables too, if you’ve put a new rear derailleur on. Because it’s amazing the
difference to indexing performance that a new set of cables can make. Next up is Athur S, who says, “Hi Jon, I’m using a
Tiagra rear derailleur in my cyclocross bike. But when I go off-road
the chain flies everywhere on the rough terrain, hitting the frame and sometimes skipping on the cassette. I thought maybe changing derailleur for Deore with a clutch mech would help. Does this make any sense and what’s more, will it work together?” Right Artur, firstly, Shimano
road and mountain bike components don’t really
work that well together. The reason being the amount
of cable that’s pulled by the shift lever isn’t
the same across road and mountain bike components. But, there is a handy
little solution for you here and it comes from a
brand called Wolf Tooth and they make something called a Tanpan. Which is a tiny little metal wheel, which the chain, sorry which
the cable can roll around and in turn can work absolutely perfect. Check out their website and
make sure it’s compatible with your levers, but
yeah all should be okay. Next up is Ben Carley-Macauly, who says, they’re thinking of going
one-by on their road bike as they rarely use the inner chain ring and have had problems
with front derailleurs. “Apart from a narrow wide chain ring, is there anything else that I would need to ensure the chain would be secure, whilst preferably keeping
my current rear mech? All the best, Ben”. Ben, nice question and also good as well you want to keep that rear mech on there, because, well, you’re
going to save yourself a little bit of cash there. Now I’ve done this on my own
bike, well one of them at home and with a good deal of success actually. I’ve never lost a chain, but something you could consider on there, is a chain guide or a chain
catcher, that sort of thing. Which could clamp onto your
existing front mech braze on, if that’s what you’ve got on the frame. If not actually a clamp on one. And Wolf Tooth as well as K-EDGE even make these solutions for you. Good luck mate and let
me know how you get on with those bits of kit. Right next up is olly cook, who says, “Can I put a SRAM 11-speed cassette on a 10-speed Shimano Freehub?” Ooh, yeah you can, but not always. If it is a Shimano actual branded Freehubs on a Shimano wheel, very unlikely. In fact, I’ve never seen it done before, unless you do some machining of a cassette on a lathe to remove some
excess material and everything and then you are able to do that. However, if you’ve got yourself a Shimano Freehub on a Mavic wheel then the chances are it’ll
work absolutely fine. Because I’ve seen all sorts go on them. They’re one of the few companies out there who have a Freehub which seems to be able to accommodate anything you throw its way. – Next up is, Jason M, who
says, “Hi Jon, great show. Is there a minimum tire
clearance between tires and fork on a disc brake bike? I’ve recently upgraded
my wheels and tires, going from 25 to 28mm. The 28mm front tire has
1.5 to 2mm gap all around.” And Jason says they
actually had to pull off all the little new tire nubs ’cause they could hear
them hitting the fork. Jason, I would be a little
bit concerned to be honest. The reason being, if your wheel
goes slightly out of true, there’s a good chance it’s
going to start rubbing on the inside of the fork there. And that’s not what
you want, let’s face it because you’re going to start
wearing away the material. Personally, I’d go back to the 25’s. It sounds to me like it’s probably an older generation disc brake road bike, because it can’t accommodate 28’s. Most of the modern ones
or recent additions, tend to be able to do that. This reminds me of the
old time trial bikes back in the 80’s and early 90’s. Where the clearances used to be so tight that if you picked up
a little bit of gravel on your tire, it would
actually start rubbing on the frame and it would cause quite horrible gauges on the paintwork. In actual fact, I just got one of these. This is a bit of fag paper and we used to call that
fag paper clearances. Because they used to say it was so tight you could just about put
one of these through there. Yeah, you don’t want that on
your bike, not in my opinion. – And the final question this week comes in from Phil Weatherley who says, “Hi Jon, here’s a question. I’ve made a bike light.” Right, okay. “6W LED at the front, 1W at the back. Cables between them, it works well. Currently using twin
flex, supply and return. What do you think about
using the frame as the return so I only have one
conductor to each light? It’s only 1A at the front
and 350mA at the back. So I thought to use copper
tape, suitably insulated, stuck where you can’t see it on the frame, so removing festoons of visible cable. Your thought sir?” Phil, what an electrifying
question there my friend. I really don’t know
how to answer this one, because I’m not an electrician. I have just done a rewire, but I’m not a qualified electrician. What I would certainly
not suggest is doing this, if you’re unsure really
and you’ve asked me and I wouldn’t, I just don’t like the idea of sending electrical
signal through a frame. I know there’s not a
massive amperage or watts or anything like that actually
going through the frame. But you are going to be wanting
to send an electrical signal through the frame that you’re riding on. On the safe side of caution
you’ve got one heart, don’t risk giving it a
shock, please my friend. I know that someone out there will be able to answer this question comprehensively in the comments down below,
so look out for that one. But my personal thought
would be, please don’t do it. Right, I hope I’ve been
able to help answer or solve your problem this week. Let me know down there
in the comment section if you’ve got a question
and I’ll do my very best to help answer it in an upcoming episode. And now, don’t forget too,
to like and share this video with your friend and
also, why not check out the GCN shop at And for two more cracking
videos how about clicking just down here and just down here.

