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# Why do two cars have different rpms at 70 mph?

## Why do two cars have different rpms at 70 mph?

Two cars of the same make with different engines will have different RPM at 70mph. Car with more number of gear and higher engine displacement will have lower RPM. RPM is also affected by wheel size. Smaller wheels give higher RPM.

### How are engine rpm and engine speed calculated?

Engine RPM, or the speed at which the engine turns, can be calculated at any speed given the vehicle’s tire size, axle ratio, and final transmission gear ratio. This calculation is used to match oversize tires with new ring and pinion gears to obtain the desired engine RPM at highway speed.

How does the gear ratio rpm calculator work?

This calculator does not take into consideration any drive train loss, road and weather conditions or driver skills. The calculated results are displayed; the higher the engine RPM, the greater the potential speed at the cost of fuel, heat, friction and engine longevity.

What should the gear ratio be at 65 mph?

Number Ring Gear and Pinion Ratio (3.08, 3.73, 4.10, 4.56, etc.) Tire Height (31, 32, 33, 35 etc.) MPH Transmission Final Gear Ratio (2.54, 1.43, 1.00, etc.) Calculated Results Engine RPM “Ideal” 65MPH Cruising Speed RPMs Based on Tire Size (estimated) 27″ 28″ 29″ 30″ 31″ 32″ 33″ 34″ 35″ 36″ 37″ 38″ 40″ 42″ 44″ 1,752 1,690 1,631 1,577 1,526 1,478

Two cars of the same make with different engines will have different RPM at 70mph. Car with more number of gear and higher engine displacement will have lower RPM. RPM is also affected by wheel size. Smaller wheels give higher RPM.

## How to calculate engine RPM at any speed?

Your vehicle’s RPM can be calculated at any speed as long as you give the tire size, axle ratio, and final transmission gear ratio. Using this calculation, you can match oversized tires with new ring and pinion gears to get the engine RPM at highway speed you desire.

Number Ring Gear and Pinion Ratio (3.08, 3.73, 4.10, 4.56, etc.) Tire Height (31, 32, 33, 35 etc.) MPH Transmission Final Gear Ratio (2.54, 1.43, 1.00, etc.) Calculated Results Engine RPM “Ideal” 65MPH Cruising Speed RPMs Based on Tire Size (estimated) 27″ 28″ 29″ 30″ 31″ 32″ 33″ 34″ 35″ 36″ 37″ 38″ 40″ 42″ 44″ 1,752 1,690 1,631 1,577 1,526 1,478

### How to calculate gear, rpm, and tire diameter?

MPH Calculator RPM: RPM Gear Ratio : Trans Gear: Tire Diameter: Inches

Which is the best rpm for fuel efficiency?

Step 4: Maintain fuel efficiency. For the best fuel efficiency, keep your RPMs between 1,500 and 2,000 RPM when driving at a constant speed. Note: Your engine burns more fuel at higher RPMs. Your RPM gauge is designed to help you operate your car more efficiently and to prevent damage to your engine when driving.

What should the RPM be to accelerate from a stop?

If you try to accelerate from a stop without increasing your engine RPMs, you’ll likely stall the engine. Increase the RPMs from idle to 1300-1500 RPMs and only then ease off the clutch pedal to smoothly accelerate from a stop.

## How to find the best rpm range for your car?

Tip: Check your carâ€™s user manual or the car manufacturerâ€™s website to find a recommended range of RPMs for your carâ€™s specific make and model. You can also do an online search to find the recommended maximum RPM range for your engine. Step 1: Observe the RPM gauge and avoid RPM spikes.

### What should the RPM be at 75 mph?

It’s a helpful write up about optimizing highway cruising RPM with rear gear selection and overdrive. The article provides a formula to calculate RPM at any given MPH. It states that about 2200 RPM @ 75 MPH is a good target.

Which is the best rpm for highway cruising?

I was reading the article “Hitting the Sweet Spot” in the latest issue of Rod & Custom. It’s a helpful write up about optimizing highway cruising RPM with rear gear selection and overdrive. The article provides a formula to calculate RPM at any given MPH. It states that about 2200 RPM @ 75 MPH is a good target.

What happens if you run a car at 40 mph?

The engine will continue to rev as the car tries to accelerate above that speed, but the car will not be able to shift into gear for further speed. Continuing attempts to accelerate can result in severe engine damage. The car likely would still run fine at lower speeds, but it should be taken to a mechanic immediately.

## What can cause the RPMs to go super high while driving at?

Today I was driving on the Interstate going 65mph and suddenly I felt a jerk in the truck and that’s when my RPMs went all the way to 5.5 and so I let go of the gas and it went back down but as soon as slightly press on the gas the RPMs went back up .

### Can a 4.2 liter engine go to 60 mph?

The 4.2 has plenty of power to stay locked at 50 – 60 mph, even with the car full of family & stuff and even on slight inclines. Actually, on a few occasions I was amazed by how much “suffocating” the engine took before the computer decided it cannot go locked anymore.

What kind of car revs up and down?

Rpm revving up and down while driving around 50-60mph. Hello. I have a 2002 Trailblazer LTZ. When I am driving usually I notice around the speeds of 50-60 mph my car revs up and you can watch the rpm’s go up and down.

How to calculate engine RPM at highway speed?

This calculation is used to match oversize tires with new ring and pinion gears to obtain the desired engine RPM at highway speed. Note: 336.13 is used to convert the result to RPM = [63360 inches per mile / (60 minutes per hour x Pi.)] Jeep SR4 (4 Cyl.)

## What’s the average speed at 2400 rpm in 5th gear?

If you’re turning 2300-2400 RPM in 5th gear then you don’t have the stock 3.08 gears. 3.08 gears with a T-5 and the stock 225/60/R15 tires, will yield a speed of about 85ish MPH at 2400 RPM in 5th gear. 3.73’s would put you at about 70 MPH at 2400 RPM though.

The 4.2 has plenty of power to stay locked at 50 – 60 mph, even with the car full of family & stuff and even on slight inclines. Actually, on a few occasions I was amazed by how much “suffocating” the engine took before the computer decided it cannot go locked anymore.

### Why is it when driving the RPM gauge drops or jumps up?

Somewhere the fuel drop then suddenly rpm decrease better check the complete fuel system from tank to injectors also check the rpm sensor . Was this answer helpful? This could possibly be your output speed sensor, related to the transmission.

When does the RPM go back to normal?

The RPM will usually go back to normal as you accelerate the vehicle, but will increase again after you stop. This is definitely not a normal situation. If you are experiencing a rough idle or your RPM is running high, then there are a variety of reasons for why this could be happening.

What to do when your engine RPM drops?

Engine have fuel problem . Somewhere the fuel drop then suddenly rpm decrease better check the complete fuel system from tank to injectors also check the rpm sensor . Was this answer helpful? check fuel pressure between fuel pump and injectors. you may have a fuel pump that is about to fail.

Ruth Doyle