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Question - Improved Camber Curve

Shocks, Springs, Brakes, Frame, Body Work, etc

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MadBill
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Re: Question - Improved Camber Curve

Post by MadBill »

With all the suspension mods under consideration, at least one more parameter will need to be addressed, i.e. bump steer.
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Re: Question - Improved Camber Curve

Post by enigma57 »

I agree, Bill. Bump steer must be addressed any time front suspension and steering mods are proposed. However, when retaining the OEM steering gear and original locations of control arm pivot points and ball joints, I have not encountered bump steer on these '55 - '57 Chevys in years past.

Initially, when I was planning for more extensive mods to steering, suspension and drivetrain in support of the 427 small block stroker engine I was building 20 years ago..... The plan was to go with optional 1975 Chevy station wagon/cop car 12" disc brake rotors and build mounting brackets for Aussie PBR calipers (functionally, the same calipers as Baer Brakes use)...... And to install a rear steer power rack and pinion unit from the early '90s Buick FWD T-type and cop cars (quicker power steering with more road feel). Because of the wider position of inner tie rod ends with the R&P unit though...... Either the R&P inner tie rod position must be shortened or the control arm pivot points and ball joint positions must be modified to prevent bump steer...... Much as Jim Meyers did when fitting the Buick R&P units to these cars.

There is a way to do it without modifying the R&P unit (retain original steering cross link and add a 2nd idler arm to replace original steering box and pitman arm...... Then fit R&P unit to move original cross link) but I see no reason to take that step.

So will rebuild original steering and add greasable needle bearings to replace OEM rubber idler arm bushings and modify only the ends of the '57 lower control arms to allow mounting the lower ball joints and larger drum brakes and spindles from the '59 - '64 cars. Planning on keeping the OEM ball joint positions (both upper and lower). May install a set of shorter steering arms I have here to speed up the slow 20:1 OEM manual steering box ratio. But other than the usual stiffening of spring rates and shock valving and adapting large diameter anti-sway bars front and rear, I will keep front suspension and steering mods to a minimum.

I will be getting back into this project when I am recovered more from the medical treatment and will let you know how it works out.

Best regards,

Harry
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Re: Question - Improved Camber Curve

Post by enigma57 »

P.S. >>> Bill, I dropped the ball in my earlier post. By increase in bump steer, I assume you mean increased toe-out from bump travel resulting from installation of either taller spindles or upper ball joints having 0.5" taller studs in an effort to increase negative camber gain?

Thanks,

Harry
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Re: Question - Improved Camber Curve

Post by MadBill »

You'll have to research the subtitles (lots of info out there), but almost everything you're planning, including caster changes, affects it and the effects especially for roll oversteer can be pronounced. Some race car builders won't settle for more than say 0.010" toe change through perhaps 5" of suspension travel. Production street cars with rubber bushings are far less sensitive but it should always be a consideration.
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Re: Question - Improved Camber Curve

Post by dannobee »

And to further show the importance of bump steer, in circle track racing I'd shoot for 0.000" toe change over 4" of travel on the right side and a toe out of 0.020" per inch of travel on the left side as that side lifts. Zero change in either side with 4" travel on the road race car.

I cringe and shake my head when I see some car build on teevee and the fabricator welds on suspension brackets by guess and by golly. No engineering or forethought in the process at all.
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Re: Question - Improved Camber Curve

Post by enigma57 »

Thanks, Bill and Danno! I will look into this further and educate myself on suspension mods more before making any hard and fast decisions on suspension mods.

Best regards,

Harry
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Re: Question - Improved Camber Curve

Post by David Redszus »

Vehicle suspension analysis is a very complicated and interesting topic. Nothing is as it seems.

While substantial time is spent on caster, camber, toe, Ackerman, bump, SAI, very little is normally spent
on the dynamic behavior.

The front geometry is impacted not only by dive, but also on lateral weight transfer, chassis roll, and steering
angle. What we really would like to know is the camber and toe in the middle (and other parts) of a corner,
not just on the alignment rack or scales. Oh, forgot to mention motion ratio, damping, wheel rate and frequency.

When we set up road racing sports cars, the first step is to use a real time infra-red temperature sensor while circling
a skid pad. It is also useful to measure turn radius, lateral G forces, slip angles, and steering angle.

This works very well if the car is already built and suitable for testing. If not, we must rely on suspension
simulation programs to get us close to where we woulda shoulda been.

