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Discussion Starter · #1 ·
Hi. I'm looking into upgrading the rear shock on my 2004 GT i-Drive.

There's two queries i have that would help me choose.

1. The current shock is 6.5 inch eye to eye (an old FOX vanilla). Does that mean my frame is absolutely only limited to that size shocks? I ask because i've seen an idrive frame fitted with a FOX vanilla which appears to be 7.5 eye-eye, unless theres a 6.5" one with a piggyback, or it never is fully extended. I've included a picture (which is not of my bike, i stumbled on this picture probably on these forums) to show what i mean.

2. And so depending on what size shocks my frame can take, what would be a good shock. I've been looking at the FOX Float range (for 6.5"). I was thinking, if propedal was to minimize pedal bob and what not, would it be redundant on the idrive or any other suspension system that already does that? I'm thinking that platform shocks on a multi pivot suspension system my make the suspension less active.

Any feedback is much appreciated
 

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On the i-drive bikes, the suspension design is made to combat pedal bob anyway, putting on a propedal shock will noticeably stiffen the suspension, so you're better off getting a standard shock or one that you can turn the platform off.
As for the stroke length, i cant help you there, but i assume you could go a little shorter (though it would affect geometry) rather than longer (the eccentric bb only rotates so far in the BB shell)
 

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I'm running a single point suspension and went from a lame 6.5" coil to a 7.5" air shock Rockshox MC 3.3, motion control, flood gate etc. No clearance problems, I raised the stem hieght up, installed a set back seat post and pushed my seat back and now I'm getting 3.5" travel vs. 1.5" from the old coil. Motion control eliminates all bob. Balance feels great, glad I did it.
 

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Discussion Starter · #5 ·
Starkonian said:
I'm running a single point suspension and went from a lame 6.5" coil to a 7.5" air shock Rockshox MC 3.3, motion control, flood gate etc. No clearance problems, I raised the stem hieght up, installed a set back seat post and pushed my seat back and now I'm getting 3.5" travel vs. 1.5" from the old coil. Motion control eliminates all bob. Balance feels great, glad I did it.
Nice. Although i have a suspension design which isn't considered a full single pivot, it may or may not allow for a longer shock. I was hoping if maybe someone has tried installing a larger shock on an iDrive (eccentric bb version) could share their experience.
 

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Discussion Starter · #7 ·
Anymore ideas about the possible shock sizes for the idrive? Or opinions on what shock to upgrade too? The Cane Creek Cloud Nine looks really good but i'm wondering if it can handle all mountain riding.
 

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Discussion Starter · #10 ·
autoduel said:
Stick with a 6.5 any longer and it will jack up your geometry.
I had a cane creek AD5 on my old I-drive and it was plush!
Just don't stand up to pedal. No bobing when seated.
Thanks, i just wanted to know if i should stick with 6.5" so then i can completely rule out other sizes.

One quick question: I know that generally longer size shocks are often used on longer rear travel bikes, but besides the actual travel difference, is the performance still the same?

eg. rp23 6.5" on a 4" travel bike and the same shock but 7.875" on a 6" travel bike, obviously the travel is different but does it perform the same? like is the progressiveness still the same (in relation to travel), damping and all that still the same?
 

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Your question of 'does it perform the same' unfortunately isn't easy to answer, as the same 6.5" shock could perform different on different frames based on several factors:
1) each manufacturer comes up with their own linkage leverage ratios. For example the Foes 2:1 frame is named for the fact the leverage ratio on the linkage to the shock is 2:1, meaning for every 1" movement of the shock, there is a 2" movement of the rear axle. My Trek Top Fuel 69er has a 2.37:1 ratio (its actually mentioned on the rocker arm). I believe the Specialized FSR are around 2.4:1 ratios.

2) The bike manufacturers work with the shock suppliers to create a shock with specific damping/valving to work best with the linkage ratio used on the frame. You may not have noticed but many Fox shocks have a sticker showing what damping level the compression tune (blue square w/3 bars) and/or rebound tune (red square w/3 bars) is set at from the factory. There are 3 settings for each, low, medium, high. Lower compression tune means less compression damping, higher tune means more compression damping. Some Examples:
Compression Low:
https://img.photobucket.com/albums/v11/MountainDog/Fox_floatcompa.jpg
Compression Medium:
https://img.photobucket.com/albums/v11/MountainDog/Fox_floatcompb.jpg
Compression High:
https://img.photobucket.com/albums/v11/MountainDog/Fox_floatcompc.jpg
Rebound Low:
https://img.photobucket.com/albums/v11/MountainDog/Fox_floatrebounda.jpg
Rebound Medium:
https://img.photobucket.com/albums/v11/MountainDog/Fox_floatrebound_b.jpg
Rebound Medium again:
https://img.photobucket.com/albums/v11/MountainDog/Fox_floatreboundb.jpg

Ideally anyone selling a shock that has this information printed on the label should mention it in their specs, as in this example:
https://shop.vendio.com/milewidesports/item/2007119986/?s=1231241771

In most cases you probably want the compression & rebound tune levels that match what the manufacturer originally spec'd on the bike. There are some instances (like on my Trek Top Fuel 69er) where some people feel the original compression tune is too firm, so they swap out the Fox RP2 shock for one with a lower compression tune.
 

