Author Topic: Cheap way to improve front suspension stiffness. (Read 31087 times)

liaudio · « **on:** November 03, 2006, 06:54:49 AM »

Yes, even cheaper than those $65. Progressive springs...

Got your attention? You cheap ass! (Like me!

) Most of the newer bikes I've owned have all had preload adjusters on the top of the fork legs. What this mod does is essentially add about an inch or so extra preload to the front.

Follow your manuals instructions on how to change the front fork oil.

When you have the top caps off:

Get some 1" PVC conduit, cut two pieces about 1.5" long.

Place on top of your existing springs.

Use a socket or wrench and push down hard on to the top cap as you screw down. (A socket is MUCH easier!!!)

Viola! It'll be a little stiffer, and reduce braking sag.

I replaced the fork oil w/ Bel-Ray 10w oil at the same time as this cheap-ass mod and it feels a whole lot better now.

cafehonda · « **Reply #1 on:** November 03, 2006, 03:16:34 PM »

Doesn't it rattle your teeth out when riding over expansion cracks? It's an old school trick, but it takes all the softest part of the spring rate out of the front end. While cheapness is a virtue when it comes to parts, Works Performance dual- rate springs were the best $110 I ever spent.

liaudio · « **Reply #2 on:** November 03, 2006, 04:11:56 PM »

it's a little stiffer initially. But stock was just too soft in my opinion. It felt more like a cruiser and not like a sport bike.

ic455 · « **Reply #3 on:** November 03, 2006, 07:42:47 PM »

See now, I've gotta try this out! Thanks, liaudio!

crazypj · « **Reply #4 on:** November 16, 2006, 08:26:22 AM »

Looks scary using a ratchet to screw down fork caps, one slip and tanks done. I have used a speed brace for years as you can press down and turn at same time
Dont try and use a flex head though as they usually move and damage things
PJ

Angry Chair · « **Reply #5 on:** November 16, 2006, 04:16:24 PM »

I have watched this thread for a bit.

PVC is easy and cheap. It has next to no longevity in fork oil. Using a piece of metal pipe would be better huh?

ic455 · « **Reply #6 on:** November 16, 2006, 06:59:52 PM »

Quote from: Angry Chair on November 16, 2006, 04:16:24 PM

I have watched this thread for a bit.

PVC is easy and cheap. It has next to no longevity in fork oil. Using a piece of metal pipe would be better huh?

Have seen PVC piping used in many automotive shops to route bulk tanks of ATF, motor oil, gear oil, etc. with no longevity issues. Commercially marketed fork oil more damaging than the above mentioned substances?

ElCheapo · « **Reply #7 on:** November 17, 2006, 06:17:13 PM »

I think you are right IC. However I have seen how this stuff can just break down in sunlight (not that there is any in your fork tubes

) I guess you have to make sure you use non-porous PVC. There is different kinds.

ic455 · « **Reply #8 on:** November 17, 2006, 07:02:12 PM »

Quote from: ElCheapo on November 17, 2006, 06:17:13 PM

I think you are right IC. However I have seen how this stuff can just break down in sunlight (not that there is any in your fork tubes ) I guess you have to make sure you use non-porous PVC. There is different kinds.

HEY!! You're back! That is you, isn't it?

ElCheapo · « **Reply #9 on:** November 17, 2006, 07:05:55 PM »

Quote from: ic455 on November 17, 2006, 07:02:12 PM

Quote from: ElCheapo on November 17, 2006, 06:17:13 PM
I think you are right IC. However I have seen how this stuff can just break down in sunlight (not that there is any in your fork tubes ) I guess you have to make sure you use non-porous PVC. There is different kinds.

HEY!! You're back! That is you, isn't it?

For now Until they lock me down again

ic455 · « **Reply #10 on:** November 17, 2006, 07:13:38 PM »

Gonna get you a Hannibal Lecter mask......

ElCheapo · « **Reply #11 on:** November 17, 2006, 07:19:52 PM »

Quote from: ic455 on November 17, 2006, 07:13:38 PM

Gonna get you a Hannibal Lecter mask......

The banishment felt a bit like......... well this

ic455 · « **Reply #12 on:** November 17, 2006, 07:22:06 PM »

Quote from: ElCheapo on November 17, 2006, 07:19:52 PM

Quote from: ic455 on November 17, 2006, 07:13:38 PM
Gonna get you a Hannibal Lecter mask......

The banishment felt a bit like......... well this

There you go!! Excellent! Now who's gonna play Clarice?

andy750 · « **Reply #13 on:** November 19, 2006, 03:57:30 PM »

Ive used the PVC inserts in my K4 forlks for a couple of years and 25000 miles later with no longetivity issues. Just regular white PVC tubing as shown in the photo above. I used regular motorcycle fork oil. Really helps with front end stiffness.

cheers
Andy

ElCheapo · « **Reply #14 on:** November 19, 2006, 03:59:11 PM »

Quote from: andy750 on November 19, 2006, 03:57:30 PM

Ive used the PVC inserts in my K4 forlks for a couple of years and 25000 miles later with no longetivity issues. Just regular white PVC tubing as shown in the photo above. I used regular motorcycle fork oil. Really helps with front end stiffness.

cheers
Andy

Good to know that it works well. What's more is that it is cheap!

chung · « **Reply #15 on:** December 04, 2006, 06:43:33 PM »

Motor oil works too

DME · « **Reply #16 on:** December 08, 2006, 01:04:52 PM »

I did use spacers in the forks of my -75 cb750.
Resulted in an oversprung, underdamped ride.
Started laborating with oillevel and viscocities.
Now running 20w Castrol fork oil.
Don´t know the exact quantity. Filled each leg with 200 cc to begin with which gave a VERY harsh ride.
Removed 10 cc from each leg at a time until I had the ride I was looking for.
Belive I ended up with 170 cc in each leg.
Fork works great!

