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Login to post Forums » Grassroots Motorsports » compact IRS rear differentials w/ low numerical ratios

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Jan. 1, 2012 11:15 p.m. JamesMcD Reader

carguy123 wrote:

Is the tranny separate from the Goldwing motor ala Harleys?

As I understand it the Goldwing output shaft turns the right way to use a car diff so that's a plus.

Another plus is that if you look at dynos you see the Goldwing engine is almost identical to a Miata engine.

It's light. It's small.

As I understand it most if not all larger motorcycles have a first gear that will take you to at least 60 mph. That's the problem with using MC engines in a car. But yours seems small and light enough so that shouldn't be a clutch issue.

Do they make a heavier clutch for the Goldwing?

You are touching on a few other reasons I was drawn to the Goldwing. Output rotation is a biggie! The other thing is that Goldwings get converted into trikes and haul tailers and it's often couples who ride them and sometimes those couples aren't skinny. So I figure the Goldwing drivetrain should stand up to a 1400lb car OK.
Jan. 2, 2012 6:34 a.m. Curmudgeon SuperDork

The Wing motor should have plenty of grunt to do what you are wanting. The 'step up' box can be as shallow as ~3", if you are using gears and making it from 1/2" aluminum plate. It can be put either on the back of the engine or on the front of the diff. If you put it on the back of the engine, it will help center the driveshaft in the car.
Jan. 2, 2012 9:54 a.m. FlightService Dork

JamesMcD wrote:

You are touching on a few other reasons I was drawn to the Goldwing. Output rotation is a biggie! The other thing is that Goldwings get converted into trikes and haul tailers and it's often couples who ride them and sometimes those couples aren't skinny. So I figure the Goldwing drivetrain should stand up to a 1400lb car OK.

There are a few Goldwing clutch upgrade kits. I don't believe you will have a problem with your layout.

Given a Goldwing is designed as a loaded 2 up tourer so figure ~850 lbs bike, 2x180=360 in passengers, 2x20=40 (saddlebags maximum rated capacity) I believe the trunk is 40 lbs. So that puts you at 80 in luggage.

850+360+80=1290. Margin of safety on these things are pretty good too so 1400 lbs shouldn't be far off the mark.

Good luck!
Jan. 2, 2012 9:56 a.m. FlightService Dork

ooh forgot one thing.

Depending on the year you may have stator issues. Honda never expected American riders to want to power their homes on the Goldwing electrical system so depending on your year power consumption is something to watchout for. (Early 1500 models)
Jan. 2, 2012 10:12 a.m. Ian F SuperDork

Gearing may be an issue since I think the od of the bike rear wheel is taller than the ~23" Miata wheel.

Do you have the motor yet? I had EXACTLY the same idea a few years ago for the same reasons. However, some subsequent discussions here revealed the motor is not that light and tend to rather pricey on the used market.

I still dream of building a Mc engined car, but will probably go with something more conventional and rig up an electric reverse using a geared starter motor.
Jan. 2, 2012 11:15 a.m. JamesMcD Reader

Curmudgeon wrote:

The Wing motor should have plenty of grunt to do what you are wanting. The 'step up' box can be as shallow as ~3", if you are using gears and making it from 1/2" aluminum plate. It can be put either on the back of the engine or on the front of the diff. If you put it on the back of the engine, it will help center the driveshaft in the car.

Can't make it with gears without reversing the drive-shaft rotation.
Jan. 2, 2012 5:31 p.m. Curmudgeon SuperDork

Use 3 gears, one as an idler. Done.
Jan. 2, 2012 7:31 p.m. erohslc HalfDork

Right, like I said, use 3 gears from 2 sets, 1-1/2 of one of these:

http://www.speedwaymotors.com/Garage-Sale-Speedway-Standard-Quick-Change-Gears,375...

Carter
Jan. 2, 2012 8:20 p.m. JamesMcD Reader

If possible, I think it would be smarter, as suggested earlier, to replace the primary reduction gears in the Gold Wing transmission case with custom gears that do not reduce, and then simply use the rear ratio that I please.

The driveshaft would pass somewhat diagonally through the center of the car, and impede slightly on passenger foot-well space, but as long as the transmission output and pinion are parallel to one another, it should work fine (the shaft won't know or care what plane it is on).
Jan. 2, 2012 8:56 p.m. carguy123 SuperDork

JamesMcD wrote:

If possible, I think it would be smarter, as suggested earlier, to replace the primary reduction gears in the Gold Wing transmission case with custom gears that do not reduce, and then simply use the rear ratio that I please.

