Cal Tracs and Instant Center????

3pedals · 07-22-2011, 10:30 PM

Quote:

Originally Posted by TOSTO RACING

Put slicks on it et streets just won't cut it. You need a stiff sidewall slick.

OK , I plan to try that type tire next
Do you have any input on the original question - does the cal tracs change the effective Instant Center of a leaf spring suspension?

Phillip marvetz · 07-23-2011, 12:23 AM

I think your putting the cart in front of the horse.
It will be pretty hard to make your car work consistently with what you have. The traction bars will help but are not the answer.

Dinsdale · 07-23-2011, 02:01 AM

I think you're overthinking the suspension. As stated, you need real slicks. Maybe take some clutch out and lower your launch RPM. Myself, and others I know struggled with Cal Tracs and adjusted them all over the place with no improvement until the rest of the setup was right. The lower pivot hole theoretically moves the I/C farther out and softens the hit. The top hole hits the tire harder. Do you have adjustable rear shocks?

3pedals · 07-23-2011, 07:09 AM

Maybee your right about over thinking it all?
Shocks are DA's on rear. they are mounted in the oem location in front of the axle.
I cant beleive 28x12.5 ET street bias is not enough tire to hook this thing?, but I'll take you guys word for it, my next tire will be a stiff sidewall slick.
Thanks for your input about the top/bottom adjustment hole's effects. I keep thinking that because slow speed video is showing the tires turning before the suspension seperates, that I need the suspension to hit the tire quicker. I guess I have the rest of the season to mess with that, because new tires are not happening untill spring time.
Thanks
Barrett

L78 Nova · 07-23-2011, 11:54 AM

Hey Barrett,
If my wheel offset will work on your car you can try my slicks for a couple passes...... not 12 ! I know how you like to make laps!! Ha ha
I know Ed doesn't buy it but I still think track prep is better on Saturday as well. Gary

3pedals · 07-23-2011, 01:06 PM

Quote:

Originally Posted by L78 Nova

Hey Barrett,
If my wheel offset will work on your car you can try my slicks for a couple passes...... not 12 ! I know how you like to make laps!! Ha ha
I know Ed doesn't buy it but I still think track prep is better on Saturday as well. Gary

I would love to take you up on that Gary, I am using 8.5" wheel w/ 3.5" backspacing
Yeah sat is probably the way to go

Tony - thanks for the advice, it makes sense. I will definately mess with the shocks to see if they can lead me in the right direction.

Jeff Lee · 07-23-2011, 11:28 PM

And I saw elsewhere that you had a pair of very old and probably worn out leaf springs. We all understand budgets but there is no "miracle band-aide cure on the cheap" when it comes to a drag race rear suspension.
I would put a pair of M/T 9x29.5 stiff sidewall slicks on it at the same time I put a pair of Calvert Racing rear springs. I'm guessing that would help a ton. Then you can save for a good clutch as offered by either McLeod or Advanced because the clutch and rear suspension are all inter-related. But I would definitely suggest the rear part of the car gets the first rehab.

Tony Curcio · 07-23-2011, 11:51 AM

[QUOTE=
Do you have any input on the original question - does the cal tracs change the effective Instant Center of a leaf spring suspension?[/QUOTE]

CalTracs most definitely change the instant center. The rear attachment point (the one directly under the axle tube), is much lower so that the angle is more acute through the the front attachment point (the one below the spring-eye), in other words, pointing upward.

I have to agree with what Dinsdale said. In back to back testing on two different cars, we found the lower hole on the front mount resulted in less separation between body and wheels, as you would expect from a lower Instant Center. The resulting hit was softer, and that enabled the cars to hook on hot tracks. In better conditions, the upper front hole sometimes resulted in better 60 foot times, but it was not nearly as consistent. These were both automatics.

But what really made it work was finding the right shock setting. Controlling the rate of separation, as you already mentioned, is key, and ADJUSTABLE SHOCKS CAN POINT YOU IN THE RIGHT DIRECTION WITHOUT SPENDING MONEY. Don't assume that it's a harder hit that you need. Try going both directions with the shocks. If a stiffer shock (when extended) improves your 60 foot, then you'll know the IC needs to be lower. If a looser extending shock helps, a higher IC. It's also possible that the shock adjustments alone will be enough.

