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Ring and Pinion Ratio Question Again - Manual Transmission
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Zeitgeist 13
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PostPosted: Sun Jul 13, 2014 12:23 pm    Post subject: Reply with quote

This is the same calculator that Flint used when prepping his reversed Passat/Quattro transaxle numbers. It also closely matched rsxr's real world numbers with his tire size. Jon's numbers seem way too conservative, but I will admit that I'm just bench racing right now.
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crazyvwvanman
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PostPosted: Sun Jul 13, 2014 12:35 pm    Post subject: Reply with quote

Lots of people use the inaccurate calculators and don't know or care that they give wrong answers. It is trivial to check the accuracy for those who do care as I do.

Mark

Zeitgeist 13 wrote:
This is the same calculator that Flint used when prepping his reversed Passat/Quattro transaxle numbers. It also closely matched rsxr's real world numbers with his tire size. Jon's numbers seem way too conservative, but I will admit that I'm just bench racing right now.
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PostPosted: Sun Jul 13, 2014 12:42 pm    Post subject: Reply with quote

For reference, my 4.86 r&p with 215/75-15 tires and a .73 4th gear gives me 65mph at 3000 rpm. Very tolerable cruising rpm and still gives good power for 'most' mountain passes. I think 75mph is around 3300 rpm.

I also have the 1.18 3rd gear and the 2-3 spread isn't awful. I only really notice it shifting 2-3 on a steep grade fully loaded behind traffic.

I'm thinking about doing the same thing when I build my 2wd ALH, but kind of want to run the taller r&p so I can use slightly shorter tires. But I do like the gearing in my syncro currently.
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Zeitgeist 13
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PostPosted: Sun Jul 13, 2014 12:51 pm    Post subject: Reply with quote

Yeah, my ultimate goal is to run with taller third and fourth gears in my 091/1 box, but couple those with a TBD, and you're talking big dollah. Ideally, I'd love to find a way to drop a 4.14 R&P in there, but those are in the platinum hen's tooth collection.

I'll have to reverse engineer the Revs per mile figures from the calculator, as they're not displayed. The site designs their own gear sets in-house, so it seems odd that they would host an inaccurate calculator, but stranger things are available on the interwebz, so I'll STFU until I get those figures.
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PostPosted: Mon Jul 14, 2014 7:22 am    Post subject: Reply with quote

crazyvwvanman wrote:
Lots of people use the inaccurate calculators and don't know or care that they give wrong answers. It is trivial to check the accuracy for those who do care as I do.

Mark

Zeitgeist 13 wrote:
This is the same calculator that Flint used when prepping his reversed Passat/Quattro transaxle numbers. It also closely matched rsxr's real world numbers with his tire size. Jon's numbers seem way too conservative, but I will admit that I'm just bench racing right now.


I use software written by Quaife Engineering for calculating/graphing the numbers, verifying rpm drops between shifts, and mph for a given rpm. I use the software for my race car and found I could easily adapt it for the vanagon.

The race car also has a quick change rear. I have found the calculated numbers to be extremely close to the real world both with the race car and the vanagon. I also have some software sold by Taylor Race Engineering, but have found the Quaife software to be easier to work with, since you don't need to input the transmission drop gear ratios.

A good pilot trusts his instruments. It is easy to verify a mph at a given rpm knowing the rpm and the tire diameter/circumference. Determining rpm drops between shifts and graphing them takes a lot more time to do manually. I need to be able to quickly select gears accurately and predict the affect on laptimes. There is not an endless of gear choices for the Vanagon, so often it is a compromise of what is available and ones pockets.

My offer stands to crunch the numbers and graph them, no charge, but better to PM me going forward. mark
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crazyvwvanman
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PostPosted: Mon Jul 14, 2014 7:47 am    Post subject: Reply with quote

If you know how many teeth are on each gear then accuracy of gearing calculations is pretty simple. The issue I raised isn't calculating from the known gear sets, it is the fact that some calculators default to using the nominal tire size as a key input value for overall gearing. The nominal tire size is not a very accurate way to do it. Yes, it can still yield results that can be used for some things since for comparison purposes the error is there for both the before and after results. But when you pick an overall gearing result out and want to use it in isolation then the error can stick out like a sore thumb, like it did in this thread.

Of course if you don't trust that BFG or Michelin etc use good instrumentation that is accurate when determining their published specs for rev/mile then trust whatever numbers you like instead.

