sewebster Posted December 6, 2011 Share Posted December 6, 2011 (edited) I made up a spreadsheet to calculate speeds and rpms based on your gear ratios. You can adjust all the parameters to calculate what you want. Here is a pic of it: Not sure if anyone cares about this, it's pretty basic, but I found myself thinking about how changing gearing would affect things and decided to stop calculating it over and over. Here is the link to the spreadsheet. Happy for any comments etc. Note that it is in km by default, but you can just change the unit value to get miles. Set up now for the manual transmission (FS5R30A). Edited December 6, 2011 by sewebster Link to comment Share on other sites More sharing options...
JamesRich Posted December 6, 2011 Share Posted December 6, 2011 Sweet! So I can do 120 mph in first gear if I can get the motor up to 23,127 rpm! That shouldn't be too hard for a nissan, maybe just need a larger fuel pump. Good job on the spread sheet! James Link to comment Share on other sites More sharing options...
1994SEV6 Posted December 6, 2011 Share Posted December 6, 2011 (edited) I thought these transmissions didn't have an overdrive year in the manuals? Does the red mean I'm going too fast? Edited December 6, 2011 by 1994SEV6 Link to comment Share on other sites More sharing options...
MY1PATH Posted December 6, 2011 Share Posted December 6, 2011 4th is 1:1 5th is od, a measly Od that only drops you about 400 rpm. Red appears to be 'redline' Link to comment Share on other sites More sharing options...
Precise1 Posted December 6, 2011 Share Posted December 6, 2011 Those numbers don't match how my first pathfinder performed (1995 5 speed with 31" tires). It sure as hell wasn't going 70mph in 5th gear at 1800rpm!! B Link to comment Share on other sites More sharing options...
adamzan Posted December 6, 2011 Share Posted December 6, 2011 Are you sure those numbers aren't in KM since he is from BC Link to comment Share on other sites More sharing options...
sewebster Posted December 6, 2011 Author Share Posted December 6, 2011 Note that it is in km by default, but you can just change the unit value to get miles. I did mention the km/miles thing If you download the spreadsheet you can switch to miles by changing the units cell to 1.6. Might as well post up a "miles" pic: Link to comment Share on other sites More sharing options...
Precise1 Posted December 6, 2011 Share Posted December 6, 2011 LOL My bad. Guess I hadn't woken up yet. Besides, who the hell wants to live in Canada?? Yeah, those numbers look right now that they are in miles... B Link to comment Share on other sites More sharing options...
rwd5021 Posted March 5, 2012 Share Posted March 5, 2012 (edited) Ok so the bottom part shows what the rpm's SHOULD be at if everything is in working order right? My 5 speed with 4.3 gearing and 31" tires is considerably higher than this chart. Cruising at 70 my rpm's sit right at 3500 in fifth gear. Anybody know of anything in particular I should check into that could cause this? Edited March 5, 2012 by rwd5021 Link to comment Share on other sites More sharing options...
sewebster Posted March 6, 2012 Author Share Posted March 6, 2012 Ok so the bottom part shows what the rpm's SHOULD be at if everything is in working order right? My 5 speed with 4.3 gearing and 31" tires is considerably higher than this chart. Cruising at 70 my rpm's sit right at 3500 in fifth gear. Anybody know of anything in particular I should check into that could cause this? Wrong speedo gear? If you have the gear for the 29" tires then when your speedo says 70 it really means 75. But 75 still shouldn't be 3500 rpm. Presumably there is either an error in the spreadsheet, or something wrong with your speedo or tach. Not too helpful, I know. Are you sure you have 4.3 gears? Link to comment Share on other sites More sharing options...
rwd5021 Posted March 6, 2012 Share Posted March 6, 2012 Pretty sure, says hg43 in the engine bay. But now that I look at the sticker on the door it does say 235/75r15, is that 29"? If so, I guess that kinda makes up for it but like you say it still shouldn't be that high... Any more ideas?? Link to comment Share on other sites More sharing options...
1994SEV6 Posted March 7, 2012 Share Posted March 7, 2012 Pretty sure, says hg43 in the engine bay. But now that I look at the sticker on the door it does say 235/75r15, is that 29"? If so, I guess that kinda makes up for it but like you say it still shouldn't be that high... Any more ideas?? i saw your problem the other day, and I went through and considered all errors. Even with 29" tires, your RPMs still wouldn't be that high. Same with the 4.6 Link to comment Share on other sites More sharing options...
pathybuilder Posted March 7, 2012 Share Posted March 7, 2012 Don't think it's your tires. I assume when you say 70mph you talking about what you're speedo is reading. You are going 75-80 but you won't know that unless your talking GPS speed or something. The speed on the speedo vs gear is related directly to your RPM. I don't think that 3500 RPM at 70mph is that out of the norm. It's been a while since I drove my truck but I'm pretty sure it revs close to 2900 or so at 60. 4.3 gears and a 5 speed. Link to comment Share on other sites More sharing options...