97 comments on “Derailleur Alignment, Gear Cables & Cheap Power Meters | GCN Tech Clinic

  1. Jon in answer to the question from Phi Weatherley. That is exactly how cars have always worked. The positive is a wire, and the chassis is negative. Except, I believe, for some older Lucas systems used on classic British cars. Where the chassis is positive.

    Using the bike frame as a conductor might cause a problem of galvanic corrosion. But then again cars have been doing for over a hundred years so it might not be a problem.

  2. #askgcntech
    1. I've given up on self adhesive puncture patches as they always seem to fail after a few rides. So, sticking with traditional vulcanising solution, how long can you keep an opened tube?
    2. What do you use for bike cloths & rags… Old t-shirts? Y-fronts? Do you wash them every so often?

  3. Hi John! I have a ~1992 Giant CADEX 980C, one of the carbon/alloy hybrids where the carbon tubes are glued to the aluminum. A local bike shop owner warned me of these bikes because the have a tendency to just fall apart after a while. Should I be scared when riding and just use it on a bike trainer?
    Bonus question: The bike is fitted with Campagnolo Chorus 8-speed, how can I fit it on a modern direct drive bike trainer? The all seem to require at least a 9-speed group set. #AskGCNTech

  4. i got a Acera-rd-m3000 derailleur working just fine with simano sora 8speed shifters , with a Suntour 11-40 , on my gravel bike

  5. IQsquare switched the design of their startup power meter due to production issues… they are producing pedals now (both road and mtn). Nothing has shipped yet, but as an early backer I’m excited for a set of road pedals.

  6. Answer to the electricity question:
    It is not anyhow dangerous at all to a human. But you should not do it, because there is a good chance the frame will not be a reliable conductor and therefore the light might stop working at some time. Not worth the hassle.

  7. Most of the wheel rubbing bike generators that have been around for 40 years have only one wire coming out to supply power to the lights and they use the frame for ground. Of course these would never work on a carbon frame because of the insulating properties of the material, but it will work on steel or aluminum frames.

  8. On the crank power meter subject. I funded the iQ2 power meter because it was a great idea and just what I was looking for. It is now about 9 months late and about a month ago they said it doesn't work so now they back to drawing board making a pedal based meter which is useless to me because I use Speedplay pedals and don't want to change. It's the second attempt a removable power meter between the crank and the pedal and neither have worked. Maybe it is impossible.

  9. It only takes 100 milliamps to stop the human heart if the current runs across it. I'd expect the tires to insulate the bike from the ground. If the frame is energized than you will be shocked if touching the frame with a barehand and you're shoes have enough conduction to ground you out (or barefoot). I doubt you'd die from it though.

