ADVrider

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

Reply
 
Thread Tools Search this Thread Display Modes
Old 03-19-2013, 04:02 AM   #3556
Gravel Seeker
Thomas
 
Gravel Seeker's Avatar
 
Joined: Apr 2002
Location: Dreary old Norway, dreaming of adventures past
Oddometer: 3,951
Quote:
Originally Posted by UnsafeHOTADVENTURE View Post
Still confused...

If a 17" tire is sized at 140/80/17 then its height is 80mm from the lip of the rim to the top of the tire.

If an 18" tire is sized at 140/80/18 then its height is 80mm from the lip of the rim to the top of the tire.

So the 18" tire is an inch larger overall every time.

Am I looking at tire sizes all wrong?
80 doesn't indicate 80mm, but rather 80% of the width (aspect ratio). The 1 inch rim difference only makes up 1/2 inch height difference if you put both next to each other on an axle. The second 1/2 inch only fill in the air between the rim and the mudguard.

https://www.denniskirk.com/help_center/tire-sizes.jsp
http://www.goodyearautoservice.com/c...eName=TireSize
http://www.autobytel.com/car-ownersh...s-mean-105706/
__________________
'01 F650 Dakar - modified as best I can

2005: Australia - 8 months/ 26.000 km (anti clockwise circle)
2009: Norway - 2 weeks/ 6000 km (Lindesnes to North cape)

Gravel Seekers.com

Hey !
It's the African ant eater ritual !
Gravel Seeker is offline   Reply With Quote
Old 03-19-2013, 04:08 AM   #3557
isgila
Gnarly Adventurer
 
isgila's Avatar
 
Joined: Jan 2012
Location: Singapore
Oddometer: 109
Quote:
Originally Posted by UnsafeHOTADVENTURE View Post
Still confused...

If a 17" tire is sized at 140/80/17 then its height is 80mm from the lip of the rim to the top of the tire.

If an 18" tire is sized at 140/80/18 then its height is 80mm from the lip of the rim to the top of the tire.

So the 18" tire is an inch larger overall every time.

Am I looking at tire sizes all wrong?
an inch in diameter of the rims with the same tyre will only gives you an half inch rise...
Why... Because you have to remember that the radius of the rims from the lip to the centre of the axle.
It is like switching from a road tyre to a full knobbies tyre. There are other ways to raise the rear. Longer shock, shorter dogbones, full knobbies and etc.
Like most of them have said, going 18' rear or 21' front gives more options of running full mx tyres
isgila is offline   Reply With Quote
Old 03-19-2013, 06:01 AM   #3558
Brash
.
 
Brash's Avatar
 
Joined: Aug 2009
Oddometer: 1
Thumb

I have done the fork conversion with 03 yammy forks (46mm) and am chasing some .52 or .54 springs. Not having much luck getting hold of any here in sunny Queensland or Australia for that matter. Can any one point me in the right direction where I could get a pair?
Brash is offline   Reply With Quote
Old 03-19-2013, 06:44 AM   #3559
dwayne
Silly Adventurer
 
dwayne's Avatar
 
Joined: Feb 2006
Location: wheelie in purgatory, Calgary
Oddometer: 3,218
Quote:
Originally Posted by UnsafeHOTADVENTURE View Post
Still confused...

If a 17" tire is sized at 140/80/17 then its height is 80mm from the lip of the rim to the top of the tire.

If an 18" tire is sized at 140/80/18 then its height is 80mm from the lip of the rim to the top of the tire.

So the 18" tire is an inch larger overall every time.

Am I looking at tire sizes all wrong?
You need to find the specs for the overall installed height of the tire/rim combo and divide the difference from stock by two.As gravel seeker mentioned the number is an aspect ratio, but even then the accuracy of that number is often a little off. Even more so with aggressive knobbies, because every manufacturer might choose a slightly different place on the knob height to call the sidewall height due to wear...knobbies tend to have very deep treads compared to other tires.

I knoW for a fact that 18" and 19" wheel/tire combos have very nearly the same overall height, the reason for the narrower sidewall on the MX bikes is better handling on groomed MX tracks, where the enduros get 18's and a taller sidewall too help deal with roots and rocks.

In the above scenario you would get a "lift".of about 15mm or 5/8" assuming that the numbers are accurate, If you used 130s it would be less but again you are better off finding the installed overall heights if you can.
__________________
Rum Runners Yukon, NWT & Alaska
Roads and Ruins Scotland
Kinbasket Lake Golden B.C.

A "Day" of Dirt Biking Rockies East Slopes
High and Dry Colorado and Utah


"When your only tool is a hammer, every problem looks like a nail"
dwayne is offline   Reply With Quote
Old 03-19-2013, 11:27 AM   #3560
Gangplank
Advenchaintourer
 
Gangplank's Avatar
 
Joined: Jul 2003
Location: Las Vegas
Oddometer: 2,294
Quote:
Originally Posted by UnsafeHOTADVENTURE View Post
Still confused...

