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Wistrick

spring rate calulator

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The ONLY way to know if the spring rate is correct is on the bike and checking both Free & Rider Sag, there is no other way!

I've said this in other threads, I think the problem is that most Pro's have a faulty spring rate calculator for the VFR model only and constantly come up with these bogus numbers. Almost always Too soft. :sleep:

So where do we find the correct calculator or formula for the do it yourself owner....????

With a single rate spring if we know the bike weight,rider weight, amount of pre load on the spring we should be able to calculate the needed spring weight. Any mathematicians out there??

Dan

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Dan,

I have no idea who might have a good calculator for the VFR! I've yet to see any numbers supplied by any manufacture or suspension Pro that come close to the trial & error method Pete & I have been working on for years to achieve desired Sag numbers.

I forget what Pete has number and spring wise, but he's tried many springs to finally achieve the numbers he desired.

I weigh 190 lbs and have a 19 kg(1065 lb) spring on a Vtec, I get the following numbers measuring by myself:

Free sag- 12mm

Rider sag- 32mm

These are real close for what I want, but I want to check it again check it again w/help to be more accurate.

So IMO if you weight 190 plus you'll need at least a 19kg spring to get close, I'll be trying a 20 kg real soon and post my numbers.

BTW I started w/a 850 lb spring on my Ohlins and had No free sag w/35mm rider sag.

BR

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So besides trial and error there seem to be nothing for the do-it-yourself unless you use RaceTech or Sonic....Interesting

Dan

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Dan,

I have no idea who might have a good calculator for the VFR! I've yet to see any numbers supplied by any manufacture or suspension Pro that come close to the trial & error method Pete & I have been working on for years to achieve desired Sag numbers.

I forget what Pete has number and spring wise, but he's tried many springs to finally achieve the numbers he desired.

I weigh 190 lbs and have a 19 kg(1065 lb) spring on a Vtec, I get the following numbers measuring by myself:

Free sag- 12mm

Rider sag- 32mm

These are real close for what I want, but I want to check it again check it again w/help to be more accurate.

So IMO if you weight 190 plus you'll need at least a 19kg spring to get close, I'll be trying a 20 kg real soon and post my numbers.

BTW I started w/a 850 lb spring on my Ohlins and had No free sag w/35mm rider sag.

BR

Hmm RaceTech Cal says you need a 16.00 kg spring and your running a 19kg wish we could see the numbers that race tech uses..

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So besides trial and error there seem to be nothing for the do-it-yourself unless you use RaceTech or Sonic....Interesting

Dan

That is true, but really you have a bunch of people here with setups that can get you into the ball park. And yes RaceTech's calculator is busted.

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So besides trial and error there seem to be nothing for the do-it-yourself unless you use RaceTech or Sonic....Interesting

Dan

That's the point, who needs a calculator when you have members here who have done it right by Trial & Error and are providing accurate real world numbers and not some flawed calculator(for the VFR numbers only). :sleep:

As mentioned in other threads, I've seen spring rate numbers recommended to members here from just about every source out there World wide for a VFR (5th/6th gen owners) who weigh 190lbs that were from 800-1400 lbs. Who's right, there's only one correct rate and all the other calculators are flawed.

Actually you could probably be within the desired numbers with spring rates that are 50 lbs either side of ideal, maybe slightly more.

RaceTech has always been high on their fork spring calculator(IMO) and I'm not sure what happened to rear spring calculator as years ago they were Extremely High, now there Extremely Low for the VFR and both were wrong by real world numbers! :ph34r:

BR

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I guess my question is this. Both Race tech and Sonic have to use some type of formula and then take the #'s u enter and plug them in. Is there a way to find out the formula then maybe a person could look at it and see what was wrong.

here is what I have gathered so far.

Base on my weight of 250 pound both sonic and race tech come up with fork spring rates of 1.0

Differences in the calculators:

Sonic has you enter rider weight and the bike weight and Race tech just asks rider weight and Model type and uses its own # for bike weight.

Since both Calculators come up with the same spring rate we can assume that the bike weight Race Tech uses is at least pretty close....

Now I had my forks redone by GP Suspension and the spring rate they installed is .95. And my Free sag and Rider sag are in range. I measured the sags numbers 3 times and came up with a 2.78% error factor due to stitchion.

I guess I am just glad GP is doing my rear Penske Shock too.....

Dan

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Get Tony Foale's book "Motorcycle Handling and Chassis Design" and his related software. You have to do a shit pot full of measuring of dog bones, swingarm lengths, rocker ratios, triangle hole dimensions, x & y coordinates of where all of these pieces pivot, blah, blah, blah.

I've got the software but haven't had the time to do all of the intricate measurements necessary.

One thing I did get quick and dirty out of his book so far: Jacking up the rear/lowering the front does not have the dramatic dynamic on weight transfer between the front and rear you would expect.

