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Discussion Starter · #1 ·
Hi all,

I've got a problem (maybe it's not a problem? I would presume it is) with my Fuji Outland 29er 3.0 (RoxShox Bar 2.1 rear suspension). Whenever I bunny hop, or have any moderate+ amount of compression on the bike, my rear wheel rubs against the seat tube. It did this really bad yesterday at the bottom of a pretty steep, long hill that had a dip at the bottom. I smelled burned rubber for a good couple of seconds while still moving.

The bike itself has a large frame, but maybe my 225lbs is just too much for the rear suspension to hold up to? Do I need to upgrade? I just don't want any possible frame damage to occur down the road or have to replace my rear tires more often than usual. I've already got the rear suspension adjusted to the stiffest setting possible.

You can see the burn mark in the "I" of the Fuji logo on the seat tube in the closeup shot below.
 

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Fat-tired Roadie
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^^^
Big +1 to this. It would be silly to use less of your suspension travel in order to (probably unsuccessfully) avoid a problem caused by using too big a tire.

Looks pretty tight at the chainstay bridge too. There should be a little clearance everywhere, and throughout the shock stroke.
 

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Huckin' trails
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My call is for the over-sized tire heigh you have on the bike. Try a shorter tire. Or maybe you are trying to fit some 650 on this ? (idk, just asking)

David
 

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Just a flesh wound
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What size Shock?

Your tire should not rub even at full compression. I would suspect that your shock is either too short, or has too much travel for the bike.

I have a C'dale Prophet. The shock length is 200mm eye to eye with 50mm of travel. That translates to 7.875" eye to eye with 2" of travel. If I had a shock that was 7.5" eye to eye with 2" of travel, I could hit the frame with the tire.

You need to make sure that you have the right shock size on the bike. People make mistakes when they put bikes together.
 

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Huckin' trails
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Your tire should not rub even at full compression. I would suspect that your shock is either too short, or has too much travel for the bike.

I have a C'dale Prophet. The shock length is 200mm eye to eye with 50mm of travel. That translates to 7.875" eye to eye with 2" of travel. If I had a shock that was 7.5" eye to eye with 2" of travel, I could hit the frame with the tire.

You need to make sure that you have the right shock size on the bike. People make mistakes when they put bikes together.
Rule number 1 : Never take anything for granted. We'd all assume he had a bike build up from stock specification. He might not. :thumbsup:

David
 

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Fat-tired Roadie
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The engineers designed the bike with one shock. The product manager got a good price on a different one. Somebody took a cursory look at the specs and said it was good enough.
 
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i still insist it is an improperly inflated rear shock. assuming that the bike is factory stock, it probably was inflated to accommodate an "average" sized rider. two hundred and twenty five bills is not "average".

big dudes always have to run their suspensions a lot stiffer than guys my size. OP, have you checked that air pressure lately?

the o ring on a properly adjusted air shock should not almost slide off the shaft when the bike is used as an XC bike.
 

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Just a flesh wound
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People make mistakes when they pack shocks in boxes to be shipped to a factory. People make mistakes when they put lenses on satellites that get launched into space (Hubble). People put the wrong shim stacks in new shocks under construction.

If the tire hits the frame at full compression, then there is a problem. It might be the tire, but if it fits between the stays, then I think it's the shock. Easy to test and easy to measure. Just need to know what the spec is for eye to eye and throw.

But I've certainly made a few mistakes along the way, and I might be wrong.
 

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Just a flesh wound
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I can let all the air out of my shock, and the tire does not hit the frame. Increasing pressure to reduce travel is not the solution. You should be able to use all of your travel without the potential for destroying your bike and possibly yourself. I think that all of us have bottomed out on more than one occasion.

What you are saying might work, but it is not the way it should work. When I look at the pictures of his bike, I see a lot of space between the seat tube and the rear triangle. It looks to me that the shock could be longer without any problem.
 

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Fat-tired Roadie
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Suppose for a moment that the bike was designed so that a correctly-sized tire could hit the seat tube at full compression.

So I'm riding my FS with my big, macho freeride tires. I've got the shock set up so it never bottoms (I wouldn't, but whatever) and I decide that today's the day that I'm going to sack up and hit the 'A' version of the line I've been doing the easier way, massive drop and all. I do a beautiful wheelie drop off of it onto the lovely, steep transition. And... my shock bottoms. My rear tire hits the seat tube and the wheel locks up. Suddenly instead of rolling out of the transition and having to stop to avoid a stoke-induced wipeout, I'm skidding and maybe I whack into a tree or something.

What idiot would design a machine that way on purpose? Especially knowing that a lot of people consider correctly tuned suspension to bottom out once or twice a ride.

It doesn't matter how heavy the rider is. FS linkages in stock spec are going to ship with a hard stop before the rear wheel hits the frame, as long as the rear wheel meets the assumptions the designer made. Probably this is going to be the bottom-out bumper in the shock. They're resilient, but they're not that resilient. Maybe a couple extra millimeters of travel, and between knowing that's there and incorporating a little safety factor, the travel should really stop before the wheel hits the frame even if the bottom-out bumper wasn't there.

Of course all bets are off if the shock is not the correct one.

A lot of XC frames are designed around a max. 2.1" tire. Some even suggest using something smaller. (I find that a little silly, but there it is.)
 
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Suppose for a moment that the bike was designed so that a correctly-sized tire could hit the seat tube at full compression.

So I'm riding my FS with my big, macho freeride tires. I've got the shock set up so it never bottoms (I wouldn't, but whatever) and I decide that today's the day that I'm going to sack up and hit the 'A' version of the line I've been doing the easier way, massive drop and all. I do a beautiful wheelie drop off of it onto the lovely, steep transition. And... my shock bottoms. My rear tire hits the seat tube and the wheel locks up. Suddenly instead of rolling out of the transition and having to stop to avoid a stoke-induced wipeout, I'm skidding and maybe I whack into a tree or something.

What idiot would design a machine that way on purpose? Especially knowing that a lot of people consider correctly tuned suspension to bottom out once or twice a ride.

It doesn't matter how heavy the rider is. FS linkages in stock spec are going to ship with a hard stop before the rear wheel hits the frame, as long as the rear wheel meets the assumptions the designer made. Probably this is going to be the bottom-out bumper in the shock. They're resilient, but they're not that resilient. Maybe a couple extra millimeters of travel, and between knowing that's there and incorporating a little safety factor, the travel should really stop before the wheel hits the frame even if the bottom-out bumper wasn't there.

Of course all bets are off if the shock is not the correct one.

A lot of XC frames are designed around a max. 2.1" tire. Some even suggest using something smaller. (I find that a little silly, but there it is.)
ok, the more i think about what you guys are saying the more it makes sense. i DO remember having to actually shave knobs from 2.25 tires on my superlight because they were rubbing the drive side chainstays.

don't remember them rubbing the seat tube, though.
 

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Discussion Starter · #19 ·
Sorry, Prophet, I only posted three days ago and haven't had hardly any free time since then between family life and work.

Thank you all for your suggestions, the bike is fully stock to answer some questions. As for the shock air pressure, I took it in to the LBS and it was way too low, as many of you said. They pumped it up to proper pressure and I went on a ride Sunday morning (with some big dips), no more rubbing or bottoming out.

Thanks again for your suggestions.
 

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Just a flesh wound
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No trouble. I am glad to hear that you don't get any rub, but I am troubled by the fact that it can hit when under pressurized. That is a serious design flaw in my opinion. As Andrew said earlier, potential for catastrophe.
 
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