Interesting disitation on speed verses cruising.
Changing the wheel & tyre size can also add complications to all of this
fun,
Having built a 5 speed gear box inside a P-type box to achieve overdrive, I
enjoyed the "launch" with the 5th gear being below 1 : 1 so much, I decided
that it would be a good idea to achieve the overdrive some other way.
Hence the first of the "Joey boxes" came to fruition on the P-something that
is now in the care of my son. We ran up to 11% overdrive which was fun for
cruising.
Supercharged 4 cylinder MMM cars are so much fun.
For my new car I am using 4.4 : diff, 15" wheels and in one of the "Joey
boxes" I have made for provisions of final drive speed @ 5,500 revs of
96mph, 106mph, 114mph and 124mph. The last of these ratios is 20 : 27 which
at 6500 rpm would show 137mph.
The factor that concerns me about all this is that the torque changes so
much as the variables change. I just hope the gear box holds together. I
hope that having a car close to 1,100 lbs will assist.
Good luck to you all as all "spin" your wheels.
Pip
AUSTRALIA
----- Original Message -----
From: Pete and Fran Thelander
To: TATERRY@aol.com ; DSBonar@aol.com ; mg-mmm@autox.team.net
Sent: Saturday, July 12, 2003 12:01 PM
Subject: Re: rear dif. ratios
Don, et al;
The difference between the 8:43 (5.375) and the 7:37 (5.285) is only 1.7%.
The 8:43 provides that little bit more torque multiplication and will give
very slightly better acceleration and hill climbing ability at the expense
of running about 70rpm higher at highway cruising speed. This is
generally
refered to as a "lower speed" (that's road speed, not engine speed) ratio.
The other frame of reference is the mathematical quotient of the ratio.
Here
the mathematical fact is that the number 5.285 is lower than 5.375. This
is
always leads to confussion in discussing "higher" or "lower" gear ratios.
Are you referring to the mathematical value or the speed range
application??
So what's "best" depends upon what you value - better acceleration or
lower
cruising rpm. If your cruising speeds are relatively low (say 50mph or
less) take the acceleration and driveablilty that you get with the 8:43.
So far as the durability goes...I have had both in the NE and both broke
after only a relatively few races. The 8:43 was most embarassing. It
failed on the first lap touring the old Ards TT circuit in Ireland last
month.
Pete
----- Original Message -----
From: <TATERRY@aol.com>
To: <DSBonar@aol.com>; <mg-mmm@autox.team.net>
Sent: Friday, July 11, 2003 5:54 PM
Subject: Re: rear dif. ratios
> In a message dated 7/11/03 14:14:28 Pacific Daylight Time,
DSBonar@aol.com
> writes:
>
> << Dividing 43 by 8 you get 5.375
> 37 by 7 5.285
>
> Not a significant difference to me. However, what does this mean (if
> anything) to performance, top end speed, or other measurement? Seems
nil
to
> me but
> have been told 7/37 was "stronger" in that there were only 7 "fatter"
teeth
> cut
> as opposed to 8.
>
> Education on gears please? >>
>
> I'd say you are lucky to have a lower ration Don......but when you start
> driving it, you'll wish you had an even lower one.....I just put a 4.875
into an N
> type and the owner was greatly pleased with the roadablity on the
> highway......others will tell you that your engine won't pull that lower
ratio....I don't
> buy it and we don't have an endless series of roundabouts to deal
with.......j
> Terry
>
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