  10. I have a braised on front derailleur and I am looking at repainting my bike in the future. My question is how easy would it be to remove the braised on hanger? I have an older model Specializes Allez Sport aluminum frame. Great content and thanks for the help.

  11. Electrical shocks of 0.1Amps are potentially enough to cause cardiac arrest. If you don't know what you are doing with electrics, please, please do not mess with it. 9/10 you may be ok but it only takes 1 mishap and you're toast.

  12. Hi John, I hope you can help me. I ride a Merida 300 and I am a big fan of the bike but ever since I bought it I have been having a continuous problem with my gears skipping. It only happens in the big front ring when I am starting to drive on a bit. When I am half way down my cassette the chain keeps slipping down to a higher gear. I adjust back to the gear I want but after a few secs it slips again and so on. I can temporarily solve the issue by giving the cable a tighten at the adjuster where it enters the derailleur but after a couple of rides it starts again. It’s really disruptive on a spin and ruins my rhythm. I have had it serviced regularly and always point out the issue to the mechanic. A couple of weeks ago I had the chain and cassette changed but still no joy. I think the issue might be the back derailleur but I am not sure. Can you advice me on how do solve this really annoying problem?

  13. #AskGCNTech
    Hello, I have gotten a problem with some gears on my bicycle. I have 1-6 gears on my bicycle and the 1st gear didnt work successfully, and the 6th gear didnt go into gear. Can you tell me info of how that can happen and why?

  14. 1:25 Originally 4iiii innovation tried to sell such a kit, but they ran into issues – they were not allowed to ship the epoxy glue.

  15. You can run a wire direct for power (+), and use the frame for the ground(-).but just know I'm laughing if you shock your nuggets. John please just call it paint unless it's custom or a fresh build

  16. You can run a wire direct for power (+), and use the frame for the ground(-).but just know I'm laughing if you shock your nuggets. John please just call it paint unless it's custom or a fresh build

  17. Bikes used to do that, back in the 50s & 60s. (Probably prior to this and after for all I know) when they had dynamos. Single wire to rear and font light with return through the frame. Frames were steel of course.

  18. iq2 did in fact not ship any hardware up till today. Their first design, which you describe, did not work. Because of that they switched to pedal powermeters. But these are also not shipped and still in development.

  19. #AskGCNTech
    Is there any way to reduce the chain slap on my bike? I've had my bike 6 months, ridden about 900km on it so I don't think I need a new chain yet but I get a lot of shake as I ride over some of the rubbish road surfaces we have here in Ireland…
    Can more tension be put into the derailleur to tighten the chain?

  20. Avio produce a power meter that you can glue on to an existing crankset. I've got one and it seems to be running consistent with results similar to my friends running stages and 4iii units.

  21. Using a frame as a conductor will work fine. Obviously it won't work on a carbon frame. Back in the 80's when I had a dynamo on my commuter that's how it was done. The dynamo was mounted to a seat stay and a single core positive wire was run to the front and rear lights. The negative came back to the dynamo through the frame. There was a screw on the dynamo mount that was angled into the seat stays, you turned it to wear through the paint so there was a contact to bare frame metal.

  22. 11 Speed Cassette to 10 Speed Shimano freehub: You can use an Edco 11 Speed Cassette that is made in 1 piece and use the Edco 10-11 speed lock ring. I suspect you can use the Edco lock ring with the SRAM Cassette if it is 1 piece too.

  23. #AskGCNTech

    Hey Jon…Here's a free hub concern that has me bothered, maybe you know the answer…I have two pair of late model Campagnolo Bora wheels; 1 set are Bora One 35's about 3 years old and the other pair are Bora Ultra 35's one year old. The Bora One rear free hub makes a nice crisp sound that we all love! However on my Bora Ultra wheel set, the free hub is nearly dead silent…virtually no sound at all when free spinning and the free hub has been silent like this from the day I unboxed them and took them on their first ride. The Ultra's are smooth as silk, quiet and roll forever…but dead silent free hub. Scares riders when I come up on them and they don't hear me. I love riding my Ultra's. Any idea Jon, why the hub makes no free wheeling rachet sound at all? Thank's Jon, appreciate your suggestions.

