Jump to content

What am I trying to correct?


CornerCarver
 Share

Recommended Posts

  • Member Contributer

Ok. I have read every thread on this board related to USD fork conversions and the myriad ways to correct the steering geometry.

These gallery_7288_2662_13186.jpg

ZX14.jpg

are on the way and questions remain.

If i go with 929 lower and 954 upper triples, how has the geometry changed? Is my rake increased? Is my trail lengthened?

If I stay with the 929 lower, can a custom upper return the geometry to stock rake and trail?

For reference, as we discuss what needs to be corrected, I have included another image...

gallery_7288_2662_12560.gif

Rake and Trail.gif

Link to comment
Share on other sites

Lots more variables involved,

- Length and Height of forks (I am not familure with zx-14 specifications)

- Length and height of rear suspension ( I raised the rear suspension 10mm ,some have left it stock)

- Offset of 929/954 triples compared to OEM

- Tire profiles will also affect your suspension settings.

Personally, I think a lot of it is taking the time to work out all the measurements because everyone has thier own combination of components. I do not think there is a defined formula.

Link to comment
Share on other sites

If i go with 929 lower and 954 upper triples, how has the geometry changed? Is my rake increased? Is my trail lengthened?

If I stay with the 929 lower, can a custom upper return the geometry to stock rake and trail?

- Trail will be lengthened.

- Both triples must have identical specs (hole spacing) or the fork tubes will not slide through them. Cannot have different upper and lower triples unless they HAPPEN to have exactly the same hole spacing (RC51 and CBR 929/954 share common hole spacing)

To combat the increased trail, you can raise the rear ride height. Your front will robably already be lowered from the shorter forks, though I'm not sure what ZX-14 fork length is.

Link to comment
Share on other sites

  • Member Contributer

OK, the rear shock was purchased on the Elka group buy about 4 years ago and was built with 15mm increased ride height.

I have also rebuilt my 5th gen forks with Race tech gold valves and F3 internals and lowered the triples on the forks to drop them 18mm below stock height. the bike currently handles amazingly well for it's heft (and my heft).

Canuck, you are stating that the trail will be increase with the triple clamps that I mentioned. Is this because the offset between fork and steering stem is greater, thereby pushing the front wheel farther out in front of the axle centerline?

Link to comment
Share on other sites

OK, the rear shock was purchased on the Elka group buy about 4 years ago and was built with 15mm increased ride height.

Good, that should help.

Canuck, you are stating that the trail will be increase with the triple clamps that I mentioned. Is this because the offset between fork and steering stem is greater, thereby pushing the front wheel farther out in front of the axle centerline?

Because the distance between the fork holes and the steering stem is LESS, you have greater trail.

Look at your diagram above. Mentally move the forks "southwest" in the diagram.

See the "vertical axle line"? It just moved slightly to the left, correct? That makes the trail longer.

Link to comment
Share on other sites

  • Member Contributer

Ok, just when I thought I was getting a grasp...I agree that the forks will move SW as you stated but in reducing the distance from axle centerline (and tire contact patch) to the point where a straight line down the steering stem would put the axle, I though you were reducing trail and making the bike less stable (lower trail-sometimes less stable at high speeds but easier to turn).

what am i missing? (besides the obvious- timmys Charm, Bailyrocks good looks, Sebs fabrications skills, etc...)

Link to comment
Share on other sites

Ok, just when I thought I was getting a grasp...I agree that the forks will move SW as you stated but in reducing the distance from axle centerline (and tire contact patch) to the point where a straight line down the steering stem would put the axle, I though you were reducing trail and making the bike less stable (lower trail-sometimes less stable at high speeds but easier to turn).

what am i missing? (besides the obvious- timmys Charm, Bailyrocks good looks, Sebs fabrications skills, etc...)

Your "Suspension Tube" line is moving SouthWest which moves the "vertical Axle" line back (to the left) but your "neck line" is remaining contant.

If you increase your suspension height in the rear, drop your forks further in the stem you will increase the angle of the "neck line" which shortens the "Trail"

Edited by VIFFER93
Link to comment
Share on other sites

  • Member Contributer

OK, Fedex says they arrive this Friday...I am just trying to get some triple clamps on the way as soon as possible.

Link to comment
Share on other sites

  • Member Contributer

Ok, just when I thought I was getting a grasp...I agree that the forks will move SW as you stated but in reducing the distance from axle centerline (and tire contact patch) to the point where a straight line down the steering stem would put the axle, I though you were reducing trail and making the bike less stable (lower trail-sometimes less stable at high speeds but easier to turn).

what am i missing? (besides the obvious- timmys Charm, Bailyrocks good looks, Sebs fabrications skills, etc...)

Your "Suspension Tube" line is moving SouthWest which moves the "vertical Axle" line back (to the left) but your "neck line" is remaining contant.

If you increase your suspension height in the rear, drop your forks further in the stem you will increase the angle of the "neck line" which shortens the "Trail"

AAAAAAAAAAAAHHHHHHHHHHHHHHHHHHH, that makes sense now..kinda.

Thanks

Link to comment
Share on other sites

  • Member Contributer

The dreaded Paralysis of Analysis.

Just get a CBR929/954 or RC51 SP-1 lower and a CBR929/954 upper and forget about it.

