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Old 10-31-2009, 04:45 PM   #46
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Track Test
Well its like having an old friend back. The car handled very well. I changed to the Matt Francis height low roll center blocks. This puts the roll center at about the ground. I also saw that I could take out more front drive axle angle by moving front arms forward I did this. (CBs suggestion). What could I do better than yesterday. I could brake all the way to the apex. In other words I could brake while steering. This is the result of slightly more cornering grip than yesterday. On this outdoor course there are a couple of sharp corners that might be best handled this way. I was keeping up with two Nitro 1/10 scales, one of which had a very good driver. I thought I would list this setup as you might want to select pieces of it to try out. It is listed below

TORQUE STEER
This is the monkey wrench that is thrown into the pot when you add a locked diff. Things may no longer tune up like they say in the full size car books. Some of this is because they don't use front locked diffs in full size cars. A tremendous amount of torque steer is thrown into the handling equation.

First my history on Torque Steer
I used to run 2 wheel drive 1/10 scale off-road truck. If the left to right weight was not even on the truck, it would accelerate crooked. The heavy side had more traction. Lets say the right hand wheel was heavy, the truck would have some torque steer from the heavy wheel and would accelerate to the left. Now on dirt, you constantly correct the steering. You might not even notice that you alway add right steering when you accelerate. I can guarantee, though, that the truck would go faster if you did not have to fight torque steer with steering throw. The best way to test this was to accelerate on the dusty concrete floor with hands off the radio. The torque steer was plain as day. With both rears spinning forward the heavy wheel gets more bite. So torque steer is caused when one wheel on an axle has more tire loading than the other. The Heavy right wheel pulls harder. It has a torque arm the length of the axle. It spins the truck to the left.

Standard ball diff
What happens up front in our touring cars with a standard ball diff. We come out of a corner to the left with the right front overloaded. But the left front is only lightly loaded. The left front spins on power, a ball diff by design gives equal torque to both wheels. Because the left is spinning and has no bite, the right side only receives a tiny torque. Torque steer does not show, but acceleration out of the corner is also weak.

Now we lock the diff
That outside front with all the load now produces plenty of torque steer. It helps steer the car around the corner. It does so only on power, not coasting in. The more weight on the outside tire, the more torque steer on power. So if we want more torque steer on power we have to load the outside wheel more. We use a heavier spring. This is exactly opposite of what you would do to get more steering with a ball diff. Does this alway hold true, well no. It depends on how you drive the corner. If you are on high grip indoor asphalt and you drive the corner like I suggested previously for a belt car, then yes it holds true. Now a recent example from the XXX-S. I said I had some oversteer on power. I said I moved the spring to correct the problem. I did not say which way. I actually tried both ways.

I ran a pack and had a couple of spins on the short side straight that is driven in an arc with good power. I had one spin coming out of a hairpin by the drivers stand on power.

I moved the upper shock pivot out 2 holes. I had 6 spins on the next pack. I moved the upper shock 2 holes in. I had no more spins. With a locked diff on Power steering had been reduced by softening the front end. This is backwards from normal and should be part of your tuning kit.

Depending how you come in the corner you may have to tune normally or in reverse. What I like to do now is tune the car up with a standard diff, then add the locked diff and rarely am I off more than a couple of holes on the upper shock position.



Setup for Outdoor Asphalt
Front
Locked Front diff, JRXS spool pulley.
Matt Francis Height low roll center blocks.
4 caster, 0 kickup, Inner hinge Pins parallel and level with 2R rear pivot block in lower holes, Arms forward.
inner camber link pivot, 3rd hole in, stock
0 toe
-1 degree camber
blue springs all the way in on top
Kit shock oil. I suspect about 35 weight
Ride Height 6 mm
My droop is set so the springs don't get loose on full droop front and back. This is what I usually do when there is only medium or less grip.

Rear
2 degree toe in + 1/2 degree graphite hubs giving 2.5 degree toe in
Camber -1
inner camber link pivot 4th hole in, stock
Rear 4 R pivot in upper holes, pins parallel to ground
Matt Francis height low roll center blocks
blue springs all the way in on top
Arms Centered
Ride Height 6mm

Tekin R8, LRP 3.5 with homemade internal and Integy external fan.
Gear 88/21. Thuderpower 40C 5000 mA-h pack. The battery is a must. SMC 6000 pack overheats badly in the heat with this much power. Sorex and Takeoff RP 40R, Traction Action.


