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PostPosted: April 13, 2008, 6:23 pm 
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There was some discussion on the forum about the utility of shocks from a yamaha R1. After buying one and doing some calculations, I believe that they're an incredible buy.

First, the data:
Travel: 6 cm realistic, 7 cm without bump stop
Spring rate: 9 kg/mm or around 500 lbs/in
Pre-load adjustable: 1 cm
Compression and Rebound independently adjustable.
Designed to be mounted upside down (better for unsprung mass.)
Weight: around 6 lbs
Size: eye to eye: 30 cm
Ends: damper end: solid 1cm hole. Spring end: 1 cm needle bearing.

I was a bit skeptical at first at warnings that the damping rate wouldn't match the springs. However, if you keep the same springs then the damping should be perfectly matched to the spring rate.

Therefore, a few calculations. Remember, I'm building a rear-engine car.

Front: unsprung weight: 90 kg/wheel
Motion ratio: .47 using cams with ball bearings. This ratio will give a total travel of 5 inches. (3.5 bump/1.5 droop)
Spring Rate (n/m) = 88290 N/m

Wheel rate = MR^2*SR = ~19500 N/m, which is around 110 lbf/in

Natural Frequency = 1/(2*pi) * sqrt((Wheel rate)/(sprung weight at that wheel)

For me, this is 1/(2pi) * sqrt(19837.7/90) = 2.36 cycles/sec.
A quick chart for natural frequency: <1hz, grandma's car. 1.5hz, average car. 2hz, high-performance car. If you have more weight, say around 330 lb per wheel, then the natural frequency is 1.83 hz, which is still really good.

For the rear, assuming you want the same natural frequency, and with the weight at 136 kg, the motion ratio came out to be .58 with a resulting travel of 4.072 inches.

The only issue (for me) with these is the lack of spherical bearings in the ends. I plan to press out the needle bearing and replace it with a spherical one. Should only add around 10 bucks to the overall price. If you had a perfectly square setup with no cams at odd angles, then you'd be fine. Plus, they're very shiny. It's hard to pass up shiny stuff.

Truly a locost option!


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PostPosted: April 13, 2008, 7:43 pm 
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I tested some R6 shocks, which are similar if not identical and decided they weren't for me. They'll work fine on some cars, but are far from a slam-dunk solution. The problem is getting sufficient spring rate and wheel travel. My math said that if I needed more than 100lb/in wheel rate, and more than 3" of travel, they are a no-go.

My measurements showed 595lbs/in for the assembly, 2" of travel max, and about 200lbs of preload from the nitrogen charge and spring precompression.

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PostPosted: April 13, 2008, 7:49 pm 
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The nice thing about bell crank suspensions is that you can vary the motion ratio to accomodate different spring weight/travel options. Mine are yielding 1:1 ratio right now with my cheap single adjustable Konis. If I don't like them, then those R1s look nice.

I would think you could mount those R1s with needle bearings. Put mounting through-bolts parallel and you're done.

For our cars the coilovers are all sprung so only total weight matters. Only one half of the push (or pull) rod weight is unsprung.


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PostPosted: April 13, 2008, 8:36 pm 
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JonW wrote:
The nice thing about bell crank suspensions is that you can vary the motion ratio to accomodate different spring weight/travel options.

Only to a point. You can trade off shock travel for wheel rate but the trouble is that the motion ratio is squared. Without decent shock travel to begin with, or really, really high spring force, I was unable to get decent travel. That is, once the motion ratio was used to drop the wheel rate down to where I wanted, there wasn't enough wheel travel.

Believe me, I really wanted them to work out, and they would have, had I been building a superlight BEC. They were a no-go in the case of my obese 1300 pounder I have in the works...

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PostPosted: May 3, 2008, 12:18 pm 
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What year R1 is that from? It looks almost identicle to the 2001-2002 R6 shock which has a travel of 1.75 inches and a spring rate of 520 lbs/in, and adjustable preload between 100-250 lbs.

I have also measured the 1998-2001 R1 shocks and found that they have 450 lbs/in spring rate, 1.875" travel and adjustable preload between 100-240lbs. The 1998-2001 R1 shocks have the resevoirs parallel to the shock body.


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PostPosted: May 4, 2008, 8:46 am 
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If the R1 shock proves to have too little travel - how about considering a BMW R1150GS shock? Thats a heavy bike with long travel suspension, it might prove easier adapting the shock than starting with one from a light bike with short travel.

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PostPosted: May 11, 2008, 10:22 am 
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Does anyone know of a website that lists springrates and shock travels for sportbikes? I'm curious to see if there is much varition in springrste-to-travel ratio.


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PostPosted: December 3, 2008, 6:32 pm 
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pretty sure www.racetech.com I know they do a ton of motorcycle front end stuff...

+1 on R1 shocks... using them on my car... end i have one on my bike :twisted:

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PostPosted: December 4, 2008, 1:05 am 
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I don't know about shock travel, but this site lists almost all sportbike shock spring rates. I am using Hayabusa shocks w/ a 13.1kg/mm spring. Wheel frequency should work out to 110-130cpm, adjustable on the belcrank.


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PostPosted: December 5, 2008, 5:47 pm 
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proximacentuari wrote:
I was a bit skeptical at first at warnings that the damping rate wouldn't match the springs. However, if you keep the same springs then the damping should be perfectly matched to the spring rate...

...Truly a locost option!
Definitely a low cost option if you can get them to work for your application, and very high bang for your buck. But I don't believe this is totally true. While the shock valving may be "ideally" suited to the spring rate, it may not be quite as ideally suited to the motion ratio. Remember that the shock is actuated through a significant motion ratio. Actuating the shock through a different overall motion ratio will change the speed of shock actuation for a given bump. This could have an effect on your high vs low speed shock valving for the given rate of wheel loading, and end up having an effect on the ride and handling of the car. I wonder if anybody has ever put one of those shock onto a shock dyno?

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PostPosted: December 6, 2008, 4:41 pm 
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FWIW most sportbikes I've looked up have about 5" of wheel travel. with 5-6cm of shock travel, that's a pretty close motion ration to what the locost will have.

Steven


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PostPosted: December 6, 2008, 5:36 pm 
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But they're supporting far less weight...

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PostPosted: December 6, 2008, 8:36 pm 
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KB58 wrote:
But they're supporting far less weight...


I'm not seeing that much:

R1 wet weight 454 lbs + 180 lbs rider = 634 lbs supported by two wheels
Locost weight 1200 lbs + 180 lbs driver = 1380 lbs supported by four wheels

317 lbs / wheel for the R1
345 lbs / wheel for the Locost

I know exactly nothing about bike shocks/suspension though.
.

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PostPosted: April 18, 2009, 3:15 pm 
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Sorry, but I'm like that famous politician...."All that math makes my head hurt" Is it possible to get a picture of a set up using R1 shocks and a thumbs up or down from the person using them? I'm sure that they aren't suitable for track use but as a Sunday cruiser?? I do have to throw this in...They sure are purty!!!

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PostPosted: April 20, 2009, 1:08 am 
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Give me about two months and ill post a thumbs up or down pic lol

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