How Big is My Rear End!!!

[reidhazelton]

The one in my car....come on!!!

Does any one out there know how I can find out what ring and pinion ratio I might have? Aside from taking it apart of course. I am getting some hard to believe numbers for mph when I am doing gear conversions.

Thanks!!!

[Garey Guzman]

This is very simple. Since you live in WI, I assume that you've run Road America more than once.

If you are pulling more than 6700 RPM and your 4th gear is numerically 1 or more (i.e. 24/26, 25/26, 26/26), you have a 10/31

If your 4th is overdrive, you have a 9/31

Of course, this is for normal rear tires on the rear wheels. Weren't you the guy ahead of me on the grid in the rain last Sunday with the front wets on the rear? That would definitely change the calculations.

[reidhazelton]

Hi Gary,

Wish I woulda had a chance to meet you over the RA event....but I didn't want to leave my dry shelter. We didn't put a boat in the trailer.

That was me on them skinnes. Doing the conversion for the skinny wet tire, my mph was a little hard to believe, and I was doing some conversions for Blackhawk and came to the same.

At RA I was running out of gear at pit out and had to maintain that to the marker. I didn't anticipate needing a higher gear than I had, especially in the rain even though the front wet is even smaller dia than the slick. I should have found another gear, but 2 changes is enough for me in one weekend.

So, to answer my question, 10:31 it is. Guess that is good news

Thanks Gary, next time I will make a point to stop by!

[cff96]

Reid:

If you are talking about the 92 VD - the car has a 9:31.

[reidhazelton]

Thanks Cindy,
That makes much more sense now. I didnt think there was a Ford on the planet that would do 155 at RA.

Thank you!!!

[Jim Christian]

The next time you change gears, examine between the splines on the pinion shaft, the ratio should be stamped right on the shaft.
Jim

[Garey Guzman]

Hi Gary,
Wish I woulda had a chance to meet you over the RA event....but I didn't want to leave my dry shelter. We didn't put a boat in the trailer.

It wasn't that bad (said the SoCal guy). I saw in the Supps that the North Paddock was reserved for EWC guys so I stayed there.

I hope to make it to RdAm a couple of times next year so hopefully a bunch of us will meet up.

And don't be afraid to drive south! Atlanta is still very nice in November!

[Charles Warner]

Pull the rear cover. Mark the pinion shaft. Mark a tire. Start turning the tire. It will either go around 10 times when the pinion shaft has reached 31 revolutions or 9 times.

[PaulT]

Don't you need to keep the diff from spinning for the tire/pinion shaft test to work ie. turn both wheels together?

Paul
Lotus 51

[Jim Gustafson]

Charles is spot on as usual

Jim Gustafson
Racing Since 1970