I have a question about shocks.

NCHLS.mrz

NCHLS.mrz

Well-Known Member
Wondering if anyone could explain why lengthening your rear travel wouldn’t work on a full squish. My friend who is relatively new to mountain biking and seems to think you always need more travel was saying he was gonna get a “160mm shock” as opposed to the 150mm he has. I understand that shocks are not measured in how many mm of travel they have because it’s the rear wheel travel not how much the shock moves that matters. What I don’t understand is why getting a longer stroke shock make you have more rear wheel travel without changing your geometry. Or getting a longer eye to eye length shock and putting the flip chip in one setting or another to off set the change.
 
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NCHLS.mrz said:
Wondering if anyone could explain why lengthening your rear travel wouldn’t work on a full squish. My friend who is relatively new to mountain biking and seems to think you always need more travel was saying he was gonna get a “160mm shock” as opposed to the 150mm he has. I understand that shocks are not measured in how many mm of travel they have because it’s the rear wheel travel not how much the shock moves that matters. What I don’t understand is why getting a longer stroke shock make you have more rear wheel travel without changing your geometry. Or getting a longer eye to eye length shock and putting the flip chip in one setting or another to off set the change.
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Does your friend who is relatively new to mountain biking own a Jeep with a 6" lift? ¿🤔?
 
Funny you mention this. This video just came up on my YouTube. It's about forks, but the gist is; does your friend think he knows more than the bike's designers?

 
NCHLS.mrz said:
Wondering if anyone could explain why lengthening your rear travel wouldn’t work on a full squish. My friend who is relatively new to mountain biking and seems to think you always need more travel was saying he was gonna get a “160mm shock” as opposed to the 150mm he has. I understand that shocks are not measured in how many mm of travel they have because it’s the rear wheel travel not how much the shock moves that matters. What I don’t understand is why getting a longer stroke shock make you have more rear wheel travel without changing your geometry. Or getting a longer eye to eye length shock and putting the flip chip in one setting or another to off set the change.
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What's the exact bike in question? There are a couple possibilities here. First, there are some bikes that are sold with different stroke shocks. Two that immediately come to mind are the Specialized Stumpjumper and the YT Jeffsy. You can purchase both of those bikes with different amounts of rear wheel travel right off the shelf. It would stand to reason, then, that if your friend has, let's say, a Stumpjumper ST that he could easily convert it into the full travel version by changing the shock and the shock link.

If it's not a bike that shares the same frame across different travel configurations then he's risking making it not work right. First, I don't think you can change the eye-to-eye or overall length of the shock or it won't fit in the bike. He could maybe increase the stroke of the shock by 5 or 10mm but that's a big maybe. The risk is that the rear wheel might contact the frame when it get's into the extra travel. If this works, the geometry of the bike won't change because the eye-to-eye of the shock is the same. It's only the stroke that changes. The travel is gained at bottom out, not at top out.
 
" What I don’t understand is why getting a longer stroke shock make you have more rear wheel travel without changing your geometry. " It doesn't. First of all there's no such thing as a 150mm shock or 160mm shock because the the amount of travel the shock has does not equate to the amount of rear wheel travel. Second, depending on the rear suspension design the same length shock (ex. 200x57) mounted on one bike could have 130mm of rear travel but if you put that same shock on a different bike with a different rear suspension, different pivot locations, chain stay and seat stay lengths and various linkages, you could have either more travel or less travel depending on all those variables. Again, shock length doesn't mean suspension travel, not like a fork. If you look at the specs of shocks you'll see the eye to eye and the stroke measurements that the bike frame is designed for. In my example of a 200x57 shock the frame is designed to fit a shock with eye to eye length of 200mm. That's the length that will fit in the frame. The stroke of that shock example is 57mm. That's the amount of movement of the two eyes as the rear suspension travels. If you try to get a longer shock thinking it'll provide more travel then you (or your friend who is new to mountain biking) will find that it won't fit on that frame. It might fit if you compress the shock but then that defeats the purpose of having a longer shock if you have to compress it to make it fit.
 
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tonyride said:
First of all there's no such thing as a 150mm shock or 160mm shock because the the amount of travel the shock has does not equate to the amount of rear wheel travel. Second, depending on the rear suspension design the same length shock (ex. 200x57) mounted in one bike could have 130mm of rear travel but if you put that same shock on a different bike with a different rear suspension design with different pivot locations, chain stay and seat stay lengths and various linkages, you could have either more travel or less travel depending on the design. Again, shock length doesn't mean suspension travel, not like a fork. If you look at the specs of shocks you'll see the eye to eye and the stroke measurements that the bike frame is designed for. In my example of a 200x57 shock the frame is designed to fit a shock with eye to eye length of 200mm. That's the length that will fit in the frame. The stroke of that shock example is 57mm. That's the amount of movement of the two eyes as the rear suspension travels. If you try to get a longer shock thinking it'll provide more travel then you (or your friend who is new to mountain biking) will find that it won't fit on that frame. It might fit if you compress the shock but then that defeats the purpose of having a longer shock if you have to compress it to make it fit.
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All correct. You went into more detail than I did.

