fork oil

[craydds]

I thinks we have posted on threads about proper suspension set-up time and time again. In general, SS pretty much covered damping, spring rates, sag, preload, etc. We can go into intimate detail in anyone wishes, or you can go to sportrider.com where there a many good suspension articles available. A few words about damping... one main purpose of forks/shocks is to keep you tires in CONTACT with the road, this usually means you want your suspension to react QUICKLY (hence the advent of cartridge forks). More damping (heavier fork oil for you 30 wt guys) means the suspension moves SLOWLY. You want your suspension to respond FAST and return to neutral without BOUNCING, that is all! We can get into rebound vs. compression, but I will call it quits for now.

[brocktoon]

This has probably been gone over a number of times, but what's the word on replacement springs? I'm planning on replacing the springs on my R75/5 during the NorCal Airhead Tech Day. Huckys sells a fork rebuild kit, which I'm going to order, as well as progressive wound springs. Anyone tried these, or should I stick with the Heavy Duty OEM spring?

[craydds]

Originally Posted by brocktoon

This has probably been gone over a number of times, but what's the word on replacement springs? I'm planning on replacing the springs on my R75/5 during the NorCal Airhead Tech Day. Huckys sells a fork rebuild kit, which I'm going to order, as well as progressive wound springs. Anyone tried these, or should I stick with the Heavy Duty OEM spring?

I hear several recommending the Heavy Duty OEM springs. I ran the Progressive Suspension springs for many years with no complaints - some say they are too stiff; previously I ran with stock BMW springs (too soft for me). I am now running the HyperPro springs - haven't had enough testing yet, still need to fine tune the LADEN SAG. So far, they feel great, but I have been taking it easy. Soon I will take it out and THRASH it. Will report my findings after.

[RecycledRS]

As has been stated previously in this post, the viscosity of different brand oils are not the same even though the weight may be. This site shows some common oils and the variations : http://www.peterverdone.com/wiki/ind...spension_Fluid

[supershaft]

Originally Posted by brocktoon

This has probably been gone over a number of times, but what's the word on replacement springs? I'm planning on replacing the springs on my R75/5 during the NorCal Airhead Tech Day. Huckys sells a fork rebuild kit, which I'm going to order, as well as progressive wound springs. Anyone tried these, or should I stick with the Heavy Duty OEM spring?

I have tried Progressive brand progressively wound springs on my own R65 and Mono. WAY too stiff with virtually no sag with no preload. And progressive recommended a lot of preload with one application if I remember correctly. You would have to be Mr Universe to get the cap back on. I have taken Progressive brand springs back OUT of many a bike in order to get the bike handling better again. Too stiff is not only too stiff but you have more stiction too and that is a big cause of shimmies and shakes. I would run the regular stock spring with a lot more preload. I think that works better than the Heavy Duty spring.

[craydds]

Originally Posted by supershaft

You would have to be Mr Universe to get the cap back on.

Ha! So true. Been there, done that. Anybody want my Progressive springs? Free. You pay shipping.

[craydds]

Originally Posted by RecycledRS

As has been stated previously in this post, the viscosity of different brand oils are not the same even though the weight may be. This site shows some common oils and the variations : http://www.peterverdone.com/wiki/ind...spension_Fluid

In previous posts inmates have mentioned mixing 10 wt. with 5 wt., (whatever) blah, blah, to get a 7.5 wt. oil. You mix sugar with water and you have sugar water. Molecularly, you still have sugar molecules and water molecules. If you mix 30 wt. with 10 wt. you do NOT have 20 wt. You only have an miscible molecular mixture of 10 and 30. Would you you "mix" 20 wt. motor oil wit 10 wt. to get 15 wt.? Run the correct wt. motor oil. Run the correct wt. fork oil. I am running 5 wt. in my forks. 7.5 or 10 wt. might be okay, hey, it's your bike. There was one of my local NM inmates said he was running 30 wt. motor oil in his forks, said he liked it... hmm. To each his own. I recommend sticking with the stock recommendations - nothing wrong with listening to the suspension gurus who have more experience than me.

p.s. I am a chemistry major. I have a degree in chemistry. That means I am qualified to dig ditches with a DIPLOMA in my back pocket.

