Ask Pinkbike: Adjusting B-Tension, Cutting Forks, Making a Full-Suspension Rigid, & Quieting Loud Hubs
Here at Pinkbike, we get inundated with all kinds of questions, ranging from the basic "Can I have stickers" to more in-depth, soul-searching types of queries like if you should pop the question or what to name your first child. Ask Pinkbike is an occasional column where we'll be hand-picking and answering questions that have been keeping readers up at night, although we'll likely steer clear of those last two and keep it more tech oriented.
Adjusting SRAM B Gap Without Tool
Question: @yeahwhy asks in the Mechanics' Lounge: I was wondering how should I set up the B gap on my drivetrain without the tool and where I should be measuring the 15mm difference. I also saw somewhere that 15mm is too much and I should run less, is it 15mm so it works better in sag?
 | This is a good question. While that little gauge from SRAM is really handy, chances are that a lot of people may not have one on hand and, the local bike shop may not be just around the corner. SRAM suggests the following for chain gap adjustment without the gauge. 1. For an Eagle drivetrain, shift the chain onto the second largest rear cog. For full suspension bicycles, measure the chain gap while the bicycle is in the sag position. 2. Rotate the B-Adjust screw until the gap between the upper pulley and the tallest teeth of the largest cog is 3mm. 3. Check the upper guide pulley alignment in the large and small cogs. Make adjustments to the high and low limit screws as needed. Following the instructions and measuring the bike while it's at sag, I've never run into an issue with or without the gauge/guide. |
Cutting Steerer Tubes
Question: @Pauley asks in the Bikes, Parts, and Gear Forum: I’m currently building a custom Ragley...I am going to get a bike shop to cut the steerer for the fork as I’m not wanting to mess it up. My question is I have no clue what height to cut my steerer to or what height my stem should be. Every bike I’ve owned has been bought complete and I’ve never worried about that. All I know is sometimes on the climbs I would get a sore lower back with bikes so I guess I was overreaching slightly. Any tips or help would be appreciated!
| Well, this is one you probably don't really want to mess up. Cut your steerer tube too short and it's a pricey fix. For length, I typically dry fit everything. Put the race on the fork, install it all, and decide how many spacers you'll need to get the handlebars where you want them. Typically, 20 - 40mm of spacers should give you enough room for experimentation with stem height. If you want a more in-depth tutorial, @mikelevy did a more in-depth write-up years ago that still applies today. Any bike shop you trust to cut your fork should also be able to help you settle on the steerer tube length that makes sense. Remember: measure twice, cut once! As far as your sore lower back goes, a higher rise handlebar could help by putting you in a more upright position, and possibly a more comprehensive bike fit could also help detect and other areas that could be adjusted. Some core strengthening exercises wouldn't hurt either. |
Leave room for things to tighten up but don't cut it too short...
Making a Full-Suspension a Hardtail
Question: @eatourfoodtina2 asks in the Bikes, Parts, and Gear Forum: Could we in theory stick a rigid shock on a full suspension and turn our full suspension into a hardtail?
| In theory, yes. Should you do it? No. You can obviously bolt a piece of metal in place of a shock and the rear end won't move, but it's not recommended. For one thing, the bike wasn't really designed to handle the forces that would go through it in a fully topped-out position. The point where you run out of suspension travel and your frame becomes rigid is at the bottom, not the top, of the travel. In this sense, the frame is in a very different position at full travel than it would be at zero. Bikes are designed to handle these "rigid" impacts at bottom out. That doesn't mean it'll break, but it does mean that you'll be subjecting it to forces it might not be able to handle. "But what about a bike with a lock out?" Even when a bike's suspension is locked out, or set up a very stiff spring rate (think putting the max air pressure in a shock) it still has some give. You'll also be altering the bike's geometry, since the rear end will have 0 millimeters of sag. Overall, it's much easier (and safer) to run more air pressure, a stiffer spring, or find a shock with a firm lockout if you're trying to make your bike to ride more like a hardtail. |
Bikes are designed to handle hard forces at full compression, not at top-out.
Quieting Down a Loud Hub
Question: @Brendanpedalpusher29 asks in the Mechanics' Lounge Forum: I have a fat bike with Borealis house hubs and when I coast it sounds like a carnival spinning wheel. It is so distracting I can’t hear the people I’m riding with. Short of replacing the hub, any ideas of a quieter hub?
| Loud hubs are a love or hate thing for most people. A hub so loud you can't hear your homies? That's no good. Many freehubs come with a fairly light oil or grease in them which serves to lubricate the pawls and keep everything working well. That lubrication needs to be light enough to allow the pawls to engage properly, so slathering a coating of thick marine grease in there isn't the way to go. Dumonde Tech's Pro-X freehub oil or grease are great options for quieting down loud hubs - it works wonders on Industry Nine's extra-noisy Hydra hubs, and it should help quiet down your Borealis hubs too. Once you have the hub nice and clean, put a little bit of grease on the spring under each pawl, and then apply the oil around the drive ring. Put everything back together and the decibel level should be noticeably reduced. |
Some people like to turn their hub volume up to 11. Many prefer nature. A slightly heavier oil or freehub grease will go a long ways in quieting things down.
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Why wouldn't you suggest just trying setting the stem higher (not more than 25-30mm of spacers is a common upper limit) first, since they're got a full steerer available. Sure more spacers also means slightly less reach, but that might help too. Definitely worth a try before spending on a new handlebar, and can always trim the steerer again if they decide to go riser bar instead of tall stem (to gain back the reach, or for looks: slammed stem & riser bars does look way better than a stack of spacers and a flat bar)
Doesn't it come with the mech? Or with new bikes? If it doesn't come with new bikes, don't you trust the assembler?
(I have one 11sp and one Eagle, can't remember where the Eagle came from though. 11sp came with a mech.
Snapping a pawl? That's above my leg grade, even on an eeber. But I'm flattered you think I could! Definitely able to use too thick a grease and gunk up a spring, but snapping a pawl? Snapping? A pawl?
as in, when I put it in 130mm 'trail' mode it will sink in by 30mm, steepening the head and seat angles and then when it's time to decent, I'll put it in 'enduro' mode full send 160mm configuration and fly off into the sunset!
I don't get why it's so hard!
This - a greased Hydra runs as pretty damn quiet. I hated I9 Torches because they were obnoxiously loud, Hydras are very different beasts. I've got some garbage OEM hub on my ICT that is an order of magnitude louder, and a completely different tone, and damn do I hate it, but I don't want to invest in a bike I mostly ride when its salty and frozen out, so I live with it. Just motivation to pedal more.