Finding the instant center on a leaf spring car

Suspension Tuning, Troubleshooting, Design and Discussion

Moderators: David Lemmond, Dave Morgan

Message
Author
User avatar
novaz
Posts: 113
Joined: Sat May 14, 2005 10:26 pm

chassis stiffness

#16 Post by novaz » Fri May 27, 2005 1:49 pm

Something I would like you guys opinion on is it possible too have the chassis(frames) too stiff I have the cage +sub frame connectors in I have a rear mounted tube section for the shocks and I now have a second drive shaft hoop in place all are welded.
Thanks
Royz

User avatar
John_Heard
Site Admin
Posts: 5684
Joined: Thu May 12, 2005 11:20 am
Location: Resume Speed, Kansas
Contact:

#17 Post by John_Heard » Fri May 27, 2005 2:06 pm

I wouldn't think having a stiff chassis would be a problem, should be a big benefit instead.

On the other hand, I do believe you can have springs that are too stiff.

Bobalos
Posts: 39
Joined: Wed May 18, 2005 12:09 pm
Contact:

#18 Post by Bobalos » Fri May 27, 2005 2:59 pm

Ditto what Beyond (sorry I cant remember your name) said. I seem to recall Dr. Hook @ the Go Fast Zone saying something VERY similar.

Bob

User avatar
Craig W.
Posts: 1254
Joined: Thu May 12, 2005 11:01 am
Location: Columbia, KY
Contact:

#19 Post by Craig W. » Fri May 27, 2005 3:09 pm

Bobalos wrote:No unfortunately not. Im on the west coast & have changed to a different company so I cant "accidentaly schedule" my business trips to coincide with races. LOL. Yea, Chris is one heck of a great guy.

You prolly dont member me, but I was the tall white guy with the Xtrm 66 Ballcap on. I helped you guys load up the car when it started to rain.

PS. sorry to hi-jack your thread :(

Bob
Yeah, I think I do remember you. Were you carrying a backpack most of the day?

Maybe it won't rain this year. At least it hasn't gotten hot and humid yet. Of course the air at Beech Bend is always a little moist down there in the river bottoms.
Craig Watson
2QuickNovas Racing
5.27@130

Sponsors:
AEM Electronics
Carnivore Performance
Bradco Converters
Rapp Racing
VFN Fiberglass

Bobalos
Posts: 39
Joined: Wed May 18, 2005 12:09 pm
Contact:

#20 Post by Bobalos » Mon May 30, 2005 1:06 pm

Yep, that was me:)

Good luck this year.

Bob

User avatar
novaz
Posts: 113
Joined: Sat May 14, 2005 10:26 pm

overarched

#21 Post by novaz » Fri Jun 03, 2005 4:25 pm

I had my rear springs made overarched to raise the rear end so even though they use the same mounting point on frame and axle how will this affect the instant Center, and would this not actually help with the weight transfer
just trying to get my head around the engineering a bit more
Thanks
Royz

grandville455
Posts: 176
Joined: Sat Sep 13, 2008 9:11 am

Re: Finding the instant center on a leaf spring car

#22 Post by grandville455 » Sun Apr 20, 2014 9:05 pm

Hey Guys, old thread I know, but interesting none the less, so the Effective IC changes when cal tracs are used cause the pin on plate pushes down on the spring creating leverage to lift vehicle and that kinda becomes the effective IC correct? I was having a problem last year with a new setup consisting of a 9" 4500 conv, 4.10 gears, and AFCO DA shocks behind the axle. a lot to take on I know lol , anyway it was hitting the tire to hard from what I believe and then running over it after the initial hit, running 16 psi in 29 hoosier slicks, so this year I have added a 1" block in between the shock the plate and spring to get the bar close to level in the bottom hole, and if I need to be able to use the top hole it will be angled more towards the top of the tire for even more pressure. I am using calverts mono 1" drop springs also. I should be hitting the track in a week or two. Final settings from last race were 22 off full tight on EXT and 13 off full tight on COMP. Those settings were on a very cold track tho too, otherwise I was closer to 16 on EXT.
74 firebird 600 hp, no brake. best 60 ft 1.46, but its not consistent and that's what I need, I think this car should 60 ft 1.43-1.45 all day.. 10.60@126.32 1.50 60 ft.
74 Pontiac Grandville
7.33- 1/8th @ 94.55/ 11.501 @117.74- 4550 pds
1.60 60 ft....all bests