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I forget what Pete has number and spring wise, but he's tried many springs to finally achieve the numbers he desired.

My nekkid weight is 255-260#. I use a 1300 # spring. I get 8 mm free sag, 30 mm rider + bike sag.

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I'm not really talking about fork spring rate calculators as forks is forks tongue.gif

Where I see a consistent problem is with the VFR's rear spring rate calculators! I'm sure it's a simple problem in the dimensions someone has plugged into their calculators related to the rear rocker ration and all other parameters used, if you knew all the correct numbers you would think it would be pretty easy to build a accurate calculator. :sleep:

I'm sure if we were all on CBR's just about every calculator would be dead nut and they sell, race and build 100 fold more CBR's than VFR's, especially here in the states. :ph34r:

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Base on my weight of 250 pound ....

I guess I am just glad GP is doing my rear Penske Shock too.....

Dan

Dan,

Unless GP suspension happens to be using the one and maybe only accurate VFR spring rate calculator and comes up with at least a 1200lb rear spring rate, It will be wrong IMO and you won't be able to achieve the numbers you yourself posted for Free & Rider Sag.

If they come up with something light like a 900lb spring and re-valve the Penske for it, the valving will be off by the time you get around to installing the correct and much heavier spring. :sleep:

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Base on my weight of 250 pound ....

I guess I am just glad GP is doing my rear Penske Shock too.....

Dan

Dan,

Unless GP suspension happens to be using the one and maybe only accurate VFR spring rate calculator and comes up with at least a 1200lb rear spring rate, It will be wrong IMO and you won't be able to achieve the numbers you yourself posted for Free & Rider Sag.

If they come up with something light like a 900lb spring and re-valve the Penske for it, the valving will be off by the time you get around to installing the correct and much heavier spring. :sleep:

You know the "Transformed Wow!" thread is one of the best threads going for info. Why don't we maybe add some setups to the front page or somewhere else that are working. We have the 3 of us so far with numbers that are 98% dialed in.

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You know the "Transformed Wow!" thread is one of the best threads going for info. Why don't we maybe add some setups to the front page or somewhere else that are working. We have the 3 of us so far with numbers that are 98% dialed in.

Thanks,

I'll look thru the thread and find your set-up info or you guys can just post it up in the "Transformed Wow" thread and I'll add it to the original post and keep adding info from any member who achieves the desired Free & Rider Sag number for all members to see.

That way like you said members can see real world numbers and almost ideal spring rates for our VFR's by rider weight. :fing02:

BR

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Base on my weight of 250 pound ....

I guess I am just glad GP is doing my rear Penske Shock too.....

Dan

Dan,

Unless GP suspension happens to be using the one and maybe only accurate VFR spring rate calculator and comes up with at least a 1200lb rear spring rate, It will be wrong IMO and you won't be able to achieve the numbers you yourself posted for Free & Rider Sag.

If they come up with something light like a 900lb spring and re-valve the Penske for it, the valving will be off by the time you get around to installing the correct and much heavier spring. :fing02:

Well GP isn't just ordering a shock and spring from Penske and just shipping it to me, the shock will get shipped to them for dyno test and setup...But if its wrong they will make it right....We will see...

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I guess my question is this. Both Race tech and Sonic have to use some type of formula and then take the #'s u enter and plug them in. Is there a way to find out the formula then maybe a person could look at it and see what was wrong.

here is what I have gathered so far.

Base on my weight of 250 pound both sonic and race tech come up with fork spring rates of 1.0

Differences in the calculators:

Sonic has you enter rider weight and the bike weight and Race tech just asks rider weight and Model type and uses its own # for bike weight.

Since both Calculators come up with the same spring rate we can assume that the bike weight Race Tech uses is at least pretty close....

Now I had my forks redone by GP Suspension and the spring rate they installed is .95. And my Free sag and Rider sag are in range. I measured the sags numbers 3 times and came up with a 2.78% error factor due to stitchion.

I guess I am just glad GP is doing my rear Penske Shock too.....

Dan

Dan:

You will need a 1250-1300# rear spring depending on your style of riding. I'd say be safe and go with 1300#. Up front you need 1.1 springs. You and I are both with just a few pounds of each other.

I ride aggressively in the mountains and I ride with a 1300#/1.1 set up. I run Diablo Corsa III's tires.

Pete

Pete

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To all:

I will climb up on my soap box one more time.

You're spending $900-1300 for a Penske rear shock. You're spending $300-500 for a RaceTech/Sonic front end.

Spend $19.95 with Amazon.com and buy a copy of Andrew Trevitt's Sportbike Suspension Tuning and read it.

Pete

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To all:

I will climb up on my soap box one more time.

You're spending $900-1300 for a Penske rear shock. You're spending $300-500 for a RaceTech/Sonic front end.

Spend $19.95 with Amazon.com and buy a copy of Andrew Trevitt's Sportbike Suspension Tuning and read it.

