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Say the rim you're building with has a 110-120 kgf tension recommendation, would you build the wheel with a bit more tension than this to compensate for the inflated tyre or would you set final tension after you've fitted the tyre?
Before. According to the Roger Mussen book.
Before and after…
It’s important to keep the tensions even whilst building, it’s important to re-tension after fitting tyres because the amount of tension you can lose when doing so on modern rims with large tubeless tyres fitted is quite surprising.
Why would the tyre affect tension? I mean, I can picture the dynamics of it (compress inner skin, pull on bead) but realistically the rim should be built to withstand this. Don't remember any wheel builder ever mounting a tyre either.
Asking as someone who has never done it.
Why would the tyre affect tension?
You're basically working in the elastic range of all the materials in the wheel, once you add an inflated tyre you're putting a uniform, compressive load around the full circumference of the rim, in direct opposition to the tensile load in the spokes. It definitely can have an effect.
you’re putting a uniform, compressive load around the full circumference of the rim, in direct opposition to the tensile load in the spokes. It definitely can have an effect.
Yes, if you have a 25 mm (1") wide rim that's 600 mm (24") in diameter inflated to 30 psi, you'll have roughly 75 square inches x 30 = 2250 pounds = 1000 kg. With 32 spokes, each spoke will be compressed by the equivalent of about 30 kg. Spokes are generally tensioned to somewhere around 100 kg force, so the difference is quite easily measurable. Obviously, with a wider rim, you would run lower tyre pressures. If you tried running 50 psi on a 40 mm wide rim, you'd be losing about two thirds of your spoke tension.
Spokes are generally tensioned to somewhere around 100 kg force, so the difference is quite easily measurable
So would you tension to 100 at build and accept 70 with tyre, or tension to 100 with tyre fitted? I would imagine the former, as if you have an impact that blows the tyre, the rim would impact at an over-tensioned state.
My buddy is a pro mech, sent me this t'other day, apparently alot the DH teams* are now running undertentioned spokes and 25mm rims.
Quite interesting.
*Yes, he's not a DH rider, I know, but a pretty handy enduro rider.
I posted this a few weeks ago - certainly worth trueing/tensioning at the upper end of the spoke tension, fitting/inflating the tyre and going around the wheel with a tension meter at the end to make sure you're above the recommended minimum.
What pro teams do with an unlimited supply of new wheels and rims, particularly carbon has little bearing on the needs of average cyclists running alloy rims - riding with under-tension spokes is never going to end well, the nipples will shake themselves loose and the spokes will fatigue/snap.
I'm not suggesting for a minute that's what we do, just an interesting observation!. Fwiw they're having the same issues as the rest of us bte, his team have to look after their forks, as they've no spares either.
What are you using to measure the tension? How well calibrated is it for the spokes you're using? Are you measuring at the same point on every spoke and in the same direction? Applying the same initial loading and so on.
Your home tension meter is likely to gain or lose more kgf depending on what day of the week it is than your spokes subject to the amount of pressure in the tyre.
So the honest answer is, unless you trust the kit you're using, don't worry about tyre on off as you can't actually measure the tension anyway, you can only compare it to other spokes on the same wheel (assuming they're the same spokes and nipples, otherwise that's out too)
riding with under-tension spokes is never going to end well, the nipples will shake themselves loose and the spokes will fatigue/snap.
My understanding is that over-tensioning doesn't actually do any good. Obviously, you don't want the spokes to be loose, but the assumption that higher tension makes the wheel stronger apparently quite mistaken (this was the assumption I had until I started reading a bit about wheel building). I believe that if the spokes are all tensioned evenly and you don't have any slack spokes when the bike is loaded, then having uniformly higher tension won't actually change how much the spokes stretch as they are loaded and unloaded each revolution. This is because all the spokes are in tension at all times and the change in tension as the wheel rotates is the same. Provided the spoke tension is within the elastic limit of the material, the amount of stretch of the spoke depends only on the change in tension, not the absolute tension.
Your home tension meter is likely to gain or lose more kgf depending on what day of the week it is than your spokes subject to the amount of pressure in the tyre.
You should actually try this yourself. I first heard about the effect of tyre pressure from someone on here and my initial thought was it wouldn't make much of a difference. But then I tried it and was quite amazed at how big of a difference it makes.
All these years that I've not taken fitted tyres into account. That'll explain the many, many wheel failures I've encountered....
Oh. Not had any.
OP - I think you're worrying over nothing.
All these years that I’ve not taken fitted tyres into account. That’ll explain the many, many wheel failures I’ve encountered….
Oh. Not had any.