As to the OP's question, the eye-to-eye needs to remain the same to physically fit in the bike but with some bikes the stroke can be altered. For example, I know the 2019 YT Jeffsy's were sold with 230x60mm shocks to achieve 150mm of rear wheel travel. The top of the line "pro race" model was fitted with a 230x65mm shock to achieve 160mm rear wheel travel. In most cases the difference between shocks with the same eye-to-eye measurement but different stroke measurements is simply a travel reducing spacer inside the shock. For example, a 210x55 shock is physically the same as a 210x50 but the later has a 5mm spacer installed to prevent the last 5mm from being used. In some cases you can increase the stroke simply by removing a spacer. I have heard of guys doing this with the new Giant Trance 29ers to increase wheel travel from 115mm to 125mm or something like that. The potential risk is having the rear wheel hit the frame or the linkages hitting the frame, etc. when the rear triangle moves more than the designers intended.

Just because this might be possible doesn't mean it's a good idea. If it were me and I wanted a bigger bike I would just buy a bigger bike.
 
What kind of shock is this friend currently using? If air, maybe it can be tuned to be less progressive. Try switching to a coil shock of the proper length for a plusher feel.
 
I'm curious as to the "why" here. 150 is a lot of rear travel. More than enough for jersey. If he's not on a top of the line shock, maybe just getting a better one with the same travel would create the feel he's looking for? Volume spacers? Tuning, as mentioned above? Just seems a bit silly to go bigger.
 
Tim said:
What's the exact bike in question? There are a couple possibilities here. First, there are some bikes that are sold with different stroke shocks. Two that immediately come to mind are the Specialized Stumpjumper and the YT Jeffsy. You can purchase both of those bikes with different amounts of rear wheel travel right off the shelf. It would stand to reason, then, that if your friend has, let's say, a Stumpjumper ST that he could easily convert it into the full travel version by changing the shock and the shock link.

If it's not a bike that shares the same frame across different travel configurations then he's risking making it not work right. First, I don't think you can change the eye-to-eye or overall length of the shock or it won't fit in the bike. He could maybe increase the stroke of the shock by 5 or 10mm but that's a big maybe. The risk is that the rear wheel might contact the frame when it get's into the extra travel. If this works, the geometry of the bike won't change because the eye-to-eye of the shock is the same. It's only the stroke that changes. The travel is gained at bottom out, not at top out.
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That’s interesting because my friend in question has a stumpjumper, the regular one. What it seems like your saying is it’s different for every bike.
 
If you take the shock out, the frame moves a certain amount. That is the most travel you’re gonna get. (Plus or minus a very small amount for things like tire clearance)
 
NCHLS.mrz said:
That’s interesting because my friend in question has a stumpjumper, the regular one. What it seems like your saying is it’s different for every bike.
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I think if your friend provides more about his current shock setup (shock model, sag setting, volume spacers) and what he's looking for, you might be able to get some good advice from the pros on here. Maybe he just needs more pressure or a volume spacer (free/cheap upgrade). If he's got a lower end SJ, maybe he can just get a better shock that'll be more plush and resistant to bottoming out.
 
Tim said:
All correct. You went into more detail than I did.

As to the OP's question, the eye-to-eye needs to remain the same to physically fit in the bike but with some bikes the stroke can be altered. For example, I know the 2019 YT Jeffsy's were sold with 230x60mm shocks to achieve 150mm of rear wheel travel. The top of the line "pro race" model was fitted with a 230x65mm shock to achieve 160mm rear wheel travel. In most cases the difference between shocks with the same eye-to-eye measurement but different stroke measurements is simply a travel reducing spacer inside the shock. For example, a 210x55 shock is physically the same as a 210x50 but the later has a 5mm spacer installed to prevent the last 5mm from being used. In some cases you can increase the stroke simply by removing a spacer. I have heard of guys doing this with the new Giant Trance 29ers to increase wheel travel from 115mm to 125mm or something like that. The potential risk is having the rear wheel hit the frame or the linkages hitting the frame, etc. when the rear triangle moves more than the designers intended.

Just because this might be possible doesn't mean it's a good idea. If it were me and I wanted a bigger bike I would just buy a bigger bike.
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This. Unless your friend is versed in suspension design, I wouldn't mess with it.
 
stb222 said:
This. Unless your friend is versed in suspension design, I wouldn't mess with it.
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Makes sense I told him he didn’t know what he was talking about but oh well. He also doesn’t need more travel. Personally I don’t even think he needs his full squish but whatever.
 
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