syntrix

Ok, rear is 4.44. Any ideas if anyone has a new ring & pinion for the rear?

I'm looking at the ration of a 6.0 for the rear. This means at 9500 rpm max speed would be:

1: 34.3
2. 54
3. 91.1
4. 103.2
5. 122.5
6. 145.3

60mph 6th gear is just under 4k rpm

All on the assumption of 26" diameter rubber (stock 18's)

Stock would be:

1. 44
2. 73
3. 123
4. 139.5
5. 165.5
6. 196.4

60mph 6th gear is just under 3k rpm

So unless we get a huge power increase (ie, turbo kit), all 6th is good for is fuel economy. I'd prefer not as tall, so you have more options running around on the streets

Omicron

Interesting analysis, Syntrix. So what was your point again?

Speed Racer

The lower overal gearing would make the car "feel" like it has little more torque and it should pull a little stronger especially off of the line.

This would be at the expense of top speed (not like the car would ever be able to redline in 6th with the stock gearing) and highway fuel economy be slightly lower because the revs would be about 1k RPMs higher for the same speed.

If someone came up with a kit that I was easy to install I would think about doing it.

Omicron

Ok, we discussed gearing in another thread, and when I hear the rear end was 4.44 - I thought that's plenty low to give good acceleration. Shhheit, 4.11 gears used to be considered drag racin gears back when I was hot roddin V8 musclecars! But this is an interesting idea, especially if it's an easy mod, which it's not apt to be.

Gord96BRG

I'm not sure how you got those numbers for stock speeds in gear, but they're all wrong... From the Road&Track RX-8 Special Edition, the correct max speeds in gear are:

1. 39
2. 65
3. 89
4. 124
5. 147
6. 148 (electronically limited)

If you want a bit shorter gearing, by far the easiest way is to install shorter tires. Something like a 235/40-17 is 6% shorter, which would get you halfway from the (real) speeds in gear to your desired speeds in gear.

I don't know if they have anything available yet for the RX-8, but Mazda Competition has offered quite a variety of different ring/pinion sets for changing diff ratios for the Miata Torsen diff.

Regards,
Gordon

syntrix

I'm using 9500 rpm, not what people claim to only be 9000.

My car bounces at 9500, not just on the tach, but with aftermarket monitoring.

Sorry if mine is more "real world",as I bounce (ever so lightly ) off the rev limiter a lot while racing.

I just used a gearing calculator with the stock tire size, input the gear and final drive ratios.

Yeah, a 4.x used to be the shizzle!

The point here would be to have the ability to rev up faster in 1st, and utilize 6th gear a little better.

There's even sometimes when I'm in 3rd at about 55-60 and it feels like some car's 5th gear

Gord96BRG

500 rpm is NOT going to get you an extra 34 mph in 3rd, nor an extra 15 mph in 4th or an extra 18 mph in 5th!!!

Your "real world" gearing calculator is obviously waaaaay out of whack, most likely in not properly calculating the effective rolling diameter of the tires. Road & Track, on the other hand, actually measures the real speeds in gears - I'd say that's more real world than a calculator... If you want the R&T numbers adjusted for 9500 rpm, here you go:

1. 41
2. 69
3. 94
4. 131
5. 155

Regards,
Gordon

syntrix

I don't know how you are doing that, but I've verified in 3 different programs so far. The only difference is 3rd gear, which was wrong in the first post. Thanks for clearing it all up for 3rd:


The facts are
Tire diameter 26"
1 3.76
2 2.269
3 1.645
4 1.187
5 1.0
6 0.843

FD 4.444

speed at 9500 rpm:

1 44
2 73
3 101
4 139
5 165
6 196

All gear ratios taken from here:

http://www.mazdausa.com/MusaWeb/disp...ehicleCode=RX8

What values and calculations are you using?

Either way, a new ring and pinion would do wonders for driveability of the car!

Gord96BRG

Doing what - coming up with speeds in gear at 9500? Simple, I just multiplied Road & Track's speeds in gear at 9000 by 9500/9000 (which is a factor of 1.05555).

It doesn't matter how many programs you use to estimate speeds in gear based on gear ratios and tire diameters - unless they are calculating the actual effective rolling diameter of the tire instead of using the unladen diameter of the tire, they are all wrong. The effective rolling diameter of a loaded tire is always less than an unladen tire because of the compression of the sidewalls.

Road & Track didn't use a program to calculate the speeds in gear, they just went out and measured them with their corrected speed equipment. It doesn't really make sense to insist that calculated values are more accurate/correct than real world measured values, does it? All that proves is that there's significant error in your assumptions for the calculated values. If you can account for the decrease in effective diameter for the weighted tires, then your calculator might give better (closer to real world) results.

Regards,
Gordon

syntrix

rpm is not the final calc, I rest my point!

Gord96BRG

I'm afraid I don't understand your point, then. You're claiming that your car on the rev limiter will do 73 mph in 2nd gear and 101 mph in third gear? I flat out do not believe it - have you actually tried it? My RX-8 sure won't achieve those speeds in gear.

