ADVrider

Go Back   ADVrider > Bikes > Old's Cool > Airheads
User Name
Password
Register Inmates Photos Site Rules Search Today's Posts Mark Forums Read

Reply
 
Thread Tools Search this Thread Display Modes
Old 11-05-2012, 02:38 PM   #16
Dmaster
Gnarly Adventurer
 
Dmaster's Avatar
 
Joined: Apr 2012
Location: Netherlands.
Oddometer: 208
Quote:
Originally Posted by LukasM View Post
It's pretty simple really, if you want to keep the stock handling but with better quality suspension then just copy the stock total offset (triple clamps + fork lugs), fork length, and stroke.
The thing is, i do add a bit extra height and especially stroke. (I'm after suspension travel)
So what to do to make it steer like stock (or at least feel like as much as possible)
Do I need more trial because of the height increase, and how to get that.
Or stock trial and another steering head angle?
Dmaster is offline   Reply With Quote
Old 11-05-2012, 02:47 PM   #17
LukasM
Beastly Adventurer
 
Joined: Nov 2006
Location: On a RTW ride - currently Central Asia
Oddometer: 5,343
Unless you are going to have it professionally done I would forget about changing the actual steering head angle on the frame.

To compensate for the longer forks you would want more offset to keep the same turning ability. Of course it's a balancing act to see when it's too much etc.

Or just increase the rear travel and height the same so the bike stays balanced?

Keep in mind that only a part of the additional travel will be actual height increase due to additional sag and the fact that the forks are at an angle.
LukasM is offline   Reply With Quote
Old 11-05-2012, 02:50 PM   #18
Prutser
Studly Adventurer
 
Prutser's Avatar
 
Joined: Aug 2012
Location: The Dutch swamp
Oddometer: 914
Quote:
Originally Posted by LukasM View Post
Hi Bas,

Probably the open cartridge 48s from a 690 or 950, have both here. Not sure if the wider or narrower spacing between the upper and lower clamping area is better?

My friend is on a tight budget so we'll have to look for a cheap set of KTM OEM clamps that will work well. I'm thinking 950/990 SM or Duke will have the highest offset.
Erik is going to make the clamps for me and Dmaster. But he is also going to do some in the WP size for the X with 210mm
The OEM 190mm WP triple size does effect the turning circle a lot !
__________________
BMW R100'91/R80'93/R75/6 R80ST'83/R65GS'87/GasGasTXT300/DouglasW20-1920

R100GS'91 (sold)
Prutser is offline   Reply With Quote
Old 11-05-2012, 02:52 PM   #19
Clay Spinner
Woodfire or Bust
 
Clay Spinner's Avatar
 
Joined: Nov 2008
Location: Nova Scotia
Oddometer: 584
Anything useful in this....
Clay Spinner is offline   Reply With Quote
Old 11-05-2012, 02:55 PM   #20
LukasM
Beastly Adventurer
 
Joined: Nov 2006
Location: On a RTW ride - currently Central Asia
Oddometer: 5,343
Quote:
Originally Posted by Prutser View Post
Erik is going to make the clamps for me and Dmaster. But he is also going to do some in the WP size for the X with 210mm
The OEM 190mm WP triple size does effect the turning circle a lot !
Interesting! He should advertise them on the forum, I bet there will be some interest. Erik really needs to get a helper to put all his stuff online..

I'm pretty sure that the big KTM street bikes (and even the LC4 SM) actually have 210mm spacing, so that should help.
LukasM is offline   Reply With Quote
Old 11-05-2012, 03:00 PM   #21
Prutser
Studly Adventurer
 
Prutser's Avatar
 
Joined: Aug 2012
Location: The Dutch swamp
Oddometer: 914
Quote:
Originally Posted by LukasM View Post
Interesting! He should advertise them on the forum, I bet there will be some interest. Erik really needs to get a helper to put all his stuff online..

I'm pretty sure that the big KTM street bikes (and even the LC4 SM) actually have 210mm spacing, so that should help.
Lets test them first before advertising
__________________
BMW R100'91/R80'93/R75/6 R80ST'83/R65GS'87/GasGasTXT300/DouglasW20-1920

R100GS'91 (sold)
Prutser is offline   Reply With Quote
Old 11-05-2012, 03:15 PM   #22
Dmaster
Gnarly Adventurer
 
Dmaster's Avatar
 
Joined: Apr 2012
Location: Netherlands.
Oddometer: 208
Quote:
Originally Posted by LukasM View Post
Unless you are going to have it professionally done I would forget about changing the actual steering head angle on the frame.
A higher or lower back would give the same result (I won't expect i need a huge difference in this one)
Quote:
Originally Posted by LukasM View Post
To compensate for the longer forks you would want more offset to keep the same turning ability. Of course it's a balancing act to see when it's too much etc.
So you would like to have less trial? Why? (technical explanation otherwise its not true )
Quote:
Originally Posted by LukasM View Post
Or just increase the rear travel and height the same so the bike stays balanced?
Well the added height will effect the steering because the center of gravity is higher. At least thats what I still think.
Quote:
Originally Posted by LukasM View Post
Keep in mind that only a part of the additional travel will be actual height increase due to additional sag and the fact that the forks are at an angle.
I know about that one ;)

