Speedometer Correction

[fzmax]

Has anyone figured out how to get the speedometer to read correctly when changing front tire sizes without going to a digital unit?

 

[Hellboy]

It's a mechanical devise geared to how far your front tire travels every full rotation. I wouldn't think that anyone could possibly figure out how to change that gearing perfectly to match a new tire size. Here is a link to a website the shows the speed difference of tire sizes. Depending on what size you want to put on it, there can be almost no noticeable speed difference anyway, especially since most bikes are already a few percent out to start with. As you can see, a 120/80/18 is basically the same as stock.
http://tire-size-conversion.com/tire-size-comparison/

Matt

 

[wildweasel_pt]

You can either buy an adapter gearing or replace that one with one from another Yamaha that uses 17" front rims.

 

[dannymax]

I figured it out, think I posted it some where on this forum. There is a blind pin holding the gearing in the speedo drive hub, drill that out and replace the gears with ones that match your new wheel.

There are only a few other drive hubs that can be used as donors so you need to choose your new wheel accordingly.

The Thundercat is one that adapts well, only difference with the VMax is the axle diameter.

 

[Hellboy]

I must have missed something, he said tire size and didn't mention the wheel. The tire size and the wheel both could affect the speed error and just putting a speedo box from a bike with a 17" wheel would only help if you also used the same size tire of the same bike, the total diameter is the only factor, not wheel size.

Matt

 

[Miles Long]

Has anyone figured out how to get the speedometer to read correctly when changing front tire sizes without going to a digital unit?

I've noted the indicated versus the actual speed of my bike, by using my GPS.
With a new Metzler 880 on the front, at an actual 100 kph, the speedo will show 104-6. Higher actual speeds generate less error, lower speeds a tad more.
Of course as the tire wears, more error can be expected, at all speeds.
The advantage of an optimistic speedo, of course, is that it keeps you "honest"- if you follow the posted speed limits, you know that you are always on the safe side.
I'm not sure how large a diameter wheel/tire can be fitted to a stock max front end, but I'd guess to obtain a true speedo reading you would have to relocate the front fender higher. Anal folks could probably calculate this,(once the true error is known) using the speedo/tire size charts already linked.
Personally, I'm not concerned at all about the error, now that I know the amount.
Cheers!

 

[fzmax]

Dannymax, thank you, that is what I needed to know.

Sorry I didn't put in the first post, but I'm probably going with 17's.

 

[JEAN PIERRE EPSTEIN]

DOES ANONE IN THE UK HAVE A GOOD GEN 1 OR 85VMAX SPEEDOMETER ? MY BEZEL IS DENTED AND NOT A REPLACABLE PART. THANKS JOHN

 

[02GF74]

Well if you get desperate, I have one in decent condition but it is in km/H.

We could come to some arrangement as I need one for testing my DIY self cancelling indicator relay; for my purposes cosmetic condition is not important.

 

[JEAN PIERRE EPSTEIN]

thankyou but i would prefer one in mph iam hoping my brother in los angeles is sending me one. thanks again jp

 

[02GF74]

OK, that's why I have it as a spare.

I managed to source one from US with virtually the same mileage as per km, not cheap as had to pay shipping, import taxes etc.

BTW the bezel is good on it, bad news it is not easy to remove and replace but can be done.