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Fork bottoming discussion

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I know all of these can affect a fork bottoming, but which would you guys say affect it the most, springs, oil level, or damping? My thoughts are springs for weight and ride height (sometimes heavier for something like SX), damping for style of riding (MX, woods, FMX), and oil level to fine tune bottoming when you are close on the rest. I know the "air spring" can have a big effect, but which has the most?

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OK...I just did some real valving changes in my rear shock and forks, so I'm a suspension expert now.:ride:

But seriously, I'd say I've learned the most about suspension action, damping, and tuning first from my long travel, high end MTB forks and then from my dirt motor. I'd say springs are the first and biggest element in bottomout...or to be more specific, controlled bottomout. If you are off to a notable degree in spring rate, everything else you do is a roundabout way to try and control bottomout. I think you have to start with proper springs.

The next is damping. Oil flow through the proper shims and orifices is critical for control of the suspension component.

Last is oil level. This is a really nice element that won't affect the spring rate and damping to any major degree, but can make a big difference in how and where bottomout will or won't occur.

Many MTB forks don't even have an oil level adjustment capability, probably based more on a weight issue than anything else, but it probably indicates the last place category into which oil level is placed. And understand, I'm not trying to claim total equity in the function of MTB forks and dirt motor forks. It's a balancing act, of course, because even though I believe that oil level is a last place contender, try filling up a fork with oil and have no air space, and it will obviously point out how important oil level can be in the extremes.

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OK...I just did some real valving changes in my rear shock and forks, so I'm a suspension expert now.:lol:

But seriously, I'd say I've learned the most about suspension action, damping, and tuning first from my long travel, high end MTB forks and then from my dirt motor. I'd say springs are the first and biggest element in bottomout...or to be more specific, controlled bottomout. If you are off to a notable degree in spring rate, everything else you do is a roundabout way to try and control bottomout. I think you have to start with proper springs.

The next is damping. Oil flow through the proper shims and orifices is critical for control of the suspension component.

Last is oil level. This is a really nice element that won't affect the spring rate and damping to any major degree, but can make a big difference in how and where bottomout will or won't occur.

Many MTB forks don't even have an oil level adjustment capability, probably based more on a weight issue than anything else, but it probably indicates the last place category into which oil level is placed. And understand, I'm not trying to claim total equity in the function of MTB forks and dirt motor forks. It's a balancing act, of course, because even though I believe that oil level is a last place contender, try filling up a fork with oil and have no air space, and it will obviously point out how important oil level can be in the extremes.

i don't know much about bicycles,but dirtbikes don't rely on the springs for bottoming resistance they are more to support the wt of bike and rider at a optimal height/sag...that being set correctly you then valve for conditions.....with that correct you then fine tune the bottoming with oil ht,it should only slightly bottom on the very biggest hits your going to encounter. remember also that the higher the oil the more rebound control your gonna need.

i think oil ht is probly the best/most important way to tune bottoming,but the rest must be correct also.:ride:

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Well said mountainman!:ride:

See...he ain't as dumb as you said he was...:D:bonk:

Very well put!:lol:

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i don't know much about bicycles,but dirtbikes don't rely on the springs for bottoming resistance they are more to support the wt of bike and rider at a optimal height/sag...that being set correctly you then valve for conditions.....with that correct you then fine tune the bottoming with oil ht,it should only slightly bottom on the very biggest hits your going to encounter. remember also that the higher the oil the more rebound control your gonna need.

i think oil ht is probly the best/most important way to tune bottoming,but the rest must be correct also.:ride:

Yeah, but just as you point out, you must start with springs that are in the ballpark. Obviously all these suspension components and tuning elements are a sum of their parts, but I thought the OP wanted to know which element would be classified as most important. You used the term "fine tune" in relationship to the oil level, and that in itself kind of indicates a secondary element, albeit an important element. Like I pointed out, you can fill the fork with oil, but that's just an extreme example. Soft springs let the bike blow through its travel...to an inevitable bottomout. And while you might be able to run ballpoint pen springs in a fork and then control the final bottomout with a very high oil level, that's hardly the holy grail of suspension tuning. Maybe this discussion comes down to a semantics thing.

