What Diameter Dropp...
 

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What Diameter Dropper Post for a 34 .9 mm seat tube?

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Why oh why do manufacturers sell bikes with stupidly short droppers... Either put a sensible length in a size large ( ie not 170mm) or just fit a cheapo non dropper and trim £200 off the price.

Anyway, need to get a decent dropper for my Slash, which has 34.9mm currently. I don't want to be in the same position in x years time when I buy my next bike only to find it has a 31.6mm post and so the 34.9mm doesn't fit.

Can anyone who's bought new bikes recently ( this slash is 3 years old)  comment on whether 34.9 is becoming the new norm, or whether I should just buy a 30.9/31.6 and a shim


 
Posted : 22/05/2025 9:59 am
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My Airdrop is 34.9. I think it's becoming more popular. The benefit is the stanchion can be a larger diameter and hence stiffer for the same weight which is useful for longer posts.im running a BikeYoke Revive max at 185mm but they do a longer version as well


 
Posted : 22/05/2025 10:02 am
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i've got a 34.9 on my Top Fuel

It's actually nicer than the oneup v2 31.6 i have on other bikes, i'm of the opinion the larger diameter reduces the post rotation among other benefits

i'd be buying another 34.9 and not shimming a smaller post in myself


 
Posted : 22/05/2025 10:07 am
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+1 for go 34.9

 It makes good engineering sense, especially now posts are getting so long, means bigger, more robust internals, bigger bushings etc, I expect that it will soon be the 'standard' for E-MTB even if they are prevented from coming on 'acoustic' bikes by weight and ride harshness concerns.

I had a 34.9 Bike Yoke Revive max and it was lovely, I'd have another in a heartbeat.  

 

 


 
Posted : 22/05/2025 10:25 am
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Posted by: hatter

had a 34.9 Bike Yoke Revive max

Blimey, that's quite pricey.

Hmmmm


 
Posted : 22/05/2025 10:57 am
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The ReviveMax is really good. Yes, it's not cheap to buy. If they have one the right length for you and you can justify the upfront cost I think you'll find it's good value across its lifespan.


 
Posted : 22/05/2025 11:17 am
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+1.

Good spares availability.

Cheap service kit

Eady to overhaul at home.

Great support from BikeYoke 


 
Posted : 22/05/2025 11:29 am
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How much drop can you use? 
Leisure Lakes have V2 One Ups for £165 in 240mm drop, but that can be reduced to 220. 
I’d also be getting a 34.9, the increased space for bushings etc is just huge. 


 
Posted : 22/05/2025 5:16 pm
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But, but, but..

The 34.9 is a shit load heavier....about 160g for the One Up V3.


 
Posted : 22/05/2025 6:00 pm
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Dumb question, but don't manufacturers just increase the tube thickness, and use the same sized internals across all seatpost diameters? 


 
Posted : 22/05/2025 6:01 pm
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They do between 30.9 and 31.6 but 34.9 gets bigger internals. It's the reason 34.9 exists.


 
Posted : 22/05/2025 6:53 pm
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BikeYoke is only 40-70g heavier than the 30.9/31.6 in the 213mm drop.


 
Posted : 22/05/2025 6:56 pm
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Stanchion goes from 25 to 28mm which I believe doubles the stiffness assuming wall thickness is unchanged 


 
Posted : 22/05/2025 7:03 pm
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Dumb question, but don't manufacturers just increase the tube thickness, and use the same sized internals across all seatpost diameters?”

BikeYoke were the first to scale up everything for the 34.9 - I have an original Revive in 31.6 and 34.9 (technically called the ReviveMax) and although the former has been more reliable and lower maintenance and smoother running than any dropper I had before, the latter has had even more use, works smoother and very very little maintenance.

I think some other brands now make 34.9 droppers that aren’t just a thicker-walled lower tube. The ReviveMax is 28mm upper tube, increased from 25mm. That’s like going from a 32mm fork to a 36mm one. Huge difference!


 
Posted : 22/05/2025 7:07 pm
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Cheers all. Much appreciated.

Went for the 34.9 1 up V3 210. Alas the 240 won't fit.

 

 


 
Posted : 29/05/2025 8:15 pm
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Just get a shim.


 
Posted : 29/05/2025 9:53 pm
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Specialized have been doing 34.9 tubes for a long time now. My 2020 M4 Fuse frame came with a 34.9 Command Post, and I've not needed to service it yet - it's a cracking bit of kit with two slight grumbles:

1) It's 160ish travel, which is short for my shortarse legs - basically, the shorter you are, the more a longer drop post will benefit you

2) The return speed is abrupt, to say the least. The post also tops out with a bit of a bang, and I'm running the bike as a singlespeed with a well-greased DT ratchet to make everything as quiet as possible, so it really is quite noticable. I've completely got used to the return speed, but it is a bit of a shocker!

I did run a spare 180mm 31.8 OneUp for a while, and while I wouldn't say I noticed loads more flex or anything, it did seem to be a little more comfortable. The bike will take a 180mm OneUp or BikeYoke, but I'm loathe to replace a perfectly functional bit of kit when I could probably do with some new forks a bit sooner...

I've got a USE 34.9-31.8 shim if anyone wants one, by the way - yours for a donation to Cancer Research.

 

 


 
Posted : 30/05/2025 10:04 am

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