shock rate / spring rate / wheel rate

http://www.santacruzbicycles.com/en/ca/news/348

i still don't totally understand it all - seems variables keep falling out of my head as i try to put the whole thing together - but i think i'm getting closer. thanks joe

cliff notes:

In Joes example:

Bike Rate - This is the leverage rate created by the suspension design. As the bike moves through it's travel, the leverage rate changes. The simple way to figure this out is divide the wheel travel by the shock travel. This gives you the simple rate, but in reality it changes throughout. If you look at Joes graph - V10 has a rising rate. Heckler is a flat rate. Blur has a falling rate at the beginning of travel before it flattens and then becomes a rising rate at the end of travel.

Shock Rate - This is the rate of the spring on your bike. A coil spring takes the same amount of force to compress it one inch, throughout the travel. So, if it takes 100 pounds to compress it one inch at the start of travel, if you're at mid stroke and add another 100 pounds, you'll compress it another inch. Air springs tend to be rising rate, to one extent or another. So, at the end of travel, it takes progressively more travel to compress it a similar distance. And the lower the volume of the air spring, the more rising rate this is.

Wheel Rate - If you add these two things together, you get the bike rate. Rising rate linkage with a rising rate shock? A whole shit tonne of rising rate. Falling rate linkage with a rising rate shot? Who knows. Something closer to a straight rate at the wheel. I think what he's trying to say is that there is no easy answer. The design of the suspension is a whole range of variables, and the shock adds another dimension on top of that.

Missing from the equation - Damping rates. On top of the "spring" portion of the shock, you have the damping curves of the shock to throw into the mix. Good luck finding any info on that from the manufacturers though. But it can impact things just as much.

Hope that helps. Might just be a regurgitation.

thanks for the dirk notes

Falling rate linkage with a rising rate shot? Who knows. Something closer to a straight rate at the wheel. I think what he's trying to say is that there is no easy answer. The design of the suspension is a whole range of variables, and the shock adds another dimension on top of that.

Missing from the equation - Damping rates. On top of the "spring" portion of the shock, you have the damping curves of the shock to throw into the mix.

i think this is where i get to, and start thinking "but what about when you mix and match, or where there's a curve in the bike rate" or yeah, the impact of hi/lo speed compression damping…

i think this is where i get to, and start thinking "but what about when you mix and match, or where there's a curve in the bike rate" or yeah, the impact of hi/lo speed compression damping…

So my answer to that would be that at this point and time it is impossible to get any further.

Bike Rate - All we get from manufacturers are vague descriptors. If anything.

Shock Rate - We get less on this. "We worked closely with the shock manufacturer" is the extent of the communication. I would imagine that there are probably 5-6 stock tunes that the bike makers have to work with? Would be great if somebody shared this with us.

Damping Rate - Once again, nothing.

So, you can never figure out a wheel rate because you've got three unknown variables to work with.

The shock rate is a variable and tuneable but the bikes leverage rate (or bike rate as Graney calls it) isn't so that's the important one as that's ultimately what you 'feel' as the suspension compresses. I think all bike manufacturers should publish the leverage rate as they do geometry.

If you look at motorsport suspension, they will almost always go with a flattish leverage rate. If not how do you get predictable results from damping and spring rate adjustments? Personally a linear falling rate (progressive) is favourable. Predictable resistance, supple at sag point, easiest to tune.

http://linkagedesign.blogspot.ca/

http://www.bikechecker.com/

Once you understand it these two link can help you dig further into it.

I've not yet found a copy and started reading but "Motorcycle Handling And Chassis Design: The Art And Science by Tony Foale" is supposed a great resource.

I've not yet found a copy and started reading but "Motorcycle Handling And Chassis Design: The Art And Science by Tony Foale" is supposed a great resource.

Interesting book. Pretty cryptic at times. Really great for driving home the "holy shit, there's a lot to this" fact.

The shock rate is a variable and tuneable.

But not really. 99% of bikes are shipped with only one choice of shock. Almost none of these shocks have tunable spring rate/volume (other than swapping the coil spring or changing your air pressure). Many of them have no compression tuning, a 3 position lever at best. So it wouldn't be all that difficult for the manufacturer to provide something.

You could probably learn a lot from browsing through Cane Creek recommended base tunes. But it would be nice to have some info straight from the manufacturer.

But not really. 99% of bikes are shipped with only one choice of shock. Almost none of these shocks have tunable spring rate/volume (other than swapping the coil spring or changing your air pressure).

Well apart from the three options of compression tune, the five choices of air spring volume and volume reducer spacers.

On my shock at least.

Back in the day I had a bike that was 4:1. It was designed for what mountain biking was in the 80s/90s and didn't fare well when I brought it to BC and started riding steeps and doing stair gaps. 4:1 was super hard on the shock, which was doubly hard given the level of shock quality at the time.

I think the RM9 had the worse leverage ratio of all time. 2" stoke for 9" of travel.

You could probably learn a lot from browsing through Cane Creek recommended base tunes. But it would be nice to have some info straight from the manufacturer.

shock tune is quite subjective, though some base knowledge could have saved me a few head aches, (AKA I know nothing). Norco provides a card with suggested tune for the Range spec'ed with the DB air. I set up the GF's bike in line with what norco suggested and she hated it. so she took it down the road to a friend who who has a similar riding style to her and experience with the DB on a specialized enduro. the way he set it up was way different then the cheat sheet provided by norco. I am pretty sure he came up with what works for him through trial and error.