Fork spring/oil for heavy riders?

For the heavier riders (220 lbs plus) what are you running for fork springs and oil?
I have recently ( last year ) changed fork oil to 30WT but it still seems really soft and has the occasional clunk on some less than desirable roads and crossing RR tracks. The bike could use new springs since they are most likely the originals.

Thanks.

I go around 235 ell bees and refilled forks after a rebuild with 180cc of Belray 15W on recommendation of a buddy. Seems fine to me.

Factory springs too?

Thank you.

You could go a set of Linear springs for your weight (think that how you spell it) they aren't progressive springs and cost a bit more but they have spring rates to your weight and work better than progressive spring, or you could fully upgrade your frontend with a fully adjustable internals, like Lansdown or similar all depend on how deep your pockets are, there are so many options to make your frontend work better but it also good to make sure everything in your frontend is working at its best without worn bits inside.
A lot of owners seem to neglect their frontends when doing maintenance on their bikes, moisture in the fork oil is a big killer of frontends in how they preform.

Ashley

the original commando dampers are rudimentary at best. You can spend a few bucks and get better performance in a few ways...

Jim Schmidt sells a damper rebuild kit for a very reasonable price which tightens up the tolerances of the norton dampers by replacing some sloppy OEM parts with his own parts which improve the performance

Don Pender sells the landsdown dampers for Norton's which are externally adjustable and a bolt up replacement part for your bike which is compression on one fork and rebound on the other

Cosentino engineering makes modern showa dual circuit dampers that also fit the OEM norton forks and are full modern dampers which are externally adjustable low speed damping and shim stack technology high speed damping (dual circuit)

*In general your springs suspend your front end based on it's weight with you on the bike. If the static sag of your front end is excessive, then you can either get a stiffer spring or shim some preload into your current spring to take out some sag to create more travel......but then you risk getting coil bound if the spring runs out of travel and that will clunk just the same as the slider bottoming out.... but certainly you could try the cheap fix of getting some extra compression preload on the spring by maybe adding 3/4" (that's just a guess to start with)

I actually made my own Cosentino style dampers for my commando so I've done a lot of research on this lately.....

Motown1 said:

Factory springs too?

Thank you.

Click to expand...

Yeah sorry, should have said still with factory springs, JSM damper upgrades and Consentino bearing bushes.

Thanks for all the replies! I have rebuilt them with factory parts but I think it’s time to do some research now and check with the long haired bank manager and make it happen.

Thanks again.

I would like to add that suspension is like Horsepower,... You can't make one change and get a dramatic increase in performance. The most dramatic increases in performance are a whole package of improvements. For HP that would be porting, bigger valves, specialized cam profile, higher compression, maybe specialized lightened pistons etc...

For suspension it's the same relativity, every aspect you can improve adds to the performance improvement. So, lightening the unsprung weight of the wheels, brake discs and components is part of the suspension equation. So is the damper technology you chose and the type of springs.

One of the things I learned recently for my project was that most modern bikes are sold with progressive springs, which are not high performance from the point of view of handling and gripping the pavement, but they do help to give a smoother, softer ride which probably sells more bikes to the average buyer. Most old school bikes have linear rate springs. I remember in the '80's when progressive springs were offered for Nortons and they were one of those things advertised to cure a harsh ride of the old school bikes when most of the newer bikes rode much smoother. I am 215 lbs and I recently ordered a set of race tech springs for my Cosentino clones. I was supposed to order 90kg/mm springs or maybe even 95kg/mm, (based on my weight) but I knew that the stock Norton springs were rated at about 67kg/mm, so I thought the racetech calculator was probably for actual racing where the extra stiffness is felt as greater control. I tried to go right down the middle and I ordered 80kg/mm springs and they are noticeably stiffer than the OEM springs, but not overly stiff for sport riding. I'm glad I didn't get the 95kg/mm springs because I'm not racing my bike, and the 80kg/mm feel good to me... without being so soft that they compromise handling or bottom out.

Anyway, there's a lot to learn about suspension to make good decisions that make sense for the kind of riding you want to do. The other thing I learned that I thought was valuable was that suspension is a reactive performance, not an active one...... If the roads are perfect, then cheap crappy suspension feels as good as the expensive technologically superior suspension because the suspension components react to the irregularities in the road surface. If there are no irregularities then there's no dramatic reaction difference to experience and say to yourself " Aha, I feel the difference!!" . Instead you feel the difference when you hit a pot hole or if you grab the front brake hard and get less "nosedive" in your front end.

