W. Ray Gibbons writes in response to Mr. Mike Passaretti >
> I don't think so, Mike. If you know the tire rolling radius, you can
> figure how far it travels in one rear axle revolution (C=2*Pi*r). If you
BFG's testing seems to conform the "flat spot" theory, yielding
Revolutions/mile numbers about 3% higher and therefore mph/1000rpm numbers
about 3% lower than the pure math would imply.
I can supply simple instructions to build a spreadsheet in your favorite
spreadsheet program to use the BFG formulae to figure any gear ratios and
tire size. I will Email the text to anyone who requests it.
If a TR4 had 175-70-15 tires, they would turn 843.96 rev/mile. (What size
tires do you really have, Mike?)
With a rear-axle ratio of 3.7 and a straight-through top gear, it would
yield 19.82 mph/1000rpm. Therefore, a redline of 6000 would be a top
speed of 118.95 mph.
Changing to a 4.1 rear axle would change those numbers to 17.89
mph/1000rpm and 107.34 mph.
> know the rear axle ratio and the 4th gear ratio or OD ratio, you can get
> at miles/1000 engine revolutions. But your math has to have come adrift
> somewhere, because 16 miles/krev is extremely high. Look at it this way,
> as you drive down the road at 3000 rpm, you would be going 48
> miles/minute. Not likely.
Look at this again, Ray. The usual way of stating this is
miles PER HOUR / thousand revolutions PER MINUTE
So what Mike really meant was 16 mph/1000rpm. (This is a typical number
for a Spridget, not for the size tires I would expect on a TR4) At 3000
rpm, the road speed would be 48 mph.
> Then too, your numbers go the wrong way. Changing from a 3.7 to 4.1 axle
> ratio will decrease the number of miles per 1000 revs.
True.
Phil Ethier, THE RIGHT LINE, 672 Orleans St, Saint Paul, MN 55107-2676 USA
h (612) 224-3105 w (612) 266-6244 phile@stpaul.gov
"These are the questions that kept me out of the really good schools"
- George Carlin
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