didn't stratos offer tapered springs on their coil shocks back in the day?
Plow bikes
- Thread starter ucsbMTBmember
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Did they really? I used to know the guy that started that company...
I never rode one of their shocks so I can't say for sure what the spring was doing. However, I do remember that they had springs that started out being sparsely wound at the bottom and as they got closer to the top the coils were much much closer together. It sounds like what you were describing but I don't know if it was doing the same thing.
It seems like if this were the case, it would be redundant to a degree. Most of those shocks also had and air assist that gave them a more progressive nature anyway.
I'll definitely have pics as I go but it probably won't be until late summer as I'm working on so many other projects right now (desktop 3d printer, animatronics,etc.) and I have three little boys to take care of- no rest for the weary!
Someone on another board did ask me to explain why I liked a high pivot swingarm design so here it goes (and this is going to be uber long so I apologize in advance.) For the record I am not an engineer so this is just what I think- if I've made any incorrect assumptions I'm sure someone like Socket that is a billion times smarter than I am will correct me and I heartily welcome it- LOL!
Here was the question:
"one thing that threw me for a loop a while back was the realization that a chain guide on top of the pivot does not completely neutralize chain growth. that said, some times it can work out pretty well. how does it do with that bike?
i like the design (i'm a sucker for single pivots with links) but that is a rather high pivot. you really seem to know your stuff though, so i'm curious as to the logic behind placing it so high? i get the whole 'roll through sharp impacts' idea, but i'm hoping that you have more wisdom to impart beyond that."
Here was my response:
You are absolutely correct that a guide on the pivot does not completely neutralize chain growth/pedal feedback. I had to play around with various pulley setups in multiple gear combos to get proper feedback. With a 28 tooth rear cog the pedal kickback is +10.17 degrees (anti-squat @132% to 108%) and with a 12 tooth rear cog it's -3.25 degrees (anti-squat @ 88% to 60%) so those are the two extremes, which is pretty good. In the middle cogs pedal feedback is very minimal- less than 3 degrees and I can still get 100% anti- squat. By changing the size of the guide roller I can manipulate the amount of anti-squat/pedal feedback.
The pivot is exactly 9" directly above the BB so it looks high but it gives an axle path that is similar to the front wheel. It's really all about axle path. I've built more than a few frames with a similar axle path and I've always liked the way they ride. I do think it absorbs square edge bumps better due to energy dissipation (for lack of a better term.) Remember that since dampers are speed sensitive (not load sensitive) the shape of a bump is more important than the size of a bump and a rearward axle path puts less energy into the damper than a vertical axle path for a given sized square edged bump. I also think that the geometry of the high pivot simply absorbs bumps better because it's a more natural motion for the wheel to take.
Since Energy = [1/2 x Mass x (Velocity)squared] the upward velocity of the rear wheel with a rearward axle path will create less energy over a given span of time than that of a rear wheel with vertical axle path for a given shape bump. Since a large square edged bump requires a very rapid increase in damper shaft velocity I think a high pivot swingarm design has a distinct advantage over a low pivot swingarm design (but only regarding that particular situation) because the increase in damper shaft velocity isn't as rapid - hence I think it may be easier to maintain better chassis stability without having to resort to something like severe digressive damping (similar to a very rapid shim stack blow off) or even regressive damping (which provides lower damping rates at high damper piston speeds.) Digressive damping means that the damping force increases with absolute velocity at a decreasing rate. Mid to high velocity digressiveness allows for a more controlled feel with less harshness when hitting big bumps but there could be a trade off in stability if you go too far as the bike could become unsettled or unpredictable. Modern bike dampers are pretty darn good though when properly matched to a given design, so we're getting really nitpicky here...
