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I’ve got a 2005 Grizzly 660 that I just put new tires on. Went with 30” Backs on it. Knew I would lose some power and need to fix that. My question is what size shim and which spring would work best for me. Just trying to get the low end power back that the tires robbed. Any help would be greatly appreciated
 

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I’ve got a 2005 Grizzly 660 that I just put new tires on. Went with 30” Backs on it. Knew I would lose some power and need to fix that. My question is what size shim and which spring would work best for me. Just trying to get the low end power back that the tires robbed. Any help would be greatly appreciated
I would try to go for the maximum shim ratio available on a 660. 2.5mm but be careful to make sure you still have spline showing. With those 30's I would run a white secondary. I believe this is what @jesus_is_lord runs with his 30's.

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Love the look the tires gave the Grizz but don’t like the power lose outta the hole. Once you get rolling it’s fine but it’s that outta the hole where it’s weak. Knew it was gonna be an issue but also knew there were ways to correct it
 

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Love the look the tires gave the Grizz but don’t like the power lose outta the hole. Once you get rolling it’s fine but it’s that outta the hole where it’s weak. Knew it was gonna be an issue but also knew there were ways to correct it
If you want the best setup get @Coop45 mod #3 and a white spring. He can help you with the best setup. I don't have his machining but I don't really need it as I run 25 inch tires and the rolling resistance is not that large. Look at it this way, is it easier to push a large hand sander or a small one. Now while this isn't the same as tires it's the same theory. We are going back to Junior high science here. Inertia. You see, while the weight is a factor, the biggest thing is to get the the larger circumference going because this makes larger resistance and do to raising your pulley ratio it makes it more work for the Grizzly.

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Or at least I think. Where's @Ridgeway81432 when you need him?

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Start with a 2mm of shims and don't use more than a purple spring. Machining is really only needed if you need the best of both worlds...low end and top speed.
 
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Start with a 2mm of shims and don't use more than a purple spring. Machining is really only needed if you need the best of both worlds...low end and top speed.
Hmmm. I thought this is what a white spring was for... At least now we know.

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I would try to go for the maximum shim ratio available on a 660. 2.5mm but be careful to make sure you still have spline showing. With those 30's I would run a white secondary. I believe this is what @jesus_is_lord runs with his 30's.

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Yes I do run a white spring. That’s what coop45 recommended I run when I got his mod3 done. So far so good.
 

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Hmmm. I thought this is what a white spring was for... At least now we know.

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White spring is a very big jump in force for a 660 or 550.

Always need to consider what engine and also what riding style.
 
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White spring is a very big jump in force for a 660 or 550.
I see. I am going to PM you as to not jack the thread this early.

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Grizzcrazy...Your question will help DUROC08 so you won't be jacking his post....

I don't recall where I gathered this spring forces. I think it was posted on Grizzly Rider by a guy that sold his Griz and went car racing. Then for some unknown reason had all of his posts deleted.

Spring forces..
white spring 3"-215lbs/1.75"-350lbs
gold spring 3"-200lbs/1.75"-330lbs
purple spring 3"-195lbs/1.75"-315lbs
orange spring (stock700) 3"-190lbs/1.75"-310lbs
blue spring (stock660 & 550) 3"-160lbs/1.75-280lbs
Red spring (stock450)3"-160lbs/1.75-250 lbs

This not my research..I found it posted on another by a cat named "Mud_dog" he had access to the equipment to measure spring force and was kind enough to post up his findings. The CVT geometry I already knew and I understand the spring force theory. However I have never had a chance to measure springs accurately.

Mud_dog's post_

"First off, let me say that if you take the time to read through this and understand it, you will find the results very interesting...

This is a long thread, so bear with me here.

As some of you may know, I have been testing different components in the Grizzly 660 cluch system. The most recent test I have performed is testing the stock secondary sheave spring to see how much force the spring applies to the belt under different circumstances.

