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Old 07-07-2008, 11:21 AM   #16
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install the rear sway bar kit, it will stiffen the back end up a bit and make the truck lean on the front tires a little more causing it to turn better. also the diff might be a touch too tight causing the rear wheels to get equal traction. read the manual for diff setup.
i am running a Jato 2.5 and had simular problems with pushing, installed the rear sway bar kit and it drove better, got that idea from the RC10T setup manual and it worked wonders. not sure if you can find one some where.
try one thing at a time, if you change two or more things it is hard to tell if you did the right thing.
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Old 07-07-2008, 11:39 AM   #17
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First change from the stock tires that come with the XXX-T to some thing like the proline's M3 Edges. Make sure to mount them with the V's on the outside though. These tires really make a difference in the amount of on power steering and will help with that high speed section you are complaining about. If you need more steering you can also shorten the rear camber link by going out one hole in the rear shock tower. This will also make the truck better in the bumps. You can also run the long VLA in the front arms if you have the MF2/CR front arms installed in place of the stock ones. These will also help increase the durability of the front end over the regular XXX-T items.
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Old 07-07-2008, 11:40 AM   #18
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Originally Posted by way2fast4u View Post
also the diff might be a touch too tight causing the rear wheels to get equal traction. read the manual for diff setup.
With respect to the diff setup, my XXX-TCR manual says to tighten until it is "very tight" when holding one wheel and the spur. Do you have any pointers on what defines proper diff tightness? Also, I've seen people spin one wheel and the other spins the opposite direction. Mine used to do that but doesn't anymore. I spin one wheel and the other spins the same direction. This doesn't seem normal to me.
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Old 07-07-2008, 11:48 AM   #19
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I was having the same problem with my XXX-CR and I put some weight under the servo horn and it helped give the front tires a little more bite in the corners. Welcome to the world of 2-wheel drive racing!
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Old 07-07-2008, 12:28 PM   #20
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Originally Posted by bprocket View Post
With respect to the diff setup, my XXX-TCR manual says to tighten until it is "very tight" when holding one wheel and the spur. Do you have any pointers on what defines proper diff tightness? Also, I've seen people spin one wheel and the other spins the opposite direction. Mine used to do that but doesn't anymore. I spin one wheel and the other spins the same direction. This doesn't seem normal to me.
You should tighten the diff so it does not slip but not overtighten it. If you hold one of the rear tires and spur with one hand and apply a reasonable amount of pressure on the other rear wheel you should not be able to turn the other rear wheel if the diff is tight enough. If it turns tighten it more. Then set the slipper so it slips about one foot on the track surface you are going to race on. This way the slipper slips before the diff. Also, try holding the spur when you are checking the diff action and you should get the wheels turning in opposite diffections action you are looking for.
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Old 07-07-2008, 01:22 PM   #21
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If you hold one of the rear tires and spur with one hand and apply a reasonable amount of pressure....
Then set the slipper so it slips about one foot on the track surface you are going to race on.
I'm sorry to nag this point but ambiguous statements like "reasonable amount" and "very tight" leave a lot of doubt in my mind. What is "reasonable amount"? When I built the truck I tightened my diff so that the spur would dig into my thumb and cause minor pain before the wheel would turn. I'm 6' and 210 lbs so I'm guessing my diff may be too tight. I've heard a rule-of-thumb that states "spin one wheel and there should be a slight delay before the other wheel responds". Is this a reasonable rule-of-thumb?

How does one tell how far - if at all - the slipper is functioning while on the track? Another rule-of-thumb I've heard is "hold both rear wheels to the ground and apply 1/4 throttle - the front wheels should want to lift slightly - if they lift a lot then the slipper is too tight". Is this a reasonable rule-of-thumb?

