'Single Pivot' rear suspension, mid drives, and chain drop..

[adriftatsea]

I'm considering purchasing an older Santa Cruz Superlight which is a 'single pivot' rear suspension design. In another thread [1], the merits of Horst Link and VPP were discussed and that it keeps chain length similar throughout suspension travel.

But for those of us who aren't going to huck the bike off huge drops - is a single pivot prone to problems of chain drop for high powered mid-drives?

[1] http://endless-sphere.com/forums/viewtopic.php?f=2&t=69598&p=1049881

single pivot:

VPP:

Horst:

 

[spinningmagnets]

I have not studied frame geometries and the various benefits/drawbacks of each, but...even though I still want to hear what experienced people have to say about this subject...I wanted to say that I have read many places where a chain-guide has fixed a bike with occasional chain drops.

 

[nutnspecial]

Imo just look at 99.9% of dirtbikes, sportbikes, motorcycles. I want as little moving parts as possible, and tensioners and/or guides take care of chain routing when you have changing distances no matter the geometry setup. I don't think you'll have any problem.

 

[speedmd]

As long as the motor sprocket is close to the pivot and near in line with it and the wheel axle, chain growth/shrink should be manageable as it is on most motorcycles with a simple tensioner. You can work out the numbers with simple trig. The more the suspension travel, the harder it will be to deal with. I am playing with the idea of mounting a motor to the swing arm on a bike with this type of setup just to make it simple. Not able to fit it just yet.

 

[amigafan2003]

But for those of us who aren't going to huck the bike off huge drops - is a single pivot prone to problems of chain drop for high powered mid-drives?

I've not had my chain come off once in 2500 miles of riding. My frame is almost an exact copy geometry wise of a Superlight. It's does have a clutched rear mech, so that probably helps.

 

[Punx0r]

I think the main "real" advantage of these complex bicycle suspensions are to try and avoid pedal bob. As others have stated, motorised cycles don't use them, so it's likely to be related to pedalling, or, being pessimistic, just fashion or a tenuous benefit about linear wheel travel.

 

[speedmd]

If you can put the drive sprocket at the pivot, no need to complicate the suspension. On pedal bikes with multiple sized chain ring sizes and limited crank position options, or limited motor position placement options, I can see some advantage to looking at it. With one chain ring as on the BBS02 build pictured, the pivot falls near perfect for chain growth. I would expect it to be very reliable chain wise. Don't quite understand what drives pedal / suspension bob. Another interesting topic for certain.

 

[spinningmagnets]

Grayborg, NYX, Mental Manno, and Vector frame-kits have the swingarm pivot concentric (having the same centers) as the BB-shell.

 

[speedmd]

They greyborg looks to be a very cool swing design. If they leave enough material off the front end of the swing clamp, you could mount a mid motor off of it forward/ below of the crank. Think it would be worth the extra bit of material for a host of customers.

 

[adriftatsea]

Thanks for the feedback guys. I also agree that the simplicity is a selling point - I just wanted to make sure it wouldn't be a hindrance.

I ended up with an older Santa Cruz Heckler w/ a Fox DHX coil shock. This older model uses a 67mm BB that will fit my GNG and the coil can be upgraded to better handle the extra weight of the batteries.

 

[nutnspecial]

Cool!

Pedal bob and travel are something to consider I guess, but I just ordered a single pivot 'st3'- looks solid, but no real namebrand- nobody seems to have one on a bike

 

[adriftatsea]

I just ordered a single pivot 'st3'- looks solid, but no real namebrand- nobody seems to have one on a bike

Nice! I was watching that one on ebay too. It looks akin to the Trek Y-series bikes and should be plenty beefy. I'll be following your build thread.

--
I spent a bunch of time watching the Santa Cruz interviews at 'Interbike' [1,2] (their PR guy is funny) where they explained the move to VPP from single pivot. Mostly it was to allow for a 'smiley face' shaped response curve so the loads on the air shock ramp up to prevent bottoming out. If you have a coiled shock, most of this doesn't seem to matter if you can live with low speed 'bobbing'.

[1] https://www.youtube.com/watch?v=tj8ZY1C1604&t=3m26s
[2] https://www.youtube.com/watch?v=_MRE_Mww630&t=2m

 

[speedmd]

I have my BBS02 on a older Santa Cruz aluminum blur. Excellent bike for this power class e build. The shock rates will progress regardless of what type of spring you have with either of their linked setups. The air springs are a bit more progressive and can vary that a bit more in setup. The new Santa Crus single pivot designs looks to be a perfect lower cost FS bike platform IMO. Need to find something like them some four to six inches longer for a higher power build.