Do you know the clamp diameters on the ZX forks? Honda seems fairly standardized at 54 lower and 50 upper, but as I posted earlier my old 636 USD were 52/50.

Again, need to have them in hand before going forward, I think..

Link to comment
Share on other sites

  • Member Contributer

Maybe Concours triples would be more relaxed, more VFR like?

By the way, I have SP1 triples and a 954 upper in hand if you want to take a look at them. (and bent up 636 triple)

Link to comment
Share on other sites

  • Member Contributer

Yes, I know I am over-analyzing it but my bike finally handles like I had hoped it would from the factory, and I definately don't to slow it down or lose much ground clearance...the fork tube diameters match up with Honda standard 50/54...

since I took my center stand off for track days I can't quite get consistent measurements of angles and dimensions I am going to pop for a rear stand or front chock and start taking better measurements this weekend.

These forks were measured (by the guy selling them so take that with a grain of salt) at 755mm in length so they are a bit shorter than my 5th gen forks but right in line with the RC-51 (sp-1) forks that I passed on so that I could have radial brakes...

Kevin, I may take you up on the offer to test fit with your triples before I splash to have some made or see what other options are out there...

Link to comment
Share on other sites

  • Member Contributer

OK, the rear shock was purchased on the Elka group buy about 4 years ago and was built with 15mm increased ride height.

I have also rebuilt my 5th gen forks with Race tech gold valves and F3 internals and lowered the triples on the forks to drop them 18mm below stock height. the bike currently handles amazingly well for it's heft (and my heft).

In my most humble of opinions, you have the bike sorted out pretty well as is.

If I can ever make the same statement, I ain't touching anything.

I wonder if any of the USD conversions done by others in the past have really yielded acceptable ROI.

Improved brakes, probably, although I wonder by how much really.

Same with the forks. I understand the improved stiffness and more knobs to turn, etc... BUT if you already have the thing sorted out. Why go through this and then face a chance of not being able to say that the bike handles even more amazingly well.

I guess to me, this suspension thing is more of a dark magic than a science and personally I'd be afraid of losing the 'magic'.

And yes, I do understand the desire to improve and change things. I'm the same way really.:comp13:

Good luck with it. :fing02:

Link to comment
Share on other sites

  • Member Contributer

Good points Rice, and that is one reason it has taken me three years to pull the trigger on the USD conversion. But these forks are as I'm running now only have the tubes and brakes as they came from the factory.

Part of it is being committed to a Duc or Tiumph single-nut rear wheel and the requirement to de-link the brakes to pull that off and the other part is to see if I can make the bike handle as well as it is maxed out right now.

I wish Honda would hurry up and call back with the job offer, I bet them a years wages that I could make a VFR from their parts bin that would sell well enough to return a profit. :goofy:

Kevin, you busy Saturday...you are welcome to come over and pick up the Staintune... :fing02:

Link to comment
Share on other sites

  • Member Contributer

Alright then.

But none of your mods will improve the top end of that bike.

I recommend replacing the old duct tape with new. You know, for looks and improved aredynamics :laughing6-hehe:

Link to comment
Share on other sites

  • Member Contributer

IF i decide to keep the 5th gen bodywork, I have 3 brand new still in the wrappers Puig screens on the shelf, 1 each in clear, smoke and dark...If I go with something else they will be posted up on VFRd for sale.

You should read my winter mods list on Sebs thread winter mod thread....I actually mention going with new duct tape for the 2011 season. :laughing6-hehe:

Link to comment
Share on other sites

  • Member Contributer

It took me riding a well sorted SP1 to commit to the swap, myself. I have been dissatisfied with the stock brakes for years, so that's why I didn't go with just an internal change. Thought I wanted radials, but when it came down to it I was just interested in the look of it. Love my stock RC51 brakes with stainless lines. They are fantastic!

Keith, have you seen the new Marvic Duc wheel? I think it's pretty bad ass! I'll try to find a pic in a little bit. (Linky)

Should be free on Sat.

Link to comment
Share on other sites

  • Member Contributer

Yes, I know I am over-analyzing it but my bike finally handles like I had hoped it would from the factory, and I definately don't to slow it down or lose much ground clearance...

Get Tony Foale's suspension analysis program (BLS has one...) and plug in your numbers, then. You will probably have to raise the rear ride height a bit to adjust for the increased trail. You will end up with slightly steeper rake than stock.

cassandtim made his own triples.

Link to comment
Share on other sites

  • Member Contributer

Kevin, I will give you call around lunch tomorrow to check your saturday schedule, if you have time to come over, i would love to borrow your stands and test fit the forks with your triples...or we could meet somewhere in ATL. I saw that thread on the wheels but really like the look of these.

gallery_7288_2662_213042.png

OZ Forged.png

a little spendy but...pretty light

Safe-T thanks for the tip on Tony Foales program. I will pm Larry and see if he has time to plug in my numbers after I gather them this weekend. I saw TimandCass write up am trying to have some triples built as well but running into $$$$ issues. approximately $4,ooo is the quote from three sources...still the way that I would prefer to go. got a lead with Ben (Talldrinkofwater) here and he may have some good news soon, fingers crossed.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...

Important Information

By using this site, you agree to our Privacy Policy.