I sent this reply to the list but of course, I forgot to delete the
trailer.....
mayf
Sandy Ganz wrote:
>Anyone running 1350's U-Joints/yokes? (stock is 1310's I think). I have a set
>of 1350 yokes and wonder if anyone has gone to the trouble?
>
>Sandy
>_______________________________________________
>
Sandy, all.... why the concern for a the ujoints? Unless you add a lot
of weight to the rear of the tiger, the road/tire grip is the traction
fuze. Do some math and it wont take long to figure out that the
coefficient of friction with the road surface is sufficiently low that
it wont really take much to loose traction. I know most of you are
uunder the assumed knowledge that those big ol ires add grip. Alas, they
do not! So even in first gear at peak torque say 450 ft lbs.... the low
gear fives another multiplication of what? 2.4 or so (what ever your
first gear tranny ratio is) times that and then once again when it goes
trhough the diff ring and pinion. so 450 x 2.4 x 3.0 = 3240 ft lbs (NOT
lbs - ft, lol) at the combined axles. Divide by two and that goes to
each tire. Or about 1620 ft lbs. Now divide that by the tire rolling
radius in FT and you get the available force. Or if the tire is a 24"
dia (makes math easier) then radius is 1 ft, so force is 1620 lbs. BUT,
the car weighs about 2400 lbs give or take. And the corner weights are
close to being the same so each rear wheel carries about 600 lbs. Even
if you could get the coefficient of friction to 1 (drag racers get more)
on your street tires the most available force that could be used is 600
pounds of driving force. It is easy to break the tires loose. Wokring
backwards from the max force that can be applied at the road tire
interface then you'll find that the drive shaft only transmits about
600 x 2 / 3.0 = 400 ft lbs. Is a 1310 big enough? Yeah. Add to that
the increased size of the 1350 means a larger yoke on each end of the
drive shaft and a larger shaft diameter you have increased inertia to
deal with as well. There is one other consideration to think about as
well and that is load reversals when doing spirited driving around a
track. In that case, you are on and off the gas pedal a lot. Each time
that happens there is a jerk load associated with gear shifting. I see
it all the time on the salt. Cars that go up in speed ie first to 2nd
have a lot of inertia and that drives the shaft at car speed via the
diff gearing. The small interval when you are off the gas and mashing
the clutch allows th ewdrive shaft to reach the same proportional speed
as the rear tires. So when you let the clutch out there is a jerk load
because the engine is turning slower The drive shaft has to bring the
engine rpm up to the speed that the car is going. If that makes sense.
In any case, make sure you really need the extra strength.
i just got out of bed a few moments ago so if the typing is crappy blame
the lack of coffee, lol....
mayf
YMMV
Mayf
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