I told TriRig's Nick Salazar last week that I intend to write about TriRig's fit calculator for its Alpha X integrated aerobar. It uses the same math, the same approach, as the other superbike calculators like those by Trek, Felt BMC and others. Just, TriRig treats its own aerobar as the integrated “superbike” aero assembly protruding up from the frame.

Over the weekend at the Slowtwitch Road Show at Bonzai Sports in metro-Washington DC I worked with a very fast Slowtwitcher who is considering what bike he might buy next. A few days prior to this Road Show he posted a video of his position on the Reader Forum and I posted back saying don't change a thing. When he showed up a few days later at the Bonzai Road Show he said, essentially, “As we have established my position is fine, what bikes work underneath it?”

This was a toughie, because we calced his pad Y and X out to, as I recall, something like 613 and 520mm respectively due to a longish torso, a quite steep riding posture and an acceptable but slightly obtuse shoulder angle. The answer to this question would have been easy a few years ago: He's a perfect fit aboard a Cervelo P3 Classic geometry. He's also a good fit aboard a QR CD0.1 or Illicito. But QR is moving toward a more mid-range geometry.

It's the Soup Nazi answer for this guy: No bike for you!

Indeed, almost all tri bike brands have coalesced around this middlin' geometry. Felt, QR, Orbea, Trek, Argon 18 (through most of the size run), Giant (through most of the size run), Cannondale, Cervelo and others have arrived at a similar place. Woe to the fellow, like this guy, who needs that abandoned long/low tri geometry.

If you can't get the lowness out of the frame, we'll just get it out of the aerobar. Instead of 60mm of pad height above the pursuit bar center, we'll go to a bar with 25mm or 30mm of pad height. This is exactly what I've done for my own bikes and I chronicled this in mathing my way from a classic P3 to a taller, narrower older Cannondale Slice back in 2010. This would be okay if there were more low-profile aerobar companies out there. Alas, these are going away as well.

This is the conundrum I was pondering for this fellow. And then I remembered the TriRig Alpha series bars! Here's what this means for a fit issue like this one: You now don't start with a bike; you start with the bars. Your aerobars are the driver of the new bike purchase. (I've had occasion to resort to this going back quite awhile, as when in 2008 I needed to road test 3T's Ventus bars and mathed my way to the perfect frame matching those bars to my fit coordinates.)

TriRig not only offers a comfortable, adjustable, slippery (to the wind) aerobar, it has a fit system to which I alluded above. It's right here and the images here are screenshots from that calculator. The way this works, you select the bike model and size. There are a pair of dialogue boxes on the TriRig calculator that automatically populate with that frame's stack and reach. Let's take a QR PR5, size 54cm as an example. If you do this right the boxes are populated with 540 and 425 for stack and reach respectively, which are very mainstream numbers (Cervelo size 56, Trek SC in size L, Felt IA in size 56, etc.).

You then look for your pad Y and X on the TriRig chart. What you find under a Pad Y of 615mm and X of 519mm are:

“5mm Pad Spacers, 20mm Stem Spacers” and if you choose this then it's “Pads at Center,” meaning your armrest will not need to be pulled back or pushed forward in their successively fore and aft mounting holes in the pad bracket. You find this in the green boxes, which denote the underbar mount for the extensions. I usually don't like undermount systems because the pursuit bar between the extensions and the pads widen the vertical displacement between them and ruin the ergonomics. But I don't mind this so much with the Alpha series bars because the pursuit bar is very thin in its Y diameter.

Pretty straightforward. The Alpha X integrated bars have aero spacers under the stem, much like those under the 3T Aduro bars on Cervelo's P5, and they then have pedestals under the pads/extensions. You see the prescription above: 20mm of spacers under the bar, 5mm of spacers under the pad.

Notice that this calculator gives the rider a number of ways to achieve his position. For this rider there are 3 viable solutions that grant him a pad X of between 519mm and 525mm. One of these does not require the undermount solution. If this rider completely slams the Alpha X bar, no pedestals or spacers anywhere, he can make this dog hunt with the standard configuration (and that's what I'd recommend).

Let's say there were too many spacers under the bar, and the prescription called for pushing the pads forward 20mm. What then? You've probably chosen a bike size that's too small. Go in and select the next size up, and then read a more palatable fit prescription.

This calculator is very handy. Not to get too far afield, but when I wrote last week about Pathways to Purchase this is precisely what I was writing about. TriRig has built for its prospective customers a pathway to purchase. Ironically, while TriRig does not sell through retail stores, in my opinion TriRig increases, with this calculator, the sales that flow through retail stores. The rider described above had no good idea what bike would accommodate his position. Now, through this calculator, he does. In a world where the LBS is under siege from mail order and "omni-channel" this is one case where the lines and arguments blur. The use of an aerobar not sold through retailers can unlock the key to the purchase of a new bike that most likely will transact through a retailer.