Spoke tension change after tire install- Mtbr.com
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  1. #1
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    Spoke tension change after tire install

    Built a set of WTB KOM's on Sapim spokes, everything is trued up tension is 120kpf +or- a bit on the rotor side (high tension side). the other side is 75-80% of that. I install a Specialized Purgatory and for shits and giggles I check the tension and it has dropped to below 100kpf on the high side.

    Do I just tension it up keeping it true or do a set of tubeless tires effect it that much? This is the first time I've built a set of wheels but it is something I've wanted to do for years. Need a little guidance if you can.

    Thanks.

  2. #2
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    Reputation: Saul Lumikko's Avatar
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    I've been told it doesn't matter but I'm open to other suggestions as well. I would feel most comfortable with spokes at specified tension when everything is together and aired up, but I'd rather not go over any limits even during assembly.

  3. #3
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    I just don't want to end up taco-ing a wheel 10mi. from the trailhead because of something I didn't do.

    I like the challenge of doing things myself, problem is we know where the blame is if it gets messed up.

  4. #4
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    I've built a lot of wheels and never did anything to them after the tires were installed. I've had no come backs and none of my own wheels have failed.
    I like turtles

  5. #5
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    The only wheel I was concerned about was a Stans Flow wheelset I built. They required lower spoke tension (95kgf on the drive side and on front disc side) and after installing Specialized 2Bliss tires and inflating them the spoke tension was very low. I ended up increasing the tension about 20kgf then mounting the tires and the wheels were much better then.

    Here's a thread from a couple of years ago on this
    http://forums.mtbr.com/wheels-tires/...on-777704.html

  6. #6
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    Quote Originally Posted by Bike Whisperer View Post
    Here's a thread from a couple of years ago on this
    http://forums.mtbr.com/wheels-tires/...on-777704.html
    Good read. Thanks, exactly what I was looking for.

  7. #7
    Chris Bling
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    I have built a number of KOM wheels and they really do need to be retentsoned after you initially install and inflate the tire to about 45 psi. Your rims will loose a substantial amount of tension. The one I just built for a customer of mine list 4-5 'ticks' on the Park scale. It detensioned it to a point where It would not be rideable. After the initial 'crush', you wont lose any more tension than a normal rim would.

    I wrote about it an another post about the KOM rims somewhere on this forum.
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  8. #8
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    Quote Originally Posted by Bike Whisperer View Post
    The only wheel I was concerned about was a Stans Flow wheelset I built. They required lower spoke tension (95kgf on the drive side and on front disc side) and after installing Specialized 2Bliss tires and inflating them the spoke tension was very low. I ended up increasing the tension about 20kgf then mounting the tires and the wheels were much better then.

    Here's a thread from a couple of years ago on this
    http://forums.mtbr.com/wheels-tires/...on-777704.html
    I have built four wheels using Stan's rim in the last two weeks and didn't even think about spoke tension, mostly because it's not on the rim and the rims include no instructions, and took them all to 120kgf. I find it pretty annoying they they would make a recommendation like that and then bury it in their website with no mention to it. Good to know though, looks like I have two wheels to loosen and two to tighten.

    I have always found that wheels loose tension (measured) with a tire installed and inflated. I will make sure they fall in the usable range (80-120 usually) with a tire on at max.

  9. #9
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    I built a set of Stan's Arch EX on DT Swiss 240s with DT Swiss Competition spokes (2-1.8-2). Took them to 120kgF which is the recommended for both the rims and hubs. Installed a tubeless ready Schwalbe Nobby Nic Evo on the front and Racing Ralph Evo on the rear. Lost 40-50% of spoke tension on both! Air pressure didn't play a role. Re-tensioned back to 120kgF with tyres on. Truing with tyres on is a bit of a pain. Especially radial trueness. Anyone got any tips for checking it with the tyre on?

    So in the other thread linked to above Stan advised to increase tension. Great. What about changing tyres? Is it safe to take them off? What's the general consensus?

  10. #10
    mtbpete
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    The old Flows had been recommended to be tensioned to 95, but 110 is fine. The Flow EX is 120, and they can certainly handle more, but it would be unnecessary.

  11. #11
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    I had this problem a few years ago when I built the first set of wheels for someone besides myself. FYI - modern Stan's rims all have 120kgf tension spec, which is why the Arch EX rim weight went up to from 450g to 480g a few years ago - they incresed the spoke bed thickness. Except the Crest (and maybe iron cross? don't build enough of those to know off the top of my head), which is still 95/100kgf.

    The wheels I had issues with were Arch EX rims. They lost a lot of tension, and went wobbly on their first ride. I did lots of experimenting, checking tension with tires on and off the rim, new tires, old tires, flat tires, inflated tires. Ultimately, the reason the wheels had issues was because the tension was too low to start with. I was using a brand new Park tensionmeter and it wasn't calibrated properly. I now have a process for ensuring my meter stays calibrated.

    But, what I learned is that new tires can drop the tension by quite a bit. But I once removed, the tension goes back where it was to begin with (dustyduke's theory on an "initial crush" isn't something I've seen....). Once a tire's been used, taken on and off a time or two, it causes much less tension drop. I even made some graphs showing the tension drop. BUT, those graphs were all made before the meter was recalibrated, so they're pretty worthless. I should do it again...

    Anyhow...tension drop is a fact of life, always has been. As long as the initial tension is high enough, and you have enough spokes, the wheels will be fine.

  12. #12
    mtbpete
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    100kgf is plenty with the tire mounted. If you haven't done a lot of stress relieving mounting the tire and riding the bike will do it for you and sometimes the tension will be a little lower when you remove the tire and check compared to when it was freshly built.

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