larger rear tire recommended?

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#1
I was wondering if a larger rear tire would be benficial over stock? Possibly a 120/90 or 130/80 any recommendations would be great. I also just resprung the front and rear and noticed that the sag was just 2 inches I heard 4 was correct.. The most sag I can get is 3 inches before I run out of threads is this right?

Dean Johnson
 

jaguar

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#2
well, it depends on your riding. fatter tires grip better but are harder to break loose for needed wheelspin.
I think the sag should be 3.5-4inches front and back but don't quote me.

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KIPS repair from manual: http://www.ioa.com/~dragonfly/moto/kips.html
my sweetheart: '89 KDX200 SR
 

dirt bike dave

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#3
Unless you are talking about a Michelin or another brand of undersized rear, a 120 or 130 is too big! Most 250's run a 110 Dunlop, and 125's/200's run a 100. The 120+ are for open bikes with most tire brands.

But there is really no standardization, and a 130 Michelin M12 rear is about the same or slightly smaller than a 110 Dunlop 756.
 

MN KDXer

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#4
Some guys used the 110/100, but I always used the 100/100. One thing of note, is that not all tires are exactly the same, even within the same brand. For example, the Dunlop 752 is slightly smaller than a 755, while a 756 is in-between. I thought the 756 was the better tire of these three.

Sag... Something sounds wrong with your measurement procedure. Either that, or you weigh 72 lbs. ;) The sag should be measured by fully extending the suspension, park yourself (on the seat for trail riders; standing for MX) and remeasure. The difference should be 95mm or so.

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-01 RM250
-Vet A Enduro and Hare Scramble Rider.
 
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#5
MNKDX,
Thanks for the input on the sag measurement, I was doing it completely wrong! Thanks for all tire input as well.

Dean Johnson
 
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#6
MN KDXer said:
Sag... Something sounds wrong with your measurement procedure. Either that, or you weigh 72 lbs. ;) The sag should be measured by fully extending the suspension, park yourself (on the seat for trail riders; standing for MX) and remeasure. The difference should be 95mm or so.
...as measured where? 95mm is a lot of sag; almost 4 inches.
 
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#7
I just happened to write this for another forum I'm on.

The static sag will only tell you if the springs preload is in spec from it's original condition.
There is a certain order to do this.

Step 1: put bike on stand and take a measurement between the axle nut and a fixed point like the rear fender or side plate.
Step 2: Take the bike off the stand and sit on it wearing all of you riding apparel and now measure it. (it helps if someone holds the bike while you sit on it so all of your weight is on it).

The difference between steps 1 and 2 is the race sag.
Once you get 100mm difference move on to step three.

Step 3: Take a third measurement while the bike is on the ground all by itself from the same place you took it from the previous steps.

The difference in measurements between steps 1 and 3 is the static sag.

If after you get the desired race sag and the static sag is too low then you probably had to crank down on the spring adjusting nut alot to get it there. This means that the spring is either out of spec or you are to heavy for that spring. The same goes in the other direction. You want a spring that can accomplish the correct race sag AND static sag so that the bike rides in the proper range of the stroke most of the time. I don't usually bother with the static number as most of the manufacturers make the springs for my weight, I'm 170 lbs so I always just look for the 100-110mm range. I also like to change the sag depending on the track and conditions. More sag=better straight line stability but loses cornering ability. Less sag=better cornering ability and a little more resistance to bottoming but jacks up the rear end a little and can kick around a bit on bumps.
And since I do ride an open bike...here is the tire I use http://www.mandhtires.com/store.php?crn=68&rn=276&action=show_detail
 
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#9
Why is it with dirt bikes nobody seems to talk about front suspension. Just talk about setting rear sag. Is front not that important for off road?
 
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#10
lemmy said:
Why is it with dirt bikes nobody seems to talk about front suspension. Just talk about setting rear sag. Is front not that important for off road?
Yes, it is, but it's harder to adjust than the rear, so I guess no one bothers....

and, oh yes, some things never die....I thought it would be fun to re-visit some of the original posts here. :cool:

Mud
 
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#11
I ran a 5.1 for a while, it is similar to a 130. Good traction, but harder to spin as others have mentioned. It also shredded the splash guard that bolts to the airbox. No real negative to it until the center wore down and hitting the throttle resulted in a slide until the side lugs caught and then propelled me towards trees and such while still leaned over. Actually, it almost made the rides more fun :).