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Question about single pivots.

kidwoo

kidwoo

Artisanal Tweet Curator
Aug 25, 2003
42,146
13,340
Squirtin ketchup n' mustard on charred flesh
Bicyclist said:
I just need to get out and ride everything possible and make a desicion based on feel.
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Actually, you should try really hard to crack that demo. Everyone of my buddies that has one did it within a year.

Get the warranty and then you've got a new frame to sell.

You know that trapezoidal "tube" welded right in front of the shock cage between the top and downtubes..... Check 'er out. You may already be in luck. :)
 
OGRipper

OGRipper

back alley ripper
Feb 3, 2004
10,654
1,129
NORCAL is the hizzle
Heh. Sounds like you've already got the bike you want.

It is just the sickness we all suffer from, or is there something about the Demo you don't like?
 
Bicyclist

Bicyclist

Turbo Monkey
Apr 4, 2004
10,152
2
SB
That would sure make it easy. :D

But then I'd be stuck with a QR 135mm wheel, a funky BB, and a bunch of other crap that's not DH standard.

It was ridden by an expert, hard rider before me so I may be in luck! I need to look really carefully. However, I don't think it's cracked. Something tells me I would have noticed.
 
Bicyclist

Bicyclist

Turbo Monkey
Apr 4, 2004
10,152
2
SB
OGRipper said:
Heh. Sounds like you've already got the bike you want.

It is just the sickness we all suffer from, or is there something about the Demo you don't like?
Click to expand...
I want something lighter and better-pedalling that's a bit slacker/lower w/ a longer CS.

The reality is I don't need a bike at all. I just don't want to dump money into making my 2 year old bike lighter, then having something that's not worth anything that I spend a fortune on.
 
kidwoo

kidwoo

Artisanal Tweet Curator
Aug 25, 2003
42,146
13,340
Squirtin ketchup n' mustard on charred flesh
Bicyclist said:
That would sure make it easy. :D

But then I'd be stuck with a QR 135mm wheel, a funky BB, and a bunch of other crap that's not DH standard.

It was ridden by an expert, hard rider before me so I may be in luck! I need to look really carefully. However, I don't think it's cracked. Something tells me I would have noticed.
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One of my friends that broke his isn't really that hard of a rider.
Good luck man!

Yours came with a qr? I traded wheels with one my demo owning friends and it was a bolt on. They're on my dj bike right now.
 
no skid marks

no skid marks

Monkey
Jan 15, 2006
2,511
29
ACT Australia
Sorry to re rail this thread.
Flyin Fatman and DW please help me understand. To start with I stated"forget about cassette size on the rear for now"in my first statement but since this was raised I'd like to know it's accurate effect on suspension. Lets use a Balfa BB7 please as an example as it's the least likelly to offend anyone.
The cassette both in highest and lowest gear with the front idler having(guessing)10 teeth,how much chain force can that possibly generate on the suspension?
I can't see to much difference depending on what gear the cassette is in or the size of the idler wheel,is there? I mean sure a massive idler would make a difference but anything below the size of the cassettes 34teeth won't make to much difference will it?
As long as both parts of the chain under tension are above the rear axle and pivot it's going to have some (trivial) amount of affect,correct?
What bike design suffers from chain induced affects less(just to put these facts into perspective)?
Compared to say a 222 as I mentioned,the effect on the suspension when peddalling would be something like over 100 times greater than on a BB7?
Orange lowered the pivot to get the bike more active whilst peddalling at the expense of loosing some square edged absorbtion.they said something else i think but that's the effects isn't it?
I've never done any engeneering schooling and I just got up so please bare with me.
Oh and my for crying out loud statement was in jest at all the posts for the sake of posting.
 
Sandwich

Sandwich

Pig my fish!
Staff member
May 23, 2002
21,080
5,999
borcester rhymes
Bicyclist said:
I want something lighter and better-pedalling that's a bit slacker/lower w/ a longer CS.

The reality is I don't need a bike at all. I just don't want to dump money into making my 2 year old bike lighter, then having something that's not worth anything that I spend a fortune on.
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if you want lighter, you'll need to look towards a single pivot. think about what you mean by better pedalling, if you mean no effect on the rear wheel, then go for something with an idler. I love the way my brooklyn feels, but it's not the right bike for you. If you want a firm platform, look for a vpp or maestro.

How about a vppfree? I don't see any reason one of those couldn't be set up as a DH bike. Otherwise, I like the look of the appalache real. Outside of flexiness rumors, that bike is high on my list. The trek is impressive but rumored to be heavy. I would look for an older diesel if you want a lighter bike.
 
Bicyclist

Bicyclist

Turbo Monkey
Apr 4, 2004
10,152
2
SB
Nah, I built mine up QR. With that rear end bolt on is overkill, plus now I can dis-assemble my bike to put it in trunks and stuff quicker.