There are two different things going on here:
1. Should the wheel be tensioned with the tyre inflated or not? AFAIK, with the tyre not inflated.
2. Does inflating the tyre change the spoke tension? Yes, it does, by a surprising amount.
You should actually try this yourself. I first heard about the effect of tyre pressure from someone on here and my initial thought was it wouldn’t make much of a difference.
I'm not suggesting it doesn't, I'm suggesting that trying to achieve a desired tension with a device which is maybe accurate to +-20% is nuts.
There are two different things going on here:
1. Should the wheel be tensioned with the tyre inflated or not? AFAIK, with the tyre not inflated.
Edited before I go down a rabbit hole.
Agreed, if you're going to put stock in the numbers. Tyre off.
There are two different things going on here:
1. Should the wheel be tensioned with the tyre inflated or not? AFAIK, with the tyre not inflated.
Hence my reply to the OP.
I build to the upper limit of the rim/spokes in anticipation of the tension reduction form tyre inflation.
Afterwards,I only adjust for trueness.
Most rim manufacturers specify spoke tension on a bare wheel, and tension drop from tubeless beads is accounted for.
However given the varying fits of different tubeless tyres and rims some combinations have a large tension drop, which can require re dishing and adjusting tension.
If it drops 10% and goes 1mm out of dish its probably not going to make any difference, if it drops 30% and goes 10mm out of dish its going to need adjusted.
Some hub rim combinations also end up with very low rear disc side spoke tension once a tubeless tyre is mounted.
Why would the tyre affect tension?
Tubeless beads compress the rim lowering spoke tension, you can check with tyre off, tyre beaded and inflated, tyre beaded but not inflated to see.
Depends on the wheel.
Some nice solid eyeletted 26" wheels. Nope, just build them to the max tension.
Stans? Build them to the recommended tension. Get increasingly frustrated that they will never stay true however much you try because the max on the RDS means the RNDS is still basically slack. Then think "f*** it there must be a margin for error and an assumption of silly low tyre pressures" and add 25% so they survive in the real world.
It doesn't matter whether the tyre is tubeless or not. The only thing that matters is the tyre pressure and the rim width.
Was gonna say, can't see the difference between tubes or not.
I can see it adding compression so that answers that question but similarly the bead should be under tension.
The rim is compressed inwards and also under tension laterally. The lateral forces are at 90 degrees to the spoke tension so make no difference to that.
The rim is compressed inwards and also under tension laterally. The lateral forces are at 90 degrees to the spoke tension so make no difference to that.
The bead will contribute to the spokes slackening. Just not by much. At a point on the bead 90deg to the spoke you're looking at, the bead is tensioning in the same direction as the spokes.
Comparable to the idea of hoop stress in a pipe. Mathematically the tension lost would be that spokes share of the 16 spokes acting in that half of the wheel.
I’ve always tensioned, then destressed, then retensioned the wheels, then after the first normal ride recheck, never really checked after putting tyres on though without a ride on the wheels.
At a point on the bead 90deg to the spoke you’re looking at, the bead is tensioning in the same direction as the spokes.
I don't see what you're on about there. The spokes all point in different directions, none of them point directly towards the hub, but that averages out and the sum of all the tensions will be as if they are all pointed directly at the hub. The compressive forces on the rim from the tyre pressure will be perfectly radial, so this will reduce the spoke tension. The lateral forces on the rim from the tyre pressure will be balanced left to right, so will just be trying to burst the rim at 90 degrees to the average of the spoke tensions. At least that's how I understand it.
I built a couple of wheels with stans rims 3 years ago. There was a big drop in tension when the tyre went on, so I pinged Stans exactly this question. They said to set tension before the tyre goes on. I set it as close to max as possible (much lower when the tyre went back on) and they've been absolutely fine and are still true.
Guess there must be some tyre/rim combos which could cause problems but asking the rim manufacturer is always a good option.
if you have a 25 mm (1″) wide rim that’s 600 mm (24″) in diameter inflated to 30 psi, you’ll have roughly 75 square inches x 30 = 2250 pounds = 1000 kg. With 32 spokes, each spoke will be compressed by the equivalent of about 30 kg.
This is only true if the spokes don't stretch. If the spokes have infinite elastic modulus and the rim low then inflating the tyre to generate that 30kg / spoke will indeed reduce the tension on the spokes by that amount. If the rim has infinite modulus and the spokes low then inflating the tyre will have no effect on the spokes.
Observations above suggest the effect is significant so I guess the rim must be quite compressible compared to the spokes.
I’ve built a few sets of wheels, from 450g DT-Swiss/Mavic Open Pro road wheels to Rigida Sputniks. All with 32 or 36 spokes, tensioned/relieved/trued with not tyre to max tension.
