[TR] RPM speed calc
notakitcar at yahoo.com
Mon Jun 1 16:34:17 MDT 2020
Thank you John, this is actually. Non-OD car with the 3.70 rear end. OD installed later in life by some PO. A very nice driving combo.
On Jun 1, 2020, at 2:36 PM, John Macartney <John.Macartney at ukpips.org.uk> wrote:
It’s important to remember that cars without overdrive had a higher axle ratio than those with it. As an example, the GT6+ had a 3.27 final drive for non overdrive and 3.89 for overdrive. Just to complicate things, it was entirely possible to order a 3.27 diff with overdrive on top! The factory never promoted this facility for fairly obvious reasons. My own GT6 mk 2 was supplied like that becxause I knew my way around the factory build books. Iit made an excellent cruiser with good fuel consumption but could not pull more than 4000 rpm, even downhill on a motorway. That said, refuelling was a little less frequent.
At the Battle of Waterloo, 1815:
Lord Uxbridge: “By God, Sir - I’ve lost my leg”
Duke of Wellington: “By God, Sir - so you have!”
> On 1 Jun 2020, at 19:41, Dave MacKay <dave at mdmackay.ca> wrote:
> >Date: Sun, 31 May 2020 16:52:23 -0500
> >From: bill beecher <notakitcar at yahoo.com>
> >Subject: [TR] RPM speed calc
> >Came across this calculator with all the right input fields. But, I wonder how accurate it really is given the following input.
> >TR3 with a 3.7 rear, OD at redline of 5,000rpm. Vredestein 165R/15 tires, 25.4? diameter. Should be moving along at 124mph!
> >Anyone get a different answer?
> Here (attached) is a spreadsheet that I wrote to calculate speed versus rpm given different parameters. I wrote it to check my speedo after I installed an HVDA transmission. If the spreadsheet doesn’t make it through the list as an attachment, just e-mail me directly and I’ll send it to you.
> With a standard Triumph gearbox + overdrive, and the parameters you gave, I calculate speed at 5000 rpm in top gear (with overdrive) as being 124.5 mph. Note that, I think that the tire diameter is 25.25”, slightly less than you indicated.
> I hasten to add that calculating a speed and believing it’s achievable are two different things!
> Dave MacKay
> 1960 TR3A s/n 68639L
> near Toronto, Canada
> <Triumph rpm to mph.xls>
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