[offtheedge]

Well, it's time again for all you engineer monkeys to sound off. it's got LOTS of features (mainly in the adjustability department) missing, but you get the idea.

66 HA, as it sits
55mm chain line
X-type BB cups in the main pivot
adjustable seat mast....carbon of course
and more pivots then a geriatric hip surgeon.

now if rohloff would only release a 150x20mm through axle I’d start building...

cuss and discuss away.

 

[coma13]

i freaking love this stuff! what are you trying to accomplish with the floating shock? leverage ratio stuff?

 

[Tame Ape]

Dude, you're only missing the G-Boxx for the ultimate!

edit: and a floater!

 

[ChrisKring]

Why not put the rolloff inplace of the jackshaft (aka Gbox)? A rolloff adds a ton of unsprung weight.

 

[Tetreault]

ahh i wish i had solid works

 

[dexter]

sickness

 

[offtheedge]

Why not put the rolloff inplace of the jackshaft (aka Gbox)? A rolloff adds a ton of unsprung weight.

Lahar style :thumbsup:
that would entail quite a bit more design work, but it's gonna happen.


i'm a huge fan of the G-boxx, but it just puts alot of limitations on the design.

 

[Tame Ape]

Lahar style :thumbsup:
that would entail quite a bit more design work, but it's gonna happen.


i'm a huge fan of the G-boxx, but it just puts alot of limitations on the design.

but it also centers weight and decreases sprung mass. A worthy trade off!

 

[offtheedge]

but it also centers weight and decreases sprung mass. A worthy trade off!

true, but with a 150 spacing this version is not rohloff-able....at least not at the wheel.

 

[WestCoastHucker]

how long are the crank arms in your model? it appears that they will smack the ground before the suspension bottoms out....

 

[binary visions]

how long are the crank arms in your model? it appears that they will smack the ground before the suspension bottoms out....

Won't most suspension designs bottom the cranks out if they're vertical and the suspension is bottomed out?

175mm crank arms are 6.89" long. Take a 14.5" bottom bracket, subtract 8" of suspension and you've got .39" of crankarm (actually a little more, since the measurement is to the center of the pedal hole) digging into the dirt.

Design looks cool, though

 

[offtheedge]

they are 170's(6.7") and they will, just like any other frame with a sub 15" BB or over 7" of travel.

 

[Tame Ape]

true, but with a 150 spacing this version is not rohloff-able....at least not at the wheel.

exactly!

G-boxx at the BB area and same high pivot. Next you figure out what yields less chain friction; one continous chain or a two chain drive system.

Put the shock in the DT in front of the gBoxx on the vertical plane.

 

[FCLinder]

Why not put the rolloff inplace of the jackshaft (aka Gbox)? A rolloff adds a ton of unsprung weight.

offtheedge I like the idea you have here, but also agree with the above too. Good luck with the design.

 

[skatetokil]

that linkage gives me a headache.

 

[offtheedge]

exactly!

G-boxx at the BB area and same high pivot. Next you figure out what yields less chain friction; one continous chain or a two chain drive system.

Put the shock in the DT in front of the gBoxx on the vertical plane.

i would imagine a one chain sytem is less, but with a two chain sytem you end up getting a balancing force on the main pivot...which i'm sure Cosmos is going to light up red in FEA.

I've done a few mock ups with the G-boxx (with the shock placement you mentioned)and even though i really think it is the next big step in drivetrains it just doesn't leave much space for the shock and gives a really tall standover....at least on my first few attempts.

I just got done modeling a Rohloff, I'm going to see if i can't get it in with little fuss.

thanks for all the feedback.

 

[offtheedge]

that linkage gives me a headache.

somehow i doubt that takes much effort.

 

[sriracha]

i really like the idea of jebus pulling tubes.

 

[WestCoastHucker]

Won't most suspension designs bottom the cranks out if they're vertical and the suspension is bottomed out?.....

Design looks cool, though

i guess so, i never looked at many bikes just sitting there in a fully compressed scenario. and i guess it doesn't happen as much as i originally thought if my frame will do the same...

but hell yeah, that design looks cool as sh!t IMO....

 

[WheelieMan]

but it also centers weight and decreases sprung mass. A worthy trade off!

Sure, the gboxx will center the weight and decrease UNsprung mass, but it will also add several pounds to the bike. I have tried designing around the gboxx specifications and I never seem to get the results I would like...

