Ask the experts

[MegaStoke]

IMO, always run the biggest rotors that are compatible, unless you’re a complete weight weenie.

[toast2266]

Intuitively this is what I was thinking as well since it’s a closed system. I hadn’t even ridden yet on the day in question but there was a very noticeable difference in the way the fork felt just riding in the lot, which prompted me to up the pressure. I wonder if it was solely temperature related as the bike was sitting on the rack in the sun all morning, maybe just enough to thin the oil a bit, black fork..

This doesn't really make sense. Increased temp will, if anything, make the fork feel stiffer in the parking lot. Air pressure goes up (a little bit) with heat. Your oil gets a tiny bit thinner, but you're not really gonna notice that in a parking lot test aside from your rebound maybe feeling a smidge faster. And really, unless you set up your suspension in below freezing temperatures and then rode it in a 100+ degree heat wave, I'm skeptical that you'd notice any significant difference from the change in temps.

Which is the long way of saying, if your fork is feeling dramatically different from ride to ride, there's something wrong with it. Leaking air? Gummed up negative chamber transfer port? Sticky bushings? I dunno, but I doubt it's temperature / atmosphere related.

[Dantheman]

And really, unless you set up your suspension in below freezing temperatures and then rode it in a 100+ degree heat wave, I'm skeptical that you'd notice any significant difference from the change in temps.

Agreed. Going to back to PV = nRT, at normal air spring pressures n is huge so changes in T probably have very little effect on P.

[J. Barron DeJong]

Atmospheric pressure should have no effect on the pressure in your air spring since it's a fully-sealed unit. Theoretically you could take it into space and the pressure wouldn't change. Ambient temperature will have an effect, but at normal spring pressures it's probably negligible, especially compared to the temperature changes caused by riding it.

To be a nerd for a minute: the above would be true if you were measuring ‘absolute’ pressure, but shock pumps are measuring ‘relative’ pressure - the difference in pressure between the ambient air pressure and the pressure inside the shock.

Ambient air pressure is about 3 psi lower at 8000 ft. vs. sea level, so a shock pumped to 100 psi at sea level would measure at 103 psi at 8000 ft.

And there is an effect on spring force in the shock - the ambient air pressure outside the shock is acting to compress it, so lower ambient pressure at higher elevation means less compressing from the outside air, which is equivalent to having a higher spring force in the shock.

Whether you can notice that change in relative pressure due to elevation, especially given changing temperatures of the air in the shock, and the change in damping from fluid temp changing is a different issue. You’d be more likely to notice it on a fork than rear shock due to the lower pressures you put in the fork.

[east or bust]

Fork is a 38 with about 30hrs on it, hopefully not fucked up yet. Suppose it could have been heavily greased from the factory and messing with the negative chamber.. Actually that might be the best explanation thus far, because adding more air would theoretically rebalance the fork.

Have a benign ride lined up for tonight with something more abusive on Sunday. Will update


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[toast2266]

Agreed. Going to back to PV = nRT, at normal air spring pressures n is huge so changes in T probably have very little effect on P.

Yeah, just running it through a quick calculator, a "normal" temp change (70 degrees to start, rising to 100 degrees) increases pressure by around 5psi (that's with initial pressure at 80psi).

Probably noticeable, but not a "fork is now completely different" kind of change.

[carlh]

Air pressure changes are more noticeable in the cold and on higher pressure shocks. Riding at 25 in the winter gets you an over damped soft spring. 70 up to 90 is much less pronounced.

[ridinshockgun]

Yeah, just running it through a quick calculator, a "normal" temp change (70 degrees to start, rising to 100 degrees) increases pressure by around 5psi (that's with initial pressure at 80psi).

Probably noticeable, but not a "fork is now completely different" kind of change.

I've had days where you go from upper 30s to low 40s starting early morning and it being in the 70s by mid day so you can get a pretty significant noticeable change in suspension performance with the temperature change on the fluid and the air pressure change. 5 psi in a fork is a pretty noticeable difference IMO.

[toast2266]

I've had days where you go from upper 30s to low 40s starting early morning and it being in the 70s by mid day so you can get a pretty significant noticeable change in suspension performance with the temperature change on the fluid and the air pressure change. 5 psi in a fork is a pretty noticeable difference IMO.

On one hand, yeah, agreed 5 psi is noticeable.

On the other hand, I basically never adjust my suspension based on temperature (except for maybe late fall riding when it's just cold all the time). And aside from any ambient air temperature changes, suspension gets pretty hot from use, so the air pressure is increasing just from riding. So really, my air pressure is plus or minus 5-10 psi on every ride, all the time, and that feels normal because that's how it always is.

If my fork all of a sudden felt way softer like EoB's, I'd be looking for an explanation other than temp changes.

[snowaddict91]

If my fork all of a sudden felt way softer like EoB's, I'd be looking for an explanation other than temp changes.

Gonna have to agree with toast here. I frequently have elevation changes from 4,500' to 11,000'+ and temp swings of 50F to 95+ and I can't notice a consistent, definite change in suspension performance. Only time I really notice a consistent performance difference is in freezing temps, but I don't ride in those conditions often, because skiing.

