alexdi profile

It doesn't require permission. 

"SRAM offers the use of the standard and XD trademark to companies that conform to the technical specification and agree to abide by the terms of our license agreement."

It does require that you don't attempt to change it or patent some modification of it, among other things. Plenty to balk at if you're Shimano.

The caveat is that these are full-suspension bikes. It's not clear to me if geometry charts provided assume a certain sag, or if the profile shots I'm using to gauge the SAA show a sagged bike. And of course, riding is quite dynamic. This approach is really just a guideline for the approximate location of the contact points. It'd be more definitive with a hardtail or a road bike.

Good catch, I updated the comparison.

ETT accounts for that. It gives us the exact position of the saddle at the bike's nominal stack height. We only care about the effect of SAA on vertical offsets from that position.

To simplify this, we can normalize reach and ETT for a desired stack and saddle height.

Inputs:

• Reach = R
• Stack = S
• Head Angle = HA
• Seat Angle Actual = SAA
• Desired Stack = DS
• Desired Saddle Height = DH

Outputs:

• Adjusted Reach = R - (DS - S)/(tan(HA)
• Adjusted ETT = ETT - (DS - S)/tan(HA) + (DH - S)/tan(SAA)

Adjusted reach is reach for a given stack. Adjusted ETT is ETT for a given stack and saddle height.

If you're doing these calculations in Excel or Sheets, enclose each angle with RADIANS(). If a manufacturer doesn't provide an actual seat angle, you can measure it with a side profile of the bike in Photoshop or equivalent.

Let's compare (for example) the SB150 and the Megatower and assume these desired values:

• Desired Stack: 665
• Desired Saddle: 720

SB150:

• ETT: 654
• Reach: 505
• Stack: 635
• HA: 64.5
• SAA: 71.7

Megatower:

• ETT: 646
• Reach: 490
• Stack: 643
• HA: 65
• SAA: 67.8

Results:

• Adjusted reach, Megatower: 480
• Adjusted reach, SB150: 491
• Adjusted ETT, Megatower: 667
• Adjusted ETT, SB150: 668

For this hypothetical rider, once the saddle and bars were set up, we'd expect identical seated positions and about 1cm more room standing from the SB150.

Lots of good stuff here, though I'd probably strike 7.6. By fancy-pants standards, every stock wheelset on a bike under $5K (and some over) is a bad set of wheels. Equally, they're all good enough. I don't know that you could readily differentiate wheelsets in the bike price range a novice rider would consider.

If that lock ring is anything like Cannondale's, I'm not a fan. Easy to misthread. Easy to mangle the tool prongs locking it into place. I usually put the tool in a vice to even try.

I drove my forehead into the ground with a Super 2R MIPS. Broke my collarbone, cracked the helmet, no concussion. Not even dazed.  

Was it MIPS? I have no idea. Will I buy a MIPS helmet again? Definitely.

Cam, if you fancy an evening read, check this out:

https://github.com/dashdotrobot/phd-thesis/releases/download/v1.0/Ford_BicycleWheelThesis_v1.0.pdf

http://bicyclewheel.dashdotrobot.com/

It's the most definitive work I've seen on wheel theory. Very recent. 

Here's a more visceral example of wheel stiffness:

https://www.pinkbike.com/news/video-friday-fails-54.html

Skim forward to 0:46. On landing, the tire bottoms immediately. Then the fork bottoms and the rider falls off. If the wheel deforms at all in this sequence, I can't see it.

There's such variability in how people ride that I'm sure someone, somewhere can make a compelling argument for narrower rims. I suspect it'd devolve into an argument for specific old-school tires on narrower rims, or for narrower tires in general. You have to actually want a big contact patch. Some riders chafe at the perceived rolling resistance. Others seem to think a lot of overhang protects the rim. I'm dubious of both. If we emulated motocross, rim width would be 60-70% of tire width, or about 41-45mm for a 2.6" tire.

Excellent review, thanks for taking the time! I particularly appreciate the assembly notes.

I've made a worksheet of a potential build that brings the bike just under 27 pounds, though the bigger question is whether to go full-29 or take the plunge to a 69er.* How much flexibility did you have on the color scheme and logos?

• I just realized the 34T thing could be a problem with a 69er. I run 32T with a 29x2.5" and a 10-42. If I downsize to 27.5 in the back, the ring has to come up to 32 to keep the top end. Hmm.