Swapping rims front with rear?

cdaly_

So my Mavic Aksiums are showing some wear on the front rim (the wear indicator is still there but with only about 1mm of depth left) while the rear rim is pretty much pristine.

Now, I understand that replacement rims (20h) are hard to get so I'm thinking it might be worthwhile swapping the rims between front and rear hubs in the hope of evening out the wear.

They've been very robust wheels thus far. I haven't had to touch the front and have only had to do minor truing of the rear. So, am I asking for a world of hurt by stripping and rebuilding these?

Lumen

Yes.

kumate_champ07

you will also save weight by using the old rim! (not sure exactly how much gets stipped off the braking surface )

gman2k

Mavic wheels - disposable items when things are worn out!

CheGuedara

Mavic Ksyrium Equipe rims - probably worth a look at as an alternative to taking your front wheel apart.

Not a bad price either.

cdaly_

Ooh! That could be just the thing! It's my front wheel that is wearing, rear is fine. They're nice wheels and I wouldn't want to ditch them for a worn out rim...

SomeFool

I have an aksium rim if you're near cork, you can take it away, condition is very good.

cdaly_

Thanks but nowhere near Cork alas. I just ordered one last night so I'll see how that build goes some day in the future...

doozerie

One issue that you may encounter if you were to swap the rims around is the spokes. In theory you should use news spokes when building a wheel, in practice you could probably re-use spokes for several builds and be fine - trouble is, I've no idea of how you could reliably determine if a spoke is actually re-usable or whether it no longer has any flex left in it in which case it'll make for a poor quality (and probbaly short-lived) wheel. The same is true of the rim too, to a certain extent, but it is easier to spot (some) issues with rims. New Mavic spokes typically are not cheap.

So I'd agree with the views that swapping the rims over is not worth the effort, better to go with a new rim or even a slightly used rim, and probably new spokes too, for your front wheel.

cdaly_

Indeed. Aksium spokes are €1.50 each (which isn't too bad).

I notice the listed rim is specified for a front wheel and there are other rims specified for rear. Is there much difference between them? Something like drilling angle?

doozerie

Some rear rims are offset (i.e. all nipple holes are offset to the same side of the rim) so that the spokes on each side can be the same length or similar lengths. I don't know off-hand whether the rear Aksiums are made like that - if not, and you were replacing with an offset rim then you'd need to buy different length spokes for both sides to build up a new wheel. I'm not sure whether the hubs differ between offset and non-offset rims - I suspect not but that's just a guess. I think my Ksyrium SL's are offset at the rear, can't recall for sure though.

cdaly_

The Aksium rear wheel is laced radial on the leftside and crossing on the right so there are already different spoke lengths. Looking at the rims on the bike, I can't see any difference between the front and rear. Both appear to have the holes centred anyhow. Hope I'm not going to discover the Krysium rim doesn't fit the Aksium hub and spokes!

doozerie

This may already be familiar to you, but in case not: a typical rear wheel has longer spokes on the non-drive side, shorter ones on the drive side. This is because the hub flange on the drive side is closer to the centre of the hub, to allow room for the cassette, effectively shortening the distance from flange to rim. Offset rims have the nipple holes closer to the non-drive side of the rim, in an effort to shorten the distance to non-drive side hub flange and lengthen the distance to drive-side hub flange. The effect is to reduce the difference in length needed between the non-drive -side and drive -side spokes, making for a rear wheel which is less severely dished than usual and thereby evening out tension of the spokes on either side.

The only offset rim that I have seen is noticeably different to a regular rim. If you were to slice a regular rear rim and look at the cut end, it would look like a V or U shape - both sides are mirror images, in that you could have either side of the rim as your drive side. Look at a slice of the offset rim I have seen and the they are noticeably different with the bulk of the rim material to one side of the rim - they are not mirror images so one side is designated as drive side and you can't swap the rim the other way around.

As regards whether you can do a straight swap of a Ksyrium rim for an Aksium rim without having to replace some/all of your spokes, this comes down to the ERD (Effective Rim Diameter) of the rims and the type of spokes each rim takes. The ERD is the diameter of the rim where the nipple (or head of spoke, depending on the type of rim/spoke) sits. If the ERD of both rims are the same, and they both take the same spokes, then a straight swap should work. It should probably work even if the ERD's are only out by a small amount (depending on how much thread there is on the spokes). You may be able to find the ERD of the rims online, though it can be tricky to find, and the Mavic website might give enough info to allow you to determine if the spokes are compatible.

cdaly_

Ah yes, I've seen those offset rim sections before. Wondered what they were about. Happy so that the Aksium rim is not offset (nor the Krysium AFAICT).

Edit: Looking at the Mavic site, the Aksium and the Krysium Equipe rims look the same. No ERD mentioned but both rims are listed as "height: 24mm". Difference appears to be primarily in the hubs.

doozerie

Oops, I was forgetting in all of this that you are replacing your front rim, so you won't have to worry about offset rims at all.

I did a quick check just now for the ERD of the Aksium and Ksyrium rims but Mavic don't seem to quote these at all for factory built wheelsets. I found this page though, which gives the ERD for their usual line of "build it yourself" rims - it's of no use to you, unfortunately, but might be of use to others. You can calculate the ERD yourself easily enough but only with the rim in your hands, and in the case of the Aksium you'll have to dismantle the wheel to do it.

kumate_champ07

Im thinking that spoke tension might be a problem, its gonna have to be pretty high with a 20h wheel. might take a bit of trial and error to get it to stay straight or you could buy a cheap guitar tuner and take note of the current tension(pluck the spokes like strings). that would be your reference when bringing up the tension of the new build

cdaly_

doozerie wrote: »

Oops, I was forgetting in all of this that you are replacing your front rim, so you won't have to worry about offset rims at all.

