Peter Juergens wrote:
> Where is the reason for these big things?
Well, let me sum up my situation, and see what you
might suggest:
I drive my TR6 every day to and from work (26 miles each way)
from May through November, as well as for any errands where I'm
taking no more people than fit in the car (me, my wife, and my
two sons) and the TR6 has enough space to hold whatever else we
need to bring along. I also drive the car on weekends for
other similar miscellaneous usage. The above usage adds up to
approximately 7500 miles each year.
The drive which puts the most mileage on the TR6 is my drive
to and from work. The 26 miles is broken up as follows:
6 miles are on twisty, roads with moderately poor
surfaces at about 30-45mph (this is the fun part)
18 miles are on a 4/6 lane divided highway where I
travel at a steady 70-75mph (4th gear at ~3750rpm)
2 miles are on city roads mostly characterized by
stoplights, potholes, and drivers who pull out in
front of you with no notice
You will see that the predominant mileage accumulated in
my TR6 are miles on the highway at 3750rpm. The engine is
working moderately hard at that speed, and heats up the oil
pretty thoroughly. I am reluctant to go to a smaller
diameter tire than what I am currently using, as this will
push up my RPMs on my most typical usage of the car. It may
be that I am worried about nothing, but I expect the wear
on the engine would be greater for the same distance travelled.
I also find that my current tires (Michelin 185R15 Redlines)
are a contributing factor in the car's cornering capability.
What tires can I buy that will give increased performance yet
will maintain overall diameter? The overall diameter is
important to me both for lower RPMs and ride height.
It seems that all the modern performance tires are made in
increasingly lower and lower profiles. (50 series is starting
to be considered the "cutoff" point for performance tires.)
Unfortunately, the only way to use a lower profile tire
and maintain ride height is to increase width and/or increase
wheel size (by moving to 16", or greater, diameter wheels).
Really, though, my "ideal" for putting tires on my TR6 would
be a performance tire (50 series) with original width and
ride height. This is conceivable, but not practical.
One may ask, what would this tire be? Well, in order to build
a tire with 185mm width in a 50 series and still get the same
overall diameter as a 185/80R15 tire, one would need to have
a 19.5 inch rim. Yes, a 185/50r19.5 tire!
Alternatively, if one was willing to go just a small bit
wider, a 195/50r19 is an extremely close match to a 185/80R15
in overall diameter. Such a tire would mount quite happily
on a 19x6 rim, and should have sufficient load-carrying
capability for a TR6. However, I haven't heard of any
tire manufacturer's making 195/50r19 tires. (Or wheels
in 19x6, for that matter.) This would, however, be the ideal
tire for my needs, I think. Anything else would be a
compromise.
The compromise I've been considering would be doing the
best I could in a 16 or 17-inch wheel, which may actually
be something I could buy.
You have suggested a 205/65R15. These would give a 4.5%
increase in RPMs. (Pushing my 3750rpms up to 3920rpms.)
Would this increase my engine wear? Would this cause
greater oil breakdown due to increased heat? Or, does
the fact that the engine is only being asked to provide
the same amount of power (despite the differing rpms)
make this an even trade?
Of course, the other concern is the reduced ride height, which
is a bit of a problem, considering the bump-infested roads
I drive over every day. Plus, I probably forgot to mention
that I go on TSD rallyes in the TR6. In one of the recent ones
I went on, we covered 110 miles of unpaved roads in one day...
Anyway, alternative ideas are very welcome!
> And, Ken, why are you looking to keep the original diameter? You can't
> be afraid of changing your overall gear ratio, because, as I assume:
> you can't even use 3rd gear (without OD!)! 2*<g> OBTW, whats your speed
> limit?:-) (Oh, how I love to say those nasty things)
I'm afraid I don't understand quite what you mean. I speculate that
this is a gentle jab at our US speed limits, and the fact that a TR6
could run up to about 50mph in second gear before hitting redline...
> Again serious:
> Ken, did you think about your suspension and frame?
Yes, and that is a concern.
--ken
'74 TR6 Daily Driver
--
Kenneth B. Streeter | EMAIL: streeter@sanders.com
Sanders, PTP2-A001 |
PO Box 868 | Voice: (603) 885-9604
Nashua, NH 03061 | Fax: (603) 885-0631
|