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1956514 tires have a diameter of 23.95 inches. 1857014 tires have a
diameter of 24.19 inches. Will 1857014 tires fit without scrubbiing any
body parts. I have been looking at the 1857014 michelin agility tires.
 

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165/65R14 OEM Insight tires have a diameter of 22.4 "
195/60R14 tires have diameter of 23.2" and I know these fit without rubbing.
185/70R14 tires have a diameter of 24.2" and the speedometer will be 8% too slow.

There is a risk that this tire will rub, but there is no way to know unless tested and also tested with the suspension compressed. Without testing by compressing the suspension it's possible everything will be ok until one day hitting a large pot hole or bump will cause the tire to rip out the fender linning
:(

I would not recommend buying a tire with such a large diameter for many reasons. The battery will drain much more quickly and often as the engine has to work much harder to accelerate the Insight. And fuel efficiency will take a large hit as well.


To solve this situation the real question must be asked:
Why do you want to buy the Michelin Agility tires?
 

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There is a cool calculator I found here:
http://pw1.netcom.com/~sgalaba/tiresize.htm

Many states have a 5-15MPH guideline buffer on highways speed limit enforcement to help catch the worst offenders, generate the most revenue per stop, and make any court challenges harder to lose. If you are trying to speed near the upper end of this range, this change will push you ~5MPH faster (rather, you will think you are going 5MPH slower than you are, and speed up even more), because the bigger tires are taking longer to rotate and the car requires mechanical rotation to determine its speed. So this may land you with an unexpected ticket. :lol:

Of course probably a stronger concern for many on this forum, is that your car will report less MPG. :shock:

So if you do this and care about MPG, you'll need to log adjusted mileage and calculate MPG at the pump using the mileage adjustment from the tire diameter changes.

-ShawnSt
 

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I agree that running such big tires is risky. But I don't agree that it will damage the fuel economy. The percentage difference is pretty small--certainly a lot less than the difference between 4th and 5th gear. And it decreases the gear ratio, so on the highway it will probably cause a slight improvement in economy, sort of like shifting into 5.1th gear.

The REPORTED mileage will be lower, though, because to go some given distance will take fewer tire revolutions. The computer will think you went 9.9 miles when you actually went 10. :D

Why wouldn't you run the stock tires? Until somebody markets a tire with better economy than the stock one, I don't see a reason to run anything else...
 

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Dougie said:
I agree that running such big tires is risky. But I don't agree that it will damage the fuel economy. The percentage difference is pretty small--certainly a lot less than the difference between 4th and 5th gear. And it decreases the gear ratio, so on the highway it will probably cause a slight improvement in economy, sort of like shifting into 5.1th gear.
Dougie, your observations that the gear ratio change affectively increasing mileage at highway speed is correct. But the more significant factor is the change in aerodynamics caused by the increase in frontal area caused by raising the car by almost 1 inch. By raising the car more frontal area of the front and rear tires are in the direct high speed air flow. And by raising the car more air will travel under the car instead of over the smooth body so air drag will increase. http://www.tfd.chalmers.se/~lelo/rvad/reports/rva2002_gr11_contribution-to-drag.pdf
 

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And as reported in these forums the lowest of the low rolling resistance tires are the OEM Bridgestones. All others have reported an MPG loss for the difference.

IIRC except a couple of euro LRR types, not available in the States.

And there are a couple of posts by single individual members that claim relatively lower losses for some type tires vs. the established -12% that Rick Reece and originalbadbob did in their tire swap test (-6% +-).

HTH! :)
 

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In Australia the OEM tyre is Bridgestone B391 165/65 R14 79T. I believe these are the same tyres used as OEM in the UK. I think that the B391 tyre is also the "equivalent" of the RE92 Potenza tyre used as OEM in North America - but I don't know if they really are the same tyre with a different name. In particular, I don't know if the B391 has the same low rolling resistance that I believe (based on what I have read on IC) the RE92 tyres have. The B391 tyres are listed on the Bridgestone Australia website but they are not claimed as being a high fuel efficiency tyre - even though other tyres on that website are.

The point of all this is that I am thinking of changing to Michelin Energy XM1 tyres. On the Michelin Australia website these tyres are claimed to incorporate "silica compounds" that are supposed to reduce rolling resistance without adversely affecting other aspects of tyre performance. In Australia these tyres are OEM on the Prius.

Unfortunately, I can't find any reference to "Energy XM1" tyres on the Michelin websites for the USA or UK. I think (though I'm not sure) that in the USA Michelin Harmony tyres are OEM on the Prius and in the UK they are Michelin Pilot Premacy. I do not know if these are the same tyres with different names. The Michelin USA and UK websites do not mention "silica compounds" in these or any other of their tyres (not that I could see anyway).

