Frame flex and climbing

Yes, give in the seat, seat pad, or seat supports are just as bad.

I saw an improvement in climbing on my P38 when I installed a wide, taught nylon strap around the seat in the lumbar area.

 

I don't know about replenishing blood to the muscles, but it's just a fact of life that even a pro's pedal circles aren't perfect. At the 'top' and 'bottom' of the pedal stroke, your legs just don't have the leverage to apply huge torque or develop power. If you flex the frame (say flex the boom down) when the pedal is at 12:00, the boom will return when your leg is least able/unable to counter it, at 3:00 or 4:00 depending on your seat/pedal relationship. The energy is not returned in a useful manner.

 

Just signed up here, so I need some posts.

Adding to the conundrum of the flexy climbing recumbent...I ride with a guy here in north Seattle that climbs very very well on his CA2. So well that he can compete with DF riders climbing hills. I was a good hill climber back in my racing days. Riding a similar bike ( his back up Stick bike) I was unable to keep pace with him up a long moderate 5-10 percent hill. He stayed with his cat 2 racer friend to the top and waited for me.

This guy is small, light and fit. I am bigger and heavier and less fit. I have concluded that there is a tipping point where the weight ( bike and rider) to power ratio allows for somewhat better climbing on a recumbent. For me, that's below 170 pounds, with a sub 23 pound bike. My vendetta has significantly less frame flex climbing and I do climb better on that bike than my stick bike. It shows up in short (800 yards ) steeper climbs. During Long climbs (miles) the weight to power ratio starts to even things out...

I went up the Mt Baker Hill climb on my Vendetta at 174 pounds and did OK ( beat my DF riding buddy by 15 minutes), but many DF riders absolutely flew by me...one skinny 60 year old grandma smiled as she went by...

Just my 2 cents

 

Thanks for everyone's thoughts. I also read Steamer's blog posts and tend to agree. I'm a physician, not an engineer, so I'm not qualified to comment much on this thread.

A number of people have confirmed Steamer's responses/blogs with data that at least has a sniff of objectivity.

FWD recumbents with triangulated bottom brackets should in theory have a lot less flex than a RWD recumbent. With flex and weight in mind, The Rev was born. That bike is about the same weight as a carbon DF and also a triangulated Bottom Bracket. Interesting, in repeated tests the REV and the M5 were both faster (but almost certainly within the margin of error) than a DF on hills. Given that the tester has logged a lot of miles on a DF, there should not be much muscle memory effect there.

As someone who has also logged a lot of miles on a DF and an M5, I would add my worthless subjective observation that I am equally horribly slow on both bikes, but equally so. I do have a power meter, and it confirms that I am a relatively weak rider (3W/Kg). On a flat, I am about 10KPH faster on the M5 at 120%FTP. On a 1-3% grade, I am still much faster. On a steeper grade the advantage gradually fades and then I'm slower eventually. This makes total sense given one is still pushing wind up to a point. If I were a pro rider, I'm sure I would still be faster on the M5 even on steep climbs because I would still be pushing wind.

The M5 has many disadvantages over my Trek Emonda. It is a little heavier, the drive train is less efficient, and there is some frame flex.

The biggest disadvantage is one that need to fix. My newish Zipp 404 wheels flex so much that the rim rubs the brakes under pedaling force. I am going to try to tension the wheels. But if anyone wants a very slightly used pair of 303/404 Zipps, make an offer. . I think I can find a wheel builder to tension them to the company specs. I think that they were built on the lower end of the specs. Very disappointing for nearly $2000 wheels!

 

On rides with other DF riders, I find that I'm riding in Zone 2-3 even with the fastest group in the local club. I'm braking on downhills when they are pedaling. So, when we hit a very steep climb, I feel relief that I can finally get a workout when the others are already tired.

 

Enid writes:
"FWD recumbents with triangulated bottom brackets should in theory have a lot less flex than a RWD recumbent."

I'm not sure I believe that is relevant. After all, on a Cruzbike the entire drive train is mounted separately from the rider, on a big swivel. I mean, limiting power input is a good way to prevent frame flex, but causes other issues.

 

I have owned 3 Bacchetta stick bikes made of different frame material (steel, aluminum, titanium). The aluminum and titanium had the same seat and seat angle. I have recorded information on all of my rides. The slightly heavier Corsa was just a bit faster.

I then purchased a Carbent Sea Dragon. With almost identical seat recline, about 1.4 LBS lighter than the ti-Aero it was significantly faster.

The seat strut on the Dragon is a large, thick single hunk of CF and the seat is permanently attached. The boom is much shorter than that on the Aero and again very chunky CF. When riding the Dragon I saw no perceptible movement if the boom. (Back then I could maintain just over 300 watts for 15 minutes)

on the ti-Aero, when climbing or mashing hard (no power meter but no reason to believe I was any stronger) the boom moved laterally so much I could hear the front brake scrape with each pedal stroke.

That being said, some bikes have surprised me. My 38 lbs Kettweisil climbed exceptionally well. Much faster than my Catrike 700 which was lighter ( I dont recall now its weight. My wife's Serian SLIi climbs exceptionally well and has a very stiff frame.

My VKHI climbs almost as well as the Dragon. I feel having a compact crank vs a triple is tbe difference there.

Enjoy your experiments. I have found most everything is a trade off. The Aero didn't climb well but the compliant frame made her a joy to ride even over rough roads.