If a 17" tire is sized at 140/80/17 then its height is 80mm from the lip of the rim to the top of the tire.

If an 18" tire is sized at 140/80/18 then its height is 80mm from the lip of the rim to the top of the tire.

So the 18" tire is an inch larger overall every time.

Am I looking at tire sizes all wrong?
"The 130 designates the tire's width in millimeters, measured in a straight line through the tire from one edge of the tire's tread to the other. The second number, 90, is a bit trickier to understand. This represents the aspect ratio between the tire's width and its height, or how tall a tire is in relationship to its width. Simply put, the higher this number is, the taller the tire will be. In this case, the tire is 90 percent as tall as its width, or 117mm."

From here:
http://www.americanmotorcyclist.com/...ignations.aspx

So if you are looking at the same tire a 130/80 will be the same height in a 17 or 18". Same height from the rim that is...

If the rim itself is 1" bigger diameter then you'll have 1/2" above and 1/2" below the axel so 1/2" of added height.

I'm not 100% sure of it works on the F650GS shocks but another way to raise the rear ride height is to add a shim or stack of fender washers on the shock clevis. This is done the GSXR-750 to raise the rear up for race use.
__________________
Ride more, bark less
Gangplank is offline   Reply With Quote
Old 03-19-2013, 11:35 AM   #3561
rmarkr
Squatter
 
rmarkr's Avatar
 
Joined: Sep 2007
Location: Lowcountry
Oddometer: 388
Quote:
Originally Posted by UnsafeHOTADVENTURE View Post
Still confused...

If a 17" tire is sized at 140/80/17 then its height is 80mm from the lip of the rim to the top of the tire.

If an 18" tire is sized at 140/80/18 then its height is 80mm from the lip of the rim to the top of the tire.

So the 18" tire is an inch larger overall every time.

Am I looking at tire sizes all wrong?
This is my take:
A 140/80/17 tire's height is 80% of its width of 140mm; that's about 112mm.
rmarkr is offline   Reply With Quote
Old 03-19-2013, 11:39 AM   #3562
Gangplank
Advenchaintourer
 
Gangplank's Avatar
 
Joined: Jul 2003
Location: Las Vegas
Oddometer: 2,294
Quote:
Originally Posted by Brash View Post
I have done the fork conversion with 03 yammy forks (46mm) and am chasing some .52 or .54 springs. Not having much luck getting hold of any here in sunny Queensland or Australia for that matter. Can any one point me in the right direction where I could get a pair?
I got mine from Ed McCoy's Offroad center in Carson City, NV. Not sure where he ordered them from.

FWIW he strongly recommended not going over .52. He said he tunes a lot of these forks for guys weighing up to 250lbs and never goes higher than .50. Keep in mind that half the bike weight is on front and half on back. So if the bike weighs +200 lbs that is 1/2 front & back.

So on the racetech site if I put in my own weight of 185 + 100 = 285 lbs and it comes back with:

FRONT FORK SPRINGS
Recommended Fork Spring Rate: 0.53 kg/mm (use closest available)
Stock Fork Spring Rate: 0.43 kg/mm(stock)

The highest they have on the site is .48 but there are .50 and .52's out there.
__________________
Ride more, bark less
Gangplank is offline   Reply With Quote
Old 03-19-2013, 01:27 PM   #3563
UnsafeHOTADVENTURE
Adventurer
 
Joined: Feb 2011
Location: So Cal
Oddometer: 49
Alright haha I think i get the tire sizes.
UnsafeHOTADVENTURE is offline   Reply With Quote
Old 03-19-2013, 04:16 PM   #3564
Gangplank
Advenchaintourer
 
Gangplank's Avatar
 
Joined: Jul 2003
Location: Las Vegas
Oddometer: 2,294
Just picked up my forks today. Looking good. Would up with .49 springs in them. Not too worried about it. The springs job is to hold the front end up in the propper sag range. I can always add preload spacer to raise it up and use the compression adjustment to tune it in if there is too much dive on braking.

On another note I found a local machine shop that can make me an ignition mount to fit on my triple with the Aplied Racing top triple.

I think either have or have ordered all of the parts I need at this point. Looking forward to when it all comes in and i can get started on the swapping

Total for my conversion front end (forks, wheel, axle, brakes, fork guards, revalve & respring, fabbing the mount for ignition and BMW pipe for ABS removal) comes to under $1000.

Super stoked on this project so far!
__________________
Ride more, bark less

Gangplank screwed with this post 03-19-2013 at 04:56 PM
Gangplank is offline   Reply With Quote
Old 03-22-2013, 10:25 AM   #3565
Gangplank
Advenchaintourer
 
Gangplank's Avatar
 
Joined: Jul 2003
Location: Las Vegas
Oddometer: 2,294
Does anyone know what size the two bolts are for the ignition mount? I'm having a mount made at a local machine shop and he asked. Are they 6mm, 8mm or 10mm?

