Gear ratio, tire size, RPM and speed questions

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Model T Ford Forum: Forum 2014: Gear ratio, tire size, RPM and speed questions
Top of pagePrevious messageNext messageBottom of page Link to this message  By Rob Heyen - Nebraska on Wednesday, February 05, 2014 - 09:42 am:

Last summer I took out 13 T on the interstate for a few miles, and GPS average was 52 mph.

Looking at this online calculator, it says my engine speed was 2038 rpm. At 45 it says the RPM is 1835. That seems high to me, am I using the correct numbers. I think the standard gears are 3.64:1?

Calculator
http://www.advanced-ev.com/Calculators/TireSize/


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ken Kopsky, Lytle TX on Wednesday, February 05, 2014 - 09:51 am:

That certainly follows this chart.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ken Kopsky, Lytle TX on Wednesday, February 05, 2014 - 09:54 am:

Change the gear ratio to 3.63 and see what you get. :-)


Top of pagePrevious messageNext messageBottom of page Link to this message  By Roger Karlsson, southern Sweden on Wednesday, February 05, 2014 - 09:55 am:

Seems legit. I think it was Ralph Ricks who posted the 40 rpm per mph rule of thumb with std gears and wheels. 45 x 40 gives 1800 rpm.
Std 11/40 gears gives a ratio of 3.6363636 => 3.64.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mike Walker, NW AR on Wednesday, February 05, 2014 - 12:27 pm:

Rob -- Most of the 30 x 3-1/2 tires these days are more like 32" diameter, not 30. That would raise the speed/rpm ratio a bit.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ray Syverson on Wednesday, February 05, 2014 - 12:45 pm:

So when I'm thundering down the road at 35, scared to go faster, with my new Firestone tires (maybe 31" diam?) , my engine is only at 1377 RPM?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dave Hjortnaes, Men Falls, WI on Wednesday, February 05, 2014 - 03:48 pm:

That is gutsy Rob. I had to drive my speedster on the freeway for about 7 miles cuz the bridge was out. I was going 45-50 and everyone else was going 70-75. Not a good feeling. I will stay on county highways.

Wood wheels, no seat belt, no helmet.......


Top of pagePrevious messageNext messageBottom of page Link to this message  By paul fiedler on Wednesday, February 05, 2014 - 04:55 pm:

think about combustion build-up on the head. how often will you have to pull it every 100 miles to clean it?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tom Carnegie on Wednesday, February 05, 2014 - 05:15 pm:

In the 2009 Montana 500, from Livingston to Billings (76 miles at 58.5 mph average), my T averaged ~2340 RPM's for one hour and 17 minutes. In that time the crankshaft rotated ~182,000 times.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Rob Heyen - Nebraska on Wednesday, February 05, 2014 - 06:41 pm:

Tom,

I was thinking of you (Montanna 500 folks) who routinely drive 50 plus. I didn't think the rpm were so high until playing with the calculator above.

I rechecked it with a dynometer printout from the Model K last summer, and it was close (35 inch tires, 3:1 gears):



At 1412 rpm and 35 inch tires the calculator said 49 mph. One mile off, maybe slippage on the dyno rollers?

Should a six cylinder engine be capable of more, less, or the same rpm as a similarly engineered four cylinder motor?

Thanks,

Rob


Top of pagePrevious messageNext messageBottom of page Link to this message  By Royce in Dallas TX on Wednesday, February 05, 2014 - 07:11 pm:

The number of cylinders is not related to RPM limitation or potential power.

The engine design is the limiting factor. Any engine is an air pump. The amount of airflow capable through the valves is the limiting factor for theoretical power in any design, all other things being optimized. This is why if displacement is the same between two engines the one with a larger bore size is CAPABLE (not necessarily does) of producing more power because a larger bore size can allow bigger ports and bigger valves if the engine designer takes advantage of that fact.

The 65 Horsepower Pierce Great Arrow of 1907 ran 60 MPH at a 1440 RPM.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Rob Heyen - Nebraska on Wednesday, February 05, 2014 - 08:42 pm:

Royce,

Did you have a chance to look for the Pierce dimensions reference last weeks thread?

I'm looking for main journal sizes of the 1907/08 Pierces. I have the 30 hp size (Model 30-NN), however am looking for Models 45-PP, 40-S and 65-Q.

Thanks,

Rob


Top of pagePrevious messageNext messageBottom of page Link to this message  By Royce in Dallas TX on Thursday, February 06, 2014 - 07:44 am:

Rob,

I can't find a reference to the actual gear ratio. However we know that the 1907 45 HP models (15th model, 500 produced) and the 1907 65 HP (16th model 100 produced) shared the same bodies and chassis.

The 45 horsepower Pierces used 34" diameter wheels. Ratio 2.57 : 1.

The 65 Horsepower Pierces used 36" diameter wheels. Same rear end ratio, calculated approximately 2.57 : 1.

This article mistakenly calls the 1907 a 66 horsepower car. Undoubtedly they made far more than 65 horsepower (ALAM rating).




Top of pagePrevious messageNext messageBottom of page Link to this message  By Neil McKay on Thursday, February 06, 2014 - 12:40 pm:

The 1922 graph that Ken posted assumes the car is always in high gear.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Rob Heyen - Nebraska on Thursday, February 06, 2014 - 04:56 pm:

I have tire sizes, production numbers, cubic inches and hp. I also have the Model 45-PP at 2.75:1 gear ratio (operators manual) but no ratio for the other models.

I have the Model 30-NN crankshaft main journal at 1.56 in., but would like to find the other model journal sizes.

Thanks,

Rob


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