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Discussion Starter · #1 ·
If you sag a 120+mm fork enough can you get the appropriate geometry? Are there any negative effects with using this method? I'm asking of course because of all the blowout deals on 120+mm forks.
 

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Discussion Starter · #3 ·
Thanks for the reply. I ask because my bike came with a shock that has never had any sag and I'm used to it so I figured a 120mm fork sagged appropriately (~20%) would put me right where I'm used to and not put any extra stress on the frame.
 

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I rode a frame that was designed around a 100mm fork for a long time. I used a Fox TALAS fork that was adjustable between 85-125mm of travel on it. I loved the way the bike handled tight fast trails with the fork set to 125mm. I personally found the geometry too twitchy with the fork set to 100mm.

The real question is how do you ride. If you aren't a full-on XC racer than I'd go for it. Even if you are used to it the way it is now you might find that you really like it better with a slightly more slack HTº. What type of frame is it and how do you have it built up? Mine was a Kona Dawg 100mm travel and I loved it with 125mm travel fork.
 

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Discussion Starter · #5 ·
It's just a '04 Giant Rainier with the XTC geometry. I like all the equipment on it (SRAM, EA50, Avid disc, etc) but the fork really sucks (Marzocchi EXR Comp). I just want a quality upgrade so I don't have to worry about components any more and I can work on riding. Once I feel I'm good enough I'll get a better bike but I don't think I'm near that now. A 120mm fork on blowout would really help the wallet.

For riding style it is mostly trail riding. Roots, bumps, rocks etc. Occasionally a foot or two jump. I'd experiment with more jumps but I don't want to hurt my frame (or myself again). My friend's a climber and I'm a descender. We switch positions on the trail depending on what part is coming up so we don't slow the other one down.
 

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One of my riding buddies has a Rainier and he switched out the fork for a Manitou Minute 3:00 which is adjustable from 90-130 (i'm pretty sure?). I've riden the bike set at 130mm and it still felt pretty good. I took it through some twisty single track and it didn't really seem sluggish to me.

-Danimal
 

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Recommened sag depends on the type of riding

dissonance said:
If you sag a 120+mm fork enough can you get the appropriate geometry? Are there any negative effects with using this method? I'm asking of course because of all the blowout deals on 120+mm forks.
If you ride downhill, the recommended fork sag settings are almost double what is recommened for XC riding. If you are going to blow through remaining fork travel, you are more likely to do that in downhill than XC. Since that does not happen, riding XC with downhill sag setting is not a problem for bottoming.

I have had a 120mm '04 MX Pro ETA on my XC hardtail, for over a year. I have used the sag recommendation for downhill. I have never bottomed the fork.

As far as increased sag compensating for the geometry change, it does somewhat, but not completely.

For flat running it is fine, except there are two issues.

One is energy loss while standing and hammering on the pedals, and the other is climbing with a tall front end.

You can feel the fork bounce more, when hammering on the pedals, and the front tends to lift more readily when climbing.

Engaging the ETA fixes those problems, but not all long travel forks have ETA, and I find that I do not engage ETA for short climbs or short standing stretches.

The reason for these two problems is the increased travel-to-top-out, caused by the increased sag. The fork can extend more without lifting the front wheel off the ground.

When you hammer on the pedals, you press hard, and then release that pressure, as you crank the pedals around. The oscillation of pedal force is what causes the front end of the bike to oscillate up and down. Upon release of pedal pressure, the fork bounces back extending a longer distance, due to the increased travel-to-top-out. So, the front of the bike oscillates with a greater amplitude, than a short travel fork with less sag. Rebound damping helps with this, but is not completely effective.

The increased travel-to-top-out also affects climbing, because the amount of sag is dependent on weight distribution between the front wheel and the back wheel. When you climb your weight tends to be loaded more on the back wheel, and so the fork sags less, raising the front of the bike.

The slacker head angle of a longer fork slows the steering response. I relpaced my 26 inch handlebar with a 23 inch bar, so the steering returns to being as quick as a shorter fork. I get less leverage, but I don't find that an issue. The 23 inch bar is also better in tight places.

Since, more sag does not help with pedal hammering or climbing, and since I have the 23 inch handlebar, I recently changed my sag to XC recommendations and just use ETA for long climbs and for pedal hammering on long flats. That way I get the benefit of greater travel for crossing over obstacles.

old_dude
 

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How about warranties?

If a frame is desinged around a 100mm fork and breaks by using a 120mm that will void the warranty?

I own a steel HT and am in the process of upgrading the fork and have the same dilema. The frame was built around a suspension corrected rigid fork (80mm) and the builder warrants it even if I use a 100mm suspension fork but what will happen if I put a 120 or 130mm fork on it, will it break? I know that the steering will also be affected but I don't mind slow responding steering because I'm slow anyway.
 

