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Tuning a Tower Pro

41K views 364 replies 36 participants last post by  Venturewest  
#1 · (Edited)
Hi all,

I've got a Tower Pro 120 mm, with QR15 and tapered steerer. I've been riding it for some months without thinking too much on adjustments. I had it mounted on a new bike, and I had to get used to many different things..

I weigh around 155 lbs, so I started inflating it at 60 psi. I felt it much soft, so I added 10 extra psi after few weeks. I mainly rode it with this setting, but now and then I noticed some dive when braking, so I rose air pressure to 180 psi. It felt good on the trail, but I wanted to follow a more rigorous process to try and find the best tuning.

I've read a lot lately. The topic on clydesdales by TrailMaker has been very inspirational, and I'm re-reading the topic on abs+ tuning by mullen119. As @mullen119 underlines, the most important aspect in the fork's tuning is choosing the right spring.

I don't want to be under- or oversprung, and yesterday I did several test runs, inflating the Tower Pro's air spring at different air pressures. I started at 60 psi, and then I repeated the same trail at 70, 80, and 90 psi.

EDIT--Absolute+ LSC set to MAX-4. Rebound damping half way through--

The main part of the test was a steep descent with several big rough obstacles--rock gardens, drops, roots...

At 60 psi the ride was harsh at times on big hits (! likely because I have only 50 mm of travel left, because of huge brake dive?), and brake dive noticeable. Small bump compliance was excellent though.

At 90 psi it felt bumpy and again harsh on big hits. I didn't exploit full travel, but only 80 mm.

The best feeling was accomplished with 70 and 80 psi. Small bump compliance was better with 70. With 80 I felt more control. I used 110 and 100 mm of travel respectively. On the trail my choice was 70.

I shot some videos of the descent, to have something more objective than just riding impressions, and see how the fork responded with different pressures. Surprisingly, when I watch the videos I feel the better response is with 80 psi. With 70 it seems the fork is constantly too compressed when I brake (it's steep and I brake way too much!)

Here's the test video for the fork with 70 psi of air:


What do you think? I'm interested in your opinion, cause I don't have much experience in what I should actually expect, and the exact interpretation of terms like over and under sprung is not crystal clear to me. It's like the first times you taste wine--what is supposed to be good wine and what bad?

I believe you shouldn't waste an awful amount of travel just for brake dive. But is the dive in the above vid too much indeed?

I'll link the video for the 80 psi test in a following post.
 
#273 ·
Gas spring force

Solitone,
Nice work. There seem to be two extremes for gas force:
  • Boyle's law isothermal compression PV= constant
  • Adiabatic compression where the gas heats up PV^1.4= constant



If the fork compresses slowly the gas loses all of its heat to the fork body and you get Boyle's law constant temperature compression. Compress the fork quickly and the gas does not have enough time to lose any heat and you get adiabatic compression.

At fork velocities anywhere in between the gas loses some of it's compression heat to the fork body and you end up with all kinds of wacky hysteresis effects where the gas spring force on compression does not match up with the gas force on rebound.

There is a bunch of motorcycle fork dyno data showing the effect. Gas force in rebound is lower due to heat loss and the difference changes with stroke velocity.



There is also a spreadsheet with that dyno data computing heat loss from the gas and the difference between compression and rebound force. The dashed line is the spreadsheet calc.

Be interesting to see if heat loss gets your calculation to lay over and match up with the fork data you have.
 
#276 ·
Solitone,
Nice work. There seem to be two extremes for gas force:
  • Boyle's law isothermal compression PV= constant
  • Adiabatic compression where the gas heats up PV^1.4= constant


  • Indeed. The exponent though gets modified by people modelling engine compression to values of around 1.3-1.35. I haven't bothered modelling the difference in this case but I have previously with turbocharger expansion ratios.

    Can anyone tell me is a 140mm Tower Pro can be lowered? to 130 or even 120mm?
    Mars spring forks can normally be reduced by shortening the compression rod above the coil spring and adding the same length to the topout bumpers.
    You don't need to give up just because there was no factory option.
 
