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OK gang, got a question on the rear tires on the AW Top Fuel dragsters. Has anyone tested to see if the size makes a big difference in how fast they are? I'm asking that since I wanna make this thing fast. Running poly mags, magnatraction rear gear conversion, 5.8 balanced and trued arm,shunts and braids, all in an original Aurora "Generation 2" chassis. Are the larger, .6 somehing diameter tires fast, or should I go to something closer to what the other 4 gear chassis run (in the .510-.525 range)? I have heard that the bigger diameter tires are slower than the others, especially out of the gate, but I was just curious if anyone has really tested this much yet? I do have urethane slip on replacements for the larger diameter, and I have several slip-on options as well as 'homemade' silifoams for the smaller ones.
Anybody??:confused:
Ron (Bondo)
 

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Ron, at our last drag race one guy had regular AFX wheels on a 4 gear chassis and it was remarkably faster than the rest of the field. we don't usually have to tech the cars and no one that noticed said anything until the race was over.
anyway, I am not sure of the outside diameter of the wheel tire combination that he used, but it would seem that the lesser weight of the smaller tires plus the ease of which the motor could attain higher RPM made a clear difference. certainly worth experimenting with for sure.
even trying some of those wonderful narrowed wheels with silifoams that Sgrig makes on a very limited basis would probably be a huge improvement over trying to get solid rubber or slip on silicone tires moving. the mass of the tire being one parameter. and I really think the diameter of the smaller tire is advantageous to reaching high RPMs quicker. and, of course, getting traction magnets closer to the rail could help performance.

good question and I look forward to other replies.

folks?
 

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I always take a few steps back.

To the axle first. Does it run true?

Then install the wheels. Do they run true? Do they add any weird vibration?

Finally install the tires and true them. Again be sure there is no additional vibration.

Assume nothing and dont accept anything that isnt dead nuts smooth.

Edit: I fergot, Al is right. The lighter the better!
 

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Discussion Starter #5
Hey Taz..I'm asking so I can beat EVERYBODY!! LOL!!;):)
And, thanx guys. I kinda thought that the smaller tires might work better. As I haven't tested it yet, I have no reference point. But during the building of it, axle is straight and true, wheels are trued, and spin smooth. Also, the chassis had very little wear, so the axle holes have very little play as well. ;) I hope to be testing this very soon. :)
Ron (Bondo) :dude:
 

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Ron on the GN that I built for SGrigs mail in race, I used wheels tires just slightly over .500 diameter, and 1/2 the width of a typical AFX wheel tire. Using larger diameter rims kept the weight of the sponge / silicone down, When I got them done the weight of the rear tires were just over 1/2 of an original AFX wheel tire combo, or a typical sili-foam setup. To me rotational mass is the key, the less the better. We are very limited in how much HP & Rpm were going to make from the arm / electrical on these cars. To me the answer is rotational mass & weight. The downfall with my tire setup was getting the silicone mixture right, as this car was shredding the silicone layers in little balls most of the way down the track on all but the last pass, the first layer on the car had more adhesive in it. The other thing that tires do is affect the overall gear ratio, shorter tires will cause it to wind out faster, where taller tires will provide more speed, If the motor can supply the req. additional torque needed to propel the car. I am sure there is a magic diameter tire size for a given distance track that works perfect, I dont have the proper facility to test this theory out for drag racing but I can easily see several tenths difference in lap times on the road car setups when you get the right size tires on them & the car is much more responsive. But a road course is a little different situation...

Boosted
 

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Boosted is right on the money with the gear ratio effect with different tire sizes. A larger tire has a longer tread distance per each 360 degree rotation. So, physics being set aside, a larger tire will move you farther in the same rotation effort. But in the real world, "rotational" weight kills a great deal of the larger tire advantage. You can make this up to a certain degree with gear changes, but torque driving the larger tires comes into play. Like others said before, reducing the weight of the moving tire/rim will improve this. I'm not familiar with the rules of the event mentioned, but you can drill out the rims, run hollow axles and use a lighter weight sponge tire compound (more porous) with a very light application of silicon. Lighten any of the rotational parts you can, axles and gears included. If the rule book allows.:thumbsup:

-Paul
 

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Reduced Moment

Hollow silicone tires should help too! They reduce the overall mass, and reduce the moment of inertia of the rear axle assembly.
 

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If you really want to run the taller tires you might try putting a Super 2 gear in the back. I don't know if it will work but it's worth a try.You'll loose some top end speed, but it will get you out of the hole faster.
 
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