650b gravel rims – DT GR531 -v- XM421

The missus is after some new wheels for her gravel bike. The current plan is going to be Pro5s, Sapim D-lights and a DT rim. (needs to be available in 650b as the toe overlap with 700c is hilarious)

I’m familiar with the XM421 – I’ve been running one on the front of my hardtail for about 5 years and its been faultless (and not treated kindly either). The “gravel” option is the GR531, but as its 12% heavier (500g vs 440g) and a whole 1mm narrower, I’m not really understanding what the point of it is? Can anyone enlighten me?

The only “advantage” I can see is that the 531 is available in 24 hole, which would even out the weight difference a little. On the other hand I’ve never built sub-32 spoke wheels. 28 feels doable, 24 possibly a little more of a challenge!

Thoughts?

Thanks

The “gravel” option is the GR531, but as its 12% heavier (500g vs 440g) and a whole 1mm narrower, I’m not really understanding what the point of it is?

Would the gravel rims be heavier because there’s a chance someone might fit road tyres at a silly PSI?

Think I found that when I was looking at Stans rims in the past.

I’d pick the 421s anyway.

The gravel rims have a more aero shape IIRC but yes they are porky. XR331 would make a nice gravel wheel (I use the 29″ version for CX wheels) but hard to get now (I do have a pair in 32h that were built then dismantled if you want to go that way). XR391 would perhaps be better than a XM421. Lighter again and the same internal width.

Would the gravel rims be heavier because there’s a chance someone might fit road tyres at a silly PSI?

Basically this, high tyre pressures place a high, constant load on the rim bed and so rims that may see 50+ PSI tend to be reinforced there to prevent the pressure from the tyres slackening off the spokes or causing premature fatigue.

Hence why alloy XC race rims are frequently lighter than alloy road rims.

Also, DT’s gravel rims have a higher weight limit, I imagine because they are intended to be used for bike packing/light touring.

They’ll be getting used with 47mm tyres, so maybe the XR331 is a bit narrow (and I can’t find it on the DT website anyway!)? XR391 is only 29er according to DT…?

XR391 definitely has been made as 27.5. In stock here for one; https://bitexhubs.co.uk/product/dt-swiss-xr-391/. XR331 has been discontinued hence no longer on DT site (sadly), I imagine the 27.5 version of the 391 might be the same. Yeah 20mm ID might be a bit small for 47mm tyres :D.

I don’t see the point in the gravel rims unless you are planning to run high PSI or you are fast enough that the aero benefits somehow outweight the weight

I’ve got XR361’s on the front of my gravel bike and commutor running 32-50mm tyres and all is good

XR391s are ideal on my gravel/dropbar MTB with initially 50mm tyres and now 55mm (29×2.2″). Definitely were available in 650b as that’s all I could find when I was looking for the 29er version at one point!

XM421s are superb too but possibly OTT for gravel use (as in lighter will be possible). I’ve had XM421s on my 140/130mm trail bike for years without issue despite weighing 90kg and lacking finesse at times.