Just Noticed

Was reading "mad-rshn's" posts about "sliders" and "easyrider" posted some RPM readings that had to do with his own sliders.  Made me remember that I had committed a couple readings to memory just this evening.  I had just been out this evening for a short joy ride of about forty miles and tried to see what I was getting at 50 and 60 mph.  First time I'd done that with the darkside tire installed.  As I checked my previous readings that I had recorded in my manual, I was very surprised to see that the before and after readings were basically the same; ie, 50 mph = 4000 rpm's...  60 mph = 4750 (more or less)... 70 mph = 5500.
I honestly thought they should have been lower than before... but then, that's what I get for thinking.  Anyway just some more fodder for discussion.

Dick, I think that those Darkside RPMs would be dependent on which Darkside tire you were using. Different brand tires have different circumferences, and the ultimate diameter of the tire is what will effect the RPM/MPH reading.

When I was using a Sumitomo tire along with 28gm Sliders my RPMs per MPH were ~500 lower. Sorry I  no longer have records of the ultimate diameter of that Sumitomo as mounted on the rim.

Hmm...But I was also using a Dr Pulley HiT Clutch too...

Tim

Isn't the speed sensor on the rear wheel? If so, doesn't matter what size the tire is, the indicated speed on the speedometer vs RPM won't change. Of course your actual speed with change but you'd needs a GPS reading to get the actual MPH.

hankster wrote:

Isn't the speed sensor on the rear wheel? If so, doesn't matter what size the tire is, the indicated speed on the speedometer vs RPM won't change. Of course your actual speed with change but you'd needs a GPS reading to get the actual MPH.

I'm thinking that with a larger diameter tire, your speedometer would be reading slower. Many forum members have reported that their speedometer reads truer to their GPS after going DS.

Well, "Easyrider", that was my thought process too... but I double checked today and included the 70 mph comparison (=5500) too and it still panned out as all being the same. Normally, I'd say it was bad note taking on my part but remember that I went to all the trouble of taking along a pen and paper and stopping to notate after each reading (the first time thru). Maybe I've got a "freaky" machine and it was reading accurately with the old MS tire ????

Easyrider wrote:

hankster wrote:

Isn't the speed sensor on the rear wheel? If so, doesn't matter what size the tire is, the indicated speed on the speedometer vs RPM won't change. Of course your actual speed with change but you'd needs a GPS reading to get the actual MPH.

I'm thinking that with a larger diameter tire, your speedometer would be reading slower. Many forum members have reported that their speedometer reads truer to their GPS after going DS.

It will read closer to GPS since it is a bigger tire. The built-in speedometer measures rear wheel RPM and we know that the stock speedometer reads low. As an example, your speedometer reads 60 MPH @ 4500 RPM but the GPS will tell you your actual speed is 55 MPH.

Since you put on a bigger tire, you now travel further in each tire revolution bringing it closer to true GPS speed. Now when your speedometer reads 60 MPH it will be the same 4500 RPM since the speedometer is tied to the rear wheel rotation but you will be actually going faster, maybe 58 per GPS.

It's the same as if you put larger tires on a truck, the actual speed is faster relative to the speedometer.

Hankster,
I believe that we are saying the same thing. LOL...

Easyrider wrote:

Hankster,
I believe that we are saying the same thing. LOL...

Sorry, I didn't see that anyone was using a GPS to measure their speed.

Yes, going DS usually corrects the 5MPH speedometer error to closer match the GPS.

Been a while since I've been back here in the Darkside section. Anyway, with a larger diameter tire, the speedometer has typically been more in line with a GPS reading. However, the odometer on the bike will read lower than actual.

Using a stock scooter tire will give a closer to actual odometer reading along with the optimistic speedometer reading; with a larger diameter tire, the bike's speedomer will be more accurate, but the odometer will be off by a few %. The amount depends on how much taller the car tire is than a standard scooter tire.