Bicycle Mechanics - skipping while backpedaling

i searched the forum but found nothing of help. i have an '08 giant stp and it likes to drop to a gear making the driveline as straight as possible. when setting up for certain things i have to backpedal. this obviously causes some unwanted situations. i've tried lubing the spots that could cause some sticking but it did not help. what would be the best way to combat this? i was thinking of cutting a few links out to tighten the chain a bit more (though the spring rate in the derailleur wouldn't change). thanks for the help. below are the bike specs.

size Regular, Large
color Black / Yellow
frame ALUXX SL Aluminum Frame Set Available
fork Marzocchi DJ1, 100mm w/20mm Thru Axle
handlebar Alloy, 31.8mm
stem Giant FR, 31.8mm
seatpost Alloy, 350 x 30.9mm
saddle Giant DJ
pedals Alloy Platform
shifters SRAM SX4 Trigger, rear only
front derailleur N/A
rear derailleur SRAM SX5 Mid cage
brakes Hayes MX4
brake levers Tektro Alloy
cassette SRAM PG-850 11-28T, 8 speed
chain Shimano HG-40
cranks TruVativ Hussefelt 36t single ring
bb TruVativ Howitzer
rims WTB Dual Duty FR
hubs Formula Disc
spokes Stainless Steel
tires Kenda K-Rad, 26x2.3

I am not sure I understand your problem, but if your derailure pulls your chain to the farthest outside cog without you initiating it with the shifters, then the trouble is most likely in your shifters - the shifters are somehow bailing out cable allowing the derailure to pull the chain to the smallest (outside) sprocket.

Start there and see how it goes. Hint; If you sprayed lubricant on your shifters, that might be the source of your problem.

the easiest speed (biggest cog) is engaged. i'm riding, i backpedal. then the chain skips down to the middle cog. the middle cog is where the chain line is straightest and it likes to skip there for some reason. when i start foward pedaling again it goes back to where is should be.

i reset everything on the derailleur when i got it home from the bike store (they don't have a clue). everything shifts great when riding normal and i adjusted everything properly with the derailleur (the only problem is backpedaling). i only lubed the guide sprokets(?). hope this clears it up. sorry if i was confusing in my first post.

This is happening in the rear, right Samurai?

I think you may be using a crossover gear, such as the big ring in front and the big end of the rear cassette. In this case there's nothing you can adjust away.
Brad

Is your derailleur bent from running over rough terrain or having the bike down? That's the only thing I can think of.

there is no derailleur in the front. it only has the 8 speed cassette in the back. i don't think it's bent as i've only went on one "rough" ride and it was happening before this.

Don't backpedal - it's common sense that the chain will drop to the most in-line position when backpedaling.

Don't backpedal - it's common sense that the chain will drop to the most in-line position when backpedaling.

i knew there would be one smart a**. did you even read the original post? it's not something i can avoid. what i want to know is there a way to limit it or somewhat fix it without going to SS.

i knew there would be one smart a**. did you even read the original post? it's not something i can avoid. what i want to know is there a way to limit it or somewhat fix it without going to SS.

What do you mean when you say "when setting up for certain things i have to backpedal. this obviously causes some unwanted situations." Do you mean when you're positionng yourself to deal with some technical feature on a trail, or doing some kind of voodoo shifting (?) or what?

What do you mean when you say "when setting up for certain things i have to backpedal. this obviously causes some unwanted situations." Do you mean when you're positionng yourself to deal with some technical feature on a trail, or doing some kind of voodoo shifting (?) or what?

Judging by the bike, Giant STP, I'd guess he' about to do something on the Street, Trials, or Park.

The following is based on logic, and not actual experience...

If you need to do some radical riding that requires back pedaling on a derailleur equipped bicycle, then your best bet is to do the back pedaling when the chain line is the straightest. It isn't about chain tension, cable tension or anything else as much as chain line.

The reason that back pedaling works well on a single speed is that the chain line is straight. On a derailleur equipped bike, the chain line is only straight for one gear combination (at most), probably in about the middle of your gear cluster. Try it in different gear combinations and find your sweet spot.

If you need to do this in a low gear for specific reasons, then you may be able to help some by either getting a smaller chainring or a shorter bottom bracket (which will move your sweet spot to a lower gear). You can also try a combination of the two.

EDIT:

You can also try removing a spacer from the drive side and adding it to the non-drive side, but this changes your dishing... not recommended.

You may also want to tinker with your cassette to have an exceptionally low geared cassette... This might put the sweet spot in the middle of the range low enough for what you want to do...

Judging by the bike, Giant STP, I'd guess he' about to do something on the Street, Trials, or Park.

:thumb:

The following is based on logic, and not actual experience...

If you need to do some radical riding that requires back pedaling on a derailleur equipped bicycle, then your best bet is to do the back pedaling when the chain line is the straightest. It isn't about chain tension, cable tension or anything else as much as chain line.

The reason that back pedaling works well on a single speed is that the chain line is straight. On a derailleur equipped bike, the chain line is only straight for one gear combination (at most), probably in about the middle of your gear cluster. Try it in different gear combinations and find your sweet spot.

If you need to do this in a low gear for specific reasons, then you may be able to help some by either getting a smaller chainring or a shorter bottom bracket (which will move your sweet spot to a lower gear). You can also try a combination of the two.

EDIT:

You can also try removing a spacer from the drive side and adding it to the non-drive side, but this changes your dishing... not recommended.

You may also want to tinker with your cassette to have an exceptionally low geared cassette... This might put the sweet spot in the middle of the range low enough for what you want to do...


as i figured. i was just hoping that there would be some type of magical fix. there never is... :( thanks for the input and i'll look into your suggestions.