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Old 02-25-2007, 06:48 AM   #961
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On my track larger tires have more grip and have faster lap times. I put on a new set to race. They work through the bumps better.

There was a full size Indi car that used small diameter front tires once. It had 4 front tires on tandem axles to keep the contact patch big. The tires were short to reduce air drag.

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Old 02-26-2007, 10:34 AM   #962
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There's a few other considerations

A larger sidewall is more forgiving since it flexes while a smaller sidewall doesn't. This means that a larger sidewall (larger foam tire) will give you better traction on a slipperier track (as John mentioned) but will actually delay your turn-in since the initial turning impetus is absorbed by the tire. If you have high bite and want fast reaction, cut down the tire to the minimum.

In addition, with a larger sidewall, the tire can "smoosh" just a bit (yeah, technical term! ) which also gives it some extra bite.

Another reason some cut down their tire (esp on carpet where wear is not as big of an issue as on asphalt) is to reach a "perfect" rollout. You can only get so far with a gear ratio (although I've always found it to be pretty much right there. . .) so many will use the tire's diameter and the gear ratio to get an exact rollout - how many mm the car will move per single rotation of the motor.

As to the past, like in F1, tires have come a LONG way. Back in the 80s, they were able to make soft compounds, but were unable to get them to last long enough for demanding races. In order to use a harder compound (durable) and get it to stick, they used some sidewall flex. Now, however, they're able to get softer compounds that last long enough for a race.

If you look at WRC, though, they still change back and forth. On tarmac they use a VERY low profile tire (that's wide); but when they race on snow and ice (contrast - as far from tarmac as you can) they run a very narrow, high profile tire which gives them more pressure psi (so it will push down harder through the snow) and gives them more sidewall flex to gain a bit more traction (you should see camera footage of the tires. . .the deflection they get is amazing. . .) - they do the same thing on gravel, really, just not so narrow (and without the studs. . . ) but the principle is the same.
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Old 02-26-2007, 03:12 PM   #963
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Thanks for the discussions of tire size guys. I especially enjoyed that technical term for tire compliance. I think we are in agreement that traction and track smoothness plays a part in which size tire works best. Rough and slippery best large. Smooth and high bite maybe a little shorter if you can bear wasting that nice new foam. I'll have some smooth high bite carpet soon.


Antisquat

I have been discussing the benefits of antisquat on a 3 link suspension. I thought I would post this photo sequence since it shows better what I am talking about. Sometimes the technical terms dont make much sense without a picture.

Photo 1, the car is at rest.

Photo 2, I simulate a little reverse torque on the pod ( I pushed on its back side a little) that is caused by the motor running up the spur gear driving the car forward. Note that the rear of the chassis elevates and not the front. The weight that is driven up, by equal and opposite reaction, drives the rear tires downward. This is one of the benefits of the 3-link.

Photo 3. 4, I increase the reverse torque simulating more throttle.

Finally in photo 4 all the travel in the suspension is used up and at this point only will the front end lift with the chassis in this condition. On the track fully shocked and loaded it does not lift so high. Only a little. The extra tire loading benefit is a lot.

The standard pan car rear suspension has some antisquat but it is mostly dampened out by the center shock and is not near as effective in loading the rear tires.

These photos are downloadable. Do a right click on the photo then save as. Then you can view them in a small slide show animation.

Note that antisquat on an independent rear end 4 wd RC car is almost useless. There is no big benefit like here. It mostly makes the rear end slide out from the stiffening that occurs. It does not help to put extra load on the rear tires of a 4wd car.

The 3-link narrow car is nearing completion. Frame Rails installed.
John
Attached Thumbnails
Pantoura, 1/10 Pan Car, 2S LiPo, Brushless, Tips and Tricks.-antisquat-sequence-005.jpg   Pantoura, 1/10 Pan Car, 2S LiPo, Brushless, Tips and Tricks.-antisquat-sequence-006.jpg   Pantoura, 1/10 Pan Car, 2S LiPo, Brushless, Tips and Tricks.-antisquat-sequence-007.jpg   Pantoura, 1/10 Pan Car, 2S LiPo, Brushless, Tips and Tricks.-antisquat-sequence-008.jpg  

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Old 02-27-2007, 02:18 PM   #964
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3-Link on Narrow Pan Car

Well this was truly a game of inches. There is not much space on either side of the motor. I think this prototype is going to work well though. There is actually room for the car to roll side to side. No part in the rear is higher than the upper bump limit of the tire. You should be able to run a really low LMP body with it. The car should have a good front to rear weight balance with a LiPo as all the suspension components are behind the axle. Here are a couple pics of the Prototype. Eventually I'll have some blue RC18 adjustable shocks. They were out of stock. The panhard bar is sufficienty stiff, but now has some flex in the left side frame rail/Panhard bar mount. This should eliminate breakage in the crashes. I have mounted the ends of the Panhard bar itself more rigidly as a result.
Motor and gear maintenance are accomplished by popping both upper shock ends. The pod then drops way down to clear all the frame extensions.

