The F4U Corsair! Whistling death has bent wings!
I knew that this would be the namesake for this bike when designs began. The infamous Vought F4U Corsair fighter/bomber took a signature stance and design to allow for a super powerful 2,000 HP engine (the largest available engine at the time) and an insane 13-foot, 4-inch (4.06 m) diameter propeller. To keep the propeller clear of the ground when landing and taking off an iconic inverted gullwing wing design was used. With that engine came top speeds of 446mph. Seeing one of these in person is like standing by an actual fire breathing dragon. They are huge and mean AF.
Similar to the Corsair warbird, this new frame takes a shape to hold a massive 32″ front wheel. A new twist on my leggy AR designs. Mean AF.
Tariff wars delayed the start of this bike a few months. I was ready to go far earlier but the increase in import taxes and uncertainty delayed it. Because of this, I dug deep into some design details and made some improvements where two weeks of infrastructural work wouldn’t otherwise have seemed reasonable. Use disasters to your advantage!
Completing this project took a month longer than expected. Between my Europe bike tour with Windy this summer, a bunch of technical slow downs, and an increased professional workload, it was just a struggle every day. I haven’t had such a hard time completing a bike in a long time. My bike is what folks should have seen at MADE for what could be done with a 32″ wheel.
I’m also having a hard time being stoked and sharing. That is another discussion.
Luckily, I had worked out a deal with Tyler at Btchn’ Bikes to supply him with a 32″ fork design for the all road bike that he was showing at MADE. This bike was a hit and many wonderful words were shared regarding both Tyler’s work and mine. Typical to Tyler, it was a wild machine. I’m glad that something of mine was in the ether at that time.
The Corsair AR is a further development on my all-road platform. A narrow gauge (Q145) format replacing the 2023 M2-F2, the Corsair moves many improvements forward. The big one, a 32″ (686BSD) front wheel option and 29″ (622BSD) options for both 100mm travel and rigid forks. These three front ends producing the same fundamental geometry within the bike. This will provide the most discrete testing of the large front wheel against traditional options.
The Maxxis Aspen 32″x2.4″ 686-61 tire is really what has woken up this size possibility. It’s a high end race spec tire with 120 tpi casing and knobs perfect for all-road and XC racing. Prior to now, only unicycle tires could be used for this diameter and they are unacceptably low performance on a mountain bike due to their construction and design.
Testing this tire size and seeing what it provides us in the dirt is the goal.
Cursory drawings showed that there were too many downsides to using the large tire in the rear of the bike, so only the 32″ front wheel will be tested. Those downsides range from tire buzz, absurdly long rear center, and significant inertial weight addition in exchange for small possible benefits in traction. The seat tube would also take a crazy form with an extremely slack exit angle that would add challenge to dropper compression and loading. It just didn’t make sense.
On a holistic level, the change in chassis geometry keep moving the bar from where we left on the M2-F2:
- 19mm longer front center, 845mm from 826mm
- 8mm lower crank axis, 290mm from 298mm due to crank length change from 175mm to 170mm
- 1 degree slacker head angle, 69° from 70°
- 2mm more rear tire clearance, 622-58mm from 522-56mm
- Front wheel trail up to 90.4mm from 89mm
- Flop height up to 32.4mm from 30mm
- 1.2 degrees higher hand grip angle, 57.7° from 56.5° (although this is due to corrections for bar sweep)
- 2 degrees more bar sweep, 20° degree from 18°
- 10mm longer seat tube, 370mm from 360mm. Improving seat tube mount bottle clearance.
- Ovalized top tube.
- Dropped seat stay junction from top tube, 20mm. Fresh modern looks.
I was hoping to make something that was a just a little more composed when riding fast on double black diamond singletrack and on sketchy surfaces. At low speeds the M2-F2 was supreme. Once things got crazy, the bike required significant attention to keep on line. Nothing that couldn’t be dealt with but not the best compared to a proper mountain bike. I want a little more breathing room and space to relax.
As stated earlier, the front wheel and fork options play a special role on this bike. It’s an all-road bike so it’s supposed to cover ground fast in a lot of conditions. Choices help with that. I figured that if I was making room for the big 32″ wheel I could also add room for a tight little suspension fork and a 29″ wheel. A SID100/29″ (FS-SIDS-SLP3-D1) fork takes up just more than the space of the 32″ fork so I just made plans for an even swap at 70% extension. After that, the size of a 29″ rigid fork was obvious. Planning the offset of the two rigid forks ensures that each configuration has the same front wheel trail and flop height as the other. Then the only effective change is the contact patch shape and moment of inertia of the differing wheels. I’ll have some good times bringing different front ends into the woods for testing. Hopefully, this will tell me what value the 32″ wheel actually has and what geometry adjustments might need to be made to offset the inertial differences.
