i dont think so???

 

Only if you want the speedo to be correct.

 

Gears yes, mufflers no...

 

This.

 

The speedometer will read incorrectly (not that they were incredibly precise to begin with, but still...) if you don't get a tune, but the inconsistency is pretty easy to spot and mentally adjust for if you are dead set against a tune. It all depends on how much you change the gearing.

For instance, let's say you change the rear axle gearing from 3.73 to 4.1. The deeper gearing means the speedometer will actually be reading faster than you're really going, as it still thinks you have 3.73s. To get the factor to multiply by to get your new speed, just take your old axle ratio and divide by the new axle ratio. In this case, 3.73 / 4.1 = ~0.91. Assuming this is the only change made, then your actual speed with the new gearing will always be 91% of what the speedometer actually reads. 60 MPH by the speedometer would be an actual speed of 54.6 MPH. You can round it off for mental calculation by just taking what the speedometer says, dividing by 10, and subtracting that from what the speedometer says.

30 MPH would be 27.3 actual
60 MPH would be 54.6 actual
120 MPH would be 109.2 actual

And so on. The formula holds true for going to shallower gearing as well, just keep in mind that doing that means you're actually going faster than what the speedometer says.

Aside from that I don't think there's any other issue with changing gearing.