74 Firebird 3580#
2016 1.377 60ft, 6.33@106.87- 10.02@ 132 mph

User avatar
Craig W.
Posts: 1254
Joined: Thu May 12, 2005 11:01 am
Location: Columbia, KY
Contact:

Re: Finding the instant center on a leaf spring car

#23 Post by Craig W. » Sun Apr 20, 2014 9:52 pm

Instant center is always going to be the front spring eye in a leaf spring car in my opinion. Changes to the Caltracs effect how much load you're applying but it doesn't change where the rear suspension rotates around.
Craig Watson
2QuickNovas Racing
5.27@130

Sponsors:
AEM Electronics
Carnivore Performance
Bradco Converters
Rapp Racing
VFN Fiberglass

User avatar
John_Heard
Site Admin
Posts: 5684
Joined: Thu May 12, 2005 11:20 am
Location: Resume Speed, Kansas
Contact:

Re: Finding the instant center on a leaf spring car

#24 Post by John_Heard » Sun Apr 20, 2014 10:59 pm

Man this is an old thread.

I'm in agreement with Craig, instant center location has to be through the front spring eye bolt regardless of what you're doing monkeying around with the caltrac bars. They are basically a glorified slapper bar, one with much more adjustment. Changes to the cal-trac pivot points only change how much resistance the spring has against housing rotation, in effect changing the initial hit at the tire (softer or harder). What most don't talk about is center of gravity / chassis height, distance from housing center to spring mounting point (spacers), front spring mounting point, front travel, and of course front & rear shocks and their settings etc. All that makes a big difference how a car reacts.

grandville455
Posts: 176
Joined: Sat Sep 13, 2008 9:11 am

Re: Finding the instant center on a leaf spring car

#25 Post by grandville455 » Mon Apr 21, 2014 6:25 am

John_Heard wrote:Man this is an old thread.

I'm in agreement with Craig, instant center location has to be through the front spring eye bolt regardless of what you're doing monkeying around with the caltrac bars. They are basically a glorified slapper bar, one with much more adjustment. Changes to the cal-trac pivot points only change how much resistance the spring has against housing rotation, in effect changing the initial hit at the tire (softer or harder). What most don't talk about is center of gravity / chassis height, distance from housing center to spring mounting point (spacers), front spring mounting point, front travel, and of course front & rear shocks and their settings etc. All that makes a big difference how a car reacts.
So How does one figure the center of gravity etc as u said above? So the only way to change AS is to adjust the front spring location higher up correct? My car has been dropped maybe a 1-1 1/2 in front using Santhuff 200 rate springs, and 1" in back with the mono drop springs, the springs are basically flat , no arch, is that good or no? Are u talking spacers to lower the car on top of the spring? I only use a .100 plate on top. Front has 5.25 " Using QA1 stocker star drag series shocks set at 4. I also dont have have any sub frame connectors, just a 10 point cage, Do u need the connectors still?
74 Pontiac Grandville
7.33- 1/8th @ 94.55/ 11.501 @117.74- 4550 pds
1.60 60 ft....all bests

74 Firebird 3580#
2016 1.377 60ft, 6.33@106.87- 10.02@ 132 mph

grandville455
Posts: 176
Joined: Sat Sep 13, 2008 9:11 am

Re: Finding the instant center on a leaf spring car

#26 Post by grandville455 » Mon Apr 21, 2014 8:36 am

Here's Video last year, I think shocks were similiar in back to above, like 12 off full tight on EXT and 6-9 off full tight on COMP. I can slow the video down in media player, to me it seems to plant the tire initially , but right after u can see it spin, this was with 12 psi, I hadn't tried the 16 psi yet, that was later in the year this was july. I also see in the video that the Rear pinion really doesnt rotate up at all, looks basically flat. The pic u can see it much better, the pic shows the cal trac kinda pointing up a little, but rear looks flat, i thought u wanted some pitch rotation to help plant tires? Last video was 08/11 of last year, i think fronts were at 6 instead of 4. 60 ft was still only 1.51 i think, I would have to look back at slips tonight.