  24. Awesome show as usual. Please satisfy my OCD and cut the steerer tube on the Celeste GCN special bike

  25. #askgcntech hi mate, love the show! Long time viewer first time poster. Is there a difference between a chain catcher for a 53/39 and for a 50/34 or moving the derailleur will also readjust the chain catcher position and work with a compact crankset? Cheers

  26. #AskGCNTech here's one I've wondered about for a long time. Every bike with a front derailleur I've ever had has been slightly quieter in the small chain ring than in the large one, and my bikes have had front derailleurs since the early 80s so I've had a few. Some have had rather noisy drive trains and some have been quiet, but they've always been quieter in the small ring. Is this a coincidence or are really all bikes like that, and if so, is there a reason?

  27. Hi Jon, really appreciate the answer to my tire clearance question! (Btw the bike is 2018 Defy Advanced 2, which says it should accommodates 28. I have about 400miles on the new set up, but it has been in the back of my mind)

  28. The electrical path for one half of your DC lights is not predictable through the frame. It will be necessary to provide attachment points for the frame path. Such attachment points are fraught with problems. They corrode easily. Paint has to be ground off to make the electrical connection. Frames have varying materials, so resistance will vary. The smaller your current, the more important your connections are. Also, there is the issue of electrical activity on bearings. This has been a real problem for some equipment. Step one: grind the paint off where the battery mounts, then remove paint at the rear of the bike. You may need to run a wire from the frame head to the fork, as you may or may not get a good connection through the steerer bearings. May depend on whether you use much grease on them. My advice: don't do it.

  29. Common return through the frame is fine for the bike light. Cars do it and have instantaneous loads of thousands of amps. And it's DC, which isn't a concern to humans at low amperage. AC is much more harmful. I'm an EE. 🙂

  30. I have a Velocomp Powerpod power meter. It is $300.

    It determines power by measuring the bike's speed through the air, the angle of the road, and acceleration. You tell the software your weight, the bike's weight, your height, tire size and some other factors which it uses to calculate power based on drag and slope of the road. You do an out and back calibration run to fine tune it. It mounts to the bike using a GoPro mount, and you can have profiles for up to four bicycles in it. It uses the Garmin speed and cadence sensors to keep track of which bike it is mounted on. It takes seconds to move it from one bike to another.

    It's not perfect. It under estimates my drag, because when I ride as hard down a 6% grade as I ride on the flat, it says my power is 0W. After about nine months, it lost track of what horizontal was, so the first half mile of a ride can show very high or very low power. It has a barometer in it so it figures out the slope isn't what it thought it was and recalibrates itself, and the rest of the ride it gives good power.

    Considering the the price and the fact I get to use it on both my commuter bike and my road bike (having power motivates me to ride harder, even on commutes), I'm happy with it.

  31. For 1x conversion, try the Praxis chain guide. Works very well, especially with the Oval chain rings too…..

  32. Regarding IQ2, they had technical issues with their powermeter solution. They switched to a pedal based system in the meantime, which they claim will be delivered in august.

  33. #AskGCNTech

    How to avoid overtightening the seatclamp bolts without using torque wrench? I am using carbon frame at seatpost.

  34. electricity question answer: if you power source is a dynamo (as opposed to a battery) this is a quite common factory ready practice on the former generation Dutch city-bikes and works fine. If you have battery, please don't. You might be fine but you don't want the stored energy to surge all at once.

  35. Looking super smart Jon. Did you have a nap in the sunshine and bake the right side of your forehead? Looks orange 🙂

  36. Far out! Those frames! SPECtacular look Jon! It's a good look mate! Side note; that question about the bike light was a bit next level.