The main clearance problem was there is no room to mount a nut on the back of the upper shock mount ballstud. Instead I sanded down some Losi Ball nuts (Female ballstuds) to .157 inch. They worked well. I used a tiny headed CRC supplied 4-40 phillips head screw so the back side would be more flush.

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Attached Thumbnails
Pantoura, 1/10 Pan Car, 2S LiPo, Brushless, Tips and Tricks.-3-link-narrow-pan-car-001-resized.jpg   Pantoura, 1/10 Pan Car, 2S LiPo, Brushless, Tips and Tricks.-3-link-narrow-pan-car-003-resized.jpg  
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Old 02-27-2007, 09:48 PM   #965
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200 mm Pan Car with 3-link ready to test.


I have the car finished now and ready for a short test tomorrow. I set the front width to 200 mm to fit the 200 mm bodies well. Rear width is also 200mm. The car is equipped with the Novak 3.5 R motor and GTB speed control. We will see. I made a better left side servo mount for this one.
John
Attached Thumbnails
Pantoura, 1/10 Pan Car, 2S LiPo, Brushless, Tips and Tricks.-3-link-narrow-pan-car-finished-resized.jpg  

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Old 02-28-2007, 05:51 PM   #966
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Track Report 3-Link Narrow Pan Car



The track was very dusty from preparations for the RC Pro Series Off-Road Race this weekend (260 entries at last count). Normally when the track is like this with a narrow stock pan car, I get on it and say "I've got nothin out there". Well I had more than nothing today, but it was not like a day with medium traction. Here is a list of problems that I solved or attempted to solve during the maiden run of this 3-link Narrow Pan car. I took the front end straight off the wide pan car with no changes and put it on this car.

Too much steering-This is typical of the difference between a narrow and wide pan car. You need to get rid of steering on the narrow car, but are adding steering to the wide car. I changed from about a 13.7 lb (Copper Associated) to a 18 lb spring (red associated). This helped

The rear end was bouncing skyward on the straightaway bumps, but there was no rear chassis contact. I lowered the rear shock oil from 30 to 20. If you compare my wide pan car with this narrow pan car you will see that the rear shocks are now behind the axle and have more travel and mechanical advantage than on the wide car where they are in front of the axle. This cured the problem.

High Speed Oversteer in turn 1, a high speed right hander and turn 5 the sweeper. I changed to a higher downforce touring style wing and then later added a spoiler as allowed in the GT class. I was running HPI's Stilletto body pictured early in the thread. Previously I could do neither of these mods on the stock pan car because the car would go airborne. The twin A-arm front suspension kept the car planted even with a much larger rear wing. I also needed to hold more throttle entering the turns. Problem solved. I increased straight line lateral stability by reducing camber.

I still had too much steering on turns 9 and 10 the hairpins. Some of this is due to a very slippery track. It does not really clean up untill I run 3 packs. I only ran one today. I added washers under the A-arm mounts and corrected the ride height at the shocks. This raised my roll center, I increased front shock oil weight to 35 from 30 and treated the front tires on only the inside. I now had a mild push. I can treat more of the tire next time or lower the roll center back.

The car is showing promise. I could actually get to full throttle on the shorter straights briefly before turn 9 and before turn one. The car has more forward traction on asphalt than the stock 3-shock pan car rear suspension. I still have some light tuning to do. The car is completely planted on the straight. This is a huge comfort. Having to increase the front roll stiffness like I did will help me with the tight clearances on the back end by reducing roll. Stay tuned.

This car is not faster on a road course than the wide one, and was not intended to be. It's only advantage is easier passing on a narrow indoor track in a class where the width is restricted, or the ability to use a wide range of 200 mm and supercar bodies from HPI and others. A narrow car does have a high speed advantage on the oval due to the lower front cross-section.