#280 ·
We had this same discussion a year ago. Matching Manitou's plots isn't important. The key is relative changes. I used both isothermal and adiabatic in my model, and settled on isothermal, just because it's easier to build the spreadsheet.

I don't think Manitou's charts are calculated, and if they were done on a dyno, this means the low volume air cavities in the lowers also add to the spring force. If the damper was present in the fork, you'd also have to include the spring force generated by the damper.

Solitone, do you have a scale laying around that you could use to measure front weight bias, roughly? That is one stiff spring you are running. I'm guessing your front bias is considerable higher than mine even though your body mass is lower. A smaller frame with a short front center being the culprit. Perfect time to reiterate that body mass is a poor rule for comparing spring setup.
 
#281 ·
Solitone, do you have a scale laying around that you could use to measure front weight bias, roughly? That is one stiff spring you are running. I'm guessing your front bias is considerable higher than mine even though your body mass is lower. A smaller frame with a short front center being the culprit. Perfect time to reiterate that body mass is a poor rule for comparing spring setup.
Yes ktm, you're perfectly right. My riding position is pretty front biased:



This became more and more noticeable in the last year, and this explains why I raised pressure from 85-90 to current 100psi.

I'll try to get a figure with a scale to compare.
 
#282 ·
Pulled up the 'ole spring model today out of curosity after reading Solitone's setup and decided to do some more testing. I did most of my spring setup in the middle of the winter and the trails have just now gotten hard and fast again. Fork has been slightly soft mid to bottom when I push it hard.

Reduced volume 5cc and started at my usual 85psi of air. Honestly didn't notice much change. Then started adding 5psi of air. Made it all the way up to 100psi before the end of the ride, liking each addition. Plan on increasing air more on next ride and might even further reduce volume.

Fork had very good support, didn't wallow in fast rolling g-outs, didn't really notice much as far as bottoming, only used maybe 5mm less travel on same drops, and small bump only got slightly harsher. Rode very good for a firmer setup.
 
#284 ·
Have done a lot testing in the last couple months and have made big improvements. First I ended up switching to a med coil, which gave up a little on small bump, but the whole curve is better. Good mid/bottom support. Not 100% sure, but I think I was bumping up against that limit of too much air with the soft coil and it was causing some midstroke harshness. This dropped the sag from 23% to 18%, for reference.

Second, I've been running too much hsc. I was to focused on getting the spring dialed. I've been softening the stack and running more lsc for better support and reduced spiking. This is all elementary, but sometimes it's takes a little testing to realize what you are missing. Planning to further soften the stack. Halfway curious to see how the soft spring would now since I've reduced the hsc. Currently running the following setup:

stack:
17 x .15
17 x .2

lsc: 4-5 out
reb: ~7%
spring: med coil, 98psi, 5cc volume reduction

At some point, I still plan to revalve the reb but it's working pretty well. Like I said, you don't know what you could be missing out on until you try it.

Just got back from a trip to Moab/Colorado. Rode Whole Enchilada, Steamboat, and Winter Park. Fork worked great. A little harsh on high speed chatter/braking bumps, but it's a 5" fork.
 
#285 ·
I weight 95 kg (210 lbs). I ride flat XC tracks with lots of roots, some trenches and bumps, small descents with some small drops (perhaps one feet max). I have 100mm Tower Pro with firm spring and trail stack on damper. Weight distribution between front and rear is 32%/68%. I run it at 95psi with 5cc of oil in air chamber. Compression dial is now 6 clicks from MAX - i.e. quite open. Tried different rebound settings.

Fork does not bottom and the mid-stroke support is also good. But I'm looking for the missing plushness when going over the roots. Also, when going over larger obstacles, front tends to bounce too much.

Can you give me some advice where to start tuning the fork?
 
