Another myth debunked

[docdoru]

Not only that the 225/55/15 back tire is working on the Spyder without throwing codes but the display speed in now identical with the GPS speed (maybe the display/speed reading was originally set-up for this tire size):

[NancysToy]

A slightly taller tire would make the speedo read correctly in most cases. Speedometers are generally calibrated to the full diameter of the standard tire. In theory, this is fine, but the weight of the machine and the rider makes the tire "squat", reducing the effective diameter. This is called the "rolling diameter", and it is a bit variable depending on conditions such as tire pressure and passenger weight, so the engineers don't use it. It is determined by marking the tire, rolling one complete revolution, then dividing that measurement by pi.

Your new tire apparently has a rolling diameter that is very close to the full diameter of the stock tire, so it effectively corrects your speedo reading. How is that tread pattern in the rain?

[WackyDan]

A slightly taller tire would make the speedo read correctly in most cases. Speedometers are generally calibrated to the full diameter of the standard tire. In theory, this is fine, but the weight of the machine and the rider makes the tire "squat", reducing the effective diameter. This is called the "rolling diameter", and it is a bit variable depending on conditions such as tire pressure and passenger weight, so the engineers don't use it. It is determined by marking the tire, rolling one complete revolution, then dividing that measurement by pi.

Your new tire apparently has a rolling diameter that is very close to the full diameter of the stock tire, so it effectively corrects your speedo reading. How is that tread pattern in the rain?

I want to know how is that tread pattern and tire with the turbo?

[Roger]

"By pi" i like pie.

[tweeder]

Stock Tire - 225/50R15 >Search Tires Tire 1 - 225/55R15 >Search Tires

Section Width: 8.85 in 225 mm Section Width: 8.85 in 225 mm

Rim Diameter: 15 in 381 mm Rim Diameter: 15 in 381 mm

Rim Width Range: 6 - 8 in Rim Width Range: 6 - 7.5 in

Overall Diameter: 23.85 in 605.79 mm Overall Diameter: 24.74 in 628.39 mm

Sidewall Height: 4.42 in 112.26 mm Sidewall Height: 4.87 in 123.69 mm

Radius: 11.92 in 302.76 mm Radius: 12.37 in 314.19 mm

Circumference: 74.92 in 1902.9 mm Circumference: 77.72 in 1974.0 mm

Revs per Mile: 872.1 Revs per Mile: 840.7

Actual Speed: 60 mph 100 km/h Speedometer1: 57.8 mph 96.3 km/h

Speedometer Difference: - Speedometer Difference: 3.734% too slow
Diameter Difference: - Diameter Difference: 3.6%

[docdoru]

Actual Speed: 60 mph 100 km/h
Speedometer1: 57.8 mph 96.3 km/h
Speedometer Difference: Speedometer Difference: 3.734% too slow
Diameter Difference: Diameter Difference: 3.6%

The Spyder was build for a 225/55/15 tire?

[bobbobtar]

If the speedometer is off by 3.734% on a stock tire is the odometer also off by the same percent, thus giving us a longer warranty than actual miles driven.

[Firefly]

If the speedometer is off by 3.734% on a stock tire is the odometer also off by the same percent, thus giving us a longer warranty than actual miles driven.

Good point.

I noticed when I rode to Sturgis with my HD buddies I put about 35-40 miles more on the Spyder per 1,000 miles..... so this jives with this. I remember them stopping once we hit the first 1,000 miles and saying they just hit 1,000--- when I was around 1,040 already.....

I thought about this as we rode and then it struck me--- if the speed is off then the mileage would be off too.....

[RShrimp]

Good point.


I thought about this as we rode and then it struck me--- if the speed is off then the mileage would be off too.....

You can't really make this assumtion. The speedo and the odo are not nessesarly directly related. If you change tire size it will affect both the same way but just because the stock speedo reads fast does not mean the odo reads high (in your case it seems that it does but it does not always work that way.)
Bike odo's are way off. We have tried to set up many poker runs with right turn at 2.9 miles then left turn at 12.3 miles ect adding the mileage. We run it with 5 different bikes and get 5 different numbers (by the end of the run between 100 and 150 miles we can be off by 15 to 20 miles between the bikes (all stock gearing and tire size)
All the bike speedos read high because the lawyers got involved.

[NancysToy]

If the speedometer is off by 3.734% on a stock tire is the odometer also off by the same percent, thus giving us a longer warranty than actual miles driven.

There is no mileage limit on the Spyder warranty, just a time limit.

[JJW SpyderRider]

A slightly taller tire would make the speedo read correctly in most cases. Speedometers are generally calibrated to the full diameter of the standard tire. In theory, this is fine, but the weight of the machine and the rider makes the tire "squat", reducing the effective diameter. This is called the "rolling diameter", and it is a bit variable depending on conditions such as tire pressure and passenger weight, so the engineers don't use it. It is determined by marking the tire, rolling one complete revolution, then dividing that measurement by pi.