I'm feeling all-thumbs today

Anyway, thanks for your input and patience (hopefully).
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Old 07-07-2008, 01:48 PM   #22
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Quote:
Originally Posted by bprocket View Post
I'm sorry to nag this point but ambiguous statements like "reasonable amount" and "very tight" leave a lot of doubt in my mind. What is "reasonable amount"? When I built the truck I tightened my diff so that the spur would dig into my thumb and cause minor pain before the wheel would turn. I'm 6' and 210 lbs so I'm guessing my diff may be too tight. I've heard a rule-of-thumb that states "spin one wheel and there should be a slight delay before the other wheel responds". Is this a reasonable rule-of-thumb?
As big as you are I would reasonably guess that "very tight" to you would fit under the parameters of "too tight." Keep in mind you're working on a toy truck and not a real one to help you decide how much is enough.

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How does one tell how far - if at all - the slipper is functioning while on the track? Another rule-of-thumb I've heard is "hold both rear wheels to the ground and apply 1/4 throttle - the front wheels should want to lift slightly - if they lift a lot then the slipper is too tight". Is this a reasonable rule-of-thumb?
I always have and always will set my slipper each day at the track, and set it so that it slips for the first foot or two on take-off, at one extreme if it's dry and dusty (loose setting) and the other extreme if the track is damp and tacky. I just put it on the track, punch the throttle wide open, and watch and listen.
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Old 07-07-2008, 03:35 PM   #23
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Moving the battery to the rear will increase steering. Read up on weight placement using a good book like Race Car Vehicle Dynamics by Milliken & Milliken. Also this is a typical practice to increase turn in in sprint car ovals.

I'll try to explain....

Adding weight to the rear will adjust the CG more towards the rear, correct?

So first consider a truck with a perfect weight balance. The CG is perfectly centered so that the weight on all four tires are identical. Tires are identical, foams, springs and shock oils are all identical. This can easily be seen as a truck that neither over steers, or under steers. It is mostly neutral. So before you break traction, pretty much where you point your front wheels is where the truck will go.

Now before I try to explain how a rearward CG biased truck can turn better, I first have to explain how a frontward biased CG truck will turn less.

Lets say that we placed enough weight in the front of the truck that the CG is now located about 2/3rds in front of the rear tires, so 1/3rd away from the front tires. Now the front tires are carrying double the load of the rear. The front tires now have to accept twice the side forces while turning (*look on bottom). This means that the front tires will now slip sooner and require a greater slip angle to achieve the desired heading. The truck now requires a greater steering angle at the front wheels to get the same turning radius as the neutral steering truck. The truck is pushing.

Now lets say we placed enough weight in the rear of the truck so that the CG is now located 1/3rd in front of the rear tires, or 2/3rd away from the front. The rear tires are now carrying twice the load of the front. In a turn, the rear has to accept twice the side forces. The slip angle at the rear will now increase faster and it will reach the end of its peak traction forces sooner. The truck oversteers because during a turn, the rear breaks traction sooner. Therefore this truck requires a lesser steering angle at the front tires to get the same turning radius as the neutral steering truck

(*) This point can be further exaggerated by considering how the side forces on the tires work. Lets say a truck tire is pushed into the ground at about 1 pound. In addition, 1 pound of side force is applied to the tire. It might not slide but it will deform a bit. However, if you push on both the bottom and the side at about 2 pounds or more, it will begin sliding at a critical point that marks the end of the traction circle.
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Old 07-07-2008, 05:18 PM   #24
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Old 07-07-2008, 05:38 PM   #25
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Quote:
Originally Posted by mattnin View Post
Moving the battery to the rear will increase steering. Read up on weight placement using a good book like Race Car Vehicle Dynamics by Milliken & Milliken. Also this is a typical practice to increase turn in in sprint car ovals.

I'll try to explain....

Adding weight to the rear will adjust the CG more towards the rear, correct?

So first consider a truck with a perfect weight balance. The CG is perfectly centered so that the weight on all four tires are identical. Tires are identical, foams, springs and shock oils are all identical. This can easily be seen as a truck that neither over steers, or under steers. It is mostly neutral. So before you break traction, pretty much where you point your front wheels is where the truck will go.

Now before I try to explain how a rearward CG biased truck can turn better, I first have to explain how a frontward biased CG truck will turn less.

