I've done a search and found nothing on this topic.

I've heard once that as the engine approaches a higher RPM, the tachometer reading becomes slightly inaccurate. I heard this is also the case for the speedometer (when hitting high speed, speedo is inaccurate). I was wondering how big is the inaccuracy difference? And what is the common cure? Will an aftermarket speedo and tacho do? Or is it always going to be inaccurate regardless?

thanks

 

Yes, both gauges become inaccurate in the upper ranges. Most aftermarket tachometers are more accurate than the stock units. As for the speedometer, I'm not sure why that would matter much anyway.