# Gear ratios and highway driving



## puddleglum (Oct 22, 2008)

Welcome to the forum. If you hang around here for a while you will learn lots. There is a tremendous amount of info here, most of it very good. 
To your question, the transmission gear ratio is only a portion of the overall drivetrain ratio. You have to add it to the final drive reduction and also factor in tire size to get an overall ratio. Omitting the transmission won't give you 1:1 because you still have a reduction in the diff. Before that does you any good, you need to know the rpm range of the power band of your motor at the voltage of your system. Then you can calculate what gear ratios you are going to need to keep your motor running in that range at the speeds you want. That 6th gear may help you if you have a big low rpm dc motor, but probably not much with a smaller high revving AC setup. good luck with it.


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## Matej (Dec 4, 2015)

Thank you for the reply.
The differential in the car has a 3.07 ratio. However, there are various other ratios that fit if I ever feel like experimenting, ranging from 2.65 to 3.91.

The 5-speed factory transmission I have has a final ratio of 0.771. The reason I am considering the T56 over the factory transmission, besides the 6th gear, is because I would like to eventually take the car to occasional drifting and autocross events and the stock transmission is not the strongest. Plus there are already adapters available for the some of the bellhousing patterns found on variations of the T56, while I would need a custom adapter made for the stock transmission.

Finally, the motor I plan to start out with will be either the Warp9 or M102. I am not sure if it can give enough power to have fun with at first, but I feel either is a good motor to start and learn with (though if it can occasionally do at least 200hp and 6000rpm right out of the box, that would be fantastic).


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## dougingraham (Jul 26, 2011)

Matej said:


> At the moment I am considering using the Borg-Warner T56 6-speed transmission for my swap. Besides being able to handle quite a bit of abuse, one of the most intriguing aspects of it is the 6th gear ratio being 0.500:1.
> 
> I am curious if such a low gear could be of any noticeable benefit at higher speeds. From my understanding the main obstacle when it comes to driving EV conversions at highway speeds is the wind resistance/aerodynamics.
> However, most common manual transmissions found in cars only have a final gear of 0.7xx or 0.8xx, and those who choose to omit the transmission altogether have a gearing of 1:1 (obviously differential gearing comes into play as well, but I am ignoring it for this scenario).


I made a spreadsheet to help with these kinds of calculations. Feel free to make a copy of it and substitute your own numbers.

Vehicle speed calculation spreadsheet

It won't tell you what the car will actually do only what it might be able to do.



Matej said:


> Could there still be a noticeable improvement to highway range with a lower final gear, and how significant would it be?


Slight at most. Electric motors have a flat efficiency curve. It could be worse at the lower RPM in 6th than it is in 5th at twice the RPM (assuming 6th is 0.5 and 5th is 1:1). In fact it is likely that at the Lower RPM the efficiency will be lower. This is because at the same power output with a Lower RPM the voltage out of the controller will be lower but the current will be higher. Resistive losses are I^2 * R which means the losses go up with the square of the current. Best efficiency is probably going to be between 3500 and 4500 RPM on a WarP 9.

Best Wishes!


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## Matej (Dec 4, 2015)

Thank you, it is always good to see some numbers.


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## miscrms (Sep 25, 2013)

Here's another interesting one to play with:
http://www.offroadvw.net/exceldyno/

Not designed for EVs, but if you can come up with a power/torque curve for your motor of interest it seems to play pretty well. I do find it gets hung up on a single speed transmission sometimes when swapping engines/motors, and just have to reload one of the standard transmissions and edit again.

It may be worth establishing some kind of baseline using a dyno curve from the original ICE (if you can find it) and comparing that to real world results (if you can find them). That would give you something to compare to.

For my case, I was lucky to find a wheel dyno graph for a Nissan Leaf. I then put in the Leaf's physical parameters, and was happy to see that 0-60 time and 1/4 mile times were very comparable to real world observations. Then I put in the physical data for the new vehicle the Leaf drivetrain is going into, and played with gear ratios, over drive etc. I couldn't really find a better balance of acceleration and top speed than the stock gear ratio, even when adding more gears. I also compared performance to some off the shelf motors that I was able to find data for, and I'm happy to say the Leaf motor held its own against any of them, even the dual AC35. In large part this was because the Leaf's higher rpm limit allowed a larger gear ratio for the same top speed.