[skaredshtles]

I run a coil.

[Beaver]

Drawbacks to bigger
Rotors is that you might not be able to get them hot enough to leave a burn scar on your calf.

[ridinshockgun]

Also, a lot of people ride around with blown out dampers and never check their pressure and can't tell the difference so "noticeable" can vary by rider.

[Dantheman]

The brakes on my commuter are older SLX (M675). This morning on my ride in the rear lever started pulling right to the bar. This is not at all surprising for this generation of Shimano brakes, so when I got home I did a quick lever bleed and figured I'd be set. I did the front while I was at it just for good measure.

The rear lever doesn't pull to the bar anymore but now it has almost no return, totally dead. I thought maybe it got over filled somehow so I pulled the wheel and pads, cleaned the pistons and pushed them back in with the funnel on the lever. Somehow that made it even worse.

The front is functioning perfectly.

Thoughts? Anyone have a rear Shimano brake from this era collecting dust?


edit: Nevermind, turned out to be a simple user error/idiot test. While readjusting the brake position after the bleed it got pushed against the shifter pod and that was making the pivot stick. Adjusted the shifter pod 1-2 mm and it's all good. Yeesh.

[jono]

edit: Nevermind, turned out to be a simple user error/idiot test. While readjusting the brake position after the bleed it got pushed against the shifter pod and that was making the pivot stick. Adjusted the shifter pod 1-2 mm and it's all good. Yeesh.

That's a good one. How long did it take after posting to the thread before the solution showed up? I like to keep my expectations calibrated for when I need this function.

[Dantheman]

That's a good one. How long did it take after posting to the thread before the solution showed up? I like to keep my expectations calibrated for when I need this function.

About 15-20 minutes Googling "Shimano brake lever not returning" and scrolling through old threads on various forums.

[snowaddict91]

About 15-20 minutes Googling "Shimano brake lever not returning" and scrolling through old threads on various forums.

At least you didn't buy any parts.

[Boissal]

Here's a new one for me. I sheared off my derailleur hanger last week on a rock. Replaced it, threw the derailleur back on without any adjustment, went riding. Shifting was fine except going up to the 2nd biggest sprocket which would take up to 4 full pedal strokes and lots of grinding around. Going to the biggest sprocket was a bit better but still hesitant and the shifter push felt hard and short, almost as if the limit screw was in too tight.

Played with the cable tension on the ride to no avail. Got home, checked B-gap at sag, looked OK, tweaked it to look perfect, adjusted limit screw, went riding. No changes. Gave the B screw a half turn in both directions, no difference. Full turn in both direction, no difference. 1.5 fucking turns in both directions, no difference.

Before I strip everything and start from scratch again on the stand, is this symptomatic of a particular problem I'm missing? New hanger is not straight?

The chain is 2 weeks old and the cassette is in good shape still (1100 miles). The derailleur itself doesn't seem to have suffered from the hit that took out the hanger. It was scratched and dinged before and didn't look any worse afterward. The clutch is fine, I cleaned and greased it a couple weeks ago.
Shimano XT drivetrain, 12 speed 10-51 flavor.

[simple]

You made no mention of if the rear derailleur got damaged in breaking the hanger.

[Boissal]

The derailleur itself doesn't seem to have suffered from the hit that took out the hanger. It was scratched and dinged before and didn't look any worse afterward

I guess the part I underlined isn't 100% accurate. The hanger didn't snap because I hit something, it broke while dowhshifting and pedaling hard. It was showing signs of fatigue (read: it was bending real easy) after taking a couple of hard hits in the past but the shifting was perfect right until the moment it broke. That makes me think the derailleur itself is fine and the problem may be a misaligned hanger.

[Dantheman]

strip everything and start from scratch

This is usually the best way to go IME.

[detrusor]

It’s very unlikely the hanger came off under power and there was no damage to the der. The cable housing/end/cable usually takes a beating in this situation as well


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[Boissal]

It’s very unlikely the hanger came off under power and there was no damage to the der. The cable housing/end/cable usually takes a beating in this situation as well

I'll check. I was going 5 mph as I had gone around a hiker and I was on the flat. Shifted down, chain went slack, stopped immediately, the derailleur was just sitting there loose on the chain.

[XXX-er]

Sounds like prior damage and then it breaks during some thing of no consequence,

I think that happens > we realize

not sure why its being problematic after the new Hanger ?

maybe it was adjusted to work while bent and then it doesn't with a new hanger ??

[JPaul]

tl:dr: Are there any good SRAM 2x10 rear derailleur options?

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I also just had a JRA rear derailleur incident I need help with. In my case, shifting under load going uphill, SRAM X9 10-speed rear derailleur hyper-extended forward, and stuck in that position. It is as If I put it in the forward locked position, but the lock is not engaged. It's bound pretty tight, but I am hopeful I can get it unstuck for a bit, but will need replacement ASAP.

Looking online, there seems to be a blind spot in 10-speed SRAM replacement derailleurs. Looks like only GX in MTB range, and possibly Apex1 in road range (not sure about 2x compat). Worse, my daughters only have X4 ders I could steal.

Are there any other options I'm missing? If not, for an XC rig, would the Apex be pref to the GX?