Once again the stars started aligning... first a formula to calculate how much gain there actually would be. Ok still ball park but at least there is some formula to work on instead of eyeball-o-meter and a butt-bounce-calibration to satisfy my pedantic nature.
And.. and and the most important thing for any proud El Cheapo is of course... CHEAP.. relative to the loss of a kidney to buy from online + shipping, the almost forgotten arrangement with the LBS finally pop up in my messages " The wizards have arrive..."
Measurement
Going by the rule of thumb that vol. increase in tire is proportional to the cross sectional area of the tire (while assuming a roundish) profile...
What is the vol. increase going from a true 2.4 (actual widest width @ 62mm) to a 2.75" (measured width @ 70mm) on a wide 48mm rim base?
Ans: [((70.0/2)^2 x 3.142)-((62/2)^2 x 3.142))]/((62/2)^2 x 3.142))% = 27.5%
Of course this is open to all kinds of errors in measurement and after physically measuring last night-- carcass wise it was not as wide. ~70mm was only at the knobs but for now let's put it as +/-10% on that 27.5%/
A second opinion with eyeball-o-meter says the Anvil-RubberWidth-Range is right on the dot. The Missus chimed in with her growing expertise on things-biking and concur with her highly accurate Finger-O-Meter too, "Yes it's bigger" she said.
So here it is - a 2.75" that measures up to the definition of a 27.5 diameter after having gain a 27.5% increase in volume... Hmmm what numbers should I be betting for this week's lottery?
Left: Wizard knob to knob on the 48mm Try-All Nowar K2 rim followed by previously measured, mounted up with 2.4 Onza Ibex. Right pics are measured smooth wall to wall.. 28mm Halo Freedom Disc with 2.4 Ardents measured wall to wall. Same Halo with Ardent measured lug to lug at widest point.
Wall to wall on the wizard was a little too wide for the caliper to find a good point but estimated ~2mm lesser @ 67mm. (update.. indeed as re-measured this morning its ~67mm)
Height wise (without knob) is 2.5mm more than the Onza Ibex 2.4- Hence the overall diameter is up by 5mm
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| Wizard on the right couple of mm taller than the Ibex |
Clearance
Very tight. With a bit of tire wobble? there's light rub (very slight) at a couple of spots on the side. Gonna massage a little more this evening to balance things up. In any case, the pressure has ben pumped up to 30 psi to let sit overnight. Since my usual riding pressure would be 15-17 and sometimes as low as 12-14psi, the sides would probably bulge out a little less. Funny thing was my initial concern after crunching all the collected data then was the fear of the diameter being overly large. No issue of that sort here. Guess it came up short on Surly's own number on this one @ 697mm.. Me estimating what I have here is ~694mm or thereabout.
(update: dropped the pressure from the initial 30 closer to my riding at 18-19 psi. Very slight rub at 1 point. Gotta check whether its due tire wobble or a slight truing is needed. In any case would likely re-dish 1mm or so nearer to drive side at a later time).
An Apple to Apple and Apple to Orange comparison
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| Left: Same 48mm rim Wizard 2.75" vs Ibis 2.4" Right: Ibex 2.4" vs Ardents 2.4" on 28mm Halo rim. |
Will leave the verdict for a final installment till more rubber has been laid on the trails
If bikes are named according to tire size.....
Oh wait, let's dust off the...
Snug but yea it fits
Hmmm - a 26+ SS hardtail next?
Golem part IV... final installment. Akan datang
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