4.10 gears...not what I expected.

[Paul Workman]

Originally Posted by 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.

_________________

Yikes!

"If you can't explain it simply, you don't understand it well enough." - Albert Einstein

(This discussion has veered off-topic, but since we're here now...)

Ratios.

No matter how you slice it, the root to questions regarding the effect on differential gears, speed, rpm, or any other equivalents resides in the ratio of one tire size to the other. Period.

Depending on the question, there may be a direct ratio relationship, or an inverse (i.e, 1/ratio) relationship, but regardless, that ratio between tire sizes permeates all calculations regarding differences in gear ratios, or distance covered per tire rotation, or rpm, or you name it.

For example: If speed over the ground and engine rpm are to remain constant, then the differential reduction ratio (ring/pinion) must be changed by the same ratio as that between the two tires. Otherwise, either speed over the ground will change for a given motor RPM, or RPM will change for a given speed.

Or, for an opposite example, to find the equivalent differential reduction ratio value resulting from a change of tire size, the inverse (1/RATIO) x differential reduction gear ratio will produce the effective equivalent rear end gear ratio (as well as the ratio correction required for the new speedo gear.

And, so it goes... (Well, almost. Practical applications typically have dynamic variables which skew results. Variables like Hog points out and many other practical bits and pieces get in to increase the ambiguity factor. But, as long as we can account for some of of the small dribbs and drabbs, and the ambiguity doesn't exceed say 5%, it should suffice for purpose of discussion, I should think.)

Hog: Good points as well.

But back to the OP's question: What are the real trade-offs between say the 4.10s vs. stock 3.45s in actual driving or racing situations??




WV: I must be staring right at it but do not see: where is that "336" factor you use in your calc's derived from?

[XfireZ51]

Dave,

Actually we had a very similar thread several years ago here for anyone interested in referring back to it.

http://zr1.net/forum/showthread.php?...ear+axle+ratio

And I in fact did what you suggested, which was to use the stock 3.45 trans gear
With the 3.73 rear gear. Based on my GPS v Speedo, I get ~ 4% error! with the speedo reading slower. Good enough for cruising. Some of the specs are in that thread.

[WVZR-1]

Originally Posted by Paul Workman

_________________


WV: I must be staring right at it but do not see: where is that "336" factor you use in your calc's derived from?

Why the 'fine print?

I've used the 336 number for years and I don't know where I got the formula for it originally but there's explanations and the formula scattered about of all places "The Internet".

I found this explanation since you asked your question and it seems pretty concise and easily understood too, I'll just post the link. I believe it should work. Regarding explaining it 'simply'? I thought I did. Understanding it? Yes I do.

There are calculators that are used by many that aren't accurate and I just displayed my math, that doesn't have anything to do with understanding or simply. There are some RPM/MPH charts in this thread and all use 'advertised' tire specifications and not a 'loaded radius' it appears. I couldn't make the numbers match unless I used the 'advertised' dimensions.

http://www.numericana.com/answer/formula.htm#carspeed

[WVZR-1]

Originally Posted by XfireZ51

Dave,

Actually we had a very similar thread several years ago here for anyone interested in referring back to it.

http://zr1.net/forum/showthread.php?...ear+axle+ratio

And I in fact did what you suggested, which was to use the stock 3.45 trans gear
With the 3.73 rear gear. Based on my GPS v Speedo, I get ~ 4% error! with the speedo reading slower. Good enough for cruising. Some of the specs are in that thread.

I recall bits of that and I mentioned a couple calculators in that thread because it seemed at the time it was easier for people to understand rather than doing the math on responses to avoid responses similar to Paul's. It appears to be complicated but after a few goes at them it's not that difficult.

I did speedometer calibrations for people to take to court and attempt to get fines and charges reduced to improper equipment etc. back in the day. I had to 'introduce' the error that we're attempting to correct these days. I don't recall any of my calibrations failing the person except a couple occasions where the person asked for an error that just wasn't likely accomplished.

I did the calibration, the buyer went to an approved certification station and of course there was an error, the person reinstalled the correct parts OR we actually corrected the error, the person returned to the certification station they certified the correction and the receipt for services went to court. Charges usually dismissed, occasionally if the JP/Judge suspected the tampering there was an improper equipment citation issued which had no points and a very low fine.

All the math was done on paper and changes sometimes by trial and error.

[Fully Vetted]

Originally Posted by Paul Workman

"If you can't explain it simply, you don't understand it well enough." - Albert Einstein

LMAO. That's funny...

I did go from the stock 17' A molds to an 18" Shelby but I made sure the overall diameter was the same (or at least very close). I've always assumed that was a determining factor. I guess I was right...

[Harvie]

Our testing, years ago, with a modified ZF trans gears (to keep the drop between shifts in the engines peak power band) and with higher horsepower engines the 391 ratio was the one that got to the finish line first.

We attempted to get the trans ratios to where we had five gears instead of 4 plus 2 overdrives, that worked real well. REEEEEEAL EXPENSIVE

Look up Gforce and look at the transmission ratios Leo makes for an example of what can be done to the ZF it money is no problem.

[Paul Workman]

Originally Posted by Harvie

Our testing, years ago, with a modified ZF trans gears (to keep the drop between shifts in the engines peak power band) and with higher horsepower engines the 391 ratio was the one that got to the finish line first.

We attempted to get the trans ratios to where we had five gears instead of 4 plus 2 overdrives, that worked real well. REEEEEEAL EXPENSIVE

Look up Gforce and look at the transmission ratios Leo makes for an example of
what can be done to the ZF it money is no problem.

Harvie,
Did that test include stock 375 or 405 hp or (??) cars?

Paul.

[Harvie]

Originally Posted by Paul Workman

Harvie,
Did that test include stock 375 or 405 hp or (??) cars?

Paul.

To quote the moderator

No I "hacked up" everything and motor I played with, christ my lt1 70 car (350-370hp stock) had a 425 hp small block so I thought the lt5 GM hp numbers were pathetic, the 650 number Lotus had made me curious.

We just never cut a hood open inorder to straighten out the intake air flow to get to their numbers. Did everything else, though.

[Paul Workman]

Originally Posted by Harvie

To quote the moderator

No I "hacked up" everything and motor I played with, christ my lt1 70 car (350-370hp stock) had a 425 hp small block so I thought the lt5 GM hp numbers were pathetic, the 650 number Lotus had made me curious.

We just never cut a hood open inorder to straighten out the intake air flow to get to their numbers. Did everything else, though.

Um, yeah...425 hp NET or GROSS?

[Harvie]

Originally Posted by Paul Workman

Um, yeah...425 hp NET or GROSS?

All the HP figures are from the same dyno, min of 5 pulls. We tested a straight out of a car LT5 and got max between 372-380HP and the 1970 based full roller motor LT1 at 423-428HP. Both GM 350 small block engines.

We always started with baseline runs to see how much GM fudged the numbers for insurance purposes. Common practice...

So I would call those numbers for both engines net at the flywheels.

When the ZR1s were introduced the LT5 option alone was $35,000.00 and there were no aftermarket engine parts for the LT5.

I still have one of the first sets of JLs lightweight pistons in my cabinet. I have I believe 2 different sets of cams because we were testing for max lift limits/spring pressure ranges. Airflow was always the restriction that limited the output.

When I started fooling around with them Lingenfelter charged $16,000 to build a motor from a new engine and Calloway was at $14,500.00.

Now guys buy their entire cars for that.

I always wonder how many of the current owners would have one, then try and modify it, if they had to pay 80K for them. even in the lower current usds.