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Old 01-02-2003, 11:31 PM   #16
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Default Re: mab_man20;

Quote:
Originally posted by popsracer
Can't you see that no one cares about your project car. We are all TOO busy arguing among ourselves about this Weight Bias thing that someone posted.

Funny though how a simple question CAN really turn into a BIG arguement online......
lol, im glad to have ruffled some feathers and started a good debate. I just didnt want people to get bogged down on an actual chassis, theoretical debates are much more fun!

Back to arguing!

If i had more weight in the front (while coasting so there is no weight transfer) wouldnt have more responsive steering because the added weight would increase friction in the tires, giving me more traction?

Following this logic, if i have 50/50 bias, under breaking the weight would shift to the front giving me increased steering. Under acceleration the weight would shift back giving me a more planted rear.

Is my logic correct?
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Old 01-03-2003, 08:27 AM   #17
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Yes, the fact is that in general the more weight that a tire has on it, the more traction ability that tire has. But there are so many things that this coversation hasn't really covered that's getting all lumped up into one topic.

In general, the end of the car that has more weight should have more traction. But traction and turning ability is about so many things which one key element is weight transfer. The rate of weight transfer and to what tire and when its transfered. Weight transferred too quickly to a tire can bring a tire beyond its traction point. Too much weight (like in the rear in this instance) could sometimes cause the rear of the car to swing around. But in most cases, weight bias to the rear will privide more rear traction.

Weight bias being set to the rear on touring cars is mostly due to the fact that the rear of the car must more abruptly react to the what the front of the car is doing. This weight provides more grip and reduces or slows down the rear tire's need for such an abrupt need for traction. Since some weight and the car's CG transfers to the front of the car when slowing down, the added rear weight bias will provide a closer to 50/50 ratio when its needed.

In most cases, people either set their rideheight to level or they "rake" the car by about 1/2mm which means the front is lower than the rear. Just one of several reasons for doing this is to give the car more steering traction.
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Old 01-03-2003, 06:49 PM   #18
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Default Cornering Power

mab_man20- Your logic is off maybe a little in the first part of your statement, maybe this will help.

As you increase load on the front tires the front tires can develop more traction. However if you have a car with a 50-50 front to back weight split and move weight forward you will get a push or LESS front cornering power. This seeming dilemma can be addressed with a concept called cornering power. First some data on a full size tire from Herb Adams Book "Chassis Engineering".

Weight on the tire (Vertical Loading) - Weight=500 lbs, Weight=1000 lbs

Maximum Cornering Force Developed- Force=700 lbs, Force=1000 lbs

Notice that as the weight on the tire increases the cornering force increases. Note also that as the weight on the tire doubles from 500 to 1000 lbs that the traction increases but it does not double. It increases from 700 to only 1000 lbs. The tire is less efficient at the high loading. For all possible loadings of the tire on a car the traction force continues to increase with added weight. I have similar data on an RC tire.

The ammount of cornering power (measured in g's) developed by the tire takes into account the fact that weight also comes with an inertia penalty. If we make the front too heavy the less efficient tires will not be able to ovecome the inertia as easily.

Cornering Power which can be measured in g's can be thought of as the ratio of (cornering traction)/weight. At 500 lbs the above tire would have 700 lbs/500 lbs or 1.4 g's of cornering power. At 1000 lbs of weight the tires can only develop 1000lb/1000lb or 1 g of cornering power. So the LESS the load on the tires the more g's can be developed.

Here is a graph of Cornering Power vs Vertical Load on the same tire above, that is derived from data and concepts in Herb Adams Book. You get the best cornering power from a car if you stay toward the left side of the graph. You do this by loading all four tires as equal as possible, on a car that must corner left and right, with a slight bias toward the back to compensate for forward weight transfer.
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File Type: jpg cornering power.jpg (18.6 KB, 122 views)

Last edited by John Stranahan; 01-03-2003 at 07:04 PM.
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Old 01-04-2003, 01:00 AM   #19
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John: I see what you are saying. I have since discovered that when the battery is placed in the forward slot the weight bias is much closer to 50/50, further backing my second statement and your statement.

Unless someone else has more to argue about (i know we can find something!) It seems that about a 45/55 weight bias with the ability to move the battery forward and rearword will be the best.


thanks, maybe we can expand this to cover some other weight issues people have.

Lets hear em!


