Planet Minis

fastbmw

Well I finally had sometime to start tearing into my ZB tonight.

Here are my goals:

1) Improve braking
2) Improve front suspension
3) Spend as little money as possible or the wife kicks my rear end.

Okay part #1 -better braking

With the ZB there are two ways to improve braking - Disc brakes or better shoes. Now with disc brakes I have to get different forks, which mean different wheels, etc etc. (unless I happened upon the unobtanium Monkey R disc brake set, but that didn't happen). A disc brake setup could possibly end up costing a $1000 if not more. I chose to go with new pads. The one that seemed to be recommended is the Ferodo brake shoe and at approx $20 a set it's a good price/performance compromise.



It's a direct replacement and supposedly is as close to a disc brake setup as possible. The shoes themselves look to be of very decent quality and have the Ferodo logo painted on the material, tres cool.



The replacement was simple even though it was my first time replacing brake shoes. All you need is a bit of muscle and needle nose pliars to get the springs on and off. The bike is still apart right now but hopefully I'll have a report on how they perform in a few days if it doesn't snow.

Okay Part #2 - better forks.

I spent a lot of hours researching forks, performance and design, so I'll do a quick recap for those who find this kind of techy stuff interesting. Now I don't profess to be an expert and I might have a bunch of this wrong but here is my best attempt at the layman's explanation....

Now the ZB50's front suspension is a telescoping damping rod fork, basically a shock absorber with an internal coil spring. Now the ZB fork was designed for teens to ride on the street, not full sized adults canyon carving, thus it is very very soft. There are two ways to improve the fork, change the spring rate and change the damping.

Springs

Changing the spring rate is pretty basic, just get a stiffer spring. Since the ZB fork shares nearly identical design to the NSR50, we have a few choices, you have a couple of HRC spring sets or you can get a custom spring made...more on this later.

Damping

Changing the damping will have the most dramatic effect on how your front forks handle. This is where real work is involved. A properly damped fork will ride over little bumps nice and smooth yet become more firm during high speed corners to give you good handling.

Now a damping rod fork works by having oil go between the top fork tube and the bottom tube through percisely sized orifices. Depending on the size of the orifice and the speed the oil squirts through them will dictate how fast or slow the forks move up and down. On these type of forks there is no provision for adjustment from the factory, you get what they give you. (I'm going to generalize between compression and rebound damping and lump them together)

Now there are 3 ways to change the damping on a damping rod fork.

1) Fork oil weight
2) Changing orifice size
3) Racetech Gold Valve emulator

Changing the fork oil weight is the easiest thing to do but not necessary the best. If you go from a light weight oil (5wt) to a thicker oil (30wt), you will generally make the fork more stiff. (The thicker oil will have a harder time passing through the orifice, thus slowing down the motion of the fork). Thicker oil can only go so far though.

Changing orifice size is a bit more difficult and involves a lot of black science that I don't have. haha. By changing the orifice size you can change the speed of oil squirting around in the fork, but unless you really know what you are doing you can't just go drilling bigger holes or welding closed orifices and hoping for the best. It is way easier to get it wrong then get it right.

The third way is the Racetech emulator. It "emulates" a cartridge fork which uses bending shim-style valving to control damping. Basically it's a valve that only allows a little oil to pass through it during slow speeds and more oil at high speeds (it completely replaces the orifices on the damping rod). It allows for better control of oil passage and some tunability. This is the hot item!

Now the best way to get your forks to work is to send them to RJP Racing who has the knowledge and expertise to do all the work for you. But with the current economic situation and Can/US exchange rate I figure all in all it would cost me around $1000 to get the forks done by RJP. I decided to muck around and see what I could come up with.

My decision

I decided to go with this route - stiffer springs, thicker oil and a Racetech Emulator. HRC offers two spring rates for the NSR50, a medium and a hard. From what I hear, even the Hard spring rate is still too soft but I got a smoking deal for a set, $50 shipped. I couldn't really pass it up. A bottle of fork oil is about $12 and Emulators are $170, so for about $250 I should have a decent set-up, not race quality but alot better than stock.