#288 ·
I weight 95 kg (210 lbs). I ride flat XC tracks with lots of roots, some trenches and bumps, small descents with some small drops (perhaps one feet max). I have 100mm Tower Pro with firm spring and trail stack on damper. Weight distribution between front and rear is 32%/68%. I run it at 95psi with 5cc of oil in air chamber. Compression dial is now 6 clicks from MAX - i.e. quite open. Tried different rebound settings.

Fork does not bottom and the mid-stroke support is also good. But I'm looking for the missing plushness when going over the roots. Also, when going over larger obstacles, front tends to bounce too much.

Can you give me some advice where to start tuning the fork?
There isn't a one step answer. First I would try lowering the air. Keep in mind it is very sensitive, 2psi is a small change and 5psi is a large change. But, based on my setup, I think you are already on the soft side for the spring. Air pressure and air volume control the majority of mid and bottoming support. As you add mid support, it can also increase harshness on square edge. A med spring can help on small bump, but it won't have much effect on square edge spiking. That is more hsc.

The best way to get what you seek is with a revalve. A straight 17mm stack (linear per manitou's guide) will provide the best trail junk eating action. This is what I run. There are two setups you can try without needing to buy any shims. Here's your stock stack:

17 x .2
19 x .2
19 x .2

First try removing one of the 19 x .2 shims. This will reduce spiking on square edge (bigger roots/rocks at speed) but will still have some level of platform (pedalling) damping. Second, remove both 19 x .2 shims. This will have the least amount of hsc and you will have to crank in the lsc. This will be your plushest setup and you may also find yourself adding more spring. Running one large shim (19mm) is the opposite of what you need. These two stacks will give you an idea of what you like/need and you can go from there.

There is a ton of info on revalving the ABS+ damper in mullen's thread.
http://forums.mtbr.com/shocks-suspension/how-guide-reshim-your-abs-hsc-shim-stack-687754.html
 
#287 ·
Haven't read the whole thread but something i noticed when trialling ride kits is the med kit uses a longer compression rod[ from memory about 5 to 8mm] .Along with the softer spring gives a more progressive set up. Any more than 85 psi and there's a definate two stage feel two the spring curve. I needed to add at least 5ml oil above the air piston on firm kit to get simialr bottom out resistance to the med kit .
From memory ,I think he is back to running firm kit,10ml of oil above the piston, about 85 to 95 psi and only one large comp shim. I suggested he should try removing all the comp shims to see if the piston porting is up to the oil flow. Much better now but still still not as good as my modified 2011 F120 on the high speed hits[ Many 32 ml forks aren't].Med spring is good set up for bike packing or conditions with wet tree roots and where you need max traction from a soft set up. Other than that it gets overwhelmed far to easy and the two stage feel at high air pressures is weird and inconsistant when pushing it hard.. Needing higher air pressures for support it only gives minimal, if any reduction in bar feedback on high speed hits over the firm kit at lower pressures.
 
#289 ·
From memory ,I think he is back to running firm kit,10ml of oil above the piston, about 85 to 95 psi and only one large comp shim. I suggested he should try removing all the comp shims to see if the piston porting is up to the oil flow. Much better now but still still not as good as my modified 2011 F120 on the high speed hits[ Many 32 ml forks aren't]
Running one large shim is the oppisite of what he needs. Great for a buff xc course as it would have a ton of platform damping and a harsh ride in anything remotely rough. The piston flows plenty of oil.
 
#292 ·
I thought I would share my experience with the Tower Pro.
Bike: Yelli Screamy.
Me: 190lbs
Fork: 140mm TP with firm spring, 130psi, 3/4 from full fast rebound, low speed compression at MAX-5, only the speed shim(17.5mm X 0.2mm) is left, 10cc of oil, sag is 20%

I experimented with air pressure first, going very high, down to very low to see what each felt like. The fork felt very mushy in the midrange but plush on the small bumps with a great bottom out resistance when at MAX-1. I had a Tower Expert before the Pro and a simple spring swap made all the difference in the world. So I made up my mind and ordered a extra firm spring from the LBS. It still did not feel right. Small bump compliance was hindered and mid range did not feel any better. Figured I would just
deal with it.

