Help! I'm getting randomly bucked forward on my new V4 Santa Cruz Nomad

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Help! I'm getting randomly bucked forward on my new V4 Santa Cruz Nomad
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Posted: Apr 3, 2019 at 4:41 Quote
Hey everyone
I'm sitting here typing this to you with a fractured wrist and grade three acromioclavicular tear in my right shoulder. Why? Because I was in a race over the weekend and the bike didn't behave quite as I expected over a jump.

I have a new Santa Cruz V4 Nomad. I love this bike, it climbs so well, descends like a beast and is a beautiful piece of machinery. I've hit some big booters on this thing too and usually I have zero problems but I in the 3 months that I've owned this bike there has been 5 or 6 occasions where I've been severely and unexpectedly been thrown forward off a jump. Usually I've ridden out of it, this weekend, however, I was not so lucky and landed on my wrists, head and shoulder when I was thrown severely forward off a reasonably small jump.

I am a bike mechanic by trade and have been meticulous to set up my suspension right. I have the rebound on the rear (rockshox super deluxe) two notches slower than the fork (fox 36 float). I have had numerous dual suspension bikes, and a 2018 Santa Cruz 5010 before this bike. I have NEVER had this case of random forward kicks before on any bike. I've heard the VPP can have negative effects on jumping, and that the firm midstroke of this particular Nomad design might have something to do with it. But can anyone help? I love my bike but I don't want it to end me up in a wheelchair!

Posted: Apr 3, 2019 at 5:07 Quote
Why 2 notches slower than the fork? You shouldn't base your rebound settings on the fork settings. Different leverage ratios will influence rebound rate so it may be that the rebound is too fast.

Posted: Apr 3, 2019 at 5:12 Quote
I should say that I get the rebound on the front and rear to work as fast as each other, then adjust it so the rear rebound is two clicks slower then that setting. Another way of saying it is, I do the curb test where you sit down, ride off a curb, adjust rebound till you have one oscillation, set the front up at about the same rate, then slow the rear rebound down two clicks from there. So its not really slow but its certainly not fast. Still, I get bucked forward. Help!

Posted: Apr 3, 2019 at 8:48 Quote
Bucking means your rebound is not set up correctly and either your fork is pulling you forward too much, your rear is pushing you forward too much, or a combination of the two. Slow things down, and try again.

Posted: Apr 3, 2019 at 10:39 Quote
Likely what's happening is that you're running into these "smaller" jumps at race speed, which will sink you further into your travel than usual. Your shock is then blowing through the rebound damping and kicking you forward. Sometimes riders that end up going OTB have a very aggressive rider-forward riding position. For those riders, setting up suspension based on the "curb test" isn't effective. Basically, in the "curb test" you're riding with something like 65% of your weight on the rear wheel, but out on the trail you're closer to 50% or even lower. The result is that you're under-damped and your bike is "bucky".

There are two good fixes to this:

1) Fix the setup

Increase your HSR damping. It'll keep your shock under control deeper into the travel, and make things more predictable. Unfortunately, your Super Deluxe only has 1 rebound adjustment. To get a similar effect, you could lower your air pressure, add a spacer, and add a few clicks of overall rebound damping. That'll lower the pressure in your mid-stroke and make the rebound more effective. Be warned, though, it will make your bike less supple over smaller chatter. You could also get a different shock with a 4-way damper, and set it up to account for that issue.

2) Fix the position

Change the front end of the bike. If you lengthen your fork, reduce fork sag, shorten your stem, increase your stack, or use a riser bar (or any combination of those), it'll help you push your weight further back toward center on the bike. That'll create additional load on the rear shock to help keep its movement under control. Essentially, you're altering your on-trail position to more closely resemble the conditions when you set up your suspension.

Posted: Apr 3, 2019 at 15:26 Quote
Amazing info guys. I really appreciate it! I currently have 170mm travel front and rear, 15mm of headset spacers and a 20mm rise handlebar. I’ve been wanting to go to a 30mm rise bar, so I will get a Renthal 30mm bar.

I can see how lowering air pressure, increasing volume spacers and increasing rebound dampening combined would make a shock that doesn’t bounce back through the mid stroke so aggressively. That said I think I’ll invest in a Fox X2 rear shock with high and low speed compression/rebound dampening for this bike.
I’ve heard the high speed rebound dampening on this shock be described as a ‘safety net’ for being bucked forward which seems like a damn good investment to me!!

Posted: Jan 19, 2021 at 9:34 Quote
How did you end up sorting this out? I'm having the same issue on my new-to-me Nomad V4. Considering the Fox X2 but wanted to explore settings first.

Running a 38 up front makes the back end feel like garbage (saw that one coming). I'm a light but aggressive rider at 145 lbs dressed. Front end floats and stays glued to the ground while the back end occasionally bucks during the fastest and most chattery sections, tipping me forward. I'm currently running 30% rear sag with one spacer. Rebound seems either too slow (wallows and then bucks) or too fast (pogo stick). I'm using all my travel too frequently (first spacer helped slightly), so I want to try option 1 below, but recognize that the Super Deluxe has limited adjustability.