I can't guarantee they are accurate accurate, but here are the motor curves I came up with for use in this spreadsheet:










Rob


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## EVfun (Mar 14, 2010)

dougingraham said:


> Slight at most. Electric motors have a flat efficiency curve. It could be worse at the lower RPM in 6th than it is in 5th at twice the RPM (assuming 6th is 0.5 and 5th is 1:1). In fact it is likely that at the Lower RPM the efficiency will be lower. This is because at the same power output with a Lower RPM the voltage out of the controller will be lower but the current will be higher. Resistive losses are I^2 * R which means the losses go up with the square of the current. Best efficiency is probably going to be between 3500 and 4500 RPM on a WarP 9.


My experience follows what Doug is saying. I run my 4 speed in 3rd gear, for a drive ratio of 5.77 to 1 at freeway speeds. I doubt the overdrive will be wanted in a street EV. Some of the EV drag racers run tall final drives, but that is about staying in the peak power range, not the maximum efficiency range. The efficiency peak is at a considerably higher rpm than the peak power, opposite most gas engines.


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## ferd (Dec 1, 2015)

EVfun said:


> My experience follows what Doug is saying. I run my 4 speed in 3rd gear, for a drive ratio of 5.77 to 1 at freeway speeds. I doubt the overdrive will be wanted in a street EV. Some of the EV drag racers run tall final drives, but that is about staying in the peak power range, not the maximum efficiency range. The efficiency peak is at a considerably higher rpm than the peak power, opposite most gas engines.


 
For the motor itself, I agree that gear ratios don't affect its torque output much since the torque curve is so flat. But we have noticed a significant difference in battery pack range. The gears can allow the motor to draw less current from the batteries during heavier loading, such as climbing hills. So you might not notice much difference in motor power, but you might notice a difference in battery range.

Of course, transmissions are part of the compromises you make when building a car. If your primary use will be racing (drifting) then you may prefer less weight (no transmission) over battery range. Most available transmissions were designed for ICE vehicles anyway, so they don't complement electric motors optimally. We've found that we only use a couple of gears in our street EVs, so now we use a 4-speed Muncie that was modified for racing use (ICE cars in medium power classes) that only has 1st and 3rd gears plus reverse.


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## Matej (Dec 4, 2015)

After doing a bit more research, it seems that while the consensus is that it is beneficial to keep the manual transmission, people generally only stick to about two or three gears. Am I correct in this observation?
From what I have seen on YouTube, people with converted cars usually start out in second gear which they also stay in on slower roads, and utilize third or fourth for faster speed limits.

As the goal with my conversion is to have a street capable car that I can also take to occasional drift events, I am now deciding on the transmission choice.
The factory five-speed transmission is not the strongest, and it is also somewhat rare/valuable. I am considering selling it while it is still in good shape, and instead going with a stronger transmission from a different make.

Originally I wanted the T56 as discussed above because I still had the ICE mentality and believed six gears would be better than five, but after having learned more, it seems that less gears may actually be better.
Thus I am now considering various 3-speed or 4-speed manual transmissions.

Do you gentlemen believe 3 gears would be enough for a possible drift car and speed limits ranging from 25mph to 65mph?
I am trying to build the car with exactly as many gears as I will utilize and hope to avoid wishing for an extra gear or finding out that I am only using three out of four.

From watching videos of the EV West BMW with their two-speed manual transmission which they call 'drifting,' it seems that they are having a bit of trouble holding a controlled drift and are mostly just doing burnouts and skids, unless the driver is just not used to the car yet or does not have much drifting experience. However, I think at least one more gear could come in handy.
Not to mention I still love the feel of shifting a manual transmission and three gears are probably the minimum that will satisfy that feeling. 

I realize gear and differential ratios play a big role as well, but those can be fine-tuned later down the road, since varying gear ratios and differentials are available.
Do you gentlemen think three gears will be enough for this specific application?