I used the mountainbike example only because it is very much like a dirt motor in many ways as it relates to suspension. Marzocchi used to rely on fork oil to tune bottomout, but now most quality MTB forks are able to achieve excellent damping, small bump compliance, and big hit control without oil level tuning. And while this mainly done for a weight reduction, it just shows that oil level is probably not the first and most important element. Like I said before, a good suspension is a sum of its parts, so maybe we're trying to go to a microscopic level when the big picture is the goal.

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My approach is a bit different, or maybe it is just semantics. The whole process is circular; you start with sag adjustments to ballpark spring rates, tune damping, then fuss oil levels. Then adjust spring rates and start all over.

Spring rates really dpend on the type of terrain, your speed, and ride quality expectations. I do only tight trail riding and want good compliance so I run springs that are way too soft according to all of the selection charts, but sag checks say they are OK. In addition to all of the above I do have some bottoming control via the low speed clickers, well really the low speed stroke speed but it affects bottoming. I also run the oil level near the maximum.

One addition that I think is important and that is to keep notes on all suspension changes and the riding results, including tire brand and pressures.

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well seeing as you don't tune bottoming with either spring rates or valving (it just adds to the problem if those things are not adequate) then that would deem oil ht as........wait for it..........'the most important' element against bottoming:smirk:

chuck unless your running nost bv's there is no low speed adjustment on the forks(thats the topic) and i've always found lighter springs need too much preload or they will ride too low in the stroke,preload past 5mm up front and 10mm out back will result in more deflection than if you just used the proper wt spring;and on the same note if your overstacking to compensate for lighter springs its gonna be harsher also. like tnc said its the sum of all parts and ya can't have one overcompensating the other.

see lew, ignorant questions+grimy paws+years of testing=knowledge:busted:

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see lew, ignorant questions+grimy paws+years of testing=knowledge:busted:

Shouldn't you be out clearing snow off the driveway? :lol::ride:

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Thanks NCmountainman, you confirmed what I was thinking as stated in my orginal post. Another thought, what about heavier oil in the outer chamber (TC forks)? Would this achieve the same thing (or close) as the bottoming collars offered by FC and others?

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Shouldn't you be out clearing snow off the driveway? :lol::ride:

got the tractor for that,i'd rather be here disturbin' the peace:p i'm seriosly considering putting some sheet metal screws in the knobs like we used to do as kids....the only thing holding me back is the fact that things just don't heal quite as fast anymore:busted:

317, i use the FC collars on my ktm and use heavier oil in the outers;depending on which manufacturer(kyb,showa,wp....) some mix more than others but as long as your cartridge seal is good i havn't found mixing to be a problem..in fact i think the heavier outer oil actually discourages it.

as far as the FC collars some say they are no different than stock but the ones i have for my ktm are .006" larger on the overall OD,that doesn't sound like much but its a 20% increase over the stock clearance so it does indeed make a difference you can feel;that difference allows you to keep the afore mentioned bottoming on the biggest hits with a buffer being the FC oil lock collars and the heavier oil....that in turn keeps you from running too high of a oil ht which can affect turn in and add mid stroke harshness:thumbsup:

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well seeing as you don't tune bottoming with either spring rates or valving (it just adds to the problem if those things are not adequate) then that would deem oil ht as........wait for it..........'the most important' element against bottoming:smirk:

chuck unless your running nost bv's there is no low speed adjustment on the forks(thats the topic) and i've always found lighter springs need too much preload or they will ride too low in the stroke,preload past 5mm up front and 10mm out back will result in more deflection than if you just used the proper wt spring;and on the same note if your overstacking to compensate for lighter springs its gonna be harsher also. like tnc said its the sum of all parts and ya can't have one overcompensating the other.

see lew, ignorant questions+grimy paws+years of testing=knowledge:busted:

I'm sure this is probably an ignorant question, as I don't know much about suspension tuning beyond knowing the shipping address of Race Tech :ride: but your statements have me thinking. It makes no sense to me to state that spring rates and damping are not how you control bottoming, and bottoming is primarily controlled by oil height. The oil height in the shock is not an adjustable parameter, therefore bottoming must be controlled with spring rates and valving. Why is it any different for forks than for a shock? It seems logical to me to assume that bottoming is controlled with the spring rates and damping, and oil height is just a handy extra tuning variable for forks.