Pete

+1.gif

You da man Pete,

You are the one who sent me a copy of Trevitt's book and we've shared a shitzload of info, data and results for a long time trying to figure just what was important to proper bike set-up and spring rate calculations and just how vital Free Sag is to it. :fing02:

I also got a great deal on your spring inventory! wink.gif

Keep Fighting to fight to help educate VFRD members one shock at a time! :goofy:

BR

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To all:

I will climb up on my soap box one more time.

You're spending $900-1300 for a Penske rear shock. You're spending $300-500 for a RaceTech/Sonic front end.

Spend $19.95 with Amazon.com and buy a copy of Andrew Trevitt's Sportbike Suspension Tuning and read it.

Pete

I have the book and have read it!!! I will call GP suspension and ask what size rear spring I am getting???

BTW I spent $480 on a GP suspension front end and $890 on the penske tongue.gif But you do make a good point.

Dan

Edited by Wistrick

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Dan,

I weigh 190 lbs and have a 19 kg(1065 lb) spring on a Vtec, I get the following numbers measuring by myself:

Free sag- 12mm

Rider sag- 32mm

These are real close for what I want, but I want to check it again check it again w/help to be more accurate.

So IMO if you weight 190 plus you'll need at least a 19kg spring to get close, I'll be trying a 20 kg real soon and post my numbers.

BTW I started w/a 850 lb spring on my Ohlins and had No free sag w/35mm rider sag.

BR

I also have an Ohlins 1085 lb (19.36 kg) spring on my lighter 5th gen, I'm 205 lbs w/out gear.

I understand the importance of selecting the correct spring but where are you setting preload when you decide a 19kg spring isn't right and you need to go to a 20kg? If you've got the preload set at 3/4 and all sag numbers are lined up, isn't that good enough? Would you bother changing the spring if you never carry luggage or passenger?

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Here is a table that I've made using the calculations I've come up with:

Rider Weight Range vs. Shock Spring Rate (lb/in)

110-145lb = 1100lb/in

145-180lb = 1150lb/in

180-210lb = 1200lb/in

210-245lb = 1250lb/in

245-280lb = 1300lb/in

To be specific, a 250lb rider calculates to 1270lb/in. Since you can't buy a spring with that rate, you have to select the closest one available. I typically go up, in this case to 1300lb/in. There are other factors that play into it as well. Hopefully this gives you an idea!

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I talked to GP Suspension this morning and they assure me they don't use any calculators. They order the shock from penske and they fit the spring to it. They use sag #'s to determine the spring rate...Guess what i am getting a 1250 or 1300 depending on dyno results...Sounds like someone has a clue...

Dan

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I talked to GP Suspension this morning and they assure me they don't use any calculators. They order the shock from penske and they fit the spring to it. They use sag #'s to determine the spring rate...Guess what i am getting a 1250 or 1300 depending on dyno results...Sounds like someone has a clue...

Dan

LOOKS LIKE THEY'VE BEEN LOOKING AT OUR THREAD! :blink:

Dan,

That's great to hear that there's at least one shop that seems to be doing it right and seem to support what Pete & I and now Jason have discovered, congrats on finding them. Your bike should feel Great! :ph34r:

BR

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Here is a table that I've made using the calculations I've come up with:

Rider Weight Range vs. Shock Spring Rate (lb/in)

110-145lb = 1100lb/in

145-180lb = 1150lb/in

180-210lb = 1200lb/in

210-245lb = 1250lb/in

245-280lb = 1300lb/in

Jamie,

Where was the problem in the flawed spring rate calculator you were using before? I remember it coming up with extremely low numbers for the VFR rear spring.

The Modified formula seems much closer to what we've been seeing on the higher end, but an 1100lb spring for a 110 lb rider seems extremely high IMO even for a 145lb rider.

If you continued down the scale with that formula to the stock spring rate of 15.3kg(850lb), the formula would suggest the stock VFR was built for a One Pound Rider! :ph34r:

Something seems amiss here!

What are your thoughts on this?

BR

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I talked to GP Suspension this morning and they assure me they don't use any calculators. They order the shock from penske and they fit the spring to it. They use sag #'s to determine the spring rate...Guess what i am getting a 1250 or 1300 depending on dyno results...Sounds like someone has a clue...

Dan

LOOKS LIKE THEY'VE BEEN LOOKING AT OUR THREAD! :blink:

Dan,

That's great to hear that there's at least one shop that seems to be doing it right and seem to support what Pete & I and now Jason have discovered, congrats on finding them. Your bike should feel Great! :ph34r:

BR

Dave from GP says they don't use those calculators on anything. The have there own data base they have created from real world numbers. He went on to say that if he didn't have those numbers for a certain model or brand say the new VFR1200 he wouldn't do work on the bike without it in his shop.

Will post some #'s for front and back once I get the shock in

dan

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