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Discussion Starter · #12 ·
Hmm, thanks for opening my eyes a bit more. I wasn't aware about the damping stickers for fox shocks - the only thing i was aware of was that the lower end fox shocks have pre-tuned propedal and is indicated with a similar sticker, but i didn't know there was a sticker for both compression and rebound too.

As you can see i'm not all that familiar with propedal. I'm having trouble finding out whether propedal would be good for an iDrive system. It seems that all the new floats have propedal (whether adjustable or pre-tuned) but it's there nonetheless and i don't know whether you can turn it off. I've looked at the fox online manuals, and the rp23 says there's an 'open' position for the propedal lever. Does that mean off? Thing is, i don't want propedal to hurt the small bump performance since the iDrive is already made to minimize bob etc. So i don't know whether to rule out the floats as consideration.
 

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Discussion Starter · #13 ·
Whitedog said:
Your question of 'does it perform the same' unfortunately isn't easy to answer, as the same 6.5" shock could perform different on different frames based on several factors:
Just came to my mind that i can rephrase this question more constructively. Same scenario, two rp23's - a 6.5" and 7.5", taking into account what you said, both have same level of compression/rebound damping (say medium) same propedal settings, and both went through a dyno run. What would be the possible differences in the results, given that they both are tested using the same simulation etc. (don't exactly know how the suspension dynos work)?
 

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peternguyen said:
. What would be the possible differences in the results,?
Completely FVCKED up geometry. Don't mess with the shock eye to eye or stroke. Longer shocks equal higher bottom brackets, equal steeper head tube angles, equal shyte you don't want
 

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peternguyen said:
As you can see i'm not all that familiar with propedal. I'm having trouble finding out whether propedal would be good for an iDrive system. It seems that all the new floats have propedal (whether adjustable or pre-tuned) but it's there nonetheless and i don't know whether you can turn it off. I've looked at the fox online manuals, and the rp23 says there's an 'open' position for the propedal lever. Does that mean off? Thing is, i don't want propedal to hurt the small bump performance since the iDrive is already made to minimize bob etc. So i don't know whether to rule out the floats as consideration.
First off, as others have said, do NOT consider putting a 7.5" eye to eye shock in place of the original 6.5" eye to eye. The extra length will jack up the rear and throw off the geometry.

Regarding Propedal, a look thru bikepedia.com at the i-drives like yours from 2001-2004 show they came with Float R shocks, and did not come with versions that had the propedal lever, so based on the i-drive system, it appears you don't need a shock w/propedal.

To answer your question, the shocks with the propedal levers, some have an 'open' and then a 'propedal' position, some have propedal engaged all the time, but different levels of propedal. The open position is 'off' per your question:
Fox RP2: Open setting or Propedal setting
Fox RP23: Open setting or Propedal setting (you can set the dial to pre-select one of 3 propedal settings)
Fox RP3: Light Propedal setting, Mid Propedal setting, Full Propedal setting

If you were to get a shock with the Propedal lever, best if you got a RP2 or RP23 so you could 'turn it off'

2007 Fox Manual (RP2 & RP3):
http://www.foxracingshox.com/fox_tech_center/owners_manuals/07/eng/2007_om_eng.htm

2006 Fox Manual (RP3):
http://www.foxracingshox.com/fox_tech_center/owners_manuals/06_RearShock_en.pdf

NOTE: Even the Float and Float R can come with a non-adjustable pre-set 'factory propedal' feature that is always on. Here's an ebay link, note the propedal label in the 3rd pic:
http://cgi.ebay.com/08-Fox-Racing-S...yZ158996QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

2005 Fox Manual where it mentions the 'factory propedal' in the Float and Float R:
http://www.foxracingshox.com/fox_tech_center/owners_manuals/05_RearShox_en.pdf

To try to answer your question about the performance of a 6.5" shock vs. a 7.5" shock with same rebound/compression/propedal features......the damping performance would be similar when cycled on a shock dyno...HOWEVER...in the real world there is a spring (air) involved. The body size of the shock (therefore the air volume for the air spring) may be different between a 6.5" shock and a 7.5" shock, and air pressures will probably be different between the two in order to get to the desired 25-30% sag. You can't assume that if you need 140psi to get 25% sag in a 6.5" shock (10mm of sag on the 1.5" travel shock shaft) means you'd use the same 140psi on a 7.5" shock to get 25% sag (13mm of sag on the 2" shock shaft).

