Triple tree offset ???

Questions and comments about converting to beefier forks..
Post Reply
User avatar
m0rie
Supporting Member I
Supporting Member I
Posts: 2220
Joined: 10:25 pm Nov 29 2004
Country:
Location: Crescent City, CA

Post by m0rie »

I think its close to 28 degrees of offset. I'll dig up the spec sheet and give you the exact number.
1989 KDX 200
2007 TTR-50E
User avatar
canyncarvr
Gold Member
Gold Member
Posts: 6943
Joined: 01:07 pm Nov 05 2004
Country: US
Location: The Mythical State of Jefferson

Post by canyncarvr »

I have no clue. Never looked it up. It never concerned me.

I didn't change my forks to increase/decrease/effect the offset.

What is it you're after?

Consider the source
Using a perceived level of knowledge to boost my self worth.
Non impediti ratione cogitationis

bike profile: !clicky!
User avatar
m0rie
Supporting Member I
Supporting Member I
Posts: 2220
Joined: 10:25 pm Nov 29 2004
Country:
Location: Crescent City, CA

Post by m0rie »

If nobody answers by this weekend I can measure my old trees and let you know.
1989 KDX 200
2007 TTR-50E
User avatar
canyncarvr
Gold Member
Gold Member
Posts: 6943
Joined: 01:07 pm Nov 05 2004
Country: US
Location: The Mythical State of Jefferson

Post by canyncarvr »

Sorry to be dense..but I do not understand.

Your KX clamps measure 18mm and you want to know how that compares to the KDX OEM clamps?

For the purpose of getting a noodle (thought on) on steering quickness? Rake effects that, too, and of course, that won't change (with a 'level' bike).

It's not important to understand I guess. I'll measure mine tonight and get you a number (empirically derived). Is that how you got your 18mm number? Or is that a spec'd number?

Consider the source
Using a perceived level of knowledge to boost my self worth.
Non impediti ratione cogitationis

bike profile: !clicky!
User avatar
canyncarvr
Gold Member
Gold Member
Posts: 6943
Joined: 01:07 pm Nov 05 2004
Country: US
Location: The Mythical State of Jefferson

Post by canyncarvr »

I measured my OEM top clamp. Said measuring consisted of marking a diameter on the steering stem hole parallel to a similar measurement on the fork tube hole.

...scientifically marked with an idelible official 'Marks-A-Lot' pen. :shock:

Impressed so far?

I came up with 24mm.

I'm assuming the red line thru the fork hole above to BE a diameter..don't know what the purpose would be of measuring to the clamp-gap.

So, there 'ya go! Empirically derived using the finest of tools...a most exact measurement I'm sure!

'Hope this helps!' (From a 'former' poster, stated in this case only to convey some sense of good will as I have no idea if it will help in the slightest!)

Cheers!!

Consider the source
Using a perceived level of knowledge to boost my self worth.
Non impediti ratione cogitationis

bike profile: !clicky!
User avatar
canyncarvr
Gold Member
Gold Member
Posts: 6943
Joined: 01:07 pm Nov 05 2004
Country: US
Location: The Mythical State of Jefferson

Post by canyncarvr »

I've always been on the fuzzy side of rake and trail. I believe rake to be the angle of the stem to the frame and trail the distance of the tire contact patch to a perpendicular through the stem. Trail will change with fork placement/length, but rake is fixed on a particular bike. Maybe there is something wrong with that thinking.

I don't see 'more' offset (greater distanced measured) increasing trail. That comes from the steering angle. That angle won't change as long as the fork length is 'correct'. That depends on how they are installed.

My bike is level the same way now as it was with the OEM forks. The KX forks sit a long ways up in the clamps to get to that 'level'..but the bike attitude did not change in my case. That was my intention.

An increased offset (again, as measured in this case) will increase the wheelbase, will it not?


I just tried this and it made more sense. I drew a picture!!

Draw three parallel lines on a sheet of paper to represent the centerline of the fork tubes. Draw circles at the ends to represent forks and one at three obviously different offsets to represent three different setups. Hold your finger/thumb over a 'stem' hole and rotate the paper. See all the lines move the same amount!

Well...it made sense at the time........ :neutral:

My geometry is failing me..... :sad:


IC! (or somebody) 'Splain this correctly!!

M0rie..do measure yours this weekend?
Last edited by canyncarvr on 01:19 pm Jul 25 2006, edited 2 times in total.

