*Originally posted by zoltiz*@Sep 7 2004, 07:47 AM

**Another car geek post from me:**

Code:

```
Rolla tC 5M tC 4A
====== ===== =====
12.477 14.983 10.804
7.503 8.661 6.020
5.163 5.645 3.872
3.488 4.116 2.795
2.857 3.282 -
```

These are final drive ratios for 5-speed corolla/matrix (and maybe Celica GT), tC 5-speed and tC Auto. Basically if you divide your engine RPM by this number you will get revolutions per minut of your tires, which in turn can be transferred to your speed.

To say that tC 5M is aggressively geared will be an understatement...

With this kind of gearing Mazda3s will not be a problem at all, even knowing that Mazda3 is lighter.

If it was up to me I would opt for a differential with lower gear ratio, though. I'm not much into racing and going at 4000rpm on the higway does not seem reasonable to me...

hey zoltiz,

I was jus checking your numbers, and I got a little different calculation. You said that with our wheel size, we have 845 revs per mile. But I got 820 or so, the 3rd grade calculations below

Tire size is 215/45/17: 45% of 215 mm, which is 96.75 mm, or 3.81 inches. Diameter of the tire 17 in. plus (3.81*2) 7.62 in. = 24.62 inches. Then the circumference is 77.31 inches. ( pi * d). 77.31 inches is .0012201 of a mile. So in one mile, there are 819.6 or 820 revs per mile. 25 less extra revs per mile, means at 75 mph, instead of 3500 or so rpms, it's 3400. Not that big of a difference, 100 or so rpms.

Aaaannnnnywaaays, just wanted to run my numbers by you, maybe you know why there is slight difference, maybe i did something wrong. But I agree, high reving on a freeway does suck, but 4000 rpm....that's some fast highway driving (90 mph by my calculations) Just wondering, at about 75 or so in 5th, is the rpms at 3400? And if you do change tires to 215/50/17, or bigger, does that mean that gas mileage would improve due to lower rpms, but at the cost of acceleration?

Just curious about all this because I'm a prospective tc / mazda 3/ rsx buyer and I got to due my research.

tc @ 75 mph = 3400

m3 @ 75mph = 3200

rsx @75 mph = 3300

p.s also any update on the moonroof pop / hatch rattles? any tsb out yet?