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Previous Thread Next Thread Print Thread Rate Thread Page 2 of 2 1 2 Re: rpm question [Re: geocrasher] #1066043 11/13/13 12:07 AM Joined: Feb 2011 Posts: 288 Alabama SledgeHammer OP Mudrunner Quote Quote at 55mph..in 5th gear with 30's it says 3500 Unless your axles have 5.29's in them (incredibly unlikely) your tach or speedo is simply off. Speedo is easiest to check with a GPS, or even a passenger with a stopwatch and an open road, milepost markers and some basic math. this is why I asked the question on what everyone is running because using gps at 55mph,it sounds like it is wound up at 3500 rpm.I mean it just doesn't feel like it wants to go much faster.I mean I can but I have had it near 3800 rpm at somewhere near 60 mph or so.I thought maybe this thing is just that weak...lol Something must be just off cause I get pretty good gas mileage. Re: rpm question [Re: SledgeHammer] #1066044 11/13/13 01:36 AM Joined: Jan 2000 Posts: 16,227 Bay Area, CA off-roader Web Wheeler Quote Quote Quote at 55mph..in 5th gear with 30's it says 3500 Unless your axles have 5.29's in them (incredibly unlikely) your tach or speedo is simply off. Speedo is easiest to check with a GPS, or even a passenger with a stopwatch and an open road, milepost markers and some basic math. this is why I asked the question on what everyone is running because using gps at 55mph,it sounds like it is wound up at 3500 rpm.I mean it just doesn't feel like it wants to go much faster.I mean I can but I have had it near 3800 rpm at somewhere near 60 mph or so.I thought maybe this thing is just that weak...lol Something must be just off cause I get pretty good gas mileage. Methinks that somethings afoot. <img src="/forums/images/graemlins/wink.gif" alt="" /> Carb issues maybe? Don't recall the history of your rig but that's high (assuming the tach's accurate). Off Roader 98 Montero with the Winter Package 89 Montero minty clean and reserved for overlanding trips or Cars and Coffee events 96SR (3.15:1 xcase, 35's) gone to the rust gods 96SR Build Up Thread Old web page Old web page Re: rpm question [Re: off-roader] #1066045 11/13/13 01:47 AM Joined: Nov 2008 Posts: 1,435 Milwaukee Wisconsin plh Body Damage is Cool Quote Quote Quote Quote at 55mph..in 5th gear with 30's it says 3500 Unless your axles have 5.29's in them (incredibly unlikely) your tach or speedo is simply off. Speedo is easiest to check with a GPS, or even a passenger with a stopwatch and an open road, milepost markers and some basic math. this is why I asked the question on what everyone is running because using gps at 55mph,it sounds like it is wound up at 3500 rpm.I mean it just doesn't feel like it wants to go much faster.I mean I can but I have had it near 3800 rpm at somewhere near 60 mph or so.I thought maybe this thing is just that weak...lol Something must be just off cause I get pretty good gas mileage. Methinks that somethings afoot. <img src="/forums/images/graemlins/wink.gif" alt="" /> (assuming the tach's accurate). Yea, maybe the Tach is off by 1000 RPM. Calculation says 2440 at 55 mph '83 Might Max: IG @83mmax '88 Raider: my OG '89 Raider: rescued '92 RS M/T: sold '93 SR: sent to crusher '05 Montero LTD: sold '18 PHEV: wife's daily '14 OL GT http://www.tuffpans.com Re: rpm question [Re: plh] #1066046 11/13/13 02:48 AM Joined: Feb 2005 Posts: 7,458 Montero Ranch rxinhed Trail Leader Math...check...exactly. <img src="/forums/images/graemlins/smile.gif" alt="" /> 30 x PI (3.1416) = 94.248 (circumference in inches) 63360 (# inches per mile) / 94.248 = 672.7 tire revolutions per mile 672.7 x 4.625 (gear ratio) = 3109 engine revolutions per mile in 4th gear Not knowing the amount of overdrive...just multiply the OD percentage by the non-OD number above. K? <img src="/forums/images/graemlins/wink.gif" alt="" /> 1987 Raider - Roxy 1988 Mighty Max 2.6L Turbo - Pearl 1997 Mountaineer V8 - Freddy 2000 Excursion V10 - Freya Re: rpm question [Re: off-roader] #1066047 11/13/13 03:14 AM Joined: Sep 2011 Posts: 628 Castle Rock WA, US geocrasher Rock Warrior Quote Carb issues maybe? Don't recall the history of your rig but that's high (assuming the tach's accurate). No carb issue will affect RPM like that. This is a matter of gearing and inaccurate instrumentation. Either your speedo is off and you're really doing 70mph or so, or your speedo is off. Its one or the other. Figure out which and go from there. And, don't have a friend drive in front of you at a specific speed, because cars, and their drivers, are commonly several mph off. 1987 Raider, 346K miles and going strong -31" tires, otherwise stock. http://tidbitsfortechs.com/ http://actionpcs.com <-- $39 remote PC repair, guaranteed. How to include pictures in threads on 4x4wire (Youtube video) Re: rpm question [Re: rxinhed] #1066048 11/13/13 03:41 AM Joined: Aug 2009 Posts: 989 Prescott AZ H haztoys Rock Warrior Quote Math...check...exactly. <img