REVIEWS DEALS BIKESHOPS TRAILS

Mountain Bike Spring Rate Calculator V5.0

59549 Views 12 Replies 8 Participants Last post by FireDog46, Jul 17, 2013

FireDog46

Discussion Starter · Sep 12, 2004

A Brief History:

Last fall I converted my bike to coil suspension. I bought a Fox Vanilla RC and, on the recommendation
of both Fox and Rocky Mountain, an 800# spring. This seemed high to me, but I deferred to the 'experts?'.
Turned out the ride was too firm. I decided to do my own research to come up with a calculator that would
provide some insight into what would be a more appropriate spring rate for different riding conditions. Also,
my bike has three travel settings and I needed to know the effect of moving from one setting to another with
the same spring or what alternate springs I might need.

This calculator, the latest ( final? ) is the end result of that research. I have added units in inches or
millimetres, three travel settings in one calculation, optional spring rates for varying degrees of preload
and a couple of extra useful links. Being honest about your riding style ( weight distribution, sag level
and preload ) in the input parameters is key to finding the correct spring rate. Also, it is a common practice
to have more than one spring.

There will always be some controversy over what is a correct spring rate. This calculator has helped me to
better understand what would be a single compromise spring rate for all three travel settings and what three
unique spring rates would be appropriate for each of those travel settings.

I now understand where that 800# recommendation came from and why I didn't like it. I prefer about 30% sag
and a 600# spring with about 2 turns of preload works well in the 4.5" travel setting. However, I prefer the
geometry of the 4.0" travel setting but ordering multiple springs from the Canadian Fox distributor was just
too expensive. Luckily, Cambria still had some Mountain Speed rear springs in my sizes at only $25 USD.

To any web designer: My apologies for the less than elegant coding. I had to find a way of keeping the whole page
under 100K bytes. That's the limit for mtbr posts. I had to load the page into Visual C++ and remove all the indenting.
This reduced the page by 30%! To restore the formatting load the page into Frontpage and save.

michael
-->

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Reactions: 1

1 - 13 of 13 Posts

biker dad

· #2 · May 11, 2005 (Edited)

Good work!

just tried it out...results I got confirmed real-world experience for setting a long travel bike up for a very light rider.

Recommend to any interested in trying it out that they take the time to play with the variables. It might not work for every setup, but it definitely illustrates the effect of changing suspension setup parameters.

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FireDog46

Discussion Starter · #3 · May 11, 2005

thanks...

Unfortunately, the one posted here doesn't work in Firefox.

The corrected one can be found here http://www.theride.ca/guru/spring-calc.htm

michael

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jrm

· #4 · May 11, 2005

That rocks....

mrdy said:
A Brief History:

Last fall I converted my bike to coil suspension. I bought a Fox Vanilla RC and, on the recommendation
of both Fox and Rocky Mountain, an 800# spring. This seemed high to me, but I deferred to the 'experts?'.
Turned out the ride was too firm. I decided to do my own research to come up with a calculator that would
provide some insight into what would be a more appropriate spring rate for different riding conditions. Also,
my bike has three travel settings and I needed to know the effect of moving from one setting to another with
the same spring or what alternate springs I might need.

This calculator, the latest ( final? ) is the end result of that research. I have added units in inches or
millimetres, three travel settings in one calculation, optional spring rates for varying degrees of preload
and a couple of extra useful links. Being honest about your riding style ( weight distribution, sag level
and preload ) in the input parameters is key to finding the correct spring rate. Also, it is a common practice
to have more than one spring.

There will always be some controversy over what is a correct spring rate. This calculator has helped me to
better understand what would be a single compromise spring rate for all three travel settings and what three
unique spring rates would be appropriate for each of those travel settings.

I now understand where that 800# recommendation came from and why I didn't like it. I prefer about 30% sag
and a 600# spring with about 2 turns of preload works well in the 4.5" travel setting. However, I prefer the
geometry of the 4.0" travel setting but ordering multiple springs from the Canadian Fox distributor was just
too expensive. Luckily, Cambria still had some Mountain Speed rear springs in my sizes at only $25 USD.

