You're right, this project is growing by the day... At first i was thinking sanding down some paint and fitting external gears would be the end of it hahahaWow! You have really gone down the engineering rabbit hole on this one!
That's some pretty tight clearance, Clarence....
View attachment 238130
You've got a 29 x 3.0 tire on a wide rim, I'm surprised it even fits at all without a special fork. Once you get it dialed in , I'm dying to see the rear susp in motion!
Acid. Reborn (finished)
- Thread starter hbn
- Start date
Help Support Rat Rod Bikes Bicycle Forum:
I would like any and all feedback or input on the thoughts expressed here. The text is somewhat complex, and maybe flawed(?) but it will be worth it!
My plan has been to position the springs at the hub, perpendicular to the seat stay, since it’s an easy way. Yet, it gives a linear suspension (ie every part of the suspension travel has the same resistance) and is a bit bulky.
And I would like to build a progressive suspension. Some might wonder what the appeal with a progressive suspension is.
Well, in a progressive suspension construction, the spring travel relative to rear wheel travel changes as the suspension is compressed. Hence, it is 'plusher' on small bumps (increased small bump sensitivity) and stiffens up as the travel is compressed (meaning it won't bottom out as abruptly).
-You know that scissor jack I cut to pieces earlier?
It suddenly popped up in my mind again, and it got me thinking about Pythagoras' theorem. You know, that a2 + b2 = c2 stuff.
Yeah, I know, I’m a bit strange.
Anyway, after using the theorem, I found out that the lift of one turn of the handle changes depending on where in its travel the jack is. -It is progressive!
In the end, I won’t be using the leftover jack parts, but I’ll use a similar construction to achieve a progressive suspension. And in the process I’ll be able to tuck the springs parallel to the seat stays and the rear fork.
My calculations indicate that the very first and the very last parts of the scissors’ travel aren’t optimal to use, as it is too weak initially and too strong at its end. So I plan to exclude the top and bottom 20mm of the theoretical maximum stroke, and place the maximum travel of my springs of 44mm, in the middle of this range. 44+20+20=84mm total possible horizontal travel (ie the length of the scissors’ legs).
So theoretically rear wheel travel is 2 x 86mm [2 x a [fully extended legs]] x (44 / 84) [wanted use of travel as percent of total travel] = 88mm.
Opinions?
My plan has been to position the springs at the hub, perpendicular to the seat stay, since it’s an easy way. Yet, it gives a linear suspension (ie every part of the suspension travel has the same resistance) and is a bit bulky.
And I would like to build a progressive suspension. Some might wonder what the appeal with a progressive suspension is.
Well, in a progressive suspension construction, the spring travel relative to rear wheel travel changes as the suspension is compressed. Hence, it is 'plusher' on small bumps (increased small bump sensitivity) and stiffens up as the travel is compressed (meaning it won't bottom out as abruptly).
-You know that scissor jack I cut to pieces earlier?
It suddenly popped up in my mind again, and it got me thinking about Pythagoras' theorem. You know, that a2 + b2 = c2 stuff.
Yeah, I know, I’m a bit strange.
Anyway, after using the theorem, I found out that the lift of one turn of the handle changes depending on where in its travel the jack is. -It is progressive!
In the end, I won’t be using the leftover jack parts, but I’ll use a similar construction to achieve a progressive suspension. And in the process I’ll be able to tuck the springs parallel to the seat stays and the rear fork.
My calculations indicate that the very first and the very last parts of the scissors’ travel aren’t optimal to use, as it is too weak initially and too strong at its end. So I plan to exclude the top and bottom 20mm of the theoretical maximum stroke, and place the maximum travel of my springs of 44mm, in the middle of this range. 44+20+20=84mm total possible horizontal travel (ie the length of the scissors’ legs).
So theoretically rear wheel travel is 2 x 86mm [2 x a [fully extended legs]] x (44 / 84) [wanted use of travel as percent of total travel] = 88mm.
Opinions?
Last edited:
Daaaanngg son.
- Joined
- Aug 27, 2022
- Messages
- 930
- Reaction score
- 1,880
ha ha ha ha Love it!!!You are so right with that picture!
Plans are to grind off all paint, and let the exposed steel rust. To fit external gears and knobby tires, making it suitable for desert use, 50 years after the apocalypse
This build is great! in the tradition of Mad Max how bout a solid chain guard with heaps of bullet holes in it! did you consider a welded chain for the handle bars, maybe those seat stays could be welded chain, . be it stainless or chromed, maybe even rusty
Last edited:
The Renaissance Man
__CERTIFIED DIVER__ (Open Water & Open Dumpster)
Staff member
Moderator
Pro Member
My biggest worry would be is that spring on the dropouts strong enough? Looks like it will be flattened out when ridding.
Thinking that spring looks like it needs to be quite a bit stronger to hold the force of your weight.
I'm all for trial and error. I've built more than one front end to bounce on it, find the weak link and fix it. Just be careful with it. I've had a few stitches and band aids from similar testing.
Thinking that spring looks like it needs to be quite a bit stronger to hold the force of your weight.
I'm all for trial and error. I've built more than one front end to bounce on it, find the weak link and fix it. Just be careful with it. I've had a few stitches and band aids from similar testing.
I would love that! Don’t know how to weld though..
That is sound advice.
Calculations are a just a start, but before I put my skin in the game, I will test load it somehow.
Any suggestions on how to test it without risking injury are welcome
Funkme
𝐰𝐰𝐰.𝐟𝐫𝐮𝐢𝐭𝐜𝐚𝐤𝐞.𝐧𝐮𝐭
Great idea.
