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Thread: 3.45 Diff ratio?

  1. #1
    Luke Skywalker
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    3.45 Diff ratio?

    I always get this confused. Would this Diff be good for better acceleration or better top end if replacing a 3.7 Diff with no overdrive?

  2. #2
    Freshman Member
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    Re: 3.45 Diff ratio?

    Better top end. The gear ratio is how many times the propeller shaft, i.e, the engine (unless your clutch is slipping badly) turns for each revolution of the axle shaft. In fourth gear, the axle would turn 1000 RPM at 3450 RPM engine speed versus 3700 RPM engine speed with the 3.7 ring and pinion.

  3. #3
    Luke Skywalker
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    Re: 3.45 Diff ratio?

    So noticeably slower when accelerating?

  4. #4
    Jedi Knight
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    Re: 3.45 Diff ratio?

    Yes, but you will pull longer in each gear. More noticeable might be earlier downshifts when pulling uphill. Fair trade off, IMO, for losing a couple of hundred rpm at speed. Mostly speculation on my part as I still have the 3.7:1 Tom
    1960 TR3A TS73117 (under restoration year 6, owned since 1964)
    1959 TR3A TS58023 (in case I never finish the one above)
    1969 Triumph Herald 13/60 (a whim)
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    1992 BMW325IC (fun to drive)

  5. #5
    Jedi Knight
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    Re: 3.45 Diff ratio?

    I have been using the 3.45 gears now for more than 5 years in the TR3&4. The only slowing of acceleration would be seen in a racing situation. When I am street driving and get a green light I am no slower than my friend with his TR6. As I am following him in this situation. He slows to shift to second and I have to back off because I am still accelerating in first. The big disadvantage is on a hill. I do have to change to a lower gear sooner. Another disadvantage is in following my fellow TR's downhill. When using the gears to retard speed I have to brake more often if following another TR.
    The actual speed increase in fifth gear (I use a Toyota 5 speed) is about 3-4 mph.
    My overall feeling is that I do like them but don't feel it is worth the cost of switching. If you need to replace a 3.7 then this is a viable alternative.
    Charley

  6. #6
    Obi Wan
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    Re: 3.45 Diff ratio?

    Ok help me out here, but please do not laugh or laugh in your coffee and have it come out your noise. Anyways, I thought those ratios were the number of teeth on the ring and pinion like for example 37 teeth on the ring and 10 teeth on the pinion. Would be a 37 to 10 or 3.7 to 1.0
    steve

  7. #7
    Luke Skywalker
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    Re: 3.45 Diff ratio?

    [QUOTE=sp53;1067416]Ok help me out here, but please do not laugh or laugh in your coffee and have it come out your noise. Anyways, I thought those ratios were the number of teeth on the ring and pinion like for example 37 teeth on the ring and 10 teeth on the pinion. Would be a 37 to 10 or 3.7 to 1.0
    steve
    Actually that is correct. So 3.45 to 1 would be 34.5 to 10....wonder about the 1/2 tooth?

  8. #8
    Freshman Member parkerg1's Avatar
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    Re: 3.45 Diff ratio?

    [QUOTE=karls59tr;1067419]
    Quote Originally Posted by sp53 View Post
    Ok help me out here, but please do not laugh or laugh in your coffee and have it come out your noise. Anyways, I thought those ratios were the number of teeth on the ring and pinion like for example 37 teeth on the ring and 10 teeth on the pinion. Would be a 37 to 10 or 3.7 to 1.0
    steve
    Actually that is correct. So 3.45 to 1 would be 34.5 to 10....wonder about the 1/2 tooth?
    I could be all wet, but I believe the 3.45 is 11 and 38 tooth..

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