src="/forums/images/graemlins/smile.gif" alt="" /> 30 x PI (3.1416) = 94.248 (circumference in inches) K? <img src="/forums/images/graemlins/wink.gif" alt="" /> And your tire is 'not' 30 in....Take a tape and measure from the ground to the center of the axle ..Then times (X) that number by two ..That will get you the 'real' tire size the 'rolling tire size'..No matter what the tire says on it they are always wrong on the real size Re: rpm question [Re: rxinhed] #1066049 11/13/13 03:58 AM Joined: Nov 2008 Posts: 1,435 Milwaukee Wisconsin plh Body Damage is Cool Quote Math...check...exactly. <img src="/forums/images/graemlins/smile.gif" alt="" /> 30 x PI (3.1416) = 94.248 (circumference in inches) 63360 (# inches per mile) / 94.248 = 672.7 tire revolutions per mile 672.7 x 4.625 (gear ratio) = 3109 engine revolutions per mile in 4th gear Not knowing the amount of overdrive...just multiply the OD percentage by the non-OD number above. K? <img src="/forums/images/graemlins/wink.gif" alt="" /> Russell, your calculation is at 60 mph. He was referencing 55 mph which in 4th gear is 2851 RPM and 5th gear 2440 RPM KM145 is 0.856 OD in 5th '83 Might Max: IG @83mmax '88 Raider: my OG '89 Raider: rescued '92 RS M/T: sold '93 SR: sent to crusher '05 Montero LTD: sold '18 PHEV: wife's daily '14 OL GT http://www.tuffpans.com Re: rpm question [Re: haztoys] #1066050 11/13/13 04:04 AM Joined: Nov 2008 Posts: 1,435 Milwaukee Wisconsin plh Body Damage is Cool Quote Quote Math...check...exactly. <img src="/forums/images/graemlins/smile.gif" alt="" /> 30 x PI (3.1416) = 94.248 (circumference in inches) K? <img src="/forums/images/graemlins/wink.gif" alt="" /> And your tire is 'not' 30 in....Take a tape and measure from the ground to the center of the axle ..Then times (X) that number by two ..That will get you the 'real' tire size the 'rolling tire size'..No matter what the tire says on it they are always wrong on the real size Absolutely sorta correct! Tire does grow at speed. a little. But to be at 3500 RPM at 55 MPH his tire "real" height would be 21" '83 Might Max: IG @83mmax '88 Raider: my OG '89 Raider: rescued '92 RS M/T: sold '93 SR: sent to crusher '05 Montero LTD: sold '18 PHEV: wife's daily '14 OL GT http://www.tuffpans.com Re: rpm question [Re: plh] #1066051 11/13/13 05:51 AM Joined: Feb 2005 Posts: 7,458 Montero Ranch rxinhed Trail Leader Yes, I calculate at 60mph for ease of calculation. Simple coefficient of 0.9167 to calc at 55mph. <img src="/forums/images/graemlins/smile.gif" alt="" /> Re: rpm question [Re: plh] #1066052 11/15/13 02:01 AM Joined: Nov 2008 Posts: 1,435 Milwaukee Wisconsin plh Body Damage is Cool Quote Quote Quote Quote I would like to know for the 4cy 5 speed guys,at hiway speed,say 55-60....what rpm are you turning and post tire size also. Mine seems kinda high at 60 mph. What making you think it's high? at 55mph..in 5th gear with 30's it says 3500 Check this: DropBox - Gear Ratio RPM MPH Calculator (Excel or OpenOffice) Updated. Now includes 5.29 rear ratio '83 Might Max: IG @83mmax '88 Raider: my OG '89 Raider: rescued '92 RS M/T: sold '93 SR: sent to crusher '05 Montero LTD: sold '18 PHEV: wife's daily '14 OL GT http://www.tuffpans.com Page 2 of 2 1 2 Moderated by  4x4Wire, Macka, Mudraider, off-roader, PHIL_, rxinhed  Hop To Mitsubishi Forums ------  Mitsubishi 4x4 and SUV Tech  Mitsubishi Diesels  Mitsubishi ArchiveToyota Forums ------  Early Toyota Trucks  Toyota 4Runner, FJ Cruiser &...  T100 & Tundra Forum  Tacoma Forum  Toyota Tech ArchiveJeep Forums ------  Jeep Talk  Jeep TechIsuzu Forums ------  Isuzu 4x4 & SUV Talk  Isuzu 4x4 & SUV Tech  Isuzu DieselsKia Forums ------  Kia Talk  Kia Sportage & Sorento TechOff Topic Chat ------  4x4 Gallery  Off-Topic Chat  Recreational Access & Land ...  Politics4xForums ------  Outdoor Gear  General 4x4 Discussion  Tools and Fabrication  General Communications  Amateur Radio  GPS and MapsParts Bin ------  Private Party - Garage Sale  Private Party - Items wanted  Vendors, Hot Deals, Group Buys4x4Wire Back Yard ------  Suzuki Forum  AZ Crawler Crew  Cal-Nev Crew  General Ford 4x4 & SUV Forum  General Dodge 4x4 & SUV Forum  General Chevy 4x4 & SUV ForumFeedback & Testing ------  Problems, Questions, Suggestions4x4Wire Staff ------  Forum Moderators  Problem Threads Print Thread Switch to Threaded Mode 5 Excellent 4 Good 3 Average 2 Bad 1 Terrible View Profile Private Message Follow User Forum Posts View Profile Private Message Follow User Forum Posts View Profile Private Message Homepage Follow User Forum Posts View Profile Private Message Follow User Forum Posts View Profile Private Message Homepage Follow User Forum Posts View Profile Private Message Follow User Forum Posts View Profile Private Message Homepage Follow User Forum Posts View Profile Private Message Homepage Follow User Forum Posts View Profile Private Message Follow User Forum Posts View Profile Private Message Homepage Follow User Forum Posts

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