Considering getting an Open Upper frame and building it up for gravel. Manufacturer says max tire clearance is 40mm. I usually ride 38mm Gravel Kings, but there are times/courses where I would prefer a 42 GK or Pathfinder. Anybody squeezed an extra 2mm onto an Upper? or done a 38/42 mullet front/rear or rear/front? Or is there a good all-rounder similar to GK or Pathfinder that comes in 40?
When considering this keep in mind that you need to worry about actual tire width when it’s mounted on your XX mm inner width rims. And the manufacturer stated tire clearance has some safety factor in it.
See here (and a few posts above that) for more info.
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true. and mud clearance. but thanks for the reminder 
This is the clearance I had on my UP with 40 mm Ramblers. I wouldn’t want to try 42 Pathfinders in the back. I’ll rip my UPPER off the trainer and measure out the clearance with my current Tufo Thundero in 40.
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Perfect. thank you!!
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I could pass a 6 mm hex wrench between the seat tube and the tire but could not pass an 8 mm, so I’d say it’s about 7-7.5 mm. The Tufo is inflated to 40 psi in this picture and mounted on a Corima G 30.5 (internal width 22 mm).
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thanks!!
No problem. Happy to answer any other questions you or someone else has. It’s a great bike and closest thing out there to a quiver killer. I have a second wheelset for road tires and it can rip on tarmac just fine.
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Open Up with 700c rim build.
Pathfinder Pro tires (700x42) rub the seatstay at pressures over 40 PSI (rated 35-65). This tire does not have treads in the middle section. There is plenty of space by the chainstays (likely can easily handle 700x47) of the same tire (threads are small, not crazy like 650s). Kinda surprised and disappointed.
What is your rim?
Corima G 30.5.
As I said earlier…
thanks for the input, everybody. went with a Cervelo Aspero for better clearance
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I think you could squeeze (as noted by @The_Conductor) 42s on the Upper, however if only had 40s on mine. However if you do do it, I would consider the conditions … if you’re riding in wet conditions the buildup could happen fast and severely.
Also, remember — the Upper is meant to take 650s easily and you can get to 2.1 (I think at that size). I’ve thought about doing that, but for almost every race I do 40s are plenty for me.
Good luck🤘
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It comes down to stated vs. measured width. You could fit 42s if you know a priori that it’ll measure out to 42.
I don’t yet have 650b wheels for my UPPER but am always on the lookout for a deal.
I had been passively looking for a 650b wheelset for when I want something wider and came across a great eBay deal. Boyd CCC wheelset plus Continental Race Kings (both unused) for $280.
The rims are 25mm internal width and the Race Kings are labeled at 2.2 inches. They measured out to 54mm/2.16 inches when pumped up to an ideal psi. The front has PLENTY of clearance. The back is a bit tighter. Lots of room between the tire and the downtube. But the chainstays are pretty tight. The non-drive side has just under 4mm which is tight but doable, but the drive side is only about 2.5mm. For dry riding I think it would be ok. But I think I’ll swap it to something in the 47-50mm range. Just gotta figure out what is available in 650b/27.5 that size that has good rolling resistance
After seeing how good the fork clearance is, I think next year I’m gonna go with 44mm front and 40mm rear on the 700c wheelset.
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