Am I watching "As the world turns"? Or is it a re-run of The Twilight Zone.... Either way If Ron Sutton is involved it will turn out kool... IF (BIG IF) Ron-Somewhere-in-the-world-or-maybe-so-cal... doesn't get involved and derail it.
Am I watching "As the world turns"? Or is it a re-run of The Twilight Zone.... Either way If Ron Sutton is involved it will turn out kool... IF (BIG IF) Ron-Somewhere-in-the-world-or-maybe-so-cal... doesn't get involved and derail it.
It's got a JRS designed C6 suspension with fabricated frame rails. Came out pretty good.
Quote:
Originally Posted by GregWeld
Am I watching "As the world turns"? Or is it a re-run of The Twilight Zone.... Either way If Ron Sutton is involved it will turn out kool... IF (BIG IF) Ron-Somewhere-in-the-world-or-maybe-so-cal... doesn't get involved and derail it.
You sure about that? Payton thought the same thing....
Quote:
Originally Posted by Ron in SoCal
It's got a JRS designed C6 suspension with fabricated frame rails. Came out pretty good.
I guess it's a good thing we got it out of Jakes before he got in deeper.
It still seems with the Sutton designed offset three link with adjustable on the fly instant center and roll center out back and Jakes stuff up front the carpet won't match the drapes.
It still seems with the Sutton designed offset three link with adjustable on the fly instant center and roll center out back and Jakes stuff up front the carpet won't match the drapes.
Hey Rob! Great to hear from you. I hope your time frees up in the near future.
As you may have heard me say a bajillion times, we can not go faster through the corner that the front end has grip. That is typically our limiting factor. I say "typically" because it is not very difficult to get the rear tire grip to match the front ... in most cars ... to achieve neutral, balanced handling. We simply need to tune the rear grip up or down to match the front grip ... for this neutral handling. If we don't, then we have a loose or pushy car.
Do I feel this will be the fastest front suspension design? No. But it's pretty good. I advised Ron against replacing it ... more as an exercise in cost vs gain. I can't speak for Ron Myers ... but I understand his goal to have a fast, fun track car without breaking the bank. It would cost $12k (parts & labor) to cut off & replace the JRS clip with my latest long arm/zero scrub design. The lap times would be measurably better ... but is spending $12k after already having this built worth that gain? I think each person has to make that decision, but I suggested he finish the car with the current front suspension and go have fun with it.
On a different note ... and just for educational sake ...
With a few minor exceptions, the rear suspension design has no impact on mid-corner "roll through zone" grip or corner speed capability.
I just heard a lot people say, "What?"
The factors that DO play a roll on mid-corner "roll through zone" grip & corner speed capability are:
CG, Roll Center & Track Width
Mechanical Roll Resistance: Spring & Sway Bar Rates
Shock Valving
Whether you have a 3-link, 4-link, 196-link, IRS, torque arm, truck arm, etc ... is irrelevant to mid-corner "roll through zone" grip & corner speed capability … because there is no torque (engine or braking) being put through the rear suspension during the mid-corner "roll through zone." The few minor exceptions to this, are if the rear tires have camber, toe or rear steer from the rear suspension design. Those items can affect mid-corner "roll through zone" grip & corner speed capability. Another exception is rear suspension bind … which can have an obvious, negative effect on handling. But frankly, all of these … camber, toe or rear steer … and even suspension bind … are possible with most suspension designs.
So why do we care what rear suspension design we run?
Corner entry & corner exit.
The choice of rear suspension design … and the key details in the rear suspension design … all play a role in how much rear grip the car has on corner entry (turn-in & braking) and corner exit (steering unwind & throttle roll on).
While there are a lot of details (18 to be exact) in optimizing a solid axle link suspension, the biggies during design, or purchase selection, are:
1. Articulation
2. Torque Distribution
3. Instant Center
4. Packaging
5. Pinion Angle Change
6. Rear Roll Center
7. Adjustability
Articulation is the amount of angle differential the housing can achieve from the chassis. Maybe not so obvious ... but we need the rear housing to articulate at least as far as the chassis needs to roll. This matters more if you're running a conventional suspension strategy that rolls 3° or more. This is less of an issue if you're running a modern low roll suspension strategy that rolls around 1°.
