[stoney]

I'm trying to calculate the change in my BB height, HA and wheelbase if I adjust the travel in my fork. My problem is that I haven't done trig in so long that I can't remember how.

I have the following measurements from the Yeti website (converted to mm):
Wheelbase: 1178.6mm
Fork Axle to crown: 520.9mm
Head Angle: 68*
Chainstay: 429.3mm
BB height: 337.8mm

How much will my BB raise if I change to the below measurements?
Wheelbase: 1200mm
Fork Axle to crown: 543.3mm
Head Angle: 67*
Chainstay: 429.3mm
BB height: ??

What about with the following (calc'd based on current fork A-C)?
Wheelbase: 1178.6mm
Fork Axle to crown: 518.3mm
Head Angle: 69*
Chainstay: 429.3mm
BB height: ??

 

[HAB]

Scenario A: Going to a 543.3mm a-c fork will give you a HTA just under 67, and a BB of about 346mm. Wheelbase won't go to 1200mm, more like 1187mm.

I'm confused by scenario B. Are you talking about an angleset to make things 1 degree steeper? Fork a-c is barely different as you've typed it.

 

[stoney]

Base = Yeti Factory spec & A-C from Fox on 32 Float
Scenario A = Proposed based on increasing my fork travel back up to 6"
Scenario B = Current. I tried to figure some of the numbers, but the only one I know for sure is that the A-C is 518.3mm. The rest are derived from the Yeti numbers.

 

[HAB]

Well your numbers in scenario B make no sense because you're changing a bunch of dependent ones in ways that are physically impossible. For example you can't make your HTA one degree steeper without changing the wheelbase (see base vs. scenario B).


Your geometry is really really close to stock. BB is ~1mm lower, HTA is about .1 degree steeper. Going to the longer fork from scenario A gives you the numbers in my last post.

 

[stoney]

Much appreciated!

 

[gonefirefightin]

just ride

 

[MMike]

What is: The War of 1812?

 

[CrabJoe StretchPants]

You can really measure these things to 1/10th of a millimeter? Do you have a CMM for a hand or something?

 

[gonefirefightin]

You can really measure these things to 1/10th of a millimeter? Do you have a CMM for a hand or something?

you have to wager first.....its the daily double

 

[CrabJoe StretchPants]

you have to wager first.....its the daily double

Alex Trebeck: Mr. Reynolds, it's your board, pick a category.
Burt Reynolds: I'll take the dog one.
Alex Trebeck: Alright, words that rhyme with dog for 400. And the answer is 'It's been a "Hard Days Night" I should be sleeping like a "this".' Burt Reynolds
Burt Reynolds: Chinese whore.
Alex Trebeck: No. John Travolta.
John Travolta: Chinese whore doesn't rhyme with dog.
Alex Trebeck: That's why it was a wrong answer. Mr. Keaton.
Michael Keaton: I am Batman.
Alex Trebeck: No, you are not.

 

[HAB]

You can really measure these things to 1/10th of a millimeter? Do you have a CMM for a hand or something?

If that was at me, no, but I can do teh mathz™ to guess.

If it was at Stoney, no, it just looks like he made some numbers up.

 

[CrabJoe StretchPants]

If that was at me, no, but I can do teh mathz™ to guess.

If it was at Stoney, no, it just looks like he made some numbers up.

It was at Stoney. He listed his "measured" dimensions to 1/10th millimeter, which is absurd.

 

[HAB]

It was at Stoney. He listed his "measured" dimensions to 1/10th millimeter, which is absurd.

His "measured" dimensions are also impossible unless he ran the bike into a garage on top of a car, or he has a way out of spec frame.

 

[CrabJoe StretchPants]

His "measured" dimensions are also impossible unless he ran the bike into a garage on top of a car

Wait, wait, wait.......didn't he actually do that though?

 

[Serial Midget]

Pay in mixed bills - hookers cant count.

 

[heavy metal]

soh cah toa brooo

 

[AngryMetalsmith]

Don't forget to factor in tire size, wall thickness, knob placement, and psi.

Or just do what GFF says and ride.

 

[CrabJoe StretchPants]

Don't forget to factor in tire size, wall thickness, knob placement, and psi.

And divide by the Golden Ratio for every + knob you trim off.