How are all measurements taken anyway? (like, steering head angle, trial, wheelbase)
Static, dynamic or high in the sky? If you compare those things all can be dramatically different.
Dmaster is offline   Reply With Quote
Old 11-06-2012, 04:52 AM   #23
ontic
 
Joined: Jul 2008
Location: Melbourne
Oddometer: 1,048
Quote:
Originally Posted by LukasM View Post
KTM triples are available in a variety of offsets, although nothing below 11mm or above 35mm I believe. Fork bottoms on the WP43 and WP48 have the axle leading by 35mm if I remember correctly.
What ktm triples came with anything close to a 35mm offset?

Also, by "axle leading by 35mm" do you mean how far the axle centre is forward of the fork tube centre? Ie axle offset?
35mm sounds about right for the USD forks, and that is the figure R-dubb was working with in this thread, so I am assuming that is what you meant.
But if anyone has these forks please measure them.

Considering my rough measurement was brought up at the beginning of this thread I thought it was about time I revised it.

I just had another look at the G/S forks verses my WP50's
Now that I've got a spare set of WP50's on the bench I could give them a proper measure.

I would like it if someone else with WP50's and G/S forks would have a got at these measurements, as it is a little tricky.

I also measured the G/S triple clamp offset because I had never actually done that before and was just assuming the reported figure was right.. it was

G/S triple clamp offset = 38mm

G/S Axle Offset = my calculations were 24.65mm

WP50 Axle Offset = my calculations were 40.26mm


I'm going to call that 25mm and 40mm until someone corrects or confirms and call that 15mm difference of axle offset between the G/S and WP50's,
and if the 35mm axle offset on the WP USD forks is right, then a 10mm difference on those forks.

Most intend to extend the front at least a bit to get some more travel and/or ground clearance.
Some people are extending the swing arms or (like my plan to move the lower shock mount forward) just raising the rear a little, to accomplish the same things and balance changes on the front end.

We worked out in another thread that a 50mm swing arm extension (with no major changes in sag) nets around 12-15mm more height, doubled to 24-30mm for a 100mm swing arm extension..

Most of us, myself included will try lengthening the forks quite a bit more than that, so even with getting more travel at the rear end, chances are for those that aim for a taller bike, the end result will be an increase in trail...

thus reducing trail at the triples or the axle with a nice big offset to get a taller bike with more travel might be a pretty good thing...

complicated stuff.

I would really like to understand it all better, but I'll be happy if I can just end up with a bike that rides like I want it to
__________________
1974 R90/6
1981 R80G/S
1994 XLR250R
ontic is offline   Reply With Quote
Old 11-06-2012, 05:03 AM   #24
Clay Spinner
Woodfire or Bust
 
Clay Spinner's Avatar
 
Joined: Nov 2008
Location: Nova Scotia
Oddometer: 584
Quote:
Originally Posted by ontic View Post

complicated stuff.

I would really like to understand it all better, but I'll be happy if I can just end up with a bike that rides like I want it to
Exactly... I guess that is why there aren't more people building these things in their spare time.
Clay Spinner is offline   Reply With Quote
Old 11-06-2012, 05:37 AM   #25
Rucksta
Chronic Noob
 
Rucksta's Avatar
 
Joined: Oct 2008
Location: Gold Coast
Oddometer: 2,589
Has anyone with a well set up transplanted front end measured how much travel they actually use?

220mm out of 270mm available is all I get from a fork that will take a front wheel landing or trickle through a rock garden wiithout skipping.

I'd be interested to find out how much others use.
__________________
My bike is slow but the earth is patient.
Rucksta is offline   Reply With Quote
Old 11-06-2012, 08:41 PM   #26
Phreaky Phil
Beastly Adventurer
 
Joined: Mar 2006
Location: NEW ZEALAND
Oddometer: 1,722
Quote:
Originally Posted by Rucksta View Post
Has anyone with a well set up transplanted front end measured how much travel they actually use?

220mm out of 270mm available is all I get from a fork that will take a front wheel landing or trickle through a rock garden wiithout skipping.

