Building an Ohlins Shock

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I think he is talking about a progressive rate vs. Single rate spring.

Ohlins has both progressive and straight rate spring for the twin shock bikes.

See the spring dyno chart in post #15
There are many more, I did not want to fill the chart with runs.

On Mono shock bikes Ohlins only offers Straight rate springs, and in fork springs only straight rate springs.
 

robs ss

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Very nice!! Beautiful bike as well!! Your thread about these is one of the drivers for me to get these Ohlins going.
I could not find a Nitron listing for the Norton, were these the triumph shocks? I relise you had the SS spacers made.
What springs did you end up going with?
I’m away from home for a few days but will advise spring number when I get home. The Australian agent (Suspensions R Us) advised me that they had previously supplied shocks for ‘70s Commandos but I think the are just R3s with 330mm eye-eye length and for 3/8” bolts.
I will also post the drawing of the spacer. It requires a very small amount to be removed from the lower spring retainer to allow the spigot on the spacer to be sufficiently robust.
 
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This graph shows the damping profile of a shock using a single orifice for its damping, the curve is exponential and has a rapid increase in damping at high shock movement speeds. You can vary the curve by choosing a different sized hole, but the curve is then fixed when on the road. I refereed to this as single rate but I should have said single orifice.



The issue with this setup is the steep curve at high speeds, if you have bumpy roads you pick a larger orifice but then lack damping on smooth surfaces. So which sized hole you choose is a compromise.

This is the Wibers and Nitron 3 set up, there are effectively 2 stages to the orifice hole, as the speed of deflection increases shims are forced open to increase the size of the hole and this removes the exponential rise in the damping forces.



This allows you to pick 2 damping curves, one for use on smooth roads and the second to kick in when the going gets rough. The first curve is as a single orifice but at the point the shims are forced open the effective size of the hole is increased and so the tall end of the curve is replaced by a lower rate of damping increase.
 

robs ss

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Very nice!! Beautiful bike as well!! Your thread about these is one of the drivers for me to get these Ohlins going.
I could not find a Nitron listing for the Norton, were these the triumph shocks? I relise you had the SS spacers made.
What springs did you end up going with?
I seem to be having trouble with posts while away from home - will send info in a couple of days.
 
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This graph shows the damping profile of a shock using a single orifice for its damping, the curve is exponential and has a rapid increase in damping at high shock movement speeds. You can vary the curve by choosing a different sized hole, but the curve is then fixed when on the road. I refereed to this as single rate but I should have said single orifice.



The issue with this setup is the steep curve at high speeds, if you have bumpy roads you pick a larger orifice but then lack damping on smooth surfaces. So which sized hole you choose is a compromise.

This is the Wibers and Nitron 3 set up, there are effectively 2 stages to the orifice hole, as the speed of deflection increases shims are forced open to increase the size of the hole and this removes the exponential rise in the damping forces.



This allows you to pick 2 damping curves, one for use on smooth roads and the second to kick in when the going gets rough. The first curve is as a single orifice but at the point the shims are forced open the effective size of the hole is increased and so the tall end of the curve is replaced by a lower rate of damping increase.
There are 3 types of VALVES, not holes, in any GOOD aftermarket shock, They are Progressive, Linear and Digressive.

Your artwork shows the damping curve to be Progressive, (green lines) something very rare to see in an Ohlins motorcycle product. Ohlins prefers a Linear valve for most MOTORCYCLE products.

With the curve you are showing, no wonder you need something to reduce damping.
This graph shows the three valves more the way they really are, not steep arcing lines.


When I use these terms, Progressive, Linear, Digressive, it is in discussing the design of the valve, as I think is the case with most suspension people. Of course you can use the terms anyway you want.


When talking about a shock or fork that uses a mechanism, that reduces the amount of damping when a higher load is applied such as a bump, that task, as you describe it here is done by a blow off valve, uncommon in a rear shock, very common in a front fork, there the type most used is referred to as a mid valve.
The reason it is used in a fork is due to brake dive, when you are using the brake hard, the front suspension travel is being used up, now when you hit a bump, it is transfered to the rider, this is reduced by allowing the damping to be reduced by the Midvalve or blow off valve. The advantage of the midvalve is it is a shim stack that can be adjusted. We have had this available to us for 20 years.
The newer Ohlins cartridge kits, and they are always getting better, reduce the brake dive better than you an imagine.

