Need help with spring rate 08 450


5 replies to this topic
  • ubu

Posted April 05, 2011 - 06:20 PM

#1

I posted this in the suspension forum, but wanted to see what the Yamaha guys were doing.
2008 YZ450
I weight 190-195 lbs w/o gear.
Riding type is Off-road/desert, Novice

Front travel from manual: 300
Front extended: 613
Front static: 581
Front rider: 527
Measured from top caliper bolt to lower triple clamp bolt.

Rear travel from manual: 310
Rear extended: 625.5
Rear static: 590.5
Rear rider: 514.5

To me the rear feels fine and the numbers are really close. I never really like the front. It seems like it's always too stiff in rocks or too uncontrolled in whoops. I can adjust clickers and be satisfied with one or the other, but not both. Since it needs fork seals (again) I want to at least get the front sprung correctly. RaceTech calculator recommends .487 to .505 depending on my 5lb weight fluctuation or adding a larger tank. I don't think my IMS3.1 is really adding that much, but I know it's there. Stock springs are supposed to be .47.
So, do I go for a 2% increase to .48 or a 6% increase to .50?

  • Steel Panther

Posted April 05, 2011 - 07:37 PM

#2

Im 195-200 in street clothes and I use .48 in the forks and a 5.7 rear for mx.

  • grayracer513

Posted April 05, 2011 - 07:40 PM

#3

First, let me say that I'm a desert racer. Your rear sag is set too deep, but the rates look pretty close. Your complaints look to me to be more a matter of valving than of springs, although you are right at the max for the stock springs. My son weighed 195 before boot camp, and now that he's in the fleet he's around 180-185 (about 5 pounds up on me) and his bike always worked good for him. It's kind of an open question regarding rates. You could go either way, stock or heavier, but I don't think I'd go 6% over stock.

Rocks are a tough one, and usually the best way to deal with them is to back way off on the compression damping. The fork tends to be a little heavy on initial rebound response, and if it doesn't recover quickly enough, it can lead to a harsh feel in cobbled ground at speed.

The squirrely feel in the front is caused by the shock. Not enough rebound response (opposite of the fork). If you crank the rebound down to get rid of the skip, the rear will start to pack in the whoops.

I recommend the full "Dell Taco" treatment from SMART Performance. You can send your stuff in, or get the parts in kit form and do it yourself if you're up to it. The difference is rather incredible. The biggest pluses are the way the fork absorbs the big hit, and in how stable the bike becomes at speed over really rough ground.

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  • ubu

Posted April 05, 2011 - 08:13 PM

#4

Thanks for the input.
$250 for springs is a kick in the teeth when they are so close. When I reduce rear sag, the bike feels to dive in the front. But you are probably on to something with the rear rebound. Based on stock settings, I currently have the rear rebound turned in, front compression out, and front rebound out. Feels great in rocks right now. I will try rear rebound out a couple clicks and see how it feels. I'm talking a like 2-3 clicks from stock on all of this and then I feel unbalanced.
What about oil level up front? Should I get the shock serviced?

  • grayracer513

Posted April 05, 2011 - 10:20 PM

#5

The fork is very sensitive to oil level. With the setup I run, the modified mid valve allows me to run a lower than stock oil level (320cc) in the outer chamber to enhance the overall plushness a bit. I also use a heavier oil in the outers than the inners, and the extra oil viscosity adds to the bottoming resistance.

Another little mod that's important is drilling the free piston in the fork:

http://www.smartperf.../YZMODASSEM.htm

http://www.thumperta...ad.php?t=650136

Servicing the shock is a good idea. The factory oil fill in both ends is somewhat suspect as to the quality of oil used. Supposed to be the good KYB stuff, but even if it is, that doesn't last too long.

  • ubu

Posted April 11, 2011 - 08:48 AM

#6

Your advice is really helping.
Had a race yesterday. The course was a torn up 8 mile silt and whoop fest. Small/medium/huge whoops, and just hammered by the end of the day. Pin it and hang on type, for me.
I added 5ml of oil, suspecting I lost some due to leaky seals. Left the sag where it was, and turned the rear rebound out 2 clicks. I also added 1 click to front compression.
Bike worked amazing for those conditions. Tracked nice and straight and I don't even have a stabilizer. No rocks, so I'll have to see how it does after I get the new seals in this week. I suspect the current settings would be a little stiff, but that is better than squirely.
The plan for now is to get the seals done and oil level correct (pistons are already drilled), get the shock serviced, sag corrected, and hopefully have enough $$ this summer for valving through a local guy or Del taco.





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