Couple of things to note:
-My background is MX racing so my take on suspension may be a little different than the hardcore cyclist
-I never experienced the "spiking" no matter what air pressure I ran
-I read that you should be standing in "attack" position to measure sag, this does not work. My sag only changed when in a seated position
-20% sag was my sweet spot, anymore and more travel was being used than I liked

Couple months ago I got the urge to do some tuning and started reading these Tower Pro tuning threads and it was like a lightbulb came on.

I decided to start over with the Firm spring and go from there. After reading the article in Decline, I decided to follow their lead as a starting point for my shim stack. I increased pressure till my mid range was firm enough to live with then proceeded to remove a preload shim. This felt much better. Somewhere along the way I added oil to reach 10cc's. This helped with the bottom resistance at lower LSC settings. Finally I decided to remove the last preload shim just recently...WOW!! I couldn't believe the difference it made!! Roots, rocks and other trail obstacles disappeared! It was like a brand new fork. Why does Manitou not send the fork from the factory with this setup? or at the very least, just one preload shim. I understand what the preload does but to me its not worth it to give up a smooth ride just to have a more efficient pedaling platform.

Bottom Line: Remove all your platform shims if you want a smooth ride. Its not hard to do at all!
 
#294 ·
evan9r,
Right on man. I'm running a similar setup and my fork is working better than ever. I've softened the stack since my last post and increased air.

Med spring
107-110 psi
5cc volume spacer
Stack: 17 x .2 x1
LSC 3-4
Reb 10%

I went as soft as 17x.15 x2. This ate up anything in its path but was a little soft on low/mid speed comp.

I was going to try one of the softer trail stacks but after studying the dyno curves, most of them have considerably more damping than the straight stack I'm running.
 
#295 ·
I agree with evan9r, that the stock trailstack has way too much preload to be superplush, but it is probably done to cater to the Xc crowd that wants a hard lock out for climbing.
I currently run the following stack:
17x.2, 13x.1, 13x.1, 19x.2
It is a stiff stack to provide some high speed control and bottom out support. At the same time I have my spring nice and linear with the firm spring and 100 psi of air pressure.
 
#296 ·
Question to all having some experience with suspension.

I’m riding now SIX XX 120mm.
I must admit that on my Anthem 29 it’s very non-linear.
My 176lbs requires only 70PSI to work on small and medium bumps (mu terraing is mostly flat with many many roots).
As long as I read this is how RS behave, hard to reach initial compression, but with lowering the pressure it becomes too plushy.
Dedicated for racing where You need almost rigid feel with big-bumps catching – and this is how it behave, in mountains there is no problem to use all 120mm but in my natural surrounding it just stay firm.

So I need something more comfy, more trip-friendly, definitely catching those small roots and saving my wrists.
I saw many of You loved in Manitou Tover/Marvel – do You think it’s a good option, if Yes which of them?
 
#298 ·
Question to all having some experience with suspension.

I'm riding now SIX XX 120mm.
I must admit that on my Anthem 29 it's very non-linear.
My 176lbs requires only 70PSI to work on small and medium bumps (mu terraing is mostly flat with many many roots).
As long as I read this is how RS behave, hard to reach initial compression, but with lowering the pressure it becomes too plushy.
Dedicated for racing where You need almost rigid feel with big-bumps catching - and this is how it behave, in mountains there is no problem to use all 120mm but in my natural surrounding it just stay firm.