  37. WattTeam closed their doors last November (2018). IQSquared…. well… Let's see how that turns out. That story is still unfolding.

  38. To answer the electrical question, i'ts no problem to send 1Ampere through a bike frame, as you are using low dc voltages which you don't feel and doesn't harm you at all

  39. ELECTRICAL QUESTION: What's the voltage? presumably quite low. Old Dynamos always used the frame as the return. Jon, you said you have just completed a rewire (Domestic?), are you aware of Part P of the Building Reg.s?

  40. Hi Jon. In regards to using a derailleur hanger alignment tool, what happens if the wheel isn’t quite true?

  41. Chiming I’m on the lights issue. Dynamos mounted on a fork have no problem using the fork as a ground provided it is metal and surfaces are all conductive. No one cared about rear light flickering and low currents/high impedance relative to ground impedance means dodgy grounding isn’t a big issue. However if you want good subtle wiring running two copper strip lines with a small dual conductor wire to go from frame along rear derailleur or brake cable up to your bars and then the light will be good.

    A bigger issue is that a poorly designed led light at 6W is going to be extremely electrically noisey depending on your design. With two long strip lines acting as a loop antenna you may well be able to swamp all nearby receivers including wireless computer/gps and mobile phones if you are lucky.

    Regarding safety, I don’t know how you can hurt yourself with 6V unless you really try.

  42. Recently bought a bike with a Shimano Ultegra group set . The gears were indexed for me whilst the bike was in the work stand and sounded perfectly smooth and quiet. However, when I am out riding in the big ring and putting a decent amount of power through the drive train in the last four gears (smallest) on the rear cassette, there is a very annoying rasping sound. I took it back for adjustment and it looked and sounded fine again. So basically, in the work stand quiet, under load noisy. As you can probably tell, I am quite inexperienced so any advice would be appreciated.

  43. I am currently running a pair of Bontrager Aeolus 5 TLR D3 wheels with a tubeless setup. I love the wheels but every time I ride in heavy rain the rear rim takes on water, this can be a significant amount by the end of a 3 hr plus ride. Is there a good way to remove the water without removing the tyre (tubeless) and is there anything I can do to stop this happening. The front remains dry?

    Thanks for an awesome show!

    Mike J

  44. #askgcntech Hey Jon, question: I recently took my gravel bike on an unusually rough trail ride, ever since there seems to be something loose at the front end. At high speeds going downhill the front end starts to wobble as well which is a little disconcerting to say the least! I've checked my headset, my hub, my wheel and spokes and everything seems to be ok and not loose, it's only noticeable when I'm riding. What could it possibly be?? Please help! It's driving me crazy! Cheers.

  45. Q: Where can I get my mitts on Bianchi Celeste green paint? I believe that is the proper name but have saw varying shades between pale blue and mint green too.I would consider mixing my own,but do I use 'ye olde' oil based model paint,or what would you recommend?

  46. Shift cable – 8 speed or less, brake housing is a ok, 9 speed plus better go with shift cable. The index tolerances are wide enough to spare the compression of a 6” section of housing.

  47. Question: Should Road Cyclists be told to wear protective equipment, such as pads and reinforced bracing, for protection against the impact of crashes. Protective equipment built into the cycle clothing or as Independant accessories to be worn under standard cycle clothing? BMX cyclist, Mountain Bike cyclist already do so, why not professional road cyclists?

  48. re the electrical question the poster didn't say what kind of bike frame it was. carbon won't conduct electricity so it won't work. metal would work but make sure negative is to the frame, you could cause metal loss – google "sacrificial anode" .
    but the best answer is don't be such a tight arse and get some good lights – irregular flashing patterns are far better on the cheaper lights so you can be seen, or if you need to see, buy some good lights, its a safety thing. anything you bodge cheaply won't have a collimator to focus the beam well for cycling, you also will be at the mercy of your waterproofing efforts.

