Tire Size & Speedometer Correction - Evidence

[MarkLawson]

I'll admit to an odd quirk I live with. That is that when I look at my speedometer, I'd like for it to tell me how fast I am going, not within 3-4 mph of how fast I am going. When I bought and installed my replacement rear tire (Michelin HydroEdge 215/60R15), I found my speedometer error rate dropped significantly. Now my speedometer reads either the same or within 1 mph of my Garmin Zumo 550 GPS. See the picture below for proof. This is typical of any speed I have checked. I've run this tire for over 11,000 miles and have had no Nanny issues associated with it. I have worn through 1/3 of the legal tread, so expect to get another 22,000-23,000 miles out of it before changing. Picture was taken last Monday night on the way home from Bible study.

http://www.spyderlovers.com/forums/attachment.php?attachmentid=78414&d=1383164913 (http://www.spyderlovers.com/forums/album.php?albumid=1424&attachmentid=69388)

[ARtraveler]

Thank you for posting. Very good information for those who use non-OEM tires. :thumbup:

[SNOOPY]

Nice :thumbup:

[ulflyer]

I got exactly the same speed results with a 205-60-15 General and now with the Pirelli P4.

[Chupaca]

if you want accurate use your gps. Not even from the factory are the spot on. Highway speed signs always differ so gps is best. Different tires can make a difference but then not that much....:dontknow:

[Highwayman2013]

What air pressure do you run in that Michelin ?

[MarkLawson]

What air pressure do you run in that Michelin ?

I'm running the BRP recommended pressure, around 28 psi. After 11,000+ miles, I ran a tread depth gauge across the tire and found that the tread depth is even across the width of the tire, so I'm satisfied. I also have the Michelin Defenders on the front (175/65R14) & am running around 18-20 psi in them. I don't have that many miles on them yet, but initial indicators are that they're wearing evenly and should last 50,000 miles or more.

[bluestratos]

Have you got a picture of the rear tire, the correct tire is a 225/50R so I was wondering what the 60 looks like and how it fits the Rim.

[Hawk]

Have you got a picture of the rear tire, the correct tire is a 225/50R so I was wondering what the 60 looks like and how it fits the Rim.

Hmm, I have noticed my speed is off as well compared to my Garmin 660 (as much as 4mph in some cases), just replaced mine with the 225/50 Khumo or I would have tried a 60 as well.

PS. You need to drive faster, old man!!

PSS. You need gas!!!

[jerpinoy]

You can't go wrong with gps reference., thanks also with the tires and pres info.

[sledmaster]

Thanks for the great post about speedo accuracy Mark, great info! :clap:

There are many of use who run 4-ply automotive tires on our Spyders. In the stock 225/50R15 rear tire size there are limited options, this is why many have tried other sizes to open up the options of what is available. As a side benefit, the speedo becomes more accurate, as Mark has shown us.

In regards to this, here are some of the other sizes and how they differ in diameter. The first number (225, 215, 205) is the tire width in mm, so going to a 215 instead of a 225 width you are going 10mm narrower (which is 0.39"). Going to a 205 is 20mm narrower (0.79").

Diameter is not as clear cut. The stock 225/50R15 tire is 23.86" in diameter (or 606mm). When you go to a 215/60R15 it is 25.16" (639mm) in diameter, or +5.4% larger. Another popular size with many options is 205/60R15 and this one is even closer in diameter to the stock tire at 24.69" diameter (627mm) which is only +3.5%, but is slightly narrower in width. Both of these sizes have been used by forum members with good success. The nanny does not care about this size difference.

There are some other sizes, but very few tires are available in these. Like 215/55R15 (+1.9%) or 205/55R15 (+0.1%) sizes, they are closer in diameter to the stock tire than the 60s. There’s also 225/55R15 but this too is tough to find, that one is +3.7% in diameter.

Here is a great link to a tire size calculator I use to figure all of this out - http://www.tacomaworld.com/forum/tirecalc.php

The 4-ply tires seem to be slightly heavier, but this is perfectly acceptable for the higher quality and durability. I have been using 4-ply tires for years on Spyder for their more even wear and greater durability. Just pay attention to their speed ratings, tread wear rating, traction and temperature ratings. Personally, I will only use a tire that is AA or A for traction, only A for temperature, and H (130 mph) or V (149 mph) for speed rating (I will not use a T rated tire, that is only 118 mph). Hope this helps!

[MarkLawson]

Have you got a picture of the rear tire, the correct tire is a 225/50R so I was wondering what the 60 looks like and how it fits the Rim.

