Inverted Forks

[corndog67]

There are some advantages to spindily forks. And a flexy chassis.

(yes, I know this started with forks, but you can't discuss forks without discussing the rest of the chassis that goes with them... )[/QUOTE]

I completely disagree with this statement. Give me some examples where flexi forks would be an advantage. Well maybe ridgid frame choppers that use tire pressure and fork flex for their suspensions. But other than that, I can't come up with any scenario where fork flex is an advantage.

As for the feel of brakes, I had an '81 GS1100E, with stainless lines, stock master cylinder, stock calipers, and some EBC high performance pads. You're right, the lever was very solid, you could lock the front wheel pretty easily. But, they did not have the feel of a late model front brake. I mean, as far as modulation at the point of lock up. In my opinion, there is no comparison. The early brakes had enough power, but not enough control.

[Nerobro]

There are some advantages to spindily forks. And a flexy chassis.

(yes, I know this started with forks, but you can't discuss forks without discussing the rest of the chassis that goes with them... )

I completely disagree with this statement. Give me some examples where flexi forks would be an advantage. Well maybe ridgid frame choppers that use tire pressure and fork flex for their suspensions. But other than that, I can't come up with any scenario where fork flex is an advantage.

First off, most custom choppers are lucky they don't kill their riders. I won't even pretend to discuss those abominations.

I didn't say flexy forks were the advantage. I said spindly forks have some advantages ;-) Lighter unsprung weight mostly. Notice that 125cc motogp bikes still run quite small forks. Those bikes are entirely about corner speed and do everything they can to reduce unsprung weight. Their 425 chain is there for the same reason.

Thankfully bikes have wonderfully low forces on them. (at least while cornering) Even at 45deg of lean the suspention only has 1.4x the weight of the static weight of the bike on it. And even then the vertical loads on the tires are the same as in a straight. (in a car the tires on the outside of the corner can see as much as double their static loads, without downforce. With downforce that number can be unlimited)

Flexable chassis generate more grip, but break away more abruptly. At least if hondas engineers are to be belived.

Back to braking though. I don't think early brakes had enough power to have the "feel". You can squeeze the heck out of them, eventually locking up the front, or doing a stoppie, but if you're concentratning on squeezing hard you're not concentrating on keeping them from locking up.

That's also to say that the single disk that came with my 1980 550 were inadequate. The master cylinder and brake combination on my 83 550 isn't nearly as sharp or as powerfull as the 80 Master cylinder and 82 650 brakes on my 1980 550. The pistons on the 83 calipers are smaller than the 650's, and I'm fairly sure the master cylinder is a larger diameter as well.

This can also lead to a fork question as well. As the forks on our GS's are pretty flexable. And under heavy braking are likely to bind. Binding up in the suspention will cause the tire to skip and hop, incresing braking distance.

[Nerobro]

http://www.vintagebrake.com/mastercylinder.htm

That might be usefull..

[morthrane]

There are some advantages to spindily forks. And a flexy chassis.

(yes, I know this started with forks, but you can't discuss forks without discussing the rest of the chassis that goes with them... )

I completely disagree with this statement. Give me some examples where flexi forks would be an advantage. Well maybe ridgid frame choppers that use tire pressure and fork flex for their suspensions. But other than that, I can't come up with any scenario where fork flex is an advantage.
[/QUOTE]

Some flex is necessary, because as the farther you lean over, the more inefficient the suspension will be. Look up the design details for the front-end on the Moto Cyzyz (sp?) prototypes-- they use fork inserts to "tune" fork flex properties.

Yamaha's made prototype/test MotoGP bikes to specifically work on chassis stiffness tuning.

Colin Edwards turned around his season in 2002, put the screws to Troy Bayliss, and won the WSBK title. Rumor has that amongst other things, an engine bolt was removed to allow the chassis greater flex.

Harley's VR1000 was a disaster for, amongst other things, having a chassis that was made as stiff as possible.

I could go on, but hopefully this gives you the idea-- yes, flex is a necessary, unavoidable, and useful thing. But like too many good things, its terrible without moderation.

[C7Z]

Inverted forks

Not that I know anything, but I always assumed that the inverted fork was superior because it reduced some of the "unsprung weight" on the front end of the bike making it ride smoother and the suspension react quicker to changes in the road surface.

My $0.02
-D Payne

[xDUKEx]

ok guys ive watched this thread long enough !!! i bought my 83 E 2 years ago and rode it bone stock all year last year !!! over the winter i did the suspension mod including inverted forks, rear swing, modern rubber, brakes. HUGE DIFFERENCE !!!!!! i ride with a couple of friends that have 05/06 crotch rockets. last year i had to really slow down in the corners and catch up on the straights. this year i can hang with them anywhere. the bike is so much quicker steering and the braking is 100 times better. the antidive forks, in my book are trash. my bike used to dive down so much under heavy braking with the old forks it would allmost lift you off the seat !!! not any more !!! i am so glad that i did the mods, i love the looks and best of all the performance !!! it is a totally different machine now !!! I LOVE IT !!!!!!!!!

[Ogri]

I'm with the XDUKEX......

My USD forks are the berries!!!

[Billy Ricks]

The USD forks are superior in every way to the stock GS units. A modified GS front end can be made to work pretty good but nowhere near as well as anything newer than about '88. Even the '88 GSXR fork I have on the bike now is light years ahead of the GS stuff. Soon I'll be going through both ends again using a '95 GSXR front end with 954 triples. I'll still run the wheels I have on the bike now with a Works shock on the rear.

[Nerobro]

The USD forks are superior in every way to the stock GS units. A modified GS front end can be made to work pretty good but nowhere near as well as anything newer than about '88. Even the '88 GSXR fork I have on the bike now is light years ahead of the GS stuff. Soon I'll be going through both ends again using a '95 GSXR front end with 954 triples. I'll still run the wheels I have on the bike now with a Works shock on the rear.

Remember that up untill just a few years ago, they were still running normal forks in motogp. JUST LAST YEAR the R6 went to USD forks.

I don't think you're describing the difference between USD and normal forks, but the difference between cartriage forks and damper rod forks.

[Billy Ricks]

Remember that up untill just a few years ago, they were still running normal forks in motogp. JUST LAST YEAR the R6 went to USD forks.

I don't think you're describing the difference between USD and normal forks, but the difference between cartriage forks and damper rod forks.

You read me right. Anything after '87 on GSXRs had cartridge forks. My '88 front end is leagues ahead of the stock front end. I expect another leap in performance once I install the USD unit. It's not just about rigidity, there's plenty of other benefits of installing newer stuff.

The newer front ends don't have near the travel of the old stuff so cornering and braking benefit. The radials that get run with the shorter travel forks do a good enough job of soaking up the little stuff that you can run more agressive preloads and not get hammered on the street.

The 600's were running normal cartridge forks up until a couple of years ago. They also happen to have the same 43mm inner tubes as the USD units. I don't think you are going to find any MotoGP bike has ever run anything other than Ohlins and maybe a few one off Showa USD forks.

[Nerobro]

Just for kicks. Look at that fork. it's USD :-) on a guzzi falcone.

[jpaul]

As mentioned before, the reduction of unsprung weight and stiffness were the primary motives behind the move to inverted forks. The reason all four manufacturers went to them at the same time is due to the rules changes in Superbike racing. In an effort to reduce the technology gap between factories and privateers, fewer modifications were permited to frames, suspensions, and engines. This drove the factories to install more goodies that really only have a significant effect at racing speeds on their streetbikes.