After 4 years, I’ve figured out the crown modeling for the fork. Earlier models were a mess and not what I was looking for but the best that I could come up with at the time. Thanks to some new methods, I have what I’ve been wanting. This design is highly durable and adjustable. It keeps a delicate look while being a beefcake. It’s a shame that, a week after submitting models for printing, I realized how to do a unitized crown more easily so that segments aren’t needed. Next time, the looks should improve even more dramatically.
I reworked the dropouts of the fork also. I wanted to keep the look of what had been done on previous forks but increase the structure. In other words, keep them small but make them bigger. We play games with light and I got something that is more and less. Fun stuff for experienced modelers.
The handlebars got some goodness to go with the other parts. I’m really glad that a gullwing bar shape is included on a bike named for a plane famous for inverted gull wings. With the high front end, but not as high as with long MTB bikes, finding a form for the bars took some time and iterations. I call them mid-bars as such. Not a regular gullwing but also not a high rise.
Earlier, I say that I changed to a 1.2 degree higher hand grip angle, 57.7° from 56.5°. This is because I’m trying to correct for the sweep angle change to correctly replicate true wrist position. I haven’t sorted this out completely but the goal is to be more predictive.
I felt that especially in an AR platform, I should push for an increase to 20° back sweep, up from the 18° used on the last few bikes. This might be too much or even better, we gamble. I’ll find out. We’re looking for as relaxed a hold as we can for long periods in the saddle.
The body of the ‘stem’ is entirely printed including the binder. This gave me some more freedom for a more compact size than would have been possible with a hybrid fabricated stem. A PMW SP2002 binder takes up a lot more space than what you in the print.
Additionally, the 2024 bar-in model has been heavily reworked as I get closer to a more optimal configuration. The bar-ins needed significantly more inward angle and shaping. Hopefully, this relaxes my hold in all three grip locations when riding the bike.
To help get the ergonomics right, I’ve constructed a master-part based design in SolidWorks for the bar-ins so that the geometry would be defined within the context of the bicycle, not the handlebar end or within the part itself. The bar-in has to be defined that way to ensure the most optimal form when in actual use. At least now my definition is helping with all that.
I’m making a move back to bent seat stays. This accomplishes two goals. Increased heel clearance and improved shape of the rear dropout. Heel clearance has been a constant battle ever since converting to riding with flat pedals in 2020 and with the narrow cranks that I design for. By adding just a slight bend in the stays, I get nicer transitions to the dropout especially on the COAX side which is much farther outboard.
This was a very large print order for me. 2583 grams of 316L. All the printed parts shown here.
Settings for constructing the frame on the Samantha Fixture. The calculator is slowly evolving and getting quite useful in a number of ways when working on the table.
The fixture calculator now has an accompanying drawing for easy confirmation of the frame for quick validation. There’s something cool about this that I need to look deeper into. I’m just trying to figure out what it is.
On this build, I got to use a new upgrade to the Samantha frame fixture. An increased head tube platform. The 4″ additional length of the steel breadboard results in an 18″ cosine bar for angular setup and more space to clamp. The resolution of the bar at this scale is about 0.015″ per 0.05° at 69.00°. That’s some amazing stuff. The seat tube plate has been kept short to ensure working room in critical areas.
Note that the cosine bar is only 16″ (406.4mm) rather than 18″ (457.2) for this setup. I need to order some lower profile handles that don’t project into the tube beam when set. Then the rail can swap with the cosine pin. We find these issues as we go. That should be complete before the next bike.
I decided to mix the color of the bike up with something more fancy that I usually do. I do love the basic RAL colors but I need to take more risks. This time with a metallic. PMB-6905 Illusion Cherry with PPS-2974 Clear Vision top coat. I’m told that this is a color used often by the Hells Angels. Ugh.
It’s quite a finish. I’m not accustomed to such class. I am a little concerned about durability as a few small chips occurred during assembly.
The assembly of the bike makes a few changes from the M2-F2. I’m moving the bike up the lovely SRAM 90 coax group and shrinking the Force Q145 crank from 175mm to 170mm. Switching from a CushCore XC in the rear to a Odyssey OPTIS pneumatic inset. This will be another bike upgraded to SRAM HS2 2.0mm brake rotors. This makes such a difference on the trail. My headset cover is in place, of course.
