New tires and GPS speed

[bobc4383]

Installed four Falken Ziex 235/55R17 (originals were 50 vs new 55) and then checked the speedometer vs a Garmin GPS.

Spe GPS

35 = 35
45 = 46
55 = 57
65 = 67
75 = 77

So no more driving an indicated 74 in a 70 zone.

Have a nice weekend.

Bob

[cewhite3]

Re: New tires and GPS speed

Installed four Falken Ziex 235/55R17 (originals were 50 vs new 55) and then checked the speedometer vs a Garmin GPS.

Spe GPS

35 = 35
45 = 46
55 = 57
65 = 67
75 = 77

So no more driving an indicated 74 in a 70 zone.

Have a nice weekend.

Bob

Revolution per mile for the OE Michelin Tires is 785. Revolutions per mile for the Falken tires is 778. The difference is pretty trivial - the speedometer should read around 99% of the same as it did with the OE tires for a given actual speed (or in other words an indicated 70 with the original tires would equate to an indicated 69 with the new tires). Or putting it another way - the difference in indicated speed due to the tire change is less than that the likely accuracy of the speedometer (probably 3% to 5%).

Did you do a similar comparison between the OE tires and the GPS? Does your GPS indicate tenth of a mph? My old one did, my newer ones don't. Of course GPS aren't perfect either. Most sites claim an accuracy of 0.1 to 0.5 mph, but caution that the accuracy will be less when climbing or descending hills (GPS altitude measurements are less accurate than planar measurements, but when going up and down hills the distance traveled is a function of the altitude change and the planar distance).

I personally trust the GPS speedometers. I am confident that the distance measurements are consistent and if those or correct, the calculated speed is likely also accurate.

One question - how did you compare the two? Did you have help, or did you shift your eyes from one to the other?

Ed

[RetroJerry]

Re: New tires and GPS speed

How do you like them? I replaced Firestone Firehawks (nice performing tire but noisy after 20K) on my PT Cruiser with Falken ZXs and they not only perform well, have stayed quiet but have over 50K on them and still have a few thousand miles left. My wife is on her second set on her Mini Cooper. I would gladly put them on my 'bird.

[HKS]

Re: New tires and GPS speed

Revolution per mile for the OE Michelin Tires is 785. Revolutions per mile for the Falken tires is 778. The difference is pretty trivial - the speedometer should read around 99% of the same as it did with the OE tires for a given actual speed (or in other words an indicated 70 with the original tires would equate to an indicated 69 with the new tires). Or putting it another way - the difference in indicated speed due to the tire change is less than that the likely accuracy of the speedometer (probably 3% to 5%).
Did you do a similar comparison between the OE tires and the GPS? Does your GPS indicate tenth of a mph? My old one did, my newer ones don't. Of course GPS aren't perfect either. Most sites claim an accuracy of 0.1 to 0.5 mph, but caution that the accuracy will be less when climbing or descending hills (GPS altitude measurements are less accurate than planar measurements, but when going up and down hills the distance traveled is a function of the altitude change and the planar distance).
I personally trust the GPS speedometers. I am confident that the distance measurements are consistent and if those or correct, the calculated speed is likely also accurate.
One question - how did you compare the two? Did you have help, or did you shift your eyes from one to the other?
Ed

Ed what site's tire calculator did you use?

This site says 235/50=748 and 235/55=742 revolutions per mile. You also show that the 55 is taller and would make fewer revolutions per mile, correct but different. Is there a difference in thread depth?

http://www.tacomaworld.com/forum/tir...0r17-235-55r17

[cewhite3]

Re: New tires and GPS speed

Ed what site's tire calculator did you use?
This site says 235/50=748 and 235/55=742 revolutions per mile. You also show that the 55 is taller and would make fewer revolutions per mile, correct but different. Is there a difference in thread depth?
http://www.tacomaworld.com/forum/tir...0r17-235-55r17

The theoretical circumference of the tire based on the tire size does not equate directly to the tire's rolling radius. Tires aren't solid rubber wheels.