I plan to do another test on kickup. This will be a cleaner test as I will only change one factor. It should stiffen the front end on power. I may have mispoken earlier about it.
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Last edited by John Stranahan; 11-25-2009 at 03:17 PM.
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Old 10-31-2009, 10:08 PM   #47
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man your car look good to today
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Old 11-01-2009, 12:57 AM   #48
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Hi John,

I've just been looking at your asphault set up you just posted, and I'm running fairly similar too it with my car.

only real main difference is my car is a G+ (graphite chassis) and I run a .060" front sway bar, and i run the 41 tooth pulley in the front using the Losi spool pads.(found this helped pull the car out of the corner if the back gave way a bit) and I run the Losi low roll centre blocks not the MF ones.

What I'd like too know is how could i improve rear traction on my car???
when i turn it rotates around like Im doing a Hand brake turn.
is fine when you know its gonna do it but can be fairly unpredictable at times.

Its summer here at the moment so failry hot (30 - 36 degrees celcious) I run the standard kit oil 30wt would increasing the oil be better as the temp comes up?

today i tried fitting a 2r block too the rear instead of the 0r block to gain some more traction as well as trying softer rear springs. this did help a bit but it was still very slippery in the rear

I run Much More 36 tyres with Paragon fx 2

Our track is fairly large an open but doesnt hav much bite/grip, plus has up and down hill sections, on camber and off camber corners.

Cheers for any Input.
Rob.
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Old 11-01-2009, 01:32 AM   #49
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hi, I have been searching for about an hour and cant find it, I'm running a 17.5 xxx-s with a 88 spur, what is the biggest 48p pinion i can fit on it, im using a 32 but its way undergeared at about 5.00, need it down to 3.7 or so but dont want to buy a big pinion and have it not fit, anyone tries a 39t?

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Old 11-01-2009, 01:00 AM   #50
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Quote:
Originally Posted by chrislow View Post
hi, I have been searching for about an hour and cant find it, I'm running a 17.5 xxx-s with a 88 spur, what is the biggest 48p pinion i can fit on it, im using a 32 but its way undergeared at about 5.00, need it down to 3.7 or so but dont want to buy a big pinion and have it not fit, anyone tries a 39t?

chris
hey mate i ran a 86 spur in mine for a while and i could fit a 39t fairly easy i could also fit a 40t but it was a bit of a jiggle to get it in . i now run a spur adaptor so i can run any final drive i want . i will go put a 88 spur in the car now and try a few pinions for you and let you know
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Losi XXX-S G+..................Tamiya M03.......................TOP Photon
Losi XXX-4 G+.................HoBao ST Pro electric........Losi Micro SCT
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ASSociated RC12L4
T.O.P PHOTON EX & Tamiya M05 - currently undergoing rigorous crash testing!
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Old 11-01-2009, 01:16 AM   #51
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i just did some checking for ya.

with the 88 tooth spur a 39 pinion will fit no problems jus some practice gettin it in an out is all. ( think even a 40 pinion will fit with some extra effort.)

I also went back and checked the 86 spur and found with fitting the pinion inside the chassis an then installing the motor after an lining up pinion and tightening etc a 42 tooth pinion can fit - its just a bit fiddly fitting it.
- this is with the low motor mount disc.
hope this helps.

As for what is the largest pinion, well biggest ive seen in 48p is 47 tooth.

hope it helps ya.
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Losi XXX-S G+..................Tamiya M03.......................TOP Photon
Losi XXX-4 G+.................HoBao ST Pro electric........Losi Micro SCT
Losi XXX-CR....................Losi Mini Baja.....................Losi XX-4 W/E
ASSociated RC12L4
T.O.P PHOTON EX & Tamiya M05 - currently undergoing rigorous crash testing!
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Old 11-01-2009, 01:23 AM   #52
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just checkin ya ratios - too get 3.7 u will need a 86 spur with the 42 pinion gear.

So in my opinion you should get the spur gear addaptor available from presicion rc made by JET racing parts part number TX-23.

Also there is alot of good info in the XXX-S thread found on here (should only be a few pages back )

hope this helps ya mate
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Losi XXX-S G+..................Tamiya M03.......................TOP Photon
Losi XXX-4 G+.................HoBao ST Pro electric........Losi Micro SCT
Losi XXX-CR....................Losi Mini Baja.....................Losi XX-4 W/E
ASSociated RC12L4
T.O.P PHOTON EX & Tamiya M05 - currently undergoing rigorous crash testing!
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Old 11-01-2009, 02:22 AM   #53
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your awesome mate, above and beyond. I have limited funds and a enduro race coming up, Hour and a half long with two drivers and two cars. So i might just get the 39T, might be a bit undergeared but thats a good thing for this race, heat will be the enemy.

many thanks

chris
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Old 11-01-2009, 02:55 AM   #54
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No probs mate
if ya gonna order pinions grab one each side any way jus incase
can never hurt too have them in ya pit bag for tuning

good luck an let us know how she goes
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Losi XXX-4 G+.................HoBao ST Pro electric........Losi Micro SCT
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Old 11-01-2009, 04:07 AM   #55
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Just went looking for that adapter, couldn't find it anywhere
tried precisionrc, losi parts house, rcmart, ebay, a main...

