Adjustable seat angle ideas

[Seth Cooper]

I got my Thor seat for my V20 in the mail. Since it's the off season I am not in a hurry to mount it, so I have some time to consider a way to make the seat angle adjustable. I just want something that when I am going slower I can sit up and have the advantages of that: little better climbing, but mostly an easier way to look around, esp to the sides, and easier to be seen by others.


Goals:
1. I would like to have way to raise the seat to about 40 degrees.
2. I would like the design to cost less that $200 dollars and weigh under a few pounds
3. I would like to change the angle while I am riding.
4. When it is down I would like it to be "pretty" stiff
5. When it is up I am am a little less concerned about flex, but I don't want to feel like I'm on a boat when I'm pedaling.
6. Manual operation is ok, some sort of dropper post like thumb operated release would be cool too.

I remember seeing a picture of a version of this but I am not sure where the images are.

I have access to 3D CAD and have made a few models and had them 3D printed, so I am comfortable creating parts as needed, but obviously buying things will be cheaper. I am interested in anyone with any ideas on a way to do this.

I think I will need to mount the seat so that a flexible rubber support is directly under my butt. That way I can sit up, reach back and lift the seat with one hand, and then some sort of support will pivot or slide into place. The support would be around 7" long, and would be largely held in place by my weight, but also a hand operated clamp or a latch, or magnets, or a sit down in a notch or some combination.

So I am planning on posting my design as it comes together so anyone can critique it.

Thanks,

Seth

 

[LarryOz]

I am hoping to build something similar Seth. I think Rick Youngblood had created a nice adjustable seat, along with a few other Cruzbike members.
I also think it would be handy if the seat hinged about 7" past the front, that way the seat area remains relatively flat. This would however make it more challenging to build using existing 1-piece seats.
Hopefully they will chime in here and give us some threads.

 

[Seth Cooper]

Ok, I did a search and it was actually easier to find that I thought:

A chap named Philip created one here back in 2015:
http://cruzbike.com/forum/threads/the-seat-of-the-problem-on-my-new-v20.8182/

Video in action:

He built a custom hinged plate to mount above the standard V20 seat, and used a 4" long metal hinge with a bungee and a release cable. Very simple design but effective. The hinged plate allows for a very stiff seat in the raised position.

Since I want to tilt the whole (Thor) seat it will make things harder I think.

 

[Seth Cooper]

so I made some progress mocking up my tilting thor seat with some wood pieces. The seat is slid back and raised a little from its "normal" V20 position to allow the front to tip down when in the raised position. I measured the two mocked recline angles (roughly measured as the thor seat is not an easy shape to measure angle) as 18.6 and 34 degrees. I don't want to do much higher raised angle as it really changes how the reclined position must be (the seat must be even farther back)

one problem I have is with the pad on and the seat raised my belly hits the bars, so I have to either get a curved slider or go to back to a shorter chainstay. I may do the chainstay as the one I have now, the 23.5" felt a little unsteady at high speeds (45 mph+)

also just sitting on it mocked up in the raised position it felt like I was sliding forward, which i did not expect, but I will have to ride it around a bit to see if that is a legit issue.

 

[ReklinedRider]

You’ve set an admirable goal and a challenging one!
I’ve included a few pics of something similar to your mock-up but it was done with no intention of adjustability; my goal was to eliminate the need for a headrest at the cost of losing some aero advantage. I’m sharing them just for comparison of angles, cockpit clearances, etc. Not the best lighting (it’s on the trainer in the garage) but you can see the vulcanized rubber block and the seat angle it produces. Using the clinometer app, the seat directly above the block is at 27deg from horizontal; at the very top it’s at 78deg. I have no trouble getting into the seat and have several inches of belly/chest clearance once in place; a curved slider would for sure improve that.