So I need something more comfy, more trip-friendly, definitely catching those small roots and saving my wrists.
I saw many of You loved in Manitou Tover/Marvel - do You think it's a good option, if Yes which of them?
I have no experience wit the SID but I have with the Revelation. All Rs forks are very reliant on the air spring as a major part of the ride feel. I could almost guarantee you could improve the ride for your situation[ flat ground trail speed over tree roots] by making the fork more progressive. What you describe is the nature of a linear fork[ not progressive] tuned for xc racing. If you make it more progressive and lower the air pressure a bit it willl be much more active at the start of it's travel over tree roots but not bottom out on the bigger stuff. With the SID you can't add oil above the air piston but you can add some elastomer from an old elastomer fork in to the air chamber above the piston. You can experiment by adding extra grease first but this will eventually work it's way past the air seals. I'n not sure what the tokens are made of in a PIke . If they are soft plastic or elastomer , then they will be fine to cut down and use.
 
#300 ·
KUdos for Rockshox for following up with retofit kits like tokens and debonair cans.
Kit part # is 11.4018.032.002.

The SId would have to be pretty bad in std guise as I don't remember the Tower being particularly good on slow tree roots.Dual air 130 Rev was much better. From memor,y swapping to med spring it was much better if you weren't going to piush the fork hard..

Can't really think of any other 120 fork to recommend though. I can tune my earlier Fox forks to be good on tree roots but the later CTD stuff has firm lsc so isn't good at slow speeds over tree roots.

Dual air reba would be simialr to the Rev so could be a contender. Not sure what the solo air characteristics are like in comparison?
 
#303 ·
The SID would have to be pretty bad in std guise as I don't remember the Tower being particularly good on slow tree roots.Dual air 130 Rev was much better. From memor,y swapping to med spring it was much better if you weren't going to piush the fork hard..
With the medium spring and the platform shim removed the Manitou is plush.
The dual air forks were good, but the solo airs cannot be setup to be usable going over rocks and roots at slow speed while climbing. My high volume front tire at low psi acts as a cushion.
 
#301 ·
I guess all the good stuff and unintelligible stuff has been said about tuning a Tower. Now we're onto RS and the occasional Fox reference.

Anyone here running one in the stock configuration, oil weight, shim stack, spring and all? I am with a 140mm with a x-firm spring (thanks to a warranty rebuild of the lower) set at the recommended pressure for my weight of 215lbs. This thing is nice. Can't believe the performance for the money.
 
#302 ·
I guess all the good stuff and unintelligible stuff has been said about tuning a Tower. Now we're onto RS and the occasional Fox reference.

Anyone here running one in the stock configuration, oil weight, shim stack, spring and all? I am with a 140mm with a x-firm spring (thanks to a warranty rebuild of the lower) set at the recommended pressure for my weight of 215lbs. This thing is nice. Can't believe the performance for the money.
I have been running a Tower 120mm for two years. Mostly happy with it out of the box, running the compression damper 2 clicks from full open. But it did seem something was lacking.

This spring Even Plews at Ridge Cyclesport removed one shim from the stack (a 10 minute job). No other changes.
Now I run the damper 2 clicks from full closed.
No wallow on the smoother sections, and it remains supple with full travel in the rough with better control.
 
#305 ·
Running a larger volume tire will help with smaller 1"-2" bumps but it is not the solution to your problem. Too little air pressure and you will be getting rim strikes. Also you cant change the rebound rate of your tire.

I would read up on valving for your fork. Or buy a Manitou and set it up like many have on here. Once the preload shims are removed, they are super plush. And unless you are a pure XC racer, I see no need for the fork to have preload shims. Even then, Ill take the cushy, non fatiguing ride over a slight decrease in platform/pedal efficiency any day of the week.

Glide - Yes, I rode my 140mm stock for a little while before making changes..why do you ask?

gvs_nz - You did not try the Tower without the preload shims, otherwise you would have been amazed at the difference in the ride.
 
#306 ·
I would read up on valving for your fork. Or buy a Manitou and set it up like many have on here. Once the preload shims are removed, they are super plush. And unless you are a pure XC racer, I see no need for the fork to have preload shims. Even then, Ill take the cushy, non fatiguing ride over a slight decrease in platform/pedal efficiency any day of the week.
Apology for silly questions :
1. What You understand by valving (have now SID XX 120mm)
2. "Removing poreloaded shims" - assume it all is about Tower tunning, not RS ?
 