The 38t chainring combined with the 10-52 cassette and 622-54 rear tire makes for some fast pedaling but still just enough to climb the mountain.
I’m going to try the new SRAM RM-DL-A1 dropper lever. It’s got 14mm of pull and matches the SRAM 90 Shifter. I love two things about this lever, it’s cheap and it has a return spring. Hopefully it works well in practice.
Assembling the 32″ wheel forced some bling spending on a carbon fiber rim from Nextie Unicorn. Keeping the mass of the wheel rim down is paramount so there was no way around this. 480 grams is the number to watch for these rims and news of a rim in the low 400s will be met with a roar.
I had purchased a box of 315mm DT 2.0mm straight gauge spokes to build the front wheel. They were the longest commonly available at the time. The issue is that they show up with no threads on them. I had to head down to Box Dog Bikes in SF and have them roll some threads onto the ends. Hopefully, building 32″ wheels has more part choices in the future.
I’ve been starting to see the arc of the evolution for my AR designs more clearly. Years and iterations have been adding up. It’s fascinating. What started out as two separate categories of bike, the klunker and the all-road, have melded into a single form. I would say that the TIE, M2-F2 and this bike are that form. What these bikes do is generally superior than either of the past models could do. They are more efficient than the klunker, they handle better, they cover ground better. The go deeper than the lighter AR bikes of the past and are more comfortable. There doesn’t seem to be much from the past that requires a bike between the Road+ and the current AR. It’s pretty cool.
2025-10-03, Shakedown #1, Tamarancho & Hobo
It was perfect trail conditions for a little shake down loop. Just enough moisture had come down in the last week that traction is at it’s highest in months. It was cool and Windy came along just in case a 911 call was warranted.
From the photos, all that needed changing was the angle of the shift lever. The rest of the bike was spot on. I kept wondering if I should lower the bars a few millimeters but resisted the urge. The riding position was very comfortable and still somehow aggressive.
The front wheel is a tricky thing to sort out without some back to back tests that I plan in a week or so. It wasn’t really crazy other than the perception and projection. It worked just fine. It didn’t even feel too heavy in use. The big takeaway for now is that this is a far more subtle change than was expected and will require a deeper test. There were a few geometry changes that cloud my initial thoughts about it.
I will say that I’m very glad to have kept the 29″ wheel in the rear. One run down Hobo cleared that up with a healthy tire buzz in a more rough section of the trail. There is already very little room with the smaller wheel.
The bar sweep felt amazing. 20 degrees is so nice. Even better when combined with the new bar ins. I felt very relaxed at the grip, like a natural position.
The bar-in angle could be a little more extreme. It’s at the edge of comfortable. I’m not sure about this.
I had forgotten to attach one of my water bottle leashes to the cage. I was proven as to why that’s important on this ride as I saw the bottle fly off to my side when going down one rough fast descent. It’s nice to see again proof that something is important and needed. That will be on for the next ride.
The look of the bike in the sun is very cool. I’m not used to metallic paintjobs. In the bright light the finish shimmers.
The feel of the SRAM dropper lever is quite a bit different than the Wolf Tooth Pro. It’s more resistant to movement, I figure that the leverage is less. It is compact though. It’s just more of a short stroke button than a big sweep lever.
I was riding at about 75% for this test. Really thinking about things and checking stuff out. The bike felt great as I got up to speed but I can’t say that I was riding very fast. I should be coming up to speed in the next few rides where I may find more to comment on.
2025-10-04, Shakedown #2, Triple C, Terra Linda Ridge & Luis Ranch FR, 680, and Solstice.
I’ve started to loosen up on the bike some. Getting my mind off of engineering and onto the trail helps. I need to loosen up some more.
I love the 20 degree sweep of these bars and used the bar-ins for a large part of the ride. I think 20 degrees is going to be my limit for now. It’s good. Bar-ins can still be improved. Both shape and angle.
The 38t ring with the 52t cog with the 622-54 produce 1.68 meters of development. For this ride with a bit of climbing (but not absurd), I’m at the limit. It may make sense to back the ring down to 36t but I’m going to be a tough guy for a little longer. That would bring it down to 1.59 meters. The M2-F2 was used with a 38t ring for the duration and I may keep with that.
Traction going up the hill for days. The front tire is very planted even with the very short rear end. I don’t need to advance any in this respect.
