Speedometer Ratio Question

My boyfriend's speedometer on his 85 yamaha maxim xj700n quit on him and of course now they are obsolete...

If we chose to get an aftermarket mechanical speedometer, what is the proper ratio to look for? Also, is there anything else I should be worried about besides the ratio?

Thanks in advance.

 

i don't think there is any such thing as a ratio. they all work the same and pretty much have the same dimension cable spinning it around. what matters is the size of the front tire. having the wrong size.

 

K Thanks. I'm new to bikes and when I was looking speedometers up, a lot of them had a ratio so I assumed it mattered.

 

oh, sorry, i was looking at them not too long ago. but don't recall anything about a ratio. i musta been looking at the wrong thing.

they aren't cheap. i'll say that much. from what i've been looking at. if you find something cheap let me know. i'm going to mounting my old blackberry for a gps speedo as it has free software. my speedo works but it's slow. odometer works perfect. but the speedo reads around 52 when i'm actually doing 75.

 

As far as I know the ratio is 2240:60 (2240 revs of the speedo drive=60miles or kms:? (blanking out here)) and it does matter (HD mostly runs 1:1 or 2:1)
Most japanese bikes (from that era?) run the right ratio.
Mikexs.com seems to be a common source for after market/chopper/bobber gauges. Acewell digital gauges seem to be popular as well.
If you're not all that picky a used gauge cluster can be found on ebay for $15+shipping.

 

There is a ratio for speedometers. 2200 rpms (for front tire, not engine) on most, I believe. That mini speedo on mikesxs.com is the most popular and is pretty much only for looks. It is horribly off... reading 5-10 mph fast, depending on actual speed. 62mph shows 70 mph on the speedo. 35 mph shows 41 mph on the speedo. But that goes for the 550 to 750, I believe and I think the 700 used the same size rims and thus the same ratio. I could be wrong on sizes but I don't think so.

 

snowwy....I think either Rick or Fitz has a tutorial on how to lube your speedo so it works better....you might want to look it up.

Any speedometer that can match 2240:60 will work. It has nothing to do with the front tire size. There is a hub with a worm gear that is in between the speedo and the wheel. That is what turns the cable, 2240 units per 60...um...some other units. Keep in mind that some digital speedometer can change their ratio and therefore won't list one.

As far as quality....honestly, there's probably too many out there to really know which ones are good or not. Unfortunately, with a premium on looks and branding...the accuracy probably has little to do with the price.

 

The drive ratio is 2240rpm=60mph. What happens is a slightly larger tire will take fewer rpms to go the same distance as a smaller tire. However, pretty much all the bikes in "our" era had 19" front rims, and nearly the same size front tires, give or take, so the manufacturers simply weren't all that fussy about it.

Instrument care and feeding: http://xjbikes.com/Forums/viewtopic/t=15303.html

With a new cable, cleaned and lubed, the original speedometer on my '81 checks out fine odo-wise and reads a hair slow as speeds increase.
The brand new NOS speedo in my '83 reads a hair fast, as expected.

Mechanical TACHOMETERS and I don't seem to get along; maybe it's my riding style.

The tach in the '83 right now is the third one; and now it appears as though the tach in the '81, although cleaned and lubed, is about to pack it in after about 6000 miles of service.

 

It has everything to do with the front tire size unless you change the gearing in the speedo drive gear housing in the front hub.

 

i've got a cell phone mount for my bike. i've seen them around town selling for $100. i ordered from the internet for $20. i'm going to find a key sourced power wire that's not getting used and only has power with the key on and wire up a 12v cigarette plug i bought from harbor freight. i've got 4 cigarette chargers for the phone i can use.

software is free for cell phones. i'm going to use my blackberry that's no longer being used.

cost of this ACCURATE speedo that works off gps. $25.

 

If front tire size matters, then why are there only 3 different types of speedometers that work for every tire/wheel combination.

It's the worm drive that you have to match the speedometer to. You don't need to know the tire size, the engineers have already taken that into account when they built the worm drive.

If you change the tire size, you can't just get a new speedo that will work.

Therefore, it has nothing to do with front tire size. It's all about the worm drive.

Maybe I seem to be pedantic, but my point is that you can't go looking for a speedo for a certain size wheel with a certain size tire. It doesn't work like that. It has nothing to do with the wheel size.

 

a smaller tire will spin the worm drive faster then a bigger tire.

16 inch rim compared to 19 inch rim. the smaller the circumference. the faster the spin.

i don't know how the worm drive is taken into effect though. as not all bikes have 19 inch tires. some have 18 inches.

the worm drive runs off the center circumference of the entire circle. the bigger the circle. the slower that center circumference will spin.

18-19 inch rims seems to be the more common size. don't know if there's anything smaller or bigger.

i'm guessing the 18 inch rim has a tire thicker in height while a 19inch rim has a tire thinner in height. overall amount of revolutions is probably the same.

200/90 x 18 vs. 170/110 x 19. as a rough example.

 

Exactly. Which is why, as I said, the manufacturers weren't all that fussy.

When our bikes were made almost everything had a 19-inch front rim. The ones with 18-inch rims used a bigger tire so the overall circumference was nearly the same.

Check out some dimensions: http://totalmotorcycle.com/photos/tire- ... /index.htm Both Dunlop and Avon have comprehensive dimensions listed, I haven't picked at the others yet.

 

That's exactly what I'm trying to get across!

The speedo drive is a series of gears. The first gear is the wheel itself. The second it the worm drive. The third is the cable itself (maybe calling it a gear is a bit of a stretch, it's a 1:1 torque transmitter). The fourth is the speedo (2240:60 torque transmitter).

The wheel ratio is chosen by the designers for reasons that have nothing to do with the speedometer. It has different sizes.

The speedometer is clearly built around an international standard, or there would be millions of different types. One standard is 2240:60.

The cable is always 1:1.

That leaves the only other variable gear. The worm gear in the hub. The engineers choose that ratio so that it converts the wheel spin to the proper amount of cable spin.

The worm drive isolates the wheel diameter from the speedometer, therefore the speedometer gear ratio has nothing to do with the wheel size! It's the same no matter what the wheel size is!

I looked at the website and did the math. There's a huge difference between the smallest and largest tire. They all likely use the same ratio speedometer.

Unless you think the manufacturers allow you to be going 70 when you think you are going 60, the worm gear translates the wheel speed to the correct cable rpm.

Remember, the question was about the speedometer itself, not the affects of wheel size on the speedometer. You don't need to know the wheel size to get the right speedometer. Therefore, it has nothing to do with wheel size.