The pic shows the Stilletto body. I actually used the same one. The front wheel fills that wheel well much better now at 200 mm front width.
Attached Thumbnails
Pantoura, 1/10 Pan Car, 2S LiPo, Brushless, Tips and Tricks.-stilletto-body-018-resized.jpg  

Last edited by John Stranahan; 02-28-2007 at 09:11 PM.
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Old 02-28-2007, 07:15 PM   #967
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I was wondering if these mods are going to be available for sale, or maybe an entire kit? Or are they just a one off deal? I am looking at getting a pan tourer and want to know if this is an option for me. Thanks
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Old 02-28-2007, 08:30 PM   #968
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Bob-I would not delay a purchase based on these one of Prototypes. You can always change cars if they become available. I believe Marty from MLP is working on producing the wide pan car prototype. He has my drawings of the custom frame pieces. He has advertized it on his Web site. His health is a little poor like mine so I hate to make any promises on production times. Hopefully some of the succesful tuning tips in this thread will help you out with any other car you may purchase in spite of the unavailability of good wide pan cars at the moment. This may change in a heartbeat or it may not. I really like the wide prototype that I made. Best and fastest electric road car I have ever run. All the typical wide pan car ills are eliminated. It does not tend to fly on a bumpy straight. The body does not rattle around over the bumps. It has plenty of steering. It has good (not great) forward traction over a dusty surface. It has Very good forward traction on a clean unprepared track (no sugar water). All of the many good pan car traits are retained. Huge run times. Great acceleration. Low maintenance. Good cornering. Low tire wear. Lightweight. You can use Lipos and the fastest brushless in the summer without excessive thermal shutdowns.

Now if someone is interested in making this narrow car we can strike up a deal. I have an additional rear ladder bar brace to add to my two frame extensions. This will stiffen up the Panhard bar mount. The difference in forward traction compared to the stock pan car suspension on a dusty track is like between having nothing and having something. More esthetically pleasing part contours could be developed, I am sure, by using some lightened blue aluminum pieces.

John

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Old 03-01-2007, 04:43 AM   #969
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OK, You read my mind, I was looking for a narrow car,(190-200) Let know what you have and what the price is. My email is [email protected].
Thanks,
Bob
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Old 03-01-2007, 06:52 AM   #970
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bob, there is a really premo pantoura if you need a starting point on ebay right now.. it's where john started and it's ~190mm..
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Old 03-01-2007, 10:29 PM   #971
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Here is a picture of the ladder bar brace I spoke of adding. It is the top red tube on the back of the car labeled 128 mm. It joins the two frame extensions. It more than doubles the stiffness of the Panhard bar mount as it not only joins two equally strong frame extensions but it prevents the downward aiming left side Panhard bar mount from twisting in a clockwise or couterclockwise direction when viewed from the back. Things are a lot stiffer now. I had some contact marks on the right side frame extension at the last outing. None on the left. I moved both frame extensions inward the thickness of one steel washer and recentered. I should have enough clearance now. It is hard to see the clearance in the photo but it is there.

I would have more clearance if I was able to exactly center the shock under the graphite frame extensions with a custom mount.
John
Attached Thumbnails
Pantoura, 1/10 Pan Car, 2S LiPo, Brushless, Tips and Tricks.-3-link-narrow-pan-car-ladder-bar-002-resized.jpg  

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Old 03-01-2007, 10:34 PM   #972
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Wow! Now that is crowded!
John, could you test this narrow car with the Lola outlaw gas body? I'm suspecting it might surprise you!
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Old 03-01-2007, 10:37 PM   #973
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Will do. It is crowded but I expect no rubbing tomorrow. The sides of an LMP body could be really low with this rear suspension.

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Old 03-02-2007, 03:15 PM   #974
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John, isn't the axle the same width as that of a 12th scale? Once the carpet track is in, it would be nice to develop a rear and front end for that.
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Old 03-02-2007, 06:04 PM   #975
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The speed 8 1/12 body is about 170 mm. This car is 200 mm. I'll put it next to Phils 1/12 scale in the shop and see if the difference is tires or axle. There probably is not a lot of benefit to this 3 link design on indoor carptet as the traction is very high. What it is doing for me on asphalt is increasing my forward traction. I would probably try CRC's new front end first and see if there were any areas for improvement. There might not be any on carpet.


Lot of dust from the offroad racers (259 entries) practicing today. You could see the dust billowing out of the building onto the sweeper. "I had nothin out there"

Cristian & Nick- you will find this interesting. I was reading an old magazine on the speed run record of 96.4 mph in a mostly stock TC3 by Cliff Lett with a Reedy 10 turn double. I always liked the 10 turn better myself for speed. They had a lightly modified pan car RC10 L30 up to 111 mph with a 2 turn brushless. The pan car had the Associated kit front horizontal shock that was discussed earlier in this thread. It connected the two upper custom A-arms that had a short upright molded on.

Tony- thanks for the article. I remember reading it the first time out. May 2001 RCCA mag.
John

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