Regards,
Gordon

greekRX-8

Gearbox:- RX - 8
Tyre:- 225 45 18
-------------------------------------------------------------------------------------------
Top Gear gives 20.619 MPH/1000 RPM and a top speed of 195.881 MPH at 9500 RPM

Engine speeds in top gear:-
30 MPH = 1455 RPM 40 MPH = 1940 RPM 50 MPH = 2425 RPM 60 MPH = 2910 RPM
70 MPH = 3395 RPM 80 MPH = 3880 RPM 90 MPH = 4365 RPM 100 MPH = 4850 RPM

Top Speed in 1 gear = 43.917 MPH
And changes into 2 gear at 5733 RPM dropping 3767 RPM
Top Speed in 2 gear = 72.775 MPH
And changes into 3 gear at 6887 RPM dropping 2613 RPM
Top Speed in 3 gear = 100.381 MPH
And changes into 4 gear at 6855 RPM dropping 2645 RPM
Top Speed in 4 gear = 139.113 MPH
And changes into 5 gear at 8003 RPM dropping 1497 RPM
Top Speed in 5 gear = 165.127 MPH
And changes into 6 gear at 8008 RPM dropping 1492 RPM
Top Speed in 6 gear = 195.881 MPH
************************************************** ****************************************
changes at 9500 rpm with actual diameter of tire ( loaded tire )

syntrix

I'm glad you finally agree with me!

Gord96BRG

That's NOT me, and I still don't agree with you. It looks like GreekRX-8 found a similar calculator to you, but I'll say this again: You're claiming that your car on the rev limiter will do 73 mph in 2nd gear and 101 mph in third gear? I flat out do not believe it - have you actually tried it? My RX-8 sure won't achieve those speeds in gear.

Go and get in your car, and try it - take into account that your speedometer will be optimistic by about 2 mph in the 70 mph range, and 3 mph in the 100 mph range. So if you indicate 71 mph at revlimiter in 2nd, that's actually 69 mph, etc.

Regards,
Gordon

r0tor

iTrader: (1)

I agree, mine tops out in 3rd gear at 93 or 94 mph

MrWigggles

From Tire rack:

You should always use the revs per mile figure as it is almost always the actual real world revolutions.

With the 225/40 tire we have 804 revs/mile. EDIT: the 225/40 is quoted wrong; it should be 225/45, but the 804 revs/mile is correct, and that is the number I used in my calculations. In fifth gear that equals 16.81 MPH per 1000 RPM.

So FWIW, 9500 in fifth gear is about 159.6 not 165. Now this is an estimate because it is not quite a linear progression. At such high speeds the force of the air on the car is enough to cause the wheels to not grip quite "one to one" with the pavement. There can be some slipping of sorts going on and that could account for the difference 155 that road and track would have at 9500 RPM and 159.6 I calculated. Bottom line it is not 165

You guys can do the rest of the math for other gears that aren't 1.000:1

-Mr. Wigggles

Ps. as far as the topic at hand, yes you can make the gears shorter but you have factor in the additional shifting times required on a 1/4 mile run etc. I think the RX-8's gear box is aggressive enough. I actually wish 6th gear was taller like most car at about 25 MPH/1000 RPM

syntrix

I just did second, and it bounces at 69. So mething is amiss, such as my non-oem tires, or Mazda has lied about specs, OR the speedo is that far off.

Too bad I don't have a gps anymore!

Gord96BRG

OR, that's exactly where it should hit the rev-limiter, your car is just fine, Mazda's specs are correct, the speedo is correct, and your speeds-in-gear calculators are simply not accurate!!!!!


PS - quite a few of us have already checked the speedo accuracy with GPS, and it tends to indicate about 2 mph high. If your 69 mph at the rev limiter was indicated, then that would be an actual 67 mph if other's speedo error measurements held true for your car. Another source of error is the tachometer - an indicated 9500 rpm isn't necessarily a true 9500 - it might be an actual 9300 rpm, for example.
Regards,
Gordon

syntrix

And neither is the other persons.

I think something changed gear ratio-wise, as I could see another 1% real speed based off the speedo because of my tire size...

Using the proper gear ratios from Mazda, and bouncing at 9500, second gear, 69 mph indicated, would be almost a 4.6 final drive, not a 4.444.

Something is just not adding up using mazda's provided specs, and what's actually showing on the speedo!

syntrix

Oh, and I do have an aftermarket pickup on the plug wires, and it's definately bouncing at 9500.

So let's say that the speed is even less, then that would be an even greater final drive ratio!

Gord96BRG

OR you're using the wrong effective rolling diameter of the tires in your calculations....

Regards,
Gordon

syntrix

It's posted above.... 26"

Or the rpm readings are wrong on the rpm reader that I have....

Whatever it is, it's just not adding up!

syntrix

And Mrwiggles... it's a 225/45/18 tire stock. You did your calcs at 225/40/18.

Despite all the debating and figuring things out, ultimately a higher ratio rear end would be very beneficial, IMHO.

Gord96BRG

That's NOT the laden effective rolling diameter, that's unladen - you know how the sidewalls compress slightly when the weight of the car is on them? The radius of the tire from centre to road surface is LESS than the radius of the tire with no load on it. That means that, effectively, the tire when loaded by the weight of the car has a shorter diameter than it does as reported by the spec sheets. For comparison purposes, it's fine to use unladen diameters - to say this tire is 2.85% shorter than that one, etc. You can't use those diameters directly to calculate speeds in gears with any accuracy - as you've demonstrated!

Regards,
Gordon

broose

This is the dumbest thread I have ever read and i am now dumber than i was when i begin. no won hav answered hiz Queshon Yet either.