Topic: 18-inch front wheel on a K0 750 - Will this mess up my speedometer?

[Patrick]

My K0 project bike came with a NOS 18-inch rim. For a long time I thought this was meant as a replacement for the 16-inch rim that came on the back of the bike, to take it back to stock size. But I was looking the rim it this morning and I discovered it is a 2.15 inches wide. That narrrow width makes it seem more likely that the PO bought this rim meaning it be to a replacement for the 19-inch front rim. The bike also came with new chrome spokes that appear to be the right length to lace the 18-inch wheel to the front hub. They appear to be 1/2 inch shorter than stock.

My question, if I do this I am assuming my speedometer will no longer be accurate - if indeed it is accurate to begin with. I figure the smaller wheel will turn more often to cover the same ground. Is there a different speedo drive unit that I could install that would give me accurate readings? Is there a way to mess with the existing arrangement? Or do I need to do what I do with my K5 750 and estimate my speed based on my tach readings?

I thought there was an off chance someone on the forum might have an opinion they would want to share.....

Thanks, in advance, for any ponderings and musing y'all may offer.

Patrick

[bwaller]

Use a speedo drive from a 400F, it uses an 18" front wheel.

[chopstar500]

Your MPH reading on the stock speedo will be incorrect with the 18" wheel up front. You probably have a few options, one that you've already noted (using your tach to estimate speed). Another would be to calculate the ratio change and make a mental note (i.e. 35 MPH on the speedo = 42 MPH actual). Or, you may be able to find another bike (Honda or otherwise) that runs an 18" wheel up front - providing it has the same 12mm cable connection & use that speedo. Just my thoughts... I'm sure others will chime in.

[chopstar500]

Use a speedo drive from a 400F, it uses an 18" front wheel.

There you go... bwaller must have been typing at the same time I was.

[Tower]

The rim height is only one component of wheel height: the other is tyre height, of course.  As long as the combined tyre and rim add up to the same as the Honda recommended combination, then your speedometer will be accurate.  The stock K0 750 wheel height is 26" (3.25-19 tyre)

edit: 400F stock front wheel height is 24.3" (3.00S18), 750 K7-K8 is 25.6" (3.50H18)

Also note, it isn't the wheel end of the speedo that calibrate the speed.  Speed calibrations are in the speedometer.  So just to followup on bwaller`s suggestion - using a 400F Speedometer might work.