jsz@bridge2.UUCP (11/04/85)
I own a '84 Yamaha FJ600 that I use mainly for fast rides on
back roads. I have been experimenting with the front suspension,
specifically air-caps. The '85 FJ600 comes with air-caps, the
'84 doesn't.
Recently an amateur racer, who also rides an '84 FJ600,
suggested I forget the air-caps and install progressive springs
in the forks and bump up the fork oil from 10w to 15w. He claims
that tuning with air-caps is impossible since the air expands and
contracts due to temperature. Also, air tends to leak somewhat.
My question is: Is he correct? Why then do most sport bikes
now come with air-caps? For hard, fast riding, which is more
likely to improve handling, the air-caps or progrssive springs?
Would some combination of the two be even better?
Thanks,
Jay
--
--
UUCP: ...!decwrl!Glacier!bridge2!jsz,
...ihnp4!bridge2!jsz
USPS: Jay Zusman/Bridge Communications/1345 Shorebird Way/Mt View CA 94043gt@hpfcla.UUCP (11/06/85)
Your racer friend is correct. The first step is to install some good
progressive springs. Put those in and then put in the same weight and
amount of oil you had. Try it. Now play around with the dampening
by changing to a heavier oil. 10W is really light oil for most sport
riding. I never use less than 20W on my race bikes unless I am on
a very rippled track with no significant bumps. Spring preload is
next and I'd suggest shelling out the $45 bucks or whatever for
some adjustable preload caps (available from RSC in Atlanta) just
because it is such a pain to play around with spacers. Just keeping
playing with everything in SMALL incremental changes and keep track
of the differences.
Next, I would suggest you give up hard sport riding! I know I have
(well mostly) because it is just too crazy. Join your racer friend
and get your high speed kicks on the track. Sure it is more money
up front, but it is thousands of times safer and you can try things
on your bike on a track that you would never have dreamed of on
a highway.
George Tatge
Fort Collins, CO
ihnp4!hpfcla!tatgespud@olivee.UUCP (John Purser) (11/06/85)
> > Recently an amateur racer, who also rides an '84 FJ600, > suggested I forget the air-caps and install progressive springs > in the forks and bump up the fork oil from 10w to 15w. He claims > that tuning with air-caps is impossible since the air expands and > contracts due to temperature. Also, air tends to leak somewhat. > > My question is: Is he correct? Why then do most sport bikes > now come with air-caps? For hard, fast riding, which is more > likely to improve handling, the air-caps or progrssive springs? > Would some combination of the two be even better? > I've never used air caps, but I do have progressive springs in the forks of my 650 Seca. My reason for going with progressive springs rather than air caps was that I didn't want to use air preasure in forks that didn't have fork seals that were designed for the air preasure. I understand that seals not designed for the preasure may bind on the forks when under preasure or start leaking. I'm quite happy with the progressive rate springs. They allow me to get on the brakes deep in the corners without anxiety, I've never bottomed them out yet and I still get a reasonably complient ride. I think the reason the factories go with air caps is that its more adjustable for the range of riders that will be buying the bikes, and its cheaper. With my progressive rate springs I spent an afternoon of placing spacers in the forks to preload the springs then racing up a near by twisty bumpy road to see how it worked then adding more or less preload and trying it again. This was a minor pain in the butt since each time through the cycle I had to take off the handle bars, loosen the top triple clamp, then take off the fork caps, put in different spacers, put it back together and try it again. The results have been more than worth the effort except that it's made the limitations of the rear shocks very obvious. Motorcyclist magazine had an article in the January !985 issue on front fork setup. They suggested starting with progressive rate springs then using air preasure and fork oil weight and quanity to fine tune the suspension. If you can find the article it would be big help to you.
toddv@copper (11/06/85)
> I own a '84 Yamaha FJ600 that I use mainly for fast rides on > back roads. I have been experimenting with the front suspension, > specifically air-caps. The '85 FJ600 comes with air-caps, the > '84 doesn't. > > Recently an amateur racer, who also rides an '84 FJ600, > suggested I forget the air-caps and install progressive springs > in the forks and bump up the fork oil from 10w to 15w. He claims > that tuning with air-caps is impossible since the air expands and > contracts due to temperature. Also, air tends to leak somewhat. > > My question is: Is he correct? Why then do most sport bikes > now come with air-caps? For hard, fast riding, which is more > likely to improve handling, the air-caps or progrssive springs? > Would some combination of the two be even better? > > Thanks, > Jay I don't know anything about aircaps. Never heard of them. I also don't know anything about racing. So I may make some inccorrect assumptions. But if I do, I *know* that those on the net will correct me. :-) Let's assume your friend is absolutely correct. Then aircaps would still be fine for reacing but useless to you. Why? Because a race is a one shot deal held under fairly constant conditions of temperature and pressure. It's not a big deal to make sure they are set correctly before every race and in the pit stops if it's a long race. When the typical casual biker rides however, he doesn't want to have to tune his suspension everytime he gets on the bike (depending on how hot it happens to be at a particular time of day.) A racer only wants his bike to perform for a limited time under controlled conditions. A rider wants his bike to be comfortable, manueverable, and safe under a wide range of conditions and road surfaces. ************* OPINION ************* When I see someone riding a racing bike, I have to assume 1) He races on the track and puts up with a racing bike on the street, 2) or he's a goofy kid who wants to look cool at the cost of practicality. Todd Vierheller There are old bikers, And there are bold bikers, But there are no old bold bikers.
