Mountain Biking - max. drop height?

another newbie question...

this past weekend i was hosing the mud off my bike after riding around the neibourhood in the rain and i noticed that some of the paint on the rear linkage had been chipped off. i took a closer look and i noticed that the portion of my seat post that was sticking out of the seat tube had been flattened out. i thought it was kind of strange because 1: my seat post only stuck out a little bit from the end seat tube. i didn’t think that it would interfere with the linkage. and 2: i haven’t been dropping anything really “huge” to think that i’d be bottoming out my rear shock – i’m only 150lbs, have a 700x1.83 coil on my fox vanilla and i’ve only recently worked myself up to dropping 4’ to flat, landing them without much problem (unlike that one post i put up a while ago where i crashed and burned).

my norco fluid has about 5” of rear travel... i know i’m not the smoothest rider in the world, but i don’t think i’m a complete hack either. i’ve tried to follow the advice of many and keep my arms and legs slightly bent while landing and letting them soak up a lot of the impact. so, i was wondering if there’s a maximum drop-to-flat height that i shouldn’t go over for the amount of travel i got on my fluid. i mean, is there a height that isn’t considered insane, which will blow my shock regardless of how smooth i land?

(oh yeah, i ended up cutting off about 2” from my seat post so that i could lower my seat and not have any of the seat post stick out anymore.)

Enh, shocks are designed to bottom out occaisionally and it shouldn't hurt anything. There's no set height or equation for what will damage a shock, and it's much harder to blow out an oil/coil shock than it is an air shock. I wouldn't worry about it. Norco's are tough bikes designed for all sorts of insanity. Thrash on it as much as you like and don't let the bike hold you back.

One condition to shock bottoming out. If you have too much preload you will bottom out the spring instead of the shock. This causes damage to the plates that hold the spring in place. Be sure not to overload the preload more than a couple of turns.

As for max height it depends on so many things. Right out of the box it could probably handle 10 to 15 ft (maybe more) but with wear and tear that number goes down until it COULD blow on a curb.

Adding to what Maelstrom posted: I talked with a Fox rep once, and to my suprise he told me that the total range of preload adjustment designed into a coil shock is only 2-3 turns. I found that mine was waaaay too tight.

As far as drop height - There is a drop I take quite often that is about 9-10 feet. It's taken at speed, onto a steep downhill transition. It does not even feel like I use my shock. There is another one, under 2 feet, where the transition is uphill - taken at full speed, about 30 mph or so, I bottom every time. I won't even take that one any more.

Ooops...I forgot to flat. No clue what the max would be. Drops to flat have no flow or speed so I tend not to like them. Very harsh unless you have excellent dropping skills.

that's strange, the rear linkage shouldn't come that close to the seat post to smack it. everyone I've talked to, regarding "fsr style" interrupted seat tubes, has said the seat post MUST stick out the bottom about an inch (that's what? 2.54cm in canada?) for structrual integrity.
you should ask a norco rep. about it, and post the reply since I'm kinda curious now.

Dumb question.

If you're only supposed to turn the pre-load only 2 or 3 turns, why is the thing threaded all the way?

I mean, to change springs you loosen the pre-load. So, why have the ENTIRE shaft threaded?

L8R

So you can run different length springs. a 300lb spring designed for a 2" travel shock may be quite a bit shorter than a 800lb spring designed for a 2" travel shock.

I know c_s, I was just trying to be funny!

L8R

Springs are designed to give a max load at solid (closed)
example: it takes 250lbs to compress the springs to closed (full compressed)
The amount of preload put on the spring will just reduce the travel of the spring
It still will handle the same amount of load from a drop

Just my .02 cents from a spring design engineer

Springs are designed to give a max load at solid (closed)
example: it takes 250lbs to compress the springs to closed (full compressed)
The amount of preload put on the spring will just reduce the travel of the spring
It still will handle the same amount of load from a drop

Just my .02 cents from a spring design engineer

But if you preload to much you do bottom out the spring before using up the shock. correct?

that's strange, the rear linkage shouldn't come that close to the seat post to smack it. everyone I've talked to, regarding "fsr style" interrupted seat tubes, has said the seat post MUST stick out the bottom about an inch (that's what? 2.54cm in canada?) for structrual integrity.
you should ask a norco rep. about it, and post the reply since I'm kinda curious now.

