Graham Rudd Posted April 11, 2002 Share Posted April 11, 2002 For some reason that totally escapes me (perhaps the fact that I'm sat at work, all packed up ready to relocate with absolutely nothing to do has something to do with it) I started thinking about gear ratios and as the only gear ratio I know on the Supra, and handily the one that also makes the maths a little easier is 5th at 1/1 I thought I'd figure out how fast I could theoretically go at 7000rpm. Bearing in mind I know *nothing* about what the gear ratio means I thought I'd apply a little common sense (which it turns out will be a tragic mistake on my behalf! ) So here was my train of thought: 1. Get rpm to rph = 7000*60 = 420000 2. Work out wheel circumf. 18" 285/30 = ~45.72+(285/10*.3*2)*PI = 197.4 3. Centimetres travelled in an hour = 82908000 4. convert result to m = 82908000 / 160934.4 = 515.2 5 WAHEY! 515 MPH in 5th at 7000rpm!!! 6. Ho Hum.. Ok, 515mph eh? Even I know this is wrong so can someone who actually knows something about this subject let me know where I've gone horribly wrong with my assumptions? Clearly I have no idea what 1/1 means, I was assuming that 1/1 meant whatever the thing that is turning at a given RPM *cough* is turning the wheels at the same speed. So what are the things that are turning? Surely my calculations can't be THAT stupid? Someone please tell me I can just divide my result by a constant that represents some mysterious component I don't know about! Yours confused, Graham Link to comment Share on other sites More sharing options...
Guest Mycroft Posted April 11, 2002 Share Posted April 11, 2002 Rear axle ratio. Link to comment Share on other sites More sharing options...
Graham Rudd Posted April 11, 2002 Author Share Posted April 11, 2002 Ahha! Thanks Mycroft. Now... umm does anyone happen to know what this rear axle ratio is? Cheers Graham Link to comment Share on other sites More sharing options...
Guest Mycroft Posted April 11, 2002 Share Posted April 11, 2002 It is the ratio obtained between the number of teeth on the crown wheel and the pinion. :biggrin: (Edited by Mycroft at 11:35 am on April 11, 2002) Link to comment Share on other sites More sharing options...
Graham Rudd Posted April 11, 2002 Author Share Posted April 11, 2002 Err yeah.. cheers Mycroft Is it the same as the final drive value? Just been browsing and found a final drive ratio of 3.266 which would give me 515/3.266 ~158mph in my example, now that sounds more reasonable! Link to comment Share on other sites More sharing options...
Guest Mycroft Posted April 11, 2002 Share Posted April 11, 2002 Yep, you're there! Happy To Help.:biggrin: Link to comment Share on other sites More sharing options...
Guest Martin F Posted April 11, 2002 Share Posted April 11, 2002 To be even more helpful have a look at this spreadsheet :- http://www.mfahie.supanet.com/Supra_6sd.xls I can not take the credit for this it was knocked up by one of the American guys, i just found that the link no longer worked so i uploaded my saved version. Is that a disclaimer ? :biggrin: Link to comment Share on other sites More sharing options...
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