[iCollector]

If you really want to tune your Tower, you can get the tuning kit which will allow you to do some pretty specific types of adjustments. It ain't cheap, but if you are a tinkerer and want to dial it in, that will pretty much handle anything you desire.

I still have to replace my spring to the firm, but I confess - I a little nervous on attacking that yet. I want to arch the videos a few more times.

 

[solitone]

All you need is to measure the height / volume of your air chamber, and then you can calculate these curves out yourself.

Is it really that easy? Is it a simple cylinder?

Do I need to just measure my air chamber's height to get its total volume, and subtract the volume of oil (should be 5 cc in my case) to know the volume of air?

But then what gas compression model should I use, to get pressure increase from volume decrease (i.e. travel)? Boyle's law? It wouldn't be appropriate, though, 'cause on high speed compressions air temperature can't be assumed as constant.

 

[solitone]

If you really want to tune your Tower, you can get the tuning kit which will allow you to do some pretty specific types of adjustments. It ain't cheap, but if you are a tinkerer and want to dial it in, that will pretty much handle anything you desire.

Yes, you're right, I'm aware of that possibility, and it's an exciting option I already explored with my old(er) Minute Expert.

For the time being, though, my focus is finding the correct spring rate for my weight/riding style. Afterwards, I'll try and tune also the shim stack.

 

[ktm520]

Is it really that easy? Is it a simple cylinder?

Do I need to just measure my air chamber's height to get its total volume, and subtract the volume of oil (should be 15 cc in my case) to know the volume of air?

But then what gas compression model should I use, to get pressure increase from volume decrease (i.e. travel)? Boyle's law? It wouldn't be appropriate, though, 'cause on high speed compressions air temperature can't be assumed as constant.

Yes, Yes, and ideal gas law. P1*V1=P2*V2

You don't have to buy the 200$ tuning kit to revalve the ABS. Download the tuning guide from mullen119's thread and go buy shims from your favorite shim supplier. Depending on what you want to do, it should only require buying a few shims @ 2$ a piece.

 

[beanbag]

Oh right, you are supposed to use adiabatic gas compression. That would account for a few extra pounds at full compression. Also don't forget psi gauge vs absolute pressure.

 

[solitone]

Yes, in fact I already have most of needed shims--Manitou CS posted them to me for free !! when I was tuning my Minute Expert.

I'll start with Boyle's.

 

[ric426]

I've been following this thread with great interest and it's got me wondering, is there a noticeable difference in performance and settings once a Tower Pro is "broken in"? The reason I ask is that I've only got about 8 hours on mine and the settings and air pressure I'm using to get the desired results are *way* different than the OP's. Should I get the recommend 20 hours in before I make any significant changes like ride kit, etc.?
I'm 183lbs. ready to ride, using a 100mm QR15 Tower Pro with a 2011 Spec Camber 29. I'm working on setting it up for maximum plushness on the small to medium hits (knowing that I'm trading that for a fair amount of mushiness when pedaling standing) because of my old, arthritic wrists. So far I'm getting the best results at 70 psi, rebound at 1/2, compression damping at 1 click from full open (!), though I'm not getting as much sag as I'd expected. At my weight, I wouldn't think I'd need a medium spring though.
Overall, my settings sound pretty light compared to what's being discussed in this thread, so I'm wondering about the break in period. My main riding area is pretty tame with the biggest drops around 1', but I've yet to notice any bottoming out.

 

[solitone]

I didn't notice any brake-in on mine, even though Manitou say it takes several hours to break it in.

As for your light settings, I also would be using lighter settings if my rides didn't include very steep descents, with rough sections.

Consider that Donn, a guy at 29eronline, weighs like me, but is using a Soft spring with 70 psi, as he commented to the following video of his, so a much lighter setting as well:

My current setting though is what I prefer for heavy trail/all-mountain riding. I'll see what changes are needed when I install the new Medium spring.

It's strange you don't get the desired sag. With 70 psi and the stock firm spring, I have a 25% sag (measured in attack position, though--probably it's a 15-20% on saddle, but I'm lighter than you).

 

[aerius]

Overall, my settings sound pretty light compared to what's being discussed in this thread, so I'm wondering about the break in period. My main riding area is pretty tame with the biggest drops around 1', but I've yet to notice any bottoming out.

I have a Minute Pro which is pretty much the same fork in a 26" wheel version. There is a break in period where the fork gets smoother and stiction goes down or disappears, and that's about it. The settings I used didn't change. Like solitone, I have a lot of super steep and rough sections on my local trails, plus I like to ride aggressively so I run much heavier settings than usual. I'm 150 lbs and run 105psi, 5 clicks from full closed on compression, and 1/8 of a turn from full open on rebound.

 

[beanbag]

FYI I redid my plot with adiabatic gas compression and got about 40 more lbs at full compression. It seems closer to real-world values. So I suggest you do it that way.

 

[solitone]

I hope I'll manage, as soon as I measure the air chamber's height.

Regarding its volume, do I need to take into account also the air pushrod?

I'm not sure, but does this rod lie inside the air chamber? Sorry for the dumb question..

