gear ratios
 

dear friends,

I was convinced in a forum that, shortening the final pinion, have nothing to do with how close the gear ratio result.

today, I was thinking about it and decide that I will buy a very long final pinion ( as long as a 400 miles/hour in 6th gear) and my gears will remain with the same relation between them ¡¡¡ :)

It ois true that changing the cwp(aka final drive, ring and pinion) has no effect on the % revs drop between gears, it does change the relationship between speed over the road and rpm. changing the cwp has the same sort of effect as changing rear tire heights.

here's an example of the effect of some different rear tires on a 911. the rpm drops between gears don't change, only the speed overground in a gear changes

Just out of curiosity, why do you want such tall gearing?

If I tell you the truth....is not easy for me to think about this ring&pinion&gearing issues....

I read a lot of posts about R&P not being useful to reduce gap between gears but, in my heart, I believe that this was not true. And, finally, I think I realice why....

for example, in a G50/20 gearbox with std R&P (std in later euro 993), if a driver exit a corner at 125,6 mph (this is 6.500 rpm in 4th gear) and change into 5th gear, rpms will fall 1.143 rpms.

if you do the same with a 8:32 R&P (at a slightly higher speed of 131 mph) in 5th gear, rpms will only fall 1.031 rpms....

and this is even more true at lower speeds

sorry for my bad english¡¡¡¡

J, You are so wrong. Here is a comparison of what happens when the cwp is changed. rpm drops are the same, you just shift at a lower speed because you ran out of revs at a lower speed. The top speed is liveable for a dual purpose car but 1 is now too short. The intermediate gears are similarly affected.

thanks Bill...

may be I am using the wrong info but I still think the same. The critical issue here is the maximum speed that 2 drivers exit a corner. I think this is the starting point.

Since the rpm drop is lower in 5th gear than in 4th gear (and this is true for the rest of the gears), then I will always prefer to exit a corner (or to start an acceleration) in a lower gear

if this is not the case, sorry for my ignorance

thanks

yes, it's true that the rpm drops normally get smaller as you go up through the gears. If you prefer to think of speed in a gear consider this. w/ a 9:31 @ 100mph you are near the top of 3, w/ the 8:32 you are a bit past 1/2 way through 4. Now these speeds in those gears may be fine. The issue w/ a too short 1 is still there

compare the above to a race trans w/ closer gears.

Top speed is comparable to the /20 w/ 8:32 cwp, I wouldn't want anything shorter for dual use. But notice 1 is now very useable. 100mph is now the bottom 1/2 of 4 instead of the top 1/2 and when you do shift to 5 the drop is only 1038 instead of the 1196 w/ either /20. doesn't sound like much difference but if you drove them back to back you would see that there is a world of difference between the 3 transmissions