If you decide to go for the big dollar suspension upgrade, it's not as dramatic as going for the big dollar horsepower upgrade (which is my point above) Suspension is a subtle thing to improve since it only gives you feedback when the road surface challenges your suspension... (which is the reason that spending a lot of money on suspension when the roads you casually ride around on are generally pretty smooth doesn't feel like it returns a lot of bang for the buck)

Here's a good link to blow your mind. This guy just flat out has the best explanations and information I could find on the subject of suspension. He details the showa suspension that I used in my damper modification in his site, and goes into the next levels of modifications like actually porting suspension valves for extra high performance.... It took me a few weeks of reading his stuff to actually start to see how deep this guy has gone down the rabbit hole.... I kinda like that myself. It helps to see the whole spectrum of choices when you see people pushing the performance envelope. I just swapped to the modern high tech cartridges and maybe at some point I would go further and do some valve customizing, but the result I got is good enough for the riding I do... HTH

Springs can sag and soften over time. Maybe try new stock springs?

Fast Eddie said:

Springs can sag and soften over time. Maybe try new stock springs?

Click to expand...

You can also go to sites like ForkingbyFrank and the site has the fork tube sizes of all the major brands listed by model of motorcycles by the diameters of their fork tubes to check against used springs for sale on Ebay. Then you check the weight of the bike intended for the used ebay springs you are looking at, and if that bike is heavier than a commando by more than 75lbs, chances are the springs are stiffer. I just bought a pair to use on a prototype test damper set for $27. They were from an 80's honda that weighed about 50lbs more than a commando... It allows me to have a complete drop in test suspension set up without spending another $150. on another set of racetech springs...

Norton fork tubes are 35mm so any springs for tubes that size or smaller diameter will work (make sure they are for a road bike not a dirt bike)


then I go check the bike out for it's weight to see the donor bike's weight here:


It's all a big rabbit hole...

Get the damping, bump stops and the preload sorted out first, only then look at stronger springs. Higher or just some damping slows things down and getting the preload right will raise the front. The bump stops are a mess as standard and metal to metal clashes are the result, get them right and the become hydraulic and progressive.

As comments above say, suspension is a very deep rabbit hole with a looking glass at the bottom. I have run a basically stock Commando for many years and long ago installed progressive springs. In terms of ride quality, I can't say enough good. But I found I needed to balance the rear springs and shocks to match. I bought some externlly-adjustable-damping Koni rears and later some other similar (Boge?) damping units. I'm no longer an aggressive rider. I have used the bike mostly for touring on good roads and like a compliant fork. That said, on an Commando Interstate with the factory pipes and mufflers, the mufflers will drag on a hard corner just when you need to shorten up the radius in a turn to avoid the oncoming RV. So one does need to think about ground clearance under load. I lived to tell the tale but others might not.

I have played around with oil weights for the front. This is a cheap way of experimenting. I have found that shock oils and fork oils have a wide viscosity index (VI) with respect to temperature. It varies a lot from brand to brand. Ultimately the shock converts the motion to heat so on rougher roads the VI matters. Then there's winter...

I rebuilt my Mk3 with the covenant conversion, with 20wgt Maxima fork oil it was harsh I changed to 15wgt Maxima and is a lot better, and yes I'm a bigger person.

For old school damping, the expected way to adjust your damping performance was simply choice of fork oil viscosity.... Since fork oil changes viscosity with temperature, you want to chose an oil with good stability relating to it's change in viscosity when it gets heated up, so it works well across the range of temperature. Here's the Peter Verdone wiki page where he charts all the popular fork oils and lists their performance characteristics


The list of oils and their properties starts half way down the page after some of the mind melting math above it.... The columns are:

40 degrees C viscosity - 100 degrees C viscosity - Viscosity Index # - Adjusted VI index # - etc...............




Regardless of what viscosity you chose (maybe different based on rider and load weight or improved parts like JSM's) the number to look at besides first 40 degree viscosity # is the "viscosity index #"


The viscosity index # should be a high number if you want the most consistent response from your forks across the range of temperatures. I use silkolene brand fork oil which has generally high VI #'s in all viscosities they produce. Sometimes poor fork performance is cheap oil that heats up, loses viscosity and has negligible damping properties at 100 degrees, so you are clunking and pogo sticking because your fork oil is like water at temperature.. Better quality fork oil may just cure clunking in some cases,... In the case of the OEM Norton commando forks, the adjustment is designed to be the single variable of fork oil viscosity,... so buy the good shit!...


Edited to add.... suspension is a next level science that few motorcyclists are interested in or know much about unlike things like horsepower which makes people bristle when they see the jewel like lightweight pistons and bulletproof connecting rods of a custom build. I think it's because the roads are generally pretty good so half way decent suspension is good enough

Once again thanks for all the recommendations. I really enjoyed the fluid article and I think Silkolene will be the way to go. As for upgrades, I am still researching and will make an eductaed guess from there

Thanks again it’s been helpful.