Also, people have a hard time with this, but changes in tread depth have very little to do with the rolling radius (revs per mile) of the tires. It does not have a zero effect, but it is much les than you would think if you try to treat a tire like a solid wheel. Think tank tread, not solid wheel.

I got the revolution per mile from the Falken and Michelin tire specs. It is the nominal number for a properly inflated new tire at 60 mph (I think they use 60), but unless the tire is very very severely under or over inflated, or you drive very very fast, it is probably within 1% of the correct value for your tire no matter what the tread depth.

Trying to use the outside diameter of a tire to calculate speed will result in inaccurate results. You could use it to compare tires in a rough way, but it won't give you accurate results if you use it to calculate vehicle speed based on engine speed and vehicle gearing. Tires are not solid inflexible solid wheels. The rolling radius is not the same as the outside circumference you calculate using the tire width and aspect ratio. The rolling radius is often different for tires of the same size, even for different tire types from the same manufacturer.

The stiffest element in a tire are the belts running around the radius of the tire under the rubber. No matter what else happens, no matter how the tire flexes, the belts have to make one revolution for every revolution of the wheel. The rubber parts (and particularly the tread blocks) can stretch and compress to a much greater degree than the belts. Think about the implications of this for bit (be sure to consider that the tire flattens out against the road). Again, think tank tread, not hard wheel.

I usually drive the same route from my house in Wake Forest to my farm in NE North Carolina. If I don't make any deviations, it is a 272 mile round trip (per the odometer in my Escape). I keep a log book for tax reasons, so I have a record of the trip. When my 2013 Escape was new, the minimum trip distance was 272 miles according to the car's odometer. Just before I replaced the OE tires last month, the minimum trip was 273 miles per the odometer (the tires had 49000 miles on them). I purchased the same tires as the OE from the Ford dealer as replacements. Amazingly the minimum trip now is 272 miles per the odometer (I was actually shocked that the old and new tires were almost exactly the same - even though they are the same manufacturer and model tires).

If you do the math, the "revs per mile" using the outside circumference of the tire based on the P235/55R17 dimensions, then you come up with 742 revs per mile. If you look up tire specs at tirerack.com, the actual revs per miles for tires in this size range from 760 to 778.

Tire manufacturer and model - revs per mile
-------------------------------- --------------
Based on calculated circumference for a 235/55R17 Tire - 742
Michelin Energy MXV4 Plus - 760
Yokohama AVID ENVigor - 763
General G-MAX AS-03 - 764
Kumho Ecsta 4X - 764
Continental ContiProContact - 764
Kumho Sense - 764
BFGoodrich g-Force Super Sport A/S - 766
Firestone Firehawk Wide Oval AS - 766
Fuzion UHP - 766
Michelin Pilot Sport A/S 3 - 766
BFGoodrich Advantage T/A - 766
Michelin Pilot HX MXM4 - 766
Bridgestone Potenza RE040 - 766
Michelin Defender - 766
Michelin Latitude Diamaris - 766
Continental ExtremeContact DWS - 767
Bridgestone Turanza Serenity Plus - 767
Continental ContiProContact LRR - 767
General Altimax HP - 767
Firestone Firehawk Wide Oval Indy 500 - 767
Goodyear Eagle Sport All-Season - 768
Pirelli P Zero Nero All Season - 768
Dunlop Direzza DZ101 - 768
Dunlop SP Sport Maxx TT - 769
Dunlop SP Sport Signature - 769
Goodyear Eagle F1 Asymmetric All-Season - 769
Hankook Ventus S1 noble2 - 769
Sumitomo HTR A/S P01 - 776
Sumitomo HTR Z III - 778
Dunlop Direzza DZ102 - 778

One last comparison:

