What are the real advantages of double wall rims?
 

A couple of months ago I got a new double wall rear wheel for my bike, and in the time being I had to true the wheel about 20 times due to spokes getting loose. I lost one spoke because it was loose for too long and the wheel even wasn't out of true.

One reason could be that the wheel wasn't built right in the first place and the other one is that, unlike on the single wall rim, the tube is not keeping the nipples in place and they are vulnerable to road vibrations.

When I got the wheel, I noticed some irregularities in true and tension, so I got the mechanic at the shop to fix it for free as it was their responsibility. Afterward, the tension and true looked great and I started riding. Wheel was quickly getting out of true and I noticed that the tension wasn't like it used to be when I got it. That went on for a while. I had to keep truing after every long ride.

I don't know if this is a common occurrence with double wall rims or I got a really cheap wheel, but it's really annoying and the whole reason is because the nipples are not supported by the tube like on the single wall rim.

So are DW rims really that much stronger because there are 2 walls? I mean they could build a single wall that's a bit thicker for the strength and nobody would worry about their spokes loosening. Also you have to buy a rim tape to cover the holes as the regular rim strip doesn't work with double walls.

Is there anything out there to limit the spoke loosening or I need to get a lot more expensive wheel? I might even rebuild my 25 year old single wall rim that came with a bike because even with old and corroded spokes, it served me well for about a year and 1/2.

I really don't see the point of double walls.

I would be interested to hear more about how the nipples are supported by the tube....

When the tube is inflated, it presses down on the nipple and that's what keeps it in place.

:twitchy:

What? It's common sense.

You're having wheel problems because the wheel was poorly built. The components are just fine. I'd look for a new bike mechanic.

As far as your understanding of the physics behind what keeps a wheel true (inner tube), you're better off reading up on it rather than making conjectures.

OP is pointing out that the nipple heads are not hidden in single wall rim as they are with a double wall rim. With either style of rim nipples should not be unthreading themselves provided the wheel was built correctly with spoke prep and tensioned properly.

For the record what is the actual rim you are using spock?

If it did, you would be having constant punctures, and the wheel could never be built / tensioned in a conventional manner (don't know how you would build one like that)

The nipples have to be tightend into the rim, not away from it to get any tension.

From the sound of ypou post, you have a very poorly built wheel, and it is very hard to loose a spoke when riding, as the head will be in the hub, and this will be very noticiable if it tries to leave. Suggest that you find another LBS to build your wheels, as they don't seem to have made a good job of this one.

I can't find it on the net. I don't know the exact model. It's a weinmann wheel 27' freewheel. Here is a pic.

http://farm3.static.flickr.com/2390/...980e0228_b.jpg

The wheel seemed to have been built fine when I walked out. Tension seemed equal and strong enough and the true was good. I think the spokes simply loosened.

I'm not sure why you don't believe us when we tell you that the wheel was NOT built correctly. The tension could not have been adequate for the wheel to fail so miserably. Again, please educate yourself on the physics behind a bicycle wheel rather than making erroneous assumptions.

There is a rim strip protecting the tube and the tube when it's inflated fully, goes against nipple heads and rim strip with some force and that way it's kind of keeping nipples from turning if there are any irregularities in spoke movement.

All rims have a rims strip of some type, this is to protect the innertube from the edges of the spoke holes; which are often sharp & can swarf in them, not the spokes. If your spokes are protruding to hit the rim tape, sounds like the spokes are too long. also, in normal use, the spokes will not move or have any 'irregularities', these will stay in the same place.

I may not know much about wheel building, but when I got my bike, it had the original wheel on it and the spokes were old and corroded while completely out of true. At that time I knew nothing about wheel truing and learned to true on that wheel. Afterward I had no problems with it for a long time. Single wall rim. Over a year later I hit a big pot hole and broke a spoke and from that moment they all started breaking eventually. It was a really old wheel too.

In this case, when I got the wheel, true and tension seemed way better then on my old wheel. Everything just changed quickly afterward.

The wheel might not have been built correctly as I really don't know how to build a wheel. You could be correct tho'. Tension might not have been strong enough and spokes started unscrewing from too much slack. I just don't think if that same build was on the single wall rim, loosening would not have happened because of tube press against nipple heads would not have allowed it.

Either it wasn't built with sufficient tension or you've put bends in it which preclude the wheel being true with enough tension in all the spokes to keep the nipples from turning (the bend is closer to the spokes on one side, with those spokes needing to be looser to make the wheel straight)

With enough tension the nipples won't turn until you bend the rim even when they're properly lubricated at the threads and sockets (anti-seize works well).

I got 12-14 years out of my last front wheel (Mavic Reflex clincher double wallked socketed rim, DT Revolution 2.0/1.5mm spokes with alloy nipples, Campagnolo hub) before I needed to touch it; and that only happened because I bent the rim on some sort of road obstacle whilst commuting with 15 pounds of luggage and 40 pounds of belly on a 400 gram rim.