My seat may be slid back a bit more than yours; it’s back enough to mount to the frame wings in the original holes without impinging on the seat ribs. What are your thoughts on securing your seat in the front with it changing angles etc?
This is just a shot of a new handlebar i’m trying in order to get my arms as straight as possible (Soma ‘el toro’ pursuit bars that i had in my “warehouse” of bike parts ha)
So far all road testing has gone well but only time and longer distances will tell.
I’m looking forward to your progress with your project and wish you good luck and Happy Holidays.

 

[Seth Cooper]

my hinge right now is nothing special, a $3.00 3" long utility hinge from the local hardware store. It has a lot more play that I would like, and so I may replace it with something tighter.

I used some instamorph to flatten out the curve in the carbon fiber, and a wood block to mount it to a metal plate screwed into the frame. Eventually the wood would be replaced with a 3D printed plastic part.

 

[Balor]

I should note that changing your seat angle alone decreases your seat-to-pedal distance and puts undue load on your knees. I have a better idea.
I know that is not exactly a 200$ project, but....

From 27 deg to 40 deg from BB 60mm above seat to 60mm below.

Can be done 'in motion' by swinging forward in seat and front braking a bit, than locking out swingarms by applying some sort of brake attached on an axle or swingarm. (Locking out shocks would not likely work - they never lock fully, to prevent hydraulic shock from a missed pothole I suppose).
A band brake seems like a nice and low-profile option, but it is said they are not grabby...

 

[benphyr]

I'm having a hard time following the diagram and description. Are you saying:
1. The front suspension goes from fully suspended to locked at completely compressed position?
2. the rear wheel is on a pivot below the seat and you change that pivot angle using the force from braking to unweight the rear wheel?

Wouldn't 1. change the steering geometry significantly (similar to amount of seat angle change)? And wouldn't that mean that you would not have front suspension in that upright position and all that entails?
Wouldn't 2. change the steering geometry by a smaller but still a significant amount? That may or may not be desirable.

Or did I miss your intent entirely?

Cheers,
Ben.

 

[super slim]

I'm having a hard time following the diagram and description. Are you saying:
1. The front suspension goes from fully suspended to locked at completely compressed position?
2. the rear wheel is on a pivot below the seat and you change that pivot angle using the force from braking to unweight the rear wheel?

Wouldn't 1. change the steering geometry significantly (similar to amount of seat angle change)? And wouldn't that mean that you would not have front suspension in that upright position and all that entails?
Wouldn't 2. change the steering geometry by a smaller but still a significant amount? That may or may not be desirable.

Or did I miss your intent entirely?

Cheers,
Ben.

The trail would go from 48.7 mm to 25.7 mm, so I assume still OK???

 

[Balor]

1. The front suspension goes from fully suspended to locked at completely compressed position?
2. the rear wheel is on a pivot below the seat and you change that pivot angle using the force from braking to unweight the rear wheel?

Indeed. Front shock get compressed and locked, rear shock gets fully uncompressed and locked. Front shock 150 x 32mm, rear 216 x 63mm (DH air shock, can be had cheaply sometimes from DF riders suffering from acute upradeditis ).
At first I thought about manipulating sag using pneumatics, but than I thought this is much simpler idea and more useful.

Wouldn't 1. change the steering geometry significantly (similar to amount of seat angle change)?

Erm? Changing seat angle does NOT change steering geometry at all. What it does is change your *cockpit* geometry - distance to bars and, to a lesser extent, distance to pedals. Neither is desirable.

Manipulation of suspension sag, indeed, DOES change geometry, but actually in a highly desirable way - you want steeper angles and less trail for better low-speed handling due to reduction of flop. In my case, however, I actually get negative flop that actively helps with steering (negative angle + positive trail), plus your boom will now serve as a 'counterweight' to center steering instead of flopping under it's own weight. Unfortunately, that would imply too upright angle for my tastes for general riding around OR too much tiller (been there - done that), and too much negative offset is ungainly, but for climbing only this is win-win.

Also, by swinging back and locking shocks in reverse position, you get a nice aero setup with lots of trail, high BB and more horizontal seat for DH. Just make sure you don't run into a pothole.

P.S.