[ontic]

Originally Posted by supershaft

I have tried Progressive brand progressively wound springs on my own R65 and Mono. WAY too stiff with virtually no sag with no preload…
I would run the regular stock spring with a lot more preload. I think that works better than the Heavy Duty spring.

For our airhead forks, I've read this conversation many times on this forum before and it begins to strike me a little odd. As you yourself said earlier SS, preload does not change spring rate. Emphasising the importance of correct preload before changing oil weight is all well and good, but of course so is starting off with the right spring rate in the first place- and here is where it gets odd to me. Often this conversation now talks about progressive or heavy duty vs regular. Two, maybe three spring rates often differentiated not by numbers (.**Kg/mm) but by brand or type. Shouldn't we be getting a little more nuanced than that?
The way I understand it:
changing oil weight is not an optimal cure for wrong sag/preload or wrong spring rate, and changing sag/preload is not an optimal cure for the wrong spring rate. Of course for fine tuning and getting the best out what you've got, you can blur the lines a little maybe, but first things first.

For a lot of us who have done front end swaps recently (the 'unholy union threads' etc), when off-the-shelf springs in ideal rates were not available we've ended up getting springs custom wound to our specifications. It doesn't cost all that much and you get exactly what you are after.
Relying on 'heavy' or 'regular' (with virtually no, or alternatively heaps of, preload) seems about as antiquated as our forks are... they might work well for a few lucky people and bike set-ups but the compromises would seem to stack up for everyone else.

My point here is basically (and it is not at all my original idea, just my understanding of the basics of suspension set-up)- get the right spring rate first. If it is not for sale, that is not really an excuse, get them made, then set sag with preload, and tweak damping performance with oil weight and/or valve modifications.


FWIW, my R90 came to me with heavy progressive springs and personally I like the way it rides- it is possible I could do with a slightly lighter spring weight, but I do not like the feel of the regular ones- way to soft for my preferences.
I am around 100KG though, and like a firmer ride. Each to their own and YMMV.
It does take a bit of pressure to get the cap down, but you don't have to be Mr Universe.
After my first fork oil change I didn't like it with the (oft recommended) 5W fork oil so after a bit of experimenting I've settled somewhere around 7.5W. It seems to be a compromise that works OK for when my bike is both loaded down for touring and completely unloaded.
It works brilliantly for neither.
Personally I'm not fussed about keeping things 'original', so if I was looking to get the most out of the forks on my R90 or another airhead I'd probably be looking towards using more modern forks to start with (as I've done with the G/S).



oh, and craydds,
are you trying to say that those of us who have mixed different rate fluids have come up with some sort of special dual rate fork oil?
I have mixed (currently 5 and 10 mix in my R90 due to not being able to buy 7.5W at the time) and have been happy enough with the results, so I'd be interested to actually know what is going on physically in there..

[Beemerboff]

I gave my so called progressive springs away too - too stiff for me.

If you actually measure the spring rate of a so called progressive spring in the normal working range the degree of progressiveness is almost too small to measure - less than 1% so you aint missing much without them.

Stock springs work just fine, if you know how to fine tune them.

And balance them front to rear , which is probably more important.

Some current BMW adventure bikes have three switchable suspension settings, soft, medium and , err, hard, with electronic control of front and rear preload, and compression and rebound damping. Works well.

Other manufacturers have similar systems which only change the damping but they are still able to make it work, although the range is not as wide is the systems which also change the spring preload.

The adjustable HPN inserts in my GS forks work best with about 80% of the available rebound and 20% of compression. The HPN springs give 55mm rider sag. The rear Ohlins has a 450 lb spring with damping at the stock setting, which is around 50 % of the available compression and rebound, but that is preset as you only have one adjuster for both.