Beam stiffness is proportional to the cube of depth and with additional material below where the tube sits a double walled rim can be a lot deeper than single walled.

Enough tension and stress-relieving + spoke line correction so the wheel doesn't settle as the spokes bend themselves around the hub flanges.

With lightish box section alloy rims you can use the Jobst Brandt method where you increase tension and stress relieve (squeeze near parallel spokes on a side hard with gloves helping; or twist spokes about themselves with something softer than the spokes like an old left crank arm or plastic screw driver handle (I use a brass drift)) until the rim deforms in waves when stress relieving which indicates it has reached its elastic limit. You then back off half a turn, true, and be happy until you crash the wheel or wear out the brake surfaces.

Or you can get a Park tension meter (at $50 it's reasonable for the occasional wheel builder). 110kgf usually works for front wheels and the rear drive side and perhaps not coincidentally the last two wheels I built the Jobst way measured 110kgf front without a tire and 110kgf rear drive side with.

You'll get a lighter rim that's strong enough and perhaps a more aerodynamic profile.

Sure, that is exactly what I meant. Tube keeps the wheel true....;) I believe you can make much better assumptions if you try.

It keeps nipples from turning because of the pressure that is applied by the tube on the nipple heads, or it makes it much less likely to unscrew as I had it happen on my double wall rim.

Properly tensioned and stress relieved spokes do not loosen in any sort of rim. You are probably right about the tube stopping the nipples from turning on the SW rim, but this is only necessary if the spokes are under-tensioned. Since you said the new wheel had more tension than the old wheel, we can assume the old wheels has spokes that are much much much too loose, and the new wheel has spokes that are only much much too loose.

THe correct fix would be to put a drop of light oil into each nipple and bring the tension up to spec, then stress relieve with a gloved hand or old crankarm, etc, then re-true and bring back up to tension again. The machine or person that built the new wheel skipped or was igner'nt to these important finishing steps.

"Attention Enterprise...come in Enterprise. We are relaying an emergency message from Vulcan regarding your Science Officer..."

=8-)

(Wheel was not built properly - period!)

=8-)

Message received already. I'm a bit stubborn tho'. What was that again....;)

Yea I know. It's slowly sinking in.

Very slowly...

How many people will it take for you to believe that the tube is NOT what holds the nipples in place? There are thousands of double wall rims that have gone millions of miles without the spokes loosening up.

Yes, the tube may keep them from going completely slack on a single wall rim. But if they're that loose you'll start breaking spokes either way. PROPER TENSION is what keeps the nipples from loosening, NOT the inner tube.

I think you're overestimating the friction between the nipple head and the rim strip, even under a fully inflated tire.
Both the friction of the spoke/nipple threads, and the friction between the rim's spoke hole and the nipple itself are far greater. If the nipple can overcome these frictions to loosen, a bit of top pressure from a rim strip isn't going to slow it significantly.

Are you familiar with the concept of spoke wind-up? It's when turning the nipple, it stays put in relation to the spoke, so you end up twisting the spoke instead. This also increase tension in the spoke, so the wheel might still look fine and dandy.
But subject it to a few road bumps and the spokes will unwind and lose tension. If you hear a pinging noise when first riding a wheel that's been worked on, this is probably it.
Although more prominent on butted spokes it can happen to any spoke.

Have you ever tried to true a wheel with a single-wall rim without deflating the tube? THere is definitely increased friction... ... at least until the nipple gets the rim strip and tube wrapped around it and tears a hole in the tube.

So, was this wheel built custom? If it wasn't, all the pre-built wheels I've ever seen with those weinmann rims are machine built, and that allows for a few bad ones to slip through. It's just not tensioned correctly. Sounds like the shop was in a hurry when they fixed it too, because it's not that hard to tension a wheel properly, it just takes some patience.

I'll just chime in to reiterate and make sure the message is clear. That wheel was built very poorly. When built properly, it should need no attention for many many miles and or years regardless of single wall or double wall construction. I was just giving some very similar wheels to a friend of mine that have never ever been trued. They were built in 1990 for a mountain-bike. 21 years in an off road application and still true.

By the way, since this has been an ongoing issue with this wheel. Spokes that have not broken yet have endured higher than normal stress levels at the bend. I would have some concern over their strength even after the wheel is properly tensioned by someone who knows what they are doing. The lowest cost fix will be to find a pro and pay the going rate to properly assess the situation. If you insist on repeated "cheap" fixes, you will pay more over time and your aggravation level will keep you from fully enjoying your bike. I would like to see you avoid this.

A bicycle wheel has 5 components: hub, rim, spokes, nipples, and build quality. Of these build quality is the most important. A skillful builder can compensate for lower quality rims or spokes but even the best quality components won't compensate for a sloppy build.