[hmcleay]

Hi all,
There are a few suspension geeks on this forum that might be interested in this article.
It's on the front page of www.i-tracksuspension.com

For those that are likely to fall asleep after the second sentence, here’s the gist of it:

Having Anti-Squat that increases with suspension travel can be used to strategically increase the wheel rate when pedalling. This would help maintain the natural frequency of the suspension system under acceleration.

Having Anti-Rise that increases with suspension travel can be used to strategically decrease the wheel rate when braking. This would help maintain the natural frequency of the suspension system under braking.

Other strategies might include making the wheel rate more or less ‘progressive’ under hard acceleration and/or braking.

For the shock tuners out there: How would this affect the way you tune shocks, knowing that the wheel rate could be quite different under pedalling, compared to coasting?

Cheers,
Hugh.

 

[Vrock]

It's a bit weird that you only talk about the slope, and not about the amount of Anti-squat, because with your bike you have a good number around sag, and then it goes even higher, DW-link it's like that too, it start with a good number. But what about VPP? sometimes it start with a low number...

Also, 0.5g seems like a lot to me, I would use something like 0.1-0.2g.

All this affects a lot to the tunning of the shock, and also the design of the bike. If the system pedals very well, you don't need compression damping, but then you need a little bit more progressive Leverage Ratio. You can hear some people complaining about the Ibis Mojo HD bottoming out to easy, but you don't hear that from Specialized Enduro users, and that bike has a similar Leverage Ratio... but the difference is that the Enduro needs a lot of damping, and that helps a bit with the bottom outs.

Best regards,
Tony.

 

[Sandwich]

As much as I love crazy **** (and I LOVE crazy ****), I'm beginning to love simple **** even more. A single pivot in the right place and a rising rate linkage tuned well, with a good stiff frame and a well-valved shock just works sometimes, as I'm starting to learn.

I don't have the engineering degree to delve that deep into kinematics, but on some bikes I've ridden, the lack of predictability was a detriment.

 

[norbar]

It's a bit weird that you only talk about the slope, and not about the amount of Anti-squat, because with your bike you have a good number around sag, and then it goes even higher, DW-link it's like that too, it start with a good number. But what about VPP? sometimes it start with a low number...

Also, 0.5g seems like a lot to me, I would use something like 0.1-0.2g.

All this affects a lot to the tunning of the shock, and also the design of the bike. If the system pedals very well, you don't need compression damping, but then you need a little bit more progressive Leverage Ratio. You can hear some people complaining about the Ibis Mojo HD bottoming out to easy, but you don't hear that from Specialized Enduro users, and that bike has a similar Leverage Ratio... but the difference is that the Enduro needs a lot of damping, and that helps a bit with the bottom outs.

Best regards,
Tony.

LSC is more for stability in dh bikes than pedalling.

Also both frames have similar leverage ratio so why would spesh need more damping? That makes no sense. Not to mention preventing excessive bottom out with damping is a silly idea.

 

[Steve M]

LSC is more for stability in dh bikes than pedalling.

Also both frames have similar leverage ratio so why would spesh need more damping? That makes no sense. Not to mention preventing excessive bottom out with damping is a silly idea.

What Vrock is saying is correct - the pedalling performance of the Mojo is substantially better than the Enduro, which means that the degree of LSC/platform required in a shock tune for a Mojo is lower than that of the Enduro, which in turn means that there is less incidental damping (from pedalling concerns) to help resist bottom out. This has to also be factored in to the spring rate required from the shock, however the practical aspect of this is that small alterations in air pressure/spring curve have more useful effects on the bottom out resistance of these particular bikes than the damping - particularly when using relatively non-adjustable air shocks such as Floats.

Hi all,
There are a few suspension geeks on this forum that might be interested in this article.
It's on the front page of www.i-tracksuspension.com

For those that are likely to fall asleep after the second sentence, here’s the gist of it:

Having Anti-Squat that increases with suspension travel can be used to strategically increase the wheel rate when pedalling. This would help maintain the natural frequency of the suspension system under acceleration.

Having Anti-Rise that increases with suspension travel can be used to strategically decrease the wheel rate when braking. This would help maintain the natural frequency of the suspension system under braking.

Other strategies might include making the wheel rate more or less ‘progressive’ under hard acceleration and/or braking.

For the shock tuners out there: How would this affect the way you tune shocks, knowing that the wheel rate could be quite different under pedalling, compared to coasting?

Cheers,
Hugh.

Interesting article Hugh! From a shock tuner's perspective, considering the effect of anti-squat on wheel rate would only be particularly relevant when tuning shocks that essentially have two separate characteristics (ie those with an on the fly lockout/platform switch). In these cases, the only way a tuner could maintain a given damped natural frequency is by altering the damping coefficient in the locked out mode in proportion to the expected change in effective wheel spring rate. Practically speaking, the LS-damped natural frequency is less of a concern whilst pedalling in a locked-out mode as the bike is usually overdamped in this setting anyway, at which point the tuner's main concern becomes the force threshold required of the platform.

For shocks with no lockout, the tuner generally has to work on two assumptions:
1. That pedalling characteristics as well as basic stability need to be accounted for by the LS circuitry, and that with frames showing poor pedalling characteristics, there will almost always be a compromise between the two.
2. That most high speed events occur whilst coasting or braking (obviously you're not going to get shaft speeds of 4m/s whilst pedalling up a hill!). Given the impracticality of separating tunes during coasting from those during braking (obviously nobody turns lockout on just so they can get on the brakes, for example), there again exists the likelihood of compromising performance whilst coasting, braking or both.

Because of the compromises any given frame may demand, the best available shock tune is still somewhat at the mercy of the frame.

 

[Vrock]

LSC is more for stability in dh bikes than pedalling.

Also both frames have similar leverage ratio so why would spesh need more damping? That makes no sense. Not to mention preventing excessive bottom out with damping is a silly idea.

The spesh need more damping because it has a less Anti-squat and bobs a lot more than the Ibis. And remember that with a Fox shock with boostvalve platform and progression are related, if you want platform, you get progression too... if you don't want platform you lose progression, even if you want to keep it...

 

[Steve M]

And remember that with a Fox shock with boostvalve platform and progression are related, if you want platform, you get progression too... if you don't want platform you lose progression, even if you want to keep it...

Assuming you're referring to Floats here (which require nitrogen charging in order to change the BV pressure anyway), that is not necessarily the case as the LS/platform adjustment can be changed quite substantially just by altering the ProPedal configuration (requires a full rebuild & special tools as well as parts that FOX don't make available to the general public however). In terms of HS characteristics particularly around the LS/HS threshold velocities, the Boost Valve behaves a lot like the preloaded shim stacks in the non-BV models, except more finely adjustable and with a fairly constant P-O characteristic, and obviously with end-stroke ramp up that the non-BV models don't have. Altering IFP depth allows you to control progression independently of HS threshold too.

In my opinion, for most leverage rates, the BV Floats are superior to the non-BV ones.