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Tweak and TC setup question

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Tweak and TC setup question

Old 02-17-2019, 01:28 AM
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I didn't mentioned the shock absorbers length, wich is very important (otherwise you'd have to mismatch spring preload). Has to be perfectly equal (at least from right to left side)
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Old 02-17-2019, 05:43 AM
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Originally Posted by jakelamotta View Post
I didn't mentioned the shock absorbers length, wich is very important (otherwise you'd have to mismatch spring preload). Has to be perfectly equal (at least from right to left side)
yes that's something that can be overlooked. But, they are perfectly equal length.
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Old 02-17-2019, 08:57 PM
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Because the way I adjust tweak is really just a way to measure chassis flex you can use it to make sure the flex is even left to right but it also allows you to measure what happens when you do things like go from a conventional top deck to a VTD or shimming the top deck or leaving screws out. You can measure the flex characteristics of changes.
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Old 02-17-2019, 09:41 PM
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If you've tried to straighten the chassis but it's still tweaked, BEFORE adjusting the shock preloads to compensate, FIRST max-out the shock preloads and check the droop screws. The purpose of maxing-out the shock preloads is so you can easily see if the car is trying to balance on three wheels -- if one wheel is slightly in the air, or even if the tire on that wheel is compressed slightly less than the others, you need to loosen the droop screw on that wheel -- or tighten the droop screws on both diagonal-opposite wheels. THEN reset the preloads to what they used to be, and adjust the preloads as necessary to achieve symmetrical ride-height.
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Old 02-18-2019, 06:23 AM
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Originally Posted by fyrstormer View Post
If you've tried to straighten the chassis but it's still tweaked, BEFORE adjusting the shock preloads to compensate, FIRST max-out the shock preloads and check the droop screws. The purpose of maxing-out the shock preloads is so you can easily see if the car is trying to balance on three wheels -- if one wheel is slightly in the air, or even if the tire on that wheel is compressed slightly less than the others, you nceed to loosen the droop screw on that wheel -- or tighten the droop screws on both diagonal-opposite wheels. THEN reset the preloads to what they used to be, and adjust the preloads as necessary to achieve symmetrical ride-height.
That's really good advice here...didn't think of that. I used the conventional method with the 2 blocks underneath the chassis. Will give this a try. Thanks
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Old 02-18-2019, 04:49 PM
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If your chassis is relatively flat and your weight distribution as close to optimal as possible, then all you need is the four corner weights to match (X pattern and side to side) when the rideheight is the same all around...Four scales works better than a tweak station....
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Old 02-18-2019, 08:24 PM
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Originally Posted by bertrandsv87 View Post
If your chassis is relatively flat and your weight distribution as close to optimal as possible, then all you need is the four corner weights to match (X pattern and side to side) when the rideheight is the same all around...Four scales works better than a tweak station....
I dont use a tweak station anymore and i agree corner scales make the whole process easier because im watching numbers but the weight gets distributed by the springs. If the springs are the same and the collars are the same but the ride height is not the same or vice versa weight is getting distributed by the chassis. Assuming the mass is evenly distributed.

Another tell tale sign is uneven wear on tires. Not inside to outside of 1 tire but a LR+FR that always has a higher temperature in left and right turns than rr+FL. The car will be twisted in a way that the LR+FR under load is stiffer that the opposite corners. The stiff corners act like a fulcrum in both turns. In this case an acceleration or brake mid corner will be different in left turns than right turns.

running a temp sensor across all tires and logging temps and tire averages tells allot about chassis rigidity.
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Old 02-19-2019, 07:08 PM
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That's true, my Nitro RS4 3's always wear-out the right-rear tire faster than the left-rear tire because that's the tire supporting most of the engine's weight. (the Nitro RS4 2 is a lot better because it has a transverse-mounted engine -- but woe unto you if you need to service that chassis.) There's only so much you can do about that problem on a chassis with a big heavy engine bolted to it. It's much easier to balance an electric chassis, because if nothing else you can put the motor and electronics on one side and the battery on the other side, then shift parts front-to-rear as needed to dial-in the balance.

Although, it could be argued that by the time you see visibly-asymmetric tire wear, the problem has existed for so long that you've subconsciously adjusted your driving to compensate.
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Old 02-19-2019, 07:31 PM
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Originally Posted by bertrandsv87 View Post
If your chassis is relatively flat and your weight distribution as close to optimal as possible, then all you need is the four corner weights to match (X pattern and side to side) when the rideheight is the same all around...Four scales works better than a tweak station....
I disagree about matching corner-scale readouts being the ultimate metric. (I intentionally called them "readouts" instead of "weights" because suspension settings and tire compliance, plus even microscopic chassis tweak, will always cause the readouts to not accurately represent the real weight of each corner.) For starters, you don't necessarily want the front corner-scale readouts to match the rear corner-scale readouts, since the front wheels follow different lines when cornering than the rear wheels do. Even though it's a useful simplification for new drivers to think about, chassis rotation is never exactly around the centerpoint -- especially when aerodynamic downforce is taken into consideration, because that is one variable that changes constantly when the vehicle is moving. As several older members here like to say, track performance always trumps bench measurements.

If you've checked the droop settings and they are correct (compensating for any remaining tweak in the chassis) and your shocks are built correctly (exactly the same length and whatnot), then you can tell if the rear suspension is adjusted properly just by lifting the front axle by its centerline. (a 0.9mm hex wrench, or a ballpoint pen, is useful for this.) If both front wheels lift off the ground at the same instant, the rear suspension has been correctly adjusted to support its weight-balance evenly. Likewise for checking the front suspension by lifting the rear axle by its centerline. Unless your chassis is perfectly balanced left-to-right, this will cause the preloads for the left and right shocks to be slightly asymmetrical, thus the corner-scale readouts will also be slightly mismatched, and the tires supporting more weight will wear-out faster, but tires are consumable items so who cares. I consider it more important to make sure the chassis is evenly supported so it doesn't lean and flex differently in left corners vs. right corners, rather than tuning the suspension to have matching corner-scale readouts. If the chassis is even slightly imbalanced, matching corner-scale readouts would actually indicate the shocks supporting the heavier corners aren't actually supporting the weight close to them properly, causing the chassis to flex diagonally as that inadequately-supported load is redistributed to the diagonal-opposing wheels. Does the chassis actually bend enough to affect handling in that scenario? I dunno, but this is the Electric On-Road subforum, where people argue over milligrams and milliseconds, so...

Last edited by fyrstormer; 02-19-2019 at 07:43 PM.
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