Just back from vacation and took the car out on a sunny Connecticut Sunday
(not as nice as the 65 degrees we left in SC). I show about 2800 RPM at 60
MPH on 185/70/15 tires.
Bob Danielson
75 TR6 - Current status at:
http://pages.cthome.net/BobD
-----Original Message-----
From: Ken Streeter <streeter@sanders.com>
To: jaltman@altlaw.com <jaltman@altlaw.com>
Cc: 'Triumph List' <triumphs@autox.team.net>
Date: Sunday, February 22, 1998 3:23 PM
Subject: Re: Tach Question
>
>jaltman@altlaw.com wrote:
>
>> Lets try this again. Would one of you 6 drivers please note
>> your tach reading at 60 MPH and let me know what it is?
>> Please. No OD.
>
>Jim,
>
> I'm sorry that I didn't reply the first time, but one of
>my TR6s in in winter storage, and the other is awaiting
>a new transmission.
>
> From my recollection of many hours in the TR6, the RPMS
>in 4th gear is very nearly 500rpm per 10mph. Within the
>accuracy of my speedometer and tach, I would see 3000rpm
>at 60mph. Actually, I seem to recall that on my car, the
>tach reading is slightly more than 500rpm per 10mph in
>non-OD 4th -- more like 3150rpm at 60mph.
>
> You can also find this figure in the Bentley manual on
>page 44. There is a chart for "Effective Gearing" giving
>"Engine speeds (rev/min) at road speeds of 10mph and 10kmh"
>
> It indicates 482rpm for 10mph (US-spec cars) which would
>be 2892rpm at 60mph in non-OD 4th gear. The same table
>also indicates 20.7mph per 1000rpm, which means 3000rpm
>would be 62.1mph. This differs from what I see in either
>of my TR6s.
>
> However, the exact number is likely to vary somewhat
>depending on things like what type of tires are on the car,
>if the wheels are stock, and even how much air is in those
>tires. So I find it quite reasonable that my empirical
>numbers differ from those in the Bentley / TR6 factory manual.
>
> If you are trying to calibrate the tach, I would suggest
>instead using an external electronic tach hooked up to the
>distributor to calibrate. You can do this in your garage.
>If calibrating the speedo, the easiest way would be to time
>yourself on an officially measured mile or quarter mile (do
>you have any aircraft-enforced speed traps with quarter mile
>marking on the road?) on a road near your house. Actually,
>if you are good friends with a police officer, there's an
>even easier way! Either of those are sure to be more accurate
>than using the tach to calibrate the speedo, or vice versa.
>
>--ken
>VTR WWW Maintainer -- http://www.vtr.org
>'70 & '74 TR6 Daily Drivers (well, 8 months per year...)
>
>--
>Kenneth B. Streeter | EMAIL: streeter@sanders.com
>Sanders, PTP2-A001 |
>PO Box 868 | Voice: (603) 885-9604
>Nashua, NH 03061 | Fax: (603) 885-0631
>
|