Tech Talks: Dropper Seat Posts - To Clamp Or Not To Clamp?

Dec 27, 2018
by Pinkbike Staff  
Tech Talks Presented by Park Tool


In this episode, Calvin and Truman go over the best way to put your bike on a bike stand when it has a dropper seat post.

Tech Talks Presented by Park Tool is a monthly video series hosted by Park Tool's own wrench whisperers, Calvin Jones and Truman. The series covers the A to Zs of some of the most prevalent repair jobs.

Bike Assembly How-To

Views: 16,034    Faves: 9    Comments: 4



Need more Calvin & Truman in your life?

Episode #1 - Tubeless tire installation and conversion
Episode #2 - Saving that bent disc rotor
Episode #3 - Derailleur hanger alignment
Episode #4 - Shimano and Crankbrothers pedal service
Episode #5 - Trailside wheel repair
Episode #6 - Trailside chain repair
Episode #7 - Derailleur limits and cable tension
Episode #8 - Derailleur setup
Episode #9 - Fork wiper seal replacement
Episode #10 - Clipless pedal setup
Episode #11 - New cleat setup
Episode #12 - Top 5 next level shifting issues
Episode #13 - Fixing cassette play
Episode #14 - Gearing hacks
Episode #15 - Fixing sticky pistons
Episode #16 - Lubing fork seals
Episode #17 - A cleat's story
Episode #18 - Tricks of a mechanical mind
Episode #19 - Handlebar Trimming
Episode #20 - Chain Line
Episode #21 - Tools for a trip
Episode #22 - Bedding in brakes
Episode #23 - Direct Mount Chainring Install
Episode #24 - Wheel Balance 101
Episode #25 - Data Under Pressure, Part I
Episode #26 - Data Under Pressure, Part II
Episode #27 - In the pits with professional mechanics
Episode #28 - Seth's Pre-Load Nightmare, Part I
Episode #29 - Seth's Pre-Load Nightmare, Part 2

Stay tuned for more mechanical how-to videos with Calvin returning on the last Thursday of every month to show you the easiest way to get the job done. Want to know more? Park Tool's how-to section has you and your bike covered.

www.parktool.com / @ParkToolCompany


109 Comments

  • + 68
 12 minutes on clamping? i'll quote a SRAM tech rep at a Park Tool seminar i attended in reference to the then new reverb.... "you can clamp the shit out of it"
  • - 10
flag dmarsh15 (Dec 27, 2018 at 7:01) (Below Threshold)
 So does that mean you can clamp your fork stanchions too???
  • + 174
 You can clamp the shit out of it, because regardless of torque applied, it still won't work correctly.
  • + 11
 @ratedgg13: Exactly.. Worst dropper I've ever owned... One up components FTW!
  • + 8
 @dmarsh15: No physical reason why you shouldn't other than the fact there is absolutely no need to.....
  • + 1
 HAas
  • + 3
 Sounds like something Micah would say.
  • + 4
 Who would buy a Reverb?
  • + 4
 @THE-GUNT: So many better options out there now.. My one up components has been flawless.. Even in the cold on the fat bike..
  • + 22
 Actually if you listen very carefully, yo can hear how Reverb is whispering ''Rebuild me'' every time when Calvin pulls it out by hand...
  • + 1
 @bohns1: I prefer my crap Easton over the Reverb. lol
  • + 1
 @THE-GUNT: The Easton/RF Turbine is surprisingly a pretty solid dropper. I've been waiting for mine to die for the last 3 seasons to replace it with a 9point8 but it works just as good as the day I bought it.
  • + 1
 @THE-GUNT: in all honesty.. My old crankbrothers worked better! Ha
  • - 8
flag aps62 (Dec 27, 2018 at 11:59) (Below Threshold)
 @wallheater: exactly!! Why would you clamp the seatpost?? Almost all bikes have plenty of tube to clamp elsewhere. Why would you bother clamping the seat tube? I’m honestly not trolling, it’s something I’ve always wondered?
  • + 3
 @aps62: Frame paint isn't nearly as durable as the finish on any mountain bike seat post. Also, a lot of full-suspension frames don't have a good spot to clamp. Regardless, in a worst case scenario, a seat post, even a dropper, is less expensive to replace/fix than a frame.
  • + 3
 @aps62: because most carbon frames have a sticker saying "Do not clamp".
  • + 1
 Anything SRAM is gonna break and clamp the shit out yer wallet bro... get with the times yo.
  • + 5
 I love the Reverbs on boths my bikes. I've never had issues with them so I don't get the hate. SRAM brakes on the other hand.........;-)
  • + 1
 @ratedgg13:

LMMFAO!

That about sums it up, time to shut this down.
  • + 3
 @devlin66: Ditto! I've had five Reverbs over the years; all worked perfectly. Did a full rebuild on my current Stealth two years ago and it still works fine. Might tear it down soon to re-grease,

I wouldn't trust any of these Reverb-moaners to sit the right way on a toilet seat.
  • + 1
 I'm glad they went full on nerd force on all the numbers. Otherwise some techno-geek pretend know it all out there would come back with some random B.S. to say the opposite of anything these 2 said.

