[video]https://www.youtube.com/watch?v=wlwnbcxBuzI[/video]

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smooth PB is pointless

It’s not single pivot though is it? It’s yet another iteration of i-drive so there’s a pivot under the BB?

It’s a single pivot. There may be extra pivots all about the place but fundamentally the rear axle is attached to the main frame by arigid ‘stick’ in this case the ‘seat stay’. Regardless of the extra bits and bobs all over the place the path of the rear axle will only ever trace a nice curve around that single attachment point on the seat tube. That point is the centre of the circle and the ‘seat stay’ with the axle at the end of it is the radius of that curve. Everything else is all to control the action of the shock, not the axle path of the rear wheel.

The only thing not single pivot about it is that the bottom bracket doesn’t appear to be a fixed part of the frame.

I disagree, the majority of the bikes COG is in the rider, so it’s the relationship between BB and axle that matters. Specialized’s design was known as 4-bar because the frame forms one of the bars, but the frame can only rotate around the BB (assuming what you want is the BB to remain still and transmit no impulse to the rider).

GT just takes that slightly differently as the frame in effect is free to move both around the BB and fore/aft.

Think of the ‘120mm travel’ as actually more like 100mm relative to the BB, and the last 20mm, is actually just the frame rotating back as one ‘link’ to kick the head angle out by another degree.

Or rather that’s how it rides anyway, like it’s got an inch less travel because the frame acts as a link.

Now this is interesting, isn’t it? I can see what you are saying about the BB being an important reference point as it is effectively a contact point for the rider on the bike and in relation to that the path of the rear wheel will not be a curve around it. But I still, on balance, disagree and maintain it is effectively a single pivot as there’s no avoiding the fact the rear axle is securely attached to a single pivot point on the bike frame.

What it does suggest is that the suspension may feel different when you are sat down (there’s no avoiding the fact that in that instance you are attached to the part of the bike that the rear axle is directly attached to) and when you are stood up. So, multi linkage suspension action when you are standing and single pivot sitting? But then the hands are also a contact point and they are directly connected to the seat tube pivot point, which is connected to the rear axle – ergo, single pivot. Standing is more important I guess, but still, remove the shock, suspend the bike and lift the rear axle and it’s going to trace a nice round curve around the pivot on the seatube. Single pivot 🙂

But who said there was nothing left to debate in suspension design eh? 🙂

Would it work better if it was red? 😉

Although the GTs look like single pivots they behave quite differently because most forces from the rider are acting through the BB. The design results in incredible performance when breaking and pedaling over rough ground and a very laterally stiff rear end.

I was actually amazed by the performance when I first got my sanction – under braking the suspension remains far more active over rough stuff than my Banshee rune or my horst link downhill bike.

[video]https://www.youtube.com/watch?v=lZhSLXAUtRI[/video]

Check the video showing how it works, it definately seems like it would behave as a single pivot assuming you remove the BB from the equation. Problem is you can’t really do that with a rider involved so looking at it like that it does appear as if seperating the BB from the mainframe makes the frame effectively another linkage when considered in relation to the bag of bones hanging onto it.!?

My main question would be how on earth is having the BB waggling around under you like that a good idea.? Haven’t ridden one so I couldn’t really comment but it does look to have shades of the dreaded URT in that it seems to have completely different suspension characteristics depending on whether the rider is seated or standing.
Perhaps someone with firsthand experience could refute.?

#edited for readability