Tire Pressure Changes Spoke Tension
02-19-16, 12:17 AM
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Tire Pressure Changes Spoke Tension
So I built up a set of wheels.
Let's discuss the front wheel as an example. For the rims I used the manufacturer suggested keeping the spoke tension under 125kgf. The average spoke tension of the wheel after it was built was around 105kgf.
I mounted the tire and inflated the tube to the recommended PSI (120). Now, due to the wheel being constricted by the fully inflated tire/tube, my average spoke tension is around 75kgf.
My question is: Should I increase the over all tension of the spokes to get them closer to 100kgf with a fully inflated tire/tube mounted, even though without the tire/tube this may be pushing the limits of the rim? Or should I just leave it, ride it, and not worry about?
Let's discuss the front wheel as an example. For the rims I used the manufacturer suggested keeping the spoke tension under 125kgf. The average spoke tension of the wheel after it was built was around 105kgf.
I mounted the tire and inflated the tube to the recommended PSI (120). Now, due to the wheel being constricted by the fully inflated tire/tube, my average spoke tension is around 75kgf.
My question is: Should I increase the over all tension of the spokes to get them closer to 100kgf with a fully inflated tire/tube mounted, even though without the tire/tube this may be pushing the limits of the rim? Or should I just leave it, ride it, and not worry about?
Last edited by mrblue; 02-19-16 at 12:25 AM.
02-19-16, 12:31 AM
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No.
The engineering guidelines for spoke tension are based on the wheel before tires are mounted. This follows the basic rule that specs and guidelines should be based on conditions before unknown variables are introduced.
Imagine if you needed to adjust spoke tension according to what happens when tires are mounted. The wheel builder would have no idea what was called for unless he knew what width tires you planned on and what pressure you were pumping to.
So, yes, tires do cause a pressure drop by shrinking the rim, but that was expected and there's no reason to compensate.
BTW - on rear wheels with different tension right and left, the drop can move the dish over a bit. Some people try to compensate o redish, but here too it isn't called for because the difference is small enough to be immaterial in the scheme of things.
The engineering guidelines for spoke tension are based on the wheel before tires are mounted. This follows the basic rule that specs and guidelines should be based on conditions before unknown variables are introduced.
Imagine if you needed to adjust spoke tension according to what happens when tires are mounted. The wheel builder would have no idea what was called for unless he knew what width tires you planned on and what pressure you were pumping to.
So, yes, tires do cause a pressure drop by shrinking the rim, but that was expected and there's no reason to compensate.
BTW - on rear wheels with different tension right and left, the drop can move the dish over a bit. Some people try to compensate o redish, but here too it isn't called for because the difference is small enough to be immaterial in the scheme of things.
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02-19-16, 01:06 AM
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02-19-16, 06:24 PM
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I mounted the tire and inflated the tube to the recommended PSI (120). Now, due to the wheel being constricted by the fully inflated tire/tube, my average spoke tension is around 75kgf.
My question is: Should I increase the over all tension of the spokes to get them closer to 100kgf with a fully inflated tire/tube mounted, even though without the tire/tube this may be pushing the limits of the rim? Or should I just leave it, ride it, and not worry about?
My question is: Should I increase the over all tension of the spokes to get them closer to 100kgf with a fully inflated tire/tube mounted, even though without the tire/tube this may be pushing the limits of the rim? Or should I just leave it, ride it, and not worry about?
You should increase rear drive side tension closer to the allowed 125kgf, especially if you're not running 2.0/1.5mm spokes and/or not using a disk wheel, because the low resulting NDS tension may allow nipples to unscrew.
2.0/1.5mm spokes stretch about 44% more at a given tension than 2.0/1.8mm so they tolerate more rim deflection before going slack and unscrewing nipples.
A disk in back moves the NDS spokes right, flattening their bracing angle and requiring more tension which produces more stretch and tolerance.
