Single pivot xc/trail performance?

DTL said:

I have a 2009 Heckler I have been riding for a few months now (large, fox rp23, fox float 32 140mm). I have experimented with suspension setup and tire pressure. I ride trails that are mainly xc/trail type. I'm not doing drops or jumps just hitting lots of singletrack with a mix of climbing and going down and lots of roots, logs etc. The bike rails turns and handles great. The problem is no matter how I set the bike up it seems I am fighting to pedal and keep momentum especially when the trail gets choppy. Unless I am going down or straight and smooth it feels as if I am towing a cinder block. I took my other bike (Giant Trance X1 maestro, 5" front and back) out and rode the same trials a few weeks ago and the bike felt like a rocketship. Climbed better, rolled and kept momentum better and it only weighs about a pound lighter. So, I guess my question is this a matter of a difference in suspension design? Single pivot vs multi link? or is there something else I should try setup wise? My riding partner took my Heckler for a spin today and made the same analysis so I know I'm not imagining this.

Click to expand...

Yep, you aren't imagining this. The high-pivot on the Heckler will causes the suspension to stiffen when you are pedaling. On level smooth ground this is great. When you switch the granny gear while going uphill this trait is actually magnified some, that means that when you go over a bump your pedaling forces are trying to keep the suspension from moving, and of course bumps try to make the suspension move. This leads to a much harsher ride and makes it harder to keep momentum/maintain traction. One of the big problems here is that it's hard to design a single-pivot bike to do well in all the gear-ranges that will be encountered. For a freeride or DH bike that will only have one ring up front it is much easier to design a "good compramise", but with a bike that shifts between different front rings, it is harder. The other aspect that you may be feeling is "squat", although this too would depend on what gear you are in. On steep uphills, one of my bikes tends to "squat" through it's travel when I'm trying to pedal in the middle ring. In the granny ring it does not do this as much. It basically starts to feel like a wet-sponge when I start headnig up steep stuff in the middle ring. It basically sucks a lot more energy than it would if it were on level ground. This has to do with how the contact patch relative to the acceleration force relates. This is another area where something like the Maestro or DW link should do better than a single pivot.

As I said before though, single pivots aren't all bad. There are single-pivots without those excessive traits, although something like the Giant Meastro or DW Link is still going to be able to perform better. There are inherent limitations of single-pivot bikes, moreso with bikes that have to run more than one ring up front.

I don't know. This bike vs. that bike may be an overly simplified way of looking at it. Several other things factor into it. I can see the comparison if they are spec'd out identically. If not, then the setup may be working against the heckler as well.

I think multi-pivot bikes do a better job at masking poor suspension setup. With a single pivot it is pretty obvious when things are off.

I have owned just about every iteration of the Heckler over the years. Every one of them ended up with a coil shock sooner or later. Over chunky terrain a heckler with an air shock dives deep into travel and kicks back too harshly (unless you are into the whole saddle catapult thing ). This results in lost traction, lost balance, and sometimes a loss of momentum if your rear tire is still on the back side of the obstacle. Suspension stiffening may have some effect, but IME not as much as the shock. I have taken a Push tuned RP3 and an Avalanche tuned 5th coil back to back up/down the same chunky section of trail. Under climbing loads the stiffening effect should be the same yet the coil shock equipped heckler will roll right up and over the same obstacles that nearly stop the air shock heckler in place. On smooth trails the air shock on the heckler is fine, but in rough terrain a coil will do better.

DTL said:

It's frustrating because the Heckler is great going down and handling turns and curves. I just wish I could get more flow out of it.

Would the coil shock eleiminate a lot of the pedal bob/squat? How much weight would a coil shock add to the bike?

Click to expand...

SC geometry has always been very good in tight, twisty, and technical.

RE bob/squat. The Heckler setup with an air shock at proper sag will ride lower/squat more even on mellow terrain. Pedal bob is another story. I can tune out pedal bob with LS compression on my shock. On previous shocks, DHX uses propedal and 5th/SPV use a platform. They avoid bobbing but ride pretty harsh up top until the platform is broken through. When set stiff the platform type coil shocks feel a lot like an air shock in the first part of travel.

Honestly with a good coil shock you have more control/adjustment range to work with. It is a lot easier to tune it to your riding preference. Fox air shocks really don't give you a whole lot of adjustment. The Manitou Intrinsic and X-Fusion upper level shocks have a lot more of the features of a coil shock. But at $500-600 I am not really inclined to take that gamble to see if they are able to tame the air spring.

Weight of a coil shock varies by mfg. My X-fusion sits at ~900g. My RP3 wieghed in at about 300g. So about 1.5lb added. With a Ti spring the weight difference can be closer to 1lb.

Just about every other MTB frame out there has some sort of rising (or progressive) rate....such that each further incremental change in suspension travel takes in increasing amount of incremental force. In simple terms, the suspension 'ramps up'.

It is not so easy on linkage frames to 'see' what is going on and to determine if a rate is falling, flat, or rising... at some particular point in the travel. Generally you would need to look some semi-complicated math that describes the movement of the suspension to make the exact determination (although, like said, the VAST majority of frames have at least a slight rising rate on average).

For simple single pivots like the Heckler, it is easy to tell what is going on in a general sense.
Draw a line from the main pivot to the swingarm shock mount
Draw a line along the direction of the shock

Now if the angle of intersection of these two lines is moving away from 90* as the suspension compresses (as in the heckler at least in the later part of the travel) the rate will be falling.

If the angle is moving toward 90* as the suspension compresses, the rate will be rising.

These are all instantaneous rates, and throughout the entire travel you could actually have portions that are rising, and portions that are falling.... but again looking at the Heckler, it is pretty obvious that the 'angle' starts near 90* and gets larger as the suspension compresses...