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Old 2003.01.16, 11:58 PM   #1
Adult_driver
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Modena, Finally Drives

Finally, I got the suspension and steering tuned so that this car drives controllably on hardwood (a severe test of man and machine). What a lot I went through to get here. It is amazing how subtle the handling influences are.

First upgrades were a Kyosho Ball Diff and MZR bearings. The MZR bearings are so free rolling that the slight unevenness in the rubber of the tire causes the heavy part of the tire to settle to the bottom. That helped, but it only encouraged me to drive faster and then I was out of control again.

Next I made a "square" rear plate. It is amazing how precisely you must drill the holes. If the pairs of holes on each end of the plate aren't exactly parallel and exactly square to the long axis of the car, you can't ever get it to steer. Finally, through careful work I finally got an accurate plate. But, I think it was too stiff and I think the front end suspension would bind on the king pins.

Next came a 3 degree toe-in (Square) and 2 degree camber knees. These are very precisely made and the front suspension compresses and rebounds with no resistance, except the spring. I went to the stiffest springs. Boy, the car ran straight but would not turn, except at very low speeds. Somewhere along the way I tightened the differential. That also helped going straight at speed.

I went down to 2 degree toe-in. Now the car could turn. But one of two things would happen--at speed in a straight away, the reaction to a steering correction would be delayed, I would over-react and turn too much, and then the front wheels would bite and it was all over (so to speak). Or, when I aimed correctly down the straight away and slowed down to turn, the oversteer was severe.

Now I start analyzing this, reading a lot in the forums, and doing my homework. The stiff back-end and stiff front end were about the worst combination I could have chosen. First, I softened my "square" plate and turned it into an 'O' plate by removing the center. This made the back-end more compliant vertically, but still allows almost no sideways twist. So, I get the benefit of no roll, but with a rear-end just moderately more stiff than stock. I think with the Modena's long wheelbase position, the stock H plate is too soft (in the med. wheelbase position it is just about right, though still too twisty). I also use the ear plug trick as a dampener, though I need slightly softer ear plugs.

At the same time, I switched the front end from the yellow hard springs to the stock springs. Now the softer front end could result in too much oversteer. But, my problem was initiating any turn at all. Softing the front end compensates for the understeer of the toe-in (I will try 1 degree next. Three degrees was too harsh. Two is drive-able.) And the simultaneous softening of the back-end gives the back-end enough additional traction to keep the rear tires on the driving surface enough to prevent the front softening from causing spinouts or excess oversteer.

Now, I am happy. The Modena is much easier to drive and I can reach higher speeds in the straight aways and still turn into the curves without slowing down too much. It really works noticeably better. I had to assemble a reasonable repertoire of different parts before I could try a good range of alternatives. It amazing how significant the effect is of such apparently (at least to our big bodies) subtle changes.

So, my theory on why the Modena, despite being one of the longest, widest stance Z's can be so hard to drive is this. Because of the huge added offset in the front wheel to increase width--easily 3/16"--the general slop of the z steering works with a very large radius so that with zero or negative toe-in, the front wheels wiggle through a very large arc at the ends of the axles. Narrower cars have the same slop, but the absolutely arc of "wiggle" is less. So, the toe-in corrects the slop, then you need to balance the toe-in to still be able to turn. I think it would be even better to elimate the slop because excess toe-in is harsh medicine that requires a lot of subsequent compensation.

So, the final setup is:

rear suspension: custom moderately stiff 'O'plate with ear plug dampener
front suspension: stock springs (moderately soft)
front steering: 2 degrees toe-in, one degree camber

The final experiment with this setup will be the adjustable front roll bar. With the Square toe-in and knuckles the suspension movement is so smooth (a good thing) that the anti-roll bar does almost nothing. I think the front wheels will stay in better contact with the driving surface with less roll in the curves. This is the final adjustment to compensate for the increased roll of the softer front springs.

There you have it.
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Old 2003.01.17, 11:08 PM   #2
Skylineboy
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Adult_driver,

Are you still running on stock tires?

They are not very good in terms of grip (on wooden floor)and it will be worth while to invest in some softer compound tires.

You'll be surprise by how well your car can be glued to the ground just by having softer compound tires.

My Z is pretty much stock (with the exception of springs, rear shock, tires and H-plate which I've changed), I've got the to the stage where oversteer does not occur at all.

If you do a search on your "tires", I'm sure you'll find a lot of info.

Have fun with your Z.

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Old 2003.01.17, 11:41 PM   #3
mini-zfuel
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my setup...:)

great post adult... my modena has:

red soft kyosho front springs...( are the stocks any softer do you or anyone know???)

powerline rear spring shock with blue spring

powerline roll shock set with yellow springs

powerline t-bar (medium one) (still considering mzr.com o plate)

stock tires on square 360 modena gt cup aluminum wheels

so far so good she runs great!!!

anyone got any ideas???
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Old 2003.01.17, 11:42 PM   #4
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oops...

forgot to add I run on a flat concrete garage track, and maybe moving up to an ozite layed garage track soon but right now shes running ok
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Old 2003.01.18, 07:12 AM   #5
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Re: my setup...:)

Quote:
Originally posted by mini-zfuel

red soft kyosho front springs...( are the stocks any softer do you or anyone know???)

miniz-fuel,

From memory, the stock springs are slightly stiffer than the red ones.

Skylineboy
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Old 2003.01.18, 09:38 AM   #6
mini-zfuel
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thanks skyline... anyone else verify this???
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Old 2003.01.18, 12:30 PM   #7
Adult_driver
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Tires on Modena

I tried the 30 tires and they were slicker than the 50s. Maybe because I had broken in the 50s on concrete. But, I took sandpaper to the 30s and they were still slippery. I think the 30s are sticky enough that they picked up so much dust so quickly that they became slippery. Anyway, I sort of came up with the notion that hard surfaces require hard tires and soft surfaces require soft tires.

Should I give the 30s another try?

I also discovered that I need to get the ball diff. as tight as is usable for good straightline tracking.
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Old 2003.01.18, 12:37 PM   #8
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you got it backwards: soft tires for hard, slick surfaces, and hard tires for, grippy surfaces.
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Old 2003.01.18, 12:45 PM   #9
mini-zfuel
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so what are the stock kyosho modena tires??? 50 all around???
thanks
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Old 2003.01.18, 12:52 PM   #10
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i think so
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Old 2003.01.18, 01:24 PM   #11
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if it's running on hardwood surface, it's better to use foam tires..
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