Facts & figures.

9 07 2015

Spent 10 minutes measuring various wheel/tyre combos. Maxxis Chronicle 29×3″ on Nextie junglefox 50mm is 766mm at my riding pressure (9psi). A WTB Trailblazer on a Nextie 650bx50mm rim is 727mm and a Maxxis DHF 2.5 on a 30mm Enve rim is 742mm. The Nate on a HED BigDeal rim is 737mm at 18psi, which is higher than riding pressure. So it may drop a mm or two?

Why the measurements?

Fox announced a 27.5plus 34 fork recently and Rock Shox announced the Lyrik and Yari in a 27.5plus/29er casting as well.

The Fox is *likely* to have an a-c of ~532.8mm in a 120mm travel setting. This is an extrapolated figure as I could not find an actual a-c. for this fork. The 34 29er version from 2013 had an a-c of 542.8 for the 130mm travel model. Take 10mm for the reduced travel and you get the 532.8mm.

Now, add sag of 25mm, leaving an actual a-c of 507.8mm – but lets call it 508mm.

If I used a WTB Bridger or 27.5×3 Chronicle when they become available, the diameter is likley to be around 737mm or so – bit less than a good sized 29er – with me? so the radius is 368.5. Along with a 508mm a-c height this takes the total to 876.5mm.

The 29plus tyre diamter is 767mm so radius is 383.5mm. 876.5 minus 383.5 = 493mm. The a-c of some readily available carbon rigid forks, more or less.

A frame designed around this ride height could use a suspension fork with a 275×3″ front wheel or by swapping to a 29+ wheel, a rigid fork, with no real change in geometry.

Interesting, eh?

Oh, btw, the vinyl tape dropped 10psi in 24 hours without sealant, with sealant, no drop in 24 hours. Pretty stoked.

Edit: Fox tech specs are here. As you can see, the 120mm fork is 525.5mm a-c. This would put the equivalent rigid fork length at 485.5mm. Not bad at all. Oh, and the Fox 27.5+ fork fits 29+ it seems.

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2 responses

9 07 2015
Stuart

Loving the geekery :).

You using anything particularly accurate to measure tyre pressures? I’m convinced my track pump is off but not sure what to try instead.

9 07 2015
velopest

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