Home Made Bikes

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Posted: Feb 24, 2021 at 10:20 Quote
R-M-R wrote:
faul,

That should work, but I've found it usually produces outlier results, compared to the other methods.
I did this at a couple different angles and got fairly consistent results!

Posted: Feb 24, 2021 at 10:21 Quote
mediocrityontwowheels wrote:
How do I find center of mass?
In Linkage it's roughly centred on the BB shell 600mm + your BB drop up. If that makes sense.

Posted: Feb 24, 2021 at 10:25 Quote
SleepingAwake wrote:
I did this at a couple different angles and got fairly consistent results!

Nicely done. Maybe I gave up too quickly.


smalltownboycustoms wrote:
In Linkage it's roughly centred on the BB shell 600mm + your BB drop up. If that makes sense.

That's the default location and I don't know how it was chosen. It's not terribly far off, but it's not accurate - well, maybe for an e-bike or laynehip's huck bike!

Posted: Feb 24, 2021 at 12:05 Quote
smalltownboycustoms wrote:
mediocrityontwowheels wrote:
How do I find center of mass?
In Linkage it's roughly centred on the BB shell 600mm + your BB drop up. If that makes sense.

Thank you, I did something close to that, I used the demo of linkage to find the COM of a similar bike and then used that.

Posted: Feb 24, 2021 at 12:38 Quote
CoM is an input, not an output. Linkage can't do much to help you find it. There's no way of knowing whether the CoM of that similar bike was accurate, especially since the CoM is about 80% from the rider, not the bike.

Posted: Feb 25, 2021 at 7:31 Quote
mediocrityontwowheels wrote:
How do I find center of mass?

http://www.peterverdone.com/the-anti-squat-problem/

My seated COM is about 825mm over the bb. I believe that very few people have actually measured COM so caveat emptor.

Posted: Feb 25, 2021 at 13:58 Quote
I wanted a bike to dedicate to my trainer. So why not learn a little in the process? I had to buy the telescoping tube from McMaster-Carr, but otherwise this is all scrap/leftover tubing. So far it has worked great. I have been doing hour long rides with slight geometry tweaks here and there. Once I'm comfortable I'm going to measure where I land for flat and for curly bars.


Thoughts? Will it translate to real bicycles?

If at the end I am just left with a way to ride my trainer without disassembling another bike, I'm okay with that.

Posted: Feb 25, 2021 at 14:14 Quote
Your going to find out...

Can’t see why not?

Does the centre of the rear wheel correspond to an actual wheel size? Or is this immaterial in this instance ?

Posted: Feb 25, 2021 at 15:48 Quote
Not a bad idea. Cheaper than a Pelaton that's for sure lol

Posted: Feb 25, 2021 at 16:33 Quote
Nice set-up, bmxsnox!


bmxsnox wrote:
Thoughts? Will it translate to real bicycles?

Yes, with an caveat.

Optimizing your fit on flat ground optimizes your fit for flat ground. Road bikes settled on approximately 73° half a century ago and, for decades, mountain bikes used the same 73° seat-tube angle as road bikes. For most people, that's a pretty good hip position when seated on flat ground. It's not ideal for mountain bikes, though, for the following reasons:

• Mountain bikes climb much steeper grades than road bikes.
• Rear suspension squats due to rearward weight shift when climbing, further slackening the angles a few degrees. The more suspension travel, the greater the effect.
• Mountain bikers often stand when descending, so our time-averaged seated position has a strong uphill bias.

I design bikes as essentially two halves: the front for descending and the rear for climbing. The other halves of the bike have minimal impact on performance in those situations. The rider's hip position should be at the ideal position (let's assume 73°) somewhere between the maximum grade that can be climbed while seated (also accounting for suspension squat) and flat ground. This is why current bikes are finally getting much steeper seat-tube angles than in the past.

Posted: Feb 25, 2021 at 19:13 Quote
Appreciate the input. Soupherb I would think the axle height is irrelevant here due to the fact that it's a static setup and no "handling" comes into play. Just BB relation to touch points matter. The fact that it's a static setup then also becomes it's drawback for the reasons R-M-R stated. That's pretty much what I was thinking, but R-M-R took it a step further with the description.

Maybe I'll try setting it up on an incline for a few rides. I bet I could rig that up.

Posted: Mar 1, 2021 at 9:17 Quote
Ok, so instead of making multiple mounting points for the floating brake could I just adjust the length of the rod to change the characteristics?

Posted: Mar 1, 2021 at 10:54 Quote
mediocrityontwowheels wrote:
Ok, so instead of making multiple mounting points for the floating brake could I just adjust the length of the rod to change the characteristics?

Yes, but it may not give nearly enough range of adjustment for your needs. Have you used Linkage to calculate the brake dive? If not, that's your first step. There's no sense plowing ahead with the manufacturing and incorporating an adjustment that covers [disastrously bad ±10%].

Posted: Mar 2, 2021 at 9:36 Quote
I haven't calculated brake dive yet, but I did do anti-squat, and (if my math is right) I got 44% at full droop. I only just figured out how to calculate it so ill have to find what it is throughout the travel to make a graph.

Posted: Mar 2, 2021 at 13:37 Quote
"Anti-squat" is a pedaling property, caused by acceleration and chain tension. Presumably this means you calculated either brake dive or brake "anti-dive", per Linkage terminology. Feel free to post your calculations, diagrams, etc. for review.


 
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