Front Coil Rates

Suspension Tuning, Troubleshooting, Design and Discussion

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oneowner73
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Joined: Tue Jul 03, 2007 10:03 pm
Location: Central Indiana

Front Coil Rates

#1 Post by oneowner73 » Sun Nov 14, 2010 1:18 pm

I have a 1973 Nova weighing 2585 with driver. The front still has 34" of original front subframe and stock type suspension. The front coils in the car are 6 cylinder 67 Camaro with 2 1/2 coils cut off. The ride height isn't bad but the springs are very stiff and can be installed without a compressor. In talking to a local chassis shop with corner weights and installed height we checked one spring at installed height and came up with 1190 lbs. They told me i needed a 16' free height spring with a 200# spring rate to compress to aprox. 10" installed height with 16" as the oem original spring free height for the car. I am new to figuring what spring for what job. Does this sound reasonable? I have been running the car with the stiff coils and have run a best of 6.08 @ 111.37 but I believe the car would work better with a little more stored energy in the front springs. Best 60 is 1.303 but not always consistant. Also adding an ARB to the rear which is a four link.
Brian

sc racing
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Location: Sahuartia Az

Re: Front Coil Rates

#2 Post by sc racing » Sun Nov 14, 2010 4:42 pm

200lbs seems like too much spring rate for a 2585lb car.Theres a lot of math to figure it and its explained in the door slammer book by Dave Morgan.

oneowner73
Posts: 12
Joined: Tue Jul 03, 2007 10:03 pm
Location: Central Indiana

Re: Front Coil Rates

#3 Post by oneowner73 » Sun Nov 14, 2010 5:55 pm

I agree it seems a little too much. The current springs were originally 289 rate load height in the Napa catalog. As far as I know they mean lb/in. and that was before the were cut. In original form they were rated for 1645 pounds. Guess you are right, I need to invest in Morgans book because it is cheaper than buying two sets of springs.
Brian

sc racing
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Location: Sahuartia Az

Re: Front Coil Rates

#4 Post by sc racing » Tue Nov 16, 2010 8:17 am

My car was 3000lbs with a 200lb spring and they were too much but I have a 3rd gen f body which has struts and require less rate anyway because they are mounted on more of an angle.

oneowner73
Posts: 12
Joined: Tue Jul 03, 2007 10:03 pm
Location: Central Indiana

Re: Front Coil Rates

#5 Post by oneowner73 » Tue Nov 16, 2010 8:43 pm

Did some more research in my Napa spring book. They show rates including free height, loaded height, rate load height and the load that it is rated for at that installed height. When you take the free height minus the installed height times the rate load height( pounds per inch) you get their load number. So I believe that in my car with its 10" installed height and a measured load with the old spring compressed to installed height of 1190 Lbs. that if I install a 16" free height spring with 200 Lbs. per inch rate that when it compresses to 10" I will have approx 1200 Lbs of support. I am convinced enough to buy a set and try.

Brian

sc racing
Posts: 1773
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Location: Sahuartia Az

Re: Front Coil Rates

#6 Post by sc racing » Wed Nov 17, 2010 8:36 am

Im a little confused as to your weight? If the car is 2585lbs how do you have 1190lbs on 1 front corner? I dont know if the Napa book is what you should follow its not for drag racing its for stock application your looking for stored energy which means you need a tall light spring compressed close to coil bind (not too close) to help trasfer weight on the launchl.Thats the way I see it but Im not saying Im correct.

sc racing
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Location: Sahuartia Az

Re: Front Coil Rates

#7 Post by sc racing » Wed Nov 17, 2010 8:38 am

I found the answer..... call Santhuff and buy what they recommend.

oneowner73
Posts: 12
Joined: Tue Jul 03, 2007 10:03 pm
Location: Central Indiana

Re: Front Coil Rates

#8 Post by oneowner73 » Thu Nov 18, 2010 5:14 pm

That weight of 1190 lbs came from taking my existing springs out and compressing them the installed height of 10". The original spring before being cut was 1645 at an installed height of 11". I don't think one corner on the car when it was new weighed 1645 lbs either. The corner weight when we scaled the car 2 weeks ago was 651 Lbs.

oneowner73
Posts: 12
Joined: Tue Jul 03, 2007 10:03 pm
Location: Central Indiana

Re: Front Coil Rates

#9 Post by oneowner73 » Fri Nov 26, 2010 10:13 am

The weight seems too high because the spring isn't mounted out at the wheel. It is called leverage.

sc racing
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Location: Sahuartia Az

Re: Front Coil Rates

#10 Post by sc racing » Fri Nov 26, 2010 2:48 pm

[quote="oneowner73"]The weight seems too high because the spring isn't mounted out at the wheel. It is called leverage.[/qu
Yeah your probably really close with the 200lb spring. Did you subtract your unsprung weight from your total front weight?

oneowner73
Posts: 12
Joined: Tue Jul 03, 2007 10:03 pm
Location: Central Indiana

Re: Front Coil Rates

#11 Post by oneowner73 » Sat Nov 27, 2010 10:15 am

Shouldn't need to subtract unsprung weight when going from spring load at an installed height.

sc racing
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Re: Front Coil Rates

#12 Post by sc racing » Sun Nov 28, 2010 9:14 am

oneowner73 wrote:Shouldn't need to subtract unsprung weight when going from spring load at an installed height.
Totally agree with you on that,but I was talking about when you scaled the car, I wouldnt use a cut up 43 year old spring as a guide line to test or compare to I would use the correct actual weight of the car. You already scaled it and have the weights. I think your setup is pretty good now and a 4 link car doesnt need to rely on the front suspension as much as a stock suspension car. Of course this is all just my opinion.

oneowner73
Posts: 12
Joined: Tue Jul 03, 2007 10:03 pm
Location: Central Indiana

Re: Front Coil Rates

#13 Post by oneowner73 » Fri Apr 15, 2011 8:27 pm

Got my 200 lb per inch springs installed and the car sits perfectly. Went to a test and tune and the car left a little better with the front up 8 to 10 inches and carried about twenty feet instead of up and down in five or six feet. Those stock car rear springs don't know where they are or care what the job is. Brian

want-a-be
Posts: 189
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Location: Southern Illinois

Re: Front Coil Rates

#14 Post by want-a-be » Wed Apr 20, 2011 10:30 am

I think the springs you went with were a good move. I would consider trying a set that are even a bit lighter. Although, the description you gave on your launch is exactly what I look for when I'm helping someone line out a few chassis bugs at the track.

What springs are you running in the rear of your car? A very common mistake is running a rear spring that is too heavy. Proper spring rates,front and rear, affect how the chassis works, no matter what rear suspension you are running.


btw,..how did this affect your 60' times?

Don

oneowner73
Posts: 12
Joined: Tue Jul 03, 2007 10:03 pm
Location: Central Indiana

Re: Front Coil Rates

#15 Post by oneowner73 » Thu Apr 21, 2011 10:59 pm

Running 110 lb. springs on coil overs in the rear and have considered lighter springs in the front and rear. Rear seems very stiff with the 110's. 60' went from average 1.32 to 1.34 on a good track to 1.36 pulling the wheels out of the beams. Last year last pass had 1.052 in box, started with 1.060 in box first pass and was .036 red. Last fall had a best of 1.303 60'.

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