Optimizing Fit - Eliminate Recumbutt/Hot Foot

[ak-tux]

I think this should be a useful thread all together about how to fix recumbutt on S40 and other fit issues). Lets discuss.

I've never ridden a V20 but Iam blessed to have a S40 gifted to me by some great friends here. I love my S40 and I ride it alot despite my initial fit and hotfoot issues.

I can personally confirm that the S40 with the stock seat indeed has a recumbutt issue (probably not affecting everyone). But I believe it can be fixed or reduced. I think it is cuased by the shape and design of the stock seat when in combination with the 40deg recline angle.


First and foremost, the boom should be properly adjusted to allow optimum knee bend(145-155deg) while at a full leg extension of the pedal stroke. (Bonus tip: If you experience numb feet(aka hot foot), set the cleats about 25mm behind the ball of your feet. I personally just drilled my old spd shoes and moved the cleats backwards. No need to spend money on custom shoes. Then adjust the boom to compensate for the change in the effective leg length.)

The stock seat has an adjustable plate at the bottom that should be extended out to give proper support and hence avoid the likelihood to slide forward on the seat.

The shape of the bottom of the stock seat also lacks the necessary bowl-like curvature and therefore cuases the glutes to seat relatively flat on the seat. Consequently they bear the forward sliding weight while pedaling. The key is to find a way to slightly suspend the glutes. I used some pieces of form padding on the edges to create a bowl like shape which reduces pressure on the glutes. I hope this makes sense.

All in all, proper shoulder/neck support (note my plastic diy neck rest), relaxed hands, a little patience plus these modifications may reduce or resolve the recumbutt issue on S40. However, you may need to give it a few rides and allow your body to adapt before you make your conclusions. (Oh yeah, and I reduced the thickness of the stock pad slightly .. -20mm or so. It was too thick for my taste.)

Cruzbike recently released an adjustable carbon seat for the S30/S40/V20/V20c which I guess probably @Robert Holler and team took into consideration these matters. I have not tried their new seat but hope it is way better and wider than the stock seat.

 

[Don1]

Love the rollers.. stick a centrifugal fan on one if the roller axles and with your power meter you've got a smartish trainer, but I diegress. ... I seem to get hot foot on the outside of my foot and am interested to see if mtb cranks with their slightly wider q factor will help as it did for you. I'm to much of a roadie to go full mid cleat..... The seat on the v20 is ok but it took a while to get used to how narrow it is. The head is more angled back(looking down the nose a bit) compared to you. I did have a little recumbutt early on but km fix that especially with ventist seems to mold to you after a while. (It's nothing compared to getting used to a road saddle)....

 

[ak-tux]

Love the rollers.. stick a centrifugal fan on one if the roller axles and with your power meter you've got a smartish trainer, but I diegress. ... I seem to get hot foot on the outside of my foot and am interested to see if mtb cranks with their slightly wider q factor will help as it did for you. I'm to much of a roadie to go full mid cleat..... The seat on the v20 is ok but it took a while to get used to how narrow it is. The head is more angled back(looking down the nose a bit) compared to you. I did have a little recumbutt early on but km fix that especially with ventist seems to mold to you after a while. (It's nothing compared to getting used to a road saddle)....

Thanks @Don1.
Unfortunately my home-made roller experiment did not work as intended. The rolling resistance was so bad , I could hardly make a few pedal strokes ! . I abandoned the project. (I think it needs higher precision, bigger diameter rolllers with smoother bearings).

My "hot foot" issue was there irrespective of the Q factor. It only finally disappeared when I moved the cleats back about an inch behind the ball of my foot. I had to drill my shoes. It's not exactly midfoot, but slightly further forward by about a 15mm. But the effect is practicaly almost midfoot for me but probably still allows some calf engagement. The new cleat position felt a little strange at first (cadence dropped a bit) but I soon got used to it. I was so happy to finally ride without thinking about my feet. It was/is a game changer for me.

Earlier, I tried many things including larger shoes, I even made a hole on the insole where the Morton's neuroma would swell after a ride. Some relief was there for maybe the first couple of hours of the ride but ocassionaly, it would still hurt badly towards the end of a 4 to 5 hr or longer ride, especially on a warm day. Particularly if there was constant steady pedalling force applied. (Strangely enough, I did not experience hot foot on my DF/upright bike, even with the same shoes)





(I used molten candle wax to seal the old factory made cleat holes)

 

[benphyr]

Hi @ak-tux ,
Can you show some more pictures or diagrams of your seat bottom solution? I am not sure what I am looking at. Is the picture of the under side of the seat? I experience similar seat pan issues (though I don’t do nearly as long of rides. Thank you for posting your solution.

 

[ak-tux]

Hi @ak-tux ,
Can you show some more pictures or diagrams of your seat bottom solution? I am not sure what I am looking at. Is the picture of the under side of the seat? I experience similar seat pan issues (though I don’t do nearly as long of rides. Thank you for posting your solution.

