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Discussion Starter · #1 · (Edited)
I am debating between running a 45mm stroke shock (corresponding to 130mm max rear wheel travel) at high pressure or a 40mm stroke shock (corresponding to 115mm max rear wheel travel) at low pressure. I'll be running a 120mm travel fork up front. This is for XC racing.

While my first reaction was to just go with a 40mm stroke shock that would limit travel to the 115mm that I'm looking to use regularly, I am second guessing myself. In theory, doesn't increasing shock pressure linearly increase the amount of force necessary to achieve a certain amount of travel? And if so, does running a 40mm stroke shock at a certain lower pressure have identical performance to a 45mm stroke shock at a certain higher pressure over the first 40mm of shock stroke?

Why not just go for the longest stroke shock possible? And in that case, why don't we all run longer stroke shocks? Sorry if this sounds naive, I'm just trying to comprehend what the disadvantages might be of longer stroke or higher pressure.

45mm is the manufacturer recommended stroke length, so I'm assuming shorter stroke with same eye-to-eye length will be just fine.
 

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I am debating between running a 45mm stroke shock (corresponding to 115mm max rear wheel travel) at high pressure or a 40mm stroke shock (corresponding to 130mm max rear wheel travel) at low pressure.

That makes no sense. How does 5mm LESS stroke on the shock equate to 15mm MORE travel. Geometry doesn't work that way.
 

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What shock comes in the same eye to eye length that has 40 & 45mm stoke?

In the old days, you used to be able toe get some Fox unites that were available in 7.825 X 2.0 or 7.825 X 2.5.

However, it most cases, if you ran the longer stroke shock, you would slam your rear wheel into the seat tube!

Bunni's point is valid. Not sure how you get more travel from a shorter stroke.
 

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Discussion Starter · #7 ·
In the old days, you used to be able toe get some Fox unites that were available in 7.825 X 2.0 or 7.825 X 2.5.

However, it most cases, if you ran the longer stroke shock, you would slam your rear wheel into the seat tube!

Bunni's point is valid. Not sure how you get more travel from a shorter stroke.
Think we cross-posted at the same time. I had shock stroke and travel backwards. Shorter stroke does indeed correspond to less travel. Not sure how it could be otherwise without a really screwy system.

The frame is designed around a 45mm stroke, so what would be the advantages of going with a shorter 40mm stroke other than just for the sake of reducing travel from 130mm to 115mm (which may not be an advantage if I run higher shock pressure?)
 

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Can you just put a larger volume spacer in the longer travel shock and get some of the effect you're looking for? The linear region could be similar to that of the shorter travel shock, but you'd have some insurance for big hits in the broad progressive end of the stroke.
 

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The frame is designed around a 45mm stroke, so what would be the advantages of going with a shorter 40mm stroke other than just for the sake of reducing travel from 130mm to 115mm (which may not be an advantage if I run higher shock pressure?)
If that's the case, there's absolutely no advantage to reducing travel. Go with the 45mm. The idea that "reducing travel" on the same frame will increase XC performance is a myth. The amount of travel isn't the issue, it's the geometry changes made to accommodate more travel. If you already have the frame, get the most out of it.
 

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If they are metric shocks (most likely) then they are the same shock anyway. The 40mm stroke one just has a 5mm spacer on the damper shaft.
 

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Fox Float DPS Trunnion for example, 165x45, 165x42.5, and 165x40. Other brands also have similar offerings.
I think you are confusing stroke w/ air volume on the same length shock. Unless the air can is smaller or larger will impact the behavior of the travel reduced or not.
 

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Both will pedal exactly the same, the short shock will simply bottom out prematurely.

Also, travel calculations don't work that way. Your 2.88:1 is the totaled average. On my frame, the leverage ratio is around 2.0:1 for a lot of the travel and ramps up to 3:1 at the end, so adding a shock that has more stroke that deep in the travel would have maybe significantly more travel than expected.
 