Like these:


aka this one:
https://docs.google.com/file/d/0B6Di...it?usp=sharing
Which is from here:
http://www.f650gs.crossroadz.com.au/...orkNotesYZ.pdf
__________________
Ride more, bark less
Gangplank is offline   Reply With Quote
Old 03-22-2013, 11:49 AM   #3566
TobyG
be happy :)
 
TobyG's Avatar
 
Joined: Dec 2011
Location: in the garage
Oddometer: 513
Quote:
Originally Posted by Gangplank View Post
Does anyone know what size the two bolts are for the ignition mount? I'm having a mount made at a local machine shop and he asked. Are they 6mm, 8mm or 10mm?

According to bmwetk.info the bolts are 8 mm.


http://www.bmwetk.info/parts-catalog...602/51/51_4140
__________________
"a scoot (that wouldn't go more than 28mph if you dropped it out of an airplane)" ~duck
"If loud pipes saved lives, then ambulances would run straight pipes instead of lights and sirens." ~Phlemdog
This is why I always wear gloves. How you gonna wipe your butt with hands covered in bandages? ~MrBob
TobyG is offline   Reply With Quote
Old 03-23-2013, 04:32 PM   #3567
xt500nz
Adventurer
 
Joined: Mar 2013
Oddometer: 42
Quote:
Originally Posted by Gangplank View Post
I got mine from Ed McCoy's Offroad center in Carson City, NV. Not sure where he ordered them from.

FWIW he strongly recommended not going over .52. He said he tunes a lot of these forks for guys weighing up to 250lbs and never goes higher than .50. Keep in mind that half the bike weight is on front and half on back. So if the bike weighs +200 lbs that is 1/2 front & back.

So on the racetech site if I put in my own weight of 185 + 100 = 285 lbs and it comes back with:

FRONT FORK SPRINGS
Recommended Fork Spring Rate: 0.53 kg/mm (use closest available)
Stock Fork Spring Rate: 0.43 kg/mm(stock)

The highest they have on the site is .48 but there are .50 and .52's out there.
hi, could you justify the reasons for not going over .50 rated springs.
xt500nz is offline   Reply With Quote
Old 03-23-2013, 06:34 PM   #3568
Schlug
JockeyfullofBourbon
 
Schlug's Avatar
 
Joined: Jan 2006
Location: put something on and stay in that position.
Oddometer: 7,314
A 2003 Yamaha YZ weighs somewhere around 230 pounds. A 2003 Dakar weighs 390, pounds dry, before we start bolting stuff to it.

Stock springs are what, .49? And sprung for 170 lbs. rider (with kit).

Add 160 lbs. more weight to the bike plus engine guards, pannier racks, whathaveyou, plus a real adult-sized rider and extra weight of panniers and the load carried, and .52 or .55 doesn't come close.

I suppose if you were a really light fellow who rode with a nearly naked bike off-road all the time you could work that scenario, but if you punch in real-world numbers to race-tech's spring calculator your eyes will be opened.

Also, we must be aware that no two tire manufacturers measure their tires the same. Not in width, not in ratio. More than one Dakar rider has gone to an 18" with disasterous results and ruined tires. If you decide to run an 18" rear remember that your choice of tires is significantly more limited than you might think given how close some of the better tires come to rubbing holes in parts of the bike or themselves. The Dunlop rally-raid 908 will NOT work.

One more thing, the suspension linkage on the Dakar, with a properly sprung shock, has very little room for movement. Simply buying a longer shock may not be the answer. I asked if I could buy a custom Ohlins with an adjustable length yoke and the answer came back-- not recommended.
__________________
"So what makes this protest different is that you're set to die, Bobby?"
--May well come to that.
"You start a hunger strike to protest for what you believe in. You don't start already determined to die or am I missing somethin' here?"
-- It's in their hands. Our message is clear. They're seeing our determination.
Schlug is offline   Reply With Quote
Old 03-23-2013, 06:34 PM   #3569
Schlug
JockeyfullofBourbon
 
Schlug's Avatar
 
Joined: Jan 2006
Location: put something on and stay in that position.
Oddometer: 7,314
Quote:
Originally Posted by xt500nz View Post
hi, could you justify the reasons for not going over .50 rated springs.
On a Yamaha YZ, I could see it. But on a Dakar? I'd ask the same question.
__________________
"So what makes this protest different is that you're set to die, Bobby?"
--May well come to that.
"You start a hunger strike to protest for what you believe in. You don't start already determined to die or am I missing somethin' here?"
-- It's in their hands. Our message is clear. They're seeing our determination.
Schlug is offline   Reply With Quote
Old 03-23-2013, 07:03 PM   #3570
WayneC1
Beastly Adventurer
 
Joined: Oct 2008
Location: Sydney, Australia
Oddometer: 2,170
The racetech calculator is recommending springs for the stock piston rod forks not a cartridge system, take a look at the KTM990 recommendations on the same racetech calculator and you will start to see the difference in spring rates between piston rod forks and cartridge forks. Cartridge forks use a far lighter spring rate

You can look at a summary graph with various models here http://www.f650gs.crossroadz.com.au/...tVspringKG.pdf
WayneC1 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 12:31 AM.


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