What you really need is the rolling radius of the tire under a load
(weighted). This will change with differences in tire pressure. This
will be different than just the radius of the tire. Once you know the
exact distance the tire will travel in exactly one revolution, the rest
is fairly easy!
Rich
>----------
>From: Jim Parent[SMTP:76276.1555@CompuServe.COM]
>Sent: Wednesday, May 29, 1996 7:11 AM
>To: 'Tiger List'
>Subject: RE:
>
>Tom,
>
>1. I see what you mean thanks. But isn't loaded radius the height of
>the
>axle above the pavement? If that's the case it seems to me that radius
>is what
>governs the effective circumfrence of the loaded tire. Dividing that
>circumfenece into a mile gives revs per mile. My quarter mile
>simulation
>program shows 22.3" diameter for a 205x50-15; 22.4" for a 195x60-14;
>22.4" for a
>185x70-13; 22.6" for a 165x80-13; and 21.7 for a 5.90-13.
>
>The revs per mile (respectively) are 906, 900, 901, 893, and 931. Not
>a lot of
>difference; only about 25 revs per mile for the 205 versus the 5.90
>(about 3%).
>That would only effectvely change a 2.88 to a 2.97; not enough to
>notice
>probably.
>
>2. Gotcha, you meant the specifcs of the Boss 302. I agree, for a
>road
>racer, with close ratio gears most of the driving would be up in the
>higher
>RPM's. Quite unsuitable for the street.
>
>At any rate I've decided to go with a wider ratio top-loader 4-speed
>transmission (2.78 low) and leave the rear end alone at 2.88.
>
>----------
>From: "Tom Ballou"
>Sent: Wednesday, May 29, 1996 6:25 AM
>To: 76276,1555
>Subject: re:
>
>1. The rolling radius (loaded radius doesn't matter - think about it)
>of a
>205/50x15 is dead stock for a Tiger (941 revs/mile) (165x13 = 185/70x13
>=
>195/60x14). BFG has published a neat little guide which shows both
>radii and
>revs/mile.
>
>2. The Boss 302 cam requires special lifters because it has a different
>
>radius on the lobes and lifters. But that doesn't really matter as
>long as
>you match them, the real problem is that the Boss 302 cam ( and the
>rest of
>the set up) was tuned to produce high rpm power for Trans-Am racing.
>The
>engine idles poorly and actually produces less power than a 289 "k"
>engine
>below about 3400 rpm; however, it is a powerhouse from there all the
>way to
>7400. I think the cam has a similar grind to the "Le Mans" cam which
>had a
>similar power band (and equally bad idle and bottom end). There are
>much
>better cams for street cars, and actually there are much better cams
>for
>racers today (remember, this cam design is almost 30 years old), the
>roller
>hydraulic cams, for example, which can package significantly more
>effective
>opening with shorter duration and much less overlap than the cams of
>the
>60's. Ain't technology great?
>
>
>
|