87 BSP - have car balance #'s - now what?
07-20-2011, 09:29 AM
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87 BSP - have car balance #'s - now what?
The car has its alignment
Caster 5.1 deg
Front camber -1.5
Front toe 1/16" out
Rear camber -1.0
Rear toe -1/16" in
Car weighs 3187 lbs without a driver
lf 836, rf 843
lr 765, rr 743
left/right weight is 50.2% / 49.8%
front/rear weight is 52.7% / 47.3%
We took a SWAG (scientific wild-assed guess - my son is an engineering student) at what adding a 200 lb driver would do
lf 884 rf 855
lr 875 rr 773
The question now is - can I do anything about the weight distribution or do I even need to?? Ideally I guess we're trying for about 850 a wheel with driver.
Thanks.
Caster 5.1 deg
Front camber -1.5
Front toe 1/16" out
Rear camber -1.0
Rear toe -1/16" in
Car weighs 3187 lbs without a driver
lf 836, rf 843
lr 765, rr 743
left/right weight is 50.2% / 49.8%
front/rear weight is 52.7% / 47.3%
We took a SWAG (scientific wild-assed guess - my son is an engineering student) at what adding a 200 lb driver would do
lf 884 rf 855
lr 875 rr 773
The question now is - can I do anything about the weight distribution or do I even need to?? Ideally I guess we're trying for about 850 a wheel with driver.
Thanks.
Last edited by mbfan72; 07-20-2011 at 09:30 AM. Reason: typo
07-20-2011, 01:45 PM
#2
Melting Slicks
My best guess is that with a driver you are about 50 pounds off in cross weight with a driver.
Right now you are high in the left front/rr by about 29 pounds.
When you add about 65 pounds to the LF, 10 pounds to the RF, 100 pounds to the LR and 25 pounds to the RR, you will come out with about 50 pounds of cross weight. That's not horrible, but you could jack about 25 pounds out of the LR and cure it.
You first need to see how it drives like it is. These cars tend to over-use their front tires. If you get it balanced, then the LF is going to be awful heavy and it is probably going to push pretty bad turning right anyway. I know the LR is a lot heavier than the RR, but you also loose more camber in the front on these cars due to frame flex (even with a camber brace) and if you get them too nose heavy the will push.
What you want to do is take it to a test and tune and run a series of lefts and rights, as well as some slaloms. Try to gage how it feels, is it looser or tighter in one direction and is it really different or just a bit different? Don't drive it like a crazy person, find where the limit is and just nibble at it. You aren't doing this testing for time, you are trying to gage what the car is doing. Does it let you drive it to the desired line at or near the limit in both directions? If the car is trying to push in one direction and tail out in the other than you need to look at fixing it. If it won't let you drive to the limit and still stay on line, work on it in that direction.
Right now it might push a bit more in rights than in lefts, but it may not be all that bad.
Right now you are high in the left front/rr by about 29 pounds.
When you add about 65 pounds to the LF, 10 pounds to the RF, 100 pounds to the LR and 25 pounds to the RR, you will come out with about 50 pounds of cross weight. That's not horrible, but you could jack about 25 pounds out of the LR and cure it.
You first need to see how it drives like it is. These cars tend to over-use their front tires. If you get it balanced, then the LF is going to be awful heavy and it is probably going to push pretty bad turning right anyway. I know the LR is a lot heavier than the RR, but you also loose more camber in the front on these cars due to frame flex (even with a camber brace) and if you get them too nose heavy the will push.
What you want to do is take it to a test and tune and run a series of lefts and rights, as well as some slaloms. Try to gage how it feels, is it looser or tighter in one direction and is it really different or just a bit different? Don't drive it like a crazy person, find where the limit is and just nibble at it. You aren't doing this testing for time, you are trying to gage what the car is doing. Does it let you drive it to the desired line at or near the limit in both directions? If the car is trying to push in one direction and tail out in the other than you need to look at fixing it. If it won't let you drive to the limit and still stay on line, work on it in that direction.
Right now it might push a bit more in rights than in lefts, but it may not be all that bad.
07-21-2011, 01:19 PM
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Thanks again for taking the time to respond. I am working my way through a book called "How to make your car handle" by Fred Puhn. The book is dated but I hope that the basic concepts remain the same. I would like to understand why I am doing certain things and why some things are more important than others.
Using the calculation for ideal corner weights from the book I think I understand how you came to your conclusion. Do you have any books that you would recommend?
I'll take your advice and try the car as is. We have back-to-back events in about a week and a 3rd event the following weekend.
Using the calculation for ideal corner weights from the book I think I understand how you came to your conclusion. Do you have any books that you would recommend?
I'll take your advice and try the car as is. We have back-to-back events in about a week and a 3rd event the following weekend.
07-21-2011, 01:36 PM
#4
Corner weighting? As they say, there's an app for that...
http://itunes.apple.com/us/app/cross...290618962?mt=8
http://itunes.apple.com/us/app/cross...290618962?mt=8