http://smg.photobucket.com/user/Grandvi ... 8.mp4.html

http://img.photobucket.com/albums/v209/ ... cad4c5.jpg

http://smg.photobucket.com/user/Grandvi ... 5.mp4.html
74 Pontiac Grandville
7.33- 1/8th @ 94.55/ 11.501 @117.74- 4550 pds
1.60 60 ft....all bests

74 Firebird 3580#
2016 1.377 60ft, 6.33@106.87- 10.02@ 132 mph

User avatar
John_Heard
Site Admin
Posts: 5684
Joined: Thu May 12, 2005 11:20 am
Location: Resume Speed, Kansas
Contact:

Re: Finding the instant center on a leaf spring car

#27 Post by John_Heard » Mon Apr 21, 2014 9:03 am

Not necessarily, you can drop the rear some, and/or use spacers to lower the car as well. Your springs being close to flat is pretty normal for a mono. Subframe connectors are typically a good idea on a unibody car.

You're not that far off on your car from what I can see in that video, it's not striking the tire hard at all footbraking it from what I can see, it's a real soft launch. I don't know how you can see what the pinion is doing from those videos, but what it does do is soft. Nothing violent going on there. Your not hitting the car hard enough to lift the front end, in fact I think it might be helpful to tighten the front shocks up a few clicks and see if it likes that. Your dead hooking the tire at the hit and if there is any spin, it's when the front shocks top out, so slow them down a touch.

Is this a bracket car? Street Car?

grandville455
Posts: 176
Joined: Sat Sep 13, 2008 9:11 am

Re: Finding the instant center on a leaf spring car

#28 Post by grandville455 » Mon Apr 21, 2014 9:12 am

Its a street /strip car, Which I do run points also, so i need that consistency. Yea I have watched other peoples videos and u can see the rear drop alot faster then mine is, but they are on a TB too? Yes in those videos I was around 1500 FB? I think the car works better tho leaving right from IDLE? When I tried that tho last fall I had to loosen the front as it wasnt rising quick enough, compared to when i foot braked it? It is hard to see the rear , it just looks like u should see more movement maybe not huh? It's weird when i talked to calvert he said I should not have to tighten anything up front at my ET level yet? When i am full loose tho its pops up so damn quick, Maybe the rear needs to be looser to balance out the front rising so quick, hitting the rear sooner?
I'm just trying to get a better game plan this year then last, it was a very frustrating year last year ,lol
74 Pontiac Grandville
7.33- 1/8th @ 94.55/ 11.501 @117.74- 4550 pds
1.60 60 ft....all bests

74 Firebird 3580#
2016 1.377 60ft, 6.33@106.87- 10.02@ 132 mph

User avatar
John_Heard
Site Admin
Posts: 5684
Joined: Thu May 12, 2005 11:20 am
Location: Resume Speed, Kansas
Contact:

Re: Finding the instant center on a leaf spring car

#29 Post by John_Heard » Mon Apr 21, 2014 9:55 am

Most of this you'll have to experiment with to find what it likes best. You could of course try looser on extension in the rear that may help a little, but from what I could tell one or two clicks tighter in the front looks like would help it out a bit. Yes a TB would make it hit a lot harder, but if you're running a No box class it's probably not legal in that class.

grandville455
Posts: 176
Joined: Sat Sep 13, 2008 9:11 am

Re: Finding the instant center on a leaf spring car

#30 Post by grandville455 » Mon Apr 21, 2014 10:14 am

Yea, the problem I had last year was one race I would have it hooking,thinking I found the setup next rave right back to hook n spin, like the car was squatting instead of seperating, one guy watched it n said it looked like back was going down, then it would spin. Which I think I was crushing the sidewall giving that illusion. My best 60 came with front shocks at 6 n rear psi at 16.. leaving around 15+1800.
But next race that didn't work lol... I do think it likes that much air tho. But with bars in bottom hole nowit may need less back to 12 like iI used to run... guess well find out soon lol.. nothing worse then feeling traction not there when u hit the fun pedal!
74 Pontiac Grandville
7.33- 1/8th @ 94.55/ 11.501 @117.74- 4550 pds
1.60 60 ft....all bests

74 Firebird 3580#
2016 1.377 60ft, 6.33@106.87- 10.02@ 132 mph

Post Reply

Who is online

Users browsing this forum: No registered users and 1 guest