rwd5021 Posted March 7, 2012 Share Posted March 7, 2012 Don't think it's your tires. I assume when you say 70mph you talking about what you're speedo is reading. You are going 75-80 but you won't know that unless your talking GPS speed or something. The speed on the speedo vs gear is related directly to your RPM. I don't think that 3500 RPM at 70mph is that out of the norm. It's been a while since I drove my truck but I'm pretty sure it revs close to 2900 or so at 60. 4.3 gears and a 5 speed. My mistake, I should have been more clear. When I said 70 that is a speedometer app reading. I always use that and didn't even think about it on my first post. The truck's speedometer is at 65 and rpm's are at 3500, 5th gear, vg30 engine, 31's, 4.3 gear ratio. Does THAT seem too high? I just want to make sure everything's ok. I never used to take the wd21 to 70 mph, but I just moved and will be on the freeway 40 miles every day now so I want to fix any problems that may cause this. It seems like I'll be wasting a lot of extra money on gas if not. Link to comment Share on other sites More sharing options...
sewebster Posted March 7, 2012 Author Share Posted March 7, 2012 My mistake, I should have been more clear. When I said 70 that is a speedometer app reading. I always use that and didn't even think about it on my first post. The truck's speedometer is at 65 and rpm's are at 3500, 5th gear, vg30 engine, 31's, 4.3 gear ratio. Does THAT seem too high? I just want to make sure everything's ok. I never used to take the wd21 to 70 mph, but I just moved and will be on the freeway 40 miles every day now so I want to fix any problems that may cause this. It seems like I'll be wasting a lot of extra money on gas if not. Well, I wouldn't worry too much at this point. Since you have a manual transmission there isn't really any way that your engine can be turning faster than it "should" unless your clutch is slipping. I assume that if your clutch were slipping that much that you would smell it So, there are four possibilities I see: clutch slipping, gear ratios/tire sizes different than expected, measurement error on speed or RPM, spreadsheet error. Link to comment Share on other sites More sharing options...
andreus009 Posted March 7, 2012 Share Posted March 7, 2012 Nice spreadsheet! Thanks Link to comment Share on other sites More sharing options...
rwd5021 Posted March 7, 2012 Share Posted March 7, 2012 Ok thanks. And yes nice spreadsheet! sorry for threadjacking. Link to comment Share on other sites More sharing options...
sewebster Posted March 7, 2012 Author Share Posted March 7, 2012 No problem. It would be nice to get some confirmation of the numbers. I'm pretty confident I did the calculations correctly though. Just went through it again... the numbers do seem a bit lower than I seem to remember from when I drive around. Really don't see how they could be wrong though. Here is the calculation for the bottom table: RPM = SPEED(MPH) * GEAR_RATIO * TRANSFER_RATIO * DIFF_RATIO / Pi / TIRE_DIA(INCHES) / 2.54(cm per inch) * 100(cm per metre) * 1000(m per km) / 60(mins per hour) * 1.61 (km per mile) In this case then: 2864 = 70 * 0.862 * 1 * 4.375 / 3.14159 / 31 / 2.54 * 100 * 1000 / 60 * 1.61 I wonder if one of the gear ratio numbers is wrong in the FSM or something. Link to comment Share on other sites More sharing options...
schro Posted December 19, 2012 Share Posted December 19, 2012 No problem. It would be nice to get some confirmation of the numbers. I'm pretty confident I did the calculations correctly though. Just went through it again... the numbers do seem a bit lower than I seem to remember from when I drive around. Really don't see how they could be wrong though. Here is the calculation for the bottom table: RPM = SPEED(MPH) * GEAR_RATIO * TRANSFER_RATIO * DIFF_RATIO / Pi / TIRE_DIA(INCHES) / 2.54(cm per inch) * 100(cm per metre) * 1000(m per km) / 60(mins per hour) * 1.61 (km per mile) In this case then: 2864 = 70 * 0.862 * 1 * 4.375 / 3.14159 / 31 / 2.54 * 100 * 1000 / 60 * 1.61 I wonder if one of the gear ratio numbers is wrong in the FSM or something. The printed tire diameter would be for an unladen tire. A real world application would depend on checking the distance from the centre of the axle/hub to the ground at recommended tire pressure in a laden vehicle and multiplying by 2. This effectively gives you a smaller diameter than the one printed on the rubber. I don't know for certain how much of a difference this would result in or how much this actually affects diameter, but I do know that if I place a jack under my rear axle, I have to lift the vehicle a fair bit before the rubber leaves the pavement (maybe an inch to an inch and a half, so my 30" tires would be 27" or 28" for the sake of the spreadsheet) Link to comment Share on other sites More sharing options...
sewebster Posted December 20, 2012 Author Share Posted December 20, 2012 Hmm. Well, what actually matters is how far your truck moves for one tire rotation... the "circumference" of the tire. This probably isn't going to change as much due to squishing as the distance from the axle to the ground. Link to comment Share on other sites More sharing options...
sewebster Posted December 20, 2012 Author Share Posted December 20, 2012 I can't seem to edit my old posts, but here is a fixed link to the spreadsheet and the screenshots. http://sewebster.com/gearmaster.xls kilometres: miles: Link to comment Share on other sites More sharing options...
fixinto Posted January 11, 2013 Share Posted January 11, 2013 Those numbers don't match how my first pathfinder performed (1995 5 speed with 31" tires). It sure as hell wasn't going 70mph in 5th gear at 1800rpm!! B ya my 96 5 speed is right at 3k at 68ish Link to comment Share on other sites More sharing options...
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