I'd be interested to find out how much others use.
That would be interesting to see. I never measured my travel used but when I had the USD front end in my GS (travel shortened to 220mm) i dont remember ever bottoming it. Probably due to the far better damping than the original forks had and possibly better bottoming resistance than original forks.
Phreaky Phil is offline   Reply With Quote
Old 11-07-2012, 10:26 AM   #27
Dmaster
Gnarly Adventurer
 
Dmaster's Avatar
 
Joined: Apr 2012
Location: Netherlands.
Oddometer: 208
I know have 265 or 270mm stroke in my DRZ fork, and I can bottom it out if I want.
Take a high jump with a ruff landing or something and its done.
Same at the back.
In my opinion if you can't bottom it out, 1 your driving to slow, 2 your springs are to stiff/ to small air gap.
You can even bottom out a proper set up MX bike if you really want to. And if you mount such stiff springs you won't all other times it will be to stiff and you will never use the stroke you actually have.
And please notice the last piece of stroke is a hydraulic stop, if you end up at the end of that one you're doing insane stuff ;)
Dmaster is offline   Reply With Quote
Old 11-07-2012, 12:40 PM   #28
naginalf
Handy Schtroumpf
 
naginalf's Avatar
 
Joined: Jan 2010
Location: Madison, WI
Oddometer: 250
Eek Yay trigonometry!

Quote:
Originally Posted by ontic View Post
complicated stuff. I would really like to understand it all better, but I'll be happy if I can just end up with a bike that rides like I want it to
I found this very helpful to understanding it, it's really not that complicated, just hard to visuallize. Personally, I wouldn't raise the front without equal in the back, the rake on a GS is already 28, a KTM is 25-27.



And, if my trigonometry is correct, the following formula should get your trail (in mm):
X = trail (the important part)
F = offset, combined from triples and axle. More offset makes less trail.
N = rake angle of the forks at the steering head. This will go up from stock if you raise the front and not the back, thus increasing trail.
r = radius of the wheel/tire at the road surface. This should be a range from the exact measurement, up to 15mm or so less for a compressed tire. A 90/90/21 tire has a 347.7mm radius, probably compresses down to 330mm.

X = (r SinN) - F
.........CosN

If you don't remember your algebra, open the calculator from windows accessories, click view, click scientific, then do the following. Take the sine (push 28, sin) of your rake angle, multiply by the tire radius (330 to 343mm depending on your tire, inflation, and weight), press equal then subtract your offset. Now press equal again and divide by the cosine of the rake angle (push divide, 28, cos), and equal again for your trail.

For example, the trail on my GS with WP4860s and HPMGuy triples will be, let's see 35mm axle offset, 41mm triple offset (this was for the WP50 triples, not sure if it changed for the 4860s), 28 angle, that makes it.... 89 - 96mm of trail.

As for what trail should be, I have no idea , I was just having fun with math. However, using the KTM example, the stock 640adv has 124mm of trail, some companies make custom triples that increase offset and thus decrease trail, perhaps as much as 115mm. That makes me worry about having such low trail and high offset with the HPMguy triples. Perhaps raking it out with longer forks isn't such a bad idea. Although by my calculations, the stock GS has around 93mm of trail. I think that the more rake you have, the less trail you need, but that's just my assumption from what I'm seeing.
__________________
'91 R100GSPD
Adventures with a Type1 TARDIS.

naginalf screwed with this post 11-07-2012 at 12:54 PM
naginalf is offline   Reply With Quote
Old 11-07-2012, 01:21 PM   #29
Rucksta
Chronic Noob
 
Rucksta's Avatar
 
Joined: Oct 2008
Location: Gold Coast
Oddometer: 2,589
Quote:
Originally Posted by Dmaster View Post
I know have 265 or 270mm stroke in my DRZ fork, and I can bottom it out if I want.
Take a high jump with a ruff landing or something and its done.
Same at the back.
In my opinion if you can't bottom it out, 1 your driving to slow, 2 your springs are to stiff/ to small air gap.
You can even bottom out a proper set up MX bike if you really want to. And if you mount such stiff springs you won't all other times it will be to stiff and you will never use the stroke you actually have.
And please notice the last piece of stroke is a hydraulic stop, if you end up at the end of that one you're doing insane stuff ;)
Setup on a mid weight is a different ball game to an MX or Enduro buke.
Even if thats where you source the grafted front end.
Sprung to unsprung weight ratios on the heavier bike work in your favour.
Controlling weight transfer is challenge
Ability to cope with high speed running and varying load conditions e.g. luggage 0 to 45lts of fuel is another.

I'm suggesting big numbers on travel is not the holy grail of supension set up and "use it cause you have it" is not the best approach to a balanced setup.

300mm travel on my G/S has the sump guard dragging before bottom out.
__________________
My bike is slow but the earth is patient.

Rucksta screwed with this post 11-07-2012 at 03:29 PM Reason: punctuation to clarify
Rucksta is offline   Reply With Quote
Old 11-07-2012, 01:37 PM   #30
robtg
Studly Adventurer
 
Joined: Jun 2007
Location: san jose
Oddometer: 609
http://www.tonyfoale.com/ -- freeware -- steering geometry calculator.
robtg is offline   Reply With Quote
Reply

Share

Thread Tools Search this Thread
Search this Thread:

.
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On

Forum Jump


Times are GMT -7.   It's 07:57 PM.


Powered by vBulletin® Version 3.8.5
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Copyright ADVrider 2011-2014