I wasn’t proud going down Solstice (single black to double depending on speed). It’s not a steep trail. Not a lot of flow on the rigid bike when I need it. A lot of rock and root bumps messing sections. I may try again if I can get into the zone. That takes repeated rigid rides and a lot of pain. That could happen as testing gets me on a bike for a bit.
Brakes functioned well enough but I’m not thrilled right now. They seem off. Might upgrade to some of the Motives for this and the added aesthetics. Fuck it. Spend money go fast.
I’m thinking of riding with clipless pedals tomorrow for the first time in about 5 years. This bike may be a good place for that although most of what I learn will be about pedals.
2025-10-05, Shakedown #3, Wheeler, 999esses, Elliot, Junction – the double blacks.
I manned up and tossed the clipless pedals on the bike. My first time in 5 years. I was expecting a ton of problems…but there were not. It was like I never stopped. Natural.
Climbing with the clipless pedals was really great. I’ve been missing that and this bike loves to have the stomp. Today had a lot of climbing.
I also felt a bit more relaxed on the trail and that helped given the challenge. Even in the tight lower section of Wheeler, the wheel diameter wasn’t an issue. The bike was as good as could be expected everywhere considering I was riding a full rigid on double blacks. I even hucked the drop on Elliot and it felt smooth and nice.
The bike was really nice on general singletrack and felt amazing when some gaps opened up and flow was possible.
I broke a spoke nipple on the rear wheel, the headset needs another 1mm spacer. The front brake was howling like crazy found a loose bolt. Motive brakes are on order. The tape on the bar-ins needs to be secured better. Had issue with the OPTIS when fixing the nipple, replace with cushcore
2025-10-11, Shakedown #4, Tamo reverse to Splitrock
Having fixed all of the issues from last Sunday’s ride…and replaced the older SRAM G2 brakeset with some SRAM Motive Bronze units…we set out to ride. The bike was dead quiet. It felt so tight and together. It is sorted and it made the difference when riding. I could really feel out the bike. It was great…or as great as a full rigid bike can be on rough singletrack. I’m really excited to put more miles into this. I’m also liking being on the clipless again and especially on this bike. Where will this take me?
Now I’ve begun the development of the models to reflect all of the improvements that I’ve discovered while building and sorting this bike out. Changes to the models and the math. The tools and everything. The iron is hot and it’s time to strike. This ensures that the next bike makes full advantage of this process.
2025-10-12, Regular Riding #5, Eldridge to Northside, Benstein, Kent, Serpentine, etc.
This is what we’ve been waiting for! Just a ride, feeling good, loosened up for full rigid riding. Great weather and dirt.
Heading up the hill was awesome. This is where the bar-ins, narrow cranks, and clipless pedals shine. I was really feeling good giving it the business on my way up to Northside. The 170mm cranks and riding position feel great going up. Yes, the bike covers ground very well. I kept wanting to push it just a little harder. Also, traction for days.
Once on the narrow trial, I was flowing. These are raw hiking trails. They are not easy. You have to be able to float at any given time… and I was. The bike felt so nice going down that I was thinking that it was more of a bike than the Supermarine Spitfire even without the 3.0″ beefcake rubber. Other than not having front suspension, I really can’t think of what was wrong. Cleaning the Benstein esses is a challenge on any bike and this bike did that today.
There is one issue that may be of note. I think that the crank axis is a bit low. This is an all road bike and that’s to be expected. Klunking through rock gardens isn’t what it’s been optimized for. Instead of 290mm, I maybe should have gone with 293mm. Just a little more clearance. Nothing too crazy. I’m not sure about this.
The bike is killer. It really is what has been said about the design goals.
2025-11-28, Longer term update
Just checking in after another month and a half with the bike.
I really haven’t ridden anything else off road since. This is for two reasons: It takes a while to truly get into the flow of riding a rigid bike and that the bike is so dam good.
Riding a full suspension mountain bike well is very hard. Riding a hardtail mountain bike is even harder. Riding a full rigid mountain bike well is impossible and terrifying. It takes a long time to get used to riding rigid and to be in the ‘flow’. I’m there as best I can be right now so I’m hanging onto that. It hurts. I’m old. But fuck it, this is sick.
The bike is so dam nice. It’s only gotten better with some recent mods (HERE & HERE). I’m really enjoying it and it’s making me smile. I’ve also changed gearing from 38 tooth to 36 tooth. And 5mm additional spacer under the bars.
Because of that 5mm spacer under the bars, I figure that I should update the geometry for the record. 837.5mm at 58 degrees with the 20 degree sweep bars at 20 degrees from earth. I’m trying to balance the chill feel with a get up and go attitude.