animal@ihlpa.UUCP (D. Starr) (11/08/85)
* there are about two pages worth of previous opinions below this point (aren't you glad you have 9600 baud?) > > I own a '84 Yamaha FJ600 that I use mainly for fast rides on > > back roads. I have been experimenting with the front suspension, > > specifically air-caps. The '85 FJ600 comes with air-caps, the > > '84 doesn't. > > > > Recently an amateur racer, who also rides an '84 FJ600, > > suggested I forget the air-caps and install progressive springs > > in the forks and bump up the fork oil from 10w to 15w. He claims > > that tuning with air-caps is impossible since the air expands and > > contracts due to temperature. Also, air tends to leak somewhat. > > > > My question is: Is he correct? Why then do most sport bikes > > now come with air-caps? For hard, fast riding, which is more > > likely to improve handling, the air-caps or progrssive springs? > > Would some combination of the two be even better? > > > > Thanks, > > Jay > > I don't know anything about aircaps. Never heard of them. I also don't know > anything about racing. So I may make some inccorrect assumptions. But if > I do, I *know* that those on the net will correct me. :-) > > Let's > assume your friend is absolutely correct. Then aircaps would still be fine for > reacing but useless to you. Why? Because a race is a one shot deal held > under fairly constant conditions of temperature and pressure. It's not a big > deal to make sure they are set correctly before every race and in the pit stops > if it's a long race. > > When the typical casual biker rides however, he doesn't want to have to tune > his suspension everytime he gets on the bike (depending on how hot it happens > to be at a particular time of day.) > > A racer only wants his bike to perform for a limited time under controlled > conditions. A rider wants his bike to be comfortable, manueverable, and > safe under a wide range of conditions and road surfaces. > > ************* > OPINION > ************* > When I see someone riding a racing bike, I have to assume > 1) He races on the track and puts up with a racing bike on the street, > 2) or he's a goofy kid who wants to look cool at the cost of practicality. > > > > Todd Vierheller > > > There are old bikers, > And there are bold bikers, > But there are no old bold bikers. * a relatively brief tutorial on air forks follows * A lot of the above discussion is based on incorrect assumptions, or that "little bit of knowledge" that so frequently turns out to be a dangerous thing. Air-assisted suspension components *are* useful, both for racing and for regular day-to-day riding, and they may be indispensable for the seemingly self-contradictory concept of "sport touring." Air caps on forks provide two useful features not found on the stock spring forks: adjustable preload, and progressive resistance. The first is easy to understand--the only way to change the preload on a spring is to compress it. This is relatively easy to do on the rear (watch carefully what the cam-type adjuster back there does when you twist it), but rather difficult with telescopic forks. Further, the adjustment range with a spring tends to be rather limited. Air, on the other hand, can be added or removed easily (there's usually plenty of it about), and because of the way it compresses it provides a much greater range of adjustability. The progressive-resistance aspect of air forks comes from a fundamental difference between the physics of spring compression and air compression. With a spring, the resistance force rises linearly with compression--that is, for each inch you compress the spring, the force required increases by a fixed amount (e. g., 100 lb for one inch, 200 lb for 2 inches, 300 lb for 3 inches, 500 lb for 5 inches...) until the coils touch. Air obeys a different rule: pressure times volume remains constant. This means that each inch of compression produces more force than the preceding inch (example--for a fork with an eight-inch air space and 10 pounds of pressure at rest, compressing four inches produces 20 lb of force, compressing 6 inches produces 40 lb and compressing 7 inches produces 80 lb.) The result is that the air produces little effect when the forks are near full extension (for soaking up those little ripples) but push back *hard* when compressed most of the way (like on a Chicago-style pothole). Air by itself is generally insufficient to support a bike at rest, and at the low end air tends to build up pressure to slowly, so the optimum setup is an air-spring combination. The spring takes care of the little jounces, then the air kicks in on the big bumps and under sudden deceleration. As for the effects of temperature on air forks, they should be minimal. Pressure in the fork will rise proportional to