Consider the source
Using a perceived level of knowledge to boost my self worth.
Non impediti ratione cogitationis

bike profile: !clicky!
User avatar
m0rie
Supporting Member I
Supporting Member I
Posts: 2220
Joined: 10:25 pm Nov 29 2004
Country:
Location: Crescent City, CA

Post by m0rie »

I'll measure my KDX clamps this weekend and i've got a pair of 94 KX 125 clamps at home that i'll measure tonight as well.
1989 KDX 200
2007 TTR-50E
User avatar
canyncarvr
Gold Member
Gold Member
Posts: 6943
Joined: 01:07 pm Nov 05 2004
Country: US
Location: The Mythical State of Jefferson

Post by canyncarvr »

Sorry, I was referring to my clamp measurements...and you to yours.

So, yeah. Your wheelbase will be shorter by some. I don't see trail º changing, though..if the 'effective' fork length is the same.

I'd be more concerned with the lesser offset causing greater tube/fuel tank interference. Any restriction in that area (lessening the turn angle) will slow steering considerably..like adding wheelbase.

..something I didn't care for on the katoom exe I rode. The forks were so dang big (don't know what size..48mm I think) and set up such that you couldn't get around stuff. Brake-steer isn't always a choice!

Consider the source
Using a perceived level of knowledge to boost my self worth.
Non impediti ratione cogitationis

bike profile: !clicky!
IdahoCharley
Supporting Member II
Supporting Member II
Posts: 1005
Joined: 06:57 pm Mar 19 2005
Country:

Post by IdahoCharley »

I'am not really sure what the question/problem is here. I give my two cents worth which is easiest done by referring to CC note since I not sure of what foots is after - other than a dimension.

RE >|<>QBB<[quote="canyncarvr"]I've always been on the fuzzy side of rake and trail. I believe rake to be the angle of the stem to the frame and trail the distance of the tire contact patch to a perpendicular through the stem.

My thinking is very similar to CC's line of thinking on "rake" and "trail": Likely the fuzzy part also.

RE - Trail will change with fork placement/length, but rake is fixed on a particular bike.

Yes trail will change with fork placement/length but can also be changed with triple tree offset: easiest to mentally view it as essential just an altered or maybe effective rake angle may be more descriptive IMO. Since, it alters the rake angle of the forks relative to the frame.

The different triple tree offsets essentially slightly alter the relationship between the fixed frame stem and the fork angle which affects wheel base, weight on forks along with other handling characterics.

RE - An increased offset (again, as measured in this case) will increase the wheelbase, will it not?

I believe this is the case if the bike was adjusted back to its attitude (your word which I like by the way): Would it not also increase the effective rake angle?

I reread this thread a couple of times - maybe I just dense right now from not riding enough this summer - :partyman: But increasing the offset (going higher numerically in the center line to centerline distance) will SLOW up the steering and free up space between the tank and fork tubes.

Decreasing the offset (going lower numerically in the stem center line to fork centerline distance will SPEED up the steering and close up the space between the forks and tank.
KTM 380EXC Mine
KDX 200 Mark's
TTR 125 L Wife's
KDX 200 Austin's
EC 300 Tyson's
WR430 Husky - mine
IdahoCharley
Supporting Member II
Supporting Member II
Posts: 1005
Joined: 06:57 pm Mar 19 2005
Country:

Post by IdahoCharley »

Just a comment on foot's drawing for someone reading this thread and wondering - red colored line is centerline of forks tubes in the triple tree and the center line of the stem which holds the triple tree in the bike frame's head. The difference between the two centerlines is the offset of the triple tree clamps. In this case it was 22.5 mm of offset. A closer or tighter offset < 22.5 mm tightens up the wheel base, changes the trail, generally make the bike a little less stable at speed and makes the bike steer quicker.

A higher offset > 22.5mm would slow up the steering, generally make the bike more stable at speed and also change the trail.
KTM 380EXC Mine
KDX 200 Mark's
TTR 125 L Wife's
KDX 200 Austin's
EC 300 Tyson's
WR430 Husky - mine
User avatar
tim
Supporting Member I
Supporting Member I
Posts: 240
Joined: 10:12 pm Mar 10 2006
Country:
Location: East Tn.

