Triumphrat

04-10-2005

After driving my new used Thruxton home from the dealer yesterday, my wife asked me why I was driving so slow. I had an indicated 80MPH, but she said I was going more like 60-70.

Today A friend was on my Harley, and I was on the Thruxton in town. The Harley speedo said 25, the Thruxton said 30.

Are the Thruxton speedo's really whacked, or does mine need service?

Dave

04-10-2005

I have had a similar experience. Nothing documented but as was crusing down the Highway at 80 MPH and everyone was passing me I new that the spedo must be off.

Thrux-ton-up · 04-10-2005

They are really wacked - seem to be off 7-10 %. I use the 10% rule to make the math quick and simple. JCW :-D

Although the odometer seems very accurate.

[ This message was edited by: Thrux-ton-up on 2005-04-10 19:38 ]

vikingdrvr · 04-10-2005

These were my results from a few weeks back:
Checked my speedo against my handheld GPS today and John is right, when indicating 80 I was doing 72. After riding for awhile I figured, when indicating 50 and below ...subtract 5, indicating 60 and above the error increases to 8 or 9 mph high. Surprisingly, the error starts to decrease a slight bit past 90. And FWIW, I had to indicate 107 to hit the ton!
And, the odo is basically spot on.
YMMV

Paul · 04-11-2005

This topic comes up now and then. I've checked the Bonnie and three other Euro bikes against the GPS, and generally figure they are all 5mph on the high side. That varies a little by bike and by speed, but is a good rule of thumb for quick calculations.
Read somewhere a year or so ago that speedos are allowed to have something like 10% error, but in Europe that error must be on the high side, while in the States, it could be either. Cannot remember the source, so take it with a grain of salt.

04-11-2005

I looked at a review of the Thruxton in (USA)MCN, and it said 60MPH indicated was something like 51MPH actual - closer to 20% error!

I wonder if they use the same speedo drive on the Thruxton as on the Bonnie. The smaller front hoop would yield more revs/mile and therefore a higher indicated speed. I hope the engineers wouldn't do that!

Anyone have access to parts fiche to see if the bonnie and the thruxton use the same speedo drive? I don't know if the speedo ratio is a known value. On harleys, you can mix and match speedo drives and speedo ratios to get the right setup for various front hoop sizes. I doubt we're that lucky.

Is the speedo serviceable? I'd like to reposition the needle for more accurate indication - I've done it on other vehicles that were nowhere near as far off as this beast.

Dave

vikingdrvr · 04-11-2005

Quote:

On 2005-04-11 10:55, Skeptic wrote:
Is the speedo serviceable? I'd like to reposition the needle for more accurate indication - Dave

I took my speedo off for a closer inspection and to possibly send it to my local speedo shop for calibration, but the trim bezel that holds the glass is crimped on the full way 'round. Meaning there's no way to get into it without trashing the bezel. I was hoping it was like most older British gauges where the lens/bezel just twisted off, but no such luck :"(

04-11-2005

Quote:

On 2005-04-11 11:14, vikingdrvr wrote:
I took my speedo off for a closer inspection and to possibly send it to my local speedo shop for calibration, but the trim bezel that holds the glass is crimped on the full way 'round. Meaning there's no way to get into it without trashing the bezel. I was hoping it was like most older British gauges where the lens/bezel just twisted off, but no such luck :"(

I've uncrimped the bezel on harley speedos, but there the dash hides the dirty work. On the thruzton it would be UG-LEE!

Dave

stevetriple · 04-11-2005

Quote:

On 2005-04-11 07:51, Paul wrote:
Read somewhere a year or so ago that speedos are allowed to have something like 10% error, but in Europe that error must be on the high side, while in the States, it could be either. Cannot remember the source, so take it with a grain of salt.

That's what I have heard as well. Euro regs state that a speedo cannot read slower than actual speed so they almost all read high. For what it is worth, from most of the magazine tests I have seen, H-D's speedos are some of the most accurate, usually dead on or within 1-2mph of actual speed.

I haven't checked mine against my GPS, but it sounds like it might be a good idea.

puck · 04-11-2005

My experience is similar, with radar based checks. There is a radar governed sign on my road, used to slow vehicles down to 25 mph, where they used to travel between 30 and 40 mph. Ah the joys of suburban development.

Anyway, this is not near as accurate as a gps, but it provides a reasonable range, and I have found as follows. Speedo is about 2 to 3 mph slow from 15 to 35 mph, with progressive increase to 5 mph slow after about 62 mph -- could not check speed beyond that, but I estimate the 5 mph difference about right thereafter, based on freeway and observing other traffic.

Your experience seems considerably off --maybe a warranty issue?

Good luck.