Your top graph describing a HOLE metering oil, is what very inexpensive forks and shocks use, or very old.
We like to call those REALLY GOOD $10 shocks.

You Said "This is the Wibers and Nitron 3 set up, there are effectively 2 stages to the orifice hole, as the speed of deflection increases shims are forced open to increase the size of the hole and this removes the exponential rise in the damping forces."

Of course as the speed of Deflection increases the shims that control the damping are going to flex more and allow more oil to pass thru.

How is that "2 stages"? That is how every shock with a valve and shim stack work, nothing special there.

Here is a link to Pictures of a Disassembled Nitron shock, (scroll down to see it) Looks very conventional to me.
 
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Pictures of Ohlins shocks mount on a Norton


]



 
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Test fitted some springs today.
We used a 25 to 35 Nmm spring, if you go back to post #15
You can see the top line is that spring
With 13 mm of spring preload and a 209 lb rider (without gear) we measured 30 mm rider sag and 10 mm static sag
I think this spring will work with a rider weight of 185 lbs up to at least 240 lbs
For under 185 lbs I will try a 20 to 29 Nmm spring
 

p400

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Can you entice a local Norton Mk3 owner to lend you a Mk3 for 6 months or so?
Maybe a free set of Ohlins?

Seat, footpegs, fuel load, chain guard, rear disc caliper would be more common to the Norton build.

1975MklllInterstateSm1.jpg
 
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Thanks
I do not need to borrow a bike, I have a 1971 roadster to test them on as well.
I would like to have some people test them, and try different springs as well as get feedback.
Any volunteers? The closer the better.

 
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I have also looked at the forks, it is possible to install Ohlins NIX 22 Kits in the Norton forks.


I also mounted up an Ohlins damper, we will have these in silver and black.
And it fits with the stock coils.

]



 
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gortnipper

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I'll certainly volunteer.

Probably not as close as you like...

What price on the SD? Mounts with 6M?
 

storm42

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So the Ohlins only have single rate but adjustable damping, so no real upgrade against most currently available damping units.

For a real upgrade then either the Wilbers or the Nitron R3 shocks would be a better option, these have dual damping rates based on speed of shock movement giving digressive damping and both rates are adjustable separately giving 4 adjustments. High and low speed compression plus high and low speed rebound.
Ha, most people have trouble setting static sag :D
 

lcrken

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Great thread, Dan. Please keep it going. I'm a big fan of Ohlins shocks and forks, having used them on several race bikes in the past. I've lately been experimenting with springs and damping settings on the ones on my Commando 961 Sport. I'm using the local bumpy, twisty roads as my test rig, considerably less scientific than your dyno, but certainly entertaining. I'm finding it quite challenging getting a good compromise between comfort and performance. It was a lot simpler on the track. I've concluded that Ohlins got the high speed compression damping about right on the forks, so I don't miss having that adjustibility. But I can see where it might be nice to have when needed. My Street Triple clearly has way too much high speed compression damping in the forks, and the only way to fix it is to change the shim stack, something I have no experience at. It would be nice to have an external adjustment for it.

On the other hand, as storm42 pointed out, most Commando owners would be happy to just have an off-the-shelf shock that was already set up properly for their bike, with maybe just spring preload adjustment to account for occasional 2-up riding or luggage. That would seem to be one of the end results you are working towards.

Just to be clear, none of the three shocks discussed in this thread (Wilbers, Nitron, and Ohlins) offer both high and low speed rebound damping external adjustment. The Wilbers and Nitron offer separate high and low speed compression adjustment, and the Ohlins a single compression adjuster. All three offer a single external rebound damping adjustment. Ohlins lists an option (C2) for high and low speed compression damping, but doesn't include it on any of the standard catalog items for the twin shocks that might fit Commandos. It's possible one could order a custom build on the STX 36 line that included it, but I'm not sure if Ohlins would be willing to build it. For sure it wouldn't be cheap.

FWIW, back when I was racing Commandos, I tried several brands of rear shocks and a couple of different spring rates, from 60/90 lbs/in dual rate to the standard 126 lbs/in straight rate. During most of my raceing years, I probably weighed between 170 and 175 lbs without gear. I ended up using 80/100 lbs/in (14.0/17.5 N/mm) dual rate springs on my Production Racer, which was a bit lighter than the standard Commando models. I also raced a heavier MK3 roadster, originally with the stock 126 lbs/in springs and Girling shocks, and later with Boge shocks and 80/100 lbs/in springs. With it's extra weight, it was pretty much a pig on the track no matter what shock setup I used. On various street Commandos over the years, I've mostly just stuck with the stock 126 lbs/in (22.0 N/mm) springs, and adjusted the preload to suit me. That seemed to work well with the stock Girlings with pretty much no compression damping. With a more modern shock design with real compression damping, I would expect the good setup to be a slightly softer spring, with a bit more preload.

