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Old 08-17-2011, 12:03 AM   #1 (permalink)
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Cross Weights and Ride Height

Not long ago, there was a discussion about ride height adjustment. I described my method of setting ride height. I recently replaced the springs, and set ride height as I described in post #15 Ride Height Adjustment I ended up with the heights very close to each other, but not exact. I think the rear was differant by 1/8", and the front was differant by 3/16".

Today I put the car on the scales. I figured with new springs and changing the collar settings, I'd better rebalance the car.
The fuel cell is full of 110 leaded Sunoco, about 18 Gallons. The car is track ready.

Here's how I set up the car on the scales:



In the front seat I piled up a bunch of heavy stuff I had in my garage, so I could simulate the drivers weight with full gear - about 200#.




So, you're wondering, how did it come out? I plugged the numbers into my spread sheet. The numbers looked so good, I didn't believe it. I rolled it back off, zero'ed the scales, and rolled it back on. Twice. This is what I got.



I never had to make an adjustment to the spring weights. Rolled it on, and it was as perfect as I'm going to get them. OBTW: Ignore the total weight numbers. The real total weight is 2578# fully loaded.


We are now ready for the track.
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Old 08-17-2011, 12:09 AM   #2 (permalink)
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Very cool Bob. Where did you get those scale arms? That looks like a more economical scale solution. Do they work well?
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Old 08-17-2011, 12:27 AM   #3 (permalink)
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Is there a tutorial to follow on how to setup a scale setup like you have?
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Old 08-17-2011, 04:54 AM   #4 (permalink)
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These are called Ruggles Scales. If you do a site search, you can find some more pictures and info about them. Apparently, they are hard to find these days. Clearly, a set of electronic scales and plates from Longacre would be better. But $3K is definatly out of my league.

I've never seen a set of step by step instructions. My scales came with a set of instructions, but it was just the basics. Over time, I'v come up with a pretty reliable procedure that gives me repeatable results.
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Old 08-17-2011, 09:46 AM   #5 (permalink)
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I got a chuckle out of your "driver" Bob! I'm not nearly as creative and just use 2 80# bags of Sakrete.

Great results

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Old 08-17-2011, 04:24 PM   #6 (permalink)
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You might want to recheck your system. I have never seen a cobra with the right side heavy without a TON of balast.
also another way to CONFIRM your system is to first weight the car get the numbers then BACK the car on the scales and see if the numbers match. I bet they dont.

also bathroom scales can be off by a much as 15 - 20 percent. and that will make for an ill handling car when you think it is set up correctly

dont zero the scales. "you" stand on all the scales and make sure all the numbers for all the scales are the same. if not, and I'm guessing they wont be then you must compensate for the error. IE: one scale reads 198lb 2nd scale reads 202lb etc
hope this helps
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Old 08-17-2011, 04:47 PM   #7 (permalink)
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I've been using some Proform scales and they work well and are about $750.

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Old 08-17-2011, 05:23 PM   #8 (permalink)
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Ride Height Adjustment process

Hey Bob,
Regarding your instructions for adjusting ride height, those need to go in the FAQ on this forum and FFR manual. I just went from the Mustang shocks and springs in the rear to coilovers. I used your process for adjustment and found out how badly I must have been cross weighted. Different car to drive and brakes much more confidently.

Thanks,
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Old 08-17-2011, 06:33 PM   #9 (permalink)
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Quote:
Originally Posted by cobraless View Post
Bob
You might want to recheck your system. I have never seen a cobra with the right side heavy without a TON of balast.
also another way to CONFIRM your system is to first weight the car get the numbers then BACK the car on the scales and see if the numbers match. I bet they dont.

also bathroom scales can be off by a much as 15 - 20 percent. and that will make for an ill handling car when you think it is set up correctly

dont zero the scales. "you" stand on all the scales and make sure all the numbers for all the scales are the same. if not, and I'm guessing they wont be then you must compensate for the error. IE: one scale reads 198lb 2nd scale reads 202lb etc
hope this helps
dave
Every time I'v weighed my car, the results have been pretty much the same, give or take a few pounds. Why the right to left balance is so good is a mystery. But it is.

The big thing with any testing is to make sure your equipment is accurate, relaible, and the results are repeatable. Being a scientist at heart, I pay carefull attention to that.

