4.10 gears...not what I expected.

[Kevin]

lets play nice gentlemen

[PhillipsLT5]

Originally Posted by tf95ZR1

This gear ratio discussion has my head (and tires) spinning!
R R R

Anyone can tell me anything, BUT I will go with 4.10's over 3.45 in any car any day, Just sayin

[mike100]

It is so difficult to put the mathematics into words, but many of us know what the final drive and tire diameter do to the car as a whole. I have been told by two different people that 3.73's really woke up their ZR-1's that they used to own. These comments were unsolicited and just came up as advice for bang-for-buck mods. I also like this idea as there is a speedo gear available for this ratio for a clean conversion. Unfortunately I'm pretty much done with projects and I'm just keeping the car in good condition at this point, but it would be the next thing on the list if the budget was available.

[Paul Workman]

Originally Posted by WVZR-1

You constantly try to mess with the conversation. Your REAL GEAR is what ever the numerical numbers (ring gear/pinion) dictate. Your tire diameters alter your 'final drive' but you constantly fail to mention that. You mention 'real world' - real world is same as 'real gear' - it's the mathematical numbers of the gear set....*.

OUCH!

In spite of perhaps using less than precise or exacting terminology, I think most of us understand what Dom was trying to get at. And, he brings a valid point: whatever conclusions or direction this thread makes or takes, tire diameter variances introduced by those that have other than the "normal" tire sizes need to be considered. (OK, he only mentions wheels, but we know what he's implying, I believe.)

Just sayin....

Paul.

[XfireZ51]

WV,

Apologies for my lack of precision. Took too much for granted. If anyone else in this thread was thrown into a technical tizzy along w WV, please allow me to apologize to you also. Precisely.

[USAZR1]

Originally Posted by XfireZ51

I installed 3.73s for mine and when power is transmitted through 19" wheels, acts like a 3.55. I would be tempted to try 3.90s

And our car has even taller rear tires than Dom,although not by a whole lot. Our 94 has 335/30/19 rears with 4.10 cogs. I like it.

No apology needed on this end,Dom. I understood completely what you were trying to say.

[WVZR-1]

Some 'real' information I believe. Dominic, I'll use your ratio and tires as an example. If you had 3.73 gears and your 315/35R17 tires and were 'happy' you need to be concerned about not your losses but rather what you need to do to compensate for the increased tire that you added or you just disregard it and don't worry.

I'll use that for a start. I picked a MPH # because one is need to start from so I chose 60 MPH and 4th gear. I always use 1:1 regardless of the transmission. A 3.73 @ 60 MPH I got 2960 RPM by this:

60 X 3.73 X 336/25.4 (the 25.4 I used from a dimension I measured with my BFG 315/35R17's many years ago) I did NOT use the advertised diameter. That skews the results which BTW I believe the charts earlier in this thread are based off advertised numbers and not real dimensions that we can measure. Those #'s are close but NOT correct.

Now when you add the tire that you mention measuring 26.25 (in this thread) I get an RPM value of 2864:

60 X 3.73 X 336/26.25

Now to get your 'performance' back you need to add gear and since we know the various ratios available for the D44-HD it's easier to experiment using available ratios substituted into the formula.

60 X 3.90 X 336/26.25 = 2995 so you've got it all back with that gear change + very few RPMs.

If a person had 4.10's with 315/35R17 and was 'happy' then these #'s if they made the same tire change would be required.

60 X 4.10 X 336/25.4 = 3254 RPM (315's)

60 X 4.10 X 336/26.25 = 3148 RPM (26.25 measured)

The add required using available ratios:

60 X 4.30 X336/26.25 = 3302 so you've got it all back again + a few more RPMs.

These were very straight forward and it's much easier using 'known' available ratios to calculate recovery.

With your particular tire choice the 'loss' if you wanted to only be concerned with the loss is 3%. 25.4/26.25 = .96761 so the 3.45 becomes 3.34 and the 3.73 would become 3.61 or so.

Done in this fashion also to calculate the new ratio 25.4 (original tire) X 3.73 (axle ratio)/ 26.25 (new tire) = 3.6092

You could confirm those numbers I'd think by checking RPMs with an accurate tach and not the cluster component.

Every tire needs to be measured at the pressures you will intend to use and dimensions will vary for various brands.

I believe my math will stand the test. I hope or I've made a much larger A$$ of myself. There are calculators out there that likely will confirm these numbers or very close. The one I posted way back in this thread should work I believe.

This is where I got the dimensions that I used for your 19's.

Originally Posted by XfireZ51

I have 19s on the back. The fronts are 18s. Just measured the rears sitting there w ~ 35psi, they stand at 26.25". Size is 325/30/19. These are the Nitto Invos which I like quite a bit. Good wet, fairly quiet, and grab pretty well on hard shifts.

[Dynomite]

When you boys are talking gear ratios to determine vehicle speed.........you should use Tire Deflected Radius.....which by the way varies with tire rotation speed just a bit. And obviously varies with tire inflation pressure. Tire Deflected Radius is the distance from the center of the wheel to the pavement.

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[WVZR-1]

I thought I'd keep this in a different post but you should be able to calculate your actual tire diameter using a formula also OR maybe just use it to confirm your measurements. Tach would need to be very accurate.

MPH X gear ratio X 336 / RPM

In the above 60 MPH X 3.45 X 336 / 2960 = 25.4 (a match to what I measured years ago) and Dominic's 60 X 3.73 X 336 / 2864 = 26.25 (what Dominic mentioned measuring)

Clint, you could use this formula with your tires already mounted and measure to confirm.

Cliff - I'm guessing my numbers maybe passed your test.

[Hog]

Just some general observations about the last couple pages

After a few burnouts all these numbers go out the window, esp. on soft tires. Then factor in tire growth due to the centripetal/centrifugal force changes at speed, tire pressure while driving, the effects of wheel alignment on tire heating, type of gas the tire is inflated, plus the manufacturing tolerances of the tires themselves, even tread squirm could be thrown into the convo.

This why there is a "fudge factor" built into any modern ABS or stability system. Accuracy has its place.

IMO If you are going to go through the trouble of a ring/pinion change, you might as well make it worthwhile.

The usual course of engine modification will move the power/torque corves to the right oi the graph, with highly modified engine making less torque at lower rpms. This would necessitate lower gearing to allow for driving below the torque.
More power=more revs(N/A)=more gear (all else equal)