Rockshox Reba SL dual air.......general tech questions.

Clockworkmark31

Good evening everyone....

I have got some Rockshox Reba SL dual air 100mm on my Specialized Hardrock Comp.

I am going to give them a lowerleg service this month as I can't seem to get the sag setting correct.

I am a heavier rider 98kg's with riding kit and running the rebas at 135psi in + and - chambers. Always seem to bottom them out just going of kerbs or use all of the travel. If I run more PSI they seem to become too stiff and I lose small bump control. So thought to give them a light service.

Questions are, should I be running equal pressure in positive and negative?

Also would I be able to convert them to 120mm travel? If I can would there be any advantage to doing this or any disadvantages? And how would I go about doing this?

If I could go 120mm, would I need more oil in the forks and higher air pressure, or does this remain unchanged?

And the last question, would the forks be realistically strong enough to handle a Shimano RT86 203mm rotor or will this be too large? I currently have the 180mm version on.

rockmonkeysc

A lower service isn't going to fix your problem. It sounds like either your compression damper or air spring has problems. I think I used to run 10psi more positive than negative air.
I wouldn't go more than 100mm on a Hardrock.
You can fit a 203 rotor but why would you want to?

Antm81

Not sure what difference a lower leg service will make, the oil in the lowers is for lubing the stanchions. Servicing the damper may help though.

As for increasing the travel, hopefully you'll have an spacer on the air shaft which can be removed although this isn't always the case as some will have a shaft for 100mm of travel not 120mm. Oil amounts would be unchanged and air pressure would be whatever is needed to get the sag you want, the pressures on the fork are purely a guide.

I can't see any reason why they couldn't handle a 203mm rotor.

Clockworkmark31

Maybe I used bottoming out incorrectly, eg, if I go down a half foot kerb I use around 70% or travel, it seems excessive to me. Or is this the normal? I have no air leaks or oil leaks or anything, everything seems to function. I do get a 25%sag when I in a upright leaning to the bars position but not when sat on the seat.

I believe I am measuring this correct?

Any reasons not to go more than 100mm?

203 rotor, I use the bike to commute daily and then weekend warrior. 180 with the XT brakes is very good don't get me wrong. Sometimes on the work ride you get drivers not paying attention and I can stop in time, think it is more of a confidence thing of having more braking force.

mcnultycop

I'm a bit heavier than the OP and run a 203mm rotor with no issues. It is overkill though, I only put it on because that was what I had knocking about when building the bike.

I set the sag on the +ve chamber to 25%. I then pump up the -ve chamber (slowly) just until the forks start to suck down and note the PSI, I then let a bit of air out then pump it back up to just less than this pressure. This works well for me.

I used to experiment with the negative, say 5 or 10 PSI less or more than I put in the +ve, but could never get the fork behaving right. The curren method is spot on.

Clockworkmark31

Mcnultycop, think I will try your method for sag.

I normally just set both pressure to the same and see what sag I have and adjust them both equally. Never seen the fork suck down.

Maybe my problem lies in setting the fork up and it is incorrectly setup.

Think I will stick to 180mm rotor then, I have locked it up in wet a few times and clenched buttocks as the front washed away haha.

rockmonkeysc

Forget about what happens whel you ride off a kerb or push the fork down. Go out and ride some trails. As long as you're using nearly full travel it's all good.
203 rotors don't really give much more power than 180 but the initial bite is sharper meaning less control and more likely to lock. Good for heat dispersal.
I use them on my downhill race bike but wouldn't use them for anything else. I certainly wouldn't want them on my commuting bike, far too sharp for wet roads.

Clockworkmark31

Rockmonley, thanks for your input.

When I ride trails I don't have a problem. Think I might have overcomplicated the situation myself.

Think I have got the instal settings correct now, after some experimenting.

160V+psi and 150-psi gives me 30% sag in an upright position. Set sag using positive then inflated negative until I could just measure it sucking 2mm.

Think I have set the sag correctly now. Will have a ride later on today.

I have read so many things on setting sag and have confused myself from the basics.

I take on board 203mm rotor will be overkill so will stick with 180mm. I have ample stopping power now with one finger, maybe I am just trying to be greedy :P.

Will feed back tomorrow after a ride, think looking at this, it has been an initial setup problem.

God help me with the rebound haha

Clockworkmark31

This bike is like my first love, even though I have just received a Trek superfly 6 2014 29er, and I haven't tried a 29er ha.

Then all the parts that I replaced on this bike, I can build another one, just need a frame.....hmmmmm spesh m5 frame or spesh fsr frame.

Damn this expensive hobby, from one bike to three bikes.

Clockworkmark31

Also with regards to 100mm and 120mm on the spesh, does anyone have any more input?

rockmonkeysc

I had my old hardrock built with a 100mm fork. It was a nice set up for the frame. I think any more might make the bb a bit high and cause the bike to flop in to turns and loose some stability.
Ot could be worth trying, you can always drop them back to 100mm.

Clockworkmark31

Hi, just a quick update,

I made a mistake, don't know how. But it is a rockhopper comp and not hardrock.

So I don't know if this would influence 120travel or 100travel.

Finally got a quick ride today, and 160 +psi and 150-psi seems a pretty good starting point.

If I want to make it softer, am I right in thinking, take 5-10psi out on both + and -?

And next is rebound, where is a good place to start?

When I turn I can't feel it click, but it certainly works slowing rebound.

Mainly ride XC fast flowing and commute, no big drops, so I think somewhere in the middle? I don't really want to feel the small bumps as this is mostly what I get.

Not sure if air pressure or rebound cures small bump or is it both?

mcnultycop

Clockworkmark31 wrote:

If I want to make it softer, am I right in thinking, take 5-10psi out on both + and -?

I'd empty the -ve, then let a bit out of the + ve then redo the -ve as I described above.

Clockworkmark31

Does it make a difference releasing pressure from -ve first?

Actually just re-read, makes sense.

Can you offer any input on rebound and air pressure for small bump control?

From what I understand, the air pressure controls how much the fork compresses and the rebound dictates how fast it returns to its original state.

Which one do you adjust for fast flowing singletrack/fire road.

Seems like adjusting either one would make for a smoother ride, just wondering what is the preferred way?

I haven't touched suspension settings before and think I understand the basics. But it seems like wither one could solve the problem.

How does this sound, drop the pressure in +ve by 10psi then repeat process for -ve and have rebound on full hare.

In theory it sounds like it should be softer and fast enough to return?

But then I lose the preferred "sag", this is where I get confused.

Thankyou for your patience so far

rockmonkeysc

Air pressures won't make any difference to small bump sensitivity, thats in the compression damper and floodgate control. If you have a floodgate knob then back it off to give more sensitivity but balance it against pedal bob.
Rebound damping needs to be fast enough to return the fork travel between bumps but not so fast that it kicks back. As a starting point, set it so that when you compress the fork as far as you can it returns quickly but controlled. I always find a bumpy corner and ride it fast several times making adjustments untill I find the fastest setting where it doesn't kick back after bumps and cause a loss of grip.

Clockworkmark31

Think we may be getting somewhere, I do have floodgate and I thought it was only to do with when the forks were locked out and you hit a big bump.

I have never touched the floodgate, I am happy(ish) with the how the fork feels at the moment, maybe I need to adjust rebound and the floodgate to try and tune it in more.

Might have rebound too high as I can feel it skipping bumps at times.

Will leave it for the weekend until I ride some more. Not going to adjust PSI as I will use that as a base. And try with the rebound halfway and try back the floodgate off and try experimenting with the flodgate.

I will experiment at the weekend on a known trail, and keep hitting it adjusting one thing at once, ie, rebound full or min, and see what I feel, same with the floodgate and see if I can find a happy medium.

Thanks so far

The Northern Monkey

Rockmonkey - Yes it will. And it does.

Takes some time to fine tune, but RS dual airs can be supeb forks (unlike the solo airs which cant be fine tuned and a pretty dire).

Supple and better small bump response = more air in the -ve than +ve.
You lose a bit of travel as the fork gets sucked down slightly, but as I said its all about fine tuning.

viewtopic.php?f=40073&t=12629675

Page 12 on the link for info.

I have Reba dual airs and they are outstanding. I had the solo airs and they were crap in comparison.

Clockworkmark31

Northern monkey thanks, will have a read over this.

Won't be making any adjustments now until the weekend when I ride.

When I first bought them they felt fantastic in every way.

But then I got concerned with or caught up with sag and never noted any original settings and changed everything (newbie mistake maybe).

Now I think I have the sag correct for my weight geared up.

I do understand less air pressure makes them easier to compress and the rebound counteracts this forcing them back down quicker or slower.

Think I need to find a good base setting first. For my weight rockshox say 135+ but I get too much sag.

I have read and heard before about more air in -ve gives a more supple ride.