[supershaft]

Originally Posted by ontic

For our airhead forks, I've read this conversation many times on this forum before and it begins to strike me a little odd. As you yourself said earlier SS, preload does not change spring rate. Emphasising the importance of correct preload before changing oil weight is all well and good, but of course so is starting off with the right spring rate in the first place- and here is where it gets odd to me. Often this conversation now talks about progressive or heavy duty vs regular. Two, maybe three spring rates often differentiated not by numbers (.**Kg/mm) but by brand or type. Shouldn't we be getting a little more nuanced than that?
The way I understand it:
changing oil weight is not an optimal cure for wrong sag/preload or wrong spring rate, and changing sag/preload is not an optimal cure for the wrong spring rate. Of course for fine tuning and getting the best out what you've got, you can blur the lines a little maybe, but first things first.

For a lot of us who have done front end swaps recently (the 'unholy union threads' etc), when off-the-shelf springs in ideal rates were not available we've ended up getting springs custom wound to our specifications. It doesn't cost all that much and you get exactly what you are after.
Relying on 'heavy' or 'regular' (with virtually no, or alternatively heaps of, preload) seems about as antiquated as our forks are... they might work well for a few lucky people and bike set-ups but the compromises would seem to stack up for everyone else.

My point here is basically (and it is not at all my original idea, just my understanding of the basics of suspension set-up)- get the right spring rate first. If it is not for sale, that is not really an excuse, get them made, then set sag with preload, and tweak damping performance with oil weight and/or valve modifications.


FWIW, my R90 came to me with heavy progressive springs and personally I like the way it rides- it is possible I could do with a slightly lighter spring weight, but I do not like the feel of the regular ones- way to soft for my preferences.
I am around 100KG though, and like a firmer ride. Each to their own and YMMV.
It does take a bit of pressure to get the cap down, but you don't have to be Mr Universe.
After my first fork oil change I didn't like it with the (oft recommended) 5W fork oil so after a bit of experimenting I've settled somewhere around 7.5W. It seems to be a compromise that works OK for when my bike is both loaded down for touring and completely unloaded.
It works brilliantly for neither.
Personally I'm not fussed about keeping things 'original', so if I was looking to get the most out of the forks on my R90 or another airhead I'd probably be looking towards using more modern forks to start with (as I've done with the G/S).



oh, and craydds,
are you trying to say that those of us who have mixed different rate fluids have come up with some sort of special dual rate fork oil?
I have mixed (currently 5 and 10 mix in my R90 due to not being able to buy 7.5W at the time) and have been happy enough with the results, so I'd be interested to actually know what is going on physically in there..

Good points and questions.

You are right: Preload does not change spring rate. Preload changes the rate of the shock from the begining of its travel to the end. It's the same spring but as far as the fork of shock is concerned, it's a higher rate spring. This seems to throw some people and it seems like it is throwing you a bit?

Preload is not a cure for the wrong rate spring. Having said that, there is nothing inherently wrong with preload. There is absolutely no advantage in having custom made springs down to the point that you don't need preload. There is absolutely no advantage in having no or a lot of prelaod as long as you don't have so much as to cause coil binding. The shock or fork could care less. All it cares about is the amount of energy it takes to compress it from the beginning to the end of its travel. As far as the shock or forks are concerned, the EXACT same results can be had with a custom made spring that needs no preload or a weaker spring that is preloaded.

[boxerboy81]

Originally Posted by ontic

oh, and craydds,
are you trying to say that those of us who have mixed different rate fluids have come up with some sort of special dual rate fork oil?
I have mixed (currently 5 and 10 mix in my R90 due to not being able to buy 7.5W at the time) and have been happy enough with the results, so I'd be interested to actually know what is going on physically in there..

Apparently the practice of mixing an equal portion of 5 & 10W fork oils doesn't necessarily leave you with 7.5W. It might, but if using different brands it's unlikely. I've read that a same brand mix of 40% 5W with 60% 10W is close to 7.5, but that's also dependant on the brand, eg Motul 10 behaves like Spectro 7.5...at least that's what I've read elsewhere.

The bottom line is that the mix will be somewhere b/w 5 & 10, and no matter what it is in the end, if it works, it probably doesn't matter too much. I s'pose for some, it's about knowing exactly what you've got, verses thinking you have it.

I usually just do a 50:50 mix of whatever I have on the shelf to get in the 5-10 zone.