And then, of course, there's tires. What camber do your tires like to run at? For how long and at what temperature?
How does tire pressure (and design) affect tire spring rate and frequency?

Brakes are another fun topic. Larger brake friction material swept area does not improve braking performance.
Not a bit. An accurate understanding of brake force distribution while under weight transfer (lateral and
longitudinal), is necessary to improve stopping performance. Again, calculations will save large amount of time and money.

All of which simply means we will spend even more time and money trying to get things right. :lol:
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Re: Question - Improved Camber Curve

Post by enigma57 »

Holy guacamole! Y'all are dead set on dragging me kicking and screaming right into the 21st century here. Gee...... All I want to do is take a 63 year old Chevy though the turns at speed on street tires in a manageable Grand Prix drift and come out the other side with at least 2 wheels on the ground. :shock:

Just kidding. Well, sort of. We used to push these '55 - '57 Chevys through the twisties pretty hard in the early '60s with the notion that any ride you can walk away from is a good ride. Reckon you can get away with quite a bit if you don't know you're not supposed to be able to do it. I remember how I set mine up back then. Would like to do a little better on this last build. Will study the subject whilst I'm laid up and give you a holler as questions arise.

One thing's for sure...... Tires have improved exponentially since then. So making the suspension work well with today's modern tires will be a definite consideration, as well.

Happy Motoring,

Harry
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Re: Question - Improved Camber Curve

Post by lewy-d »

"Larger brake friction material swept area does not improve braking performance"
to make sure I understand. are you saying a larger disc does not improve braking performance?
What are the ways to improve braking performance?
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Re: Question - Improved Camber Curve

Post by David Redszus »

lewy-d wrote: Thu Nov 19, 2020 8:49 am "Larger brake friction material swept area does not improve braking performance"
to make sure I understand. are you saying a larger disc does not improve braking performance?
What are the ways to improve braking performance?
Now that you asked, here are a few brake component relationships to consider:

+ disc dia = + brake torque, + wheel force
+ tire dia = - wheel force
+ puck dia = + brake torque, + wheel force
+ MC dia = - brake torque, - wheel force
+ pad Mu = + brake torque, + wheel force

Brake pad surface area has no effect on brake performance, except that larger pads last longer.
Pads with a higher friction coefficient (Mu), require less pedal force.

Calipers with multiple (or larger) pucks will also use larger pads, but it is the increased hydraulic force produced
by the pucks that is responsible, not the pads.

Now the fun begins. What combination of disc dia, tire dia, puck dia (and number of), master cylinder dia,
and pad friction coefficient, will produce the best braking for a specific vehicle?

Forgot to mention tire grip and vehicle weight transfer as affecting brake balance.
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Re: Question - Improved Camber Curve

Post by Kenova »

David Redszus wrote: Thu Nov 19, 2020 11:59 am
Now the fun begins. What combination of disc dia, tire dia, puck dia (and number of), master cylinder dia,
and pad friction coefficient, will produce the best braking for a specific vehicle?

Forgot to mention tire grip and vehicle weight transfer as affecting brake balance.
I have seen the mathematical formula for figuring that out.

It made my head hurt.

Ken
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Re: Question - Improved Camber Curve

Post by MadBill »

David Redszus wrote: Thu Nov 19, 2020 11:59 am Forgot to mention tire grip and vehicle weight transfer as affecting brake balance.
Also downforce and thus maximum braking force diminishing with the square of the speed as you slow...
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Re: Question - Improved Camber Curve

Post by David Redszus »

MadBill wrote: Sun Nov 22, 2020 11:53 pm
David Redszus wrote: Thu Nov 19, 2020 11:59 am Forgot to mention tire grip and vehicle weight transfer as affecting brake balance.
Also downforce and thus maximum braking force diminishing with the square of the speed as you slow...
We have examined the braking forces required for aero race cars. We find that almost none can
produce enough brake force to match grip at maximum speed and downforce.

The practical solution is to have the driver lift at max speed to allow air braking and then apply
brakes as the vehicle slows.
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Re: Question - Improved Camber Curve

Post by MadBill »

The broadcast cockpit data readouts from current Formula 1 cars show as much as 6 Gs deceleration at high speed. :shock:
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Re: Question - Improved Camber Curve

Post by David Redszus »

MadBill wrote: Tue Nov 24, 2020 12:05 am The broadcast cockpit data readouts from current Formula 1 cars show as much as 6 Gs deceleration at high speed. :shock:
And, those decel Gs don't wear out tires. :D
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