Dish changes a fair bit once a tyre is added and maybe a 5% drop in tension. Last build steps for me is the final dish and small tweak to get the tension back up there.
Never had problems with coming out of true, cracked eyelets or taco-ing the rims, but I’m not using crazy light carbon ones.
Just curious how people get the dish right if they don’t check with the tyre on, do you account for the tension drop so it becomes central only with the tyre?
Dish changes a fair bit once a tyre is added and maybe a 5% drop in tension.
I've built alot of wheels
Never once seen this happen in a tensioned and stress relieved wheel.
More so. If we account for fitting tire..... What happens if we lower or up pressures to suit conditions ?
I have how ever seen the wheel uniformly lose tension when pressured up. Always on the overly light options mind - mostly once we fitte dtubeless bead hooks and dropped brake walls
@trail_rat - Could just be down to me not building properly, as I’m self taught from the Musson book?
I normally try to get the j-bends tapped to follow the flange, twist the spokes together etc. Then a couple of goes with flexing the wheel with the hub resting on a block, then grabbing the spokes in pairs while wearing gloves.
Think there is a big difference between a wheel with no tyre/tube, but assume the difference is less marked between the useable range of say 45-50-55 or 85-90-95 psi according to the tyre/rim combination?
Ryanbuildswheels told me that tension loss with tubeless is an issue and that he would retension after fitting the tyre.
Ryanbuildswheels told me that tension loss with tubeless is an issue and that he would retension after fitting the tyre.
He’s a reputable wheel builder with a good name, and makes a living from his craft… Trust him, he knows what he’s talking about. I’ve discussed this with other reputable wheel builders I know at length before, it’s a very real phenomenon caused by increasingly lighter and less inherently strong rims, and increasingly larger and tougher tubeless tyres (despite what you might think, tubed tyres won’t drop the spoke tension anywhere near as much as tubeless do)…
Don’t obsess over the tension figures. Spoke tension meters are a guide rather than an absolute. Obsess over getting even tensions from spoke to spoke on the same side of the wheel. As long as spoke tensions are “within range” (usually front disc side and ear drive side will have to be at the upper end for the front non disc or rear disc side to remotely come into the tension range) and tensions are pretty equal from spoke to spoke on the same side still once the wheel is fully built, de-stressed and tyres fitted, then it has every chance of being able to withstand a decent amount of abuse…
Never read Roger Musson’s book, have heard it’s good, but would suggest also that things have changed since the book was written a while ago…
tubed tyres won’t drop the spoke tension anywhere near as much as tubeless do
Having a tube or not won't make any difference because the air pressure is transferred to the rim either way. The rim width and tyre pressure will. Proper tubeless rims and tyres tend to be much wider than the old tubed versions, so my guess is that people aren't comparing the same tyre setups when they talk about tubes versus tubeless.
In the olden days, a standard XC rim was 17 mm (roughly 3/4") wide with a 1.95" tyre. Tyre pressures of 30 to 40 psi were normal to avoid pinch flatting the tubes. Now a 25 mm wide rim is fairly normal, but pressures have dropped to 20 to 30 psi with wider tubeless tyres. A 29" wheel is approximately 600 mm (24") across the rim bed, a 26" is about 540 mm (21.5").
The force on the two rims is approximately as follows:
26": 3/4" x 21.5" x pi x 40 psi = approx. 2025 pounds force
29": 1" x 24" x pi x 30 psi = approx. 2310 pounds force
If you bump that up to 50 psi and 40 psi to account for people overinflating tyres you get:
26": approx. 2530 pounds force
29": approx. 3080 pounds force
If you increase the 29" rim width to 35 mm and drop the max pressure to 30 psi, you get slightly over 3100 pounds force. That is massively higher than an old 26" XC rim. Modern wheels with wide rims and larger diameters will result in more loss of spoke tension than older skinny rims.
Taking your time to get even tension is the most important, I always go just under max tension and once the tyre is on I check the wheel is still true, especially after wrestling with a stubborn pig of a tyre rhats required standing on it, then if the spokes are still evenly tensioned I wouldn't worry, giving the spokes a squeeze together let's me know they're within a decent range and not to loose, I read somewhere Loic Bruni's mechanic alters tensions for different courses and Manon Carpenters mechanic used to build her wheels looser than usual.
If your spoke meters accuracy is a concern see if your LBS will let you check it against similar set ups on the shop floor.
During building I stress the spokes by doing a few push ups holding onto the rim with my hands at 3 and 9 o clock, do a quarter turn and repeat a few times on both sides, never had spokes ping or come loose while riding after doing that.
I don’t see what you’re on about there. The spokes all point in different directions, none of them point directly towards the hub, but that averages out and the sum of all the tensions will be as if they are all pointed directly at the hub.