Torque Distribution is not understood by most. We've been trained (wrongly) to just look at anti-squat for our rear tire loading geometry. But when you attach suspension link brackets to a live axle with torque coming through it ... the link brackets become levers ... and the location completely affects how much of the torque is pushing the lower links & car forward ... and how much of the torque is lifting the chassis & loading the rear tires for grip. This is CRITICAL for optimum forward bite on corner exit ... especially with harder TW200 tires. 3-links & 4-links ... if room above the housing allows the brackets to be tall ... allow optimum torque distribution for grip. Offset 3-links allow optimum torque distribution side-to-side ... for zero torque steer ... allowing equal handling on LH & RH corners. The Offset, Decoupled 3-link offers separate & optimum tuning for corner entry & corner exit grip.
The Instant Center is your rear suspension pivot point as well as the point it picks up on the chassis to load the tires. Where it is in relation to the CG is very important. Too short & it will lose traction late on corner exit. Too long and it will spin the tires upon initial throttle roll on. This needs to be tunable & optimized to your car. I typically start with it under the CG & fine tune for track conditions.
Packaging in the PT world is probably at the top of the list. When someone is asking for my recommendation for their car ... the first I ask is, "Are you keeping the rear seat?" If the answer is yes, we should eliminate all three versions of the 3-link ... because where they really need to mount conflicts with the rear seat. Frankly so do parallel 4-links, unless the top links are ridiculously low & short. If the back seat stays ... the triangulated 4-link & Torque Arm suspensions are the best of what will fit & allow a back seat. If the back seat goes & we can remodel the sheet metal in the rear floor & trunk area... it's wide open. 3-links & 4-links allow optimum torque distribution for grip. 3-Links offer the most articulation. Offset 3-links allow optimum torque distribution for zero torque steer ... allowing equal handling on LH & RH corners. The Offset, Decoupled 3-link offers separate & optimum tuning ... for the ultimate grip on corner entry & corner exit.
Pinion Angle Change happens greater when the top links & lower links are short or have a large difference in length. It also happens with weak/soft leaf springs & lots of power. It's not the end of the world. You just have to plan & deal with it.
Rear Roll Center adjustment ... to me, from my experience, for track tuning ... is one of the easiest, more predictable tuning devices you can ever have to help balance & neutralize the handling of the car. It's simple. Raise it to free the rear end up. Lower it for more rear grip. Don't go outside the sweet spots. Having a rear suspension with no adjustment for the rear roll center really ties your hands. It eliminates one of the best tuning devices out of your tool box. You can run a double adjustable panhard bar or adjustable Watts link with any suspension but IRS. Yes ... even leafs & triangulated 4-links.
Adjustability is KING for track cars. if you can adjust the instant center height & distance ... adjust lower links for rear steer ... adjust the rear roll center ... you have a rear suspension you can optimize for your car. Not adjustable? How do you optimize it?
Lastly, all rear suspension designs are a compromise for corner entry grip versus corner exit grip ... with the exception of a decoupled 3-Link. (See illustration below) With IRS & all link style suspensions the geometry needs are different for corner exit & entry. So your goal is to find the best, fastest "compromise" ... which is the best grip available on corner exit without making the car loose on corner entry.
The exception is the decoupled 3-link ... because we can set the accel link for optimum corner exit grip ... with no affects on corner entry. Conversely, we can set the decel link for optimum corner entry grip with no affects on corner exit. Because they decoupled from each other. But everything has it's cons. The decoupled 3-link takes up a lot of room behind the roll cage main hoop ... and rides rougher (like it has a stiffer spring rate).
Summary:
• The highest performance rear suspension for track purposes is the Offset, Decoupled 3-Link.
• Next would be the Offset 3-Link.
• Next would be a regular centered 3-Link or 4-link (as long as articulation is not an issue).
• None of these will fit well under a seat, unless the top links are super short (not recommended).
• The best that fit under the seat are triangulated 4-links & torque arms.
• Regardless of choice ... make them adjustable ... as well as the rear roll center.
Brian Hobaugh SCCA National Tour June 2014
First Hemi 'Cuda Convertible Ever Built
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