(08-11-2009, 09:11 PM)Marco Wrote: Hi to all. I have a doubt about the official TT course lenght used by the timekeepers to calculate the average speed of the laps. I hope that this may be an interesting and not boring subject for the ttwebsite articulists (and in particular for the TT experts).
Well, the official TT course lenght is 37.733 miles and all the books seems to agree that this is the only official TT course lenght used by the TT timekeepers since 1922. But arithmetic seems to have a different opinion. Take for example the 2007 TT edition. In this edition the absolute lap record was improved two times in the Senior race by nonother than John McGuinness:
lap 1 - 17m25.77s / 129.833 mph
lap 2 - 17m21.99s / 130.354 mph


An interesting theory Marco............ Does anybody know when the TT mountain circuit was last officialy measured by the IOM goverments surveyors dep't ?. I remember that in the late 50's, perhaps very early 60's the course was measured by MCN, I cant remember the outcome, perhaps somebody can, or they have a copy of the edition of MCN that ran that story.

Pat.
A simple calculation allow us to obtain the lap lenght used by the timekeepers:
lap 1 - 37.715 miles
lap 2 - 37.730 miles

Even if we try and take in account in the calculation the rounding to the third decimal place we're not able to remove in the calculation the discrepancy between the two laps lenghts.
Now it comes my question: which is the explanation of that discrepancy? It does not seem to be due to a length correction for the first lap as it's absent in other TT editions (for example the 2006 one when McGuinness had the same racing numer, no.3).
I add that:
- the discrepancy between the calculable lenght values of the race laps seems to afflict many TT editions (also '20s and '30s TT editions).
- the calculation on the TT official absolute lap records data (i.e. lap time and average lap speed) gives (lightly) different values of the TT course lenght through the years.

(08-11-2009, 10:29 PM)pat slinn Wrote: An interesting theory Marco............ Does anybody know when the TT mountain circuit was last officialy measured by the IOM goverments surveyors dep't ?. I remember that in the late 50's, perhaps very early 60's the course was measured by MCN, I cant remember the outcome, perhaps somebody can, or they have a copy of the edition of MCN that ran that story.

Pat.

(09-11-2009, 02:10 PM)smokey125 Wrote: Interesting question Marco. There have been several discussions over the years about length but I’ve never seen anybody highlight the point you have. As a thought is it possible that there has been a typing error somewhere along the publishing route that the figures you used might have in them?
Does anybody know if there is a way of checking the original times?

(09-11-2009, 04:08 PM)NickJ Wrote: There has been much discussion on this subject over the years. Nobody can convince me that the course is the same length as it was when first used in its present form in 1920. As I see it there are four different ways of measuring the course.
a) Round the outside of the course.
b) Round the inside of the course.
c) Round the centre line of the course.
d) Round the racing line.
My opinion would be round the centre line of the course. It beats me with all the fancy gadgets around these days that someone can't establish EXACTLY how far round it is.
There is another side of me that romantically wants to see the 37.73 distance remain unaltered, and used as THE standard against which we measure lap times.
When I raced there I used to laugh when asking another rider what they got round at, they would reply, "just short of 114", or "just short of (say) 117". What mattered to me was what TIME did you go round in. 19minutes and 10 seconds is faster than 19m 15s, but they both might be 117mph.
Five more laps at five seconds slower and you're HALF A MINUTE behind.
So, to me it's an irrevelance. The man (or woman) who completes the course in the least TIME will be the winner, and who gives a stuff about the average speed?
And another thing. It must be a mystery to the non British anyway, as everyone else except America/Canada uses Kilometers. Yes?
However, in hindsight, obviously there has been the romance of the first, 60,70,80,90,100,110,120,130 etc, and I'm one to speak as I can name them all! Only one date mattered to me when I was growing up, and I could name the day far more easily than I could remember the Kings and Queens of England. June 7th 1957. Bob Mac sets first 100mph lap, Gilera 4 riding number 78, second lap, 101.12.
So, back to course distance. Leave it as it is!!
And DON'T let anyone else mess with the course as they have at Windy and Brandish.

(09-11-2009, 04:08 PM)NickJ Wrote: June 7th 1957. Bob Mac sets first 100mph lap, Gilera 4 riding number 78, second lap, 101.12.

(09-11-2009, 06:43 PM)Bill Snelling Wrote:

(09-11-2009, 04:08 PM)NickJ Wrote: June 7th 1957. Bob Mac sets first 100mph lap, Gilera 4 riding number 78, second lap, 101.12.

If things work out, we will have a film of the 1957 Senior TT at the Laxey Photo exhibition next year.