Steering, Suspension, & Brakes

tips, technology, tools and techniques related to non-driveline mechanical components

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rficalora
Rob Ficalora
Willis, TX
(2634 posts)

Registered:
10/24/2007 02:46PM

Main British Car:
'76 MGB w/CB front, Sebring rear, early metal dash Ford 302

authors avatar
IRS set-up
Posted by: rficalora
Date: March 11, 2011 06:48PM

Bought my IRS from Todd too long ago - memory has faded & apparently didn't put the info in my book... Have a call into him but in case I don't hear back before the morning, how should I have the alignment shop set it up? Three adjustment points - one on each side of LCA's & one on the upper control arm. Any suggestions?


DiDueColpi
Fred Key
West coast - Canada
(1259 posts)

Registered:
05/14/2010 03:06AM

Main British Car:
What if the Hokey Pokey really is what it's all about?

authors avatar
Re: IRS set-up
Posted by: DiDueColpi
Date: March 11, 2011 07:11PM

Haven't seen your set up Rob,
But in general the upper arm adjustment would be used to set the tire to wheelwell clearance. Once that is set it gets left alone.
The actual alignment is done on the lower arm. Camber set with the front adjuster and toe set with the rear one. A combination of the two adjustments will be needed to get it "on the money".
Normal specs for a street car would be 1/2 to 1 deg. neg. camber and 0.5 to 0.8mm toe out.
If you find the rear too loose on hard braking you can go up to 0.8mm toe in to counter act that but it will loosen it up on hard accel.

Cheers
Fred


rficalora
Rob Ficalora
Willis, TX
(2634 posts)

Registered:
10/24/2007 02:46PM

Main British Car:
'76 MGB w/CB front, Sebring rear, early metal dash Ford 302

authors avatar
Re: IRS set-up
Posted by: rficalora
Date: March 11, 2011 08:07PM

Sounds like the same three adjustment locations (although I don't understand why both the front & rear adjustments on the LCA wouldn't control toe? Here's a pic that may confirm...
IRS Alignment.jpg


DiDueColpi
Fred Key
West coast - Canada
(1259 posts)

Registered:
05/14/2010 03:06AM

Main British Car:
What if the Hokey Pokey really is what it's all about?

authors avatar
Re: IRS set-up
Posted by: DiDueColpi
Date: March 11, 2011 08:28PM

Either one will set toe in and camber.
Front and rear is just a routine that I follow so as not to screw up too badly.
Can your LCA's be reversed?
The adjustment would be far more effective on the outboard sides.
As it is now a toe adjustment will affect the wheel base and LCA angle.

Cheers
Fred


rficalora
Rob Ficalora
Willis, TX
(2634 posts)

Registered:
10/24/2007 02:46PM

Main British Car:
'76 MGB w/CB front, Sebring rear, early metal dash Ford 302

authors avatar
Re: IRS set-up
Posted by: rficalora
Date: March 11, 2011 08:39PM

Thanks Fred. They can't be reversed; hey're wider at the inboard end than the outboard end. So sounds lkke I go with the numbers above.


DiDueColpi
Fred Key
West coast - Canada
(1259 posts)

Registered:
05/14/2010 03:06AM

Main British Car:
What if the Hokey Pokey really is what it's all about?

authors avatar
Re: IRS set-up
Posted by: DiDueColpi
Date: March 11, 2011 08:50PM

Should work out just fine.
And it looks good too.

Cheers
Fred


302GT
Larry Shimp

(203 posts)

Registered:
11/17/2007 01:13PM

Main British Car:
1968 MGB GT Ford 302 crate engine

Re: IRS set-up
Posted by: 302GT
Date: March 15, 2011 06:05AM

There is no one setting that is right for all cars; feel free to experiment with the settings. When doing so there are a few things to keep in mind.

Toe in/out:

During acceleration the wheels move forward as they push the car and this increases toe in as the A arms pivot on their bushings. During braking there is an opposite motion that leds towards toe out. Ideally, the toe will be zero during maximum acceleration and braking (because this gives the maxiimum traction), but clearly this is not possible. With your car, the forces are probably greater during acceleration (you can smoke the tires on acceleration, but the brakes should be set to keep the rears from locking). It would therefore make sense to set a slight amount of toe out to get neutral toe during acceleration and not worry too much about braking.

But there is another consideration: oversteer/understeer. With toe in, the outer, heavily loaded tire will turn on a tighter radius than the car as a whole. This tends to counter oversteer. With toe out, the outer wheel turns on a wider radius than the car and this tends to aggrevate oversteer. Since you have no experience with your car and how it handles, I suggest you start with slight toe in settings. The car will be more stable and it will be easier to learn its behavior. You especially want to minimize the tendenancy towards trailing throttle oversteer as a trailing throttle is normally resorted to to try to gain control. After you are comfortable with the car, then you can experiment with other toe settings.

