Fork spring upgrade on the cheap; watch out, we're doing math! - Stromtrooper Forum : Suzuki V-Strom Motorcycle Forums
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post #1 of 14 Old 09-04-2013, 05:23 PM Thread Starter
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Fork spring upgrade on the cheap; watch out, we're doing math!

So I just had Jamie rebuild my rear shock and respring it, and according to my wishes and waistline, he sprung it with a 900lb rear shock. Shazam that thing is stiff. Being low on funds, I figured I'd figure on figuring the front. So, tldr version: I cut the front springs and added a longer spacer.

Long version:
My bike came with .90 fork springs, already better than the stockers but not stiff enough for my weight. I pulled the springs out and started mathing at them. The forks have 6.3" of travel. The springs have 33 active coils, with average of .25" space between the coils. Therefore, the spring has 8.5" of compression available before coil bind. Taking the 6.3" of travel, plus the .5" or so of built-in preload, that gives me an 'extra' spring length of 1.7". Grabbing my trusty caliper, I measured the spring wire diameter and coil diameter, and plugged the numbers into a spring rate calc I found on google. Assuming that racetech was honest about the spring rate, I calculated a conversion factor between their claimed .9 and the calculated .81, then started changing the number of coils. Turns out that taking three active coils removes .75" of potential compression, still leaves me with about an inch of leftover compression, and changes the effective rate to just under 1.0. So, I cut three coils off, heated and bent the new end, and ground them flat like stock. I then cleaned the springs up, dropped them in and measured for my spacers. There was 4.45" of space between the tops of the springs and the tops of the fork tubes. The fork caps, fully assembled, are 1.5" long to the spring mount surface, and I wanted .5" of preload built in, so I cut the spacers down to 3.5" and put everything back together. It all works fine, but I haven't had a chance to adjust for sag and check for travel so I'll update this as soon as I get to it. Until then, does anyone have questions or corrections on my math?
whodat

Edit: potential downsides to this. The spring could sag earlier than it would due to overcompression. The spring could break due to overcompression. Meteors could hit my bike. Honestly there's not a lot of downside to this I see. Realistically I figure I may have decreased the life of the spring by some amount, but not much. Also if you look at spring rate graphs side by side, you'll see why it's actually a more controlled and better ride to go with a higher spring rate than a softer one with the preload cranked up.

Go soothingly on the grease mud, as there lurks the skid demon. Press
the brake foot as you roll around the corners, and save the collapse and
tie up.

In order, current to oldest, *denotes still have
DL1000K5*, VFR800X, MT-16*, DL650K4, XR400R, XR650R, XR400R, FZ1, GL1000*, VF750C, CB250, GL1100, GL650, DT50. I'm sure there's others but I forgot them.

Last edited by whodat; 09-04-2013 at 08:36 PM.
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post #2 of 14 Old 09-04-2013, 09:18 PM
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Who's Jamie?
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post #3 of 14 Old 09-05-2013, 12:58 AM
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I like your thinking but hate mathematics.

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post #4 of 14 Old 09-05-2013, 07:28 AM Thread Starter
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Tread, Jamie Daugherty at Daugherty Motorsports - Motorcycle Suspension Performance and Modification . I met him through my VFR, he made me a shock. Great prices and excellent service.

Rolex, remember in school 'we're never gonna use this stuff!' Turns out that sometimes I have to. I'm cautiously optimistic that this will keep me from buying new springs anytime soon. If you look at the actual part number for the fork springs, racetech sells these springs for a huge number of bikes from Harleys to Aprilias, so there's clearly some give and take in the applications based mostly on spacer length.

In case anyone was wondering or didn't know, this is how progressive springs work. The closer wound section is not softer than the rest, it just goes coil to coil before the rest of the spring. As soon as coils touch, the effective coils are reduced and the spring is stiffer.

Go soothingly on the grease mud, as there lurks the skid demon. Press
the brake foot as you roll around the corners, and save the collapse and
tie up.

In order, current to oldest, *denotes still have
DL1000K5*, VFR800X, MT-16*, DL650K4, XR400R, XR650R, XR400R, FZ1, GL1000*, VF750C, CB250, GL1100, GL650, DT50. I'm sure there's others but I forgot them.
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post #5 of 14 Old 09-05-2013, 01:00 PM
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Thanks for the clarification. Looks like great pricing for suspension services. I need to do something with my rear shock and this may be the ticket. Really appreciate your post and follow up. Thanks again.

FWIW, I lived in Purcellville in 1998 for a year. Had a job in Woodbridge that I commuted to daily. I blame that commute for my aggressive driving to this day. F'ing crazy! Great area though. I think I would have appreciated the area more if I had my Strom at the time.
Cheers,
Brent
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post #6 of 14 Old 09-06-2013, 12:44 PM Thread Starter
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Holy crizzap, Purcellville to woodbridge. That's insane. FWIW I moved from woodbridge to manassas to purcellville to get away from the traffic madness.
Anyway, I highly recommend Jamie, the prices are great and the service excellent. Stock shocks are cheap enough that you could buy one used, ship it to him and have it reworked and have no bike downtime.
I can report that the fork springs work fine, the rate is definitely increased somewhat but not as much as I was hoping. This seems to be fine for tuning the rate, but not a large enough difference to actually hop from one rate to another. I did notice that I don't measure a full 6.3" of travel, but I wonder if that's because they include the topout springs in the suspension travel, and there is simply an inch or so that we don't see at rest? I'll take the forks apart soon and measure the travel when not limited by the springs or internals.

Go soothingly on the grease mud, as there lurks the skid demon. Press
the brake foot as you roll around the corners, and save the collapse and
tie up.

In order, current to oldest, *denotes still have
DL1000K5*, VFR800X, MT-16*, DL650K4, XR400R, XR650R, XR400R, FZ1, GL1000*, VF750C, CB250, GL1100, GL650, DT50. I'm sure there's others but I forgot them.
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post #7 of 14 Old 10-28-2013, 06:23 AM
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Question

Whodat,

Roughly how much was it to have Jamie go thru the rear shock and respring it for you?
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post #8 of 14 Old 10-31-2013, 07:53 AM
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I'm wondering if anyone has had their suspension revalved or resprung with Daugherty and how you liked it? I did a search and this is the only thread that comes up.

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post #9 of 14 Old 10-31-2013, 08:11 PM
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post #10 of 14 Old 11-24-2013, 12:57 AM
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Quote:
Originally Posted by whodat View Post
So I just had Jamie rebuild my rear shock and respring it, and according to my wishes and waistline, he sprung it with a 900lb rear shock. Shazam that thing is stiff.
900 is perhaps more than I'd like.... do you mind sharing the "wishes and waistline" behind the decision? Thx.
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