I'll continue my quest when I open up the fork tubes tomorrow.

gstegman

Good luck with your saga. Interesting read.

s_10onbagz

how much fork oil do you put in each fork on an NSR or ZB50?

tmas

The ZB manual states....In each ZB fork tube you put 131- 133 cc or 4.43 - 4.49 US oz. or 3.69 - 4.75 Imp oz. Manual recommends ATF (Automatic trans fluid).
tmas

fastbmw

I had a little computer hiatus but to bring everyone up to speed, I plan to do my fork upgrade in a few stages so see if there are any dramatic changes to the front end.

Step 1 - HRC "hard" springs & Preload spacers- May or may not make a big difference but I'll let you know.
Step 2 - Fork oil change - I'll go from the standard ATF that the Honda manual recommends to a heavy weight oil
Step 3 - Damper rod orifice change - I'll play around with compression and rebound damping
Step 4 - Race Tech Emulator


In my research I happened upon this free google book that has a few chapters on suspension set-up for big bikes. Pretty interesting read for those inclined and has some really good info just for general knowledge.

101 Sportbike Performance Projects - Google Book Search

tmas

fast..... Did you get a chance to try any of the steps?
tmas

s_10onbagz

I put 15w oil in my forks and they feel a little better but hardly noticable. I am going to try some simple fork mods and we can see if they help at all. The dampening is a little too soft and the stock nsr springs are way too soft. I will post info if any of it works.

fastbmw

Sorry guys, I've been lazy and haven't done much too the bike since the last update. I'm going to finish up the bike tonight and let you guys know soon.

fastbmw

Finally got off my ass and put together the bike. I decided to skip a step so I combined the HRC "hard" springs, spacer and 30 wt fork oil. Visually the HRC springs look identical to the stock springs so I didn't take a picture of the springs but here are some of the assembly.



I made the spacer out of a nylon rod I purchased at a plastic supply store. It is extremely hard so it won't deteriorate under the stress. I hack sawed off two 25mm spacers.



I used Belray 30 wt fork oil. It was pretty pricey for a litre, $18. It has a nice green colour though. haha.



This picture below has the spring, spacer and top of the fork. Unfortunately I miss measured the diameter of the nylon rod when I bought it, so it's a bit narrower than I would have prefered but it didn't really affect the spring compression. In the service manual it says to put the spring with the thicker coils at the bottom, but during my research I found that a lot of racers put them the opposite way to reduce unsprung weight. I don't know if that really will make a difference but they went in upside down none the less.



I haven't un-winterized the ZB50 yet so no ride report but compared to my stock ZB, the modified front fork is easily 30%-40% stiffer in the bounce test. (pushing down on the handlebars). My stock fork ZB is so soft that it doesn't take much effort to compress the front end down, the new front end definitely has way more resistance.

hooptytank

So NSR springs are the proper size for the ZB forks? What p/n?
Are pre-load spacers required?

Now un-winterize already, we want to know how it turned out, as this is the next thing up for mine.

Are the new shoes better than OEM?

fastbmw

Sorry I don't have a honda part number but the part number from bikebandit.com is 3871253-001

The spacers are not required, it's just something I'm trying.

Bike is still sitting in the garage, hopefully by next week....

hooptytank

I was able to score a pair of the stiff springs (SPRING, FR. FORK (K=0.55) (SHOWA) 51402-NLA-003) for $70, but I'll make up the extra cost by using $2 ATF vs the expensive stuff and as an added bonus the ATF better matches the stock ZB paint scheme than the green stuff

Also got new seals.. 20 year old rubber is done.

Fast, are you using the NSR emulators? Race tech support wanted to know the OD of the damping rod at the top before they would give their blessing for use in the ZB. Not being lazy, I want to have all the parts before tearing the legs apart.

Thanks for the help