Ken
 
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Great thread, Dan. Please keep it going. I'm a big fan of Ohlins shocks and forks, having used them on several race bikes in the past. I've lately been experimenting with springs and damping settings on the ones on my Commando 961 Sport. I'm using the local bumpy, twisty roads as my test rig, considerably less scientific than your dyno, but certainly entertaining. I'm finding it quite challenging getting a good compromise between comfort and performance. It was a lot simpler on the track. I've concluded that Ohlins got the high speed compression damping about right on the forks, so I don't miss having that adjustibility. But I can see where it might be nice to have when needed. My Street Triple clearly has way too much high speed compression damping in the forks, and the only way to fix it is to change the shim stack, something I have no experience at. It would be nice to have an external adjustment for it.

On the other hand, as storm42 pointed out, most Commando owners would be happy to just have an off-the-shelf shock that was already set up properly for their bike, with maybe just spring preload adjustment to account for occasional 2-up riding or luggage. That would seem to be one of the end results you are working towards.

Just to be clear, none of the three shocks discussed in this thread (Wilbers, Nitron, and Ohlins) offer both high and low speed rebound damping external adjustment. The Wilbers and Nitron offer separate high and low speed compression adjustment, and the Ohlins a single compression adjuster. All three offer a single external rebound damping adjustment. Ohlins lists an option (C2) for high and low speed compression damping, but doesn't include it on any of the standard catalog items for the twin shocks that might fit Commandos. It's possible one could order a custom build on the STX 36 line that included it, but I'm not sure if Ohlins would be willing to build it. For sure it wouldn't be cheap.

FWIW, back when I was racing Commandos, I tried several brands of rear shocks and a couple of different spring rates, from 60/90 lbs/in dual rate to the standard 126 lbs/in straight rate. During most of my raceing years, I probably weighed between 170 and 175 lbs without gear. I ended up using 80/100 lbs/in (14.0/17.5 N/mm) dual rate springs on my Production Racer, which was a bit lighter than the standard Commando models. I also raced a heavier MK3 roadster, originally with the stock 126 lbs/in springs and Girling shocks, and later with Boge shocks and 80/100 lbs/in springs. With it's extra weight, it was pretty much a pig on the track no matter what shock setup I used. On various street Commandos over the years, I've mostly just stuck with the stock 126 lbs/in (22.0 N/mm) springs, and adjusted the preload to suit me. That seemed to work well with the stock Girlings with pretty much no compression damping. With a more modern shock design with real compression damping, I would expect the good setup to be a slightly softer spring, with a bit more preload.

Ken
Thanks for the spring info.
If you would like some help setting up your 961, let me know I think, I can suggest some things to try. And loan you the parts as well.
If nothing else provide the Ohlins spec sheets.
I came across your
Norton vs Ducati at Willow Springs 1987 Thread
I was there that day as well, and was at all the Willow springs races in 1987. Small world.
 

robs ss

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Nearly forgot to do this.. pics of the mods to the Nitron R3s.
The spigot at the top of the new spacer means that the ID of the lower spring retainer needs to be skimmed (41.6mm out to 43.1mm) otherwise the spigot would, in my opinion, be too fragile.
I'm still in love with the improvement in ride these shocks deliver.
IMG_0238.jpg
 

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Nearly forgot to do this.. pics of the mods to the Nitron R3s.
The spigot at the top of the new spacer means that the ID of the lower spring retainer needs to be skimmed (41.6mm out to 43.1mm) otherwise the spigot would, in my opinion, be too fragile.
I'm still in love with the improvement in ride these shocks deliver.
View attachment 17888
What's the travel of that Nitron shock?
 

p400

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Dan, Is there a spring sleeve that Ohlins offers to accomplish what i see with this pictured Nitron build?
Moving the larger diameter spring up the cylinder to clear the bottom install.
I am not sure I like the debri/roadgrime cup this sleeve provides nor the potential to not allow the bump rubber to function properly, but it does allow Norton bottom install.


NitronMod1.jpg
 
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