2" mini speedometer , what ratio?

[dahondaboy]

wanting to run those 2" mini gauges but have no idea what ratio to buy. i have an 80 stock front mag wheel. would it be the 2:1?

 

[pamcopete]

Well, all Japanese motorcycle speedometers are calibrated to show 60 MPH when the cable is spinning at 2240 rpm. With a front wheel diameter of 19" the rolling distance is about 80" per revolution, or 80/12 = 6.66 feet. At 60 MPH or 1 Mile Per Minute the wheel will rotate 5280/6.66 = 792 RPM. So, you would need a speedometer drive with a 2240/792 = 1:2.828 ratio.

If you want to calibrate your speedometer, then ride down a stretch of highway that is a known speed trap at an indicated speed of 25 MPH above the limit. When the cop stops you, he will tell you how fast you were actually going so you can then apply that information to recalibrate your speedo.

Alternatively, you can Velcro your GPS to the gas tank and just note the difference.

Or, you can calibrate your tach and use this spreadsheet to figure out how fast you are going for a given RPM:

RPM vs MPH for any combination of gears, sprockets and tires

 

[willyguzzi53]

Pete, you forgot to mention that there may be a small charge by the local law officials for the speedometer test.

 

[Phail]

I have one of those from MikesXS. I was going down the road the yesterday at what it said was 45MPH. My wife was behind me in the car and said I was going more like 55MPH. This is a stock front wheel. That's a lot to be off by. I'm going to use my GPS next time I go out to make sure.

She also said I took off like a bat out of hell and I find that strange because I know that 08 Mini Cooper S can flat take off. I'm also geared at 18/30 so I should have a slow take off.

 

[TampaSVT]

Mikes seems to be out of most of the 1.9" ones. Any suggestions on where to find them?

Thanks,


Rich

 

[pamcopete]

Pete, you forgot to mention that there may be a small charge by the local law officials for the speedometer test.

Buying an XS650, $1200
Buying a mini speedometer for the XS650, $45
Getting the mini speedometer calibrated by the local police, Priceless...

 

[dahondaboy]

damn pete, you is one of them Mathmagicians aint ya! but really thank you for the info, and the gauge is a chinese one on ebay i see alot of guys using the same one. they are in all different ratios

 

[TampaSVT]

Does anybody know if the 2:1 mechanical speedometers sold here would work?

http://www.demonscycle.com/Shop/Con...507682/set_num/2/menu_num/1/prods_per_page/96

Looks like they have them in stock.

Thanks,


Rich

 

[RacerRex]

^ thats what i want to know.

 

[dahondaboy]

^ thats what i want to know.

i know right? i wanted a simple answer but thanks to pamcopete i have to take a math class to comprehend. lol?!

 

[occam22]

I got mine from dime city cycles. I told them it was for an xs650. It seems to be pretty close right out of the box.

 

[RacerRex]

i know right? i wanted a simple answer but thanks to pamcopete i have to take a math class to comprehend. lol?!

Hahahaha!

 

[pamcopete]

Well, simple is as simple does, so in this case the terms 1:1 and 2:1 ratios are Harley terms because they have those two ratios in their various models. The Japanese use the scheme that I outlined above, and just for a sanity check, I happened to change the speedo drive in my '81 CB750 and I checked the ratio roughly and it is something less than 3:1.

That's the way the Japanese industry works. They compete on the showroom floor, but not on the factory floor where there is a sharing of standards and parts that do not affect the marketability of their product allowing them to order from the same suppliers in a combined greater quantity then if they all used different parts and specs.

 

[TampaSVT]

Pete:

From a cable / thread perspective, are they relatively interchangeable?

Thanks,


Rich

 

[pamcopete]

Tampa,

Not necessarily. They may have the same internal gears, for example, because that is the expensive part to make. Like, the internal parts of the starter motors may be the same between Honda and Yamaha but the case has to be designed to fit the engine, and the engine is a showroom floor item.

 

[TampaSVT]

Thanks, man.

Means I have to wait for Mikes to get some in stock...



Rich

 

[jchrisk1]

"If you want to calibrate your speedometer, then ride down a stretch of highway that is a known speed trap at an indicated speed of 25 MPH above the limit. When the cop stops you, he will tell you how fast you were actually going so you can then apply that information to recalibrate your speedo"

This is how we once did my friends car. Although not intentionally. As we were passing people at lightning speeds I asked him how fast he was going. He said 60. When we got pulled over, the cop said it took them 5 miles to catch up to us.

"Pete, you forgot to mention that there may be a small charge by the local law officials for the speedometer test."

Not true for us. They just emptied our beers out and sent us on our way. When we got up to 55 they lit up their bar lights so we would know what the speedometer read.

 

[OctoberNotice]

So, with a 1980 xs650 stock front end mag wheel, the ratio is 1:2.828, and not 2:1?

I'm also on the market, it's really easy to find 2:1 ratio aftermarket speedos, but don't wanna buy something I can't slap on.

 

[OctoberNotice]

For instance....

http://www.dimecitycycles.com/vinta...-speedo-speedometer-trip-readout-37-0002.html

^^Says it's calibrated for 60mph @ 2240rpm

and...

http://www.ebay.com/itm/MINI-CUSTOM...es&hash=item35bc01f824&vxp=mtr#ht_7565wt_1193

Are set at the 2:1 ratio, but I like that this second set comes with the mounting clamp and all so I can just set them where I want on the bars and roll.

 

[RacerRex]

Just picked up one off ebay for cheap (Mikesxs #03-0748).
Shoud be good. I'll let you guys know.