#307 ·
The RS dampers are the problem, not the spring, and the XX is the worst of the bunch. The don't flow enough oil on high speed equal spiking on square edge. This also affects small bump.

I agree, the stock Manitou tune is over damped, but so are most forks. I think this is part of why some fast riders don't like Mars spring. I wasn't completely satisfied until I finally pulled a bunch of hsc out of the damper, cranked in the lsc, and was able to go up on air for the support it was missing.
 
#308 ·
From what i can gather it's not HSC that's the problem?I think he's after seated flat terrain tree root compliance i.e. low LSC.. I think the the Tower with a med spring is a good option but i'm pretty sure a more progressive tune on the Sid should almost be as good. That initial movement of the Mars spring does give slight bar feed back. That's why i wouldn't rate it top of the list in small bump compliance.It's got great mid range compliance . So up the speed a little and it's in the zone.
 
#310 ·
I wasn't really commenting specifically to the dude that jumped in with RS problems. But, tree roots even at slow speeds can easily dip into the mid speed range which is easy overwhelmed in a RS damper. Besides, if you tune the fork specifically for this condition, slow seated roots, it's going to be too soft everywhere else.

I don't follow your comment about the Mars spring providing too much bar feedback (spiking?). My experience is quite the opposite and a big reason why the Mars has better small bump than a standard air setup. An air spring has too much friction to respond to dynamic loads compared to a coil.
 
#311 ·
Slow speed tree roots is hsrdly spiking. and no nwhere near HSC constrictions of a damper. Pure and simple linear air spring.
Are you running your Tower without air seals now? At some point in that iniatial travel the air sping also moves with the spring.
The Tower has to overcome the same seal friction as well as the intial inertia of the spring without the help mof a negative spring. That's why there is just a slight hessitation, like stiction, when riding slowly over a tree root AT SLOW SPEED. I've got plenty of forks too benck mark it against.I got a giant OEM[ whatever tune that is] F100 RLC that cam on my Ax 29er and it eats the 120 tower pro in any situatiuon. Square round big small hit it sucks it all up . The Tower is great when you pick up speed a bit 10 to 14 mph but then spikes when you start hiitting them hard[now it's too much HSC]
You can tune an air fork for what he wants. Make it more progressive. Earlier fox short travel forks were briliant over Tree roots at any speed. Very low HSC and a progressive spring. that formula doesn't work for long travel forks . Too much dive.Hence they cam unstuck when the Floa stretched to 140mm. The rest is history.
 
#313 ·
I didn't say slow roots were hsc, and they definitely aren't purely lsc. Its in the mid speed transition area. It depends on bike speed and root size. A big root at slower speeds can dip into the msc/hsc range.

The mars coil can compress without the air piston moving, especially under dynamic loads. There is also a small helper coil spring under the piston that reduces initial seal friction. Coil inertia??? Drop in the bucket.
 
#316 ·
Ask about RS on some other thread.

I think the Tower / Minute stiction comes from either the bushings or dust wiper seals.

And yes, even slow roots can reach into high piston speeds if you hit them just right. You'd be surprised how even mundane things reach into the high speed damping range.
 
#317 · (Edited)
Ask about RS on some other thread.

And yes, even slow roots can reach into high piston speeds if you hit them just right. You'd be surprised how even mundane things reach into the high speed damping range.
You would possibly be the only one who thinks so. But then I don't ride with a data logger mapping shaft speeds.Maybe you do. I believe you'd be looking at shft speeds close to 2m/s before you would feel HSc spiking? Sure there is a crossover but if the HS stack has much influence at those shaft speeds then it's not set up very well.
Don't forget the SID, if it's using still the original XX system[ uses the MC damper] which was just a variable orifice. Hence air spring curve is paramount in the low/ mid range tuning.
Stiction, too linear air curve and too high LSC are the more likely culprits for low speed event bar feedback.
Stiction especially. How many RS riders regularly grease their air cartridge chamber?