Recently, I helped a new unicyclist order their first non-beginner unicycle. They don’t live near me, so they will have to assemble it themselves, or pay some bike shop a crazy amount to do it for them. It got me thinking about the first one I assembled. It was a while ago-it was a Torker 24. When I got to the bearings, it said to “tighten the bolts to 45 inch pounds”. I just froze there. How in the world was I supposed to know what 45 inch pounds was? So, I asked a friend. He said that all his fancy tools measured in newton meters or ft/lbs. I figured since they were bearings and the whole thing revolved around them (quite literally), it had to be pretty important. So, I sat several days trying to figure out what to do, so I wouldn’t mess up my new purchase. I finally got the advise to just tighten them loosely and try it.
Over the years, this same question has purplexed me.
Nimbus says, “Do not over tighten; they only need to be tight
enough to hold the wheel in place without it rattling. The wheel should spin easily; if it does not, loosen the bolts until it does.”
Kris Holm says, "tighten the bolts with slight hand pressure. To test whether the bearing housing bolts are too tight, give the wheel a spin. The wheel should spin freely. If it does not turn perfectly freely, the bearing housings are too tight, and should be loosened slightly. Overly tight bearing housings will damage the bearings, and will not be covered by warranty."
I have worn out bearings and had bearings that ended up clicking. So I am extra sensitive to what is the exact right amount of pressure to tighten. I don’t want too tight to bind the bearings, and I don’t want too loose to have them wiggling around. …and I don’t want “will not be covered by warranty.”
One friend said that he uses the short end of his allen wrench and tightens till it is tough with that end. Another person said that they tighten it pretty good and then spin the wheel and loosen just to the point of free movement. One person told me they go on the looser side but use some locktite on the bolts to keep them from loosing further. QX and a few other companies still put neoprene nuts on the other end to help insure that the bolts don’t loosen themselves over time.
How would you advise a new person to the sport on how they should properly assemble their bearings???
Torque wrenches also come in inch pounds. They are physically smaller than the foot pound type. If you can’t find someone that owns one, 45 inch pounds is less than four foot pounds. I‘d guess, just take it past snug.
I’m brand new at the uni game. I got my new 26” Nimbus in early August. I did not know about the 45” lb. recommendation. As you stated the Nimbus instructions said ‘not too tight’. Well that certainly leaves a lot of room for error for a ham fisted guy like me. I snugged mine down to what I thought wasn’t too tight. I think I will set my inch pound torque wrench to 45 inch pounds and see if I get a click. I’m pretty sure I’ve passed that torque. If so I’ll back the bolts off and reset them.
Sometimes cheap is good, if you only use it once in a while. I have one of these Harbor Freight torque wrenches, and it works OK, as far as I can tell (I’ve never tried to “calibrate” it, there’s no real method supplied for doing that). I mainly use it for the small hardware on my Schlumpf hub.
Apologies to those in other countries who may not have access to this particular vendor. Harbor Freight is known for cheap Chinese tools, but sometimes they get decent stuff.
BTW, I don’t use the torque wrench on my bearing caps, I just put a drop of blue Loctite on the bolts (clean them first!), tighten until they are tight, then loosen up just enough so the wheel spins easily. Never had any problems.
(4 inch-pounds is equivalent to 3.37 foot-pounds.)
LanceB 4 inch pounds is 1/3 of a foot pound. Anyhow, gwymer, I loosened off my bearing caps and tightened the bolts back down with my allen key holding the short end in my fingers. I tightened it as much as I could. I then torqued it to 45” lbs. it turned the bolt less than 1/4 turn. Your friend that does it by holding the short end of the allen key is pretty darn close. Good tip.
LanceB, that is a great price for a click type torque wrench. We have an equivalent store up here called Princess Auto. They also sell the cheap Chinese tools, probably from the same supplier with a different name put on them. If you only use the tool once in a long while they are the way to go.
The bearings can seat themselves in the holders over time too. When I reinstall a wheel I take the bolts to “just past snug” and they’re generally fine to begin with. Often after some heavy braking I’ll end up with a tiny bit of noise and movement and I snug them up a tiny bit more.
I find it usually takes 3-4 rides after a wheel install for the bearings to fully seat. It’s especially noticeable on my 36er.