I'm not a very "hard" rider at all. I'm not that fast and I definately don't hit stuff hard.
 
Bicyclist

Bicyclist

Turbo Monkey
Apr 4, 2004
10,152
2
SB
Sandwich, I want something with more of a "platform" effect (but also something w/o chain pull).

The VP-Free has horrible geo w/ that skyscraper BB.
 
R

RumDuK

Chimp
May 23, 2005
29
0
Orange County
Idk, i havent really ridden to many bikes but i recently picked up a turner dhr, atleast to me if pedals just as well as my bullit did. Now this could be that theyre both single pivot bikes and keep in mind that i have romics on both my bullit and dhr. But with decent platform shock i bet the dhr would pedal quite nice anyways just my .02
 
bikenweed

bikenweed

Turbo Monkey
Oct 21, 2004
2,432
0
Los Osos
The first generation Demo8's break when you land sideways.

Find a good sized jump, throw that rear end out into a racer hella moto whip hella, then freeride and land the jump while still sideways. One good hit will break the Demo. Or just hit a hip jump and freeride the landing on that, that works well too. Whistler breaks many, many Demo8's when kids freehuck with tons of dead sailor kick outs down Aline.

Oh, and casing a straight double of 40 feet shouldn't be a problem for the Demo, it's a very strong bike when flying straight. The only thing that might break would be your wrists, ankles and back.
 
Bicyclist

Bicyclist

Turbo Monkey
Apr 4, 2004
10,152
2
SB
So basically it can't handle side loads? I try not to land sideways for my wheels' sake anyways.
 
T

thaflyinfatman

Turbo Monkey
Jul 20, 2002
1,577
0
Victoria
no skid marks said:
Sorry to re rail this thread.
Flyin Fatman and DW please help me understand. To start with I stated"forget about cassette size on the rear for now"in my first statement but since this was raised I'd like to know it's accurate effect on suspension. Lets use a Balfa BB7 please as an example as it's the least likelly to offend anyone.
The cassette both in highest and lowest gear with the front idler having(guessing)10 teeth,how much chain force can that possibly generate on the suspension?
I can't see to much difference depending on what gear the cassette is in or the size of the idler wheel,is there? I mean sure a massive idler would make a difference but anything below the size of the cassettes 34teeth won't make to much difference will it?
As long as both parts of the chain under tension are above the rear axle and pivot it's going to have some (trivial) amount of affect,correct?
What bike design suffers from chain induced affects less(just to put these facts into perspective)?
Compared to say a 222 as I mentioned,the effect on the suspension when peddalling would be something like over 100 times greater than on a BB7?
Orange lowered the pivot to get the bike more active whilst peddalling at the expense of loosing some square edged absorbtion.they said something else i think but that's the effects isn't it?
I've never done any engeneering schooling and I just got up so please bare with me.
Oh and my for crying out loud statement was in jest at all the posts for the sake of posting.
Click to expand...

Ok say you've got a swingarm length of about 450mm (0.45m) (from pivot to axle) on a bike LIKE a Balfa, but imagine the idler is concentric instead of being mounted below the pivot on the swingarm. Say the idler at the front has 10 teeth (I'd bet it's more like 14-16 in reality, 10 is tiny) and a pitch diameter of about 40mm (therefore pitch radius is 20mm). Rear cog say 11t and roughly 44mm pitch diameter (radius therefore 22mm). For this gear combo you're looking at about 0.25 degrees between the chainline and the axle-pivot line, therefore absolutely bugger all chain extension or force induced on the suspension. You'll get about 0.87mm of chain extension over 8" (200mm) of travel... totally insignificant. Chain input into the suspension (again ignoring all other factors) also absolutely bugger all.

Bump that rear sprocket size up to say a 32t (1st gear on a DH bike with an 11-32 cassette) and a ~128mm pitch diameter (these diameters are a bit bigger than in reality but never mind, it gets the point across), and the angle between chainline and axle-pivot line becomes about 5.6 degrees. This adds up to about 19.5mm of chain extension over the 200mm travel (still not a whole lot, see the debate I had with Aaron on Farkin for more info), and a now-significant component of chain force (over 22 times as much as the first setup) acting to try and extend the suspension.

Say the chain force was about 2000N (roughly representative of a heavy rider stomping on the pedals), you'd have an extensive force acting on the axle of about 30.3N in the first scenario (small rear cog), and and about 195.2N in the second scenario (large rear cog).

