# Thread: 25vs24 wheel-size comparison (aka too much free time)

1. Originally Posted by ala
. . . Thanks.
You're welcome, and Thank you.

I suspect others may be thinking "Oh, please don't encourage him."

2. Originally Posted by ~Lin
That's what I was wondering for myself after reading brianms post. I started a thread about it, I wondered if going up to 25 wheels would increase my pushing efficiency since I cant further lower my rsh. The response I got for me was no, maybe I need to go back and look over things again!
Lin, if you provide pertinent measurements, I'll be glad to run the math for you.

3. ## Major OOPS

Accurate dimensioning is critical!!!!

This morning, my wife measured me, and the difference is dramatic!! a complete reversal!! Sketch shown below. Apparently I've had my RSH too low all this time.
Attachment 47153

4. Originally Posted by chasmengr
... empirically I already observed that I wished for a tighter elbow angle....
Did you not go from 5 degrees less to 4 degrees less? My eyes are playing tricks with me. Where is the reversal?

5. Originally Posted by nonoise
Did you not go from 5 degrees less to 4 degrees less? My eyes are playing tricks with me. Where is the reversal?

The reversal is empirically I was wrong - I need to trust math more than my empirical senses. My self measurements yielded a current elbow angle of 131DEG; my wife's measurements (much more accurate) yielded a current angle of 92DEG. The target elbow-angle range is 100-130DEG. So instead of needing a lower RSH, I actually need a higher RSH.

Grommet said it: "Some one once told me that you can get used to something unnatural until it feels natural and I think that happens a lot with chairs. Something isn't right but we figure that's how it is."

6. Very interesting stuff Chas.

I've only got as far as figuring out RSH based on Arm Length, Shoulder Height and the Seat Surface to Axel Height (I think). Does this mean that the elbow angle and COG also affects the RSH?

Originally Posted by chasmengr
Accurate dimensioning is critical!!!!

7. Originally Posted by elarson
Very interesting stuff Chas.

I've only got as far as figuring out RSH based on Arm Length, Shoulder Height and the Seat Surface to Axel Height (I think). Does this mean that the elbow angle and COG also affects the RSH?
Determining RSH from arm length (aka fingertip-touching-axle rule) is the easy, aproximate way. Actual research shows pushing efficiency is better determined from the elbow angle, but (as can be seen from this thread) the elbow-angle method is much more complex.

What I am doing is trying to use the complex method (including shoulder-to-axle relative positions, etc), for which measurement accuracy is super critical. I'm working up a spreadsheet, which I'll post when it's further along.

8. ## One Word...

ICON :P

E

PS I am teaching Law of Cosines and Sines right now to my Trig students. Do you mind if I "word problem" your situation?

9. Originally Posted by Essie
ICON :P

E

PS I am teaching Law of Cosines and Sines right now to my Trig students. Do you mind if I "word problem" your situation?
I'd be honored It's always wonderful when students can experience real-world uses for what they're learning.

10. that paper's too complicated for my brain, lol.

so does that mean the 88 degree is better than 92 in pushing efficiency?

#### Posting Permissions

• You may not post new threads
• You may not post replies
• You may not post attachments
• You may not edit your posts
•