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PostPosted: Tue Sep 22, 2009 11:12 am 
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L8 apexr wrote:
Nothing shady,he buys the bikes minus engines and electrics from the t-rex kit car guys.They buy a dozen at a time and take what they need and then he does the same.

I'm in the same boat(as blue devil),just need to get the thing built on a budget and then fine tune from there.I figure I can add a sway bar up front to get the roll resistance needed with the bike dampers.I would prefer to be barless for the weight and that after many years of mucking with production based cars I'm convinced sways are the fastest way to make you slower.



Ah yes the Campagna guys… you live in Canada? I just switched to R6 shocks because the packaging. I have two 2006 R1 shocks that I would make you a much better deal on. Shoot me a PM

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PostPosted: Tue Sep 22, 2009 5:06 pm 
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wow I love this tread!!! I have been looking for spring rate/ damping values of bike shocks. is there a reason that only the r6 is being used? what about Honda, Susuki? or the liter bikes?

I'm designing for a max of 2g's down force on the suspension as far as wheel travel goes. what is everyone else using? I want to have 2 different belcrank settings. one for street and one for race. 4.5 in and ~2 in of travel max respectively. it has been a while since I designed it but I made my design so that the forces increase exponentially as it gets close to bottoming out. this way it should keep me from having as much impact loading transferred to the frame.

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PostPosted: Tue Sep 22, 2009 5:37 pm 
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nkw8181 wrote:
... I'm designing for 4.5 in...

What wheel rate for the street do you want to go along with that 4.5"? The trouble is that bike shocks have very little travel, usually somewhere around 2" with the bumpstop removed. So if you figure a 1/2" bumpstop, that leaves 1.5" of clear travel. You want 3X that much, so whatever springs are on the shock, your wheel rate will be 1/9 that.... yes, really.

The R1 units I tested had 500 lbs springs, so you'd end up with 56 lbs. Stiffer springs can be used, but since most people want around 150 lb wheel rate, that means you'd need 150 x 9 = 1350 lb/in springs. This is why, unless the car's very light, or a track-only car, bike shocks don't adapt well to street cars.

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PostPosted: Tue Sep 22, 2009 6:01 pm 
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well I can't remember my ratio off hand but I think it was like 3 to 1 on one setting on 2 to 1 on the other. my car is a bike build so i don't expect it to be no more then 1200 lbs. this is with a full rollcage. just for clearifcation, where did the 1/9 come from? the motion ratio?

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PostPosted: Tue Sep 22, 2009 6:35 pm 
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Zx14 stock spring is 9.7 so its about 550lbs(off the top of my head).Thats a little stiffer than an R1 spring,I don't know the bell crank dimensions however.


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PostPosted: Tue Sep 22, 2009 6:50 pm 
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nkw8181 wrote:
well I can't remember my ratio off hand but I think it was like 3 to 1 on one setting on 2 to 1 on the other. my car is a bike build so i don't expect it to be no more then 1200 lbs. this is with a full rollcage. just for clearifcation, where did the 1/9 come from? the motion ratio?


Yes. It's the unfortunate squared term that makes it tough to adapt them. It can be done, but it's always a tradeoff.

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PostPosted: Tue Sep 22, 2009 7:12 pm 
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With the risk of sounding stupid I'll ask what equation makes it 1/(MotionRatio^2)?

Sorry I'm just not following :(

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PostPosted: Tue Sep 22, 2009 8:43 pm 
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From my book:


Attachments:
installation ratio.jpg
installation ratio.jpg [ 90.94 KiB | Viewed 1963 times ]

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PostPosted: Tue Sep 22, 2009 9:42 pm 
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ok now I see where I was going. I was still thinking in force and didn't go as far as to calc the relation for spring rate. now this makes since, thanks for explaining it. here is the data that I calculated for mine a while back using proE. the range of motion is alittle to much but just so you can see where I am coming from.


Attachments:
File comment: this was with a K value of 300 lb/in on the spring
wheel travel with 300 lbin spring.JPG
wheel travel with 300 lbin spring.JPG [ 54.95 KiB | Viewed 1952 times ]
race posistion.JPG
race posistion.JPG [ 32.79 KiB | Viewed 1950 times ]

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PostPosted: Wed Sep 23, 2009 3:58 pm 
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with this being said, what does everyone run for wheel travel? street? track?

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PostPosted: Wed Sep 23, 2009 4:47 pm 
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I have to be careful that I've answered this right... Let me see if I can rescue this.

There are two factors at work, displacement and force:

Let's take a simple example, a 100 lb/in spring located directly over the wheel at the outer end of an A-arm. The installation ratio is 1:1, and the wheel travel will be whatever the shock is, let's say it's 1".

If you want to double the wheel travel, the shock must be moved inward along the lower A-arm until 2" of wheel travel equals 1" of shock travel. One inch of wheel travel results in 1/2" of spring travel.

What happens are two separate things:
1. The spring is now compressed half as much (1/2"), so the spring rate must be doubled to balance it.
2. The leverage of the spring is now half; requiring double the spring rate to balance it.

Each factor require a doubling of the spring rate in order to maintain the original 100 lb/in force at the wheel. This is where the squared term comes from in the installation ratio.

So for a bike shock, you'll have to work out the installation ratio to see what you end up with, then decide if the resulting rate is acceptable.

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PostPosted: Wed Sep 23, 2009 4:51 pm 
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nkw8181 wrote:
with this being said, what does everyone run for wheel travel? street? track?

1" droop, 3" compression, plus another inch for a bump rubber.

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PostPosted: Wed Sep 23, 2009 5:16 pm 
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KB58 wrote:
I have to be careful that I've answered this right... Let me see if I can rescue this.

There are two factors at work, displacement and force:

Let's take a simple example, a 100 lb/in spring located directly over the wheel at the outer end of an A-arm. The installation ratio is 1:1, and the wheel travel will be whatever the shock is, let's say it's 1".

If you want to double the wheel travel, the shock must be moved inward along the lower A-arm until 2" of wheel travel equals 1" of shock travel. One inch of wheel travel results in 1/2" of spring travel.

What happens are two separate things:
1. The spring is now compressed half as much (1/2"), so the spring rate must be doubled to balance it.
2. The leverage of the spring is now half; requiring double the spring rate to balance it.

Each factor require a doubling of the spring rate in order to maintain the original 100 lb/in force at the wheel. This is where the squared term comes from in the installation ratio.

So for a bike shock, you'll have to work out the installation ratio to see what you end up with, then decide if the resulting rate is acceptable.


yea thats what I meant. I knew the equations just never simplified it to see the square function. lol. the exchange of knowledge is allways welcome. to me atleast.

?
KB58 wrote:
nkw8181 wrote:
with this being said, what does everyone run for wheel travel? street? track?

1" droop, 3" compression, plus another inch for a bump rubber.


does this mean you design for a 4g bump? thinking about it, it makes since?

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PostPosted: Wed Sep 23, 2009 5:19 pm 
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i'll rerun the calcs later tonight but it looks like if i had a spring rate of 600lb/in it would be about right?

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PostPosted: Wed Sep 23, 2009 6:40 pm 
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nkw8181 wrote:
i'll rerun the calcs later tonight but it looks like if i had a spring rate of 600lb/in it would be about right?

What's the installation ratio for that. In other words, if the wheel's moved one inch, how much is your spring being compressed?

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