FAT front wheel axle modification/upgrade... ???

[Lasse]

Hi !

I'm looking for a "How To" make a FAT Front Wheel Axle modification tread as yamaha_george described.

Maybee some one can write one up and put it in the WIKI / FAQ / FZR-600 section ???????

I really want to do this mod for my FZR600

However a front fork brace will not cure the problem of your tyre cupping
(tyre cupping has been discussed before).

The solution is a bigger diameter front axle (this is discussed on the forum & parts (bearings) are listed ).

How do I know this works ?
Eric Buell (Ex. Buel Motors) & I back In the early '80's were discusing bits & bobs to do with stability and ridabilty of one of my race bikes.
His solution to my high speed weave problem was to reduce front shock flex.

With a wimpy size axle (back in the day it was 15mm) allowed the two front shocks to work independantly of each other as the
axle flexed under load we are talking 90mph with knee down & a very nerve wracking back end wiggle.

What I did was replace the 15mm axle with 25mm axle ( I was lucky the bearings were the same O/D ) the corners I used to testing went
from 90 mph to 125 & 130mph and the bike tracked as though on rails

I was gone so long testing grinning like a jackal that my mechanic had closed the shop early to come and find out if I was ok.
I let him have the bike and he was out for an hour and had trouble taking his helmet off past the grin.
Needless to say he wanted a new set up to.

If you look at fast state of the art bikes (Ducati's ) they have massive front axle tubes (part of the size is required because it is a tube axle).

Please take a look at the idea as no one so far has had the facility to do it on an FZR-600
(myself included as my friendly neighbourhood machine shop boss retired earlier this year.)

yamaha_george makes a vary good point about the axle .
I will be doing this axle mod as well as the fork brace.
He said the axle flexed under load, we are talking 90mph with knee down & a very nerve wracking back end wiggle.....
mine was doing the exact same thing so i also installed a GPR stabilizer designed for a Kawasaki ZX6R (2006).
It helped with the wobble...
I will do the axle mod in a few weeks when I tare down my front end to inspect & replace headset bearings, fork seals & do a general tune up.

The NEW bearing sizes for the bigger front axle are already in the WIKI.

HOWEVER I have not checked how much "meat" there is in the bottom of the fork where the damper rod Allen head bolt goes.
You will need to bore out or remake the wheels internal spacer and the two wheel side spacers.

Please be aware that the wheel internal spacer is a high accuracy piece as far as length is concerned.


As a personal request as Site Director & one of the WIKI keepers PLEASE document with dimensions & part numbers plus the usual request for lots of pictures.

There is no need to write this stuff up your self in the WIKI if you send plain text & pictures to me I will WIKI'ize the deal for you.

E-mail me at: george@saltmine.org.uk if you need any help or advice.

yamaha_george,
I checked out lower shock tubes.... there's not enuff materal on the left (cluch side) shock tube.

Thanks for heads up,
but I know away round it !

When you say the clutch side leg, that has no thread for the axle in it right ?
So leave the diam of the axle the same that side but make it longer and thread the bit that sticks out.
The fat axle bit slides in from the right and the shoulder (ie the difference between diameters butts up hard to the left hand fork leg and is secured by the axle lock nut.

As an experiment I would make a sleeve that went over the original axle and thro the right hand fork leg & the wheel right up to the LH leg.

The benefit of this is a sleeve is cheap to make (compared to an axle (unless you are just turning down another bikes axle & threading it for your needs))
Also getting a sleeve lenght right to:-
a} get the wheel centered
b} cinched to the right torque without locking the bearings will be easier.
c} If the results are not better than the original handling you have not "lost" any parts in the process

I dont know what the FZR600 axel is but the diameter of the YZF600R (FoxEye) is about 17mm.

[Lasse]

Or like this :

Tyre cupping is when the front wheel patters and skids momentarily and wears "dents" in the tyre .

The flexing originates from the fact that the 2 fork legs are NOT working in unison on a parallel framework but against each other in the worst case,
the root cause being that bit of wet string that Yamaha gave us as an axle that is actually flexing under load.

If you look at the likes of Moto GP , & knock offs as street "race bikes" like Ducati they have massive diameter axles (hollow to save weight and because the forces we are concerned with are acting thro skin effect rather than thro the core of the material.

If any of you care to look up Eric Buell's
( now owns the second largest US made motor cycle company )
white paper on axial loads he wrote back in the '80.

I read it way back then and all my race machines (drag, street,MX)
have massive axles usually 25mm or as big as I can go with the wheels I have to use the smallest being 20mm.

The difference is doing what was 80 MPH sweepers at 120 +like the bike was afright train on rails not the hint of a wobble

1. OK, so if I understand you right, you are saying that the front Wheel Axle is made way to thin and/or of a cheap shit material.... , Or have I miss understood you ?

2. How thick is the front wheel axle on the FZR-600 ?

3. Any suggestion of an alternative steel quality to make a front wheel axle of ?

1. Yup spot on

2. when I get the suspension set up then I can address the axle problem.

3. I will know that after I have taken the axle out tested it for hardness and seen what bearings are available to us and wether the whole thing is do able in a meaningful way.

Fork braces do NOT cure the source of crap front ends PERIOD.

I was as sceptical as you all when I read Eric's paper.
BUT being an engineer I decided to try it out on my street drag racer.