Your new tire apparently has a rolling diameter that is very close to the full diameter of the stock tire, so it effectively corrects your speedo reading. How is that tread pattern in the rain?

I noticed my speed and GPS didn't match, thanks for the info!

[JJW SpyderRider]

I want to know how is that tread pattern and tire with the turbo?

Spyder + Turbo = no tread!

[altonk]

true mine are going away fast

looks like a new rear every oil change

[QuadManiac]

Well if the 225/55-15 is the magic tire there is a problem, tire selection. There just isn't anything to choose from. However if you step up to a 225/50-16 this tire matches the magic tire almost spec for spec (see link) and at the Tire Rack your choices go up to 36 just in summer performance tires more if you include all season. Yes you have to get a custom rim made but look at the options it opens up. I think this would be the route to travel down IMHO.



http://www.miata.net/garage/tirecalcold.html

But where do we get a 16" rear wheel for the Spyder?

[pauly1]

There is a direct correlation of the indicated speed and miles/km traveled. The assumed distance per tire/wheel revolution is what the speedometer uses to calculate speed and distance. The professor's rolling diameter explanation is spot on: rolling diameter is smaller going less distance per revolution. So if a mile was supposed to be 1000 revolutions and the rolling diameter was 3% small, then it would take 3% more turns to make the full mile and the odometer would indicate the 3% longer distance.

RShrimp stated "off by 15 - 20 miles over 100 - 150 mile run". I'll bet none registered less that the true mileage run and someone had a lot of weight/low tire pressure to result in the 10-15% difference in mileage.

Wayne

[SethO]

But where do we get a 16" rear wheel for the Spyder?

DO not go that high, I have one I will give you a hella good deal on, it has about 10 miles on it. after 1 mile it trips the limp mode, its past the point the tcs will do. I tried it to get more top end for the salt flats in 09.

any change in handling doc?

[bone crusher]

As far as stick and digital speedo go compared to GPS, it doesn't mean much...

The GPS is not using formulas based on your tires, it's using satellite feed. Your bike is going with what it has...

To get true mileage, simply test it on road sticks (on most highways)...you can do this over a 5-10 mile run and you'll have a good idea of how accurate/inaccurate your bike is...

Tire pressure would play in too...less tire pressure, under load, creates a smaller diameter...we can go from there on how this affects things...

[SethO]

I can only see TCS becoming a problem if you are running too big at the back with stock sizes at the front. Now I'm not even close to being an expert here but if you are running the same diameter at all three corners it shouldn't be an issue. Yes/no?

people have told me if you do increase all three the same it will would just was so pissed off about it and if was for a nominal gain that I just look at that tire and am pissed, if someone could do the man and tell me what fronts to put on i would try it.

[mjw930]

Don't always assume your GPS is 100% accurate, it isn't. I have done tests with the speedo, GPS and radar and have found that both my GPS's (Garmin and TomTom) read low compared to the speedo and radar. In fact, our Spyder and Victory speedo's are within 1% of the radar readings while being roughly 3% higher than the GPS.

All I can assume is the GPS refresh rate effects the calculation to the slow side while the Radar and Speedo do not suffer from that limitation.

[NancysToy]

Don't always assume your GPS is 100% accurate, it isn't. I have done tests with the speedo, GPS and radar and have found that both my GPS's (Garmin and TomTom) read low compared to the speedo and radar. In fact, our Spyder and Victory speedo's are within 1% of the radar readings while being roughly 3% higher than the GPS.

All I can assume is the GPS refresh rate effects the calculation to the slow side while the Radar and Speedo do not suffer from that limitation.

While this isn't necessarily the most common situation, you are absolutely correct with some GPS units or geographical locations. The GPS measures your movement relative to the satellites. It more or less assumes you are traveling in straight segments on a flat plane. If you go up or down hills, your road distance is greater than the distance "as the crow flies". If you go around corners, the update time comes into play, as the GPS assumes you went in a straight line between each update interval. Again, your road distance is greater. The number of availablle sattelites and the signal strength affect accuracy, too.

For the most part, a GPS is more accurate than a motorcycle speedometer. Motorcycles are almost always optimistic. That being said, the only good way to judge how your particular vehicle and GPS compare, and which is more accurate, is to time mile posts over a distance, or to run through a certified radar. Don't trust those radars signs...get a cop to let you run by his certified unit. The signs are often way off...sometimes intentionally.

[docdoru]

...get a cop to let you run by his certified unit.

Not again...

[NancysToy]

Not again...

Maybe you should have asked him first!

BTW, how did your speedo compare?

[Bob Denman]

....But they're always checking on my forward progress when I don't wany them too!

[docdoru]

Maybe you should have asked him first!

BTW, how did your speedo compare?

Dead on: 100 mph is 100 mph, not 104 mph...

[retired1]

On my way to SITS in '09 I ran across a measured 10 mile speedo check. On my '09 GS, the odometer would record 1/10 mile more for every mile traveled, according to the mile post markers.