5mph slow??

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01 Apr 2006 21:07 #36073 by timber
5mph slow?? was created by timber
on the way home i was running around 65mph or so i thought. when we got home my wife who followed me all the way home asked why i was driving so slow. i told her i was doing 65mph most of the time. there is a 3.50S19 for a front tire. would that size tire give that kind of reading i thought that was the stock size front tire on a 79 KZ650C.

should i go with a smaller tire to get it closer right??

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01 Apr 2006 21:28 #36076 by steell
Replied by steell on topic 5mph slow??
A larger tire would make it closer.
Unless your speedometer reads 5 mph when you are sitting still it is off by a percentage, in this case a little less than 10%, and that's assuming the speedometer in the car you wife was driving is accurate (not usually the case).

I think all the KZ speedometers are only approximate in their readings :D

KD9JUR

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03 Apr 2006 13:23 #36464 by N0NB
Replied by N0NB on topic 5mph slow??
Back when these bikes were new, Cycle World used to publish the measured speedometer error. As I recall, the speedometers generally read somwhere around 5 to 10% fast, meaning the bike was going slower than indicated.

I found, by way of using my GPS, that at an indicated 65 MPH I was actually going 60 MPH. Showing 70 MPH results in just under 65 (speed limit for most of the local roads).

YMMV. ;)

- Nate >>

Nate

Nates vintage bike axiom: Riding is the reward for time spent wrenching.
Murphys corollary: Wrenching is the result of time spent riding.

1979 KZ650 (Complete!)
1979 KZ650 SR (Sold!)
1979 KL250 (For sale)
1994 Bayou 400 (four wheel peel :D )

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03 Apr 2006 16:02 #36494 by Biquetoast
Replied by Biquetoast on topic 5mph slow??
I pass alot of those "slow down" police radar speed indicators (with the large digital speed readout) around here that I pass, many times alone so I'm sure it's me that is indicated.

I've come to the conclusion that around indicated 30mph I'm actually doing about 27. At an indicated 55 I'm doing about 50.

I say, "good". It'll keep me from getting tickets in all the towns I ride through in my commute..

Post edited by: biquetoast, at: 2006/04/03 19:03

(1.) '75/'76 KZ400D - Commuter
(2.) '78 KZ750B3 Twin - Commuter
(3.) '78 KZ750B3 Twin - Commuter
(4.) '75 KZ400D - Sold
kz750twins.com

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03 Apr 2006 16:45 #36500 by timber
Replied by timber on topic 5mph slow??
slower speedo is always better than faster. like ya said better to be going a little slower so johnny law isnt messin with me. it sounds like i'm with everyone here so far on 5mph slow.

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05 Apr 2006 21:59 #37134 by savedrider
Replied by savedrider on topic 5mph slow??
Yeah, I would say mine is 5-10mph off. If I'm doing 60 on the speedo it's really around 50.

Post edited by: savedrider, at: 2006/04/06 01:40

Get right or get left! <*{{{><

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05 Apr 2006 22:15 #37137 by Sandy
Replied by Sandy on topic 5mph slow??
Mine seams to be stuck at 99 mph...errr...wait...I was GOING 99 mph!(or was I only doing 94?):lol:

I've always wondered about how accurate these speedos were...I'll have to try and remember to test it,this season.
Do You think that if I were to fly by a Cop at 90,that He would understand that I WANTED Him to stop Me,so I could ask HIM...exactly how fast I was going?...and NOT get a ticket?:whistle:

1977 KZ1000 A-1

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05 Apr 2006 23:37 #37150 by 77KZ650
Replied by 77KZ650 on topic 5mph slow??
Sandy wrote:

Mine seams to be stuck at 99 mph...errr...wait...I was GOING 99 mph!(or was I only doing 94?):lol:

I've always wondered about how accurate these speedos were...I'll have to try and remember to test it,this season.
Do You think that if I were to fly by a Cop at 90,that He would understand that I WANTED Him to stop Me,so I could ask HIM...exactly how fast I was going?...and NOT get a ticket?:whistle:


:woohoo: lol I think the thing to do, would be to drive normal til you see a cop, then wave him over and get him to put on the lights and clock you.
Scott

07 MDP Rookie of the Year
01 ZX-12R street/drag bike. 8.97 @155.7 pump gas, dot tires, no bars, no power adders. top speed in the 1/4: 161MPH

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06 Apr 2006 08:30 #37214 by Sandy
Replied by Sandy on topic 5mph slow??
77KZ650 wrote:

Sandy wrote:

Mine seams to be stuck at 99 mph...errr...wait...I was GOING 99 mph!(or was I only doing 94?):lol:

I've always wondered about how accurate these speedos were...I'll have to try and remember to test it,this season.
Do You think that if I were to fly by a Cop at 90,that He would understand that I WANTED Him to stop Me,so I could ask HIM...exactly how fast I was going?...and NOT get a ticket?:whistle:


:woohoo: lol I think the thing to do, would be to drive normal til you see a cop, then wave him over and get him to put on the lights and clock you.
Scott


LMAO...Hey Scott...I could GO places with that idea...hmmm...I could pretend that I was the lead Man in a high-speed chase(in My mind,I'd be doin 120)...LOL...I could just lead the cop all OVER the place...take Him on a nice cruise...stop for lunch...take a ferry-ride across the lake...get Him to escort Me home...then We'd sit in the garage and b.s. over a couple frosties...LOL...the whole time,I'd be TRYING to convince Him that I WAS still testing My speedo when I was doin the 120...LOL...:whistle: :lol:

1977 KZ1000 A-1

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06 Apr 2006 13:19 #37267 by Duck
Replied by Duck on topic 5mph slow??
timber wrote:

on the way home i was running around 65mph or so i thought. when we got home my wife who followed me all the way home asked why i was driving so slow. i told her i was doing 65mph most of the time. there is a 3.50S19 for a front tire. would that size tire give that kind of reading i thought that was the stock size front tire on a 79 KZ650C.

should i go with a smaller tire to get it closer right??


Speedo essentially counts the revs. Smaller tire will rev more at the same speed so you'll see a higher reading.

If you want to know how much of the discrepancy is caused by the count being off, you can set trip meter to 0 at a mile marker and ride until it says '1'. Measure distance to the marker to see how much the tire size is contributing to the slow reading.
h
-Duck

Post edited by: Duck, at: 2006/04/06 16:19

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