I think there might be some merit to regressive damping if you could separate spring and damper forces by having the wheel rate linear and the damping regressive but that would require separate mounting of the spring and damper, which really isn't practical for weight and packaging reasons (but I'm working on it.) Now granted I'm not a damper engineer so I could be way off base here but let's say you have a low pivot swingarm bike that has a vertical axle path and you go into a bumpy corner hard. The bike will more than likely have a fairly progressive wheel rate. Now you start hitting some of those square edged bumps and I'm willing to bet that the bike hangs up. Bump inputs like that are at high frequencies and the damper can't cope with it in that situation because the suspension is already heavily loaded- this is where regressive damping might help- and this is where a rearward axle path with a linear rate would really shine. As far as I know, both Ohlins and Penske have been working on regressive damper valving for the last few years and I believe Penske recently filed for a patent. No idea if it will make its way into bike dampers...
I think that's why we're seeing more and more long travel bikes with short bar four link systems- it allows the designer to better manipulate axle path and anti-squat values, but you can still only go so far in terms of rearward axle path without using an idler or gearbox due to chain extension. So these bikes tend to start out with a rearward axle path for the first half of the suspension compression and then go more vertical/inward to manage chain extension.
This is a highly debatable point, but I also think a rearward axle path does a good job of managing weight transfer by keeping wheelbase more constant -assuming you could actually get a perfect linear axle path parallel to the front fork (this design is close enough for me.) I say it's debatable because you never really have the front and rear suspension compressing the exact same amount at the exact same time, so the wheelbase is constantly changing no matter what type of suspension system you have- the goal is to minimize it because no rider can react fast enough to a radical weight transfer shift caused by an imbalanced suspension system. By trying to minimize weight transfer you're going to have a more stable bike that handles better, especially as speed and travel increases. With a low pivot swingarm bike (vertical/inward axle path) I'd be inclined to have a more rising rate suspension since weight transfer will shift a bit more rearward as the suspension compresses vs. a rearward axle path bike will probably be more linear rate since the rearward weight transfer wouldn't be as severe.
In some ways it's like racecar design where you're always trying to maintain a consistent aerodynamic center of pressure except with a bike you're trying to maintain a consistent center of traction/center of mass. It's all about proper balance and manipulation of weight transfer under acceleration, braking and bump forces.
The other thing I like about the pivot placement is that there is a very direct load path from the head tube to the rear axle. Structural efficiency has always been important to me and I always try to have designs that have good specific torsional rigidity.
The downside to the high pivot is chain extension/pedal feedback so you have to have an idler pulley or gearbox to minimize this. The increase in friction is a definite disadvantage but I feel that an idler pulley is worth the trade off in this case and is still more efficient than a gearbox. So while high pivots can work for DH bikes they really don't belong on traditional XC/AM bikes due to drive train inefficiencies- the only exception being a URT or floating BB bike and that's a whole different topic! The other issue is the suspension stiffens a bit under braking but fitting a brake torque arm can cure that (of course that adds additional friction into the system as well- there's always a trade off...)
At first the wheelbase may look a bit short, but with the increased stability of the high pivot I don't think it will be a problem. The other reason is that wheelbase (along with traction) ultimately determines turning ability and high pivot bikes don't usually want to turn as well as low pivot bikes, so a shorter wheelbase can help compensate for this. Everything is a compromise in bike design and you have to look at how the whole system works together. Torsional rigidity, tire clearance, geometry, friction, etc. all play important roles. Every system out there has it's positives and negatives- you just have to find what works best for you.
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OK- I see. Yep that's a bit different. That is a progressive wound spring in that the coil pitch gets tighter as you get to the top of the spring. One end has greater distance between the coils than at the other end of the spring. As the coils compress the coils closest to each other touch, (become coil-bound), which effectively reduces the number of active coils. They're pretty common in aftermarket car lowering springs. That's different from the way Porsche did it as it can effectively reduce the spring travel for a given length spring as opposed to a constant pitch spring (depending on exactly how progressive the spring is and at what point it becomes coil bound.)
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Nice cut an paste from your pinkbike post bra
You mean someone actually read all that! It's got to be some kind of record for the longest post. Re reading my drivel actually forced me to go back and edit a few things that were screwed up. What can I say- ask me what time it is and I'll tell you how to make a watch. Most of my co workers have just learned to give me a blank stare so I'll shut up... LOL.Nice cut an paste from your pinkbike post bra
Is it one of those Reprap kits?
