question about rear wheel

[weisan]

I got a true and dished rear wheel that maintains its true but loses its dish when a tire is installed and pumped up. I noticed one of the spokes on the non-drive side loses its tension when the tire is mounted and aired up.

May I ask: What's the fix to this problem?

[AngryScientist]

how many spoke wheel and what's the lacing pattern?


generally speaking, the solution is to increase the overall tension of all of the spokes, and make sure the spoke tension is relatively even.

[thwart]

Yeah, I'm sure someone who builds lotsa wheels will chime in, but mounting a tire puts circumferential pressure on the rim and to some degree de-tensions the spokes. If you're losing dish (in other words, the DS spokes are no longer pulling the rim off-center) and one non-DS spoke obviously loses tension, then going around the wheel with a spoke wrench to tighten all spokes (and maybe an extra 1/2 turn on that loose spoke…) would be the likely solution.

How much to tighten? Well, a spoke tension meter would be very helpful here; some folks say they can get by with acoustically tuning the spoke tension.

[carpediemracing]

Sounds like the rim is bent and the only way to get it straight is to have some uneven tension. The pressure from the tire is enough to push the spoke over the cusp. I know that HED, for example, recommends lower pressures for their wheels else stuff like that happens.

However I bet that even with lower pressures you'd have some wonky handling when you're out of the saddle.

If it were my wheel I'd do one of two things.

One, even out the tension. I'd much rather have a slightly out of true wheel that's strong than a weak straight wheel.

Two, replace the rim. This is pretty much necessary if the rim is indeed bent and you want a straight/round wheel.

[weisan]

Thank you my friends for responding!!!

Sorry I was busy in my cave doing some mechanical meditation, just came out of it. It's wet and cold here today, perfect day for building up a bike or fixing stuff here and there like this problem rear wheel. I took your advice and went the route of evening out the tension, as carpidiem pal said, much rather have a strong wheel that is slightly out than one that looks good on paper.

I was hoping the Ribble package will arrive today but since it didn't, I went ahead and re-built my old trusty GT hardtail. It was my first MTB. Stripped it down several weeks ago, gave the frame a good scrubbing from head to toe in a bubble bath, revealed the volcanic paint work underneath, which is still in super nice condition, and extremely durable. Upgraded it to 9 speed. Took it outside for a quick spin to make sure everything is working right, barely make it back alive from the freezing wind. All good to go! :D

[CNY rider]

That's a beauty weisan.
I refurbed my 24 year old Univega MTB last winter and now commute on it with lights, fenders, the whole shebang.
How old is yours? I'm guessing similar vintage. Mine still has the original Shimano 7 speed stuff. Incredibly durable and you can replace chains and consumables for practically nothing.

[Ken Robb]

Did it come with that tall stem and riser bars?

[weisan]

CNY pal, it's exactly 24 years old like yours!
I agree with everything you said, the 7-SPD stuff it came with are still working great, pretty much still got all the original components except the rubber grips have "melted" in the heat while sitting inside my friend's barn.
My plan is to use it as my backup commuter and for baby carrier duties.

Ken pal, i just got the stem and the bar last Tuesday at Austin's Yellow Bike Project, in their parts bin. I was looking specifically for a long quill stem that has an opening front plate. That plus a pump holder, they accept donation only -- $15 is my contribution to the general fund. :D

[AngryScientist]

funny stuff. i picked this up off ebay this year for stupid cheap money. mounted semi slick tires and it's my town bike that is a blast to ride. it literally goes over everything and i just dont care. 8-sp drivetrain that works just fine. cheap old MTB's are awesome fun.

http://2.bp.blogspot.com/-teNiyiEWv70/U7p_Gt7KCvI/AAAAAAAABuQ/kl5agMBa6GI/s1000/IMG_0011.JPG

[weisan]

Very cool, angry pal!
How's the cheapo tandem working out with the family?

Ken pal, a couple more closeup of the stem and the bar, not sure of the maker, it didn't say. How's the recovery? What do you have in mind?

[Black Dog]

I know that HED, for example, recommends lower pressures for their wheels else stuff like that happens.

HED does not recommend lower pressure to avoid taking their wheels out of dish or causing structural problems. That is silly talk... :rolleyes: They do recommend lower pressure for a better ride and less rolling resistance on their wider rims.

[carpediemracing]

HED does not recommend lower pressure to avoid taking their wheels out of dish or causing structural problems. That is silly talk... :rolleyes: They do recommend lower pressure for a better ride and less rolling resistance on their wider rims.

There's some Q&A where they mention lower tire pressures for rim related things. I can't find it but it relates to the Jet fairings. If the tire has too much pressure it can wrinkle the fairings. HED recommended taking out some of the pressure to eliminate the wrinkling. HED did not consider this a defect, it was considered normal/expected behavior.

Although this doesn't have to do with dish or whatever, it does illustrate that tire pressure can compress the rim enough to make the fairing wrinkle. If that's the case then tire pressure is also affecting spoke tension.

Having said that the more likely scenario is that the rider stands up and rocks the bike back and forth and the loose spoke is even more loose, leading to the rim almost collapsing on itself at the loose spoke point. Although the rider sample is just n=1 (me), I've had this happen to me a number of times, including my own front Bastogne/Ardenne rim. Other rims were lightweight rims, 280 and 330 g tubulars that were either crashed or, in one case, my teammate ran over with his car. The rims were fine in the truing stand, fine when riding seated in a straight line, but got wonky when either out of the saddle or cornering.