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Old 12-28-2011, 02:52 PM   #631
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Widening the track width reduces lateral weight transfer, which increases lateral grip. So in theory, given that less weight is transferred, it *should* react faster since the maximum load on the tire is reached sooner. However, track width changes are much less influential on roll center characteristics as compared to the arm mounts for example, SO I'm not sure that you would even notice a change in reaction time based off just that, except in very high bite situations. The increase in lateral grip would be more noticeable I'd imagine.

In low bite, max track width aids grip and stability. In high bite, narrowing the rear end increases lateral weight transfer, which decreases lateral grip, giving you more steering. I always like the front of the car 3-4mm wider than the rear.
That's how I see it........
I disagree on the track width aspect. A narrower car has a relatively higher center of gravity, therefore it induces more weight transfer, which generates more body roll, which makes more traction. This is why when a car is too twitchy (and especially in offroad cars) they are made wider in the front than the rear- to make them less reactive, i.e. less grip.
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Old 12-28-2011, 02:55 PM   #632
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I would say you can have the same grip but different handling characteristics..... so making the car more reactive might not necessarily take away or add grip.

Thoughts?
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Old 12-28-2011, 03:08 PM   #633
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And I never know I'm wrong until someone else points it out, so at the least I can just provide fodder for discussions

On a related note, got the new ballstuds yesterday....... BUTTER SMOOTH!
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Old 12-28-2011, 03:10 PM   #634
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To control reaction, I typically use the springs (a heavier one allowing quicker reaction), but mostly oil to control reaction time.

To me, reaction time kind of goes hand-in-hand with grip, the more grip one end of the car has, the quicker it will react. Obviously, everything goes in a bell curve. At the extremes, the effects are not linear, if not contradictory.
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Old 12-28-2011, 03:22 PM   #635
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Originally Posted by CristianTabush View Post
To control reaction, I typically use the springs (a heavier one allowing quicker reaction), but mostly oil to control reaction time.

To me, reaction time kind of goes hand-in-hand with grip, the more grip one end of the car has, the quicker it will react. Obviously, everything goes in a bell curve. At the extremes, the effects are not linear, if not contradictory.
SO in certain conditions my presumptions might be correct.....?....

I've had my car traction roll with 2 and 3B... going to 3A or 0B helped. The car had less roll (weight transfer) but too much lateral grip, and increasing the difference of weight transfer between the inner and outer tire took away that lateral bite.
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Old 12-28-2011, 03:38 PM   #636
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What you might be experiencing that causes the traction rolling is suspension jacking.

Read up on one of the John Stranahan threads on it. Or do a google search for it.

How I understand it, a higher roll center gives less body as it requires more leverage due to the position of the roll center. But on the extremes, so much force is exerted trying to make the body roll that it actually induces a violent traction roll. From what I understand, this is caused by what is called "suspension jacking". Lowering the roll center decreases the possibility of suspension jacking, therefore decreasing the tendency to traction roll, however, with the lower roll center, you need a stiffer spring to control the body roll.

As for the presumptions, yes. However, you are so far out on the curve that you are actually coming to your findings sort of "accidentally". The results would not be consistent in a case to case basis.

I learned a lot about tuning with car widths when I raced Mini-Z a lot. It was one of the main adjustments we used to fine tune our car. Typically in a high grip track you ran a long, wide car. In low grip circumstances, you ran narrow and short.
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Old 12-28-2011, 03:50 PM   #637
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Originally Posted by CristianTabush View Post
I disagree on the track width aspect. A narrower car has a relatively higher center of gravity, therefore it induces more weight transfer, which generates more body roll, which makes more traction. This is why when a car is too twitchy (and especially in offroad cars) they are made wider in the front than the rear- to make them less reactive, i.e. less grip.
Track width has no impact on CG height. Cory, you are correct that increasing track width decreases weight transfer laterally. However, decreasing weight transfer by itself and leaving everything else constant would decrease lateral grip. Weight transfer is rate independent. Rate of weight transfer is constrained by the geometry of the sprung mass relative to the unsprung mass, the moment of inertia of the sprung mass and the lateral acceleration induced. The rate is controlled by all the springs and dampers (including the tires) within that system.

Increasing track width also increases the overall moment arm of the tire contact patch to the CG. This tends to provide increased grip in steady-state conditions after the transient weight transfer is completed. The balance comes in where you can decrease weight transfer more than you increase your moment about the CG (on a % basis) and you have less overall grip. Track width spacing at the hub is particularly effective for increasing the moment without large impacts to weight transfer, but does have the side-effect of offset change, which changes your scrub radius. Track width spacing at the inner arm points is particularly effective for decreasing weight transfer and I use it all the time to take reactivity out of the front end.
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Old 12-28-2011, 03:50 PM   #638
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SO softer springs with the lower roll center would also cause traction roll. On our low/sometimes medium bite carpet, you almost strive for traction roll to keep grip.