The most important measurements were taken at the spring lengths that matter most. They will be explained in greater detail later with measurements, but for now here they are...

-Sheave Fully Closed with No Belt. This is the amount of pressure that the spring can exert on the moveable sheave face without any restrictions except for the stationary sheave face.
-Sheave Fully Closed with Brand New Stock Belt This is the amount of pressure that the spring can exert on a new stock belt via the moveable sheave face.
-Sheave Fully Closed with Old Belt at Maximum Wear Service Limit. This is the amount of pressure that the spring can exert on a used belt at service limit via the moveable sheave face.
-Sheave Fully Opened. This is the amount of pressure that the spring can exert on the moveable sheave face.

All of the following measurements were taken by me with precise measuring tools. I think you'll find the results interesting...

Stock Spring Length Measurements

Spring Free Length (uninstalled, sitting at rest) - 4.8750"
Spring Installed Length w/ No Belt (installed, with no belt) - 3.0625"
Spring Installed Length w/ New Belt (installed, with brand new belt at 1.310" width) - 2.8525"
Spring Installed Length w/ Old Belt (installed, with old belt a 1.180" service limit width) - 2.9825"
Spring Length w/ Sheave Fully Opened - 2.0075"

Sheave Width Measurements

Sheave Width Fully Closed w/ No Belt - 1.1000"
Sheave Width Fully Open - 2.1550"
-From this, you can gather the moveable sheave face moves 1.055".


Okay, now for the important stuff.

Stock Spring Load Measurements (Spring Length [refer to lists above] / Spring Load)

4.8750" / 0 lbs
3.0625" / 157lbs*
2.8525" / 169lbs
2.9825" / 155lbs
2.0075" / 251lbs
1.7500" / 290lbs**
*One Measurement Compared to EPI's Blue Spring Spec
**Another Measurement Compared to EPI's Blue Spring Spec (Measurement not applicable to secondary since sheave cannot physically compress the spring that far)

EPI Blue Spring Load Measurements (spring that comes with clutch kits) Listed in ( ) with 5% Tolerance Specs on either side.

3.0000" / (152) 160lbs (168)
1.7500" / (266) 280lbs (294)

Results
Well, if you look at the specs in bold in the Stock Spring Load list, you'll see that the stock secondary spring (that is factory-installed from Yamaha) is within the 5% Tolerance limits that the EPI Blue Spring holds. Basically, the EPI Blue spring is the SAME as the stock spring in the Secondary. Hmmm....interesting...[;)]

Another thing to look at is the difference in applied spring force when using a Brand New Stock belt, and an Old Belt used to its Service Limit.

A difference is 14lbs should NOT go un-noticed. That's a large difference in the clamping force of the belt, ESPECIALLY when in the thick mud where every bit of belt grip is needed in order to transfer maximum torque from the engine to the transmission and rear wheels."
 

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On a 660, the axles become the weak link in the drive system as the pulley ratio comes up and the tires get taller. I use a purple spring and made it into the G.A.C.C. with 26.5" tall tires.
Most 660's will accept 2.5 mm's of shim, but a few have been found that only accept 2 mm's. Once you max out the amount of shim your machine accepts, know machining will raise the ratio more than shim alone.
Shim reduces the top speed because the shim mod is a linear mod, you gain down low and loss on top. COOPS machining changes the sheave face angle for more down low and nothing removed were the belt rides at high speed.
If you like the shim mod and stop there, the top speed lost can be returned by cutting the cam plate.
What is the true tire diameter of the 30" stated size tires? If they went under the rear on a 660 with much trimming or lifting, they should near 27.5"s to 28"s.
 

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Discussion Starter #13
Already replaced rear axles with partsdiscount ones. Had one popping so went ahead and replaced them before putting the tires on it. Got a lift on the way for it since the 30’s rub a little bit more than I want. Just trying to get the low end power back and keep the top speed if possible
 
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