Yes
The compressive forces on the rim from the tyre pressure will be perfectly radial, so this will reduce the spoke tension.
Yes
The lateral forces on the rim from the tyre pressure will be balanced left to right, so will just be trying to burst the rim at 90 degrees to the average of the spoke tensions. At least that’s how I understand it.
Kinda.
I was refering to the tension in the tyre bead acting on the rim and compressing it. Which is probably not negligible with road tubeless and carbon fibre beads.
There will also be a component of air pressure that is expanding the rim (or rather, partially countering the compressive force). The cross sectional area of the tyre is acting against the tyre bead tension.
There's also the outer surface of the tyre being pushed outwards, but that's being taken by the tyre bead (hopefully)!
Having a tube or not won’t make any difference because the air pressure is transferred to the rim either way.
For whatever reason. That isn't the case. You can see it fairly obviously in road wheels which haven't got that much wider (or get run with/without tubes even with the same tyres). And DH wheels haven't been skinny for a long time, they've even got narrower in some cases.
I suspect it's partially down to the way the tube deforms inside the rim makes it effectively anything upto 4mm narrower, which might be a third of the internal width once you account for the width of the tyre bead being 5mm each side. And it having less of an effect on the opposing 'expanding' forced I mentioned above.
Having a tube or not won’t make any difference because the air pressure is transferred to the rim either way. The rim width and tyre pressure will. Proper tubeless rims and tyres tend to be much wider than the old tubed versions, so my guess is that people aren’t comparing the same tyre setups when they talk about tubes versus tubeless.
In my experience on tubeless MTB wheels its the tubeless tyre beads compressing the rim, not the tyre pressure contributing to the majority of the tension drop.
This can be seen by measuring spoke tension with the tyre inflated and then the tyre beaded but deflated, the tension then increased when the beads were broken
Obviously different tyre/rim combinations result in different tension drops.
In my experience on tubeless MTB wheels its the tubeless tyre beads compressing the rim, not the tyre pressure contributing to the majority of the tension drop
If they were tight enough to exert 1000 kg radial force on the rim, I don't believe you'd ever be able to remove them without cutting them off.
I suspect it’s partially down to the way the tube deforms inside the rim makes it effectively anything upto 4mm narrower, which might be a third of the internal width once you account for the width of the tyre bead being 5mm each side. And it having less of an effect on the opposing ‘expanding’ forced I mentioned above.
This makes sense. A tube will reduce the effective width of the rim that air pressure acts on, assuming you have identical tyres. A tyre with thicker sidewalls and beads will too. So, yes, a 17 mm rim might actually be 10 mm effective width, whereas a 30 mm rim with the same tyre setup would be 23 mm. This has little to do with the tube though, just the effective width of the rim.
I can't re-tension the spokes on my road wheels with the tyres fitted. They have deep section rims with upside down nipples accessed under the rim tape.
Ive had lots of issues with my roval 28h carbon rims de tensioning. This became even more apparent when fitting a black diamond tire to it.
Ive started to build to full tension (destress etc) thenfit the tyre and have a quick spin up and down the road. I then re tension with the tire installed and inflated to just below the max tensions.
this seems to work. but im a complete newbie to all this.
a black diamond tire
Please tell me that's the name of a Specialized tyre, not that I've been timewarped back 15 years and Black Diamond, All Mountain, etc. are still in vogue. I was always more of an Aggessive XC guy, my dick shrivels up when I hear "Black Diamond".
In which case you'd either build to MAX rim tension (and maybe a little beyond) and accept the drop. of build and tension the pair and the inflate a tyre on one of them and measure the tension drop and then re-tension the pair to take up the eventual slack.
I'd do the former. My experience of carbon rims is that they're far less sensitive to lower spoke tension than their aluminium equivalents and all my rims are now carbon.
I was always more of an Aggessive XC guy,
Aggressive xc.....is that where you pass close in an unappropriate place pushing the other rider off while shouting *podium rider coming through* ?
Aggressive xc…..is that where you pass close in an unappropriate place pushing the other rider off while shouting *podium rider coming through* ?
I guess. TBH, my experience of passing other riders is fairly minimal. It seems to require riding faster than them.
yup specialized thick carcass jobbie.
its quite a lot of tension drop. about 20%
Never read Roger Musson’s book, have heard it’s good, but would suggest also that things have changed since the book was written a while ago…
What, like the laws of Physics? 😀
OP – I think you’re worrying over nothing.
This is the best advice you've been given on here.
I'd suggest building with tension measurement before mounting tyre, but potentially re-verify the tension is within acceptable range after mounting and pumping up the tyre if this is likely to have a significant impact - e.g. a tubeless road setup for a larger person who runs high pressures.