Hunting for marginal gains

I wrote back in May about the changes I'd made to my old crit bike to turn it into a sub-16 lb climbing monster for Wintergreen. My goal then had been to spend as little as possible to get the bike back on the road and just see what I could do with it. The result was a 15.7 lb 1x setup with a 40T ring driving an 11-36 SRAM 11-speed cassette. At the time it seemed perfect, even if I had failed to adequately tighten the cable in the derailleur. Oops.

But then I got a little greedy. The bike had been my main steed for 8 years, and getting it so cheaply back on the road made me want to ride it more. I had an idea to use it as a backup crit bike, just in case. That would be easy enough to accomplish with a cassette and ring swap. I raided the parts bin and found an old SRAM RED 11-28 and ordered a cheap ($25) 48T ring. 48 x 11 is kinda small for a top gear, but it would preserve the chain length perfectly. A few (dozen) turns of the B-screw, and I had a bike that was almost as fast on the flats as it was uphill, but now at an incredible 15.15 lbs.

This, of course, made me want more.

For months I've dreamed of finding a way to shave off that magical 0.15 lbs that would put the bike on UCI minimum weight. 2 principle options emerged:

1. tubeless -> TPU tubes

2. 32T chainring...somehow

The first option would be exponentially cheaper, and would seem like the obvious easy answer: TPU tubes typically weigh somewhere around 35 - 45g each, generally 1/3 that of butyl tubes, and also a fair amount less than sealant. I have about 2 oz in each 700x25 GP5000 S TR. Making the swap to TPU could net as much as 150g, or 0.3 lbs, in savings. That would put me under 15 lbs, and it wouldn't vary with sealant top-ups. But it would be a big job to clean out ALL of the sealant, and with rim-brakes, the lightest TPU tubes aren't really an option, as they're prone to heat failure from braking. Maybe fine for just pure climbing, but not for coming back down the mountain.

It also only achieves that weight goal with deeply sub-optimal gearing. The 11-28 cassette might rocket up the local hills with either a 40 or a 48T ring, but it would make Wintergreen harder than ever.

To hit that climb successfully, the math says the right chainring is a 32T. At 90rpm, 32 x 11 produces 20.5 mph, which is typically the highest speed I see at the base of the climb. 32 x 28, however, is a gear ratio of 1.14:1, very close to the 1.11:1 of 40 x 36 that was so good on the steepest slopes of the mountain.

32 x 11-28 also has 16 fewer chain links than 40 x 11-36.

It's physically less metal in the chainring, so reasonable to assume it would be lighter, as well.

But. My crankset is a 5-bolt 130BCD, meaning the 40T is really already the smallest it can support. To go lower would be expensive. It's also a BB30 crank in a BB30 frame, so the bottom bracket is an outdated, but insanely light, standard.

So here's where things get complicated quickly. Mountain bikes and road bikes typically cannot share components around the cranks and bottom brackets. The exact same standard, whether it's BB30 or Shimano Hollowtech or whatever is different based on road vs mtb. They may say the same thing, but they're not the same. This is usually in regards to the width of the bike frame itself, but also bolt-circles and chainring tooth profiles and all sorts of DEEPLY UNNECESSARY COMPLEXITY.

TL;DR: there is no such thing as a 1x 32T road chainring. There are plenty of 1x 32T options for MTB. If I want my unicorn, I must create it.

As luck would have it, though, the MOUNTING interfaces between road and mtb cranks and their chainrings--the spider--do appear to be identical. 8-bolt SRAM is 8-bolt SRAM. 3-bolt is 3-bolt. So if I get the proper crank arms and mount the correct spider, in theory I could run any size chainring I want. In theory.

In theory.

In reality, while there are a million bottom bracket specs and a million various crank manufacturers and standards, the options diminish significantly when factoring for matching road & mtb interfaces, future supportability, and cost. That pool basically comprises SRAM and Rotor.

While SRAM spiders are available in 3-bolt or 8-bolt interfaces, SRAM no longer makes the necessary crank arms & spindles for 3-bolt. So if you don't want to rummage through parts bins or hope for unicorn finds at the local bike swap, it's 8-bolt on a DUB spindle. Not a deal-breaker for most frames, but they used to make GXP and 30mm spindles, too. Shame they're out of that game or this conversation would already be over: my bike is a native BB30.

