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Printed on the side of a 650 x 2.6 Specialised Slaughter box that came through the door today.
21mm = approx 2.35"
30mm = approx 2.4"
38mm = approx 2.55"
So a 40mm rim for the full 2.6" experience?
I’m not sure how useful this is but having recently got wider rims on my hardtail (30mm id instead of something like 19) I found that on the front the 2.25 tyre felt awful, just didn’t feel right in the turns. I presume because it was now too square or flat in profile. So this weekend fitted a 2.6 tyre (biggest that would fit in the non boost fork as it turns out) and it now feels normal again. On the back the squared off 2.25 on 30mm rim doesn’t feel any different, but I’ll be looking to go wider for more comfort/slightly lower pressure.
I haven’t tried the opposite ie 2.6 tyre in a 19mm rim but imagine it won’t work as intended, less grip in braking as the tall side knobs won’t be in contact.
I think wider tyres need wider rims but how wide is a grey area
Specialized tyres have always come up a bit small. I think trying to stretch out the tyre with a very wide rim will square them off quite badly and effect handling. I run a 2.6 hillbilly on a 30mm rim & its just about spot on even though it measures just under 2.5. When I put my 2.3” slaughter on the same rim it is pretty squared off & as such I find that I’m riding on the side knobs all the time at my favoured lowish (with inserts) pressures. The tyre can’t bulge upwards to let you roll along on the low profile centre tread, negating the rolling benefits of a semi slick.
With spesh tyres it’s just best to ignore the size printed on them & treat them as a smaller tyre. Going above 30-35mm on the rim will make them weird and slow. Their 2.3s are really about 2.1/2.2 and their 2.6s are more like a Maxxis 2.5 or ever so slightly bigger than a schwalbe 2.35.
I would have said Specialised ID's were a tad to wide in relation to real world experiences of posts on this forum I've been researching.
I have tried the going the opposite for the last 2 weeks. On a ID 19 rim I replaced a good condition 2.3 Purgatory with a 2.8 Mich WildAM I took off my plus bike (more like a 2.6 Schwalbe). It comes up rounder than a round thing - side knobs are half way down the side. However it feels much better than the Purg in everyway - sidewall support, grip, that rollover volume feeling. Yeah, I definitely need to get some wider rims very soon but until then the WildAM is staying on for sure.
Those Specialized recommended widths are way OTT.
I've had a 2.8 Michelin Wild AM (as above, it's more like a 2.7/2.6) fitted on an i25 rim since last summer, and it's great, no problems with sidewall roll, etc. at all.
On my Stooge I've got 2.6 tyres on 30mm id rims (Flow Mk3) and they're spot on. You only really need 40mm + rims for big 3" plus tyres.
I just thought it was interesting that in order to get 2.6 out of a 2.6 tyre - Spech recommend rims wider than anyone would actually use.