Your readings with that brew is quite correct . During dynamic compression the spring inside the forks will absorb most of the load . The oil will show it's character mainly during rebound . Manufacturers preloads forks & shock-absorbers as per their definition of the bikes expected load and road etc . Not every person or riding condition will fall within that defined range , or maybe the manufacturer have been simply careless about it . Since you like the stronger dampening action with this bit heavier oil , I am sure it shall suit you . Rest assured , nothing will happen to your forks , if anything , the oil shall actually withstand a bit longer & better in use , than standard fork oils . This is because multigrade SAE engine oils have additives designed to prevent degradation of the oil under much more severe service conditions inside the engine sump . You see , forks and shock absorbers are quite primitive devices .
I also have a splendor . It's engine is the same one Honda uses in it's CUB / CT-Trail bike range . In 2006, in a show on the Discovery Channel, "The Greatest Ever", a series of documentaries on various motor vehicles, in the episode on motorcycles, they tried to destruct the CUB by various means . One of them was to fill it with used cooking-oil from a fast-food joint , instead of engine oil . It actually ran a little better on it . Finally after making it pull enormous loads and throwing it off the roof of a three storey building , it's frame bend , but the engine still started up & ran just fine . Rating it the best in a top-ten system, deemed the Honda Super Cub "Number One", declaring it "the greatest ever motorcycle". So I may be tempted to take your suggestion , brake oil ??!! awww , not just yet .
The Honda SuperCub


Coming back to fork oils , there is a vast difference in operation of forks and engines . Inside a fork , the role of the oil is that of a hydraulic fluid , it's only desirable characteristics being not to lose it's fluidity in operating temperature and not to foam or sludge up quickly , on passing through the small orifice of the fork plunger . Although specific fork oils are really low-tech low-single-weight oils , multigrade engine oils / ATF perform admirably in this role too , since they too are designed not to foam/sludge up or lose viscosity easily . In that case , the first number of a XXwYY multigrade oil is it's working number inside a fork . i.e 10wt for a 10w30 . This is because forks don't heat up the oil much at all . Neither are they subject to shearing stress like in an engine . ATF is about 7.5wt , consistently , all over the world , which is why people like it . Many bike comes with an engine oil recomended for use in it's forks too . See this page I dug up ... The page on fork oils from the Honda CB250/Cl250/CB350/CL350 workshop manual ...

pinaki.....man thats a pretty detailed expalnation...........

btw.....i liked that M80 ........eerrrr....honda cub photo.........

@Pinaki : Thats an Amazing explanation, i do see that many local mechs here use Engine oils for their Forks,,, too when we ask they will say Fork oil is costlier and engine oil will not do any harm to the forks,,,, but after reading your explanation only i can figure out that what they are doing is actually no harm,

To be in precise i've changed my fork oil only once since 2 years

OT @prince
If it's the bike , it's popularity does not seem to diminish , and so you can still buy the cub new ; it is being made and sold in japan , malaysia , vietnam etc asian countries and australia , new zealand , usa etc . The CT90 / CT110 variant ( honda trail ) , which has a high-low range lever to instantly switch it's all four gears to a lower ratio to climb steep inclines , is the official post-office bike for Australia post ( postie bike ) . In 2008 it was 50 years in production and the sales has increased this year too . The PGMFi fuel injection technology used by HeroHonda ZMR in India was first developed , tested and incorporated by Honda on the cub in 2007 . The horizontal engines used on HeroHonda splendors , super splendor , passion , glamour etc are CUB engines .
Key milestones of Honda Super Cub Series

• August 1958 Sales of Super Cub C100 began (air-cooled 4-stroke, single-cylinder OHV engine, 49cc, 4.5 horse power)
• Production site: Yamato Plant (later became Saitama Factory Wako Plant)
• 1959 Exports to the U.S. began
• 1960 Production at Suzuka Factory began
• 1961 Cumulative production reached 1 million-unit milestone
• 1961 Production based on component parts sets began in Taiwan (first production outside of Japan)
• 1964 Sales of Super Cub C65 (the first OHC engine) began
• 1966 Sales of Super Cub C50 (OHC engine) began
• 1967 Cumulative production reached 5 million-unit milestone
• 1974 Cumulative production reached 10 million-unit milestone
• 1983 Fuel consumption of 180km/liter (30km/h constant-speed test value) achieved (Super Cub 50 Super Custom)
• 1988 Sales of Press Cub began
• 1991 Production was transferred to Kumamoto Factory
• 1992 Cumulative production reached 20 million-unit milestone
• 1997 Sales of Little Cub began
• 2005 Cumulative production reached 50 million-unit milestone
• 2007 An electronically-controlled fuel injection system, Honda’s PGM-FI, was installed on Super Cub 50, Press Cub 50 and Little Cub.
• 2008 Cumulative production reached 60 million-unit milestone (April)

Postman delivering mail on a Honda ct110 melbourne .

