Changing the shock spring rate?

[maz20]

I'm looking to soften up the rear suspension on the FZ-07. I swapped out the stock rear shock with an Ohlins YA-419, which comes with a 115N/mm spring. It still feels rather stiff (even after revalving to remove some of the compression damping), so I'm considering getting a lighter spring. Ohlins carries a wide range of springs for this rear shock, all of which come at 170mm free length but vary all the way from 40-230N/mm (usually around 5N/mm increments).

 

From basic calculations, I can easily keep proper static sag even with their 65 N/mm spring, but the suspension dealer I was talking about near my area said to not go below 95N/mm as that would require "too much preload". But, whereas my 115N/mm was taking 41% of available preload, the 65 N/mm would just take 87.5% of available preload adjustment (for proper rear static sag). For reference, 95N/mm would take up 53% of the maximum preload adjustment distance (for proper rear static sag).

 

So, what exactly does it mean for a shock spring to take "too much preload"? Is that just something related to the "spring" itself, or am I just not supposed to go past some preload distance on the preload adjuster??? : /

 

I generally just ride around mostly in the city (crappy roads ton of bumps and potholes), and am thinking of trying out the 75N/mm spring. If anything, I'd still get to keep my 115N/mm spring if the 75N/mm turns out too soft (or, likewise, I could purchase afterwards the dealer-recommended 95N/mm, right between 75 and 115!)

[stickshift]

75 n/mm is far too light, that's over 33% reduced spring rate compared to standard ohlins. You'll be bottoming out (bump stop) everywhere regardless of your preload setting.

 

How much do you weigh with gear?

 

I'm 70 kg with gear, I ordered a different spring with my ohlins, will check for you when I get home.

 

 

[maz20]

1 hour ago, stickshift said:

75 n/mm is far too light, that's over 33% reduced spring rate compared to standard ohlins. You'll be bottoming out (bump stop) everywhere regardless of your preload setting.

 

How much do you weigh with gear?

 

I'm 70 kg with gear, I ordered a different spring with my ohlins, will check for you when I get home.

 

 

Ahh with gear I'm a little heavier at 100 kg

[stickshift]

The stock ohlins spring (115 n/mm) was too stiff for my weight, I went for a lighter 110 n/mm. I could have gone for the 105 (around 10% lighter than standard), but I prefer a setup erring on the harder side for occasional track riding.

 

You should really be judging whether the spring rate is correct for you by referring to the ohlins setup figures - if you're not within the rider sag range (+/- 5 mm or so) a change of spring is recommended (get a helper to measure):

 

Free sag (adjust via preload): 6 mm

Rider sag (adjust via spring rate): 30 mm

 

[faffi]

Too much rebound will make the shock feel like the spring is way too stiff. I have a Nitron shock and cannot detect any difference in compliance regardless of where I set compression damping, but rebound has a massive impact. 

[pattonme]

100kg you should be running a 125N/mm but such an animal doesn't exist. stick with the 115 and check your rebound like Faffi said. The Ohlins comp side was already 'weak' from the factory so I'm surprised you took more shims out. Bear in mind too that for a given bump (hole) you hit the amount of force imparted into the shock is the same. The stiffer the spring the slower the action on the piston. So conversely the weaker the spring the faster you demand that piston push thru it's stroke. Which will expose flow problems in the piston/shim stack.

 

The rebound should be as loose as possible without inducing oscillations. If you're still not happy, use a thinner shock oil.

[gregjet]

On a side note. Are you sure the stiff feeling isn't the tyres. The stock Bridgies or say, Dunlops, can make your suspension feel stiff. I have seen plenty of riders change springs all over the place and discover when they change tyres it was the type of tyre that was the problem ( and vice versa BTW).

You sound like you know what you are talking about but just a reminder that tyres factor into the feel equation as well. So I am not saying it IS the cause just consider it if you haven't.  If like me you favour a more compliant tyre ( eg Michelin feel), you may be blaming the suspension rather than the other component.

[Beemer]

21 hours ago, gregjet said:

On a side note. Are you sure the stiff feeling isn't the tyres. The stock Bridgies or say, Dunlops, can make your suspension feel stiff. I have seen plenty of riders change springs all over the place and discover when they change tyres it was the type of tyre that was the problem ( and vice versa BTW).

You sound like you know what you are talking about but just a reminder that tyres factor into the feel equation as well. So I am not saying it IS the cause just consider it if you haven't.  If like me you favour a more compliant tyre ( eg Michelin feel), you may be blaming the suspension rather than the other component.

Just curious, when you talk about a different tire causing a 'stiff feeling' is the focus on the stiffness of the sidewall or does that feeling have more to do with the belts inside the tire, the compound? (or all???)

[shinyribs]

On 1/8/2018 at 4:46 AM, faffi said:

Too much rebound will make the shock feel like the spring is way too stiff. I have a Nitron shock and cannot detect any difference in compliance regardless of where I set compression damping, but rebound has a massive impact. 

Too little compression damping can do the same. Less compression isn't always smoother. If loose compression is allowing bottoming it's feel harsh. 

[gregjet]

Beemer,

Too be entirely honest I am not sure whether it is one or several things that cause it. Could even be like suspension problems where you feel one end is a problem, but it is actually the other end.

I do know that some tyres feel "harsh" , though explaining exactly what that means is difficult. Dunlops and The Bridgies that come on the 07 feel almost like you are riding on solid rubber in a way. Michelins feel like they are conforming and sticking to the surface ( Michelins feel the same in car tyres I have found).

I have trouble racing with Dunlops , for example because they feel ( to me) like they are skating rather than sticking ( though often the timing numbers do not bear that out). It is consistant enough to be a "thing'. But exactly what that "thing" is I am at a loss to quantify.

As I have said on several occasions the Bridgies that come OEM on the 07 have a harsh feel that I find quite uncharacteristic of the brand. Having said that I have experienced Bridgies with theat feeling before. Noteably a long gone model with a similar model number the truely aweful BT23's. Interestingly even the model number isn't enough with Bridgies , as the OEM tyres ( BT45's) that came fitted to Honda Spada and VTR250's were harsh as hell AND made the bike feel like it was falling into a corner, whereas the aftermarket ones felt planted and smooth transitioning.

The first thought is to blame the construction , and it is probably the cause , but I haven't seen anything that bears that out .

Interestingly in dirt tyres THE most stiff carcassed tyre of iron I ever had on a bike was a Trelleborg. 45mins to get a tyre on a rim where I usually took 5 to do and entre change. It was also THE most smooth tyre I have ridden on, so  difficult to draw a definitive construction link.