Part of the set up includes checking all 5 scales with the same weight. I use a 5-6 gallon jug of fuel for the lighter weight. And then me holding 1-2 5 gallon jugs for the heavier weight.

before rolling the car onto the scales, I set all of them to 0.

That particular slab of flooring is very flat, I'v checked it as best I can. I always set it up in the exact same place.

I set the car up for track use, and usually start with a full tank. I don't think it really matters that much, because the fuel should not change the cross weights any. Not enough to matter, anyway. It will change total and rear weights, though. Since I don't need a weight for my class, I don't worry about that. The sway bars are disconnected. I over fill the tires a little bit, as it makes the car easier to roll.

I weigh the car and write down the numbers. I roll the car off the scale and then back on - twice. I compare all the numbers. If they don't match, I start again.

Once the numbers match, then I can make any changes I deem necessary. Then start the process all over again. It's tedious, time consuming, and hard work. But......


Quote:
Originally Posted by davidk View Post
Hey Bob,
Regarding your instructions for adjusting ride height, those need to go in the FAQ on this forum and FFR manual. I just went from the Mustang shocks and springs in the rear to coilovers. I used your process for adjustment and found out how badly I must have been cross weighted. Different car to drive and brakes much more confidently.

Thanks,
I don't think the FAQ has been updated in a long time.
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Old 08-17-2011, 08:58 PM   #10 (permalink)
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boB

Could you post your ride height thread in either the maintenance or improvement
of the FAQ

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Old 08-18-2011, 12:32 AM   #11 (permalink)
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OK, I did that. I put it under Build Tips.
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Old 08-18-2011, 03:39 AM   #12 (permalink)
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Bob,

You and I have discussed this weighing system before. In fact, I think it was you that introduce them to me. Thanks for following up with these pictures and notes.

The Ruggles Scale set up has become almost impossible to find. They are also used to weight airplanes and Spruce Specialty used to carry them, in sets of three, but they no longer list them.

Check out this site for pictures of them being used to weight an airplane.
Weight & Balance

Racing catalogs also used to sell them but no longer. I found some a while back for $100 but they are heavy and would probably have cost another $100 or more for shipping.

I don't know what I will do when the time comes but seems I'll have plenty of time to figure it out as my finish date keeps getting pushed out.

George
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Old 08-18-2011, 03:53 AM   #13 (permalink)
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Bob, It is important to remember that all the tires should be set to the exact same pressure. If this step is missed and adjustments are made to the coil overs to correct corner weights then when pressure is added the corner weight may change. How drastically will have to do with how much pressure is added or taken away. Good tutorial, many forget or don't know the importance of corner weighting the car and it's effect on braking and handling. Many here instead blame the brakes or tires for the cars characteristics.
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Old 08-18-2011, 02:35 PM   #14 (permalink)
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Quote:
Originally Posted by GWL View Post
Bob,

You and I have discussed this weighing system before. In fact, I think it was you that introduce them to me. Thanks for following up with these pictures and notes.

The Ruggles Scale set up has become almost impossible to find. They are also used to weight airplanes and Spruce Specialty used to carry them, in sets of three, but they no longer list them.

George
Yeah, I don't know why they're not around any more. Maybe because companies like Pro-Comp are meaking relativly inexpensive electronic scales.

The balance beam is a pretty design. It's definatly something I could make in my garage in probably less than a day, and for about $200 or so. I'd consider making and selling them, but I'd bet there's a patent on them.

Quote:
Originally Posted by frankeeski View Post
Bob, It is important to remember that all the tires should be set to the exact same pressure. If this step is missed and adjustments are made to the coil overs to correct corner weights then when pressure is added the corner weight may change. How drastically will have to do with how much pressure is added or taken away. Good tutorial, many forget or don't know the importance of corner weighting the car and it's effect on braking and handling. Many here instead blame the brakes or tires for the cars characteristics.
In theory, that's true. But a couple years ago tested that out and it wasn't a measurable amount.

You're right, if you're running on the ragged edge of handeling and braking, corner weights really make a differance. Maybe if there was a of 25-30 # it might matter. But I only added an extra 10# to make the car easier to push back and forth, and make the contact patch smaller.
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