Tire - Tire revs per mile - Actual vehicle speed at 2000 RPM engine speed
----- -------------------- -----------------------------------------------------
Calculated 235/55 Tires - 742 - 60.2 mph
Michelin Energy MXV4 Plus 235/55 Tires - 760 - 58.8 mph
Dunlop Direzza DZ102 235/55 Tires - 778 - 57.4
Calculated 235/50 Tires - 768 - 58.2 mph
Michelin Pilot HX MXM4 235/50 Tires - 785 - 56.9 mph

Ed

[HKS]

Re: New tires and GPS speed

The theoretical circumference of the tire based on the tire size does not equate directly to the tire's rolling radius. Tires aren't solid rubber wheels.
Also, people have a hard time with this, but changes in tread depth have very little to do with the rolling radius (revs per mile) of the tires. It does not have a zero effect, but it is much les than you would think if you try to treat a tire like a solid wheel. Think tank tread, not solid wheel.
I got the revolution per mile from the Falken and Michelin tire specs. It is the nominal number for a properly inflated new tire at 60 mph (I think they use 60), but unless the tire is very very severely under or over inflated, or you drive very very fast, it is probably within 1% of the correct value for your tire no matter what the tread depth.
Trying to use the outside diameter of a tire to calculate speed will result in inaccurate results. You could use it to compare tires in a rough way, but it won't give you accurate results if you use it to calculate vehicle speed based on engine speed and vehicle gearing. Tires are not solid inflexible solid wheels. The rolling radius is not the same as the outside circumference you calculate using the tire width and aspect ratio. The rolling radius is often different for tires of the same size, even for different tire types from the same manufacturer.
The stiffest element in a tire are the belts running around the radius of the tire under the rubber. No matter what else happens, no matter how the tire flexes, the belts have to make one revolution for every revolution of the wheel. The rubber parts (and particularly the tread blocks) can stretch and compress to a much greater degree than the belts. Think about the implications of this for bit (be sure to consider that the tire flattens out against the road). Again, think tank tread, not hard wheel.
I usually drive the same route from my house in Wake Forest to my farm in NE North Carolina. If I don't make any deviations, it is a 272 mile round trip (per the odometer in my Escape). I keep a log book for tax reasons, so I have a record of the trip. When my 2013 Escape was new, the minimum trip distance was 272 miles according to the car's odometer. Just before I replaced the OE tires last month, the minimum trip was 273 miles per the odometer (the tires had 49000 miles on them). I purchased the same tires as the OE from the Ford dealer as replacements. Amazingly the minimum trip now is 272 miles per the odometer (I was actually shocked that the old and new tires were almost exactly the same - even though they are the same manufacturer and model tires).
If you do the math, the "revs per mile" using the outside circumference of the tire based on the P235/55R17 dimensions, then you come up with 742 revs per mile. If you look up tire specs at tirerack.com, the actual revs per miles for tires in this size range from 760 to 778.
Tire manufacturer and model - revs per mile
-------------------------------- --------------
Based on calculated circumference for a 235/55R17 Tire - 742
Michelin Energy MXV4 Plus - 760
Yokohama AVID ENVigor - 763
General G-MAX AS-03 - 764
Kumho Ecsta 4X - 764
Continental ContiProContact - 764
Kumho Sense - 764
BFGoodrich g-Force Super Sport A/S - 766
Firestone Firehawk Wide Oval AS - 766
Fuzion UHP - 766
Michelin Pilot Sport A/S 3 - 766
BFGoodrich Advantage T/A - 766
Michelin Pilot HX MXM4 - 766
Bridgestone Potenza RE040 - 766
Michelin Defender - 766
Michelin Latitude Diamaris - 766
Continental ExtremeContact DWS - 767
Bridgestone Turanza Serenity Plus - 767
Continental ContiProContact LRR - 767
General Altimax HP - 767
Firestone Firehawk Wide Oval Indy 500 - 767
Goodyear Eagle Sport All-Season - 768
Pirelli P Zero Nero All Season - 768
Dunlop Direzza DZ101 - 768
Dunlop SP Sport Maxx TT - 769
Dunlop SP Sport Signature - 769
Goodyear Eagle F1 Asymmetric All-Season - 769
Hankook Ventus S1 noble2 - 769
Sumitomo HTR A/S P01 - 776
Sumitomo HTR Z III - 778
Dunlop Direzza DZ102 - 778
One last comparison:
Tire - Tire revs per mile - Actual vehicle speed at 2000 RPM engine speed
----- -------------------- -----------------------------------------------------
Calculated 235/55 Tires - 742 - 60.2 mph
Michelin Energy MXV4 Plus 235/55 Tires - 760 - 58.8 mph
Dunlop Direzza DZ102 235/55 Tires - 778 - 57.4
Calculated 235/50 Tires - 768 - 58.2 mph
Michelin Pilot HX MXM4 235/50 Tires - 785 - 56.9 mph
Ed

