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Old 01-16-2003, 12:13 AM   #46
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Quote:
Originally posted by AMGRacer
You are doing an awful lot of guessing here. I was actually at the track with these guys and they specifically were saying that they true the tires 1mm less on the front to give better handling. This was for a 5 minute heat.

Instead of arguing whats best or not lets just accept that some people like it and others do not. Like I have said it worked great for me, and I am 672nd in the country.
Amg.

You know... it is afterall your story... so by all means, tell it how you want. The fact of the matter is that I have in noway disputed what you're saying. Running 1mm could arguably yeild better handling as well as being good wear management. Kind of like an orange can taste good and be good for you. If you hadn't got all defensive, you would not of overlooked the fact that I prefaced my opinion on overdrive with "I personally". meaning what matters to me...or as you say " some people like it and others do not." So let's not get hypycritcal. Aight!!!
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Old 01-16-2003, 02:30 AM   #47
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Quote:
Originally posted by Jonathan
Amg.

You know... it is afterall your story... so by all means, tell it how you want. The fact of the matter is that I have in noway disputed what you're saying. Running 1mm could arguably yeild better handling as well as being good wear management. Kind of like an orange can taste good and be good for you. If you hadn't got all defensive, you would not of overlooked the fact that I prefaced my opinion on overdrive with "I personally". meaning what matters to me...or as you say " some people like it and others do not." So let's not get hypycritcal. Aight!!!
I was clarifing that it was NOT for "good tire management" as you claimed. Cant see why that was defensive, you just obviously felt the need to try and interpret (incorrectly) my story. I was just clarifying what you said was NOT what happened. Aight.

Last edited by AMGRacer; 01-16-2003 at 02:51 AM.
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Old 01-16-2003, 03:40 AM   #48
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I see a lot of people here make claims or statments according to theory or what they think before doing any test on the track. most of the time track experiment is different from theory and even result of the experiment is different from track to track.
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Old 01-16-2003, 03:49 AM   #49
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That I definately agree with. I use different ratios on different tracks to obtain the best outcome. Even on my local club track where we can change the layout around the islands I find that I can have a large change in ratio.
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Old 01-16-2003, 04:43 AM   #50
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Quote:
Originally posted by Manticore
I see a lot of people here make claims or statments according to theory or what they think before doing any test on the track. most of the time track experiment is different from theory and even result of the experiment is different from track to track.
I agree....

I personally true my tires 2mm smaller on the front. Why? I feel it gives me more turn, and as a bonus, it evens out the wear rate during the main.

Am I overdriving the front? ..... Yes, by 0.968%

If I ran the same size am I overdriving the front? .... Yes by 1%
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Old 01-16-2003, 10:00 AM   #51
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Quote:
Originally posted by sparksy
I agree....

I personally true my tires 2mm smaller on the front. Why? I feel it gives me more turn, and as a bonus, it evens out the wear rate during the main.

Am I overdriving the front? ..... Yes, by 0.968%

If I ran the same size am I overdriving the front? .... Yes by 1%
Okay, I'm confused.

I thought that OVERdrive was having fronts larger than rears and UNDERdrive was the opposite. . .

But if you've got smaller tires on the front. . .and you've got overdrive. . .

I'll have to try the smaller fronts - I've been running smaller rears and I really like it. . .but will have to try the other.
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Old 01-16-2003, 10:25 AM   #52
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Quote:
Originally posted by sparksy
I personally true my tires 2mm smaller on the front. Why? I feel it gives me more turn, and as a bonus, it evens out the wear rate during the main.

Am I overdriving the front? ..... Yes, by 0.968%
Sparsky:

Do you have a chart with overdrive ratios for the MTX3? Trying to calculate, but so many pulleys and so many belts (have mercy with me, I'm a previous shaft racer )
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Old 01-16-2003, 10:28 AM   #53
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Not necessarily Boomer. You can have the front tires smaller than the rear and still achieve overdrive. It all depends on the pulleys you are running and the rpm your engine is running at.
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Old 01-16-2003, 11:59 AM   #54
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Quote:
Originally posted by modellor
Not necessarily Boomer. You can have the front tires smaller than the rear and still achieve overdrive. It all depends on the pulleys you are running and the rpm your engine is running at.
question : how does the rpm of the engine affects the over drive of the car ? i know by changing the diameter of the tire changes the distance traveled per revolution of that wheel. by changing the pulley ratio of one axial changes the rotational speed of that axial. either way will create a differential in linear speed between the two axial thus achieving over drive or under drive. i have problem connecting an engine’s rpm with over drive/under drive of the car, maybe you can help me to understand this.