The tire fits the rim perfectly

http://www.spyderlovers.com/forums/attachment.php?attachmentid=78461&d=1383240003 http://www.spyderlovers.com/forums/attachment.php?attachmentid=78460&d=1383239999

[BLUEKNIGHT911]

It's been discussed here many times before.....with the stock size tire ( 225/50 - 15 ) the speedometer is not accurate. With the 205 0r 215 / 60 it's much closer to accurate ..........and don't look for the Michelin Hydro- Edge they stopped making them ( :gaah:) quite awhile ago, .......but you may still find some hidden away....Mike :thumbup:

[MarkLawson]

It's been discussed here many times before.....with the stock size tire ( 225/50 - 15 ) the speedometer is not accurate. With the 205 0r 215 / 60 it's much closer to accurate ..........and don't look for the Michelin Hydro- Edge they stopped making them ( :gaah:) quite awhile ago, .......but you may still find some hidden away....Mike :thumbup:

www.TireRack.com (http://www.TireRack.com) says they have 'fewer than 3' in stock ( http://www.tirerack.com/tires/TireSearchResults.jsp?customSizeSearch=&width=215%2F&ratio=60&diameter=15 ) @ $108.00 each (Closeout) + shipping. I understand their Defender is the replacement for the HydroEdge.

[bluestratos]

Looks close to stock width wise and gives a lot more options in tires.


The tire fits the rim perfectly

http://www.spyderlovers.com/forums/attachment.php?attachmentid=78461&d=1383240003 http://www.spyderlovers.com/forums/attachment.php?attachmentid=78460&d=1383239999

[den1953]

That's another thing about car tires, specifically how they perform in rain. Hydroplaning is the last thing you'd want. I changed aspect ratio on the rear tire of that Triumph Rocket III and the circumference was something like 2 percent smaller on the longer lasting Michelin I went to. That made the odometer register 100 miles when I had only covered 98. That doesn't sound like much until you multiply the odometer error. 1000 miles only being 980 or 10,000 being 9,800 miles etc. My guess if you're car tire gets you closer or dead-on with your GPS there should be zero or near zero odometer error as well.

[xmanjr]

It's been discussed here many times before.....with the stock size tire ( 225/50 - 15 ) the speedometer is not accurate. With the 205 0r 215 / 60 it's much closer to accurate ..........and don't look for the Michelin Hydro- Edge they stopped making them ( :gaah:) quite awhile ago, .......but you may still find some hidden away....Mike :thumbup:Tire Rack.com has a few left. I just bought one on Saturday for 108.00 plus shipping. Ordered it Saturday and it was delivered on Tuesday. Can't wait to have it installed to see how it rides, I have 12,200 miles on my Kendall, center is worn into the wear strips. Russ

[tigerdr]

Only 2 Michelin HydroEdge remaining. I order one 5 minutes ago.

[MarkLawson]

Another picture @ another speed taken this past Sunday:

https://scontent-a-atl.xx.fbcdn.net/hphotos-frc1/t1/1780702_761083220568790_1829167559_n.jpg

[SPYD3R]

215/60R15.....????
you should be riding on a 225/50 R15.... the '50' vs. '60' is what's skru'n u up....
the 225 vs. 215 is the width.... no issues there, except you don't have as much 'rubber' on the ground...
'50' vs. '60' is the diameter of the tire... that makes all the different in speedo numbers... as well as MPG...
burn the BAD-BOY up, and get u a 225/50 R15 ASAP.....

[spydajohn]

Hi all with the tyre being a little bigger in diameter how much harder is it to take off with the trailer attached because I have a 2010 rt manual and have already replaced a clutch because 1st gear is so tall.

[OldCowboy]

215/60R15.....????
you should be riding on a 225/50 R15.... the '50' vs. '60' is what's skru'n u up....
the 225 vs. 215 is the width.... no issues there, except you don't have as much 'rubber' on the ground...
'50' vs. '60' is the diameter of the tire... that makes all the different in speedo numbers... as well as MPG...
burn the BAD-BOY up, and get u a 225/50 R15 ASAP.....

Actually, the statement about 'rubber on the ground' is incorrect. On the same vehicle at the same inflation pressure, all tires put the same amount (area) of rubber on the ground. 500 pounds setting on a tire inflated to 28 psi will generate a contact patch of 27.14 sq in, regardless of whether the tire is 250 mm wide or 180 mm wide. The difference will be the way the contact patch is aligned relative to the direction of travel. The tire with the greater width will have a contact patch which is wider and shorter than the narrower tire.

[BLUEKNIGHT911]

215/60R15.....????
you should be riding on a 225/50 R15.... the '50' vs. '60' is what's skru'n u up....
the 225 vs. 215 is the width.... no issues there, except you don't have as much 'rubber' on the ground...
'50' vs. '60' is the diameter of the tire... that makes all the different in speedo numbers... as well as MPG...
burn the BAD-BOY up, and get u a 225/50 R15 ASAP.....

Dan I beg to differ on this .......50 vs. 60 is the aspect (?) ratio ....it has nothing to do with the tire diameter.........:hun:.....:2excited:....:thumbup: :thumbup::thumbup:...Mike

[MarkLawson]

215/60R15.....????
you should be riding on a 225/50 R15.... the '50' vs. '60' is what's skru'n u up....
the 225 vs. 215 is the width.... no issues there, except you don't have as much 'rubber' on the ground...
'50' vs. '60' is the diameter of the tire... that makes all the different in speedo numbers... as well as MPG...
burn the BAD-BOY up, and get u a 225/50 R15 ASAP.....