 

[ktm520]

Consider that Donn, a guy at 29eronline, weighs like me, but is using a Soft spring with 70 psi, as he commented to the following video of his, so a much lighter setting as well:

Keep in mind that body mass is not an absolute when determining spring rate. It is merely a starting point. Frame geometry, cockpit, rider height, etc. all play a role in how the weight is distributed between the front and rear wheel.

I hope I'll manage, as soon as I measure the air chamber's height.

Regarding its volume, do I need to take into account also the air pushrod?

I'm not sure, but does this rod lie inside the air chamber? Sorry for the dumb question..

No, the pushrod is outside of the air chamber.

 

[solitone]

No, the pushrod is outside of the air chamber.

Ok, thanks, it's simple then!

EDIT: Here's a nice picture from the Clydesdales thread showing this:

 

[solitone]

Standard volume of semi-bath oil in the air chamber is only 5 cc, as written in 2012 Service Manual, isn't it?

EDIT: yes, it is. I've read it in several other places too.

 

[ric426]

I think I just took about 1/2 pound of weight out of my Tower Pro. I opened it up for the first time tonight to try a different coil spring and couldn't believe how much grease was packed in there. I think they must be having a contest at the factory to see who can use up the most grease in the fewest forks and I found the winner. The spring and stanchion were pretty much filled with grease and it has already mixed with the semi-bath oil and turned it into a murky sludge that I need to clean out. What's the best way to clean out the lower part of the stanchion and the inside of the casting before I reassemble it? I don't want to use any solvents that may cause problems with the plastic and rubber parts. I've cleaned some of the small parts with isopropyl alcohol but haven't sprayed any in the big parts yet.

 

[beanbag]

Just wipe it out with a paper towel, and expect some of the remnant grease to mix with your next batch of oil.

 

[jeffw-13]

I really have nothing to add to this thread except that it scratches my OCD where it itches the most. Thanks to all of you :thumbsup:

 

[ktm520]

Got my new Tower Pro 120 mounted on the SB95 and got a short ride over the weekend. I'm 165lb, 6'2". Initial setup (firm spring) was 60psi which netted 20% sag. Not what I was hoping for as Manitou suggested the firm spring. I typically prefer closer to 25%. Set the lsc wide open and left it there. Lsr at 3/4 out.

Compared to the Reba XX, this fork has amazing action. No spiking on square edge and stayed up in the stroke, except for heavy braking. As I feared, with only 60psi, the dive wasn't terrible, but too much for my taste. I bumped the air up to 70 and although it fixed the dive, plushness took a big hit. I've got a med spring on order. I guess I'm not surprised that I need a softer spring as my body position and cockpit setup favors more rear weight bias. For reference, I was only running 70psi in the Reba. The SB also has a fairly slack front end.

I didn't really play with the lsc at all, but the stock trail stack definitely had too much platform for me when closed. I pulled one of the platform shims (19 x .2).

Only complaint is the lsr adjuster. Why did they go with such a small adjustment range and no detents??? I will get over it, but it's nice to be able to reach down and dial a few clicks.

 

[aerius]

Compared to the Reba XX, this fork has amazing action. No spiking on square edge and stayed up in the stroke, except for heavy braking. As I feared, with only 60psi, the dive wasn't terrible, but too much for my taste. I bumped the air up to 70 and although it fixed the dive, plushness took a big hit.

Try running 60-65psi with the compression knob 4-5 clicks from full open. The fork stays quite plush until you get to 6 clicks, and 4-5 clicks should be enough to help with brake dive issues.

 

[solitone]

In any case, I made some plots for MY fork. I guessed on the spring rates. Also, the final force came out to be a little too low so I am missing various air pockets trapped in other parts of the fork.

I finally managed to take a measurement of my Tower Pro air chamber. As I wrote here, its height is 107 mm.

Taking the air cap shape and the oil volume (5 cc) into account, I end up with an effective air height of 105 mm.

I started by plotting a spring curve for the XX-Firm (Clydesdales) spring, with a pressure of 130 psi. We have real data for this curve (purple line in the following graph), so it's possible to compare my results with real data.

I didn't remove my stock coil spring, so I didn't measure it. I assumed it compresses 60 mm before it bottoms out. Here is the curve I get (continuous line is my curve, dashed line is Manitou's):

As you see, I get significantly higher forces in the second half of travel. Please consider I did not even use adiabatic compression law here, but isothermal law, because otherwise I would have got even higher results.

Looking at Manitou's curve, it seems coil spring compresses much more than 60 mm. I tried with 95 mm, and I got a better fit:

In the last portion of travel, though, I still got an excessive rise in force.

So I thought I made some error when measuring air chamber height. I thought the fork was fully extended, but perhaps the piston was not at its lowest position? Maybe the coil spring was pushing it up and my measurement came short?

The point is I get a better fit if I suppose the air chamber is taller. With a 119 mm air chamber I get this curve:

If I use a height of 140 mm ( :eekster: possible??), as well as adiabatic law, I get the best fit:

which also fits quite well the 90 psi curve:

So, my question now is--is it possible that my measurement (105 mm) was sooo wrong? A height of 140 mm does not seem reasonable to me.

@beanbag how did you measured your chamber height? How tall is it for your Minute Pro?