Mark
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PostPosted: Mon Jul 14, 2014 8:00 am    Post subject: Reply with quote

We take a tire and inflate it to operating pressure. We put a small dap of grease on the tire face. We roll it across the shop floor leaving two dots of grease. We then use a tape measure and measure dot to dot to determine the tire circumference. A racing slick can grow as much as 2 inches in circumference at temp. Yes for calculating ratios for the Vanagon, I am stuck using manufacturer dimensions, which may or may not be accurate. I do trust the software.

For my desired results, the taller tire was not enough of an rpm drop for the speeds I prefer to drive on the highways.

I guess I missed the calculation I did wrong that sticks out like a sore thumb. I am the author of this thread and I believe when I posted it, I was looking for internal hard part info, not trying to get into a debate about gearing. I posted back a few times updates to what I did and my experienced results. Zeitgeist 13 rather than start a new thread revived this one that has been dead for quite some time. Fri Nov 06, 2009
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PostPosted: Mon Jul 14, 2014 8:03 am    Post subject: Reply with quote

Zeitgeist 13 wrote:
This is the same calculator that Flint used when prepping his reversed Passat/Quattro transaxle numbers.


rsxsr wrote:
I use software written by Quaife Engineering for calculating/graphing the numbers


maybe you guys could post links

here is the software I use
http://users.rcn.com/derekdrew/syncrotireandgearratios.xls
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Zeitgeist 13
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PostPosted: Mon Jul 14, 2014 8:09 am    Post subject: Reply with quote

rsxsr wrote:
We take a tire and inflate it to operating pressure. We put a small dap of grease on the tire face. We roll it across the shop floor leaving two dots of grease. We then use a tape measure and measure dot to dot to determine the tire circumference. A racing slick can grow as much as 2 inches in circumference at temp. Yes for calculating ratios for the Vanagon, I am stuck using manufacturer dimensions, which may or may not be accurate. I do trust the software.

For my desired results, the taller tire was not enough of an rpm drop for the speeds I prefer to drive on the highways.

I guess I missed the calculation I did wrong that sticks out like a sore thumb. I am the author of this thread and I believe when I posted it, I was looking for internal hard part info, not trying to get into a debate about gearing. I posted back a few times updates to what I did and my experienced results. Zeitgeist 13 rather than start a new thread revived this one that has been dead for quite some time. Fri Nov 06, 2009


Sorry about that. I honestly was just looking for some background data regarding your real world experiences with this engine/trans combo...not looking to spark arguments. Confirmation of your tire size was exactly the data I sought-thanks
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PostPosted: Mon Jul 14, 2014 8:12 am    Post subject: Reply with quote

Jon_slider wrote:

4.57 R&P with 215x75x16 at 3000rpm = 63.5 mph


Zeitgeist 13 wrote:
My calculator returns the following 3000rpm speeds:

4.57 215 75 16 = 68 mph


I do not know which calculation is accurate, but the software I used to calculate 63.5 mph relies on 729 Rotations Per Mile specs provided by TireRack, for tires I looked up in 215x75x16
http://www.tirerack.com/tires/tires.jsp?tireMake=G...mpare1=yes

Different brands of the same tire size have different rotations per mile, this one
http://www.tirerack.com/tires/tires.jsp?tireMake=K...mpare1=yes has 719 Rotations Per Mile, which produces a speed of 64.5 mph with a 4.57 R&P and a .85 4th

to be more accurate Zeit would need to provide the rotations per mile of the tires he plans to use. Similarly rsxsr would need to provide the Rotations Per Mile he used.

The calculation also depends on which 4th gear is being used. My calcs are based on a .85 4th
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PostPosted: Mon Jul 14, 2014 9:09 am    Post subject: Reply with quote

Using a circumference of 2290 mm for the 215/75/16 and a circumference of a stock 185/14 of 2051 mm I get the following with a 4.57 ring and pinion and a .852 forth gear.

Gearbox:- Vanagon Air Cooled Transmission 4.57 - .852 4th gear
Tyre:- Goodyear 215/75/16
--------------------------------------------------------------------------------------
Top Gear gives 21.927 MPH/1000 RPM and a top speed of 87.709 MPH at 4000 RPM

Engine speeds in top gear:-
30 MPH = 1368 RPM 40 MPH = 1824 RPM 50 MPH = 2280 RPM 60 MPH = 2736 RPM
70 MPH = 3192 RPM 80 MPH = 3648 RPM 90 MPH = 4105 RPM 100 MPH = 4561 RPM