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Old 01-16-2003, 12:15 PM   #55
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It doesn't. Engine RPM has no effect on overdrive ratio. I belive what he was trying to say was that Overdrive ratio is affected by tire diameter and tire diameter affects engine RPM and hece and here comes another one, roll out. This is why in 1/8th we often use a gear ratio and roll out chart. This factors in rear tire diameter, pinion and spur gear size and will give you the roll out for both 1st and 2nd gear. This allows you to make gearing choices (i.e. how many teeth difference between 1st and 2nd pinion or spur) and also alows you to see how your ratio is affected by changes in tire size. Overdrive and everything it entails is a lot more complicated than just truing some tires down so that you can mount a body lower.
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Old 01-16-2003, 12:18 PM   #56
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I will assume that you understand the theory of volume. If you double the length each side of a cube you actually quadruple the volume of the cube.

The same thing happens with increasing the rpm of an engine. The more rpm an engine produces the faster a car goes. This is due to the gear ratio. Now, at a fixed rpm the rear wheels will rotate at a fixed rate. The front wheels are overdrive so they are rotating at a faster fixed rate.

If you increase the rpm in the engine the rear wheels will rotate slightly faster to match the engine but because the front is overdrive you will increase the front wheel rotation speed at a much larger percentage.

Hope this helps
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Old 01-16-2003, 12:58 PM   #57
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Quote:
Originally posted by modellor
I will assume that you understand the theory of volume. If you double the length each side of a cube you actually quadruple the volume of the cube.

If you increase the rpm in the engine the rear wheels will rotate slightly faster to match the engine but because the front is overdrive you will increase the front wheel rotation speed at a much larger percentage.

Hope this helps
yes, but calculation of the volume of a cube involves an equation to the third order, whereas gear ratio, over drive/ under drive ratio involves just a simple linear equation. I think the over drive/under drive ratio does not change at any rpm, unless you look at it as an absolute value, not as a percentage.

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Old 01-16-2003, 01:42 PM   #58
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i think your making it more complicated then needed

overdrive front wheels and it will drive like front wheel drive pulling car around making it easier to drive

underdrive the front wheels and it will be more like rear wheel drive more steering but rear could slide out

the ratio stays the same through all rpm as the fronts and rears are still driven at one point from 2 speed shaft

and of course its also used to equalize tire wear
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Old 01-16-2003, 02:19 PM   #59
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modellor, overall tire diameter decreases due to wear. This tire wear is rarely equal front/rear. This will affect or change the overdrive ratio during a run and also as the tires wears or become smaller the engine rpm will increase. However if we take wear (tire diameter) out of the equation, overdrive does not affect engine RPM. If we take an MRX-3 to have an overdrive ratio of 1.0 running a 26t side pulley tire diameter would be 69.5mm frotn, 77.0 rear. It does not matter if the engine is turning at 5k rpm or 35k rpm, the front tire is still turning 1 time for every 1 revolution of the rear tires. The ratio is fixed and stays constant just like a bicycle. If you lift the rear for every revolution of the sprocket the rear wheel turns 3 times, you get on the bile and pedal to 40 mph the rear wheel still turns 3 times per sproket revolution. These are fixed numbers and do not change (again unless you factor in tire wear).
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Old 01-16-2003, 02:24 PM   #60
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I understand what you are saying but look at the wheels as the third order. Take into consideration the volume of the wheels (by which I mean different diameters equal different mass).

At a given rpm the rear wheels will rotate at a certain speed related to the gearing given. If the front wheels are smaller they have to rotate faster to keep up. Now, if you apply overdrive the front wheels go faster again at the percentage set.

Now, if you increase the rpm the rear wheels will increase speed to match the rpm of the engine. But because the front wheels are smaller and have less volume they will rotate at a greater speed again. The percentage of overdrive may stay the same but the front wheels will rotate faster at a greater percentage in comparison to the rear wheels.
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