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Discussion Starter · #15 ·
I see, you guys bring up a lot of a good points. I'm not sure how leverage ratio changes through travel on my frame, I'd have to look at the linkage analysis, but I'm pretty convinced at this point it will be best to go with the longest stroke shock available (which the frame was also designed for). I'll plan to play around with pressure until suspension duties feel balanced.

It sounds unorthodox to run 130mm travel in the rear and 120mm in the front, but if only 110-120mm of travel is being used in the rear 99% of the time, I guess I shouldn't worry about semantics.
 

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Higher leverage near bottom out?
Yes, it's not uncommon. Without the rate increasing towards the end, it can be difficult to actually use all the travel.

A rising leverage ratio at the end is a falling rate suspension. The progression falls as the leverage ratio rises.

That gets silly and confusing. A little bit of ratio increase is needed to feel linear and allow can volume tuning. Too little or no falling rate and you end up with impossible to bottom suspension that keeps too much on reserve.
 

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Btravel calculations don't work that way. Your 2.88:1 is the totaled average. ...so adding a shock that has more stroke that deep in the travel would have maybe significantly more travel than expected.
I think your math is wrong there. an average is an average, regardless of the elements that builds that average.
think of a group (20?) kids, each weighing 50lbs. they will weight together 20x50 regardless of what each one weighs. even if the last kids in the row weigh 80, and the first kids weigh 30.
that's how average works ;-)


now... if on the added 5mm shock travel the LR is significantly different so that the average moves (as an example...) from 2.88 to 3.2 - in that case your claim is correct.

Oren
 

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I think your math is wrong there. an average is an average, regardless of the elements that builds that average.
think of a group (20?) kids, each weighing 50lbs. they will weight together 20x50 regardless of what each one weighs. even if the last kids in the row weigh 80, and the first kids weigh 30.
that's how average works ;-)

Oren
One Pivot is not wrong in the concept of extending the shock stroke creating more travel than expected, which they clarified is due to the leverage increasing towards the end.

I doubt One Pivot needs schooling on averages, and I can't find any motive behind your post besides insulting them for nothing more than your own misunderstanding.

now... if on the added 5mm shock travel the LR is significantly different so that the average moves (as an example...) from 2.88 to 3.2 - in that case your claim is correct.
I see you edited your post to add this line. Can you demonstrate how you got this #?
 

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One Pivot is not wrong in the concept of extending the shock stroke creating more travel than expected, which they clarified is due to the leverage increasing towards the end.

I doubt One Pivot needs schooling on averages, and I can't find any motive behind your post besides insulting them for nothing more than your own misunderstanding.



I see you edited your post to add this line. Can you demonstrate how you got this #?
I specifically wrote ‘I think’ in there. Then rethought my post and added the last line.
I did not intend to insult or school no one.

As this is going the wrong way, as sometimes posting on forums goes, I will apologize and stop here.

Oren


Sent from my iPhone using Tapatalk
 

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I recently removed the shock from my stumpjumper. First, I placed a floor jack under the bottom bracket and adjusted it till perfect and the shock bolts come out rather easily.

While the bike was sitting there waiting for a new shock. I removed the floor jack to see how close the rear wheel is to hitting the seat tube. It was rather fun to explore the mechanical range of movement and see how things move and how leverage changes. If your pulling your shock. You might want to give it a try.



About shocks... first i know only that i know almost nothing.

But... Shock pressure is not increased because shock stroke was limited by a travel spacer. It increases if the the size (surface area) of the air piston decreases. Or you got heavier. So different models or brands of shocks with a different air piston size would result in different pressures.

What shock were you looking at.

Does anyone know how travel is adjusted in the same brands model.

The negative spring equalization position should be moved when stroke is changed. Imo.

Eg. 200mm shock at 30% sag is 60mm, changed to a 140mm with only a travel spacer could mean a 60mm sag and 80mm travel or a zero negative spring and 140mm travel. Or perhaps its split with two spacers.

As i said above im not sure what they do. Only to be aware of what the difference is.
 
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