Why Is Final Drive Ratio Important? Accelerate Faster!

What is a final drive ratio? What does changing it do?

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The final drive ratio is typically the gear ratio for the differential, or the final location where the gearing is altered before being sent to the wheels. Changing the final drive ratio heavily impacts the way the car behaves. If you increase the final drive ratio, each gear will have greater wheel torque, while sacrificing top speed. If you decrease the final drive ratio, each gear will have a higher top speed, however deliver less torque. Raising the final drive ratio also means you'll be at higher RPM in your top gear, raising your engine's speed on the highway. You'll also need to correct the speedometer.

How To Calculate The Top Speed Of A Specific Gear In MPH:
Top Speed = ((RPM*60)/(Final Drive*Current Gear Ratio))*((Wheel Size (in.) +(2*(Tire Ratio/100)*(Tire Width (mm)/25.4)))*Pi)/(5280*12)

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[Jake-wfbh]

"And you're gonna hit vtec at some point"

That is gold.

[revans]

Also changing final drive to a more aggressive set up can also increase the amount of times you need to shift in order to reach 60mph and may alter acceleration time.

[andrewkline]

wow, that old gears video... your marker skills have improved greatly on the whiteboard.

[TheChasingK]

I believe the proper term is "VTEC Yo!"

[viewerlogic]

Great info, why don't manufacturers put super tall 6th gears in? If I'm on interstate and have to downshift no big deal, that's what I signed up for by driving manual.

[PhlBrs]

Thank you so much for thinking of all non-Americans :) Love your channel, keep up the great work! Best wishes from Germany

[Rickyboy]

I've tried to explain this subject to some of my knucklehead friends who think that the taller (numerically) the gear, the faster you'll go in a quarter mile. Yes, to a certain extent, but the elapsed times, and more so, MPH, will eventually drop off. I know this because I experienced it in my own racing career. This video explains very well what happens, so I'll be sending this link to some friends. But, alas, they probably still won't get it.

[TheOnlyHMR]

Thanks now I can tune my car on forza horizon 3 hhaha

[itsyaboia-dub]

Can you do a similar video in relation to increase/decrease in wheel and tire sizes?

[emp]

Details mentioned that could be included: how to change the gear ratios, and what device/where do you get one to correct the speedometer. If they're mentioned (the first being kind of the tpoci), I'm thinking it's always good to include details. Great vid!

[blingbling]

Consider strengthening your driveline, especially for the drag strip. I snapped an axle at the line, and that was on foot wide drag radials.

[Militaristics]

years ago when i was street racing with a 79 monty with a 355 and 3 speed auto I learned a lot of this the hard way. my car was traction limited by the real wheel size i could fit and my transmission ratios were set in stone because I couldn't afford to change the ratios or add a OD. I did run a much looser converter 3500 rpm. after doing some testing and basic math I figured out a 4.56:1 ratio would be the best ratio for 1/4 mile, because it would let me run through the traps in 3rd near my TQ peak, I also learned the 4.56: would over power the traction limits of my rear tires with the suspension setup i had at the time. it took a bit of tweaking with the geometry of the 4 bars to get the pinion angle corrected and the reaction of the setup to plant the tires instead of wheel hopping and wasting energy twisting things. this was around 30 years ago. thanks for the videos that shed some new light on things

[JPRTonundFilmstudio]

I would tune the car the other way, increasing the top speed to finally get a lower rpm when driving on the highway (especially with older cars...)

[magistermurray]

Just wanted to say how much I enjoy your videos. I love cars and have always been fascinated with how they work. Your explanations of automotive systems make me appreciate the complexity and beauty of cars that much more. Thanks!

[AndrewFRC]

Thank you for the great explanation! I am doing a rear end swap on my '87 Cougar and I am glad to see that your anaysis and selection criteria agrees with mine. Are you looking at the 4.57 ratio, I presume? 11.5% torque increase seems worhwhile and fuel mileage is not going to suffer much. I myself am going from a 2.73 ratio to a 3.55, which is a staggering 30% increase, and it'll still keep my freeway rpm just under 2k, which is great for a V8. Its fun to breathe a little new life into these older cars, isn't it? :)

[TheIrishPhantom]

Going from 3.21 to 3.92 in my truck tomorrow. Also dropping a positraction in. With 8 Gears I'm not too worried about top speed suffering.

[tripointkid]

A big disadvantage you didn't mention is the effect to throttle response, say mid turn feathering the throttle. The 4.77 is very very jerky in these conditions and can often unsettle the rear end. Taller gearing smooths out the jerkiness at the expense of less torque. I think this is very important to mention.

[DefWun]

There's also added stress on components. Axles come to mind.

[DENicholsAutoBravado]

In computer gaming. I got a lot more performance out of cars by increasing the final drive ratio. Then, for the last manual gear I could use, I'd make it taller than how the car was stock. Why? Because I needed a higher top speed. It was extremely effective.

Occasionally, when a track wouldn't work out if I did my normal adjustments, I'd go for a taller 2nd to last manual gear to meet in the middle.

There was 1 track where even the last gear needed to be shorter and if it was like the scenario in this video, I even made the 6th gear shorter than the 5th gear.

If you know exactly what you want a car purposed for, you can dial in gear ratios, if you don't, or if you just want a car that's more fun, but you don't want the highway to break the bank? Well..tough choices unless you can also change the "over drive" gear.

Apologies, I was a bit vague on the final gear number, and I wasn't referring to the final gear ratio when I said last manual gear. I don't remember anymore how many gears I had to chose from.

[PhaQ]

I had an old mid 70's Chevelle that had 2.73 gearing. It was a complete pig off the line. (145 bhp/250 lb.-ft) With bigger 15 inch tires and enough road, I could do 155 mph/250 kph. I miss that old boat.