Deciding between two DT swiss aluminium rims

[mstateglfr]

Originally Posted by robertbb

It'd be a no-brainer if I could get the asymmetric rim with the RR481 dimensions. I'm just concerned that a 20mm inner width (nor a 22mm outer width) wide enough for where bikes and tyres are going...

If you are going to use 32mm - 42m tires, then it really doesn't matter where the industry is going with tire width. They may go narrower or may go comically wider, but that doesn't need to be a factor for you in this situation.

For a 22mm to 42mm tire range, I wouldn't hesitate to select rims that are 20mm wide internally and 24mm wide externally.

- They are lighter, so since neither rim gives aero gains, you may as well higlve lighter wheels.
- They are plenty wide to easily and competently handle your tire width range.
- They are offset and allow for a better build.

For years I used H+Son Hydra rims on my gravel bike- it's 20mm internal and 25mm external, and 23mm deep. So pretty similar measurements as the RR421. I used 42mm WTB tires and 43mm Panaracer tires and never thought twice about tire width compared to rim width when I was actually riding.

[coffeecherrypie]

Originally Posted by robertbb

Do you find that they bulb too much? I know it'll work but I guess tyres perform best when the shape is correct for the tread. I don't care about aero.

I can't say that it looks (or feels) particularly bulby to me, to have 38s on 18mm internal width.

[robertbb]

Thanks everyone for your inputs and experiences - I've decided to go with the RR421.

A question on spokes choice. Since the RR421 rim is lighter and has a smaller profile than the RR481 (and therefore likely less stiff) should I be choosing aero comp spokes all around?

I had considered going with aero comp / aero lite combo if I'd chosen the RR481, but with the asymmetrical RR421 rim I'm guessing that's not really going to help much other than a miniscule amount of weight savings which is of no interest to me.

I'm choosing the bladed spokes not for "AeroGainz", but to help me with the build to avoid wind up. This will be the first set I build. I'll be using DT's squorx brass nipples. Sorry OldPotatoe, if I lived in the US I'd for sure be employing your services, alas I do not. Much as I'd love to.

[tellyho]

I think worrying about windup is overrated. If it were me, I'd be using good old double butted spokes. Bladed spokes are a pain to work with.

[CampyGrampy]

Originally Posted by robertbb

I'm choosing the bladed spokes not for "AeroGainz", but to help me with the build to avoid wind up. This will be the first set I build. I'll be using DT's squorx brass nipples.

Get the Park Tool spoke clamp and the DT Swiss T-handle squorx wrench. That combination + working very slowly should make for an enjoyable build.

[robertbb]

Originally Posted by tellyho

I think worrying about windup is overrated. If it were me, I'd be using good old double butted spokes. Bladed spokes are a pain to work with.

Interesting. In what way are bladed a pain to work with?

“Da Interwebs” is full of fearful stuff saying DB round spokes will wind up and bladed spokes are easier to observe. I’d be thrilled if that could be debunked - bladed are quite pricey.

[robertbb]

Originally Posted by CampyGrampy

Get the Park Tool spoke clamp and the DT Swiss T-handle squorx wrench. That combination + working very slowly should make for an enjoyable build.

Great shout! Will pick up the Park Tool - the DT T handle tool is already in the mail to me

[oldpotatoe]

Originally Posted by robertbb

Thanks everyone for your inputs and experiences - I've decided to go with the RR421.

A question on spokes choice. Since the RR421 rim is lighter and has a smaller profile than the RR481 (and therefore likely less stiff) should I be choosing aero comp spokes all around?

I had considered going with aero comp / aero lite combo if I'd chosen the RR481, but with the asymmetrical RR421 rim I'm guessing that's not really going to help much other than a miniscule amount of weight savings which is of no interest to me.

I'm choosing the bladed spokes not for "AeroGainz", but to help me with the build to avoid wind up. This will be the first set I build. I'll be using DT's squorx brass nipples. Sorry OldPotatoe, if I lived in the US I'd for sure be employing your services, alas I do not. Much as I'd love to.

Oval spokes won't prevent 'windup', using a tool like the TwistAssist will. I guess easier to see but..the tool will help with that.

If you aren't interested in the 'aero-ness' of oval spokes, nor the 'weight savings, I'd just use DT Comp spokes(and the brass nipps)...

[oldpotatoe]

Originally Posted by tellyho

I think worrying about windup is overrated. If it were me, I'd be using good old double butted spokes. Bladed spokes are a pain to work with.

What makes them a 'pain', first is paying for them. A CXRay/CXSprint from Sapim are 4X the price of Sapim Race or DT Comp...

BUT, these oval are thin spokes..'windup' happens more easily. AND the resulting wheel, when compared to a wheel made with round, double butted spokes, performs just the same...Lots of marketing going on. Proper choice of appropriate rim, spoke count, way more important...along with a good build.

[robertbb]

Thanks OldPotatoe , I think you've got me onto the round spokes train for this.

Question, with the asymmetric rim would you just go with Comps (2,1.8,2) all around or would you consider Revolutions (2,1.5,2) for the rear NDS and front DS?