 

[thaflyinfatman]

A couple of notes:
1. 48" wheelbase is very long... Lahars are long bikes and even they're only 47".
2. 18" chainstays are REALLY long, especially given the high pivot design
3. You're going to put a LOT of force into that seat tube pivot (middle pivot of the top rocker link) and the top linkage in general. Consider a 400lb x 3.0" spring being bottomed out, that's 1200lbs at the shock (before you even worry about progressive shocks or the bottom out bumper etc)... and a ~2:1 leverage ratio of the shock over the compression link on the other (rearwards) side of the rocker means you're putting about 2400lbs through that compression link. Summing forces in the direction of the shock axis gives 1200lbs + 2400lbs = ~3600lbs (or about 1.5 tonnes, the weight of an average family sedan) through that top rocker pivot. If you'd happily hang a whole car from that pivot alone then go for it, otherwise I'd say it's probably worth reconsidering the geometry there.
4. What kind of shock rate does it get with that setup? Just seems like a fairly convoluted way to do things unless you're achieving a very specific rate that you couldn't otherwise get.
5. Rather than dimensioning the actual top tube, it might be worth dimensioning the size by the downtube length. I have a feeling your long wheelbase is partly due to the fact that you've dimensioned the bike from a seat tube that is offset from the BB (ie if you extended the seat tube all the way down, it wouldn't intersect with the BB like most top-tube-dimensioned XC/road frames do).

Looks pretty cool though.

 

[offtheedge]

i really like the idea of jebus pulling tubes.

dude has got to unwind

 

[sriracha]

dude has got to unwind

...i cought the vaporz.

 

[offtheedge]

A couple of notes:
1. 48" wheelbase is very long... Lahars are long bikes and even they're only 47".
2. 18" chainstays are REALLY long, especially given the high pivot design
3. You're going to put a LOT of force into that seat tube pivot (middle pivot of the top rocker link) and the top linkage in general. Consider a 400lb x 3.0" spring being bottomed out, that's 1200lbs at the shock (before you even worry about progressive shocks or the bottom out bumper etc)... and a ~2:1 leverage ratio of the shock over the compression link on the other (rearwards) side of the rocker means you're putting about 2400lbs through that compression link. Summing forces in the direction of the shock axis gives 1200lbs + 2400lbs = ~3600lbs (or about 1.5 tonnes, the weight of an average family sedan) through that top rocker pivot. If you'd happily hang a whole car from that pivot alone then go for it, otherwise I'd say it's probably worth reconsidering the geometry there.
4. What kind of shock rate does it get with that setup? Just seems like a fairly convoluted way to do things unless you're achieving a very specific rate that you couldn't otherwise get.
5. Rather than dimensioning the actual top tube, it might be worth dimensioning the size by the downtube length. I have a feeling your long wheelbase is partly due to the fact that you've dimensioned the bike from a seat tube that is offset from the BB (ie if you extended the seat tube all the way down, it wouldn't intersect with the BB like most top-tube-dimensioned XC/road frames do).

Looks pretty cool though.

where you been all day FFM? I've been itching for a reality check .

thanks, all issues that i can see, but with just a couple days work this is what fits. the shock clearance is really tight for any piggyback type and even the slightest changes are getting it in a possible interference with the seat tube area. that and keeping clearance for the legs and the chainline and ect...... the wheel base is an easy fix, but most my concern is in the as mentioned upper linkage, lots of stress and high up in the frame.
i try to keep the design criteria at a do-able state, meaning could i actually make the frame.....now if CNCing 6" chunks of billet or hydroforming comes into my near future look out, but for now it's 'what can i build from the rem pile'?


i forgot that the dimensions are absolute and not coplanar:
CS is actually 17.5 and the WB is 47.5"

keep it coming.

 

[SinatorJ]

I know that maybe in a few years the future will be gear-box, But I have no issues with an 83mm BB shell, outboard cranks and an XO r. derailer. I just don't have drive issues. the stuff is readily availible and easy to service.

 

[trialsmasta]

Whats with the 27" tires? Not challenging just curious.

 

[DHS]

definitely going to need a floater on there.

yet interesting design. when can i test it for you in the real world?

 

[thaflyinfatman]

where you been all day FFM? I've been itching for a reality check .

thanks, all issues that i can see, but with just a couple days work this is what fits. the shock clearance is really tight for any piggyback type and even the slightest changes are getting it in a possible interference with the seat tube area. that and keeping clearance for the legs and the chainline and ect...... the wheel base is an easy fix, but most my concern is in the as mentioned upper linkage, lots of stress and high up in the frame.
i try to keep the design criteria at a do-able state, meaning could i actually make the frame.....now if CNCing 6" chunks of billet or hydroforming comes into my near future look out, but for now it's 'what can i build from the rem pile'?


i forgot that the dimensions are absolute and not coplanar:
CS is actually 17.5 and the WB is 47.5"

keep it coming.

haha sorry if I came across harsh, just things you might want to have a think about. That chainstay length is more reasonable, though if you were able to go even shorter it'd probably be better still, because they will obviously extend quite a bit under sag - a 17.5" stay length is fairly typical on low/mid pivot bikes, but when the bike sags further out then it's going to end up being fairly long. Your linkage might get in the way here though. Fair call on the construction abilities thing too.