 

[gonefirefightin]

and if you take a dump and have a shot before riding, you will be faster

 

[cannondalejunky]

try it NOW!

 

[stoney]

His "measured" dimensions are also impossible unless he ran the bike into a garage on top of a car, or he has a way out of spec frame.

Yeti factory numbers were converted from inches to mm. The calculator gave me the decimals. The fork lengths I got from the Fox site, also with decimals.

I clearly f*ed the math that I was trying to figure out regarding angles and lengths. I haven't done trig since 1997, so I was trying to go off of memory and what I could scrounge from the nets (that I understood).

And a 2* change in HA with an increase in BB height will change how the bike handles. I know via numbers how the bike should handle, I just don't know how to calc the numbers as variables change. I just need to figure out how much longer the TT will become, as my TT is already a bit too long...

I think the Fox Float Volume Spacer kit the Kidwoo was talking about wil fix my sag issues, so that should offset my excessive TT length due to over compression of the shock.

 

[stoney]

Don't forget to factor in tire size, wall thickness, knob placement, and psi.

Or just do what GFF says and ride.

These are set variables as they will not change between the fork height adjustment and shock rebuild. Nice try for the rimshot though.

 

[HAB]

Yeti factory numbers were converted from inches to mm. The calculator gave me the decimals. The fork lengths I got from the Fox site, also with decimals.

I clearly f*ed the math that I was trying to figure out regarding angles and lengths. I haven't done trig since 1997, so I was trying to go off of memory and what I could scrounge from the nets (that I understood).

And a 2* change in HA with an increase in BB height will change how the bike handles. I know via numbers how the bike should handle, I just don't know how to calc the numbers as variables change. I just need to figure out how much longer the TT will become, as my TT is already a bit too long...

I think the Fox Float Volume Spacer kit the Kidwoo was talking about wil fix my sag issues, so that should offset my excessive TT length due to over compression of the shock.

Ok, I'll stop being a douche and try to be helpful again.

1. Slackening the bike with a longer fork will (slightly) make the bike feel shorter, since the horizontal distance from the pedals to the BB, i.e. the reach, will decrease a little. Your seat tube angle will also get a bit slacker, so you may end up wanting to move your seat forward a little if you make that change to counteract the seat angle thing.

2. What's the sag issue you're having? Unless the issue is that in order to stop the shock from bottoming out you have to run very little sag, it's not going to help much. All that fix is going to do is make it ramp up a little harder at the end of the stroke- its effect on mid stroke spring rate will be minimal. If your issue is that you're getting too much sag with reasonable bottoming out you probably want to go the other direction and do a higher volume air can with more pressure in it.

 

[stoney]

Ok, I'll stop being a douche and try to be helpful again.

1. Slackening the bike with a longer fork will (slightly) make the bike feel shorter, since the horizontal distance from the pedals to the BB, i.e. the reach, will decrease a little. Your seat tube angle will also get a bit slacker, so you may end up wanting to move your seat forward a little if you make that change to counteract the seat angle thing.

Great, my seat is almost all the way forward as it is!

2. What's the sag issue you're having? Unless the issue is that in order to stop the shock from bottoming out you have to run very little sag, it's not going to help much. All that fix is going to do is make it ramp up a little harder at the end of the stroke- its effect on mid stroke spring rate will be minimal. If your issue is that you're getting too much sag with reasonable bottoming out you probably want to go the other direction and do a higher volume air can with more pressure in it.

I need to figure this one out. When I get my sag right, the leverage keeps me in 'mushy land' while I am pedaling and I blow through my travel. The design is a very linear ratio. I was thinking that by ramping up the back end of the stroke I would be able to run a lower preload (psi). Which in turn would allow me to open up my propedal. Currently I have my propedal at 3 (of 3) and it pedals well, but I need to really jack up the psi to keep from blowing through my travel. When I jack up the pressure I end up riding a board.

 

[HAB]

From what I'm understanding of your problem you've got the solution ass backwards. If you're feeling like the mid stroke is mushy, less pressure and less compression damping are going to be counter productive. If you're not having bottoming issues currently, a higher volume air can at a little higher pressure is apt to help. The extra air pressure would then probably let you back off the pro pedal a little to keep it from feeling harsh again.