OK Ed,
I will check with Tirerack to see which 215/55R17 would best match the Michelins 235/50R17 revs per mile since I am evaluating the 215 for an almost full size spare tire replacement that will fit in the tire well.

HKS

P.S. It would seem that recommended tire pressure and sidewall/design/stiffness would make a great deal of difference in revs per mile. It can't be measured correctly without being mounted. It needs the right weight and side wall deflection. So, the revs per mile depend a great deal on the car's weight and recommended tire pressure.

[HKS]

Re: New tires and GPS speed

OK Ed,
I will check with Tirerack to see which 215/55R17 would best match the Michelins 235/50R17 revs per mile since I am evaluating the 215 for an almost full size spare tire replacement that will fit in the tire well.
HKS
P.S. It would seem that recommended tire pressure and sidewall/design/stiffness would make a great deal of difference in revs per mile. It can't be measured correctly without being mounted. It needs the right weight and side wall deflection. So, the revs per mile depend a great deal on the car's weight and recommended tire pressure.

P.S.2 It would seem that, if you don't put the exact same tire brand on the car as OEM then the tire inflation pressure will not be optimum. If you go by the sticker on the door (listing recommended tire pressure).

I noticed this when I replaced my OEM Bridgestone tires on my Jetta with Michelins. Now at 35 psi the front tires have a noticeable bulge (sidewall deflection). Two more psi makes things OK. Strange, the same car calls for 39 psi in Europe.

[bobc4383]

Re: New tires and GPS speed

Amazing analysis of the Revs per mile comparison for OE Michelin and Falken tires.

"Did you do a similar comparison between the OE tires and the GPS? Does your GPS indicate tenth of a mph?"
No for both unfortunately. In the past I used my older daughter's philosophy: speed but don't be the fastest person. Works for me.

"how did you compare the two? Did you have help, or did you shift your eyes from one to the other?"
Eyes and cruise control on level roads. I was on a straight stretch with little traffic so would set the speed, punch cruise, watch it for a bit and then check the GPS. Did the same up to the 65 and 75 on the interstate. Luckily not much traffic so could just set it, watch for 10 seconds or so and then check the GPS. Sort of the TLAR method (that looks about right).

Bob

Revolution per mile for the OE Michelin Tires is 785. Revolutions per mile for the Falken tires is 778. The difference is pretty trivial - the speedometer should read around 99% of the same as it did with the OE tires for a given actual speed (or in other words an indicated 70 with the original tires would equate to an indicated 69 with the new tires). Or putting it another way - the difference in indicated speed due to the tire change is less than that the likely accuracy of the speedometer (probably 3% to 5%).

Did you do a similar comparison between the OE tires and the GPS? Does your GPS indicate tenth of a mph? My old one did, my newer ones don't. Of course GPS aren't perfect either. Most sites claim an accuracy of 0.1 to 0.5 mph, but caution that the accuracy will be less when climbing or descending hills (GPS altitude measurements are less accurate than planar measurements, but when going up and down hills the distance traveled is a function of the altitude change and the planar distance).