Interwebs says using heavier spokes on rear DS and front NDS (on disc builds) will even up spoke tension and improve reliability but I wonder if the gains in doing this are negated by the asymmetric rim anyways and may even result in a weaker wheel considering it's a light/shallow rim.

[oldpotatoe]

Originally Posted by robertbb

Thanks OldPotatoe , I think you've got me onto the round spokes train for this.

Question, with the asymmetric rim would you just go with Comps (2,1.8,2) all around or would you consider Revolutions (2,1.5,2) for the rear NDS and front DS?

Interwebs says using heavier spokes on rear DS and front NDS (on disc builds) will even up spoke tension and improve reliability but I wonder if the gains in doing this are negated by the asymmetric rim anyways and may even result in a weaker wheel considering it's a light/shallow rim.

You will save a very teeny amount of weight with Revs rear NDS and non disc side front. BUT tension won't be any more 'even'. Tension is tension, when measured on a spoke tension gauge. And the NDS rear or Non disc side front actual tension would be pretty much the same with either Revs or Comps.

[Mark McM]

Originally Posted by robertbb

Thanks OldPotatoe , I think you've got me onto the round spokes train for this.

Question, with the asymmetric rim would you just go with Comps (2,1.8,2) all around or would you consider Revolutions (2,1.5,2) for the rear NDS and front DS?

Interwebs says using heavier spokes on rear DS and front NDS (on disc builds) will even up spoke tension and improve reliability but I wonder if the gains in doing this are negated by the asymmetric rim anyways and may even result in a weaker wheel considering it's a light/shallow rim.

The right/left tension balance is determined only be geometry, or more specifically, by the difference in the right/left bracing angles.

Mathematically, the tension balance will be inversely proportional to the sines of the bracing angles, but because the angles are shallow, the tension balance will be nearly the same as the inverse ratio of the hub flange offsets. For example, if the hub flange offsets are 36mm left/18mm right (left flange offset 2 times the right flange offset), then the L/R flange offsets will be 2:1, and the L/R tension balance will be inverse of that or 1:2 (left spokes half the tension of the right spokes).

Offset spoke hole (assymmetric) rims change the effective flange offsets, with spoke hole offset being subtracted from the left flange offset and added to the right flange offset. So in the example above, if the spokes were offset by 3mm, then the effective L/R flange offsets would be (36-3)/(18+3) = 33/21, or a flange offset ratio of 1.57:1, and a tension balance of 1:1.57 = 0.636:1 (left spokes have 63.6% of the tension of the right spokes.

From the above example, offset spoke hole rims can make the tension balance more even, but there will still be a large difference in tensions.

So what is the advantage of using different thickness spokes on either side of the wheel? Although the difference in tensions will not be effected, the difference in spoke stretch will be effected. Here's why this matters:

Spokes can only support a load when they are under tension - a completely slack spoke can't support any forces on the rim. So obviously we want to keep the spokes under tension under all the external forces a wheel will experience. Under tension, a spoke will stretch, and this effects how much a wheel can deflect before a spoke becomes completely de-tensioned and slack. A thinner spoke will stretch more under the same tension, so a wheel built with thinner spokes will be able deflect more before the spokes slacken, and the rim looses support from the slackened spokes.

On highly dished wheels, the left spokes will be under much less tension than the right spokes. Therefore, the left spokes will have less stretch than the right spokes. If the left spokes are thick and under very little tension, they will have very little stretch, and will easily slacken and stop supporting the rim under small wheel deflections. To prevent this, we can use thinner spokes on the left, which will start out with more stretch, so they are less likely to slacken when the wheel deflects under load. This can make a wheel more reliable. So maybe another way to say it is not that thicker spokes on the right make a wheel more reliable, but that thinner spokes on the left make a wheel more reliable.

In the case of the RR 421 rim and DT 350 hubs, the hubs have flange offsets of 33.0mm left and 20.2mm right, which means the tension balance with a non-offset rim would be 1:1.64 (right spokes have 64% more tension than the left). The RR421 rim has a spoke hole offset of 2.7mm, so the effective flange offsets are 30.3mm/22.9mm, which means a tension balance of 1:1.32 (right spokes have 32% more tension than the left), which is much better. Let's compare this to the "stretch ratio" of the spokes. The stretch of a spoke will be inversely proportional to its cross sectional area, and the cross section of a spoke will be proportional to the square of its diameter. So for round spokes, the ratio of stretch (under a given tension) between two spokes will be the square of their diameters. Comparing a 1.8mm spoke to a 1.5mm spoke, the 1.5mm spokes will stretch (1.8/1.5)^2 more, or 44% more. For a non-offset rim on the DT 350 hubs, this difference in stretch ratios would help better balance the L/R spoke stretches under the 1:1.64 tension ratio. But with the offset rim, with its smaller tension differential, the advantage of using the thinner spokes on the left is less pronounced (and in fact would cause the left spokes to stretch more than the right spokes), and there is less argument for using different spoke thickness on either side.