But because it's a true actual skinny BB30 frame, and DUB spindles are not designed for 68mm inboard-bearing frames, the only purported option that I could find was a $300+ adapter from BBInfinite. That ain't gonna happen.

But what about Rotor? They offer a 30mm spindle (98g, $35) with an extremely modular design that makes swapping cranks MUCH easier, so no bottom bracket work, and I could choose pricey carbon cranks in pretty much any length I want (all the way down to 155mm/255g for $351!).

Rotor's spline interface appears identical across their road & MTB ranges, and they've been around as a brand with reliable staying power for many years, so while there's 0 chance they'd stand behind this unholy union, at least the parts would be available?

Looking at the available spider options on PowerMeterCity, it seems there are a couple in the $400 range, but they're all out of stock for now, including the new Sigeyi AXO that allegedly only weighs 83g.

I really don't think I want to drop $825+ on a silly idea to tackle one single race, but dropping the crankset mass from 690g to ~485g would be absolutely insane, more than accomplish my rush to the UCI minimum--in theory the bike would weigh just a tick over 14.6 lbs, and I could still throw in a pair of TPU tubes for Wintergreen (the race explicitly prohibits riding back down), potentially rolling up the mountain on 14.25 lbs of carbon.

When the Aeroad arrived in June 2023, I never expected to ride my old Blue Axino again. She's harsh AF by today's standards, but her evolutionary cycle is not yet complete. For now, she's a dedicated trainer bike for the winter, but it's exciting to know there's a potential path to even greater glory.

Dirty Kitten '25: 5th

My official AARP invitation arrived just 2 days after this race. I'm feeling it.

Dirty Kitten is a 2-day affair. Saturday is for the hitters: the folks who want to race 60 or 80 miles. It has also seen worse weather almost every year. Sunday usually has a more casual vibe, with race options of 40 or 20 miles. Saturday's fields are typically packed; Sunday's rarely exceed 45 riders in any given field.

This year was weird.

The men's 40-mile Sunday race had 93 registrants, almost equal to the *entire* grouping of men's entries for Saturday's fields combined. The women's 40 was close to 30 registrants, putting the Sunday 40 firmly into "biggest race of the weekend". 101 people started. Crazy.

Saturday, though, was even more hampered by weather than usual. The forecast called for crushing heat, as it did 2 years ago. In 2023, the Saturday races saw temps hovering right around 100F. With a similar forecast for this year, organizers sent out a last-minute race reduction that pulled a lap off of everyone's registered distance for Saturday. 80 became 60, and 60 became 40. But then it also rained. Like biblically. The opening climb was marked with deep ruts, the grassy section was underwater, big puddles everywhere, and most worryingly: the descent from the Crusher was purportedly rutted. Lap times were way off from previous years, and folks were reaching out to me Saturday night to warn me about the conditions.

And, of course, it also rained Saturday night after the race.

But I had a brand new rear tire that should be extra grippy, and suddenly that 36T ring up front felt extra validated by the slower lap speeds. And at the starting line, I asked the organizer about the day's conditions, and he said the course had dried out nicely overnight, and that the worst of the ruts were clearly marked.

Alastair and I had a plan to start at the front, punch over the opening climb, form a rotation with any other survivors, leave a cooler in an elevated chair so we could swap bottles after lap 1, and keep things neutral until the 2nd ascent of the Crusher, after which it would be an open race to the end.

Things did not go to plan.

We knew the biggest risk of the day was heat. The race started in fog at 80 degrees, and was forecasted to finish at about 90 degrees with a real-feel well over 100. Alastair struggles mightily in those conditions, so that bottle-swap was the pivotal element of the day's plan.

Unfortunately, while the first half of the plan went great, one rider punched over the first ascent of the Crusher, leaving 5 or 6 of us to chase. We were not a confident group of descenders, either, so by the time we were back on open roads, the guy was way up the road, just barely visible. Instead of a neutral rotation, we were a chase group. Alastair and I were on our limits for the next 3 miles, and I'd already spent entirely too much time in the wind just establishing the group's separation.

When we got to the pit to swap bottles, he was empty. I was able to continue without stopping, but tried to gum up the group a little to buy him time to catch back up. The group was not impressed nor impeded, and suddenly I was also in chase mode, but this time starting to feel chills in the sunshine. I let the 2 attackers from our group go, catching them again briefly for a moment before my body screamed to stop, and then settled into limp-mode with one other rider from our group.

