Saturday, December 28, 2013

Xpress assessment

This post is more or less from my bike geek side that enjoys the technical side of bicycles so no real poetic musings not that I've done that yet, but more of a techie musing...





I've been meaning to put these new SOMA Xpress tires through the paces after my Hetres developed a case of slash and burn! So last night I mounted them on the A. Homer Hilsen and went on a ramble over Pasadena way this morning. I put a leisurely 27 miles on them and I admit that is hardly enough miles to make a detailed assessment, yet it did allow me to develop a few observations. But first the looming question I wanted answered was what were the Xpress tires actual measured width mounted? The SOMA Xpress have a pressure range of 55 psi to 75 psi or 3.9 bar to 5.3 bar.



Mounted on Velocity Synergy rims which measure 23.34 mm ~ 


With a tire pressure of 55 psi/ 3.9 bar the width was 34.37~


So I figured I also needed to caliper at the max pressure 75 psi.



I calipered a half dozen times and 35.22 mm ~ was the widest. Sorry but that's less than a mm larger and nearly 3 mm smaller then SOMA's claimed width of 38 mm. Okay so I was a bit disappointed that they were significantly smaller than advertised...remember I have been riding the GB Hetres & the Force Field Fatty Rumpkins both measuring between 41 mm & 42 mm.

Back to the ride characteristics, I have to say there is a whole lot of daylight between these tires and my fenders which is nice because with a 42 mm tire often times you need to tweak the fender stays to eliminate rubbing.My first impression is how narrow they seemed and how did I ever ride a 23c tire before? 

I ran the Xpress at their suggested minimum tire pressure to take advantage of what ever plushness they had...and these tires roll fast! Perhaps not as fast as the Hetres but noticeably fast,faster than the Rumpkin's or Marathon greens. Okay maybe as fast as the Hetres but that's hard to quantify. Climbing they felt good and didn't seem to hold me back, if anything held me back it was my own legs as I had a relapse of that cold from early December and stayed off the bike this week.

Cornering I didn't have that sure footed feeling I had from the wider Hetre or Rumpkin's but once I relaxed they handled fine, I did notice a slight bump to the ride and at this point I am attributing it to my poor seating of the bead to the rim. These tires have a kevlar bead and  like the Hetres (folding bead) seem to be more difficult to seat then say the Rumpking's which have a wire bead. I'll know more once I put some decent miles on them.

Back to the shop to do a bit of wrenching and get ready for next weeks riding and collect more data points on the Xpress tires.

Thanks for reading and keep the rubber side down.

~Hugh

4 comments:

  1. Dear Hugh,

    The Xpress are a bit narrower than the B-lines despite using the same mold. The B-lines are a true 38mm wide. You can expect the Xpress to expand another mm or so (they're usually 36-37mm wide once they relax). They'll wear well. I prefer the B-line (quicker-feeling) or the Hetre (smooth-riding) to the Xpress, but I've never had flat or casing integrity problems with 650B tires.

    Cheers,

    Will
    William M. deRosset
    Fort Collins, CO

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  2. Thanks Will for the feedback. I didn't give any thought to the casing relaxing.

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  3. Since the wider New Xpress tires are made using the Pasela mold, the raised sizing info on the sidewall is based on the non hypertex width. Adding the extra layer of material constricts the volume, especially in a brand new tire that hasn't stretched out at all. We could easily change what's listed on the patch, but not the raised text. It's possible we could ask Panasonic to redo the mold to reflect the real world size, but it would probably be very costly (to the tune of thousands of dollars) which would be reflected in the cost of the tires. And as Will pointed out, they do swell a bit over time, so if someone had very tight clearance out of the box it would potentially cause a safety issue later on.

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