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## piotrsko (Dec 9, 2007)

My $0.02 and not worth more than that:

3 speeds are rare anymore and the ratios between gears is awful.

Kinda ditto for 4 speed close ratio like a 853 19 spline dodge.

You can not use a gear, but you cant add something not there. You don't need overdrive, and won't use low.

If you drift you need something that will hold up unless you really like tranny swaps.

If you go direct drive you need more motor watts, like say 270 Kw worth which will be a couple of hundred volts at a couple of hundred amps.

I use a 5 speed with a 2speed splitter. I use about 7 forward, but not all the time. Daily driving I use about 4, 5 when idiot honda is along side at the light.

YMMV


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## piotrsko (Dec 9, 2007)

That might work IF: the tranny doesn't scatter when you tromp hard. These were supposed to sit behind a six, or in an old man stripped econo pick up, or a chick 'stang. A properly set up conversion is incredibly fun.

Which adapter? Motor to bellhousing or bell to trans? I see Cologne patterns are common, but little in that era above 4 liter.

Might be a reason why they are cheap.  And the pistol grip fits anything with a round end 3/8-16 thread.

Im not saying don't do it, but be aware.


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## rwaudio (May 22, 2008)

If you do end up with an AC motor, a transmission that can handle high RPM's might be desirable. Something that can take 7500-10000rpm might be nice. I try not to take my stock 944 Turbo transmission above around 7000rpm, that's where the gas guys peaked, and it makes quite a bit more noise above 5000rpm (which you would never notice in an ICE) I cruise at 4000ish rpm and that's where the Siemens/Transmission seem happy and 3rd gear at 120km/h give me better efficiency than 4th or 5th gear. More gears definitely aren't better, but having the right ones will be important.

On the other hand brush wear with a DC motor is exaggerated at high RPMS (ask me how I know), Although you can rev DC motors to 5000+ rpm you don't want to be there very long with much load. A warp 11HV, 300v battery and 1000 amp controller make it too easy to be at high rpm and high load, the power band is spectacular though.


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## jwiger (Oct 18, 2014)

Matej said:


> ...From watching videos of the EV West BMW with their two-speed manual transmission which they call 'drifting,'...


That car was built for Pike's Peak, where sticking to the side of the Mt. is ideal and "drifting" will get you killed, or worse, waste battery power.

I'm starting with a T-5 behind a Warp 9 in my car. Check out this article below.

http://www.mustangandfords.com/how-to/drivetrain/m5lp-0401-mustang-t5-transmission/


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## Matej (Dec 4, 2015)

jwiger said:


> That car was built for Pike's Peak, where sticking to the side of the Mt. is ideal and "drifting" will get you killed, or worse, waste battery power.
> 
> I'm starting with a T-5 behind a Warp 9 in my car. Check out this article below.
> 
> http://www.mustangandfords.com/how-to/drivetrain/m5lp-0401-mustang-t5-transmission/


The EV West E36 seems to work great for racing, which is obviously what it was built for. I was mainly referring to the videos of it that have 'drifting' in the title, though it turned out they just do burnouts, short skids, and spin out. It is hard to to tell how their setup would really behave if one actually tried linking corners of various speeds and such.

Guess I will just have to finish my car and see for myself. 

I am not sure what you plan to use your car for, but unfortunately the T5 is known to be very weak. You can build it up to handle a bit more power such as the one in the article, but for the amount of money such upgrades cost you may as well buy a T56 or two, which will probably still be stronger than a built T5 even in stock form.


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## jwiger (Oct 18, 2014)

I plan on all forms of spirited driving. Saving the gears for engine braking later on. The BMW in those videos is using a two speed powerglide with manual shift. It's great for upshifting and acceleration, but they depend heavily on brakes to slow down. Most folks are relatively pleased with a stock style transmission to begin with (a clutch is always a good safety backup on DC motors!) once you get a feel for how the car handles with those gears, you can upgrade later.


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## Soulless (Jan 24, 2016)

answering a lot of questions i had on transmissions.


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