They use tall gears (numerically) in small cars for the same reason you run them in your drag car, motivation. The HHR does not run at 4G's at highway speeds, so that shows your calcuations incorrect. Do I have the correct formula? Nope. But I know at 70mph mine with the same gears (5speed)run's just under 3G's. I think you are trying to use the same formula for a RWD and you can already see, it does not work. Small cars, especially a performance model will use a tall gear ratio, I had one with a 4.41 final ratio. Yes, I know tires can change that. But that is not the question is it (or TC size/stall RPM). That car ran about 2800 rpm at 70 mph (5 speed also).

I'll go back to the one explaination I was able to find about final drive ratio on FWD and until someone can show me different, I'll stick with that.

Which translates to me, the final drive ratio for a FWD is the same as the ring and pinion ratio for a RWD. So a 4.17 final drive ratio in a FWD is the same as a 4.17 ring and pinion in a RWD. Now if I'm wrong, you need to show me where that is incorrect. You have already shown us your formula does not work factoring in what a FWD final drive ratio is.

 

I believe I was told the same thing as presented in Solman's last paragraph. Absent of any further confirmed information, I tend to agree with him.

 

That formula is not correct at least not for a FWD transaxle car. It does nto work using the final drive ratio that GM quotes. I was just out for a trip across the bay and hit close to 70mph at 2500 rpm.

I need to look the actual tire diameter and do the tire rollout calculation that we used to figure out mph.

Its obvious that if it was a final 4.17:1 ratio that motor would be reving pretty high to cruise down the freeway just like a RWD car using 4.10:1 gears.

The formula I used was the one someone else posted here earlier.

 

I think this is because of the overdrive. The final drive ratio appears to be taken at one to one, so that would be in third gear in the automatic and fourth in the 5-speed.

 

Not sure if you are referring to the formula I posted or not, but with only slight rounding error, it is mathematically correct and has worked for every car I have owned. Other factors to consider are: loaded effective tire diameter can be slightly different and vary with tire pressure) tire diameter can grow slightly at higher speeds, speedometer error, tachometer error. If you want to derive the formula yourself, it is just basic Junior High School math (or at least used to be). Convert tire diameter to circumference (how far you go in one revolution) convert inches to miles (5280 ft/mile and 12 inches/ft), convert rpm to rph, just keep track of your units and it is easy!

 

For the record, 4.17 = short, 3.09 = tall (er)

 

Hey C2

Where did you get the 3.91 ratio for the auto in your original post? I have yet to fond that in any of the GM data for that tranny.

 

Hmm, I know a few Auto guys that got beat by a stick care that was heavier, has a smaller motor, and a smaller turbo last year. so what's this I hear about drag racing is better w/ an auto?

http://www.livernoismotorsportstv.com/video/3396

 

WHERE DO YOU SEE WHAT I SAID IS NOT ON TOPIC?

Yes forgive me but I`am yelling now too

You were the one that came up will 86 mph with an auto at 2500 rpm and 66 mph with a manual at 2500.The reference to the MPG was if your calculations were right how would the manual get better MPG than an auto.

You said QUOTE Now you can see that there is a huge difference between the manual and the auto.

And I don`t no what all that other stuff you said about 1000hp wheel stands and floats yer boat and 5pm in LA traffic has anything to do with me or the TOPIC.

 

So you think those cars in that video are Manuals? When the guy mentions getting the clutch to work correctly hes talking about a clutched automatic. This is what the pro stock NHRA guys use as well as the exteemly high HP cars in like the outlaw or 10.5 tire classes.

Lets not get into the auto vs manual drag racing debate. I know this guy or that guy thing.

I ran a 8 sec 1970 Camaro 897hp with 500hp of nitrous on top of that and used a 2 speed automatic. No one ran or runs manual running those kind of numbers!!!

Its a known fact that autos rule the drag strip.