I checked the wheels and they could take the same size oputer diam bearings BUT with 25mm inside instead of 15 mm (?) memory is iffy on that figure but it was way thin.
I made the axle from a 1" construction bolt 14" long and turned & ground to suit the new bearings.
I bored the stantions to take the new diam fitted it up on the saturday morning.
Told my riding buddy I was gonna take it out for a trial.

The trial was simple we had a piece of hiway with 6 sweepers over about 2 miles that connect 2 hiways at each end there were roundabouts.
The max on the bike was 80 ish mph thro those sweepers and you had better be good to do that.
Over the next 3 hours I got that top speed upto 120 + and ran out of bottle (traffic was getting exciting at that speed ) without a wobble,
twitch or any other oddity.
I lined the bar end up with the white line & RODE.

When I got back my buddy was glad to see me in one piece he thought I had got into a wreck I was gone so long.
I told him ride the bike, that alone signified that something was definitely odd, you could probably ask my wife for sex and get a better odds than asking to ride any of my bikes.
He went out and I swear he had trouble getting his helmet off afterwards due to that stupid grin.

He decide then and there that hid bike had better have one and bought the bearings then at the store and by Sunday we both had fat axles.
Neither of us have ever had skinny axles since.

I have not done the FAT front axle mod on my FZR600,
...YET due to the fact that I want the suspension done first because no amount of axle will stop those dead springs from diving and wriggling under braking.

yamaha_george

Please keep us updated on this one with pictures, dimensions and so on !

THANX !

Over the next few days I will be tearing the front end of the bike off and setting up the suspension.

I will dig the wheel bearing sizes out as they are now and give my mate at the bearing company a call to see what we can use that is bigger. (usually 2 alternate sizes) the fork legs will be the deciding factor as to max axle size.
Pictures of the tear down and tooling i make for the forks etc will appear on my web site starting at: http://www.saltmine.org.uk/fzr/fzr.html

You will have to find your way from there as the page for this is not even drafted yet.

Any news about this subject ?

It was posted that It was on the wiki as of yesterday,
been on my site as promised for the last two weeks or so...............

, Sorry yamaha_george, but I can not find it !! ,
Maybee I'm a bit stupid...
The only thing I find is the suspension tuning, nothing about the beefy front axle and so on....

As to beefy axle mod I would not do that until I knew my suspension was right
(as you will read my original springs were some 5 mm under specification due to wear )
or recommend anyone else doing it until the shocks were set up correctly.

I'm not have the economy right now to buy the expensive YSS PD Valves (Cartridge emulators ) , so I thought of doing this Fat axle mod first !!

The result was so good YSS PD Valves ( Cartridge emulators ) that I did not bother with the big axle mod.

Have someone done the "FAT axle front wheel mod" ?

[neroneuman]

Did anyone ever did this mod?

I'm looking for a bigger front axle.

Any ideas/options guys?

[pefrey]

I don't think anybody has done it because once you think it through, it is too much work for not enough gain. You will still be left with relatively weak 38mm front forks. The stock FZR600 front axle is 15mm and solid. I think it would be better to swap a YZF600 front end (41mm forks and 17mm hollow axle) onto the FZR.

So in theory I think it is a good idea to beef up the front axle, however it will take a lot of time and effort and a little bit of money. With just a little bit up money you can upgrade the entire front end (YZF600 fork swap).

[DonTZ125]

I haven't done it because I've already bought a full front end that - one day! - will be bolted up. That said, I disagree that it's a waste of time and effort. Lots of guys ride and race with the stock front end, and it can be made quite competent with uprated springs, oil and cartridge simulators. This axle upgrade is simply one more option.

If you re-read the quotes by Y_G, you'll note that by going from a 15mm to a 25mm axle, his experiences through a particular corner went from ass-puckering at 90mph to smooth sailing at 125-130. THAT is significant!

A pair of standard 6004 bearings, with a 1mm shim each, will allow you to use a 20mm axle on the stock front wheel. Obviously, modified spacers etc. Worth it for the street? Probably not. For a racer in a category that requires stock forks? Hmmm ...

[pefrey]

My comment that the 38m FZR forks are weak was meant to describe their ability to resist flex. The 41mm YZF forks are stronger in that regard. I still think that putting in a larger axle is too much work and money, even if you are required to stick with stock forks. Unless of course you have access to machine shop equipment and a machinist willing to do the work and for cheap.

[RoadDogma]

Sure, I replaced mine with a 25mm axle, but I had to swap in R6 forks to make it happen. I don't have 38mm forks, laying around anymore, but I'm betting there isn't enough material in the stantions to fit a 25mm axle. Possibly 17mm, but would that be large enough to overcome the issues at hand? George only reported results with a 25mm axle. It would also be helpful to know which forks he used in making these findings. This could lead to an interesting theoretical discussion, but as far as a practical solution, I think George's conclusion as quoted above is telling.

yamaha_george wrote:

"The result was so good YSS PD Valves ( Cartridge emulators ) that I did not bother with the big axle mod."

Cartridge emulators and appropriately rated springs addresses most of the ills common to FZR forks, but I think the pertinent question is, what issues are you experiencing that you want to focus on? Unless specific handling problems have been identified that could be improved with a larger axle, I wouldn't attempt upgrading just for the sake of it. Even so, unless class limitations dictate otherwise, swapping forks may prove to be the answer.