Am I way off base here?

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I have the FC collars also, but wanted a little more at the bottom. I have a decent setup on my forks, but I'm just trying for less compromise. I know what you mean about the snow. We had 7" of snow with a 1/4" of frozen rain on top that made a shell on top of the snow. I couldn't even get in my truck yesterday. I'm a school pricipal, so at least I can tinker out in the garage because there was no school Friday and most likely Monday. :ride:

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chokey,if you were to set up a fork like a shock it would jar your teeth out of you head,some of the number wiz's can tell you the exact leverage ratio's involved but its significantly more than the 1:1 of the fork,so its kinda apples and oranges....both fruit but significantly different.

you can't valve the fork against bottoming....been there tried that,as said it will jar your teeth out;you can however set it up properly to the point that it doesn't add to a bottoming problem. as far as spring rates in the fork..you are stuck with the proper rate for your wt and thats it, go any more and its gonna what?.....jar your teeth out of your head.

the question was whats the most important tuning aspect against fork bottoming? i'll say it again....OIL HEIGHT:bonk:

keep in mind that i'm the bottoming king,there hasn't been a stroke designed that i can't blow through!!

man that sounds bad:lol::ride:

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chokey,if you were to set up a fork like a shock it would jar your teeth out of you head,some of the number wiz's can tell you the exact leverage ratio's involved but its significantly more than the 1:1 of the fork,so its kinda apples and oranges....both fruit but significantly different.

you can't valve the fork against bottoming....been there tried that,as said it will jar your teeth out;you can however set it up properly to the point that it doesn't add to a bottoming problem. as far as spring rates in the fork..you are stuck with the proper rate for your wt and thats it, go any more and its gonna what?.....jar your teeth out of your head.

the question was whats the most important tuning aspect against fork bottoming? i'll say it again....OIL HEIGHT:bonk:

I see what you're saying about the leverage ratios, but it just isn't clicking in my brain. It just doesn't seem logical to me that you HAVE to control bottoming with the springs for a shock, but you CAN'T control bottoming with the spring rates for the forks. Not trying to argue, just trying to learn. :ride:

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I see what you're saying about the leverage ratios, but it just isn't clicking in my brain. It just doesn't seem logical to me that you HAVE to control bottoming with the springs for a shock, but you CAN'T control bottoming with the spring rates for the forks. Not trying to argue, just trying to learn. :ride:

go ahead and try it.....come back with your results,i'm pretty sure you would then agree.

in plain english....in a FORK,you MUST for optimum overall performance have the proper spring rate with minimal preload (no more than 5mm) then VALVE for CONDITIONS then most importantly set the OIL HT where it doesn't BOTTOM but only on your biggest hits.

if you really wanna get technical the oil ht is in a way a spring...air spring that is, so i suppose in some twisted way your right....it could be compared to a progressive spring on a shock,if ya squint just right i could see that.....but oil ht is still the most important aspect of bottoming in a fork:p

lew's right i need to go shovel sumthin' (besides $hit !!)

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people think to black and white, fork bottoming occurs because the forces from the rider/bike overcome the forks ability to control it, thats the key word, control, so if we up the spring rate we get more bottoming resistance, but its a poor way to control bottoming as springs dont cope with speed well, damping however does, so we increase damping and we help bottoming, but then we get small bump problems, so we back off the damping so it works on small bumps and we use the air gap(progressive) to help the fork over the last half of the travel, then finally we have the bottoming cones for the last inch of travel,these are the last chance saloon so to speak.

ALL things help bottoming, but none should be used to control bottoming, a well designed fork system will bottom slightly and just need to be fine tuned.

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yes i agree it all plays together, i guess what i was trying to convey (from my experience anyhow) oil ht is what you use to control bottoming when everything else is right,and by right i mean not overcompensating in spring or damping for your application. it also seems to me that oil ht gives way more latitude(as far as tuning out bottoming goes) without as much consequence:excuseme:

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