# Help tuning mid-motor JRX-S for VTA



## gndprx (Aug 30, 2006)

Howdy all.

I have an older mid-motor JRX-S that I'm using for VTA racing on a concrete short and tight track. 27T/4-Cell with the battery in the forward position. 

The car was perfect with takeoff 27's on it, but as soon as I switched to the HPI tires, obviously traction went down the tubes immediately.

So what types of adjustments to you guys make to take out some of the push into the turns and the loose off of the turns caused by these tires?

Does anyone have a setup sheet that would make a good starting point?

I can tune an oval car fine, but never wrenched much on a touring car.

Thanks!


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## sportpak (Dec 23, 2005)

If the car was good on 27's, you shouldn't be too far off. You might have to alter your style a little, but you could try adding a little extra droop to both ends of the car. I run the type R and I usually run in the neighborhood of 3.5-4.5mm of droop. Droop is a pretty powerful adjustment, so a dab will do ya until you find what's right.


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## gndprx (Aug 30, 2006)

Thanks for the suggestion. I'm planning to put a full day of testing in on Monday. I figured I probably wasn't too far out and I quickly adapted the driving style, but I'm still loosing corner speed in relation to the top few cars.


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## sportpak (Dec 23, 2005)

I run 2 deg caster blocks with a tick of kick up as well. It helps get the car in, but loosens you up a touch. If you can stay smooth and let the car roll, you'll eventually find that corner speed. Smoooooth, and then sneak up on the aggression.


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## gndprx (Aug 30, 2006)

I think there is 4 deg on there now. I'll have to double check.

Only running about 1 deg of camber and pretty much neutral on toe. Tire wear seems to be about right.


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## sportpak (Dec 23, 2005)

Your probably closer then you think. A day of running with some small adjustments will get you there. 
Honestly, on carpet anyway, a box foam setup is pretty damn good. I just changed tires and it was awesome, so something weird might work for you. Fiddle with it and let us know.


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## rjvk (Aug 27, 2003)

gndprx said:


> Howdy all.
> 
> I have an older mid-motor JRX-S that I'm using for VTA racing on a concrete short and tight track. 27T/4-Cell with the battery in the forward position.
> 
> ...


Since you have the "pushy loose" condition, you mostly are lacking traction. Soften the whole car up, and and some droop as mentioned. You may also want to drop the camber links down to try to get more camber gain.

Going forward, you may also need to change the hinge pins for a better roll center, but the other stuff may work just fine.


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## MarTay6 (Oct 4, 2008)

Beginners question: What is "droop"- and how is it controlled?
Thanks-
Wes


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## Crptracer (Feb 19, 2007)

Droop-Is the amount that the chassis travels downward after the car is dropped and the wheels touch the ground;it is also the amount that t The chassis travels upward before the tires lift from the ground. The red portion is one the way to go with A t/c.

Adjustment is made via the allen screws known as droop screws in your suspension.

you can use a ruler to measure droop or you can order a droop gauge and droop blocks from Integy or xray etc

1.When measuring make sure the car is ready to run with out body. Place on a flat level surface prefably a setup board pushdown on the center of the car compressing the suspension and release and alloow the car to settle.

2.place the ruler vertical at the rear of the chassis see how much distance there is between the surface and the chassis.

3.Keeping the ruler in place slowly lift the car a the rear in the center and the chassis rises and the tires lift. On the ruler note the distance between chassis and the flat surface before the tires lift.

repeat for the front...Droop=the amount of chassis uptravel before the tires lift from the surface.


:wave:Hope that helps ...


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## Crptracer (Feb 19, 2007)

loose entry: reduce frnt droop--off power
loose exit:increase frnt droop---on-power
push entry:increase Rear droop---off--power

push exit:reduce frnt--on power
push mid:Reduce frnt or increase rear--nuetral
loose mid:increase frnt or reduce rear--neutral


This my rule of thumb I am sure we can get some more opinions


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## sportpak (Dec 23, 2005)

^^ what he said. It's basically how you control some of the weight transfer. Think of it as the chassis leaning forward or back or even side to side planting the tires you need to plant to make traction.

Spring changes are drastic adjustments. Droop is more subtle, and useful as the track changes through the day if you need more/less traction at either end of the car.


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## MarTay6 (Oct 4, 2008)

Wow... thanks for some really informative answers, guys! Much appreciated!
Wes


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## Crptracer (Feb 19, 2007)

A good droop starting point would be1.5mm frnt and 2.0mm rear...IMO


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## Crptracer (Feb 19, 2007)

Also I forgot to mention when you set the droop always remember that if you change your ride height you must change your droop:

Increase ride height=Decrease droop
Decrease ride height=Increase droop


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## Crptracer (Feb 19, 2007)

gndprx said:


> Howdy all.
> 
> I have an older mid-motor JRX-S that I'm using for VTA racing on a concrete short and tight track. 27T/4-Cell with the battery in the forward position.
> 
> ...



Push into corner: assuming off power
1.soften frnt springs
2.stiffen rear springs
3.move frnt shock mnt in
4.move rear shock mnt out
5.reduce frnt droop
6.increase rear droop

I would try to fix the push and it will probably settle the loose exit sounds like your in the middle of being just right as Sportpak said. You will know when your close because you will probably become a hair loose on entry and you will need to back your adjustments a little....


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## gndprx (Aug 30, 2006)

Good info all around. Definitely gives me some starting points to get this thing fine-tuned.

Thanks!


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## ToddFalkowski (Aug 31, 2006)

I don't know if this will help, but here's a setup I ran on carpet... Basically, it's the Josh Numan JRXS setup, that works pretty well. I highly recommend a one-way in the front on these...

http://www.michianarc.com/index.php?option=com_docman&task=doc_download&gid=11&Itemid=96


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## Torinogt1971 (Dec 11, 2003)

What LiPo will fit in the mid motor car without serious modifactions?


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## ToddFalkowski (Aug 31, 2006)

I "think" some will, depending on what one it is. Never tried it, though... Think the new SMC's with the wires out the top might not work.

Dunno- I'll look at mine tonight...


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