Hey!
This is the compression plug for my cannondale topstone. Cannondale tells you not to use spacers on top of the stem in the manual.
This is the insert depth the plug actually sits at, the top cap is screwed almost completely in in the picture.
It was my understanding that the plug is supposed to counteract the clamping force of the stembolts. Does it do a sufficient job that far down, and is this normal?
I've had some Storck and KTM bikes in my hands over the summer where the expander was much longer, extending to the end of the steerer tube.
Thank you!
Thank you!
by thebauzzo
6 Comments
Cannondale has been supplying shitty expanders for a long time. They know better, but they just don’t care. As shown in your picture the bottom of the plug actually lines up well with the bottom stem bolt. However, to be effective you want the entire stem supported by the plug. The top section of plugs with a fixed diameter need to be a very tight fit in the steerer, and those top sections are almost all a loose fit. [It’s not ideal.](https://www.youtube.com/watch?v=8bSnbjHiFXc)
Whisky makes a 50mm compression plug that’s pretty good and will cover the whole stem. They’re designed to be set up with 2-3mm of steerer extending ABOVE the stem, and a 5mm spacer on top. Because Cannondale supplies a plug which is too short, and of shit design, they mandate that the steerer is cut 2-3mm below the top of the stem and that you don’t run spacers on top for risk of even more of the stem being unsupported.
Whisky, Origin 8, Necco (amazon brand), Specialized (though this one is annoying to remove), and others make a good compression plug that Raul (youtuber above) would approve of.
This is normal, I have the very same on one of my bikes, never had any problems with it.
Yes, it works well. You just have to follow the Cannondale manual.
That kind of plug seems like trouble waiting to happen to me, although I guess if it was so bad Cannondale would be getting hit with a recall and/or lawsuits over it. That said, a good quality long compression plug that supports the whole top of the steerer tube can be bought for $20-25 from Whiskey Parts and others, so IMHO that would be a small amount of money, well spent.
It’s not my favourite design by far, but it doesn’t cause any issues. We see the same number of cracked cannondale steerers as we do any other bike. And pretty much every time (regardless of manufacturer) it’s because the owner has overtightened the stem
In my personal experience wrenching for over 20 years now 13 in the industry (along with working with industry engineers), and my years of learning thru young idiocy.
My rule for compression plugs: they need to push against the lower bolt, and go past the bottom edge of the stem. Even when they don’t specify spacer above, I like putting a spacer up there.
That said I prefer taller plugs that extend from the upper bolt to past the lower edge of the stem.
When you fail to get a plug past the bottom edge of the stem, you create a stress riser there, because the steer tube isn’t supported from behind… and the bottom edge of the stem digs into the steerer tube and breaks the steerer. And you, your bars and your face meet pavement or dirt.
The taller plugs back the surface/point stressed by the stem, and disperse some of that energy down and around the tube or to the opposite side of the tube. More tube area fighting that stress makes for a stronger system.