Last edited by mab_man20; 01-04-2003 at 01:06 AM.
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Old 01-04-2003, 09:29 AM   #20
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Default Oval

If you only corner left on an oval then you preload the inside tires by moving weight left in the car. This results is more even tire loading after weight has transferred to the right in a corner. This gives you the best cornering power to each axle. This left weight bias works very similar to our rear weight bias on a touring car. It is an attempt to even out the tire loading while the car is cornering. An oval car will also have an optimum fore aft weight bias that probably has more weight in the back as well. Moving weight in the oval car is a major tuning tool.
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Old 01-05-2003, 12:19 AM   #21
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Today i got XXX-mains tuning guide and the first topic is weight transfer and it does an increadable job describing it. John was correct when he said that the weight should be just behind 50/50 so under breaking the car will be almost 50/50.

Everyone who has ever even thought about racing should pick up the tuning guide, it is simply that good!
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Old 06-17-2009, 11:53 AM   #22
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If most of the time you corner when accelerating, eg drifting, would it be better to have more front biased weight? I mean people have found that the best drifter is the TA03F, with its front mounted motor.
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Old 06-17-2009, 05:42 PM   #23
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Quote:
Originally Posted by NightKidZ View Post
One thing that many people seemed to have ignored so far is the fact that RC cars have much lower ground pressure than their full sized counterpart.

For a tire footprint that is 1/100 that of a full sized car, there is only 1/1000 of the weight on that tire. That translates into 1/10 the per unit area pressure on that tire compared to a full sized car. All else assumed similar (tire compound etc), let us not forget that for tires, the graph of traction vs pressure (weight) over it is convex ( inverted U shaped).
Now full sized car tires with their higher per unit ground pressure operate closer to the "falling" part of the curve where more weight over the axle actually causes it to grip less. I suspect that the much lower per unit ground pressure of RC car tires actually means they operate on the "rising" part of the curve, where having more weight over a particular axle actually means more traction over that axle
Remember not so long ago where super narrow 21mm tires were all the rage??
I think ist all about the scale factor here, teh physics are the same just that the scale factor has to be taken into account.

Cheers
i always wanted to see that curve for RC rubber tires. It would make a lot of sense why when you change some things like rollbars on a few tires the opposite of what you expect happens...
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Old 06-17-2009, 08:39 PM   #24
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Quote:
Originally Posted by Lab-driver View Post
Basically the more weight you have towards the front of the car the more steering it will have, atleast that's my experience with changing the weight bias.
Incorrect

Quote:
Originally Posted by JeffC View Post
I don't know if this holds true to 4wd r/c cars, but in a full size rear wheel drive stock car, more front weight will make the car push, more rear makes it loose. This is because more weight carries more momentum. A heavier front will resist turning, and a heavier rear will resist straightening out, making the car loose in the middle and exit of the turn.
Correct

The heavier end of the car will change directions slower, it will also not hold a tight line in a corner, centrifugal force will force the heavy end towards the outside of the turn. If the rear is heavier than the front, the rear will slide towards the outside of the corner, thus making the the rear loose. Same for the front creating push.
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Old 06-17-2009, 08:43 PM   #25
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Quote:
Originally Posted by mab_man20 View Post
Today i got XXX-mains tuning guide and the first topic is weight transfer and it does an increadable job describing it. John was correct when he said that the weight should be just behind 50/50 so under breaking the car will be almost 50/50.

Everyone who has ever even thought about racing should pick up the tuning guide, it is simply that good!
Thats an excellent guide... covers everything very well and the cheat sheet in the back is handy to have at the track... mine's pretty beat down (I bought mine back in 01 I think, whenever it first came out) Its good to hear theyre still available.. I'll have to order one.
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Old 06-17-2009, 09:44 PM   #26
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Is the xxx main setup guide any different from the Xray setup guide book that comes with all their TC kits?
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Old 06-18-2009, 09:24 AM   #27
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Seeing as this thread has been brought back to life, the cars have moved on quite alot since then esp as diffs were still standard on most if not all cars then. What are the current day cars with spools running in terms of fr/rr weight bias?
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Old 06-18-2009, 09:29 AM   #28
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On the scales my cyclone is pretty much 50/50 +-5g

I would guess thats the best starting point on a setup.... I makes sense to me that would be the easiest weight distribution to work with on tuning the rest of the car.... If it was off from the begining you'd probably chase handling issues with setup that might otherwise be resolved with a "centered" bias.
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Old 06-18-2009, 05:34 PM   #29
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when trying to balance an rc car front to back do you find the center of the chassis measuring between the center of the front and rear axles?Also,is everyone still on a disagreement on the 60/40 or 50/50.My cars as it sits is at 60/40 i think but if 50/50 is a better place to start the front of my car sits at 50/50 with 1oz added to the front measuring front to rear axles.
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Old 06-18-2009, 05:47 PM   #30
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50/50 will do the best i think then just tune from there
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