Top Speed in 1 gear = 19.769 MPH
And changes into 2 gear at 2180 RPM dropping 1820 RPM
Top Speed in 2 gear = 36.276 MPH
And changes into 3 gear at 2447 RPM dropping 1553 RPM
Top Speed in 3 gear = 59.308 MPH
And changes into 4 gear at 2705 RPM dropping 1295 RPM
Top Speed in 4 gear = 87.709 MPH
*************************************************************
Gearbox:- Vanagon Air Cooled Transmission 4.57 - .852 4th gear
Tyre:- 185/R14
--------------------------------------------------------------------------------------
Top Gear gives 19.639 MPH/1000 RPM and a top speed of 78.555 MPH at 4000 RPM

Engine speeds in top gear:-
30 MPH = 1528 RPM 40 MPH = 2037 RPM 50 MPH = 2546 RPM 60 MPH = 3055 RPM
70 MPH = 3564 RPM 80 MPH = 4074 RPM 90 MPH = 4583 RPM 100 MPH = 5092 RPM

Top Speed in 1 gear = 17.706 MPH
And changes into 2 gear at 2180 RPM dropping 1820 RPM
Top Speed in 2 gear = 32.490 MPH
And changes into 3 gear at 2447 RPM dropping 1553 RPM
Top Speed in 3 gear = 53.118 MPH
And changes into 4 gear at 2705 RPM dropping 1295 RPM
Top Speed in 4 gear = 78.555 MPH


An RPM drop of about 320 rpm at 60 mph.

Disclaimer: your results may vary. I could live with the taller tire, looking at the numbers above. You could run 65 mph and get decent mpg.
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PostPosted: Mon Jul 14, 2014 9:39 am    Post subject: Reply with quote

215/75/15 BFG spec rev/mile of 729 = 2210mm circumference, not 2290

So applying a correction factor,

2210/2290 x 21.927 x 3 = 63.48 mph at 3000 rpm which is what Jon said, 63.5

Mark
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PostPosted: Mon Jul 14, 2014 10:24 am    Post subject: Reply with quote

From above:
Quote:
Disclaimer: your results may vary.

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PostPosted: Tue Jul 15, 2014 7:21 am    Post subject: Reply with quote

Below is a pic of the Jetta Cluster in my '84 Vanagon with the ALH TDI engine. The tranny is a DK 4.57 R&P and 0.77 4th gear. I'm running 215/75/15 Uniroyal tires. I crunched the numbers using Excel and an on-line tire calculator.

Mark is correct in that results will vary but will be close in the real world.

This pic was taken a few days ago in Saskatchewan, Canada on the way to Alaska pulling a popup camper. The .77 4th gear seems to be perfect for the task.

Image may have been reduced in size. Click image to view fullscreen.




Anyone interested in following our Road Trip can keep up at this link: http://forums.tdiclub.com/showthread.php?t=417129
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PostPosted: Tue Jul 15, 2014 7:43 am    Post subject: Reply with quote

AndyBees wrote:
Below is a pic of the Jetta Cluster in my '84 Vanagon with the ALH TDI engine. The tranny is a DK 4.57 R&P and 0.77 4th gear. I'm running 215/75/15 Uniroyal tires. I crunched the numbers using Excel and an on-line tire calculator.

Mark is correct in that results will vary but will be close in the real world.

This pic was taken a few days ago in Saskatchewan, Canada on the way to Alaska pulling a popup camper. The .77 4th gear seems to be perfect for the task.

Image may have been reduced in size. Click image to view fullscreen.




Anyone interested in following our Road Trip can keep up at this link: http://forums.tdiclub.com/showthread.php?t=417129



AndyBees,

how did you get your gas gauge to work right with the Jetta dash?

Please see my last post on the Passat gauge cluster thread/

Andrew-
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Zeitgeist 13
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PostPosted: Wed Jul 16, 2014 8:17 am    Post subject: Reply with quote

Andrew, if you check out pages 10 and 11 of his TDI club build thread, you'll see that he grafted a Mk4 sender potentiometer onto a T3 sender holder.

http://forums.tdiclub.com/showthread.php?t=276798&page=10
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PostPosted: Thu Jul 17, 2014 8:22 am    Post subject: Reply with quote

Yes, I did use the MK4 fuel tank components to make the fuel gauge functional...... key word is functional.

Due to the long range of movement in the MK4 fuel tank vs the short range of movement in the Vanagon fuel tank, I had to make a decision as to how I wanted the reading to be... show more full or less full.

So, I set it to let me know when the tank is getting empty. Thus, when the tank is full, the gauge registers about 3/4 and hangs there for a long time. When the indicator light comes on, there is about 2 gallons left in the tank.

I reset the trip meter at each fill-up. I can go over 400 miles per tank easily, which is about 34 MPG. Pulling the camper I don't go past 300 miles and here in Canada due to distance and availability of fuel, I fill-up between 200 and 250 miles!
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