I have compared my speedometer to my GPS and the bike is consistently 4.5 miles an hour slower than the spedo reads. And as an added support to this, the town I live in had recently bought one of those little trailer mounted speed check devices that tells you how fast you are going, and I can now in a 25 mph zone, run my spedo up to 31 and I'm still in the zone. So at 65 mph indicated I'm doing the speed limit on the highways. And for me that all the faster I will ever need to go. In 6th gear at 60 I'm right at 7000 rpm's. Recently I did a couple of rides on the highway 50+ both days this weekend, and the bike cruises perfect.

 

The confusing thing here is that your bike is modded as are most peoples. Mine is still pure stock with stock gearing. On flat highway I can hit 90 Mph on the Speedo. The Rpm's read about 8600. It feels safe to me now that I have the Kenda 270 on the rear. The front is still a Dunlop 603. At 7000 Rpms Mine is showing about 72 Mph on the Speedo.

 

I did 78MPH indicated and I started to get wobbles! I try not to go on the freeway with my KLX. I did 185.7MPH on my ZX10 with my gps on board. The fastest I've ever been on a bike is uh...I dunno...it was on an 06 turbo CBR1000! That was fast!

 

Stock gearing, with a gps I've maintained 75mph for 20min or so and touched 80 for a second. I'm sure with my 150lb frame it would hit 85-90+ but I don't care to rev it that high. My speedo is like 5-7mph fast and the tack is actually a better speedo 7,000rpm = 70mph gps (stock front tire). Oh and I got an 06 with 300 exhaust, re jetted, de smoged, and kdx snorkle.

 

What is confusing? Bigger sprocket in back = higher RPM's

 

I just went out and ran 94 on gps 110 on the speedo but thats with the 15/40 and 17" wheels there was a headwind also i've seen 96 with a slight tail wind.

 

Also a good headwind along with the rider's weight can really slow you down.

 

People here drive pretty fast on the freeway and any speed under 75mph is too slow. That's why I stay away from freeways on my KLX.

 

I guess it doesn't matter if the gearing changes don't affect the speedometer. I keep thinking that a bigger back sprocket will throw off the speedo bit I guess it won't.

 

I hit 86 on the speedo in a full tuck. bike is all stock except for the 13t cs. The best part is I was just keeping up with traffic at that speed. When I leaned back the bike droped back down to 74. The normal top speed for a Klx 250 running a 240 lbs rider such as myself. I bet Deej can back me up on this one.