You want some preload (i.e. extra tightness) on your bearings, because when you ride seated, your weight pushes the top bearing cap into the bearing - which pushes the bottom cap away from the bearing. If there isn’t some preload the bearing will be loose when riding.
(Also the other way around, when you are standing and pulling up on the handle - the bearing is driven into the bottom cap, and would come loose on the top side).
Anyway “just past snug” sounds like a decent guess. It should definitely be more than just hand tight, and more than just enough to keep the wheel from rattling around when unloaded.
I own the 26" Oracle with the cap-mounted D-Brake. I learned that, when the bearing cap is tighter, the brake is less likely to send vibration through the entire uni. I figured it out only after relieving the tension on both caps (the wheel wasn’t making enough rotations when spun freely) then going on a ride. While braking down a hill, I could hear two frequencies an octave apart. I felt the vibration coming through the seat. I call it an “Oracle-gasm.” Anyway, it only took me a few years to figure out why the brake made noise intermittently! Nimbus has moved away from the “inferior” D-brake system.
I complained to another rider about wanting greater braking power. He suggested I use a larger rotor. I think accommodations can be made for rotor size on frame-mounted brakes but not on the D-Brake.
I’ve done the bearing tightening dance many times. I can tell they need tigtening when I push the tire to the left and right in the crown with my fingers and feel the click. Of course, what prompts that test is when I feel/hear it while riding. That test tells me it’s bearing play, rather than, say, something like saddle bolts or cranks.
I cut a strip of innertube long enough to go around the bearing and lay it into the bearing holder when bolting everything together. I haven’t had to do the dance since. My bearing holders are stamped. It might not work with machined ones. When I replace this strip (the rubber degrades after awhile), I’m going to only line the end cap (the part that bolts onto the rest of the frame) with rubber instead of going all the way around. The idea being to make it less tight/fiddly and prevent compression of the rubber causing the sort of wheel deflection that frame flex does, though I have not noticed such deflection in practice.
Love the comments and suggestions! I really like the idea of adding the rubber strip. I am generous with the lubricant when installing the bearings, to help with metal against metal rubbing, but might try adding the other.
BTW-if you are in Nashville, you aught to consider coming down to Birmingham one weekend to ride with a couple of us. Definitely need to check out our STOMP festival in October each year.
45 in-lbs is about 4ft-lbs. The same as hanging a 4lb weight on the end of a 1 foot long wrench =8lbs on a 6 inch long wrench, etc. So grab your wrench 6" away from the bolt and apply the same force as lifting a 1 gallon jug of water (gal =8.3 lbs, so at 6 inches =4.15 ft-lbs). Or better yet hang the jug by fishing line on the wrench (just make sure the wrench is parallel to the ground at the point it tightens, so you have a true 90 degree gravity vector force). Personally, I just snug up until no play in the wheel and feels feels smooth (a firm hand grab on the frame) when the wheel is spun.
Holding my “L” shaped 5mm hex tool at the short end, I tighten the bearing cap bolts to the point where I start struggling. That’s my rule of thumb. If I had the added leverage of the long end of the tool, I could easily over-tighten the bearing caps.
I recently had the LBS modify a 26" Nimbus Muni frame for installation of my Schlumpf hub. I explained the installation options to the repairman and gave him Schlumpf’s installation instructions. He chose to install it without the tiny metal plugs that fit into the gaps between the frame and caps. Anyhow, I was concerned that this could result in slipping. I asked him if he tightened the caps to a particular spec. I think the answer I got was “snug”. So, took it home, went on a few rides, swapped out the tire a couple times (had to remove the bearing caps for this), and I’m happy to say there has been no slipping of the bearings. I don’t understand the mechanics of the Schlumpf hub very well, but some other riders pointed out that slipping bearings could cause it to freewheel (whereas the same situation on a conventional hub would not cause freewheeling. Bottom line: the bearing cap tightness may matter more on my Guni than on my other unis.
45 inch pounds is about 5 Newton Meters (N-m)… (for europe riders) and that is very loose.
My lightest torque wrench is 5 to 30 Newton Meters (N-m) and at 5 Nm my bearing is already a little “tightend” and the wheel a little bit slowed down…