Honda cub 2010 model - courtesy Autopro Magazine .

Now that's an amazing bike , isn't it ?

Replies in bold....

LOL psr'jee
( sorry mods for sms lingo )

So pinaki , what is the best forkoil for a stiffer ride.
BTW I hear adding 10-15ml extra oil make ride stiffer. What about the oil seals, ? will the hold up ??

Yes , a little more oil in there will stiffen it up too . The standard seals should be able to handle 20-50ml extra easily , since there is much air space in there already , I mean it's not like that there is no space to contain the extra oil that the seals shall be stresed anyway . The stiffening is not by the extra oil itself . By adding more oil , you reduce that air gap inside it to alter it's hydraulic property .
I am not that much of an fork oil tester , and I am just 58kgs , so I don't know whats best , but since it's not that expensive a deal to try out a few different fork configs with just oils ( atleast way cheaper & simpler than experimenting with K&Ns & jetting etc ), you can experiment and find out what works best for you . A good mechanic should have an better idea from experience .

Ten years back i had tried 2T oil in fork with very good results.....I had always found that filling fork oil a little extra leads to early oil seal leakage,and filling to the spec with a slightly thick..10W30 or ATF/Power steering oil, gives better balanced drive .....
Mr. Pinaki your advise on this ?

@PSR: Good ol' days of 2T. I remember my old mechanic using 2T oil to lubricate my dad's TVS XT fork arms and then slopping loads of grease on it. He used to add (5 mL) that oil in cylinder whenever we used to take it to him for service. I have seen 2T oil becoming rancid after prolonged exposure to atmosphere. I lived very near to sea coast (Chennai), and have seen it darkening as time progresses, didn't this cause you any issue PSR ?

No issues....even the normal Fork oil becomes black within a few months..just like the HH engine oil . I used to change it every year,and so never faced any problem. After the regular fork oil had become easily available switched to it...

Awesome thread guys.. Keep experimenting..
I also want my front to be stiff a little, because i ride on the india's worst road may be world's.. Its with lots of big fat potholes & speed breakers, my front forks use their full travel length almost all the time. It gives a thud noise when forks bottoms out. After reading all this I feel using 10w30 oil is good for me. So, what's your suggestion guys?
<Posted via Mobile>

Sorry , for late reply .. was slogging out all day . It is dreadfully hot and humid in kolkata today . Had to ride around in that burning noon sun too .
Yes , that horrible thud sound of your fork bottoming out ... happens to me too often .. kolkata city roads are no better . Yes , you can try out a 10w30 , no harm in it . Also remember , you don't even need a motorcycle specific ( jaso MA etc ) oil for this purpose , some leftover car oil would do fine , isn't it ? .
@psr'jee - most of the time I see mechanics keep new seals on the garage floor etc before fitting and fit them like that with dirt & sand or use screwdrivers etc to poke and drive them in . Oil seals damaged like this will fail early anyway , forks or elsewhere . I mean I am not sure how a little extra oil would cause a leakage , it is unlikely . Possibly you had a coincidence ? I have had leakage from good branded fork oils and standard volumes too .. just like that . Also while replacing the oil , don't forget to clean out the gunk that settles in the bottom , mechanics ignore that and there is a lot of it there sometimes .

and how to clean the settled dirt in fork bottom.....by petrol or somethiing?

Don't petrol use like that bro; it's carcinogenic , flamable , low-flashpoint ,makes toxic fumes and getting pricey now . Once I was tinkering inside a Maruti Zen bonnet , pulled the fuel line to check if the fuel-pump was working . It was , and it spilled some petrol inside there , then I selfed it and the whole engine compartment burst into flames with a big bang . Scary day ! now I am a lots more careful around petrol. Kerosene is an excellent high-flashpoint govt subsidised cutting solvent . The dirt in there is hardened sometimes from long neglect . You may need to poke/scrape it with something long like a straightened shirt hanger or a bottle brush etc . Older bikes had a drain-bolt at the bottom of the fork .. sigh .. not anymore nowadays .