Rim swapping - advice

The Rookie

OK, so I've done most jobs on my bike, and I have previously replaced spokes and trued wheels (with varying degrees of success), but I've never built a wheel or done a rim swap.

Starting in the logical place and I am now in a position to try a rim swap from the current Superstar vapours (Mach1 MX rebranded) to some Rigida lighter weight rims.

ERD is meant to be about 2mm smaller on the knew rims (531.8 v 534), so should be no issue with re-using the original spokes (DT swiss Comp DB with brass nipples - hubs are SS superleggera/superfast) as the current spokes end about 1mm or more below the top of the nipple.

As I understand it the easy way to do this is to tape the 2 rims together fairly tightly, swap one side spokes over, then the other? Obviously the first side has to be left loose enough to allow the rim to be pulled over central.

Have I got this right, anyone any hints and tips? how tight/loose should i leave the first row? Was thinking of visually setting the spoke tip about 1mm higher in the nipple given the ERD change.

I have some old front forks I'll use as a truing rig for the front (an old frame for the rear) by my usual technique of attaching a ruler so I can get dish as well as trueness correct.

Finished wheelset should be about 1672g and set me back about £100 which sounds too good to be true, if I louse it up, as long as I get the wheel close to true the LBS will only charger a tenner/wheel to sort it out for me anyway!

Front first as I have an old spare front to chuck on.....no spare rear!

pilch

http://www.wheelpro.co.uk/wheelbuilding/book.php

Really good £9 worth every penny

The Rookie

Already have that thanks!

rrsodl

I think that is the technique for rim swapping, I have never done that, just build wheels from scratch.

If your spokes fit the nipples as you described then you should be OK but I'd still use a spoke calculator to double check. Also measure the ERD yourself.

I'd start by loosening the spokes half a turn to a turn on your current wheel and gradually incrementing the turns. For safety reason DO NOT LOOK DIRECTLY AT THE BACK OF THE NIPPLES while you begin to turn the nipples.

Use the tension on another wheel that is properly tensioned to judge the tension on your new wheel. Use tone to balance the overall tension. If you leave some spokes loose then before long your wheel will go out of true.
When balancing the spoke tension do one side at a time.

Good luck

The Rookie

Thanks for the tips....I've measured the ERD's and the diameter across the INSIDE of the eyelets is identical (to the accuracy I can get anyway!).

mrmonkfinger

The Beginner wrote:

Thanks for the tips....I've measured the ERD's and the diameter across the INSIDE of the eyelets is identical (to the accuracy I can get anyway!).

Should be fine then. 90% of MTB rims wind up around 260mm spokes anyway. Worst case, you can always buy longer/shorter nipples which gain/lose about 1mm.

Anyway, getting the initial tension - make yourself a nipple driver from an old flat blade screwdriver (grind off some of the sides so you leave a 1mm x 3mm point). That gets all the spokes/nipples done up a known amount.



Then just go at it slowly, add a 1/2 turn to each nipple, go round the whole wheel. You'll know when you have a good start point when the spokes are no longer 'floppy'.

BTW which Rigidas? Edge 7s?

The Rookie

Ok thanks, did consider makjng a spaced nipple driver like that!

Yup Edge7's.....lighter than Mav 717's

mrmonkfinger

Yeah they're flyweight and a half.

1672g

I'd have guessed closer to 1600g. The superfast are light (150g?), and the superleggera isn't exactly beefcake (300g?), add 400g for spokes, 370g per rim.

The Rookie

Lighter would be nicer.....1672 is based on current weight less the Mach1 rims plus the Edges, That tallies with the claimed weight of the 717 build SS used to offer, using 380 for spokes and 60 for nipples, I get 490g for both hubs.

mrmonkfinger

Fair enough.

I forgot, dt comp, they're 2/1.8/2, come out a touch heavier than the aci 2/1.7/2 I'd used recently.

Superleggera must be closer to 350g then, is it an older model or the current one?

The Rookie

MF - they are older ones from when the SuperLegera/fast were first launched, I have the claimed weights for the Mav 717 build which use the same spokes and nipples as my wheels, using those weights and the 717 rim weights I get 490g for the 2 hubs, if I take the same weights off my wheels plus the 500g for the Mach1 MX rims it comes to the same, the spoke weights are well known (within a couple of grams for different lengths), Brass nipples also fairly well known within a few grams.

Cyd - Ok thanls for the tip.

mrmonkfinger

cyd190468 wrote:

After you have the new rim on don't forget to seat the nipples by laying the wheel on the ground and putting weight on the rim. Work your way round putting sideways load on the rim, then flip the wheel and repeat. Otherwise it'll take forever to get the tension even and stable.

Drawback is, you can't get enough extra tension on any individual spoke that way, at least without seriously deforming the rim and overstressing the hub bearings.

I use a big spanner to destress spokes & seat. Just stick it between two spokes near where they cross, and use it to lever the spokes a bit. Or you can grab parallel pairs of spokes and give a decent squeeze.

Most of this stuff should be in the Roger Musson book.


Some good advice re: stress relieving from Jobst Brandt:

Stress relieving to relax these high stress points is accomplished by over-stressing them in order to erase their memory. It is not done to bed the spokes into the hub, as is often stated. Bedding-in occurs sufficiently from tension. However, stretching spoke pairs with a strong grasp at midspan, can momentarily increased tension by 50% to 100%. Because spokes are usually tensioned no higher than 1/3 their yield stress, this operation has no effect on the spoke as a whole, affecting only the small high stress zones where spokes are near yield. By stretching them, these zones relax below yield by as much as the overload.

Stress relieving with a light grasp of spoke pairs is worthless, as is bouncing the wheel or bending it in a partially opened drawer. Pressing axially on the hub, while supporting the rim, requires a force larger than is manually possible but is effective for spoking machines (except the left side rear spokes that would collapse the rim). Another not recommend method, is laying the wheel on the floor and walking on it with tennis shoes, carefully stepping on each pair of crossed spokes. The method works but bends the rim and is difficult to control.

The Rookie

I am reading the book, I also have the benfefit that I will be using pre-used spoke/nipples (unless the spare spokes I've got are lighter anyway!).