temperature--absolute (Kelvin) temperature! This means that, on this planet, you'd have to heat the air in the forks to about 590 degrees F to double the pressure in the forks. Not very likely. What about progressive springs and heavy oil? Progressive springs are rather expensive and aren't adjustable. Heavy oil affects damping, not springing, and is probably a good idea with air caps also. Do air forks lose air? Of course they do, over a period of several days. If your forks don't hold air for at least a week without leakage, you've probably blown your fork seals. If you're going to fit air caps, I offer the following two recommendations: install a setup with a tube connecting the two fillers, so that you can get the same pressure in both sides (something that's very difficult to do otherwise), and buy a syringe pump with attached guage for filling them. The syringe pump (marketed under the "Quik" name, among others) allows you to fill forks easily and gives an accurate readout of the pressure (checking with a tire guage is guaranteed to lose at least one psi each time you do it). And never, NEVER fill an air fork from a gas-station hose; you're almost certain to blow the seals. ...and one last benefit of air caps: If you have them, you can change your fork oil without pulling the fork caps and watching your springs fly into the next county. Just pull the crossover tube and inject the new oil through the air fitting with a turkey baster (found at your local supermarket; don't go looking for one at the motorcycle shop!). On bikes with fairings this can save a lot of work! Dan Starr
jsz@bridge2.UUCP (11/09/85)
> > Recently an amateur racer, who also rides an '84 FJ600, > > suggested I forget the air-caps and install progressive springs > > in the forks and bump up the fork oil from 10w to 15w. He claims > > that tuning with air-caps is impossible since the air expands and > > contracts due to temperature. Also, air tends to leak somewhat. > > > > My question is: Is he correct? Why then do most sport bikes > > now come with air-caps? For hard, fast riding, which is more > > likely to improve handling, the air-caps or progrssive springs? > > I don't know anything about aircaps. Never heard of them. I also don't know > anything about racing. So I may make some inccorrect assumptions. > But don't let that stop you. :-) -- -- UUCP: ...!decwrl!Glacier!bridge2!jsz, ...ihnp4!bridge2!jsz USPS: Jay Zusman/Bridge Communications/1345 Shorebird Way/Mt View CA 94043
evincent@oberon.UUCP (Eric Vincent) (11/12/85)
Sender: toddv@copper.UUCP Organization: Tektronix, Beaverton OR >************* >OPINION >************* >When I see someone riding a racing bike, I have to assume >1) He races on the track and puts up with a racing bike on the street, >2) or he's a goofy kid who wants to look cool at the cost of practicality. > > > Todd Vierheller Question - What do you consider a racing bike? Are you saying that everyone who rides a GPz, Interceptor, Ninja or FJ should be a racer or is just a 'goofy kid'? ---- Eric Vincent University of Southern California University Computing Services - Arpanet Address: EVincent@Usc-ECLB -
toddv@copper (11/19/85)
>>> Recently an amateur racer, who also rides an '84 FJ600, >>> suggested I forget the air-caps and install progressive springs >>> in the forks and bump up the fork oil from 10w to 15w. He claims >>> that tuning with air-caps is impossible since the air expands and >>> contracts due to temperature. Also, air tends to leak somewhat. >>> >>> My question is: Is he correct? Why then do most sport bikes >>> now come with air-caps? For hard, fast riding, which is more >>> likely to improve handling, the air-caps or progrssive springs? > >> >> I don't know anything about aircaps. Never heard of them. I also don't know >> anything about racing. So I may make some inccorrect assumptions. >> > >But don't let that stop you. :-) > >-- >-- >UUCP: ...!decwrl!Glacier!bridge2!jsz, > ...ihnp4!bridge2!jsz >USPS: Jay Zusman/Bridge Communications/1345 Shorebird Way/Mt View CA 94043 Since when has ignorance stopped a lively discussion on the net? Are we starting something new? :-) But, just in case the point wasn't clear, here it is: Sometimes equipment that is specifically designed for a particular purpose (ie. racing under tightly controlled conditions) isn't the optimum for more general purpose use (ie. commuting or touring under a wide range of conditions). The particular piece of equipment isn't highly germane to the issue involved. Read the above without the parenthetical portions. A good example might be the tires used on racing bikes. They might be great for racing, but they wouldn't be the best for touring. (The rubber would wear to quickly.) And the treadless variety could be downright dangerous in the rain. Todd Vierheller