180 Rear and Speedo Recalibration

[gwade]

So for those of you who have gone to a 180 rear (which I intend to do when I toast the stock tires), what has been your impression with speedo error? Does anyone know if there is an easy way to recalibrate the speedo to work accurately with a 180. I know the manual says that the bike "could" come with a 190 or a 180, so I imagine they have provisions in the computer to do so. I hate to have to do mental math at speed...

[ckruzel]

it will not affect the speedo

[gwade]

it will not affect the speedo

Because? :confused:

[Exdukenut]

It will affect speedo if the actual diameter of the tyre is different. Read here for the why's, and where fors. It won't be out by much but maybe a km or 2, max.

http://www.apriliaforum.com/forums/showthread.php?t=93361

:cool:

[AZRen]

Yea, I piped in earlier then realized I was incorrect on the tire changing the speedo. The difference should not be that much. The gearing has no affect.

How close is it now anyway? Mine is already off with the 190. A 180 might fix it. Actually in my case it will make it worse.

I haven't heard of anyway to correct it.

[Ed / AF1 Racing]

Yea, I piped in earlier then realized I was incorrect on the tire changing the speedo. The difference should not be that much. The gearing has no affect.

How close is it now anyway? Mine is already off with the 190. A 180 might fix it. Actually in my case it will make it worse.

I haven't heard of anyway to correct it.


how do you know yours is off? You cant go by dyno speeds. Aprilia has one of the most accurate speedos out there....way better than any Jap bike.....magazines back in the day tested them accurate to like 150mph.

[DaleInPhoenix]

how do you know yours is off? You cant go by dyno speeds. Aprilia has one of the most accurate speedos out there....way better than any Jap bike.....magazines back in the day tested them accurate to like 150mph.

Ed,
I've got a Garmon GPS I tested mine with. It's pretty accurate till about 75 mph, then it gets 4 mph off (optimistic). That's better than my VTX and way better than my ST1300.

Dale in Phoenix.

[AZRen]

how do you know yours is off? You cant go by dyno speeds. Aprilia has one of the most accurate speedos out there....way better than any Jap bike.....magazines back in the day tested them accurate to like 150mph.


That's exactly what I went by. I assumed it was correct because my Mille on the same dyno was right on. I believe Dale's bike was too. (Correct me if I'm wrong Dale.) My GPS is dead so can't go by that.

If its on I'm surprised Johny Law hasn't let me know it because I'm always speeding plus another 7mph.

It was about +1mph for every 10 on the dyno.

I'll have to get Dale to clock me.

[DaleInPhoenix]

Actually, my bike was set to Kph on the dyno and I didn't get to watch the speedo. I watched the dyno screen run up to 180 at least 4 times at the end of the break-in run. I was impressed!!! :burnout:

Too bad the GPS doesn't work on the dyno!

Dale

[AZRen]

That's right. I asked you this before didn't I? :confused:

[DaleInPhoenix]

I just couldn't resist taking the bike out tonight for a short ride. I slapped the GPS on to confirm those numbers.

It appears the speedo is about 3 mph fast at 45, 4 mph fast at 65 and 5 mph fast at 80. I didn't want to temp Phoenix's finest past that point.

Since the speedo pick-up is mounted on the rear brake mount and uses the disk bolt heads to trigger pulses, only rim or tire size will affect the accuracy. You'll need a taller tire to correct the indicated speed.

I took the opportunity to clean and lube the chain after the rain we've had.

Dale

[Nimskov]

I had my RSV dynoed recently (190 rear tyre), and when the dyno said 250km the colck read 252, so its very accurate!

Regarding the 190/180 question, you have to remember, that they have different profiles... they are 180/55 and 190/50.

The last number is supposed to be the hight of the tyre in percent of the width.

So the hights would then be: 190 = 95mm
180 = 99mm

That would mean that there IS a difference....

/Nimskov

[oatisc]

Google, " Speedo Healer ". I just put 1 on a ZX-14. It's a great product and easy to install.

[mfbRSV]

...Aprilia has one of the most accurate speedos out there....way better than any Jap bike.....magazines back in the day tested them accurate to like 150mph.

:plus: Mine was off by 1 mph at 127mph on the vMax. I know this because the nice State Trooper said he had me clocked at 126. :whiner:

That was with a 180/55 btw.

[williamr]

IThe last number is supposed to be the hight of the tyre in percent of the width.

So the hights would then be: 190 = 95mm
180 = 99mm

That would mean that there IS a difference....

/Nimskov
True, but remember that the rolling circumference is a function of the whole wheel and tyre diameter. The wheel's about 325mm. Add 2 * 99 and you've got 423mm. 8mm in 423 is less than 2%. Without my glasses I can't see the speedo as more than a blur, and with them I can't see the road, so I can live with a 2% speedo error.

Rob