I don't have enough experience on really high bite, so usually when I spout off it's based off of what works for me on low bite.
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Old 12-28-2011, 03:59 PM   #639
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SO softer springs with the lower roll center would also cause traction roll. On our low/sometimes medium bite carpet, you almost strive for traction roll to keep grip.

I don't have enough experience on really high bite, so usually when I spout off it's based off of what works for me on low bite.
Generally, yes - though not in all cases. Softer springs can also reduce traction roll tendencies depending on what else you have going on with your geometry. What is the hardest to ascertain while driving is where exactly the traction roll happens: entry, middle or exit. Exit is rare but can happen via throttle application. Entry usually means you aren't controlling your weight transfer rate effectively and so you need to look at things like springs & dampers, glued tire sidewalls and camber. Middle is where your roll centers and track width can be most effective at combating traction roll.
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Old 12-28-2011, 04:04 PM   #640
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Track width has no impact on CG height. Cory, you are correct that increasing track width decreases weight transfer laterally. However, decreasing weight transfer by itself and leaving everything else constant would decrease lateral grip. Weight transfer is rate independent. Rate of weight transfer is constrained by the geometry of the sprung mass relative to the unsprung mass, the moment of inertia of the sprung mass and the lateral acceleration induced. The rate is controlled by all the springs and dampers (including the tires) within that system.

Increasing track width also increases the overall moment arm of the tire contact patch to the CG. This tends to provide increased grip in steady-state conditions after the transient weight transfer is completed. The balance comes in where you can decrease weight transfer more than you increase your moment about the CG (on a % basis) and you have less overall grip. Track width spacing at the hub is particularly effective for increasing the moment without large impacts to weight transfer, but does have the side-effect of offset change, which changes your scrub radius. Track width spacing at the inner arm points is particularly effective for decreasing weight transfer and I use it all the time to take reactivity out of the front end.
Brian, thanks for the correction, it's not the cg I am referring to, but perhaps relative CG? Instant Roll center? My terminology is off.

I don't remember the specific schematic, but there is more weight transfer with a narrower car. A narrower car will generate much more mid corner traction. Can you clarify what is at play here?
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Old 12-28-2011, 04:08 PM   #641
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Originally Posted by Brian McGreevy View Post
Generally, yes - though not in all cases. Softer springs can also reduce traction roll tendencies depending on what else you have going on with your geometry. What is the hardest to ascertain while driving is where exactly the traction roll happens: entry, middle or exit. Exit is rare but can happen via throttle application. Entry usually means you aren't controlling your weight transfer rate effectively and so you need to look at things like springs & dampers, glued tire sidewalls and camber. Middle is where your roll centers and track width can be most effective at combating traction roll.
Springs are confusing, because every car comes with different ratings. Associated includes 14.5/12, XRAY is 17.5/14 or the 3.0/2.6 black springs. I've heard the TOP likes nearly 22 up front...........
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Old 12-28-2011, 04:14 PM   #642
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Springs are directly related to your roll center. Basically, you have to match the 2.

The TC6 comes with a high Roll center, therefore, soft springs. The XRAY comes with sort of low roll center, hence the stiffer springs.

John Stranahan used to always say that you should try to get away with the softest spring possible. It aids in road compliance, allowing for better acceleration through bumps. However, you have to match the spring rate with roll center. High roll center, soft springs, low roll center, stiff springs.

Roll center theory is just that a theory. From what I have read, and learned through out the years, it really makes no difference, so long as you match it with your spring rates. All roll centers can work, however in bumpy conditions, you might want to run a high roll center with soft springs, to get better bump compliance and in high, high grip conditions you want to run a low roll center with stiff springs, to reduce suspension jacking and traction rolling.

If you are anywhere in the middle, as long as your car gets around the track quickly, then you are doing it right.
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Old 12-28-2011, 04:15 PM   #643
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Originally Posted by CristianTabush View Post
Brian, thanks for the correction, it's not the cg I am referring to, but perhaps relative CG? Instant Roll center? My terminology is off.

I don't remember the specific schematic, but there is more weight transfer with a narrower car. A narrower car will generate much more mid corner traction. Can you clarify what is at play here?
(Car weight x CG height)/Track width

Using the example from Martin Crisp's setup app....

(1500g x 20mm)/185 = 162g weight transfer

So lowering the CG and/or increasing track width reduces lateral weight transfer, which increases lateral grip in *most* conditions...... yes?
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Old 12-28-2011, 04:19 PM   #644
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So in both scenarios you would generate more grip depending on the springs and/or roll center.
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Old 12-28-2011, 04:21 PM   #645
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Reducing lateral weight transfer, takes away lateral grip. I think you read wrong Codyin what Brian corroborated in his statements.

Just think about it this way. If you have more weight move to the outside tire, there will be more pressure on that tire, therefore creating more grip.
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