Forrest, A 28.7" tall tire has a circumference of PI * 28.7 or 3.17*28.7 or 90.98" or 7.58 feet. 3,000 motor rpm *1 drive shaft revolution / 3.27 rear axle revolutions = 917.43 rpm 917.43 rpm * 7.58 feet circumference of tire = 6,954 feet / minute * 1 mile / 5,280 feet = 1.317 miles / minute * 60 minutes / hour = 79.02 miles per hour.
At 3,000 rpm, with no transmission, or the transmission in high gear (1:1 ratio) the 3.27 rear end will spin at 917.43 rpm making a 28.7" tall tire run 79.02 miles per hour. To get the most acceleration and usable speed from the setup, you should find the maximum safe rpm of the motor, and gear the vehicle just under that rpm by a safe margin, at a maximum speed that you will not exceed. Some conversions use second or third gear to get the motor rpm's up. You could use a shorter tire. One drag racer went to a smaller diameter DC motor that could spin faster, and then used two motors. I hope this helps, Alan On Tue, Nov 26, 2019 at 12:42 PM forrest.whitmore via EV <[email protected]> wrote: > Hello, > > I've read through everything I could find on rear diff setups, however, > most > have been using motors with low RPM capabilities, along with being quite > dated (2008). > > The following are the current specifications for my project: > > *Motor* > Max. RPM: 10000 > Peak power (kW): 170 > Peak power (Nm): 250 > > *Rear Diff IRS* > Ratio: 3.27 > > The motor efficiency is at the higher end of its performance curve. > > That being said, if the vehicle is traveling approximately 80 MPH and the > wheel is spinning at 3000 RPM with 28.7" tires, where does that leave the > motor's RPM? Would it be the wheel RPM /multiplied /by the diff ratio? 3000 > * 3.27 = 9810 RPM? Or would it be the wheel RPM /divided /by the diff > ratio? > 3000 / 3.27 = 917 RPM > > I'm trying to verify where my motor's RPM would reside along its respective > curve. > > Thank you in advance, > Forrest Walker Whitmore > > > > > -- > Sent from: http://electric-vehicle-discussion-list.413529.n4.nabble.com/ > _______________________________________________ > UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub > ARCHIVE: http://www.evdl.org/archive/index.html > INFO: http://lists.evdl.org/listinfo.cgi/ev-evdl.org > Please discuss EV drag racing at NEDRA ( > http://groups.yahoo.com/group/NEDRA) > > -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20191126/eae89645/attachment.html> _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub ARCHIVE: http://www.evdl.org/archive/index.html INFO: http://lists.evdl.org/listinfo.cgi/ev-evdl.org Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/group/NEDRA)