Going back to your original question..and your comment that you assumed the Fox Vanilla with piggyback in the pic you posted was 7.5" eye to eye, no, they made them in shorter lengths....here's a completed ebay auction for a 6.5" piggyback vanilla:
http://cgi.ebay.com/FOX-VANILLA-RC-...yZ158996QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
It appears the shock in the bike pic looks the same as the ebay pic, so looks like we can assume the shock on the bike is 6.5"

So to summarize, for your shock upgrade, you should look for a 6.5" eye to eye Vanilla w/piggyback or a Float.
 

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As others have said, don't install a longer shock. Heck, the dog bone may not even allow it.

For real plushness, when I had my i-drive, I was using this custom made Rock Shox coil over. It was built by Rock Shox for GT bicycles (where a friend worked). That was the best shock I had on that bike.
 

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Discussion Starter · #17 ·
Whitedog said:
So to summarize, for your shock upgrade, you should look for a 6.5" eye to eye Vanilla w/piggyback or a Float.
Thanks Whitedog for that detailed response. Yeah, i will completely rule out getting a different size shock, but i also wanted to know the difference because i thought a shorter shock could have like 'less room for performance' - haha yeah, probably sounds stupid but wanted to be 100% sure what the possible differences are, because then i might reconsider my options.

But so it seems that i won't be ruling out fox completely - i'll have to do more research on their shocks. I don't want to spend too much money on an rp23 if i'm not going to make use of all it's features, so if the rp2 with propedal off performs as well as the rp23 with propedal off, and its cheaper, then ill go for that.

So far these are what i'm considering, (still same as before, but recap):

Cane Creek Cloud Nine
Fox Float RP2
Manitou Swinger x4 (still yet to do more research on that and it's SPV damping)
and RockShox Ario
 

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peternguyen said:
Thanks Whitedog for that detailed response. Yeah, i will completely rule out getting a different size shock, but i also wanted to know the difference because i thought a shorter shock could have like 'less room for performance' - haha yeah, probably sounds stupid but wanted to be 100% sure what the possible differences are, because then i might reconsider my options.

But so it seems that i won't be ruling out fox completely - i'll have to do more research on their shocks. I don't want to spend too much money on an rp23 if i'm not going to make use of all it's features, so if the rp2 with propedal off performs as well as the rp23 with propedal off, and its cheaper, then ill go for that.

So far these are what i'm considering, (still same as before, but recap):

Cane Creek Cloud Nine
Fox Float RP2
Manitou Swinger x4 (still yet to do more research on that and it's SPV damping)
and RockShox Ario
Stay away from cane creek air shocks. Air damping is a horrible idea. Think about the physics of it - air is extraordinarliy elastic and very susceptable to change in volume due to changes in temperature. Bad bad BAD idea.

RP3 and RP23 shocks are not all damped alike - there are about 9 different variations/options, just in terms of damping when it comes to Propedal. To get what you want, you're really going to need to test ride them on the bike you intend to run them.

These options are notated on this shock via the three little white bars - there are 3 options for compression and 3 for rebound.

Manitou Swinger is in fact a great shock. The SPV is infinitely adjustable - from completely off (plush) to very firm. You can usually find them cheap. This is a great option - due to it being infintely adjustable. Unlike the Fox propedal where you are stuck with which ever option you go for.

BTW - there is no "off" mode on Propedal - there is always a baseline amount of propedal (the "off" position) and then firmer from there.

If I were you, I would seek out either the Manitou or look for one of the Rock shox SID rear shocks that came on the Idrives back in the day. Great shock.
 

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Discussion Starter · #20 ·
Yeah i was pretty skeptical about air damping, i figure it would not be able to take as much as hydraulic damping, that's one thing that would stop me from getting it, however looking here, many people seem to rate it highly, and it also isn't a platform shock like the float and the swinger...

...but if the spv can be adjustable to off (which i didn't know it could be), then the scales are tipping a bit more in favor for the swinger.

As for the floats, yeah it'll be tough to be able to test ride them on an idrive.. damn.

And the old SID shocks, I thought those weren't very good shocks?
 
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