Great infos here!
I also read in Mike Martin's book that many races (back then at least) use smaller tbars but larger swaybars as you wrote.
Since I decided now to take composite leafsprings I really need to know what spring rate I should order to get this car not to oversteer or understeer like crazy.
Yesterday I did get the car on a truck scale in my near! In Mike Martin's book they do it without person in the car, but I think that's an important point since that's how the car will be driven, so I removed the bench seat (I measured it today, it's 99lbs!!!! I will get a light single race seat in there for racing) and put my girlfriend in there on the floor that is just about 20lbs lighter than me. Moved my battery to the trunk passenger side and the tank was pretty empty.
The total weight of this car was 2 years ago bone stock with 1/3 full tank 4010lbs. Now it was (without girlfriends weight) 3630lbs!!! That without bench seat, with edelbrock heads, intake & waterpump. Unbelievable... the truck scale is +/- 10lbs I was told.
I will loose another 20-30lbs with the fiberglass leafsprings on the rear.
The car was with girlfriend 3770lbs. Front weight was 2116lbs, rear weight 1653lbs. So I got a 56.1%front weight bias. So looking at Mike Martings book I need 75% or more front roll couple to get a car that is neutral or understeers. (don't really want an oversteering car)
Center of gravity is (115" wheelbase) 50.2" behind front wheels and 64.8" front of rear wheels.
I did measure the center gravity height but the scale wasn't accurate enough and I just lifted the car 11" up so I got a CGH of 4"-6.85" and that seems to low to me, altough the car is very low (on the front almost touching the LCA bumpers and rear the leafspring is totally worn down)
Anyway, I did some measurements today on the swaybars! My rear swaybar I didn't measure, it's a totaly different system than the one firmfeel has (AAR type) so it doesn't make sense to measure mine. But I did average the length of the lever looking at the firmfeel pictures and I would say their swaybar lever length is about 11.8" +/- 2". So I will go from there. it attaches right behind the perch so I can take the motion ratio I used for the leafsprings. (57.8" perch-perch / 62.13" track = 0.9303)
On the front it was more interesting. I removed the swaybar link and lifted the car on a lift. I put my scale on the floor, took a straight piece of wood and put it between scale on floor and swaybar end. I then measured the distance between swaybar and LCA. I then lowered the lift, did 2 measurements (weight & distance difference) and I got a swaybar static rate of 275 and 270lb/inch AT the endlink. I would think that's with the lever length already included. If I would make it shorter the static rate would increase quick. The lever length is about 7.7" +/-1".
Also, should I have blocked the other wheel so it can't move up since the swaybar probably pushed it up?
The swaybar is mounted about 6.1" after the pivot point of the LCA (tbar) and if I undertand it right (now I am not sure anymore...):
motion ratio: attaching point or spring centerline / LCA (I'll take now the length from the pivot point to the wheel centerline instead just the LCA length) length = 6.1"/16.3" = 0.3747
Roll rate = static rate * motion ratio = 270lbs/in * 0.3747 = 101 lbs/inch
wheel rate = static rate * motionration^2 = 38lb/inch.
Now, what I am not sure also: in Mike Martin's book it's written confusing. Do I need to add all roll rates together OR wheel rates to get the roll couple distribution? I first thought roll rates because of this roll rate names but somewhere he writes about to get the wheel rate for the leafsprings. So I probably need to get the wheel rates for all and that will give me the roll couple distribution right?
(by the way, a Tbar would perfectly fit where the swaybar is, the only thing that would have to be done are some nice hex-brakets that fit on the end of the swaybar and voila, a tbar swaybar would have been done!)
What also confuses me:
On Tbars I found out that you get the diameter^4 and divided by the rating you will always get the same constant. Don't know why ^4 and not ^2 (since it's an area) but it works. I can now tell by the diameter of the Tbar what rating it will have, although the ratings of the Tbars is always shown.
BUT on the swaybars this doens't work, the diameter^4 divided trough the deflection lb/degree is not proportional to the next value. Why is that? Are the stock swaybars empty inside, because there is a formula for that: OD^4-ID^4?
I hope you can find those values in that book.. I will try to order that soon, I totally forgot about that you told me to get it!
thank you