I did a quick check just now for the ERD of the Aksium and Ksyrium rims but Mavic don't seem to quote these at all for factory built wheelsets. I found this page though, which gives the ERD for their usual line of "build it yourself" rims - it's of no use to you, unfortunately, but might be of use to others. You can calculate the ERD yourself easily enough but only with the rim in your hands, and in the case of the Aksium you'll have to dismantle the wheel to do it.

I actually ordered two rims with the intention of doing the rear at some stage too. At some point I'll have a worn out front rim so I can measure the ERD then.

kumate_champ07 wrote: »

Im thinking that spoke tension might be a problem, its gonna have to be pretty high with a 20h wheel. might take a bit of trial and error to get it to stay straight or you could buy a cheap guitar tuner and take note of the current tension(pluck the spokes like strings). that would be your reference when bringing up the tension of the new build

Nice idea, thanks. I'll just have to steal a tuner from my (rocker) son...

Keep_Her_Lit

There are some variations in the design and length of Mavic Aksium spokes, depending on the year of manufacture (2007/8/10). This site provides a handy summary:

http://www.pedalon.co.uk/acatalog/copy_of_mavic_aksium_spoke.html

For general reference, a few spoke length calculators:

1. http://www.tech-mavic.com/tech-mavic/uk/calcul.htm#

2. http://lenni.info/edd/

3. http://www.dtswiss.com/SpokesCalc/Welcome.aspx?language=en

4. http://www.sheldonbrown.com/rinard/spocalc.htm

5. http://www.wheelpro.co.uk/spokecalc/

Some component specs are available here:
http://velospec.com/
However, this site does not seem to be maintained.

cdaly_

cdaly_ wrote: »

I just ordered one last night so I'll see how that build goes some day in the future...

Gah! Just got an email to say they are all sold out! :mad:

markdrayton

doozerie wrote: »

One issue that you may encounter if you were to swap the rims around is the spokes. In theory you should use news spokes when building a wheel, in practice you could probably re-use spokes for several builds and be fine - trouble is, I've no idea of how you could reliably determine if a spoke is actually re-usable or whether it no longer has any flex left in it in which case it'll make for a poor quality (and probbaly short-lived) wheel. The same is true of the rim too, to a certain extent, but it is easier to spot (some) issues with rims. New Mavic spokes typically are not cheap.

I vaguely recall from the wheelpro.co.uk book that reusing spokes is fine. The thing to ensure is that you use them in the same positions -- they'll be a bit bent where they cross the first spoke on the hub end (well, on a traditional wheel, anyway; not sure about flat Aksium spokes and their funny hubs) so you don't want to then stress them in a different direction. In general spokes tend to break at the hub end, often on the bend, so this is already a fairly stressed area. Won't be an issue if you rebuild by taping the new rim to the old one and moving a spoke at a time.

Also I don't think spokes are supposed to be flexy. Surely flexy spokes make bendy wheel which will flex under power? Strong wheels have tight, evenly tensioned spokes.

doozerie

markdrayton wrote: »

I vaguely recall from the wheelpro.co.uk book that reusing spokes is fine. The thing to ensure is that you use them in the same positions -- they'll be a bit bent where they cross the first spoke on the hub end (well, on a traditional wheel, anyway; not sure about flat Aksium spokes and their funny hubs) so you don't want to then stress them in a different direction. In general spokes tend to break at the hub end, often on the bend, so this is already a fairly stressed area. Won't be an issue if you rebuild by taping the new rim to the old one and moving a spoke at a time.

Also I don't think spokes are supposed to be flexy. Surely flexy spokes make bendy wheel which will flex under power? Strong wheels have tight, evenly tensioned spokes.

By "flex" I mean that the spokes haven't gotten close to their metal fatigue point yet. Probably the wrong terminology on my part but I'm too lazy to dig out the appropriate terms (Sean Kelly would approve of my energy-saving laziness, although he'd probably criticise me for not lying down while typing this).

If the wheel has had an easy life, then re-using the spokes is no doubt fine, though it is hard to gauge how often you can safely reuse them - maybe once, maybe twice, maybe 10 times, I've no idea to be honest. If the wheel has been stressed at any stage, whether by a crash or even something less dramatic, then you'd have to wonder whether any of the spokes are really safe to re-use. If you have been the sole owner of the wheel then you are well placed to judge whether it has had an easy or tough life, for a second-hand wheel I'd be more wary.

If reusing the spokes, I'd still replace the nipples - again, the existing nipples may be fine but whatever about the state of the threads, the outer body of the nipples takes a bit of a hammering when spokes are being tensioned so re-using nipples leads to a greater likelihood of them being rounded and that is a real pain when it happens.

Interestingly, a piece of advice I stumbled across recently, from Sheldon Brown, is to not lubricate the threads of spokes on radially spoked wheels. The logic of it makes sense but that web page takes a dim view of radial spoke patterns generally so it seems a little at odds with current trends generally (doesn't necessarily mean it is inaccurate, of course) so it's a bit of advice that might be contentious. I've not built a radially spoked wheel so I can't comment one way or the other, though I have had issues with seized nipples on a factory built radially spoked Mavic wheel which might not have arisen if they'd been lubricated (though the counter argument is that the wheel may have needed re-truing much earlier if the threads had been lubricated - Who knows? Certainly not me).

cdaly_

SomeFool wrote: »

I have an aksium rim if you're near cork, you can take it away, condition is very good.

Got a rim from SomeFool the other day. Thanks very much. Now all I need is for my existing rim to wear out... *



* Oh, and to practice building on an old wheel...