[preppie]

Hello,

I was wondering if this was a 'good' idea.
I have a BigHit DH with the BETD 26” seatstays and a 170mm Super-T)
This new 26” wheel seatstay increases the bikes :
- wheel base by 20mm (0.7874”)
- BB height by 5mm (0.196”)
- Travel is increased to 8.9"
- HA is minus 1*

The eye2eye shock length is 222mm (8.24”), but I have a ‘spare’ 200mm (7.874”) shock.

This 200mm shock should :
- lower the travel from 8.9” to around 7” or less
- lower BB
- slacker headangle
- lower standover
- lower center of gravity
- higher leverage ratio

Would this work or do I make my bike completely ?
I like a slack HA, around 65 and I don't 'need' 8.9" travel.

any advice is welcome.

thx

 

[DHS]

um are both shocks the same stroke?

 

[preppie]

um are both shocks the same stroke?

Oops, forgot to tell they have a different stroke.

The Fox RC = 222mm with 70mm stroke (2.75")
the Swinger= 200mm with 50mm stroke (2")

thx.

 

[DßR]

222mm is 8.75" , not 8.24". This is a very big difference.

By putting a shock with 1" less overall length to it on your bike, it'll be VERY slack, I would definitely not recommend that.

Also, it will not change your leverage ratio at all.

However, your idea is a good one. My SGS has a 8.75 x 2.75 shock that I replaced with an 8.5 x 2.5 shock, it lowered the BB by nearly an inch, cut 1" off the travel (to 7"), and slacked the head angle out a bit. It's AWESEOME. See if you can trade your swinger for a 8.5 x 2.5 model, it'll probably be very nice.

if 1/4" (6mm) of overall length change created such a big difference on my bike, I think 22mm would be far too much.

 

[DßR]

so i did some quick math -- your shock ratio is 3.2:1.

Swapping shocks would lower your BB approximately 2.5", slack out your head angle something ungodly, and probably make the bike unrideable.

 

[math2014]

if you put a shorter shock with shorter stroke the leverage ratio will change.

At least that is how it would work on my SX.

 

[DßR]

how does the leverage ratio change if you don't change the linkages????? I understand that the travel will go down, but unless you rearrange the mechanics that move the shock, how does the leverage ratio change?

 

[math2014]

I had the same q DBR, when someone told me that my SX with a 50mm stroke shock 190mm i2i will get 145mm of travel. Given a 2.57-1 ratio on the stock setup of the SX this looked like impossible. I went on a small cad proggy to see what really happens, and it seems that on the SX/Enduro, i2i changes the leverage ratio, since the 2.57-1 is not constant throughout the travel. So by lengthening the i2i you directly affect the leverage ratio

 

[MikeD]

how does the leverage ratio change if you don't change the linkages????? I understand that the travel will go down, but unless you rearrange the mechanics that move the shock, how does the leverage ratio change?

Leverage ratio = frame travel/shock stroke, no? Changing shocks (stroke-wise) changes an element of the equation, unless I'm missing something.

MD

 

[preppie]

...
if 1/4" (6mm) of overall length change created such a big difference on my bike, I think 22mm would be far too much.

Yes and damn, I don't think it will improve my bike's handling.
I could live with a low BB, but the 3.2:1 leverage ratio is way too much and a extremely slack HA would feel like I'm riding tank.

But I was 'hoping' that the 26" wheel would eliminate the 22mm difference...but it's a No Go.

Thanks for the advice.

preppie.

 

[vitox]

Leverage ratio = frame travel/shock stroke, no? Changing shocks (stroke-wise) changes an element of the equation, unless I'm missing something.

MD

progressivity curve

 

[vitox]

you are changing

stroke --> less travel
overall length ---> lower bb
leverage rate ---> "progressive" frame ---> lower leverage rate in l ater portions of linkage movement
bottom out position ---> 7 7/8" - 2 2/8" = 5 5/8" v/s 8,75"-2,75" = 6"

this could be a problem, check if the wheel doesnt contact anything when compressing the linkage further than normal.

 

[Discostu]

The whole idea of a progressive suspension is that the leverage ratio reduces as you compress the suspension. Unloaded, there is a high leverage ratio (easy to compress) and at the end of the stroke there is a low leverage ratio (hard to compress), thus reducing bottoming. On a bike like the big hit, it makes sense that the overall leverage ratio would be somewhat different with a shorter stroke shock, what that ratio is exactly, i don't know.

