Mark90 Posted March 2, 2006 Share Posted March 2, 2006 The subject of changing gearing (gearbox, transferbox, tyres, diffs) and how it will affect the vehicle come up often enough that I thought it'd be useful to update the old spreadsheet I knocked up when I was considering gearbox options myself. I 'think' I've made things clearer and easier to use, but just in case there's some instructions. I have left it as two sections so you can compare your current set up with any intended changes and see the effect. I've also expanded the sample data section, although I can't find a ratio for a GKN overdrive so that's the main omission in the data section. Thanks to Red90/John for letting me use the data from his website, otherwise there would have been far more omissions. Anyway let me know what you think.... Clicky link Quote Link to comment Share on other sites More sharing options...
Troddenmasses Posted March 2, 2006 Share Posted March 2, 2006 Any chance of the username and password? Thanks. Quote Link to comment Share on other sites More sharing options...
istruggle2gate11 Posted March 3, 2006 Share Posted March 3, 2006 Hi Mark, Thats much much better, I have tidied my previous version up, buty not as much as that. One thing I have done to my old copy was to use the calculated data to create a simple bar chart on an other page - very easy to see the options. As much as I appreciate your efforts, I curse you at the same time! Now, because of your calculator, I have gone with the LT95 which can run 35" and still have the same gearing as my LT77 with 32". Youve cost me hundreds of ££££££ Thanks again. Quote Link to comment Share on other sites More sharing options...
Mark90 Posted March 3, 2006 Author Share Posted March 3, 2006 I suppose I could put some charts on another sheet. I'll have a look at that when I get a mo. TM, why do you need to unlock the worksheets? Quote Link to comment Share on other sites More sharing options...
Troddenmasses Posted March 3, 2006 Share Posted March 3, 2006 (edited) I suppose I could put some charts on another sheet. I'll have a look at that when I get a mo.TM, why do you need to unlock the worksheets? I don't. I clicked on the link, and it asked me for a username and password to be able to look at the file. Edited - I clicked cancel, and it took me into the program. Really good - thanks very much. Edited March 3, 2006 by Troddenmasses Quote Link to comment Share on other sites More sharing options...
Mark90 Posted March 3, 2006 Author Share Posted March 3, 2006 Ah right, dunno what that was all about, there's no restrictions on accessing the file. At least you managed to get in. Quote Link to comment Share on other sites More sharing options...
honitonhobbit Posted March 3, 2006 Share Posted March 3, 2006 Mark Calc problem? 200TdiLT77+1.222:1TBox+3.45:1diffs+30.5"tyres does not equate to 81mph at 3K rpm, about 14mph out Quote Link to comment Share on other sites More sharing options...
Mark90 Posted March 3, 2006 Author Share Posted March 3, 2006 I'm pretty sure the calculation is right, I will double check though. As that sounds like your motor are you sure the actual rolling diameter of your tyres is 30.5? The only way to get an accurate figure for this is with chalk lines on the ground and rolling the vehicle. Quote Link to comment Share on other sites More sharing options...
landrover598 Posted March 3, 2006 Share Posted March 3, 2006 does not equate to 81mph at 3K rpm, about 14mph out Your doing 95 at 3000 rpm Quote Link to comment Share on other sites More sharing options...
honitonhobbit Posted March 3, 2006 Share Posted March 3, 2006 Found this early am so just checked tyre height by tape/calc - then checked RPM and then checked Speed with GPS/terratrip pace vehicle Am doing 67.8 at 3000rpm Tyres are 30.5inches in diameter Diffs are 3.45:1 T-box is 1.222:1 Did VM boxes have different gearing (don't think so) Quote Link to comment Share on other sites More sharing options...
Mark90 Posted March 3, 2006 Author Share Posted March 3, 2006 Found this early am so just checked tyre height by tape/calc - then checked RPM and then checked Speed with GPS/terratrip pace vehicleAm doing 67.8 at 3000rpm Tyres are 30.5inches in diameter Diffs are 3.45:1 T-box is 1.222:1 Did VM boxes have different gearing (don't think so) Here's the calc (I've just stuck the numbers in manually and it gives the same as the spreadsheet) Total gearing = main gear x transfer gear x diff = 0.77 x 1.222 x 3.54 = 3.33 So it takes 3.33 revs of the engine the for each turn of the wheel Now each turn of the wheel equates to a distance of = diameter x pi = 30.5 x 3.142 = 95.82 inches now to convert this into mph/1000rpm...... (1000 x 60 x 95.82) / (3.33 x 63360) = 27.2 mph/1000rpm 1000 for 1000 rpm 60 to go from mins in rpm to hours in mph 63360 cos that's how many inches in a mile 27.2 mph/1000rpm so 82mph at 3k rpm I don't reckon your gearing isn't what you think it is or your tyres aren't 30.5" rolling diameter. To get this accurate you really do need to measure how far the truck moves for one full revolution of the wheel. I used this when I was looking at gearing options on Alf and it was bang on with the GPS readings for the the existing setup. Quote Link to comment Share on other sites More sharing options...
honitonhobbit Posted March 3, 2006 Share Posted March 3, 2006 The calcs add up nicely. I wonder why there is such a discrepancy... Mmmm wonder if the rev counter is out? Quote Link to comment Share on other sites More sharing options...
Mark90 Posted March 3, 2006 Author Share Posted March 3, 2006 Or your clutch is slipping Quote Link to comment Share on other sites More sharing options...
honitonhobbit Posted March 3, 2006 Share Posted March 3, 2006 Maybe some more air in the tyres would help Quote Link to comment Share on other sites More sharing options...
Mark90 Posted March 3, 2006 Author Share Posted March 3, 2006 Working back from your 68mph then either your tyres have an effective rolling diameter of 25", which I'd be quite suprised if the difference in measured diameter / nominal diameter of tyre size / actual rolling diameter was that great. I doubt the VM gearbox would be that different ratio in 5th, likely 0.7-0.8 and would have to be 0.92 to give 68mph. You could try it in 4th which there's no question of ratio it being direct drive. Assuming your diffs are 3.54 then that leaves transfer box and oddly enough a 1.41 ratio transfer box would fit the figures quite well. Quote Link to comment Share on other sites More sharing options...
Turbocharger Posted March 3, 2006 Share Posted March 3, 2006 I'd suspect the tacho - my new VDO one is days out (because I've not adjusted it yet) and the OEM ones probably aren't much better. Max unloaded revs on the engine should come out slightly above 4500rpm - when I can see 5500rpm on mine I know it needs turning down a bit. Quote Link to comment Share on other sites More sharing options...
honitonhobbit Posted March 3, 2006 Share Posted March 3, 2006 I know the T-box is 1.222:1 'cos I checked it when I changed it about 12K ago I thought the only difference with the VM box was the input shaft diameter. My tacho can't be more than 200rpm or so out at the worst surely... Quote Link to comment Share on other sites More sharing options...
Mark90 Posted March 3, 2006 Author Share Posted March 3, 2006 With the quoted setup 68mph should equate to 2500rpm Quote Link to comment Share on other sites More sharing options...
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