 

[stoney]

From what I'm understanding of your problem you've got the solution ass backwards. If you're feeling like the mid stroke is mushy, less pressure and less compression damping are going to be counter productive. If you're not having bottoming issues currently, a higher volume air can at a little higher pressure is apt to help. The extra air pressure would then probably let you back off the pro pedal a little to keep it from feeling harsh again.

That would make sense. To educate me, how does the larger volume add to the mid-stroke support? Wouldn't a higher volume and higher air pressure just be the same thing?

http://www.pushindustries.com/2009/index.php?menu_id=60&type=products&title=FOX FLOAT Air Sleeves&product_id=59

FOX FLOAT Air Sleeves
Standard Volume air sleeves provide provide a progressive spring curve, whereas the High Volume air sleeves offer a more linear spring curve.

This is confusing me. I don't need more linear, I need more mid-stroke support.

 

[stoney]

Another note regarding my sag. When I get my sag levels right (30%), I blow through my travel and can bottom out just pedaling up the hill. That's part of why I want to make the shock more progressive. The suspension is completely liner, so I have no point where the bike wants to just sit in the travel. I'm either super stiff with 20% sag or blowing through with 30%.

 

[HAB]

Higher volume isn't inherently more mid stroke support exactly. It just means its more linear, like it says on the Fox page. The reason I think that makes sense for you is that it would let you run a bit higher pressure while still using all your travel effectively. That's where the better mid stroke support would come from. And then once you've got the better mid stroke support from the higher air pressure you can back off the pro pedal some and still maintain decent small bump compliance.

 

[HAB]

Another note regarding my sag. When I get my sag levels right (30%), I blow through my travel and can bottom out just pedaling up the hill. That's part of why I want to make the shock more progressive. The suspension is completely liner, so I have no point where the bike wants to just sit in the travel. I'm either super stiff with 20% sag or blowing through with 30%.

Oh. Well then maybe the shims wouldn't be so bad, but I still don't think you want less air pressure. Maybe some tweaking of the damping makes more sense in that case. What damping tune does the shock have? There'll be little bars on the side of it somewhere, 1-3 for both compression and rebound.

 

[stoney]

Oh. Well then maybe the shims wouldn't be so bad, but I still don't think you want less air pressure. Maybe some tweaking of the damping makes more sense in that case. What damping tune does the shock have? There'll be little bars on the side of it somewhere, 1-3 for both compression and rebound.

It's a Fox RP23. I have a ton of rebound adjustment, but no compression - only propedal. I have the propedal at 3 to firm up the pedaling though.

When my sag is right, it feels like I need more low speed compression and less high speed. But I'm not really sure how to get that...

I'm debating getting one of the custom tuned Rockshox from Pushed to see if that will help. I'm hesitant to though because I don't want to throw down the coin if I'm getting the SB66 in a few months.

 

[HAB]

Yeah I know it's an RP23. I meant which tune of the RP23 is it? Fox does different versions of it to spec on different bikes, as in 3 different rebound and compression adjustment ranges. That's what I was asking about.

 

[stoney]

boost 150
rebound M
velocity F

 

[Polandspring88]

PM TheMontasheu. He is in pre-calc and should be able to derive the answer for you. Just integrate his feedback and you should be able to find the limits of your bike set up. There should be a finite difference, but the factorial of the matter is that there are bounds on the free variables. As long as you are aware of the maxima and minima, you should be able to create a log of what you are looking for.

 

[I.van]

This site is a good geo calculator

http://bikegeo.muha.cc/

 

[MMike]

What is: "DA DOO DOO DOO, DA DA DA DA"?

 

[Ithnu]

What is: The War of 1812?

Wasn't that when the British came back to the US after calling the Revolutionary War a mulligan?

 

[Mr Jones]

use a
P
R
O
T
R
A
C
T
O
R

and a

T
A
P
E

M
E
A
S
U
R
E

 

[CrabJoe StretchPants]

use a
P
R
O
T
R
A
C
T
O
R

and a

T
A
P
E

M
E
A
S
U
R
E

And a tube stretcher so he can measure hypothetical length changes?

 

[stoney]

Wasn't that when the British came back to the US after calling the Revolutionary War a mulligan?

Yes, but they got smarter and allied with pretty much every known Indian tribe except the Cherokee and chockwa. But they still lost, despite the burning of Washington.
That being said, it was a war of American aggression in trying to take Canada.