Post by tim »

Idaho are you saying that if you change the offset and make the wheel base longer it will be more stable at higher speeds?
06 200H

GALLERY!
IdahoCharley
Supporting Member II
Supporting Member II
Posts: 1005
Joined: 06:57 pm Mar 19 2005
Country:

Post by IdahoCharley »

Tim - Yes, I believe this is the general consensus.
KTM 380EXC Mine
KDX 200 Mark's
TTR 125 L Wife's
KDX 200 Austin's
EC 300 Tyson's
WR430 Husky - mine
User avatar
canyncarvr
Gold Member
Gold Member
Posts: 6943
Joined: 01:07 pm Nov 05 2004
Country: US
Location: The Mythical State of Jefferson

Post by canyncarvr »

Here comes 'da fuzzy parts!!

How is it that changing the offset changes the steering quickness if the attitude remains the same?

Re: 'Would it not also increase the effective rake angle?'
The angle of the fork to the bike does not change. The angle of the bike changes only if the effective fork length (and/or clamp position) changes. 'Effective' in this case meaning the change required to get the bike back to 'straight' if the offset is changed.

Consider: If you raise the fork tubes in the clamps (lower the bike), steering gets quicker, bike is less stable, wheelbase is shortened. Correct?

If you keep the fork tubes in the same place in the clamps, the more offset you have, the <what> the frontend gets?

It gets lower, correct? But the wheelbase still increases!

There are two type of steering 'quicker' to consider. One comes from shortening the wheelbase and that is not to be confused with changing the angle of the stem or the angle the bike presents to the ground (that depends on fork length).

The larger the offset, the longer the forks have to be to sit the bike at the same level.

I'd bet, generally, that offset works with fork length to make the attitude of the bike 'correct'. Less offset comes with shorter forks, more offset comes with longer forks.

Of course, the height of the rear axle is critical to the attitude part.

Exaggerate the deal to make the point: You can drop the front enough that the forks would be perpendicular to the ground. Likewise, you could raise the front enough to make the forks horizontal to the ground.

Well, the 'ground' is not at all a straight line in the first place.... :wink:

The more often I read this, the more convince I am that I don't know.

How 'bout that?

There are lots of interesting articles on the web about rake and trail:

http://www.msgroup.org/TIP163.html

http://www.tonyfoale.com/Articles/RakeEx/RakeEx.htm

Consider the source
Using a perceived level of knowledge to boost my self worth.
Non impediti ratione cogitationis

bike profile: !clicky!
IdahoCharley
Supporting Member II
Supporting Member II
Posts: 1005
Joined: 06:57 pm Mar 19 2005
Country:

Post by IdahoCharley »

CC - That second article was great. Never seen a write-up on front end suspension quite like that article. Really gets you thinking - would have liked to been apart of that project (imagine the stares they got riding the bike through London. LOL - would have been a Hoot)

I agree whole heartily with everything you stated except your response to -
Re: 'Would it not also increase the effective rake angle?'

CC wrote "The angle of the fork to the bike does not change. The angle of the bike changes only if the effective fork length (and/or clamp position) changes. 'Effective' in this case meaning the change required to get the bike back to 'straight' if the offset is changed."

RES - this just did not compute in my little noodle. But then it just dawned on me. (light bulb time/symbol) You are assuming that both the upper and lower triple trees have the same offset thus keeping them parallel to the stem on the bike. CORRECT???

I have been assuming essentually that ONLY the upper triple tree offset is changing but the bottom offset is remaining unchanged except for the angle of the machined holes for the fork legs. (necessary of course in order to have the two triple clamps accept a set of straight tubes thus you buy a matching set of triple tree clamps)

As has been happening since I was about 16-18 years old (when I really knew everything worthwhile knowing in life) I am likely WRONG again. Well I guess I should not say I'm wrong until it is proved that it is - the way you think it is verses the way I assumed it was - :oops:

FWIW - I've never really played with various offset triple trees on a dirt bikes but I have built and helped to build a few BSAs, Triumphs, and even a couple vertical twin Yamahas back in the early 70'sa - 80'sa. My thinking was based having triple trees which were off-set dramatically on the bottom triple tree and fixed near the stock off-set on the upper tree. This was done of course to kick out the front end (rake) of the bike and we would go 6 to 10 inches over on the fork tubes to end up with the chopper stretched out look. This saved us from the hassels of cutting the bike frame, jigging the frame, and then relocating the front stem and allowed up to keep the frame serial numbers. Anyway I had just assumed the dirt bike off-set variations was essentiality the reverse chopper TT application. I've probably lost anyone reading this dribble but since it has been entered you WILL BE EXPOSED TO THIS DRIBBLE if you read this thread - SO SORRY!! :lol:

Bottom line - We are both fuzzy or maybe I should say I may be completely lost in this area it seems - maybe some young wippersnapper will set us straight. I'm gong to grab a beer and hope that someone REALLY knows the off-set triple tree "Answer" since this is starting to bug me!