I don't think you're understanding the point of my post. With the different tire installed, my speedometer is now running true, for the most part. At some speeds it shows 1 mph different. Overall, I think this is a good change. I cannot speak to contact patch sizes, but the change in width is minimal. I have not found this tire to present any perceivable change in traction.


Dan I beg to differ on this .......50 vs. 60 is the aspect (?) ratio ....it has nothing to do with the tire diameter...Mike

Actually, as I understand it, the aspect ratio measurement is based on the tread diameter. A '50' means the side height is 50% of the tread width. On a 225/50R15, that would mean the sidewall height is 112.5mm. For a 215/60R15, the sidewall height would be 129mm, resulting in a 'taller' tire than OEM.

Someone please correct me if I am wrong, which is always a good possibility...

[tigerdr]

Right. And the difference between 50% and 60% is small. Best thing is the speedometer is running true.

[bobnaquin]

I have always found it interesting that we are not allowed to adjust our speedometer reading to be more accurate. It would be easy enough to do since these are all computer readouts and there is no reason that we could not adjust the speedometer 4 or 5 miles per hour since it is pretty much off that much in any case. I suppose there is some liability issues underlying it all.

I had the ability to do this on my last boat. Boats have notoriously inaccurate speedos due the design. I was able to adjust mind to being spot on with the gps. Of course there is no speed limit on the water and service intervals are determined by elapsed hours not miles travelled. It would be a nice feature to have. It would not be any harder than adjusting the time of day clock.

[NancysToy]

I have always found it interesting that we are not allowed to adjust our speedometer reading to be more accurate. It would be easy enough to do since these are all computer readouts and there is no reason that we could not adjust the speedometer 4 or 5 miles per hour since it is pretty much off that much in any case. I suppose there is some liability issues underlying it all.

I had the ability to do this on my last boat. Boats have notoriously inaccurate speedos due the design. I was able to adjust mind to being spot on with the gps. Of course there is no speed limit on the water and service intervals are determined by elapsed hours not miles travelled. It would be a nice feature to have. It would not be any harder than adjusting the time of day clock.

The reason probably has more to do with the odometer laws. Changing the speedo means also changing the odo. It is perfectly logical that to do so makes things more accurate, and should be allowed (or even desired), but since when did Congress worry about logic?

[BLUEKNIGHT911]

I don't think you're understanding the point of my post. With the different tire installed, my speedometer is now running true, for the most part. At some speeds it shows 1 mph different. Overall, I think this is a good change. I cannot speak to contact patch sizes, but the change in width is minimal. I have not found this tire to present any perceivable change in traction.



Actually, as I understand it, the aspect ratio measurement is based on the tread diameter. A '50' means the side height is 50% of the tread width. On a 225/50R15, that would mean the sidewall height is 112.5mm. For a 215/60R15, the sidewall height would be 129mm, resulting in a 'taller' tire than OEM.

Someone please correct me if I am wrong, which is always a good possibility...

( Aspect Ratio )..... And I think it's in reference to the sidewall height combined with the tread width.....Mike :thumbup:

[den1953]

I always thought the Aspect Ratio had to do with the height of the sidewall relative to the tread width. Say a 70 series tire might have a sidewall height that is 70% of the tread width and a 60 series would be 60% etc. At least that was always my interpretation of it.

[Bob Denman]

My question: Have you noticed any difference in the handling of the bike with the narrower tire? :dontknow:

And for those of you; who want to have some fun with numbers...
http://www.tacomaworld.com/forum/tirecalc.php

[OldCowboy]

( Aspect Ratio )..... And I think it's in reference to the sidewall height combined with the tread diameter.....Mike :thumbup:

From the Tire Rack:"Sidewall Aspect Ratio Typically following the three digits identifying the tire's Section Width in millimeters is a two-digit number that identifies the tire's profile or aspect ratio.

P225/50R16 91S
The 50 indicates that this tire size's sidewall height (from rim to tread) is 50% of its section width. The measurement is the tire's section height, and also referred to as the tire's series, profile or aspect ratio. The higher the number, the taller the sidewall; the lower the number, the lower the sidewall. We know that this tire size's section width is 225mm and that its section height is 50% of 225mm. By converting the 225mm to inches (225 / 25.4 = 8.86") and multiplying it by 50% (.50) we confirm that this tire size results in a tire section height of 4.43". If this tire were a P225/70R16 size, our calculation would confirm that the size would result in a section height of 6.20", approximately a 1.8-inch taller sidewall."

http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=46

[BLUEKNIGHT911]

OldCowboy you are correct ......after re-reading my second Post I realized my error and corrected it .........Mike :thumbup:

[MarkLawson]

My question: Have you noticed any difference in the handling of the bike with the narrower tire? :dontknow:

And for those of you; who want to have some fun with numbers...
http://www.tacomaworld.com/forum/tirecalc.php

I have not found this tire to present any perceivable change in traction or handling. As the original post is several months old, I doubt the HydroEdge is easily found. I put Michelin Defenders on the front, which I understand is Michelin's replacement for the HydroEdge. The Defenders seem to work well up front.

[Bob Denman]

Thanks! :thumbup: