Hi all- I recently purchased a secondhand (yeah, not the best idea in retrospect) diamondback podium equipe frameset. The build went fairly smoothly except for one major problem-- the seatpost is slipping like crazy. Even with carbon paste and the specified torque I can still turn my seat with a moderate amount of force and the post will slip ~1-1.5" during the first 30 min of my ride. I have tried multiple seatposts, but the result is always the same. I already got a replacement wedge from diamondback and installed that, thinking it might solve my problem, but it didn't. I know its a bit of a long shot, but does anyone here have any experience with this or a similar aero wedge seatpost binding assembly?
Triathlon Forum
Login required to started new threads
Login required to post replies
Re: diamondback podium seatpost slipping [jschm13]
[ In reply to ]
Two possibilities here:
- the first is that the seatpost you have is out of spec. I prefer aluminum seatposts to carbon, because they tend to be much more accurately sized. Try a different seatpost. Thomson are - and always have been - the gold standard. Plus the textured surface of the Thomson makes them extremely resistant to slippage.
- the second is that you don't understand how to adjust the DB wedge. There are two bolts. The 4mm hex bolt is the one that tightens the binder. This should be torqued to 6-7Nm. There is a second smaller bolt. This adjusts the spacing between the two wedges. The TIGHTER this bolt is - the smaller the space between the wedges - the LESS force exerted by the wedge mechanism. If your seatpost is slipping, you want to LOOSEN this bolt (it's 2.5mm, I think...) to spread the wedge parts further apart.
Lastly, expansion wedges should NOT require any friction paste. And, in fact, I think it probably makes things worse. Clean it off. Especially if you go to an aluminum post.
The other thing you want to do is to push down on the expansion wedge as you are tightening it initially - to keep it seated in the frame fully. Once it "bites" (expands enough), it will hold itself in place, but initially, it will want to push up out of the pocket.
In my experience, the expansion wedge design is THE BEST and MOST SECURE seatpost design on the market. I first used it on the Specialized Transition and have loved it ever since. The only real downside is that you have to make sure to pack the wedge securely when you travel.
But:
- swap your seatpost (inaccuracy of measurement here is a problem, especially with carbon posts that can be both wrongly sized and ovoid as opposed to perfectly round)
- spread the expansion mechanism further apart for greater clamping force
It's a great design. I've never had an issue with it.
"Non est ad astra mollis e terris via." - Seneca | rappstar.com | FB - Rappstar Racing | IG - @jordanrapp
- the first is that the seatpost you have is out of spec. I prefer aluminum seatposts to carbon, because they tend to be much more accurately sized. Try a different seatpost. Thomson are - and always have been - the gold standard. Plus the textured surface of the Thomson makes them extremely resistant to slippage.
- the second is that you don't understand how to adjust the DB wedge. There are two bolts. The 4mm hex bolt is the one that tightens the binder. This should be torqued to 6-7Nm. There is a second smaller bolt. This adjusts the spacing between the two wedges. The TIGHTER this bolt is - the smaller the space between the wedges - the LESS force exerted by the wedge mechanism. If your seatpost is slipping, you want to LOOSEN this bolt (it's 2.5mm, I think...) to spread the wedge parts further apart.
Lastly, expansion wedges should NOT require any friction paste. And, in fact, I think it probably makes things worse. Clean it off. Especially if you go to an aluminum post.
The other thing you want to do is to push down on the expansion wedge as you are tightening it initially - to keep it seated in the frame fully. Once it "bites" (expands enough), it will hold itself in place, but initially, it will want to push up out of the pocket.
In my experience, the expansion wedge design is THE BEST and MOST SECURE seatpost design on the market. I first used it on the Specialized Transition and have loved it ever since. The only real downside is that you have to make sure to pack the wedge securely when you travel.
But:
- swap your seatpost (inaccuracy of measurement here is a problem, especially with carbon posts that can be both wrongly sized and ovoid as opposed to perfectly round)
- spread the expansion mechanism further apart for greater clamping force
It's a great design. I've never had an issue with it.
"Non est ad astra mollis e terris via." - Seneca | rappstar.com | FB - Rappstar Racing | IG - @jordanrapp
Re: diamondback podium seatpost slipping [Rappstar]
[ In reply to ]
Yeah I figured out how to adjust it using the second bolt, but it seems to require an inordinate amount of pressure to keep the wedge in the pocket
Re: diamondback podium seatpost slipping [jschm13]
[ In reply to ]
It shouldn't. Like, in my case, i just sort of hold it in place with my thumb while I'm tightening it until it engages. It doesn't need to stay fully seated - if it comes up a bit out of the pocket as it expands, that's fine.
Based on your description, I'd say that your seatpost is out of spec. In my own experience, especially with carbon posts, that's quite common.
If you're really stuck (pun intended), I'll video adjustment on my own bike for you.
"Non est ad astra mollis e terris via." - Seneca | rappstar.com | FB - Rappstar Racing | IG - @jordanrapp
Based on your description, I'd say that your seatpost is out of spec. In my own experience, especially with carbon posts, that's quite common.
If you're really stuck (pun intended), I'll video adjustment on my own bike for you.
"Non est ad astra mollis e terris via." - Seneca | rappstar.com | FB - Rappstar Racing | IG - @jordanrapp
Re: diamondback podium seatpost slipping [Rappstar]
[ In reply to ]
Yeah I'll go check with a shop and see if that's the case-- though this seatpost worked fine in previous bikes. FWIW, I've talked to two shops (including the one i bought it from) and you're the first person to mention the second adjusting bolt-- albeit they may have just assumed I knew.
jschm13 wrote:
Yeah I'll go check with a shop and see if that's the case-- though this seatpost worked fine in previous bikes. FWIW, I've talked to two shops (including the one i bought it from) and you're the first person to mention the second adjusting bolt-- albeit they may have just assumed I knew.Sadly, I would say it's a distinct possibility that they didn't know. There's a reason I do 100% of my own wrenching...
I think the expansion wedge design's one weakness is that it is perhaps more reliant on the seatpost dimensions/finish - also make sure it doesn't have a super smooth, high gloss finish; just a bit of emery cloth if it does - because you're basically "squeezing" the post into the frame. With a pinch bolt collar, the mechanism of retention is weaker - you are tightening something that is applying shear force (perpendicular to the load) - but it's easier to have it deform to the specific post. I.e., you can tighten the collar around the post, and then your weight keeps it in the frame. In the case of the expansion plug, you are actually applying the clamping force in the direction of the load - the expansion plug is directly resisting vertical movement of the post, which is why I like it.
"Non est ad astra mollis e terris via." - Seneca | rappstar.com | FB - Rappstar Racing | IG - @jordanrapp