Posted: Jan 19, 2021 at 14:25 Quote
tsattler wrote:
How did you end up sorting this out? I'm having the same issue on my new-to-me Nomad V4. Considering the Fox X2 but wanted to explore settings first.

Running a 38 up front makes the back end feel like garbage (saw that one coming). I'm a light but aggressive rider at 145 lbs dressed. Front end floats and stays glued to the ground while the back end occasionally bucks during the fastest and most chattery sections, tipping me forward. I'm currently running 30% rear sag with one spacer. Rebound seems either too slow (wallows and then bucks) or too fast (pogo stick). I'm using all my travel too frequently (first spacer helped slightly), so I want to try option 1 below, but recognize that the Super Deluxe has limited adjustability.

What about speeding the fork rebound up some more rather than trying to slow the rear down?

There is the old adage "less is more". I have seen the advice "when in doubt, move to less damping". If it is only bucking once and a while in the fastest chattery sections, it may be packing down because it isn't rebounding fast enough. Experiment. Try less sag with no spacer to get you higher in the travel?

Posted: Jan 19, 2021 at 14:57 Quote
ShawMac wrote:
tsattler wrote:
How did you end up sorting this out? I'm having the same issue on my new-to-me Nomad V4. Considering the Fox X2 but wanted to explore settings first.

Running a 38 up front makes the back end feel like garbage (saw that one coming). I'm a light but aggressive rider at 145 lbs dressed. Front end floats and stays glued to the ground while the back end occasionally bucks during the fastest and most chattery sections, tipping me forward. I'm currently running 30% rear sag with one spacer. Rebound seems either too slow (wallows and then bucks) or too fast (pogo stick). I'm using all my travel too frequently (first spacer helped slightly), so I want to try option 1 below, but recognize that the Super Deluxe has limited adjustability.

What about speeding the fork rebound up some more rather than trying to slow the rear down?

There is the old adage "less is more". I have seen the advice "when in doubt, move to less damping". If it is only bucking once and a while in the fastest chattery sections, it may be packing down because it isn't rebounding fast enough. Experiment. Try less sag with no spacer to get you higher in the travel?

The fork is so composed and not divey I'm not currently inclined to mess with that. It rides pretty high in the travel already. I've had bikes during experimental tuning that are too springy on both ends, teetering front to rear is no fun either.
True I've heard similar guidance that suggests suspension packing out can mimic rebound that's too high. Currently hard to tell where I'm sitting in the travel when this is happening. It's pretty jarring when it bucks or deflects, so I suspect I'm too deep in the travel and just smacking a wall. Let the experimenting continue.

Posted: Jan 19, 2021 at 15:31 Quote
Packing down is where I would look first. Damping need is related to the pressure (spring rate) so if you are running lower pressure than on the chart for your weight, you'll need less damping.

I had the same thing happen with a previous set of forks. I was bouncing all over and feeling really jarred; went back to recommended rebound setting and then went a click or two faster because I had lower pressure and boom, things got better. I had at least three too many clicks of damping so I was just packing way down.

Posted: Jan 19, 2021 at 15:42 Quote
That all makes sense, thanks for the suggestions. Going to try a little more air and same rebound. Unfortunately these shocks only have a single adjustment so we'll see. I think more tokens will get too progressive since the Nomad is already a progressive frame.

Posted: Jan 20, 2021 at 4:30 Quote
The rebound tune on the Super Deluxe is partially why I sold mine (Megatower). If I set it slow enough to feel good on jumps it would pack down in rock gardens. I've been jumping bikes for a long time so it's not me being overly cautious by trying to run super slow rear rebound either. I went to an X2 which has been awesome.

Posted: Jan 22, 2021 at 23:50 Quote
you also need to look at the tire pressure everything contribute to a more harsh chattery trails. if you can go back to that trails and do it over and over again you can sort that problem easily.

Posted: Jan 23, 2021 at 23:53 Quote
Some thoughts :
Is the rear too active?
What happens if you set the damping at each extreme?
What is the stack height?
Is the reach just too long and there is too much upper body forward?

There does come a point where the current "longer, lower, slacker" mantra ceases to be a benefit.

Posted: Jan 24, 2021 at 5:54 Quote
Before you can fix it, it is important to understand wheat is happening. When you are getting bucked while riding it typically means you are riding too low in the stroke, valving or spring rate is too soft and you are bouncing off the bottom of travel. In moto, it is called riding on the bumper. Dirt bikes have a rubbber stop on the shock shaft that creates a "soft" stop. Ever see those guys bikes kick sideways thru a section of rough terrain? I take it the bike is working good thru a section then bam, kicks? When you have no more travel and hit something only thing that can happen is that energy gets transferred to you. Correct air pressure, less rebound damping, more compression damping. One or a combo of these should correct your problem.

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