Determining gear ratios

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Model T Ford Forum: Forum 2018: Determining gear ratios
Top of pagePrevious messageNext messageBottom of page Link to this message  By David Heavner on Thursday, August 30, 2018 - 11:20 am:

I raised my T up with both wheels of the ground. In trying the determine the gear ratio, I cranked the crank 17 revolutions with the rear wheel going around once. What is the gear ratio? Any help would be appreciated.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Henry Petrino in Modesto, CA on Thursday, August 30, 2018 - 11:31 am:

Put one wheel back on the ground, then do it again being sure the planetary is in high and any auxiliary gearbox is in direct. Turn the crank counting turns until you get 1 revolution on the wheel that's off the ground. Divide that number by 2 and you'll have your ratio.


Top of pagePrevious messageNext messageBottom of page Link to this message  By David Heavner on Thursday, August 30, 2018 - 02:12 pm:

Henry. Thanks. I will give it a try.


Top of pagePrevious messageNext messageBottom of page Link to this message  By James A Bartsch on Thursday, August 30, 2018 - 02:41 pm:

Dave; Both wheels turning together, ratio you give is 17 engine revolutions to one axle revolution = 17:1


Top of pagePrevious messageNext messageBottom of page Link to this message  By Scott Conger - Wyoming on Thursday, August 30, 2018 - 03:30 pm:

Yeah.......no.

Put your brake lever full forward and repeat. You're going to most likely find either 3.63, 3.0, 3.33, or 3.25:1 ratio. In eastern US with a closed car, possibly 4:1

Not even a TT is going to have 17:1


Top of pagePrevious messageNext messageBottom of page Link to this message  By Henry Petrino in Modesto, CA on Thursday, August 30, 2018 - 03:39 pm:

I suspect David was counting wheel revolutions on one side only. I further suspect the unwatched wheel did quite a bit of turning not synchronized with the other wheel making the count on the one wheel completely meaningless.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Hal Davis-SE Georgia on Thursday, August 30, 2018 - 04:56 pm:

Yep


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Gregush Portland Oregon on Friday, August 31, 2018 - 11:12 am:

Unless the fan belt is slipping...With the car on flat ground, lever forward, spark plugs out; roll the car forward in high one revolution of the wheel (does not have to be a rear wheel) and count the number of times the engine or fan turns. You could even do it by yourself by marking one blade of the fan and use the crank.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Neil Kaminar on Friday, August 31, 2018 - 07:03 pm:

Mark,

The fan turns more than the engine.

Neil


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Gregush Portland Oregon on Friday, August 31, 2018 - 07:55 pm:

Never mind the fan, use the pulley. LOL
You could still use the fan but would require a bit of math. :-)


Top of pagePrevious messageNext messageBottom of page Link to this message  By David Heavner on Monday, September 03, 2018 - 02:26 pm:

I jacked the car up on one wheel. I then cranked it three revolutions. The wheel rotated a bit over one revolution. Is my gear ratio 3.25:1 or 3.0:1 or somewhere in between? Thanks for any help.


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