I just need a good base to work from. My rides are fast when I get off road and have no jumps or drops. its just dips and tree roots I would say firetrack rides. Hard gravel that is not too bumpy, as I stand now the forks skit over them bumps or it feels like I have rigid forks.

If I lower pressure it cures it, but then I loose correct sag.

Fully kitted I am 98kgs, the fork is 100mm. It is dual air, I have rebound and floodgate adjustment and lockout lever. It all seems to work, I just cant tune it for me.

I am sure I have setup problems.

With 160 +ve and 150-ve I don't dive under braking. So one of the pressures must be correct and I a good or ideal sag rate.

So all that is left is rebound and floodgate to adjust, then it should just be fine tuning.

Sorry for ranting on, late and tired and just want to write how it feels so someone can understand.

The Northern Monkey

Having less air in the negative chamber than the positive chamber will make the fork a lot firmer and harsher.
If you want a plusher ride over the bumps, put a tad more air in the -ve than the +ve.
Small differences in pressure make big differences on the trail.

So.
Set your sag with the same air setting in +ve and -ve.
Add 5 psi to the -ve to increase small bump sensitivity.
Eg 160+ve and 165-ve

I have a lot less pressure in mine than the book levels. Ignore them and use whatever works for you.

Clockworkmark31

Will give it a try at the weekend, I have heard and read before that more -ve gives more small bump control.

Am I right in thinking the floodgate is just for when the forks are locked out and you hit a bump? Or does it play a bigger role?

Clockworkmark31

Think I understand the theory behind more -ve, you have more air pressure pulling the fork down and thus eliminating the fork to compress more so you get better small bump control. But where does rebound come in to it?

It sounds like both could cancel each other or am I missing something really obvious?

The Northern Monkey

Correct, threshold is only for the lock out. It determines how big a bump is required to allow full travel as riding bumps with the lock out on can potentially damage the fork.

The Northern Monkey

Rebound is how quickly the fork returns to full travel.
Set your air 1st, then rebound.

A good starting point for rebound is to habe is so when you compress the fork and lift the front wheel off the ground, the fork *rebounds* back to full travel just before the wheel leaves tbe ground.

Clockworkmark31

Well thanks for the help guys.

Think I have by fork pretty dialed in now.

Seems to be subtle and good small bump control.

Gone with these settings +ve 155psi -ve 170psi and rebound 3/4 toward the hare and get between 30 to 35% sag depending on what gear I have on.

Guessing if I go down to 20 to 25% sag the fork will firm up quite abit?

coulddobetter

On my dual air sid it's markedly different running 25 or 30 percent. At 25 percent the fork never reaches top out. Even a couple of psi either way makes a big difference.

The Northern Monkey

Not necessarily, you should be able to run 20% sag and have the fork supple.

However, I also run my reba at about 30% sag as the compression does ramp up quite progressively as you use more travel.

Tbh, ignore the book figured and just get it to a point that works for you!
As long as at some point you use all the travel but it isnt constantly topping out and it feels good....

Clockworkmark31

Will try and set sag for 20% tomorrow.

But think I will be at 170psi +ve and 190psi -ve.

Can the forks handle this pressure? And will such pressure loose the small bump control.

I noticed under braking I will use around 70% of travel and not bottom out, 70% of travel whilst braking seems lots.

But they feel good riding.

Does it sound like setup problems a service is needed?

Knowing the feel of these forks I think 20% sag will feel stiff, could this be an indicator to service them?

One last question, if you increase the sag do you loose travel? ie, 20% sag you get 80mm of travel and 35% you get 65mm travel or does the travel stay consistent no matter what sag you run?

Clockworkmark31

Stupid question maybe.......should i be sat on the seat measuring sag or stood lent over the front?

Have read different things on this and maybe this is where my issues are coming from......

When I set the sag I have pedals at 3-9o'clock position stand on them and lean to the front.

The Northern Monkey

Tbh... just ride the bike.

Took me a month or so of riding well known trails to get the fork dialled.

Clockworkmark31

I do 80+ miles a week on the bike so I do ride it.

But I can't find a happy medium with the front end, either too stiff or too soft. Either I am doing something wrong or I need to service them.

I have owned them for 5 months after buying them from someone who had done four rides on them in total.

Think I will just buy a complete seal kit and redrum etc and service them.

If I have problems after then I will know I am to blame in setting them up.

The Northern Monkey

Have you tried only a touch more pressure in the negative?
Should only need 5psi difference, 20psi is way too much and is likely to make the fork quite soft on the initial stroke.