Sounds like a good idea too.
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Old 11-01-2009, 04:15 AM   #56
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try here

http://www.precisionrc.com/nv/car/pr...uct_name=xxx-s
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Losi XXX-4 G+.................HoBao ST Pro electric........Losi Micro SCT
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Old 11-01-2009, 05:16 AM   #57
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Or you could buy this one.

http://cgi.ebay.com/ws/eBayISAPI.dll...=STRK:MEWAX:IT
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Old 11-01-2009, 08:05 AM   #58
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Thanks for the posts.

Dick Thanks. I was keeping up with Jasons Nitro for a while.

Paraletic-First Rear toe. You need to run about 2.5 degrees. You did not mention if you had the .5 degree hubs on to add that extra bit of toe.

Then there is the reverse tuning option. You may be too stiff in the front with the sway bar causing (torque steer induced) oversteer. Try sway bars front and back and then, try going softer in the front until the roll stiffness front and back are about equal.

My car is not oversteering. It was, however, with the front springs only 2 holes out. It is a pleasure to drive now.

I never liked the thought of the different size pulleys with the tires slightly fighting each other the whole time. Most Touring cars don't offer this option. I suggest going to standard 42 teeth pulleys and tuning the car with roll stiffness changes.
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Old 11-01-2009, 01:07 PM   #59
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im sorry i know this is not a for sale sight but you guys seem pretty hard core xxxs. buy the way it is a fantastic car my boy and i ran them for years. last winter the fastest car at the local carpet track in 13.5 was still a xxxs g+. anyway i have four complete cars in all in great shape 2 graphite 2 stiffzel all with threaded shocks and litterally hundreds of spares (when the jrxs came out i bought up everybodys spares) ihave every losi option part including one-ways and springs a brand new chassis and neerly all irs and trinity hop-ups including aluminum outdrives and 2 of the trinity matt francis spur gear adapters that allow you to run any spur gear made. anyway this is all good stuff that needs agood home if anyone is interested you can pm me
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Old 11-02-2009, 09:36 AM   #60
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Kickup-I noticed this last track session that my kickup addition was not very helpful. I did have a few more on power mistakes. I removed the kickup with little change noticed.

Lightening, Depowering
I depowered to an LRP X12 4.0 from a 3.5 to be able to run the Tekin RS Pro to lighten the car and more importantly to change the on track performance. I am looking for a little more punch out of the corners at the expense of acceleration mid straights. Speeds on slow parts of the track have a bigger effect on lap times.
I am also trying to achieve better performance from the tires. I noticed previously with the 4.0 that I got a good wear pattern on the tires (micro ripples lined up with the circumference) instead of a smooth scuffed tread, I get most of the time with the 3.5. This should improve tire grip in the corners.
I also lightened the Stiffzell chassis using cutouts similar to the graphite plus. Weight including the speed control change went from 54.8 ounces to 52.6 ounces. This is still heavy for a LiPo powered car, but I should see the difference on the track. Weight is also moved inward. Note the edge of the battery is just outside the rail now instead of 1/4 inch outside. I remounted my inside battery rail and will still use one wrapping of of tape mid battery. I feel my car was as fast as the other touring cars yesterday, but I could be faster in the chicane and left side of the track. We had some small but significant layout changes there that I am still getting used to. I plan to kill a tiny bit more steering to decrease driving errors. I will use reverse tuning for the locked diff. I will move the rear upper shock pivots out just a hole or two.

Note the Tekin is mounted on the edge so that the LRP fan can blow on the bottom and solder posts. This really makes a difference in getting it to go 6 minutes. A Novak monster size capacitor is installed. The Integy fan mount has been lightened. A Novak fan is installed. Fans receive full battery voltage.
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LOSI XXX-S, Tips and Tricks, Open Mod, etc-lightened-losi-xxx-s-001.jpg  
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Last edited by John Stranahan; 11-03-2009 at 09:50 PM.
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