The driveshaft would pass somewhat diagonally through the center of the car, and impede slightly on passenger foot-well space, but as long as the transmission output and pinion are parallel to one another, it should work fine (the shaft won't know or care what plane it is on).

1) do you have a pic of how the gears fit in the tranny case to show the primary reduction gears.

2) why would the driveshaft have to pass somewhat diagonally thru the center of the car? As best I remember the driveshaft is located only slightly offcenter from the motor AND you could locate the diff offcenter to give yourself a straight shot.
Jan. 2, 2012 9:42 p.m. JamesMcD Reader

carguy123 wrote:

JamesMcD wrote:

If possible, I think it would be smarter, as suggested earlier, to replace the primary reduction gears in the Gold Wing transmission case with custom gears that do not reduce, and then simply use the rear ratio that I please.

The driveshaft would pass somewhat diagonally through the center of the car, and impede slightly on passenger foot-well space, but as long as the transmission output and pinion are parallel to one another, it should work fine (the shaft won't know or care what plane it is on).

1) do you have a pic of how the gears fit in the tranny case to show the primary reduction gears.

2) why would the driveshaft have to pass somewhat diagonally thru the center of the car? As best I remember the driveshaft is located only slightly offcenter from the motor AND you could locate the diff offcenter to give yourself a straight shot.

1) No, I wish I did. I have found it is way more difficult to find information about bikes than it is to find info about cars.

2) If the shaft takes a straight shot to an offset rear diff, there probably won't be enough passenger-side fanny room. (Small car = people sit pretty much on the floor.)
Jan. 2, 2012 9:43 p.m. carguy123 SuperDork

But isn't the driveshaft just 1-3 inches off center?
Jan. 2, 2012 9:57 p.m. JamesMcD Reader

In reply to carguy123:

From pictures it's looks to be about 4". And if the diff is off center I either have to use unequal-length half-shafts or use some kinda jack-shaft arrangement...That would just complicate things.
Jan. 2, 2012 10:39 p.m. carguy123 SuperDork

Many cars have unequal length half shafts so that shouldn't be that hard to find. I'm surprised it's as much as 4" off center, but then it's been a while since I looked at a Goldwing.

I've got an almost new S&S engine I'm going to put in one soon. I bought the remains of a FSAE rear end to mount it and it came with unequal length half shafts. IIRC it was the standard shafts from a Honda Civic. I'm going mid engined, not front and I'll be using chains so the driveshaft and fanny room is one less thing for me to worry about.
Jan. 3, 2012 6:48 a.m. Curmudgeon SuperDork

A little Googling shows the GL1000 (4 cyl) has a chain primary drive.

I'm assuming your engine is a GL1500/1800 (6 cyl) which has a gear primary drive.

For purposes of controlling backlash and thus gear whine it's going to be pricey to cobble up a set of custom primary gears, unless there is a different factory set available. I am lazy, I like to take advantage of others' engineering whenever possible.

I think (and of course I am not standing there looking at it) that it would be simpler to put a 3 gear step up box on the back of the powerplant, which would move the output toward the center of the car, thus killing 2 birds with 1 stone. The power transmission industry calls them 'paralell shaft reduction boxes'.

The gears do not have to be in a straight line, if done in a V pattern then the shaft centers can be really close together. If it howls etc it's also a lot easier to fix an add on box than going into the motor! It would also take up much less room than the Morse chain or Gilmer belt setup.
Jan. 3, 2012 7:28 a.m. Graefin10 HalfDork

I too have wondered if the 6 cy. Hondas have potential to power a small car. Do you plan to operate it on the road? If so, how will you register it? Have you considered a reverse trike drive train? You can legally register a home built trike in some states. Use the bike's swing arm and rear tire with a mid mounted setup and most of the drive train issues are done. Google 3 wheel cars and if you haven't already you'll be amazed at what comes up.
Jan. 3, 2012 8:47 a.m. Curmudgeon SuperDork

A Miata pinion is offset toward the passenger side probably 2". So unless the diff is offset in the car, the driveshaft is bound to intrude on the passenger footwell and/or have some angle to it.

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