running taller rear tire...I think this was a bad idea.


8 replies to this topic
  • waterdog3

Posted August 21, 2005 - 06:59 AM

#1

I just changed out my rear stock tire to a 120/100. Now the bike has terrible headshake. The back end is way to high now. I raised the triple clamps all the way up. have not had a chance to ride after this change. I hope it will help. I mainly ride trails and hare scrambles. I am 6'1 and could stand flat footed on the bike, now i am on the tips of my toes. I may have to eat this tire and purchase a new one. would a 120/80 be taller than or shorter than a 110/100????????? I just ordered a new rear spring "6.2" and new front springs "50's", I think i will wait till everything gets here and TRY to get everything working together.

BEWARE of taller tires........

  • grayracer513

Posted August 21, 2005 - 12:37 PM

#2

A 120/100 is a huge tire. I used to run 120/100x18's on my CR500, and it's one big mass of rubber. But unless you either switched your rear rim size, or are in the wrong forum, you should be running a 19" rim, and your tire should be a 120/90, not a 120/100.

Here's what the numbers mean: The first one is the width in mm of the body of the tire (not the tread). The second number is the aspect ratio. A 100/100 is 100mm wide, and is 100% as tall as it is wide, from the bead seat to the top of the tire body. A 100/90 is 100mm wide, but is only 90mm tall.

Your stock tire size, assuming it's a YZ426/450, is 110/90x19, which makes it (more or less) 110mm wide, 99mm tall, and and mounts on a 19" rim.

A 120/90, which is what I run, is 108mm tall from the bead, whereas a 120/100 would be 120mm tall. Quite a difference.

Comparing between 18's and 19's, a 19 is an inch taller, which raises the bike half of that amount. So, a 110/100x18 would be about 26.7" tall overall, and a 110/90x19 would be roughly 26.8", making the two wheels nearly identical.

As to your question, then, about a 120/80, you take the 120mm width, multiply it by .8, and you come up with 96mm, which makes it 3mm shorter than you original tire size.

If you are looking at a 6.2 and a pair of .50's, either you are some heavier than I am, or you do actually own a WR. Compressing your front forks too much because of weak springs could be why it shakes.

  • waterdog3

Posted August 23, 2005 - 12:15 PM

#3

I have a 04WR450. and am running a 120/100x18. the rear end is jacked up now and am having terrible headshake. also changed out the front to a Maxxis SI. Tried lowering the forks back down into the clamps to raise the front up to balance it out and that made it worse.thought maybe the front axel may have been misaligned so i did the small flat screwdriver between the right clamp bolts to re align.....that has not helped either.????????

  • Edge316

Posted August 25, 2005 - 08:36 PM

#4

Try readjusting your sag.Sounds like you need to add more sag to compinsate for the higher rear tire.

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  • bob333

Posted August 27, 2005 - 10:57 AM

#5

ya i bet it is the sag

  • fowler175

Posted August 27, 2005 - 06:54 PM

#6

Correct me if I'm wrong, but shouldn't sag be adjusted strictly for your wieght? ei... so it sags approx 95-105mm with your wieght. If it is set properly for your wieght, and you use it to lower your ride hieght 10-20mm, wouldn't you have a little to much sag, like around 115-120? Just a thought.

  • grayracer513

Posted August 28, 2005 - 07:20 AM

#7

Jonesy, you're right. But what he would do by lowering the ride this way is to trade 15mm of compression travel for 15mm of extension travel, basically moving the bike down in the swing of the suspension. If bottoming does not become an issue, and the rear end doesn't take on a harsher feel, it's an OK fix.

  • Shawn_Mc

Posted August 28, 2005 - 09:38 AM

#8

Jonesy, you're right. But what he would do by lowering the ride this way is to trade 15mm of compression travel for 15mm of extension travel, basically moving the bike down in the swing of the suspension. If bottoming does not become an issue, and the rear end doesn't take on a harsher feel, it's an OK fix.



At this point, its a band-aid style fix, but the best until the tire is worn out..

One other issue is he's probably going to have the rear tire banging the rear fender and air box too. Probably before he bottoms the shock...

If it were me, id take the behemoth tire off. or go do burn outs in the street :D

  • bob333

Posted August 28, 2005 - 12:51 PM

#9

go do burn outs in the street :D

i like that idea :eek: :D :D





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