Lets say that we placed enough weight in the front of the truck that the CG is now located about 2/3rds in front of the rear tires, so 1/3rd away from the front tires. Now the front tires are carrying double the load of the rear. The front tires now have to accept twice the side forces while turning (*look on bottom). This means that the front tires will now slip sooner and require a greater slip angle to achieve the desired heading. The truck now requires a greater steering angle at the front wheels to get the same turning radius as the neutral steering truck. The truck is pushing.

Now lets say we placed enough weight in the rear of the truck so that the CG is now located 1/3rd in front of the rear tires, or 2/3rd away from the front. The rear tires are now carrying twice the load of the front. In a turn, the rear has to accept twice the side forces. The slip angle at the rear will now increase faster and it will reach the end of its peak traction forces sooner. The truck oversteers because during a turn, the rear breaks traction sooner. Therefore this truck requires a lesser steering angle at the front tires to get the same turning radius as the neutral steering truck

(*) This point can be further exaggerated by considering how the side forces on the tires work. Lets say a truck tire is pushed into the ground at about 1 pound. In addition, 1 pound of side force is applied to the tire. It might not slide but it will deform a bit. However, if you push on both the bottom and the side at about 2 pounds or more, it will begin sliding at a critical point that marks the end of the traction circle.
Here is the description right out of my XXXT-MF2 book on battery location:

Battery Location is sometimes overlooked, but can be a useful adjustment. Start by running the battery spaced in the middle.
Moving the battery back can improve rear traction on slippery tracks. Moving the battery back too far can cause the rear end to
swing though turns on some tracks. This is a result of having the weight too far back. Moving the battery forward will give the
truck less forward traction, but it will gain on power steering. Moving the battery forward should also smooth out the steering a
little. This may be good on high bite tracks.

Going by this guide moving the battery forward will increase on power steering which is what this particular person that started this thread is complaining about. His truck is pushing on power not on corner entry.
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Old 07-07-2008, 05:44 PM   #26
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Quote:
Originally Posted by bprocket View Post
I'm sorry to nag this point but ambiguous statements like "reasonable amount" and "very tight" leave a lot of doubt in my mind. What is "reasonable amount"? When I built the truck I tightened my diff so that the spur would dig into my thumb and cause minor pain before the wheel would turn. I'm 6' and 210 lbs so I'm guessing my diff may be too tight. I've heard a rule-of-thumb that states "spin one wheel and there should be a slight delay before the other wheel responds". Is this a reasonable rule-of-thumb?

How does one tell how far - if at all - the slipper is functioning while on the track? Another rule-of-thumb I've heard is "hold both rear wheels to the ground and apply 1/4 throttle - the front wheels should want to lift slightly - if they lift a lot then the slipper is too tight". Is this a reasonable rule-of-thumb?

I'm feeling all-thumbs today

Anyway, thanks for your input and patience (hopefully).
When I talk about reasonable I mean to use your head and not to try and break the thing. Like the above post said these are just toys and can take only so much pressure.
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Old 07-07-2008, 10:26 PM   #27
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Quote:
Originally Posted by sport10 View Post
Here is the description right out of my XXXT-MF2 book on battery location:

Battery Location is sometimes overlooked, but can be a useful adjustment. Start by running the battery spaced in the middle.
Moving the battery back can improve rear traction on slippery tracks. Moving the battery back too far can cause the rear end to
swing though turns on some tracks. This is a result of having the weight too far back. Moving the battery forward will give the
truck less forward traction, but it will gain on power steering. Moving the battery forward should also smooth out the steering a
little. This may be good on high bite tracks.

Going by this guide moving the battery forward will increase on power steering which is what this particular person that started this thread is complaining about. His truck is pushing on power not on corner entry.
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Old 07-13-2008, 11:08 AM   #28
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Try moving your turnbuckle balls to the outer holes on the front bulkhead or taking out washers. Adjust camber and try that out. See if it makes it steer.

It might make it too touchy though.
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Old 07-13-2008, 01:19 PM   #29
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Tires!
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Old 07-14-2008, 02:43 PM   #30
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Lightbulb how about your servo/servo-saver?

If you have a high-bite track or plow into a corner at a fair amount of speed.. it could be a under powered servo.. or the servo-saver is too loose...

Just thought I'd mention it...


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