Packard Forum Index » Pre-War (1899-1942)

yes of course, Im hoping to have more updates within the month.
hopefully it wont slip out much further than that

I'm very interested in your progress. Please keep me posted. What ratio(s)are you thinking of making?

thank you
tyamashiro@mozartdev.com

most have suggested 4.00 to 4.07, the engineering dept is still working on the actual size, I should have it shortly once the design is in place.
Thanks

The 29' Packard model 645 that I'm interested in changing gears; I believe has a factory 4.07 gear currently.

Would you consider making a 3.70 range set?

Gee, given the wheel circumference on a 645 and a 4.07 rear axle, you should already be able to comfortably cruise at any speeds you wish, within the limitations of the rest of the vehicle, brakes, suspension and handling, lights, etc. Anything much over 60 mph as a sustained speed and you're probably driving pretty much at the practical design limitations of the vehicle.

Check the following for the 745, I believe 645 had the same size tires.

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I'm continuously amazed at the facts, tables and data that Dave (OD) can pull out of his files to share with all of us and his RPM chart is another example of what he has in his goody box. I took the 4.69 data at 90 mph and 4,296 rpm plugged it into an Excel spreadsheet and generated the information found in the table "745 Data' and added to it additional ratios. As you can see the data aligns fairly well with that in Dave's table, which leads me to think the added ratios are OK

Next I went and measured the radius on the 19 inch 6.50 tires (Lucas) that I have on my 901 and found that it shows a radius (center of wheel to the floor) of 15+ 0.25 inches. This calculates to a circumference of 7.85 ft. Sixty miles is 316,000 ft and would require 40,357 tire revolutions to go that distance. To cover that distance in an hour with my tires (assuming I've done everything correctly, the engine would need to be at 3,094 rpm. This differs by about 8% of that found in the table. This would require the height of the rubber for those in the chart to be about an inch less than mine (again assuming I haven't made an error).

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The disadvantage of going "too far" in high speed rear axle ratios is that you can find yourself spending time in lower gears on upgrades that you previously cruised up easily in high gear. If you can, borrow a ride in a similarly powered and weighted Packard with the ratio you want before making a final decision. Or....consider an overdrive which can give you the best of both.