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06-04-2004, 08:58 AM

#12656

EVOLUTION

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Re: 16/19 Questions..........and answers.....

Quote:

Originally posted by Bivens
Not to be harsh....but.....there seems to be a LOT of questions concerning the 16/19 conversion that indicate that MANY people do not fully understand the concept.....the above post is not the only one, simply the latest....let's see if this helps....

The stock rear drive ratio from the center shaft to the front and rear wheels is 2.526:1 (SAME front and rear....thus, you must run the same diameter tires to have a non-overdriven condition)

The FRONT drive ratio with the 16/19 conversion is 2.375:1 (while the rear remains unchanged at 2.562:1). With the conversion, the front of the car has a drive ratio that results in the front-tires spinning approximately 6% FASTER than the rear tires....therefore, that 6% difference must be compensated for by tire sizes.

The proper tire size to achieve a non-overdriven condition may be determined by calculating the rollout of the front and rears for each turn of the center shaft and picking the proper tire size to achieve the condition you desire.

To simplify things, here are some example tire combinations that achieve a near-even drive ratio front to rear.....(it is not specifically a constant split...but it's close as you will see)

Front.........Rear.........Overdrive #
50mm.........53mm............1.004
52mm.........55.5mm.........0.997
54mm.........57.5mm.........0.999
56mm.........59.5mm.........1.001
58mm.........61.5mm.........1.003
60mm.........64mm............0.997

As you can see....an approximate 3.5mm split achieves a non-overdriven condition (rollout for front and rear equal) for a large range of tire sizes. (slightly less split for small tires... and more split for larger tires)

The main thing to understand is that this conversion allows you to get more even tire-wear (Fronts and rears wear together...without having to constantly true the front tires down to match the ever-shrinking rears). You also get to run the front of the body lower over the wheels......if you like to SLAM the body to the ground. You get the benefit of having less foam on the front tires......good turn-in without excessive tire flex and traction-roll issues (and they're lighter). Finally, assuming you keep a similar rear tire-size to what you would normally run....the front roll center is changed slightly due to the suspension geometry change of adapting to the small front-tires without compromising ride-height.

One last thing to remember......the overdrive percentage of 1.000 is only one option.....you can use an overdriven condition to alter the handling of the car...especially on low-bite tracks. A number higher than 1.00 means that the front tires tend to "pull" the rear of the car.....a number less than 1.00 means that the rear tires "shove" the front around.......each has a slightly different feel. This is easier to distinguish on low-bite tracks and is not so apparent on high-traction surfaces.

If you do not run SOME split front-to-rear....then you will unnecessarily stress the drive-train and wear out the belts and pulleys faster.........recall from above that there is a 6% overdrive created with the conversion and if the tires are equal-sized front-to-rear then the front tires are trying to pull the rear along 6% faster than it wants to pull itself......

If someone has a place for me to post an image....I can take a screenshot of a chart I have created in excel for ease of tire-size selection......I can send it to anyone in excel or pdf format also. PM me if you'd like a copy. I'd be happy to answer any questions about this post....please PM me.

I sent you a PM.

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