Depth of fork compression?

Started by stopintime, August 28, 2010, 02:42:46 AM

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stopintime

My forks work very well with magically reworked internals.
The Öhlins tech guys at Misano WDW thought they had cartridges [cheeky]

However, they never ever bottom out - I have about an inch and a half left.

Rough roads, spirited riding, track days.

Do you think I need to use the whole travel? If so, why?
252,000 km/seventeen years - loving it

Raux

isn't there a magical guide to suspension setup that everyone points to? what does that say?
I'm going to be working the same issue as well. that's why I'm asking.
The 1198 forks on the bike have ohlins springs and new valves. there is a rubber ring around the right fork that will help me see how much compression I'm getting. right now I have about the same 1 1/2" - 2"

ducpainter

Ideally you should use more travel than that, but the only time you'll do that is under very hard braking.

Try removing a couple of clicks of compression and try it...there is no hard and fast rule for settings
"Once you accept that a child on the autistic spectrum experiences the world in
 a completely different way than you, you will be open to understand how that
 perspective
    is even more amazing than yours."
    To realize the value of nine  months:
    Ask a mother who gave birth to a stillborn.
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Speeddog

Another option that's slightly more work is to remove some oil.
This increases the air volume and thus reduces the pressure rise of the air that's compressed in the forks.

What rate springs are you running?
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~~~ "We've rearranged the deck chairs, refilled the champagne glasses, and the band sounds great. This is fine." - Alberto Puig ~~~

stopintime

Quote from: humorless on August 28, 2010, 03:00:25 AM
Ideally you should use more travel than that, but the only time you'll do that is under very hard braking.

Try removing a couple of clicks of compression and try it...there is no hard and fast rule for settings

At the end of the long straight at "my" track the pavement is a bit uneven - rear-wheel-lifting hard braking there, will make my bike jump (skid?) on it's front weel. I keep thinking it would do that less if it had some more travel available. Maybe not, but that's the only situation I wish my front behaved differently.

This kind of adjustment isn't covered very well in the litterature. I believe it comes down to personal preference regarding how much dive the bike and rider wants or needs. If it dives more during turn in and trail braking, it might turn easier than it really should.

I don't have adjustability, so I need to decide before upcoming suspension service.

The Italian Öhlins guys and the British racer I consulted agreed that there might be too much oil.

Have you seen good litterature describing these considerations?


Quote from: Speeddog on August 28, 2010, 08:59:29 AM
Another option that's slightly more work is to remove some oil.
This increases the air volume and thus reduces the pressure rise of the air that's compressed in the forks.

What rate springs are you running?

I was typing while you replied, so maybe yes to the oil.
My linear springs are 9.3 rate. (rider weight at 220 + gear)
252,000 km/seventeen years - loving it

Speeddog

Here's some info from Ohlins, it's a bit specific to their forks, but has a good bit of general application.


Shock too, not so relevant here but since I found it...:


I'd lower the oil level by about 10mm and try it.
- - - - - Valley Desmo Service - - - - -
Reseda, CA

(951) 640-8908


~~~ "We've rearranged the deck chairs, refilled the champagne glasses, and the band sounds great. This is fine." - Alberto Puig ~~~

stopintime

Quote from: Speeddog on August 28, 2010, 09:19:01 AM
..............

I'd lower the oil level by about 10mm and try it.

Thanks [thumbsup]

Possible to remove oil without taking the forks off/apart? If so, I can try that before service-time.
252,000 km/seventeen years - loving it

Speeddog

It's not easy to remove a consistent amount of oil with the forks on the bike.
It can be done.

I remove forks to do that kind of thing, it's a bit more stuff to take off, but it's all much less struggling.
- - - - - Valley Desmo Service - - - - -
Reseda, CA

(951) 640-8908


~~~ "We've rearranged the deck chairs, refilled the champagne glasses, and the band sounds great. This is fine." - Alberto Puig ~~~

ducpainter

Quote from: stopintime on August 28, 2010, 09:29:59 AM
Thanks [thumbsup]

Possible to remove oil without taking the forks off/apart? If so, I can try that before service-time.

I used a piece of steel tubing as a pipette with a mark on it as an approximation of a real level tool. I knew what level I was looking for though.

If you know what level yours were filled to you could do the same.
"Once you accept that a child on the autistic spectrum experiences the world in
 a completely different way than you, you will be open to understand how that
 perspective
    is even more amazing than yours."
    To realize the value of nine  months:
    Ask a mother who gave birth to a stillborn.
"Don't piss off old people The older we get, the less 'Life in Prison' is a deterrent."



BK_856er

Bottoming out your forks is probably a situation you want to avoid.

When I was setting up my Matris forks I dropped the oil level 3-5mm at a time and then hit a section of test road for a series of maximum braking runs.  I stopped dropping the oil level when I had a few mm travel remaining, relative to the previousy established physical maximum travel.  The total possible physical travel might be less than the amount of chrome slider showing.

I got really good at quickly removing/adjusting/installing my forks.

BK

J5

Quote from: Speeddog on August 28, 2010, 09:59:45 AM
It's not easy to remove a consistent amount of oil with the forks on the bike.
It can be done.

I remove forks to do that kind of thing, it's a bit more stuff to take off, but it's all much less struggling.

using a large syringe and tube it is quite easy
i dont care if you have been a mechanic for 10 years doing something for a long time does not make you good at it, take my gf for an example shes been walking for 28 years and still manages to fall over all the time.

colin748916

Quote from: stopintime on August 28, 2010, 09:02:24 AM
At the end of the long straight at "my" track the pavement is a bit uneven - rear-wheel-lifting hard braking there, will make my bike jump (skid?) on it's front weel.

The Italian Öhlins guys and the British racer I consulted agreed that there might be too much oil.


I have the same symptoms with my S2R1000, same track and also elsewhere. I've been told the oil level is probably too high and described as "hydraulic lock"? Front fork travel reads at max 95-100mm even with redused preload and compression. They never bottom out, with should be 120-130mm of travel?

stopintime

Quote from: colin748916 on August 29, 2010, 10:41:47 AM
I have the same symptoms with my S2R1000, same track and also elsewhere. I've been told the oil level is probably too high and described as "hydraulic lock"? Front fork travel reads at max 95-100mm even with redused preload and compression. They never bottom out, with should be 120-130mm of travel?

I remember you talking about this in our local DOC forum. Did you solve the problem?

BTW - will you be joining us on the season's last track day Sept 10?
252,000 km/seventeen years - loving it

suzyj

Just a quick point.  Once the level has been established with the fork out of the bike and vertical, as long as you remove the same volume from each fork, the level will match in each fork.  So there's no need to pull the forks out of the bike after the initial oil fill - all you need to do is pop the caps off and use a syringe with a tube to draw the same amount of oil from each.


2007 Monster 695 with a few mods.
2013 Piaggio Typhoon 50 2 stroke speed demon.

devimau

IMMO IF the sag is set @ 40mm or so front and the oil level is correct you should use the compression adjustment to dial the fork travel (10 mm from bottoming is optimal) and the rebound adjuster to smooth out the ride....with that being said you should also check rear sag and set it @ 30mm to start since it'll influence the front if not set up propertly.....to proper diagnose the issue and try to help you as the other members are also doing let me ask you this:
how much sag in the front and how much preload?
how much sag on the rear and how much preload?
what oil weight did they used on the forks?
whats your comp and rebound settings counting from full in how many clicks out?
The reason why you want to use the full travel IMMO is because you want the suspension to be as plush as possible, that will give you feeling, won't loose traccion (under normal conditions) and won't make you tired as fast among other reasons.
You don't have to remove the forks to remove oil.