Gauges and ratios

[WelderDave]

ok, so I got a speedometer and rpm gauge, I suspect they are both off. Speedo is off by like 50 mph and the rpm gauge is a 1:67 ratio and I read ours are 1:5 supposed to be. I’m trying to figure out how far off the rpm gauge actually is. I’m running the standard 16t front drive sprocket with stock 39 in back for my 78 xs400e.

Can anyone help me figure out what my rpms are supposed to be standard and what they would read on the one gauge that’s off? Let’s make an easy number of comparing 1000 rpms. So if I’m at 1000 rpms, what is my gauge going to read?

 

[WelderDave]

I was just thinking about it, I think they made a typo, I’m guessing it should have been 6 or 7, not 67. Because I know the gauge is off, but not that far off to be 67, lol. So roughly 170 rpms off per 1000 rpms. That’s why I was thinking I wasn’t getting the right numbers.

One other question, I know we redline at about 9k, was wondering since I’d be doing about 65 at 6600rpms, it must be safe brought to drive for long stretches at those rpm ranges, correct? I just don’t feel like blowing my motor. It’s just hard for me to believe but I’ve only driven cars for the longest time so I’m used to cruising at 3k

 

[xschris]

2240:60 for the speed-o. Running stock 90/90-18" front tire and 110/90-18 rear with 16-37 sprockets I get 4800 rpm at 60mph. Two of my xs400 bikes have this setup and do the same. They also have stock gauges.