Seat angles and BB height is pinpointed experimentally - it seems to work for me best from a combination of ergonomics and aerodynamics standpoint - on flat ground. When climbing, however, I would get exponentially increasing drop in power delivery due to decrease in blood delivery to legs, the steeper the hill - the worse it gets, I've actually tried that with manipulating wheel height on my trainer.
Other people might get away with much higher BB.

 

[Balor]

The trail would go from 48.7 mm to 25.7 mm, so I assume still OK???

Indeed. Compression of front suspension (in my case) adds about 25mm of negative offset increasing trail by that amount, hence it stays positive.

 

[Seth Cooper]

I should note that changing your seat angle alone decreases your seat-to-pedal distance and puts undue load on your knees. I have a better idea.

Building a new bike is an interesting idea, but it will have to wait for another time.

Interesting to think about a way to change the seat angle without changing the hip to pedal distance. I think I would need a back-and-forth slide as well as a hinge, or a curved track to slide the seat along, so that the virtual pivot for the seat was at the hip socket. A quick estimate shows I would need about 2" of slide if I assume the hip socket is 5" above where the seat pivots.

 

[dtseng]

I go by two-bike solution instead of one-bike with adjustable seat angle. The bike with higher seat angle can use wider tires and preferably with rear swing arm suspension for group ride, sight-seeing, and commuting. The one with lower seat angle and slick tires is more aero and is for speed. (That is, own both S40 and V20.)

 

[Balor]

I go by two-bike solution instead of one-bike with adjustable seat angle. The bike with higher seat angle can use wider tires and preferably with rear swing arm suspension for group ride, sight-seeing, and commuting. The one with lower seat angle and slick tires is more aero and is for speed. (That is, own both S40 and V20.)

Indeed. Unfortunately (at least for me), you may want to swap those bikes before each hill. That is where adjustable *geometry* comes in handy.

 

[McWheels]

I suppose the simplest is the deck chair arrangement. You sit up, pull the seat forward with you and it [the seat support post] falls into the ratchet. Going back you still have to sit yet further up to take the weight off and then sort of flick the support out and hope (more engineering can take hope away[!]) it catches on the way down.

I also saw a youtube video of a chap with an adjustable recline by spinning a threaded bar under the seat; it wasn't desperately quick but it clearly worked over the 30s it took.

 

[Balor]

One of strengths of Cruzbike frame is "integrated seat" it makes its construction extremely stiff and light.
Adding a lot mechanical doodads will negate both, and seat stiffness is extremely important for power delivery too.
I'm all for techical solutions for problems, but seat interface is highly loaded and making sure it is easily adjustable AND reliable AND light is no small feat!

I think, however, that 'intermediate' variant is possible - by using flat seat like stock Cruzbike and manipulating angle of the upper portion (hence making the seat articulate somewhere above lumbar support).

This way rising and lowering the seat should not affect seat-to-pedal distance (because 'bracing point' is unchanged), but it will rise your heart more above legs and will make your position more upright for a bit better balance - yet you will retain full back support without need of rising in the seat, and this element is NOT highly loaded, hence some leeway is possible.
It will affect distance to bars though.

 

[Balor]

It will require making a custom, two-piece seat though.

 

[Balor]

By the way, did some modelling and turns out that, say, Silvio with stock seat at 27 deg equivalent to any other bent with Thor seat at 17 deg

 

[super slim]

It will require making a custom, two-piece seat though.

OR an OLD fibreglass two piece Cruzbike seat!

 

[Seth Cooper]

It will require making a custom, two-piece seat though.

The youtube video I linked to in the 3rd post in the thread has a nice and simple solution. An aluminum plate with a wide hinge fastened to the standard carbon fiber seat halfway up. Exactly what you propose, only raising the top of the torso, so the hip to pedal distance is unchanged. The cable actuated raise / lower mechanism is simple but effective as well.

Having just bought a Thor seat, I am still thinking about trying to make it work, but I can't deny the simplicity and effectiveness of Philip's (the video's author) solution.