Author Topic: What is the perfect Front to Back weight ratio?  (Read 11337 times)

Offline jspell

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What is the perfect Front to Back weight ratio?
« on: September 18, 2014, 04:30:25 AM »
I'm sure every car is different, but are there ratio boundaries? i.e. 80/20%

Offline GlennLever

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Re: What is the perfect Front to Back weight ratio?
« Reply #1 on: September 18, 2014, 05:42:52 AM »
I'm sure every car is different, but are there ratio boundaries? i.e. 80/20%

There is some discussion on this topic here

http://www.frontenginedragsters.org/forum/index.php?topic=1206.0
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Offline George

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Re: What is the perfect Front to Back weight ratio?
« Reply #2 on: September 18, 2014, 05:59:12 AM »
We changed our engine combination from an injected stock block to a blown Dart Little M that is fully filled. I weighted it with electronic scales on all four corners. Here's what I found the weights to be: LF 186 RF 198 LR 571 RR 582. Our car is 223" with the SBC 41" out. I run a 40# battery in the nose and 2-10# fire bottles as far forward as the cables would allow. The 3+ gallon fuel tank is about 4' from the front axle. These weights are with the car race ready less the driver and his equipment. Total weight would be around 1700# with the driver.

The car runs very well about 50% of time ,the other 50% it is smoking the tires as soon as it hits the wheelie bar. I am going to add about 30# out front and try to get it to come up on the bar with a lighter hit . It seems like a lot of weight but tried lowering the bar and raising tire pressure with no luck. My other options include a different bar design with a spring loaded bar as one option.

I am sure moving the engine out would also help but I would rather sell this car before I go to that much work. George

dreracecar

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Re: What is the perfect Front to Back weight ratio?
« Reply #3 on: September 18, 2014, 07:52:55 AM »
How many racers do you know that own scales, most rely on the "needs more weight on the front " theory

Offline George

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Re: What is the perfect Front to Back weight ratio?
« Reply #4 on: September 18, 2014, 08:16:15 AM »
I know of one who owns scales. He uses them to help setup his 4 link cars. A good friend and 10 minutes away.

dreracecar

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Re: What is the perfect Front to Back weight ratio?
« Reply #5 on: September 18, 2014, 10:14:24 AM »
Scales are very important to a door car set-up primaraly because the driver is offset.

But with the type of dragsters we run and of the thousands of combination variables, there is no set formula for front to rear weight %'s for the basic style of cars we run that if there was a 22% to 78% standard fomula for all cars but yours worked better at 25% to 75% THEN---that is the standard FOR YOUR CAR.

 It was years before I knew what the front to rear was, only because GG's wanted to get weight data on the cars and the scale would only weight 1/2 the car at a time. And there were times when I had to stick a different driver in place of my regular one and there was 60# difference, changed nothing and the car still did everything the same.

Now modern big show racing is different. There are standards for the cars themselves both funny and dragster, and the teams with multipal cars and because of all the data they collect are able to baseline a new build at the shop and even with that they still move things around. There will be a time in the near future(or they are doing it now,they are not telling) that they will have track specific cars (like NASCAR) based upon what works best at that track at that time of year haveing that type of weather. with the data collected and hopfully a consistant track prep, will move weight %'s to optimize that condition at that track.

Offline rooman

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Re: What is the perfect Front to Back weight ratio?
« Reply #6 on: September 18, 2014, 01:52:14 PM »
#1  A lot of the big show flopper teams move the fire bottle from front to rear to change the balance of the car depending on track conditions.

#2  The NHRA's rule that only permits one car change during an event was originally to allow a team to replace a damaged car but they added an additional clause saying that once you changed you could not change back as some pro stock teams were planning on running a different car (especially for night qualifying) to suit changing track conditions.

#3 Putting the fuel tank as far forward as possible can be a plus in a dragster as the fuel acts as ballast on the start line and goes away down track when front end weight is needed less.

#4 The position of the driver also has an effect. Cen-Pen cars have the shoulder hoop quite a distance behind the rear end centerline and although the driver generally needs to slide his butt forward to get his legs over the rear end, overall his CG is further back than in most cars--I guess that this one really depends on whether you have a big head or a big butt   :)

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dreracecar

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Re: What is the perfect Front to Back weight ratio?
« Reply #7 on: September 18, 2014, 03:57:53 PM »
My post was not to suggest that changing cars during an event was ever going to happen, my thought was having a known setup working at Dallas would be a completely different car at Charlette

Offline George

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Re: What is the perfect Front to Back weight ratio?
« Reply #8 on: September 19, 2014, 06:50:02 AM »
Bruce & Roo, What do you guys think about a spring loaded type of wheelie bar? I could rebuild my bars to gain more flex but the spring deal might allow a larger range of adjustment.

Thanks. George

dreracecar

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Re: What is the perfect Front to Back weight ratio?
« Reply #9 on: September 19, 2014, 09:25:45 AM »
The bar on the back of my car is spring loaded. The wheel bottoms out when the front is 1' off the ground. The bar is just a safety precausion if somthing stupid happens. I am not in favor of useing the bar to launch the car, too many repetitive poundings and something is going to break and I have been called upon many of times to have to weld the tabs back on. Learn your car and get it working without haveing to use it and you will be much better off and quit trying to emulate the big show cars---APPLES AN EGGS

Offline wideopen231

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Re: What is the perfect Front to Back weight ratio?
« Reply #10 on: September 19, 2014, 10:52:49 AM »
Not to hijack thread.  If you feel you can move some weight back,say front end is not picking up at all. How much effect would it have moving weight more to middle say in front of motor.Not added weight but say fire bottle. I have two 5 lb bottles going on car one engine and one yours truely. Not required for what I am doing. Have bracket made so its can be moved a mounted easy,cable is issue. If I moved both back removing 10# front and adding to middle.Would it have less effect on chassis  working than moving to rear? Hopefully understandable.
Relecting obama is like shooting right foot because it did not hurt enough when you shot left foot

dreracecar

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Re: What is the perfect Front to Back weight ratio?
« Reply #11 on: September 19, 2014, 06:41:42 PM »
If you are not picking up the front, moving the bottles back but still in front of the engine is not going to be enough. Removeing them or placing them behind the tires is the only thing that will give you measurable difference.

Get a long 2x4 equal to the wheelbase and put one end on a stand and the other on a bathroom scale,zero the scale and, mark the areas that the bottle will fit and start at where it is now  and move back and record changes in weight. all you are looking for is the weight difference from baseline.What you want to read is say total of 15#(bottle and contents),move back 2' and it might read 13# for a total of 2# weight loss by moving it back, Double that figure for 2 bottles in the same spot

Offline hotrod316

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Re: What is the perfect Front to Back weight ratio?
« Reply #12 on: September 21, 2014, 05:52:34 PM »
Bruce the 2 x 4 is a great idea i'm going to borrow it and see if it works on a idea i been working on for to long
thanks for yours thoughts
hotrod 316
steve morgan