If you're keen to be exact you can use this...but it doesn't adjust for brands.

http://widman.biz/English/Calculators/Mixtures.html

[brocktoon]

So, for my particular situation I have no idea what the current state of my fork springs are. I only know the front end dives significantly when braking with fresh 7.5 wt fork oil. I'm not particularly large: 5'10" and 160 pounds after dessert.

Swapping the front springs is mostly for my peace of mind. The previous owner left the bike in a miserable state, and it's only now up and running. At 40 years old the front end could probably stand to be freshened up. Seems like everybody hates progressives, so it's down to the OEM regular springs or the OEM heavy duty springs. Supershaft, your ideal setup is non-HD stock springs preloaded to taste? Preloaded with some cut-down pipe?

[supershaft]

Originally Posted by brocktoon

So, for my particular situation I have no idea what the current state of my fork springs are. I only know the front end dives significantly when braking with fresh 7.5 wt fork oil. I'm not particularly large: 5'10" and 160 pounds after dessert.

Swapping the front springs is mostly for my peace of mind. The previous owner left the bike in a miserable state, and it's only now up and running. At 40 years old the front end could probably stand to be freshened up. Seems like everybody hates progressives, so it's down to the OEM regular springs or the OEM heavy duty springs. Supershaft, your ideal setup is non-HD stock springs preloaded to taste? Preloaded with some cut-down pipe?

Yes. Cut CV pipe. I also fine tune by stacking big washers. You probably don't need new springs or new damper rod wiper rings. Chances are all they need are new bumpers top and bottom, cleaned up and put back together with some preload spacers. Some of those bikes came with them and they have since disappeared. BMW used thin sheet metal rolled into tubes. I have seen them three inches long? Take your springs out. If your free length is close to what it is suppose to be, start making some preload tubes. I would probably start with two inches? Start big and work your way down. You can always make them shorter. It's a big time saver.

[ontic]

Originally Posted by supershaft

You are right: Preload does not change spring rate. Preload changes the rate of the shock from the begining of its travel to the end. It's the same spring but as far as the fork of shock is concerned, it's a higher rate spring. This seems to throw some people and it seems like it is throwing you a bit?

Yes, what you are saying here 'throws' me if that is how you would like to put it. It seems contradictory to me. Preload, to me, changes the position of the shock/fork in its travel, not its rate of travel, as you seem to be saying. If it did, and this seems to be what you are saying, changing preload would be the equivalent of changing the springs rate.
Please explain more.

Preload is not a cure for the wrong rate spring. Having said that, there is nothing inherently wrong with preload. There is absolutely no advantage in having custom made springs down to the point that you don't need preload. There is absolutely no advantage in having no or a lot of prelaod as long as you don't have so much as to cause coil binding. The shock or fork could care less. All it cares about is the amount of energy it takes to compress it from the beginning to the end of its travel. As far as the shock or forks are concerned, the EXACT same results can be had with a custom made spring that needs no preload or a weaker spring that is preloaded.

You seem to be responding as if I've said there is something wrong with preloading a spring? The point I am emphasising, and it is a blindingly simple one, is to get the right rate spring first, and then set the sag by preload, and the right rate spring is determined by the weight of the rider, the set-up of the bike (big tank, etc) and of course personal preference, etc, etc.
My whole point is that selecting from two options of 'regular' or 'heavy' springs is kinda like shopping for underwear in XS or XL sizes only. That is why I mention custom winding springs, to get a given rate, not to eliminate preloading the spring.
I also find it difficult to imagine any correct weight spring (custom wound or not) that gave the correct sag and required NO preloading...
no spacers required for preloading maybe, but no actual preloading? I doubt it.
FWIW, my custom wound springs have about 3 inches of spacer, for preloading, on top.

So yes, I am a little thrown by how you describe all this, it seems blatantly contradictory to my theoretical understanding of the relation between spring rate and preload- but I am more than open to learn where my mistakes have been made.

[chasbmw]

Tom cutter was of the view that if you fitted progressive springs, with the tight windings to the bottom, this resulted in very stiff suspension because the tight windings raised the oil level too high