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When you need to pull your wheel up to get over something - you are going to have to lift it 20mm before it ever leaves the ground.

Unweighting the bike would change it's geometry.

Hopping would be interesting don't you think?
 

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Buy one that allows the travel to be reduced

dissonance said:
If you sag a 120+mm fork enough can you get the appropriate geometry? Are there any negative effects with using this method? I'm asking of course because of all the blowout deals on 120+mm forks.
either externally or interally. I for one wouldnt run more then 100mm
 

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Discussion Starter · #12 ·
zenorb said:
When you need to pull your wheel up to get over something - you are going to have to lift it 20mm before it ever leaves the ground.

Unweighting the bike would change it's geometry.

Hopping would be interesting don't you think?
Well Fox and Marzocchi both recommend a sag of approximately 20%. So whether it's a 100mm fork or a 120mm fork you still have to lift it 20mm or more. Isn't that normal though for anyone who sets their fork up with the proper sag?

The cheap 100mm EXR Comp that came with my bike has never sagged. I really like the geometry how it is. It feels real powerful and I feel it is fine for climbing. So once I get a decent fork I would only be sagging the 120mm the recommended amount (around 20mm), which in theory would put me right about where I'm used to on my no sag cheapo fork. I think anyway... I'm hoping to order a Marathon S soon if this all makes sense.
 

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dissonance said:
If you sag a 120+mm fork enough can you get the appropriate geometry? Are there any negative effects with using this method? I'm asking of course because of all the blowout deals on 120+mm forks.
Yes. At 5 inches out, another 20 is a lesser percentage of change. People do it on 60-80 forks, and 80-100mm forks all the time, and it's not horrible. It's abit of sag sure, but then sag is a constantly variable dimension, and there are guys riding around with more than that on new forks anyway. If you leave it topped out at 120mm, there will be an amplified torque moment on the head tube, but any modern frame designed for a 5" fork should have a saftey margin far greater than 20mm is going to infringe upon. To be completely realistic, you can get used to riding anything and enjoy it. Go nuts with Neg Air spring or whatever you want. Play with it and learn. If you hate it, you won't lose a ton of cash on the deal when you sell it, if you're picking up your new toy on closeout anyway. Then you can write messages and tell everyone else who is merely specualting how it really works on your particular fram/fork pairing. Good luck, enjoy.
 

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Where are the blowout deals?

I haven't seen any exceptional closeout deals on 120 mm forks lately. Thanks.

I rode a hardtail (Surly Instigator) like that for a while with a 130mm fork (Fox Vanilla RL) and I liked it but I had lockout to use when I wanted to hammer. With a softer than normal fork spring you get a lot of squishing up and down when sprinting and climbing unless you have lockout. I never had any problems with bottoming despite springs that were too soft for me. The extra sag gives you more tube overlap though too which generally makes the fork stiffer torsionally. That bike was designed for a long travel (100-130 mm) fork however.
 

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dissonance said:
...The cheap 100mm EXR Comp that came with my bike has never sagged. I really like the geometry how it is. It feels real powerful and I feel it is fine for climbing. So once I get a decent fork I would only be sagging the 120mm the recommended amount (around 20mm), which in theory would put me right about where I'm used to on my no sag cheapo fork. I think anyway... I'm hoping to order a Marathon S soon if this all makes sense.
You never adjusted your stock fork? They are not that tough to tune and the EXR Comp is not bad when adjusted for the rider.
 

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Discussion Starter · #17 ·
tl1 said:
I haven't seen any exceptional closeout deals on 120 mm forks lately. Thanks.

I rode a hardtail (Surly Instigator) like that for a while with a 130mm fork (Fox Vanilla RL) and I liked it but I had lockout to use when I wanted to hammer. With a softer than normal fork spring you get a lot of squishing up and down when sprinting and climbing unless you have lockout. I never had any problems with bottoming despite springs that were too soft for me. The extra sag gives you more tube overlap though too which generally makes the fork stiffer torsionally. That bike was designed for a long travel (100-130 mm) fork however.
2004 Marzocchi Marathon S 120mm $275
2004 Fox Vanilla 125R OEM $299
2005 RockShox Pike SL $324.99 (in black or silver)
 

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Discussion Starter · #19 ·
Well I ended up getting the 2004 Marzocchi Marathon S. I wanted something of high quality, durability, and minimal maintenance. I think it will do all of that. Hopefully I'll have it Monday or Tuesday. It should be a big step up from my stock fork. With the recommended sag I should be riding right where I'm used to. Thanks for the help everyone.
 
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