A few months ago, there were several posts from owners and former owners lamenting that their Savage just could not go any faster than 80mph.  I found out why... The hard way.

On my way to Sandusky on Friday, I was reminded by a very nice Ohio State Trooper that the speed limit on the Ohio tunrpike is 65mph.  He was nice enough to give me a $108.00 reminder.  Somehow, he clocked me doing 78mph in a 65.  Thats impossible, since I had my throttle lock set at 70mph.

Once I met up with Mrs. Skrapiron, I had her pace me in the CR-V.  Sure enough, my 60mph (indicated) was registering 66mph in the CR-V.  

Since there was such a discrepency, I used her odometer to calculate my fuel economy.  According to her odometer, I traveled 141.5 miles from my parents to home.  According to the bikes odometer, I only went 127.7 miles.

Why the big discrepency?  I change my final drive ratio.

I put on a 140/90-15 rear tire.  The stock tire was 140/80-15.  That difference in circumference is enough to make the speedometer even more inaccurate.

The speed is measured by engine revolutions, not tire revolutions.  By changing the drive ratio, it affected the speedometer.  (When I am showing 50mph (indicated) I am actually travelling 55mph).

That being the case, if someone does the chain drive conversion, they will expereince the same discrepency.  If they do the chain conversion WITH a larger rear tire (140/90-15) that sill be as much as 15-20% speedometer inaccuracy.

So if your bike is topping out at 80mph (indicated), you are likely in excess of 85, perhaps 90mph.

Next time, before you blame the bike, check the accuracy of the speedometer.  Or, you can do like me, and use the freindly neighborhood State Trooper to verify the accuracy....

justin_o_guy2 wrote on 05/26/08 at 13:46:28:


The sermon must have been really boring for you to want to leave that fast!  

Did Obama ever do 90+ going home?

If I sped home every time I heard a homily that made me sick to my stomach, I'd have a wall of tickets.

As a catholic, you get used to garbage sermons.  The upside is, when someone really gets up there and preaches the faith, you're on cloud nine for a few days.

Btw, I've found if I break the TON much, I only get 80 miles to the tank, insead of 100.  I ain't rich enough to push the throttle these days.

actually the speedo on my wife's reads about 7% faster than she's actually going, so a bigger tire would probably make it pretty close to right on, depending on the % diameter increase.

furious70 wrote on 05/27/08 at 06:57:15:
7-10% over-read is what you can expect on the majority of factory standard bikes and cars on the road.
The manufacturers have to be sure that the gauge doesn't under-read for legal reasons, and they don't mind going on the safe side because it makes people think their vehicle is faster than it actually is.