I personally trust the GPS speedometers. I am confident that the distance measurements are consistent and if those or correct, the calculated speed is likely also accurate.

One question - how did you compare the two? Did you have help, or did you shift your eyes from one to the other?

Ed

[bobc4383]

Re: New tires and GPS speed

I was never that 'alert' as to road noise but last Saturday we drove the car with the top up and low speed on the A/C on both the interstate and city streets. The thing I noticed and seemed different to me was the tire and vehicle noise of those around me. For someone on the interstate or highway (35-55mph), I could hear cars and trucks around me more so I think the tires are quieter (I am 67 so ears not what they used to be either). The ride seems about the same and the grip is excellent (test it when alone since my wife doesn't have a handle to hang onto -G). So, I like them - they look great (BSW). Price wasn't bad either at TiresPlus $121 each plus the other stuff).

Bob

How do you like them? I replaced Firestone Firehawks (nice performing tire but noisy after 20K) on my PT Cruiser with Falken ZXs and they not only perform well, have stayed quiet but have over 50K on them and still have a few thousand miles left. My wife is on her second set on her Mini Cooper. I would gladly put them on my 'bird.

[AZTB]

Re: New tires and GPS speed

I was never that 'alert' as to road noise but last Saturday we drove the car with the top up and low speed on the A/C on both the interstate and city streets. The thing I noticed and seemed different to me was the tire and vehicle noise of those around me... Bob

Just replaced the Falkens with Vogue Signature VIII's ... can't believe how much quieter they are. When the Falkens were on the car, at one point I thought I had a wheel bearing issue & took it to the dealer...and that's when I learned it was the tires (dealer rotated them and double checked the noise...it was the tires). Now that Vogues are in place, the noise is gone...who'd thunk?

[Brad]

Installed four Falken Ziex 235/55R17 (originals were 50 vs new 55) and then checked the speedometer vs a Garmin GPS.

Spe GPS

35 = 35
45 = 46
55 = 57
65 = 67
75 = 77

So no more driving an indicated 74 in a 70 zone.

Have a nice weekend.

Bob

Bob, how do you like the Falken tires you installed in 2014? I'm looking at Ohtsu which are apparently made by Falken so I'm curious about your experience, especially if you've driven them in rain or snow....Thanks!

[4LOWBIRDS+7]

Brad have you looked at the Summit tires? I was going to buy a set of these and then they were sold out. Now they have them.

http://www.ebay.com/itm/4-New-235-55...5ZtqbF&vxp=mtr

[Brad]

Hi Ron, thanks for the reply, just noticed Bob hasn't been on here for a few years so I probably won't hear from him. The shop by my house has the Ohtsu's for $74 99W SL BSW in stock but the ones's you posted would be $37. plus tax cheaper for all 4...not sure that's worth the trouble (unless you think it's a better tire).

[4LOWBIRDS+7]

Hi Ron, thanks for the reply, just noticed Bob hasn't been on here for a few years so I probably won't hear from him. The shop by my house has the Ohtsu's for $74 99W SL BSW in stock but the ones's you posted would be $37. plus tax cheaper for all 4...not sure that's worth the trouble (unless you think it's a better tire).

I would sure go with the ones by my house. I have been lucky with my choices and no one near me can even come close on price. That is why I have been trying something out of the ordinary.

[qzztv3]

Hi Ron, thanks for the reply, just noticed Bob hasn't been on here for a few years so I probably won't hear from him. The shop by my house has the Ohtsu's for $74 99W SL BSW in stock but the ones's you posted would be $37. plus tax cheaper for all 4...not sure that's worth the trouble (unless you think it's a better tire).

Bob again. To be honest, I traded the T-Bird about three years ago. It was becoming a money pit, but looking back, I wish I still had it. Being 72, I have a RMD due (have to take IRA money out each year) so about have the wife talks into buying another one.

i was surprised how many comments I got on my original post about the tires. Lots of detailed analysis.

Glad the forum is still here.

Bob