The leader was long gone, the 2 chasers were gone, and this was now a trudge to finish in the top 5.

I never saw Alastair again (until after the race, obvs).

I managed to hold on for dear life with one other guy until after the 2nd Crusher, which--for the first time ever--I successfully climbed twice (woohoo gearing choices!). Once we got into the final sunshine-exposed climb by the farmhouse, the chills came back, and I basically just stopped pedalling. I watched my final companion ride away and just limped to the finish line in 5th place.

It was my slowest ever DK40 at 2:26:58, with my worst finishing position of 5th.

Alastair incredibly did not buckle in the heat, but kept a steady rhythm and came across the line just a few minutes after me for his fastest ever at 2:34:47, and his best finishing position of 6th!

https://www.bikesignup.com/Race/Results/79259#resultSetId-569185

Gearing

I spent the previous posts opining about gearing options, and used this space as a place to openly explore the idea of making the least-expensive change possible on the bike to produce the biggest improvement: a 36T chainring to replace my usual 40T.

I pulled charts of gear-usage from previous editions of Dirty Kitten and Monstercross to examine the amount of time spent at either end of the cassette, along with power distribution across the gears showing that even when I got to the fastest gears, it wasn't really meaningful for keeping power.

My theory was that moving from the 40T to the 36T would roughly adjust the time distribution chart by 1 gear toward the top end, but should reduce the bias at the extremes from 4:26 in the 44 and 0:54 in the 10. I ruled out a 38T chainring as being insufficiently different to make a meaningful change, and could potentially throw me into oddball cadences at the typical cruising speeds on this course.

I'm incredibly happy to say it worked out exactly as I'd hoped. Even with slightly odd course conditions and PR's on some of the flatter segments, the gears got me over the Crusher both laps, and I never had any chain drops. In fact this was the first year I've made it through the entire race without putting a foot down.

The following images show gear usage by time and power. The left side are 2025's race, the right are 2024.

Note the more even distribution of power across the cassette with the 36T chainring, as well, with no dips in the 38 or 11. Power was very low in the 10 this year, but even with the smaller 3.6:1 max gearing, it was really only useful on gentle descents.

What this year's gearing did not do was make the Crusher easy. With ramps reaching 23%, nothing will ever make that thing easy. But it did make it manageable, without taking away from the rest of my race. The heat did that on its own.

https://www.strava.com/activities/15255288036

Want to see the Crusher rip our little grupetto apart? Start at 48 minutes: https://youtu.be/r0Wf1c4B2TY

Horses for courses

Well, I did it. Ordered that 36T chainring and let it sit on the bench for a few days, nervous I'd made the wrong choice, in spite of the maths. But Monday I put it on and also mounted up a brand new rear tire, and...

It's hideous.

The 40 was never a big ring, but it looked "right" on a gravel bike. The 36, with that big 10-44 cassette out back, looks like it can't decide if it wants to be a mullet or a wayward mountain bike.

That bar tape I put on the top tube--initially as a joke, but left on when I realized how horrible shouldering that skinny tube was in CX races--doesn't win any style points, either. Nor does the pannier mounting brick on the seatpost. This bike has become a mockery of itself, and...

It's perfect.

I was worried I'd have to take a couple of chain links out, but while the derailleur folds up almost to its limit, the chain is taut in the 10. Biggest surprise of the change was having to adjust the B-screw. I don't think I'd ever had to do that for any previous chainring changes, but it absolutely would not get up onto the 44 until I made a couple of full rotations.

And the ride feels exactly the same, except now I can easily spin up some climbs at Pocahontas that used to have me grunting a little. Nothing that quite replicates the savagery of the Kitten Crusher I'll face next weekend, but sufficient to get my hardened teenage son to notice how high my cadence was while he was grinding away.

For giggles, I dug up the AXS report from 2024's MonsterCross to compare gear usage to Dirty Kitten. In that 3-hour race, I spend only a few seconds in the bail-out 44T cog, and only half a minute in the "big dog" 10T. The 40T chainring remains, in my mind, the ideal solution for that event. So this change becomes a "horses for courses" event-to-event change based on elevation profiles.

For the rear tire I stuck with the tried & tested WTB Resolute in 700x42. On the cheap-but-indestructible Sun Duroc G30 wheels, it sets up wider than a 44, and fresh rubber should help keep power delivered to the ground at the steepest parts of the climbs and when my son attacks me in the final sprint.