BTW - what was the reasoning behind the floating shock? Because having it use two linkages doesn't reduce the number of loaded points on the front triangle, ie you have two linkage pivots plus the main pivot on the front triangle, whereas otherwise you'd only have one linkage pivot plus main pivot plus shock mount. If you were looking to reduce the number of loaded points on the front triangle(like the Sunday does by using the concentric lower pivot/shock mount), what you might be able to do is extend the swingarm past the main pivot, and run the shock directly between that and the lower pivot - that would reduce the number of loaded points on the front triangle, and thus (at least theoretically) make it easier to strengthen those points without making the frame heavier. However, if you're doing it for a specific shock rate then fair enough... but most useful shock rates (and a whole lot of useless ones too!) can be achieved with a single linkage anyway (especially if you run the shock between the linkage and the swingarm instead of linkage and front triangle).

Trialsmasta: DH tyres are actually about 27" in diameter; the 26" spec is intended to be measured with 2.0" bag tyres, however if you have 2.5" bag tyres then you add roughly another half inch to the radius (and thus obviously a full inch to the diameter).

 

[davep]

looks very nice...does look like a grat candidate for a mianframe rohloff.... but,

that thing is LONG. Do you truely want 18" (going to 20+") chainstays and a 48" wheelbase? Speed demon!!

 

[FarkinRyan]

Hey mate, I'll just throw in my .02c about chainstay length on a high pivot bike like that. I'm by no means an expert on this sort of stuff, but starting at even 17.5" with a pivot that high is going to make the bike nearly impossible to manual / pop the front up on once it sits into its sag and even less manageable as the suspension compresses.

Check out this homebuilt frame on our forums. Aside from being one of the coolest home jobs I've ever seen, they've based their design on sagged chainstay length, giving them a 15.5" static length and a 16.5-17" length when sagged, which to me seems to be the way to do things. Another to look at would be the BCD Inedible, super short stays when static that extend to a DH-worthy length under sag.

 

[RMboy]

YOU MUST TEACH ME.....HOW!!!!! lol

 

[offtheedge]

fatman: not harsh at all. i welcome the constructive critisism's/suggestions. you were on my list of expected why the F's.:thumsbup:
the floater started as a 'why not' but ended up being a really good way to keep the stand over low and the main linkage shorter, mostly cool factor though.

davep: No, it's way to long. it has about 1.25" of room to move the wheel forward and the DT will get shortened a bit also.

FarkinR: couldn't see the frame. i did this design quickly and mainly based on a low stand over and a 9.5" i2i, the cadillac-esque WB and CS will need some help though.

thanks, and anyone with a Haas just sitting around that wants get in on a prototype frame............

 

[ÆX]

Well, it's time again for all you engineer monkeys to sound off. ]

well, as it is said b/f the cs are a little long with sag.
maybe try and roll the seat area froward on the bb axis.

rework some links to get your tire tucked in by the bb.
i start at 16.75


my new bike is running a jackshaft this year, better ground
clearance and less chain guides and less chain movement
for better shifting.

can i borrow your fork part? maybe rear shock?

alex

 

[offtheedge]

well, as it is said b/f the cs are a little long with sag.
maybe try and roll the seat area froward on the bb axis.

rework some links to get your tire tucked in by the bb.
i start at 16.75


my new bike is running a jackshaft this year, better ground
clearance and less chain guides and less chain movement
for better shifting.

can i borrow your fork part? maybe rear shock?

alex

with almost two inches of growth at the CS I'm reworking from a static 16.5".....the Rohloff in the frame has created some space issues however

yeah, i figured the same thing on the jackshaft, it also positions the chains a little tighter to the frame and hell it's just cool.

borrow? like borrowing a smoke? j/k
you can have. let me klnow.

 

[ÆX]

Trialsmasta: DH tyres are actually about 27" in diameter; the 26" spec is intended to be measured with 2.0" bag tyres, however if you have 2.5" bag tyres then you add roughly another half inch to the radius (and thus obviously a full inch to the diameter).

yeah, and 29 tires are all about just that. my kenda nevegals are
actually 28.875 b/c i have 38mm rims now. Legal with the UCI
rule that they can't be over 29''.

so my wheels are really only 1' radius bigger.

 

[alexchannell]

You can use that fifth element I modeled up if you want, let me know the eye-to-eye and stroke and I'll resize it. Pm me if you want it.