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Yea, I know the answer is probably i27.5! but DT don't offer this width.
Using modern 2.35" maybe 2.4" tyres.
Used on a 120/100mm FS XC bike, local 3hr loops are usually 100 feet per mile, most ever is 10000' in 75 miles.
Lots of roots, lime stone, steep ups, no drops, some tarmac.
No plans to use inserts. Lightish bike build planned.
N1no and his cohort all seem to be on i30 these days but carbon rims aren't an option for me.
I’ve crept up to 29/30mm rims on the Solaris. I’m not sure it’s worth the extra weight but hugely dependent on tyres. Big Rekon and 30mm rim on the front is great in the drier half of the year- for this winter I’ll probably go back to a wheel I’ve still got built up with a 23mm crest and a hillbilly (meant to sell, ever got round to it).
If I put another dent in the kom on the back of the Solaris I’m going to drop to either an Xm421 or whatever the XR equivalent is. I’ll likely stick to 30mm at the front- could probably justify carbon there to save the weight instead as I’ve only ever broken a front rim through ‘whole wheel’ twisting, not local impact.
I’d go 25 for what you’re describing.
I'm happy on 25mm internal for what you describe.
Maybe 30mm on the front if you want to be clever?
Can you clarify what you mean by XC.
Cross country racing?
Going for a ride somewhere benign
Or just generally mountain biking as some of us have viewed it for the last 35 years?
I'm not trying to be funny, but different people have different definitions.
My idea of XC is basically any ride that doesn't use uplift, and for that I went 30mm with 2.6" tyres.
Thought about going 25 for lightness but then realised that the stuff I do in XC rides is just as gnarly, ( or not) as what I do with an uplift, so going lighter/weaker might be a bad idea.
( Admittedly the key differentiator is that when going XC I am unlikely to do more than 2000m of descent, whereas on an uplift I might do 3 times that so perhaps taking the cumulative abuse into account it makes sense to go lighter/ weaker on xc)
Sorry, reread your post.
25mm
I run 25mm internal on my 100mm FS XC bike for everything from actual XC racing, 6, 12 and 24hr solo races and for erm just bumbling about.
Light... XC... Fast rolling tyres...? Then go 25's if you're sticking DT Swiss... But there are other rim manufacturers producing in intermediate widths, albeit not many...
FWIW, I go through this dilemma regularly. I'm convinced my 30mm rims are too wide on my Trail bike for most of my riding, but the 25mm on my XC bike are perfect with 2.25's but a little narrow for 2.35-2.4's... I used to own a carbon wheelset that were 28mm internal, I found this the perfect compromise for width, but also got over carbon wheels in the end as found I preferred the better damping qualities of alloy rims. I have 30mm rims on my eBike with 2.6" tyres and this is a great setup, so I'd say 27-28mm is ideal for 2.35-2.4" tyres if we're being picky.
Don't write off tyre inserts. Some of the new breed are really rather good, and there's various lighter weight XC offerings on the market now too.
New Stans Arch Mk4 is 28mm internal FWIW... 👍🏻 https://www.notubes.com/arch-mk4-rim
I'm using 2.4s on a 25id rim for pretty much everything including uplift days. Never felt any need to go bigger.
I think some things can be over thunk.
25mm rim with 50mm tyres on my gravel bike
30mm rim with 2.3-2.4 on my XC 29er
Can't see any drawbacks with the wider rim for XC/trail etc. The added weight makes no difference to me (I don't think it really does for anyone except committed XC racers) but I do prefer the way the tyres set up on a 30mm compared to the 24mm rims I had before.
Another way of looking at it is, how wide a rim is too wide for a 2.4? 30mm isn't. 40mm, maybe. Find the tipping point and then dial it back a bit.
I'm currently running i25 on my XC / light trail bike. Schwalbe 2.35 front and 2.25 rear. Works fine for me but my next bike will be i30 front and rear because that's what a lot of newer intermediate rubber (2.35 / 2.4ish) is being designed around.
For example, I've been running a 2.35 Nobby Nic on the front for 4 years now. Plenty grip and low rolling resistance for the riding I do. However, the newest Nobby Nic looks a bit narrow on my i25s. On emailing Schwalbe about this, they said that it will work on an i25 but was designed around an i30.
Also, a lot of the top XC racers have started running i30 due to the more technical nature of modern XC courses.
On the flip side though, there's plenty of DH riders running i25 with 2.5 tyres.
Conclusion - either rim size will work for XC, but it seems like the industry is pushing i30.