07-23-2011, 12:23 AM	#2
Phillip marvetz Senior Member Join Date: Oct 2008 Location: Lynden ,WA Posts: 820 Likes: 0 Liked 3 Times in 3 Posts	Re: Cal Tracs and Instant Center???? I think your putting the cart in front of the horse. It will be pretty hard to make your car work consistently with what you have. The traction bars will help but are not the answer. __________________ 2009 V/SA Record Holder

07-23-2011, 02:01 AM	#3
Dinsdale Member Join Date: Oct 2004 Location: Canada Posts: 313 Likes: 0 Liked 6 Times in 2 Posts	Re: Cal Tracs and Instant Center???? I think you're overthinking the suspension. As stated, you need real slicks. Maybe take some clutch out and lower your launch RPM. Myself, and others I know struggled with Cal Tracs and adjusted them all over the place with no improvement until the rest of the setup was right. The lower pivot hole theoretically moves the I/C farther out and softens the hit. The top hole hits the tire harder. Do you have adjustable rear shocks? __________________ Dale Posnick

07-23-2011, 07:09 AM	#4
3pedals Junior Member Join Date: Oct 2006 Posts: 10 Likes: 0 Liked 0 Times in 0 Posts	Re: Cal Tracs and Instant Center???? Maybee your right about over thinking it all? Shocks are DA's on rear. they are mounted in the oem location in front of the axle. I cant beleive 28x12.5 ET street bias is not enough tire to hook this thing?, but I'll take you guys word for it, my next tire will be a stiff sidewall slick. Thanks for your input about the top/bottom adjustment hole's effects. I keep thinking that because slow speed video is showing the tires turning before the suspension seperates, that I need the suspension to hit the tire quicker. I guess I have the rest of the season to mess with that, because new tires are not happening untill spring time. Thanks Barrett

07-23-2011, 11:54 AM	#5
L78 Nova Junior Member Join Date: Dec 2009 Location: Winnipeg, MB Posts: 92 Likes: 253 Liked 23 Times in 13 Posts	Re: Cal Tracs and Instant Center???? Hey Barrett, If my wheel offset will work on your car you can try my slicks for a couple passes...... not 12 ! I know how you like to make laps!! Ha ha I know Ed doesn't buy it but I still think track prep is better on Saturday as well. Gary

07-23-2011, 11:28 PM	#7
Jeff Lee VIP Member Join Date: Jul 2007 Location: Anthem, Arizona Posts: 2,766 Likes: 0 Liked 3 Times in 3 Posts	Re: Cal Tracs and Instant Center???? And I saw elsewhere that you had a pair of very old and probably worn out leaf springs. We all understand budgets but there is no "miracle band-aide cure on the cheap" when it comes to a drag race rear suspension. I would put a pair of M/T 9x29.5 stiff sidewall slicks on it at the same time I put a pair of Calvert Racing rear springs. I'm guessing that would help a ton. Then you can save for a good clutch as offered by either McLeod or Advanced because the clutch and rear suspension are all inter-related. But I would definitely suggest the rear part of the car gets the first rehab. __________________ Jeff Lee 7494 D/S '70 AMX

07-23-2011, 11:51 AM	#8
Tony Curcio Member Join Date: Mar 2002 Location: West Chester, PA Posts: 271 Likes: 1 Liked 4 Times in 1 Post	Re: Cal Tracs and Instant Center???? [QUOTE= Do you have any input on the original question - does the cal tracs change the effective Instant Center of a leaf spring suspension?[/QUOTE] CalTracs most definitely change the instant center. The rear attachment point (the one directly under the axle tube), is much lower so that the angle is more acute through the the front attachment point (the one below the spring-eye), in other words, pointing upward. I have to agree with what Dinsdale said. In back to back testing on two different cars, we found the lower hole on the front mount resulted in less separation between body and wheels, as you would expect from a lower Instant Center. The resulting hit was softer, and that enabled the cars to hook on hot tracks. In better conditions, the upper front hole sometimes resulted in better 60 foot times, but it was not nearly as consistent. These were both automatics. But what really made it work was finding the right shock setting. Controlling the rate of separation, as you already mentioned, is key, and ADJUSTABLE SHOCKS CAN POINT YOU IN THE RIGHT DIRECTION WITHOUT SPENDING MONEY. Don't assume that it's a harder hit that you need. Try going both directions with the shocks. If a stiffer shock (when extended) improves your 60 foot, then you'll know the IC needs to be lower. If a looser extending shock helps, a higher IC. It's also possible that the shock adjustments alone will be enough. __________________ Tony Curcio 1860 STK