I'm using RepRap electronics from MakerBot but the chassis is all mine using industrial linear slides since I wanted to be able to do CNC machining as well as 3d printing (mostly prototype circuit boards and small parts.) A RepRap Mendel or a MakerBot is nowhere near rigid enough to do any kind of accurate machining. The other thing I got were some Linistepper drivers so I could compare how it would run CNC programs using Linux EMC vs. using the RepRap code.
I started a blog here: http://multi-bot.blogspot.com/
Hopefully I'll have an update on the blog before the weekend is over.
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Funny i was thinking of doing that exact same thing, so i could increase the footprint of the machine and also use it as a mill and perhaps also a plasma cutter just by changing the tool. Ill be keeping an eye on your blog, i hope it works out well for you.
Low SP bikes can feel good on Tunnel. My R9 feels fantastic on it for example. When I rode the same DHR you have on it, I felt like I was about to wad up and die the whole f'ing way down. You're welcome to try the R9 sometime.
A large M6 would probably feel great up there if you wanted to go that route. The M3 I had did well on the deep choppy stuff but it was just too damn small. Good geo and good feel, but it's an Intense..
Try to find one of the original Yeti 303's. That thing would eat the SB trails for breakfast and **** them out by lunch. Heavy, but whatever.
A large M6 would probably feel great up there if you wanted to go that route. The M3 I had did well on the deep choppy stuff but it was just too damn small. Good geo and good feel, but it's an Intense..
Try to find one of the original Yeti 303's. That thing would eat the SB trails for breakfast and **** them out by lunch. Heavy, but whatever.
Dejavu is preventable.
http://www.ridemonkey.com/forums/showthread.php?t=230429&highlight=plow
http://www.ridemonkey.com/forums/showthread.php?t=230429&highlight=plow
There are a few of the FB-10s left I think. (Replacement for the R9.)
dejavu x2......this link was posted and referenced earlier this thread
Honus, if you don't mind, post up a few pics of your earlier creations. I dig the home-made stuff
I actually don't have many pics of bikes I've built. I lost a lot of the earlier pics of frames that I built in the mid 80's when I moved from Arizona to L.A. and then on to Colorado. Back then I built several road frames, a couple of curved tube time trial frames along with my first mountain bike frame and a neat lugless fillet brazed BMX frame for a kid that used to hang out in the shop where I worked.Honus, if you don't mind, post up a few pics of your earlier creations. I dig the home-made stuff
I didn't build any frames while working at Onza and I built two suspension frames and one road frame (which I still have) while at Real Design. I know I don't have any pics of one of the suspension bikes but I might have a pic somewhere of the other- man was it ugly! It did form the basis for my last bike which is here:
http://sites.google.com/site/opensourcesuspension/
I'll be adding more pics (especially of the construction process) and updating the site as I build new designs. Then I'll just post a pic and a link to the site- I figure it's better to do that than have an epic long post here trying to explain everything. For some reason the animations on the site aren't working so I need to fix that.
I still have quite a few pics of the component design work I did while at Onza and Real in the 90's.
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Cool.....thanks for sharing.
Almost forgot clifcat, dark cycles, brooklyn, Balfa, or the "MAD MAX" model Demo 7 straight outa austrailias ebay
Complete with tractor seat for the extreme gnar of tunnel.
Complete with tractor seat for the extreme gnar of tunnel.
Not trying to add fuel to the fire here, but as I understood it (lat least I thought anyway) that the VPP bikes were all USA made bikes. Is this not the case?
Nope, just the V10.
Aren't some (all) of the V-10 parts made in Taiwan? Aren't they just "assembled" in the U.S.? I remember a bunch of my buddies a few years ago were waiting like an extra 6 weeks for their v-10's because of some issue getting the bikes on time from Taiwan.
Karpiel Disco
Nope. Front and rear ends are cut, shaped and welded in US (used to be done by Control Tech, now maybe someone else?). The carbon link is probably from the same Asian factory that makes their carbon frames.
I was in the same group of customers waiting (if you mean spring '08). I heard that there was a problem with a batch of rear triangles. Stupid American welders
