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Old 09-05-06, 01:08 PM   #1
Curtis_Elwood
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Fox F100R set up question and geometry changes due to fork compression

I've had my new bike (Marin Pine Mountain) for a couple months now and have ridden it hard. After taking quite a few 2+ feet drops with tons of roots (no snickering from the freeriders, I know it sounds small to you all), I've been watching my travel. I'm getting about 3 inches. This is about the hardest I'm ever going to slam the front end down, so I'd like to soften it up a bit and use at least another half inch of travel, maybe 3/4". I'm afraid that if I let out enough air to get it to use that much travel, it'll feel saggy when I'm on the smoother sections of trail. Right now, I'm running about 85 PSI with one click of rebound slower than the center click. I'm about 175-180 lbs. That nets me about 5/8" of sag.

So, my question is how much does an inch of travel make in the head tube angle and would I feel a difference in geometry if my fork was compressed further on normal riding and when taking drops? The head angle is listed at 71 degrees. I just want to make sure my head angle doesn't get too steep when the fork fully compresses. I already have enough endos to last me a while. Thanks.

P.S. down the road, I may send the fork to PUSH and have it PUSHED and converted to the RLC model. Would the addition of compression adjustment help my situation?
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Old 09-05-06, 01:17 PM   #2
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I've always used the 1/3 travel set-up rule of thumb. Meaning you should set your initial sag at 1/3 of your total travel. That equates to about 30 to 35 mm of travel.

Your current 5/8" converts to about 16mm of travel, thus it's too stiff. Increasing your sag (decreasing your air pressure) will make your fork perform better.

The rule of thumb with travel vs. head tube angle is 20mm equals 1 degree. So, if you increase your fork from a designed 80mm fork to a 100mm, you are changing the effective head tube angle by one degree (making it slacker).
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Old 09-05-06, 01:34 PM   #3
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Thanks. Think I'm going to feel the difference of one degree steeper head angle when my fork is fully compressed since I'm only getting 3 inches of travel at the moment?
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Old 09-05-06, 01:52 PM   #4
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Quote:
Originally Posted by a2psyklnut
I've always used the 1/3 travel set-up rule of thumb. Meaning you should set your initial sag at 1/3 of your total travel. That equates to about 30 to 35 mm of travel.
Fox advises that sag should be 15%-25% of travel...see:

http://www.foxracingshox.com/fox_bicycle/bike_index.htm
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Old 09-05-06, 02:13 PM   #5
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I have my Fox F80RL sag like 30% but I still have like 1" more to compress after my rides. And I don't see myself being able to hit harder landings than I'm currently doing. How can I use more of my precious 3" of travel w/o sagging more? I'm only using about 2" of it so far.
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Old 09-05-06, 02:14 PM   #6
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Originally Posted by jm01
Fox advises that sag should be 15%-25% of travel...see:

http://www.foxracingshox.com/fox_bicycle/bike_index.htm

Thanks, didn't know that.

At 5/8", he's right at 15%.

I'm a clydesdale and always get stiffer springs. With my new fork, (air), I'm playing around with the air pressures to find out what feels best.

I started at 33% for initial sag and found that too soft, so right now I'm at about 25% and that feels pretty good. I went down to 15% and found the ride way too harsh.

You really have got to play around and find out what works best for you.
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