More photo visualisations. You might remember my DIY-take on a H-D sport glide headlight:
Softly rounded, harmonizes with an old-school look. Subtle modern vibe, with the LED light.
However, I really like the look of the Yamaha 'Hyper Naked' motorbikes, and especially the MT-03 2020+
Since the bike is ment to look like it's made from other cannibalized bikes and scavenged parts, I'm contemplating another path.
Maybe you'll think me being blasphemous in this, but this look is growing on me:
Less bulky. Sharper lines. Also a bit comtrasting to the rest of the bike. But is it in a good or bad way..
What do you guys think?
or 
More photo visualisations. You might remember my DIY-take on a H-D sport glide headlight:
Softly rounded, harmonizes with an old-school look. Subtle modern vibe, with the LED light.
However, I really like the look of the Yamaha 'Hyper Naked' motorbikes, and especially the MT-03 2020+
Since the bike is ment to look like it's made from other cannibalized bikes and scavenged parts, I'm contemplating another path.
Maybe you'll think me being blasphemous in this, but this look is growing on me:
Less bulky. Sharper lines. Also a bit comtrasting to the rest of the bike. But is it in a good or bad way..
What do you guys think?
or
Last edited:
Since you asked so nicely; .
This bike either needs a real industrial looking head light, or maybe even none at all. I like the 'no holds barred' look of the build. A headlight might be too 'tame' for this one.
. This bike either needs a real industrial looking head light, or maybe even none at all. I like the 'no holds barred' look of the build. A headlight might be too 'tame' for this one.
Thanks for your honesty. I you mean more iron/rust/“steam punk style” headlight I assume. I appreciate your advice.Since you asked so nicely;
This bike either needs a real industrial looking head light, or maybe even none at all. I like the 'no holds barred' look of the build. A headlight might be too 'tame' for this one.
I agree with not necessarily going the standard route (obviously haha) I’ll think it over. Thanks for your input.I don't know, I think it might be good to see a change in the kind of decisions that people usually make, so yeah - try out something like that!
Loving this build! The rear suspension design is really clever. The forks are super cool. I like all of the rusty patina finishes. Headlight or none it looks pretty cool. The streetfighter headlight looks good and is something I haven't seen on a bicycle. Really nice build, looking forward to seeing how it rides!
The headset is finally in place. As I’ve told you about, the steerer is close to standard 1” 24TPI, but it doesn’t fit.
First problem was the thread.
Second problem that a standard 1” crown race was too loose.
A threadless 1” (yes they do exist) solved the thread issue. The top of the fork is clamped around the steerer, kind of like an ahead stem anyway.
The crown race though. I ordered two similar threadless 1” headsets, one with a 27.0mm ID crown race, the other one 26.4mm.
The 27.0 felt just loose enough for me to place a shim made from a thin 1” clothes rail, over the steerer.
The crown race fit perfectly snugly and was tapped into place with a homemade tool. I thought I was done.
-Turned out the shimmed steerer now didn’t go through the bottom cup of the headset. So I had to trim the shim down to match the height of the crown race.
Success 
First problem was the thread.
Second problem that a standard 1” crown race was too loose.
A threadless 1” (yes they do exist) solved the thread issue. The top of the fork is clamped around the steerer, kind of like an ahead stem anyway.
The crown race though. I ordered two similar threadless 1” headsets, one with a 27.0mm ID crown race, the other one 26.4mm.
The 27.0 felt just loose enough for me to place a shim made from a thin 1” clothes rail, over the steerer.
Convoluted but overall a pretty good solution. The 1-in threadless mix and match of parts has saved more than a few people in the past. That's why I keep every bit of headset pieces I can over the years. Bins full of them so I can go through them and find any combination I might stumble acrossThe headset is finally in place. As I’ve told you about, the steerer is close to standard 1” 24TPI, but it doesn’t fit.
First problem was the thread.
Second problem that a standard 1” crown race was too loose.
A threadless 1” (yes they do exist) solved the thread issue. The top of the fork is clamped around the steerer, kind of like an ahead stem anyway.
The crown race though. I ordered two similar threadless 1” headsets, one with a 27.0mm ID crown race, the other one 26.4mm.
The 27.0 felt just loose enough for me to place a shim made from a thin 1” clothes rail, over the steerer.
View attachment 239029The crown race fit perfectly snugly and was tapped into place with a homemade tool. I thought I was done.
View attachment 239028-Turned out the shimmed steerer now didn’t go through the bottom cup of the headset. So I had to trim the shim down to match the height of the crown race.View attachment 239030 Success
Suspension linkage done from good old Swedish “bondjärn” (nicknamed ‘peasant steel’, formally C9D (SS 1312) steel.
Tested it today. As requested by @OddJob, here is a video it in motion
Overview video
Closeup video
Turns out @metalchewy was perfectly right, the springs are too weak. Probably need about double the force. Either parallel springs or just beefier ones.
Test was successful though, as I’m quite happy with the suspension travel range and its progressiveness; gradually reduced mechanical advantage for the linkage through its travel, so it doesn’t bottom out harshly but very gradually
Tested it today. As requested by @OddJob, here is a video it in motion
Overview video
Closeup video
Turns out @metalchewy was perfectly right, the springs are too weak. Probably need about double the force. Either parallel springs or just beefier ones.
Test was successful though, as I’m quite happy with the suspension travel range and its progressiveness; gradually reduced mechanical advantage for the linkage through its travel, so it doesn’t bottom out harshly but very gradually
Last edited:
That's really cool! The suspension direction of travel and response looks good. Heavier duty springs should help.
Swedish ingenuity strikes again!
Swedish ingenuity strikes again!