To any web designer: My apologies for the less than elegant coding. I had to find a way of keeping the whole page
under 100K bytes. That's the limit for mtbr posts. I had to load the page into Visual C++ and remove all the indenting.
This reduced the page by 30%! To restore the formatting load the page into Frontpage and save.

michael
-->

Now only if someone could come up with a calculator for rear air shock Psi....

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Warp

· #5 · May 11, 2005

mrdy said:
Unfortunately, the one posted here doesn't work in Firefox.

The corrected one can be found here http://www.theride.ca/guru/spring-calc.htm

michael

mrdy... a dumb question. I have a 600 spring for a 2.00 travel shock. I need a 400-450 spring. Is this lower rate spring going to be shorter or longer than my 600 for the same stroke??

Is -15mm (600 longer 15mm than 450) an acceptable variation?? Where can I find more info on this. Thanks!

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spinjocky

· #6 · May 13, 2005

jrm said:
Now only if someone could come up with a calculator for rear air shock Psi....

Yea, I wish Fox, manitou, and 5th would give numbers for piston area, and volume (full and at bumper) of their shocks. Otherwise it's a guessing game.

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biker dad

· #7 · May 13, 2005

Warp2003 said:
mrdy... a dumb question. I have a 600 spring for a 2.00 travel shock. I need a 400-450 spring. Is this lower rate spring going to be shorter or longer than my 600 for the same stroke??

Is -15mm (600 longer 15mm than 450) an acceptable variation?? Where can I find more info on this. Thanks!

A softer spring with the same stroke capacity needs more winds, so if it is wound out of the same stock, it will be longer. Usually all springs in a series are wound out of the same stock, however, if it is wound out of lighter stock, the length could be similar or even shorter.

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Warp

· #8 · May 13, 2005

biker dad said:
A softer spring with the same stroke capacity needs more winds, so if it is wound out of the same stock, it will be longer. Usually all springs in a series are wound out of the same stock, however, if it is wound out of lighter stock, the length could be similar or even shorter.

Thanks... the one I'm getting gotta be lighter stock then, as it's actually shorter than current.

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LonesomeCowboyBert

· #9 · Jun 10, 2008

Well, using the preset 60% rear weight bias the result I get for my 6.6SS is quite a bit off, it recomends 315 lb for my 150lb rider weight
In real life I use a 350lb which is a little soft and a 400lb which is a tad stiff (swap em on type of riding im doing), the mojo calculater gave me 388lb, iirc, so seems far more accurate for this particular bike

I suspect the discrepency is in the 60% rear weight bias figure that is default on the calculator, this may only be right for a cross country bike, only problem being I (and I suspect most others) have no idea what my front to rear bias is, it would be a total guess (I dont have 2 bathroom scales)

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Strelok

· #10 · Mar 31, 2009

THANK YOU!! I have been trying many different calcs to see what spring I need for my first coil shock (I'm coming off an air shock), and this is consistent with other calc's results as well as real world experiance, yet its also FAR more in-depth and comprehensive then any other clac I've yet seen.

Great work! More people should see this.:thumbsup:

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· #11 · Jul 15, 2011

Bump: This should be a sticky

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Rannelator

· #12 · Jul 12, 2013

Another calculator for Fox Shox.
Been trying to figure what spring I need for my Van RC.
Mountain Bike Spring Rate Calculator

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FireDog46

Discussion Starter · #13 · Jul 17, 2013 (Edited)

Rannelator said:
Another calculator for Fox Shox.
Been trying to figure what spring I need for my Van RC.
Mountain Bike Spring Rate Calculator

and who do you think wrote it...but it's out of date...
there is a version 7.0...but i don't hang out around here any more
damn fox racing...they have no shame
no accreditation

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