People are so desperate to nay say and poo poo that they were "forced" to go to the testing extent they did.
  • + 1
 The best thing I ever did to my bike was throw my reverb through the sheetrock in my garage and use it as a helmet rack. What an overpriced piece of shite.
  • + 17
 I would like to know how much force is put into a seat post just from sitting on it. My SA is 73.8 degrees and I'm 180lbs, I'd imagine my body weight is putting much more force on the seat through a ride than the bike being held in a clamp.
  • - 4
flag loganskis (Dec 27, 2018 at 7:56) (Below Threshold)
 In opposite directions though. I get worried about pulling up on the post. Will it break a seal and pull air into my cartridge? Id rather not find out, so i always take the 15 extra seconds to grab a 4 mil and raise my seat enough to clamp the outer part
  • + 3
 @loganskis: Didn't watch this video but I've read/watched in the past that your option is actually the worse option, although it's counter intuitive.

The stanchion is rock hard, the leverage on the seatpost is negligible compared to what you put on it while riding, it's fine to pull on a seat/seatpost provided it's fully raised, and it's worse to clamp the post outer that's filled with all the post's internals.
  • + 4
 Approx the same as a baby rhino charging in the month of may in 25 degree heat after a good meal.
  • + 1
 Well that is exactly what they say in the video
  • + 18
 I actually liked it... Puts to bed some of the arguments i've had with other wrenches.
  • + 8
 I agree. I've worked in shops where the service area is visible to customers. I've had customers say they wouldn't ever let me work on their bikes because I clamped a dropper. These are always customers that "do all their own work" anyway. I'm sure some of those customers will read this.
  • + 11
 @dangeraem: yep, the guys who power wash their bike every ride and use wd40 as chain lube.
  • + 2
 @Trudeez: Then they bust be retarded. WD40 should only be used on brake rotors!
  • - 2
 @Pavel-Repak: brake clean on rotors or isopropyl bud!
  • + 7
 @bohns1: whoooosh!
  • + 11
 Mr. Madison, what you've just said is one of the most insanely idiotic things I have ever heard. At no point in your rambling, incoherent response were you even close to anything that could be considered a rational thought. Everyone in this room is now dumber for having listened to it. I award you no points, and may God have mercy on your soul.
  • + 10
 Some dodgy conversions going on there (2.2 square inches = 55.9 mm^2 ?!? Nope, you need to multiply by 25.4 twice when converting area). I'm not sold on their clamping force to pressure conversion either (shouldn't it bear some resemblance to a hoop stress calculation?). Also, they should use the diameter of the post that the collar actually operates on (30.9?), but it looks like they used the diameter of the stanchion so got a higher wrong result than the wrong result they should have got.
  • + 5
 So I should not clamp?
  • + 4
 @Tinus96: Clamp away , just put a towel around the post Wink
  • + 4
 you're right that their calculation of the force/stress isn't quite accurate. You should use the force from the bolt to calculate a hoop stress in the collar, then you can use P = stress * radius * thickness to find the average normal pressure on the seat post. However, it makes little difference, because clamping your seat post still will be a low stress for what the metal can handle. Additionally, you might be able to get more precise than even this method.

As for as the moment on the post (which is my primary concern when clamping) their analysis is is a bit hand-wavy, but not far off the truth. Assume you sit on your seat post such that all of your body weight is on it (an assumption, not doubt, but the force going to your bum when you hit an unexpected rock while sitting down will be much more than your weight anyway). Say you weigh 160lbs (about 73kg). Using a rough approximation, you're bum is about 5cm behind the collar. This yields about 36N*m at the collar (again, this is a lower bound for the internal moment in the seat post. when you hit that rock, it will be much, much higher, especially on a hard tail). so 36N*m is greater than their measurement of about 30N*m.

Bottom line, if you raise your dropper to the top of the travel and clamp like a normal human, your post will be fine, (unless its a reverb).
  • + 13
 Nerds! Thanks for this. I clamp to the post. I also double dip and like the smell of my farts.
  • + 2
 double dipping the chip, bro?
  • + 5
 remember the old TNT BMX seat clamp that came in two halves with two bolts?
Would something like that with more cuts in the seat tube distribute clamping forces more equally for people that have problems with dropers slipping ?
  • + 4
 Scooter clamp!!! Four bolts and purple ano!! Must be faster!!
  • - 2
 I painted a light layer of epoxy on my dropper post right around the clamping area and let it dry before reinstalling. It provides enough friction so it can stay put without too much torque on the clamp bolt
  • + 5
 I have a bike with a dropper post. The first time I put it in my stand it took me less than 11:52 minutes to figure out where to clamp it.
  • + 4
 So, in a nutshell - compared to dead sailoring a Red Bull Rampage Gap Jump and Casing the back wheel - clamping your dropper whilst spannering your broken bike will be fine. Sometimes people can just be a little precious.
  • + 4
 What's so revolutionary about clamping the TT just to be safe? This whole topic has always seemed like creating a problem for the sake of discussion.
  • + 12
 Don't go clamping carbon TTs though. Did that once. Once...
  • + 1
 @Bob-Agg: Crushed tube in a park clamp? I've clamped hundreds of carbon TTs (shop mechanic) without issue but I can see how that could happen without testing the clamp tightness first
  • + 10
 @HaggeredShins: #worldsworstbikemechanic
  • + 1
 @NORTHender: ohh well if you insist ????
  • + 1
 I have a nice bontrager bike stand that has a saddle nose hook on the top by the clamp. So this enables me to hang the bike by the nose of the saddle and while the bike may sway I find this is acceptable for 95% of my wrenching.