 

[Gary]

My SGS has a 8.75 x 2.75 shock that I replaced with an 8.5 x 2.5 shock, it lowered the BB by nearly an inch, cut 1" off the travel (to 7"), and slacked the head angle out a bit. It's AWESEOME. See if you can trade your swinger for a 8.5 x 2.5 model, it'll probably be very nice.

Wouldn't it have been a lot simpler (and cheaper) to have just run more sag with the original shock?

 

[JoeRay]

The leverage ratio won't change. Leverage ratio is the multiplying effect from the shock mounting point(not necessarily the shock stroke) to the wheel travel. Most bikes have a it of play either way when you pull the shock out, this stops you bottoming out the frame movement when you bottom the shock out.

Roughly the leverage ratio as it stands on your bike is 3.23:1. This wont change if you add a new shock. So your new travel with the shorter stroke shock is 161mm about 6.3 inches. Not as much as previously thought!

The decreased length of shock will be like chopping out 66mm out of the travel. They reckon an inch is good for half a degree or so so there goes about 1.5* out of your head angle when fully extended. Allow sag when you sit on it and you could be losing up to 3* in head angle.

The feel of the suspension will behave differently through the travel too. If the link is rising or falling rate the effect here will be increased because you're already further through that 'ramp up' or 'ramp down' curve.

Never know you might hit some dumb luck and have an awesome outcome, the down side is that you could end up with a frankestein job. Too many variables than just whats apparrent here. I agree just set more sag into the current set up is a wiser move.

 

[vitox]

joeray theres a slight problem with your logic, thing is, youre assuming the leverage is constant.
supposedly this bike is significantly different from linear in terms of leverage rate v/s travel.
on top of that, theres the effect on leverage ratio stemming from the fact that now the linkage is going to be used in a portion of its movement that before wasnt used, in that portion the rate could be anything, but normally it will be lower than in the rest of the linkages movement because its supposed to be a progressive frame.
so basically you should be dropping a relatively higher leverage portion of travel for a relatively lower leverage portion, if so, the overall rate is going to drop no matter what.

 

[Gary]

theres the effect on leverage ratio stemming from the fact that now the linkage is going to be used in a portion of its movement that before wasnt used.

yeah, 2mm of shock stroke just before a complete bottom out - so almost irrelevant (especially if it is rising rate)

The Fox RC = 222mm with 70mm stroke (2.75")
the Swinger= 200mm with 50mm stroke (2")

end point of the linkage for each shock:
222 - 70 =152mm
200 - 50 = 150mm

I think if you really want to change your big hit to a 6" travel horst link FSR style bike with a 26" rear wheel YOU BOUGHT THE WRONG BIKE.
there are loads of bikes that fit that bill aroung already

 

[DßR]

Wouldn't it have been a lot simpler (and cheaper) to have just run more sag with the original shock?

Probably not, b/c that would entail a) getting a too-light spring for the susp. rate and having it then bottom out on me; b) have the shock revalved by craig @ avalanche to prevent said bottom-out, which would entail a lot more money and hassle, and c) have the bike probably pedal like ass. It was much easier for me to purchase a $100 used 5th element to see what happend; I liked it, so I'll have the Avy re-sized to work appropriately.

 

[Gary]

DßR

a) sorry, I thought SGS's came with 5th's or swinger's

b) if it had, 50lb lighter spring and couple of turns on the volume adjust would have given you more sag but stopped it bottoming too easy.

c) SGS's pedal well even without the platform so running a lot of sag isn't a problem - I run 45% sag on mine.

 

[JoeRay]

joeray theres a slight problem with your logic, thing is, youre assuming the leverage is constant.

Yeah I didn't feel like doing research into whether or not its a rising/falling rate, so I asssumed a linear set up. Also I couldn't be stuffed doing a trigonometric differential equation.

I'm just too plain lazy

Still I think it gives enough of an idea to be helpful.

On the whole leverage ratios are just expressed as an average for the bike. Who'd understand a leverage ratio equal to half x cubed to the power of arctan pi. Where x is ofcourse the postion of the wheel in its travel.

 

[preppie]

I think if you really want to change your big hit to a 6" travel horst link FSR style bike with a 26" rear wheel YOU BOUGHT THE WRONG BIKE.
there are loads of bikes that fit that bill aroung already

No, I have the right bike but my 'idea to swap shocks' was wrong.
But like I said before, the difference between the 24" and the 26" seatstay 'could have' been eliminated by running a shorter eye2eye shock, but the difference is 22mm and that is too much.

I'll stick to the 222mm Fox RC for a few months and sell my 200mm Swinger with my old frame.
With a new 222mm Swinger or 5th, I can run a lot more sag without bottoming out, like I would do with the RC and a lighter spring.
So that will be my only solution.