I don't know if these numbers mean much to you, but basically the first scenario = absolutely SFA chain extension and very little extension force on the suspension, whereas the second one gives a bit more chain extension but a lot more extensive force.
 
wirly

wirly

Monkey
Mar 19, 2002
110
0
San Diego
thaflyinfatman said:
Ok say you've got a swingarm length of about 450mm (0.45m) (from pivot to axle) on a bike LIKE a Balfa, but imagine the idler is concentric instead of being mounted below the pivot on the swingarm. Say the idler at the front has 10 teeth (I'd bet it's more like 14-16 in reality, 10 is tiny) and a pitch diameter of about 40mm (therefore pitch radius is 20mm). Rear cog say 11t and roughly 44mm pitch diameter (radius therefore 22mm). For this gear combo you're looking at about 0.25 degrees between the chainline and the axle-pivot line, therefore absolutely bugger all chain extension or force induced on the suspension. You'll get about 0.87mm of chain extension over 8" (200mm) of travel... totally insignificant. Chain input into the suspension (again ignoring all other factors) also absolutely bugger all.

Bump that rear sprocket size up to say a 32t (1st gear on a DH bike with an 11-32 cassette) and a ~128mm pitch diameter (these diameters are a bit bigger than in reality but never mind, it gets the point across), and the angle between chainline and axle-pivot line becomes about 5.6 degrees. This adds up to about 19.5mm of chain extension over the 200mm travel (still not a whole lot, see the debate I had with Aaron on Farkin for more info), and a now-significant component of chain force (over 22 times as much as the first setup) acting to try and extend the suspension.

Say the chain force was about 2000N (roughly representative of a heavy rider stomping on the pedals), you'd have an extensive force acting on the axle of about 30.3N in the first scenario (small rear cog), and and about 195.2N in the second scenario (large rear cog).

I don't know if these numbers mean much to you, but basically the first scenario = absolutely SFA chain extension and very little extension force on the suspension, whereas the second one gives a bit more chain extension but a lot more extensive force.
Click to expand...

Cool example, thanks.
Just a quick math question...you said the extending chain force with the larger cog is 22x that of the insignificant smaller cog extending chain force. 195.2N is not 22x greater than 30.3N. 19.5mm is, however, roughly 22x 0.87mm; maybe you were refering to this relationship? Are the force values still accurate?

Thanks-

Oh, and for the rest of the us non-physics majors, for every-day values of force, Newtons are easily converted to pounds by multiplying by roughly 0.22 (call it 1/4) so the extending chain forces would be about 7 lbs. vs. 43 lbs. (Just dont try to launch a mission to Mars using that...)
 
T

thaflyinfatman

Turbo Monkey
Jul 20, 2002
1,577
0
Victoria
wirly said:
Cool example, thanks.
Just a quick math question...you said the extending chain force with the larger cog is 22x that of the insignificant smaller cog extending chain force. 195.2N is not 22x greater than 30.3N. 19.5mm is, however, roughly 22x 0.87mm; maybe you were refering to this relationship? Are the force values still accurate?

Thanks-

Oh, and for the rest of the us non-physics majors, for every-day values of force, Newtons are easily converted to pounds by multiplying by roughly 0.22 (call it 1/4) so the extending chain forces would be about 7 lbs. vs. 43 lbs. (Just dont try to launch a mission to Mars using that...)
Click to expand...

Ah woops, yeah you got me there - I punched sin0.87 into the calculator when it should have been sin0.25, my mistake. The 22x relationship is valid, but the first force value should have been 8.72N, not 30.3.

Basically, chain force component acting on the rear axle is directly proportional to the amount of chain extension you get (again keeping in mind that true chain extension is not just a measure of change in distance from BB to axle). People can tolerate some amount of chain extension before it becomes noticeable, but there is definitely the potential to have too much.
 
Rye_Bread

Rye_Bread

Monkey
Mar 22, 2006
437
0
Boulder
Bicyclist said:
Without starting a sh!t storm about whether or not single pivot is "better" than any other design, I have a question.

Is it true that with a certain chainring that is "inline" with the pivot, a single pivot bike will not have pedal feedback? I've noticed when riding a SP with multiple rings, they will have feedback in certain rings and not others. Is there are reason for that or not?

If that is the case, is there a way to determine what size ring would negate the effects of pedal feedback?

Like I said no arguing, I just want to know the answer to that question.

EDIT: This is assuming no idler.
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i can't believe this thread went on this long, if the chainline is alligned with the pivot you won't have pedal feedback, it the chainline is below the pivot your suspension will stiffen as you pedal and your chainline is above the pivot you will get gnarly pedal bob.

that is the answer
 
T

thaflyinfatman

Turbo Monkey
Jul 20, 2002
1,577
0
Victoria
Rye_Bread said:
i can't believe this thread went on this long, if the chainline is alligned with the pivot you won't have pedal feedback, it the chainline is below the pivot your suspension will stiffen as you pedal and your chainline is above the pivot you will get gnarly pedal bob.

that is the answer
Click to expand...
No, you are wrong on all counts. Every single thing you just said is flat out WRONG.
 
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