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Old June 14th, 2018, 01:58 AM   #1
nikeeric86
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fork bottom out

Anyone know how far fork bottom is from the lower triple?
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Old June 14th, 2018, 01:04 PM   #2
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Mine's about 1/2" from bottoming after full day at track. I'm right about 12.8 stones.

Using 0.8kg Racetech springs
Preload-adjusters with about 1/2" preload
Emulators
15w fork oil with higher level
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Old June 15th, 2018, 05:27 AM   #3
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Quote:
Originally Posted by nikeeric86 View Post
Anyone know how far fork bottom is from the lower triple?
This is dependent on the position of your forks in the triple clamps. It is not a good way to determine ho close you are to bottoming. A more accurate measurement would be to take the top off one fork leg, collapse the fork leg completely and then measure the distance to the wiper seal.
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Old June 15th, 2018, 08:15 AM   #4
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I pull the springs out of my forks, compress them fully, then using a punch put a small dimple on the inner fork tube right above the dust seal. This gives a static position to measure from.
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Old June 15th, 2018, 09:26 AM   #5
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Quote:
Originally Posted by tgold View Post
This is dependent on the position of your forks in the triple clamps. It is not a good way to determine ho close you are to bottoming. A more accurate measurement would be to take the top off one fork leg, collapse the fork leg completely and then measure the distance to the wiper seal.
Quote:
Originally Posted by ck.mecha View Post
I pull the springs out of my forks, compress them fully, then using a punch put a small dimple on the inner fork tube right above the dust seal. This gives a static position to measure from.
Yes, but what if you have your fork-tubes slid up triple-clamps to lower front-end? What happens if your "bottomed" position occurs when dust-seal (punch-mark) is above lower triple-clamp?
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Old June 15th, 2018, 10:40 AM   #6
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Quote:
Originally Posted by tgold View Post
This is dependent on the position of your forks in the triple clamps. It is not a good way to determine ho close you are to bottoming. A more accurate measurement would be to take the top off one fork leg, collapse the fork leg completely and then measure the distance to the wiper seal.
completely overlooked this. I have my forks 22mm above the top triple.
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Old June 15th, 2018, 10:53 AM   #7
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Zip tie after my last track day. Since the forks are raise, i'm farther from bottom than i thought?
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Old June 15th, 2018, 02:34 PM   #8
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Originally Posted by nikeeric86 View Post


Zip tie after my last track day. Since the forks are raise, i'm farther from bottom than i thought?
yep
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Old June 19th, 2018, 01:41 PM   #9
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Originally Posted by DannoXYZ View Post
yep
Bottoming is usually referred to with respect to what happens internally with the fork.
The fork hitting the underside of the lower triple would be no bueno for sure.

If you are worried about that, I would suggest that you pull the fork caps and collapse the fork leg fully to check.

On a side note: Measuring the distance that you are measuring to see how fork sticks above the top triple can be tricky to measure because the top surface of the triple is not perpemdicular to the axis of the fork tube. I compensate for this by taking my measurements for each leg where the pinch bolt gap is.

My measurement there is currently 16mm and I do not have any issues with the top of the fork sliders hitting the lower triple. I suspect 22mm is ok too, but it depends on where you are measuring.
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Old June 20th, 2018, 01:23 AM   #10
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Originally Posted by ck.mecha View Post
I pull the springs out of my forks, compress them fully, then using a punch put a small dimple on the inner fork tube right above the dust seal. This gives a static position to measure from.
Rather than "dimple" your fork tube why not just wrap a nylon zip tie around the fork tube.

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Old June 20th, 2018, 06:41 AM   #11
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Quote:
Originally Posted by tgold View Post
If you are worried about that, I would suggest that you pull the fork caps and collapse the fork leg fully to check.
That's a good idea of course, but depending on how much oil is in there, they may not actually go that far when they're together. I'm not sure if anyone actually runs that much oil though.

I do know that when I got my 250, I could bottom the fork pretty easily with a very hard stop. After installing Sonic springs and putting the amount of oil Sonic recommends in, I can't bottom them, or even get very close to bottoming by using the brake, and it's not just the different springs causing that.
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Old June 20th, 2018, 07:31 AM   #12
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That's a good idea of course, but depending on how much oil is in there, they may not actually go that far when they're together. I'm not sure if anyone actually runs that much oil though.

I do know that when I got my 250, I could bottom the fork pretty easily with a very hard stop. After installing Sonic springs and putting the amount of oil Sonic recommends in, I can't bottom them, or even get very close to bottoming by using the brake, and it's not just the different springs causing that.
I'm running PJ-1 15 weight fork oil and I can't imagine bottoming my forks. But then I don't do "stopies" either.

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Old June 20th, 2018, 08:11 AM   #13
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Doing a stoppie and doing an emergency stop are not very different from the fork's point of view.

It's not so much the viscosity of the oil as how much you put in. More oil means higher air pressure when compressed, and at some point you have so much oil that you can't fully compress the fork.
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Old June 20th, 2018, 08:16 AM   #14
ck.mecha
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Quote:
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Rather than "dimple" your fork tube why not just wrap a nylon zip tie around the fork tube.

Bill
Well because the zip tie has the possibility of being moved. For me its very important to have a guaranteed static reference point for suspension adjustment. On USD forks the reference is easy, the fork lower is static. On traditional forks when I adjust my fork height I dont want to have to throw away all the fork compression data I have because my reference point changed. The dimple is above the dust seal, so it does not interfere with the sealing.

Instead of a zip tie I also use a o-ring around the fork to see my fork travel between races. It doesnt work any differently than a zip tie - I just think it looks cleaner.
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