Off to kill a few more brain cells.
:partyman: :partyman:
Last edited by IdahoCharley on 10:57 pm Jul 28 2006, edited 1 time in total.
KTM 380EXC Mine
KDX 200 Mark's
TTR 125 L Wife's
KDX 200 Austin's
EC 300 Tyson's
WR430 Husky - mine
User avatar
canyncarvr
Gold Member
Gold Member
Posts: 6943
Joined: 01:07 pm Nov 05 2004
Country: US
Location: The Mythical State of Jefferson

Post by canyncarvr »

Well, (from when written) I'm ahead of you, cuz I'm on my third Wild River (local brewery) IPA (India Pale Ale for the non-drunkards in the room...named so 'cuz the Brits hopped the heck out of the beer they sent round the cape to India back when they owned India so it would 'keep' during the voyage...).

Re: 'I'm assuming...'

They are not the same? How do you get the two clamps different? If they ARE different that would make the forks approach the bottom clamp at more than a simple angle. It would needs be a compound angle! You could not change the offset on a top clamp without angling the bottom clamp on two angles.

Uh...right?

Don't the two have to match?

Increase the offset on the top, keep the bottom the same and you will have a fork tube hitting the bottom clamp toward the front at the top of the bottom clamp and toward the rear at the bottom of the bottom clamp.

Which is indeed what you say: '...the bottom offset is remaining unchanged except for the angle of the machined holes for the fork legs.'

I hate to show my extreme ignorance, but IS this the way it works?

Yes. I have assumed the offset of the two clamps to be the same.

Thus, I am also bugged.

Whippersnapper, please!

:wink:

Uh oh..it's time for #4!!!!!!!!!

Consider the source
Using a perceived level of knowledge to boost my self worth.
Non impediti ratione cogitationis

bike profile: !clicky!
IdahoCharley
Supporting Member II
Supporting Member II
Posts: 1005
Joined: 06:57 pm Mar 19 2005
Country:

Post by IdahoCharley »

The answer is laying in someone's garage for sure. If someone would grab a KDX upper and lower triple tree and measure from the stem to the hole for the fork tube on both the upper and lower triple trees and then post their caliper readings. :grin: PLEASE

We would just need to compensate 50% of the difference in stem diameters between the upper and lower TTs; and then (I think) we would have an answer.

NOTE - It would not be the off-set reading per se, but it would tell us whether or not the forks tubes run parallel to the stem.
KTM 380EXC Mine
KDX 200 Mark's
TTR 125 L Wife's
KDX 200 Austin's
EC 300 Tyson's
WR430 Husky - mine
IdahoCharley
Supporting Member II
Supporting Member II
Posts: 1005
Joined: 06:57 pm Mar 19 2005
Country:

Post by IdahoCharley »

CC - Where have all the Whippersnappers Gone???

"Whippersnapper" as used by CC and I in this thread is a POSITIVE reference and not the standard dictionary definition. "We" look FORWARD to hearing from you to set both of us straight on what the heck triple tree off-set means relative to BOTH THE UPPER AND LOWER TRIPLE TREES.

I will hence forth alway refer to you as the - Whippersnapper of Triple Trees- :prayer: if you can shed some light on this subject for us. Thanks in advance! :grin:
KTM 380EXC Mine
KDX 200 Mark's
TTR 125 L Wife's
KDX 200 Austin's
EC 300 Tyson's
WR430 Husky - mine
User avatar
canyncarvr
Gold Member
Gold Member
Posts: 6943
Joined: 01:07 pm Nov 05 2004
Country: US
Location: The Mythical State of Jefferson

Post by canyncarvr »

Long time passin'.

That's where.

Along with the flowers.

Jackanapes all, anyway! :wink:

Now...when was the last time you read/heard/said THAT word?? :wink: Right up there with coxcomb I'll bet!

If you happen to be cheeky and presumptuous, that don't necessarily mean you don't know what you're talking about. ...sometimes....

Consider the source
Using a perceived level of knowledge to boost my self worth.
Non impediti ratione cogitationis

bike profile: !clicky!
Post Reply