On specialized bikes there is a hole mid seat tube that is the optimum spot to put the seatpost down to. Usually about half way. You definately don't NEED it sticking out the bottom

But if you preload to much you do bottom out the spring before using up the shock. correct?


thats correct.... kinda



A spring has a fixed solid height and that does not change. The preload adjustment is more like for sag. It makes a softer or stiffer top end and does not effect the bottom end in any way. Each spring is designed for a certain load at solid height, and when it is at a certain height it will give the same load. It's called "spring rate". Say you have a 5" spring with a 10#/in rate, if you set the preload at 3" length, you are starting with 20lbs,(2" deflection of travel times the rate) if you set preload at 4" length, you get 10lbs and so on......but the spring will give the same load at its full travel.
The point I was trying to make is it takes lets say 300lbs to bottom out the spring on his bike....with the preload cranked in, that may only be 2" of travel...
with it backed off, it may be 4" of travel, but the 300lbs of shock from the drop will bottom it out either way.....

hope this makes sense....I'll quit now SORRY

One condition to shock bottoming out. If you have too much preload you will bottom out the spring instead of the shock. This causes damage to the plates that hold the spring in place. Be sure not to overload the preload more than a couple of turns.
i don’t think i really need to worry about having too much preload for now. i have the preload adjuster turned only enough to keep the spring in place without putting much of a load on it. unless my wife made a mistake in measuring when she was helping me set up the shock, the sag right now is less than the recommended sag found in the fox shox owner’s manual.

that's strange, the rear linkage shouldn't come that close to the seat post to smack it. everyone I've talked to, regarding "fsr style" interrupted seat tubes, has said the seat post MUST stick out the bottom about an inch (that's what? 2.54cm in canada?) for structrual integrity.
you should ask a norco rep. about it, and post the reply since I'm kinda curious now.
i’m not sure when i put the flat spot in my seat post, but i’m sure it flattened out after i’d made a few drops because there’s more than one spot on the linkage where the paint’s chipped. i know i’ve fooled around with different seat heights to see what height works best when... usually i have the seat at a “normal height” so that i can peddal easily and get proper leg extention. at that height, before cutting the seat post, it didn’t stick out of the seat tube. right now, at that height, after cutting the seat post, the seat post is probably about where that hole maelstrom mentioned should be if my bike had one.

But if you preload to much you do bottom out the spring before using up the shock. correct?


thats correct.... kinda



A spring has a fixed solid height and that does not change. The preload adjustment is more like for sag. It makes a softer or stiffer top end and does not effect the bottom end in any way. Each spring is designed for a certain load at solid height, and when it is at a certain height it will give the same load. It's called "spring rate". Say you have a 5" spring with a 10#/in rate, if you set the preload at 3" length, you are starting with 20lbs,(2" deflection of travel times the rate) if you set preload at 4" length, you get 10lbs and so on......but the spring will give the same load at its full travel.
The point I was trying to make is it takes lets say 300lbs to bottom out the spring on his bike....with the preload cranked in, that may only be 2" of travel...
with it backed off, it may be 4" of travel, but the 300lbs of shock from the drop will bottom it out either way.....

hope this makes sense....I'll quit now SORRY

No that does make sense. I do understand spring rate and what preload is doing. My point really had nothing to do with spring rate exactly it had more to do with a fully compressed spring regardless of pressure. When doing a drop if the preload is set to high the spring will bottom out before the shock which is what fox and other companies warn against. They want the shock to bottom out with some spring left over (or close to equal) It is possible to run the sag/preload higher however this usually causes fox to not warranty a shock.

I know c_s, I was just trying to be funny!

L8R
yeah right :rolleyes:

maybe we are looking at this different......
I don't have a FS bike so this is from theory only
My point is..
if a spring has 8 coils of .250" each, its solid height is 2.00"
it doesn't matter if it has .5" preload or 1.00" preload it still bottoms out at 2.00" height , which is a certain load.....with the adjuster crancked way in, the spring would bottom out first, but the load on the spring would be the same

I know c_s, I was just trying to be funny!

L8R


Hahahahahhaha your just making it worse!!!!!!http://www.gamers-forums.com/smilies/contrib/Bizkit/sweat.gif

If you never bottom out you have too much preload, or your spring is too stiff. Your bike specs should tell you the max amount of seatpost to have sticking out. Your preload should be set that it just bottoms out when you do the biggest hit you expect, that way you use all your travel.