If the toe in or toe out settings are excessive, a sympton will be instability under hard acceleration or braking on uneven surfaces. The wheel with the best traction will steer the rear in the direction it is pointing. With equal traction, the car will go straight no matter what as the tires counteract eah other.

Camber:

Negative camber helps to keep the outer wheel upright under hard cornering. How much yoiu need depends on the camber gain during suspension compression and how much the car leans in corners. Excessive camber can derease traction in a straight line (both acceleration and braking) as the tires are not loaded evenly. So there can be a trade-off. But do not be afraid to experiment. Looking at vehicles on the road, it is obvious that most have way more negative camber in the rear than in the front. I suspect you could run up to 4 degress of negative camber if you wanted too, but it is good advice to start with a small amount such as the 1 degree that was suggested.

Shock Settings:

I do not know if your shocks are adjustable or not. After much experimentation I found that for the real world (bumpy pavement) optimal results are achieved with soft compression damping and firm rebound damping. This soft compression damping allows the wheel to easily deflect on bumps to maintain traction, then the firm rebound damping ensures rapid recovery after the bump. With stiff compressdion settings, the wheel tends to bounce on the pavement and traction is less. I do not recommend shocks where one setting changes both the compression and rebound settings together. Shocks with independent settings are very expensive, but good results can be obtained with shocks with fixed compression damping, and an adjustment for rebound damping.



roverman
Art Gertz
Winchester, CA.
(3006 posts)

Registered:
04/24/2009 11:02AM

Main British Car:
74' Jensen Healy, 79 Huff. GT 1, 74 MGB Lotus 907,2L

Re: IRS set-up, anti squat ?
Posted by: roverman
Date: March 18, 2011 04:27PM

Roll caster gain, or ? Rob, would those be QA 1 coil-overs ? If so, "tech line" should confirm possible use upside-down use,(less unsprung weight). Cheers, roverman.


rficalora
Rob Ficalora
Willis, TX
(2634 posts)

Registered:
10/24/2007 02:46PM

Main British Car:
'76 MGB w/CB front, Sebring rear, early metal dash Ford 302

authors avatar
Re: IRS set-up
Posted by: rficalora
Date: March 19, 2011 09:11AM

Hi Art -- They are QA1's; I'll have to call them... I have variable rate springs on them now & installed them upside down for that reason but didn't think about the shocks themselves.


roverman
Art Gertz
Winchester, CA.
(3006 posts)

Registered:
04/24/2009 11:02AM

Main British Car:
74' Jensen Healy, 79 Huff. GT 1, 74 MGB Lotus 907,2L

Re: IRS set-up/upside-down ?
Posted by: roverman
Date: March 21, 2011 02:15PM

In the "picture", they appear, body on bottom ? roverman.


roverman
Art Gertz
Winchester, CA.
(3006 posts)

Registered:
04/24/2009 11:02AM

Main British Car:
74' Jensen Healy, 79 Huff. GT 1, 74 MGB Lotus 907,2L

Re: IRS set-up/upside-down ?
Posted by: roverman
Date: March 21, 2011 02:32PM

In the "picture", they appear, body on bottom ? roverman.


rficalora
Rob Ficalora
Willis, TX
(2634 posts)

Registered:
10/24/2007 02:46PM

Main British Car:
'76 MGB w/CB front, Sebring rear, early metal dash Ford 302

authors avatar
Re: IRS set-up
Posted by: rficalora
Date: March 21, 2011 06:23PM

Shocks are installed "normal" -- variable rate springs are upside down. Note the coils are tighter at the top than the bottom -- coils are where most of the weight is. I am going to check into flipping the shocks over too but that's low on my priority list -- behind getting axles fixed & A/C freon lines crimped & filled (I'm not totally weight conscious as you can see).


J Man
jason adkins
NW OH
(194 posts)

Registered:
01/21/2009 08:49PM

Main British Car:
'61 Morris Minor panel, '70 MGB GT, '74 MGB GT MGB 1.8, unsure yet on the GTs

Re: IRS set-up
Posted by: J Man
Date: April 23, 2011 04:15PM

Who is Todd and can you offer more details on the IRS?


J Man
jason adkins
NW OH
(194 posts)

Registered:
01/21/2009 08:49PM

Main British Car:
'61 Morris Minor panel, '70 MGB GT, '74 MGB GT MGB 1.8, unsure yet on the GTs

Re: IRS set-up
Posted by: J Man
Date: April 23, 2011 06:24PM

I found the answer to my question but the Custom Rod Works site is down.


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