Cheers
Daniel

phylo101 · « **Reply #17 on:** December 12, 2006, 02:43:45 PM »

Okay, here's a definitive answer, proven by three years' nine hours a day despatching on my K7.....and 16 years' total ownership.

Inserts like the PVC ones do have a limited performance, but don't eradicate the damping issue, and WILL selfdestruct if you hit a really big pothole....or fender! Also, the seem to give a harder ride but work by JUST eliminating free movement, which on these old forks isn't well-managed.

So how do you carry out a dirt-cheap modificationthat retains as much length of travel as possible, but also changes the preload of the spring? AND makes the ride stiffer?

Simple - copy the PVC spacers - but in metal tube. That's the first step. Then set them on your bench.

NOW - REMOVE YOUR FORK SPRINGS AND USING AN ANGLE GRINDER REMOVE A FEW COILS OFF THE TOP TO THE EXACT LENGTH OF THE SPACERS!

The function of a spring is not only governed by its gauge (thickness of wire), the stifness of the wire, the spacing of the coils....but ALSO - which a lot of people forget - by it overall length!

So reassemble the springs in the fork, plop the spacers in and you'll find the whole thing is no harder to get the fork tops on than on the standard springs BUT on the road you've altered the preload of the spring by altering its total length inside its working limits. Stiffer fork, AND you've removed the problem of spacers on their own compressing the spring and robbing you of travel.

Ever wondered why modern road bikes use short springs and long spacers? :-) Its NOT because the modern Jap factories can't make long springs LOL

As for fork oil - remember the simplest piece of advice of all - these forks were designed when STRAIGHT monograde oil was used in forks, not multigrade fork oils. Castrol for one still do 20weight and 30weight oils for classic bikes, use this instead. You'll find the equivalent modern-rated multigrade fork oil is runnier, the mongrade is a heavier thicker oil even at the same grade, and is what the fork was designed to use.

P.S. engine oil CAN work, but seems to emulsify and break down even quicker than fork oil :-(

Regards, Phylo

chung · « **Reply #18 on:** February 25, 2007, 03:54:13 PM »

I saw someone using super stiff fork springs and used a valve spring to take that inital "shock" off the small stuff. Might work in reverse in the right combonation?

bshadbolt · « **Reply #19 on:** February 27, 2007, 10:15:14 PM »

Quote from: Angry Chair on November 16, 2006, 04:16:24 PM

I have watched this thread for a bit.

PVC is easy and cheap. It has next to no longevity in fork oil. Using a piece of metal pipe would be better huh?

The progressive fork springs for my sportster came with pvc spacers, I figure they should know.

Cheers,

Brett

Shadowjack1020 · « **Reply #20 on:** February 28, 2007, 05:15:03 PM »

When I bought new Progressive springs last fall, the included spacers were PVC. Or at least what looks like PVC.

andy750 · « **Reply #21 on:** March 01, 2007, 05:35:05 AM »

PVC spacers have worked fine for me for the last 5 years. (with progressive springs in a CB750K4).

cheers
Andy

jeanhank · « **Reply #22 on:** November 06, 2007, 04:22:01 PM »

Hey, here's another idea, that works great for me.

Instead of using metal tubing or PVC, I have about a 1 inch very firm spring about the same diameter as the fork springs. The original (soft) springs compress first, and when the fork continues to travel up, the firm spring then starts to compress, really firming up the suspension. I've never felt them bottom out with this setup -- that firm spring really does well when the forks are stressed under hard breaking or big bumps.

I have to wonder, though, if it would behave any differently if i put that short firm spring in the tube first, then the fork spring. Any ideas on this one?

crazypj · « **Reply #23 on:** November 07, 2007, 12:08:08 AM »

you add the two spring rates together and get something softer than you started with. the short spring increases the number of working coils an decreases spring rate. What is firmer is the initial inch or so of travel as you have some extra preload.
PJ

savannahcafe · « **Reply #24 on:** November 07, 2007, 08:43:34 AM »

While we are on the issue of front forks, Im new to motorcycle repair but Im almost finished with my rebuild. I did notice one of the front fork arms had almost no resistance and rebound but the other felt fine. Do I just need to replace the seals and oil or is there a bigger problem here?

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Author Topic: Cheap way to improve front suspension stiffness. (Read 31087 times)

liaudio

liaudio

Angry Chair

phylo101

bshadbolt

Shadowjack1020

savannahcafe