Testing: Tire / Speedo / Differential Calculator - try it out! - Page 6

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  1. #51
    CelicaSupra.com Member
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    No problem about it needing updating for what's actually available. This is not anyones job and these things are all wonderful contributions done on someone's free time and freely shared. This doesn't explain why it suggests different ratios / gear combinations than what Toyota has always used for the exact same configurations. I do understand that the accuracy can change over time but both of mine have always been off by about the same amount towards the high side and certainly not within the mentioned tolerance of 3.75% being more like 5% over. Either may have changed over time but only very slightly if at all. This is not something I just noticed.
    Where did this recommended tolerance come from anyway? Maybe it really is a reasonable tolerance to expect in the real world but I would expect that the calculated results would be exact and that the recommended ratios would be as close as possible to them based on the closest gear sets available. But it sure seems to me that if this was true, the actual results achieved would be within a certain tolerance of expectations and not off even more and in the same direction as stock. The one thing I can think of that does indeed vary some in reality is the exact diameter and rolling circumference of different types and manufacturers tires in the same size. This might just be why the real world tolerance is as generous as it is but I would think OEM's would generally be much closer and probably well under half of this.
    Of course this doesn't apply in the motorcycle world. I've seen and known of bikes that their indicated speed was sometimes well in excess of 110% of reality and this isn't much of a secret.
    And, even this wouldn't necessarily be of much concern if it's calculated solutions were within approximately the same tolerance either way. But all the examples I tried suggest ratios that were off towards the high side by an even larger amount than the stock combinations are. This is why I asked what causes this. Certainly the formulas listed are indeed correct. Either some part of something isn't being implemented correctly or some part of its database is incorrect by some small amount somehow or something else is causing a small but consistent error.
    If its suggested solutions were a bit off towards the other direction from OEM and actual results showed even better accuracy, I would think that this had either used more accurate data or a more accurate implementation of the formulas or something else that further improved real world results. My tests showed the opposite. This is why I mentioned my results as they weren't what I expected.
    Hopefully there's some possible explanation for this. If anyone finds anything I'd like to know what it might be.

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  3. #52
    CelicaSupra.com Member SupraFiend's Avatar
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    My experience with the formulas within this calculator produce perfect results. I'm quite positive the math is correct. I think you're just running into the realities of running an analog speedo driven by a cable on a 30ish year old car with many miles on it. My high mileage daily driver mk2 still reads high after putting in the correct speedo gears (it had the wrong one in due to a tranny swap for a bit, all stock and oem size tires). Its just old and worn. While my project car is showing the indicated variance the calculator reports with the gears and tires I'm running, and the other car I swapped the correct gears into is dead on.
    Black 86 mk2 Project Car
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  4. #53
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    Hi guys..is there a latest link available ? Cant download from the old one.

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  6. #54
    CelicaSupra.com Member SupraFiend's Avatar
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    I'll bug Deanfun to rehost or fix the link, not sure what's wrong but he's still around and the original author so the first post should continue to maintain a link to the current version. However, goto this post for a mirror. Not sure if any changes were made since that duplicate was made.

    https://www.celicasupra.com/forums/sh...l=1#post391059
    Black 86 mk2 Project Car
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  7. #55
    CelicaSupra.com Member Deanfun's Avatar
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    Updated link in first post.

    Over winter I'll come back and improve usability.
    Dean L.
    1985 Toyota Supra - Hidden Content
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  8. #56
    CelicaSupra.com Member Funkycheeze's Avatar
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    Some information for R154 folks;

    -The speedo driven gears are the same as W series transmissions but the drive gears are not.
    -The R154 drive gears with the tone ring for the ABS sensor are discontinued, impossible to get (10 tooth 33481-14080 and 11 tooth 33481-14071 / 14070)
    -Below are some part numbers for R154 compatible drive gears that do not have the tone ring (since we don't use the sensor for our swaps, in fact you can plug it using 96411-41800)


    33481-35130 N=10, MARK 10X31-33
    33481-35210 N=11, MARK 11X25-27
    33481-35070 N=11, MARK 11X28-30
    33481-35190 N=11, MARK 11X31-33
    '84 P-type, 5spd, Super red, black/grey leather - 2JZGTE swap, Precision 6262 on cast manifold, ECUmaster black with 875cc/min injectors, 465 WHP at 17 psi, built R154 with OS Giken twin plate, one piece driveshaft with 1310 joints, Truetrac with 3.73 R&P, 450 lb/in front coilovers, 300lb/in rear springs, Image BBM wheels 17x8 and 18x10, 4 corner BBK, AGX shocks, Whiteline bars, poly bushings, T3 GTX2 front control and steering arms etc. etc.

  9. #57
    CelicaSupra.com Member SupraFiend's Avatar
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    Nice info! This old thread and calculator just keeps on truckin and being useful
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  10. #58
    CelicaSupra.com Member Funkycheeze's Avatar
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    I did find that I had to enter the manufacturer specific revs per mile rather than using the calculated value (it is usually more as the tire deforms when rolling so it doesn't have the full rolling radius). Found that my speedometer/odometer works out to around 1012 revs per mile. I ended up ordering a speed reducer from here https://speedometercablesusa.com/gear_box_adapters.html to get my speedo just right for the current 285/30R18, and I can remove it if I ever go to 285/35R18.

    They can build it with M22 x 1.5 and a 0.187" tang input / 0.191" saw slot output to fit our cable at the gearbox end.
    '84 P-type, 5spd, Super red, black/grey leather - 2JZGTE swap, Precision 6262 on cast manifold, ECUmaster black with 875cc/min injectors, 465 WHP at 17 psi, built R154 with OS Giken twin plate, one piece driveshaft with 1310 joints, Truetrac with 3.73 R&P, 450 lb/in front coilovers, 300lb/in rear springs, Image BBM wheels 17x8 and 18x10, 4 corner BBK, AGX shocks, Whiteline bars, poly bushings, T3 GTX2 front control and steering arms etc. etc.

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