The Traffic Accident Reconstruction Origin -ARnews-

Re: Deceleration by downshifting

Dick Smith (rsmith@gulf.net)
Sat, 1 Mar 1997 16:47:01 -0500 (EST)

Thanks to Mike for his response, in part as follows:

After obtaining model number and serial number of the truck's transmission, contact the transmission manufacturer who can then
give you gearing ratios for each gear set within this transmission. This information coupled with operating engine r.p.m., differential
ratios, tires sizes, etc., can then be utilized to establish range of velocities throughout the gearbox/engine r.p.m. range. Simple math
should then be able to allow you to establish acceleration changes from each gear set.

I still don't quite get it completely. All those ratios together give a torque multiplier which relates engine torque to force at the driving wheels. I can see how this would work to find upshift acceleration rates, since I can find engine torque under load. But in a downshifting situation, I think I need to know the engine "drag" under reverse load, and I don't know how to get at that.???

Thanks for your continuing help.

Dick Smith
rsmith@gulf.net

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