Slant Six Forum :: Speedo Gear Question

I checked with Claude and the tire size is 185/70R14. Where do I look up the calculations you guys did?

Quote:

I checked with Claude and the tire size is 185/70R14. Where do I look up the calculations you guys did?

You need a 35 tooth gear on the nose....

I have an old spreadsheet that does the calc...don't remember where I got it, but it is sure useful.

Do you also have calcs for the early tranny?

Closest I have is a 33.

what matters is the actual distance would be the measurement from the exact center of the hub/wheel assembly to the ground

when shopping for tires that some of the same tire sizes (for example - a 235 60r 15) have different spec'd tire diameters

overlap to allow for slight difference in diameter ...for instance a 25.1 and 25.6" tire both use a 28 tooth gear with 2.76s.

Author:	DusterIdiot [ Tue Mar 28, 2017 4:08 pm ]
Post subject:	Yep...
Quote: I checked with Claude and the tire size is 185/70R14. Where do I look up the calculations you guys did? You need a 35 tooth gear on the nose.... I have an old spreadsheet that does the calc...don't remember where I got it, but it is sure useful.

Author:	Chuck [ Wed Mar 29, 2017 9:48 am ]
Post subject:	Re: Yep...
Quote: Quote: I checked with Claude and the tire size is 185/70R14. Where do I look up the calculations you guys did? You need a 35 tooth gear on the nose.... I have an old spreadsheet that does the calc...don't remember where I got it, but it is sure useful. Do you also have calcs for the early tranny? I have to adjust my '63 too.

Author:	DusterIdiot [ Wed Mar 29, 2017 3:54 pm ]
Post subject:	Nope...
Quote: Do you also have calcs for the early tranny? Sorry Chuck, the table was setup only for the late trannies.

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Speedo Gear Question https://slantsix.org/forum/viewtopic.php?t=60935	Page 2 of 2

Author:	FrankRaso [ Thu Mar 30, 2017 6:07 am ]
Post subject:
I have some calculations on my Tire Upgrade page. Don't forget to include the rolling diameter correction in your calculations. Tire Upgrades Barry's Tire Tech - Tire Dimensions

Author:	Killer6 [ Fri Mar 31, 2017 7:25 pm ]
Post subject:
Quote: Thanks Dan! Just to make sure this isn't overlooked, the speedo pinion housing is marked and offset(eccentric) to accommodate the different diameters needed for the various tooth counts. Make certain you have it indexed properly for the one You're using!

Author:	Chuck [ Sun Apr 02, 2017 4:36 pm ]
Post subject:
Quote: Closest I have is a 33. Thanks for checking.

Author:	shadango [ Thu Apr 20, 2017 9:22 am ]
Post subject:
The charts I have seen all look at diameter/tire height, not the numerical tire sizing..... what matters is the actual distance would be the measurement from the exact center of the hub/wheel assembly to the ground.....but suince that is tough to do right, I figured that taking as accurate a measurement from the ground to the top of the tire would get me close enough. I have seen when shopping for tires that some of the same tire sizes (for example - a 235 60r 15) have different spec'd tire diameters. Just bought a set of 235 60r 15s for our 80 Volare and found that some brands said one thing and another was a half inch different....and there is a difference between what a targeted size should be versus what it actually is when installed and rolling.....so I would never rely on the advertised tire height to do this calculation. When I re-geared my Barracuda some time back I just used the diameter of the new tire as mounted, sitting on the ground, and used the gear ratio and found the right number of teeth on the chart,.....worked out well. Worked for me..... about to do the same for the Volare..... Keep in mind the the chart has overlap to allow for slight difference in diameter ...for instance a 25.1 and 25.6" tire both use a 28 tooth gear with 2.76s.

Author:	SlantSixDan [ Thu Apr 20, 2017 1:22 pm ]
Post subject:
Quote: what matters is the actual distance would be the measurement from the exact center of the hub/wheel assembly to the ground Yes... Quote: when shopping for tires that some of the same tire sizes (for example - a 235 60r 15) have different spec'd tire diameters Yes, but only a little bit different, and... Quote: overlap to allow for slight difference in diameter ...for instance a 25.1 and 25.6" tire both use a 28 tooth gear with 2.76s. ...this is what makes it easiest to just do the calculation based on the numerical tire size. You might be off by a tenth or two, but it doesn't matter because it's going to be less than the difference between two adjacent pinions. Let's use your numbers, a 25.1" versus a 25.6" tire: that's a 2% difference. 28- vs. 29-tooth pinion, that's a 3.5% difference. Or 28 vs. 27-tooth pinion, that's a 3.7% difference. What makes it best to use the numerical tire size is it's very difficult to accurately measure the diameter of the tire by eye with a yardstick or tape measure.

Author:	Greg Ondayko [ Thu Apr 20, 2017 1:34 pm ]
Post subject:
Keep in mind the tranny end of the gear/speedo cable on an 80 volare is different than your e body. The outside hole is the same but the clocking afapther and gear is a different design than 67-75 for example... Fyi. Compare Late 70's - 80's style: http://www.brewersperformance.com/prodd ... 2L&cat=216 To THe Muscle Era Style: 1966-1977ish: http://www.brewersperformance.com/prodd ... 26&cat=216 Greg

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