  49. If the LEDs run on 12V youre totally fine. Furthermore no matter where you touch the frame, there will be now voltage across your body since, so no current will run through your body. I would be concerned about the efficiency of the system tho… You´d have to do further testing.

  50. Routing power through the frame would work absolutely fine. In fact, that's how it was commonly done with dynamo powered lights back in the day.

  51. Hey John, great show as always! I think the last question is really interesting and given your custom build bikes maybe you could get some expert advice and give sending a signal through a frame a go, GCN has made so much content that it must be hard to think up new fun ideas yet you still manage to do it week in week out! I would name it "Can you do DI2 on a budget!". One of those question that seems stupid at first, but given the advent of things like Graphene could really be possible in the future, no cables, no wires, just frame, because removing those integrated cable holes saves 0.2W, PER HOLE!

  52. having a tyre rubbing because it is too big for the fork can cause sidewall damage . this makes them quite unsafe, you could have a blow out

  53. Hi Jon. I've got a question. I have a Cube Attain with a Shimano Claris groupset fitted to my bike and I'm thinking of upgrading to a 105 R7000 groupset. What would you recommend in regards to free hub, would it be replaceable or will I need a complete new hub to accommodate the new cassete?

  54. Hi Jon, I had changed my road bike drop handle bar for a bull horn one. My problem is that I could not find brake handles so I am using the old road ones but my brakes are a little spongy. The brake handles I have are for hidden routing of the cable housing. What is your advise in this matter? Thanks a lot.

  55. The electrical question. Led lights are low voltage so no danger of a shock. It depend where your battery is. If you want to pass current to a light mounted on the handle bars it will need to go through the bearings on the forks this could be a problem with the grease affecting conduction. If both lights are mounted on the frame it should be no problem.

  56. #askgcntech so i think my through axle is seized in the back wheel. Anyway for it to get unseized or a bodge to get it out? It is a 142×12 mm axle with a allen key end, but even then i cant get it unstuck. Thanks in advance!

  57. Regarding using the frame as a return for the current to your bike lights. It sounds like you will be using something like 6V, so you have no need to worry about safety. What you should be concerned about is corrosion. If you stick copper to iron, aluminium or even carbon, and add salt water, you will effectively create a battery, which will eat away your frame. Besides that, I am quite sure that that was the way dynamo lights were made when I was a kid, and probably still are.

  58. #askgcntech Hi, i Resently purshed a 2nd hand disc frame that came installed with 12x142mm rear Thru Axle. I then went and bought a set of shining new Wheels. When i close the Quick release on the axle i meet no resistence, and the Wheel Rattles around the axle when i handle the bike. I measured the internal Width of the frame to 142.2x mm and the Wheel axle Width to 142.1x. The Wheel Company even sent me some new adapters to solve the problem but no luck. Am i at a spot where the tolerances of the frame and Wheel just dont meet up, not all Wheels and frames are made to match. Can i add a spacer, and then where to place it to solve this ?

  59. #askgcntech #gcntech
    My Question comes with Pictures… (Its the german way to provide all information xD )
    So i sent my Question+ Pictures on Instagram. Hope To get an answer :))

  60. #askgcntech #gcntech I have the opportunity to purchase an old NJS frame is there away to put brakes on them. To make them street legal?

  61. How do you adjust the B tension screw on Shimano rear derailleurs? (it is also on old Suntour mechs as well). The Shimano manual says: Mount the chain on the smallest

    chainring and the largest sprocket, and turn the crank arm for shifting. Then turn the B-tension adjust bolt to adjust so that the guide pulley does not interfere with the sprocket but not so close that it touches the chain. Next, set the chain on the smallest sprocket and repeat the above procedure to make sure that the pulley does not come into contact with the sprockets.
    I cannot understand what they mean when they say "not so close that it touches the chain" as the chain is in contact with the pulley wheel and the sprocket all the time. What exactly am I aiming for with this B screw? #AskGCNtech

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