I'm trying to figure out whether or not an AP1 with 4.57 rear gear set has an overdrive in 6th. My questions are:

Given these ratios -
1st 3.133
2nd 2.045
3rd 1.481
4th 1.161
5th 0.971
6th 0.811

is this the ratio of drive shaft revolutions to rear axle revolutions? That had always been my understanding.

Does that then make the calculation (using 1st gear as an example):

old ratio * (new rear gear / old rear gear) = new ratio
3.133 * (4.56/4.1) = 3.133 * 1.1122 = 3.485 ?

This isn't life or death, merely personal edification. If you're going to tell me to do a search, please provide the search string or just a link please. I've searched this site and Googled without an answer (at least that I understand).

 

I think this is where your understanding took a bit of a "loopty-loop".
Using the following gear calculator:
http://www.turnzero.com/technical_resource...gear_calculator
You must look at the "total gearing". 5th and 6th are still "overdrives" in that for every revolution of the engine, the transmission output shaft is spinning MORE than one revolution. The FD ratio incorporates an additional calculation after this and doesn't really affect whether or not a given gear stops being an overdrive.

Corrected for brain fart.

 

I guess that is where my confusion begins. If the only change is the rear gear, what can wheel/tire size or RPMs have to do with the "effective" change of the gearing (if neither has changed)? At any point along the radius from the wheel hub to the tire tread, the time to make one revolution remains unchanged. The only difference is the speed of the hub (slower) vs. the tread of the tire (faster).

I knew I should have paid more attention in physics class.

 

Changing the overall tire diameter (on the drive tires) is no different than changing the FD gearing.

 

Dang it. I knew xviper was going to beat me to that link.

 

Isn't it the other way around

 

All the gear hype is great and all, but back in the FWD glory days, we'd just run 15's or 14's instead of messing with gears. I'm curious to know what the equivalent of changing from the stock 16's to 15's [theorhetically using the same tire proportions] would be. I'd guess around 4.40. They'd be lighter as well.

 

[QUOTE=Mikes256,Feb 28 2006, 10:27 PM] Isn't it the other way around

 

You're not quite getting the point with this line of thought. It's not just the rim size. It's the overall tire diameter that changes the gearing. You can run the same rim diameter, just reduce the aspect ratio of the tire.
EG, if you have a drive tire that is 25" in diameter (like the S2000 OEM tire) and you replace that with a tire that is 23" (you might have to go to a 35 or 30 aspect ratio in the OEM 16"), this would be like going from the stock 4.10 FD to a 4.44 FD. It's not magic, just math and physics.

Oh, and BTW, the "glory days" you speak of is all relative. Before those days, this whole nation ran on RWD for a LOT longer than FWD has been around.

 

[QUOTE=xviper,Feb 28 2006, 08:33 PM]Unless my meds hadn't kicked in, I don't think so.