Hi @benphyr ,

Thank you for your interest. Unfortunately I used a mix of black and white pieces of form padding making it difficult to get a good contrast in the picture. What you are looking at is the top of my seat pan with the cushion rolled back .

In brief the idea is to make the gluteus maximus (the two large muscles forming the buttocks) to "float" slightly. So by putting a ring of 20mm thick form around the edges of the seat pan (and a bit in the middle) I reduce the pressure placed directly on the two glutes. I experimented abit until it felt comfortable. I don't know whether this will be exactly the same for everybody. Iam just sharing what seems to work for me. It takes a few rides for the body to adapt to it.



The genesis is the recline angle of the seat, followed by the shape and design of the seat. At 40degs or higher we are placing more weight on our buttocks compared to say V20 users who seem not to experience much of this problem.

The more reclined you get the harder it is to climb steeper hills, but the result is more comfort and aerodynamics. The more upright we get , forward visibility improves, maneuverability and climbing power increases but then we place more pressure on the glutes which we need to pedal, resulting in recumbutt. Bicycle design is about compromise, a fine balance between efficiency and comfort. S40 is a fine fast bicycle once the comfort and fit is dialed in. We need to document a good fit procedure for the cruzbike that is as simple as what ordinary upright road bike folks use.

Someone else on this forum tried a radical idea using leather, which explains the need to get the glutes free to move without bearing too much weight: Check this thread by @Kenneth https://forum.cruzbike.com/threads/custom-seat-build.12691/#post-150410

Note: This is not my bike:



Looking at the human anatomy, one understands why recumbutt occures. We are seating on some important muscles while pedaling , something that does not happen on a regular upright bike becuase the saddle is between the legs. (Offcourse a regular bicycle saddle creates other problems, but you get the point)



Looking at the above anatomy probably the bottom seat section should be concave in shape. Further maybe it should have a pair of depressed or flexible or even hollow section around the glutes? It's easier to use padding to achieve the same effect. Otherwise, if I had the tools I would experiment with the following design:

 

[benphyr]

I definitely want to try out your solution as I have two problems with my older s40 seat. First, I slide forward whenever I am not pushing hard I find myself trying to lock my position with my arms and stabilizers them noticeably within a short period of time. Second, the recumbutt sets in sooner than on my Cruzbike conversion kit in my avatar which has the more basic two-piece seat in a similar angle but the seat pan is less level.

Can you draw a diagram that shows an exploded view of your modifications to the seat padding?

 

[ak-tux]

Can you draw a diagram that shows an exploded view of your modifications to the seat padding?

Iam sorry I don't have sufficent skills to give a better drawing . I have edited the little drawing on my previous message. The most amount of padding is at the nose of the seat (with the adjustable plate fully extended out) making it look like the Thor Easy seat. It stops me from sliding forward.

 

[Bill Wightman]

My "hot foot" issue was there irrespective of the Q factor. It only finally disappeared when I moved the cleats back about an inch behind the ball of my foot.

I have only had a hot foot issue on hot days where there was a vigorous start on the ride and it happened usually after about 2-3 hour of riding. I did two things to fix it. The first was to remove the hard stock insoles and replace with a trimmed Dr Scholes viscoelastic type liner. I assumed it would eat energy but it felt so much better. The second thing (which may not work for many) was to place the cleat attach point as close to the toes as possible. I have not had any issues with hot foot since and I think the cleat placement also smooths out my power and perhaps gives my upper leg muscles a break. Also it is just not possible to stomp on the cleat which I think causes stress and maybe even bruising in the ball of the foot region. If you do this I would go easy for a while as the calf muscles and Achilles tendon are now more engaged and may need some strengthening time.

 

[Always-Learnin]

This is my slightly different mod inspired by ak-tux's mod! I solved the sliding forward and recumbutt issue on my S40 by adding ~1" of military grade polyethene foam with the 'cut out' in the middle and ~1.5" raised section at the front. It isn't pretty and could be more refined but I rode my 2021 S40 in this year's Texas BikeMS150 and had no problems whatsoever. ;-)

 

[Bill Wightman]

~1" of military grade polyethene foam

You can also use 1" thick x adhesive backed pipe insulation foam. I laid out 2" wide strips in the upper back area for vibration damping. It has been on the bike over 5 year with no degradation. Works very well much like memory foam. I have the Ventisit on top.

 

[ak-tux]

This is my slightly different mod inspired by ak-tux's mod! I solved the sliding forward and recumbutt issue on my S40 by adding ~1" of military grade polyethene foam with the 'cut out' in the middle and ~1.5" raised section at the front. It isn't pretty and could be more refined but I rode my 2021 S40 in this year's Texas BikeMS150 and had no problems whatsoever. ;-)

Glad to see the idea has helped someone.