I did one time clamp my fox transfer post and a bolt for the clamps had slightly come loose and it scratched the shit out of my stanchion. That was my fault for not checking but I wont be clamping ever again.
  • + 2
 Just compare the weight the seatpost can afford when YOU are climbing versus the weight of the entire bicycle when is on the bikestand for maintenance, and sometimes without the weight of both wheels...
  • + 1
 I got a PCS10 stand a year ago (which clamps the seatpost) which I thought would completely replace my old Tacx T3000 cyclestand. The Tacx wouldn't work nicely with my full suspension frame (Cannondale Prophet) because it needs to clamp the downtube where the (main) pivot is. A taco type bashguard was never an issue, actually. I've got to say the PCS10 is nice when the wheels are completely removed so you can tilt it in all orientations. Good for bleeding brakes etc. But it is not really stable. The bike rotates easily as the clamp grips the round tubes. But (because I ride my hardtail and BMX more than the fully) I found myself still using the Tacx most of the time. It is way more stable, making it more comfortable to use. Should I ever get a dropper seatpost, I wouldn't need to worry about any of this (in the article). I think if I'd get one now I'd get one of these that require you to remove the front wheel and hold the forks and bb. It may still not work for certain frame designs (e-bikes and Pinion in particular) and obviously you can't use it for adjusting the front brake.
  • + 1
 It's about time someone settled this one. It's not even an air sealing surface on most droppers either. But even with command posts and fall lines I have never caused an air leak by clamping the shaft.
  • + 0
 I relate it to doing a fork rebuild. I would never clamp the fork CSU on the stanchion but would i clamp a magnesium lower without hesitation. i will continue to raise the post slightly to get it in the stand. I feel it also just looks much more professional to spend the extra time to clamp it where it's bin designed to take clamping forces. I would never clamp my own dropper stanchion so
  • + 0
 I don't clamp the inner post because I don't like having to verify my clamps are perfectly clean. Wrapping with a cloth just makes the stanchion, already narrow and slippery, even more likely to slip. Most bikes have enough housing slack to raise the post a few inches so you can clamp the outer.
  • + 8
 It would literally take 5 seconds to look at/ white off the clamp. Takes longer to find an allen key, move your seat post up, re tighten then clamp rather than just cleaning your clamp. Your clamp shouldn't even be dirty in the first place unless you wanna scratch everything you clamp in it
  • + 3
 Save yourself now ....life is too short
  • - 3
 Haha, I got a hair cutter for Christmas, all the informational, DIRECTLY IN THE GARBAGE.
  • + 3
 i bent my seat post with me glutes.
  • + 1
 Impressive!!!
  • + 1
 Why not clamp to the frame? That's what I do. It doesn't need to be clamped super tight. Just barely enough to hold the bike in place.
  • + 1
 Is it okay to clamp the top tube of a carbon bike? That’s what I always do.
  • + 1
 Luckily I'm lanky enough that I can clamp the lowers and not the stanchion of my 150mm Fox Transfer.
  • + 2
 My daddy warned me about loose women that could give me the clamp.
  • + 2
 Anybody else catch the Jeb Bush Reference?
  • + 2
 whys everybody complaining tf
  • + 2
 Dropper post, what?
  • + 1
 What’s the problem with clamping on the seatpost collar?!
  • + 2
 May risk damaging the bushing in the seal head?
  • + 1
 Jesus I'd never clamp a stanchion. CLAMPS GIVE HIM THE CLAMPS BOSS
  • - 1
 Or how bout you ignore his video entirely, take an old slip on grip cut once lengthwise and there you have it a dropper stanchion protector ready for all your clamping needs.
  • + 1
 Mythbusters of bike repairing
  • + 1
 Went strait to the comments and got my answer right away. Thank you. ????
  • + 1
 These guys are good, but I really want a Click and Clack of bike repair
  • + 2
 "Our staff saddle tester is Mike Easter."
  • + 0
 I...what? Why? No. Forget I asked.
  • + 1
 I don't math.
  • + 0
 Did this feel like 'It's Always Sunny in Philadelphia' to anyone else?
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