I "Googled" silica compounds and low rolling resistance and there are many hits. The Continental brand also seems to promote the use of silica compounds in low rolling resistance tyres.

If I was to use the Michelin tyres I would prefer either 175/60 R14 or 185/60 R14. The 175/60 is .79% smaller circumference (and slightly lower ride height) than the B391 OEM tyres and the 185/60 is 1.32% larger circumference (and slightly higher ride height).

Does anyone have any helpful comments or suggestions about my choice? I am specially interested in:
1. Anyone know anything about the use of silica compounds in tyres - is Michelin just talking a lot of BS?
2. My preference is for the 175/60 because they are closest circumference to the OEM tyres and do not raise the ride height (keeping in mind Guillermo's comment above) - but would the 185/60's be better handling?
 

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ghillie said:
1. Anyone know anything about the use of silica compounds in tyres - is Michelin just talking a lot of BS?
I remember way back when Michelin first "claimed" a higher silica formula in their tires. Toll booth operators _hated_ them. The reformulation allowed a static charge to build-up and they would get a painful zap when driver's paid the toll. The re-re formulation also required a higher % of carbon-black.

IMO the silica % isn't LRR magic. I would think it takes an overall approcah to the cord and sidewall too. Your % differences in ride height between tire choices is so small as to be under the MPG radar.

Yes, as reported here the Euro (and apparently down-under too) Bridgestone B391 is the RE92 Potenza equivalent. Sorry I don't know the Prius equivalents.

HTH! :)
 

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A big factor in rolling resistance is the heat loss from flexing of the sidewall, so an LRR tire tends to have a thin sidewall which makes it light for its size. So one thing to look at is the overall weight of the tire, although there are lots of other factors, too.

For example, if you look at the RE-92 on the Tire Rack web site, the 165/65R13 is 19 pounds, our 165/65R14 is 13 pounds, and the 175/65R14 is 15 pounds.
 

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ghillie said:
1. Anyone know anything about the use of silica compounds in tyres - is Michelin just talking a lot of BS?
2. My preference is for the 175/60 because they are closest circumference to the OEM tyres and do not raise the ride height (keeping in mind Guillermo's comment above) - but would the 185/60's be better handling?
1. Most if not all quality tires include silica compounds some more then others. I've read marketing material that states it "improves grip on wet roads". But marketing loves to grab a key cool sounding tire ingredient that's not top secret and use it in marketing. The art and science of manufacturing of tires is one of the most highly guarded secrets in the automobile industry. Try to get a tour of tire plant... good luck. I would not take the marketing literature about tires too seriously because they reveal very little info that could be useful for comparing different brands of tires of the same category.
The michelin Energy series of tires are designed and marketed as low rolling resistant tires. They are OEM on many VW diesel cars.

2. Comparing the exact same brand and model tire in these 2 sizes I can say with confidence the 175/60R14 would result in better mileage then the 185/60R14 tire because it's 10 mm narrower so it's more aerodynamic. (and a less significant reason in this case would be because it's slightly lowers the car). Realistically the difference will be small. Mesureable difference? maybe. Tires are responsible for causing up to 30% of the total air drag in a typical car.

Using a GPS i've found that the OEM Insight tires cause the speedometer to display 2% faster then reality. The slightly larger diameter of the 185/60R14 tires actually cause the speedometer, odometer and mileage in the dashboard display to be more correct, compared to using the OEM tires. Therefore the Insight is about 2% optimistic in the mileage display with OEM tires. since the 175/60R14 tires are 0.79% smaller then the OEM tires the Insight would theoretically display a mileage that is almost 3% optimistic compared to reality.

Comparing the exact same tire brand and model on the same 5.5" wide rims:
The 185/60R14 tire would provide slightly better lateral grip and handling compared to the 175/60R14 tire simply because it's wider.

Michelin Energy XM1 tyres are all season tires just like the Insight OEM Bridgestone RE92 tires. So they both provide huge compromise in many tire characteristics for a long tread life and mediocre/adequate grip in most road conditions. The advantage of the Bridgestone OEM Insight tire is that it provides the best mileage for the car.

What advantage are you hoping to get by switching to Michelin Energy XM1 tyres?
 

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Thanks for the answers :)

I want to use the Michelins to improve handling (especially in wet weather) without sacrificing fuel economy. I thought that if tyre technology has advanced since the OEM tyres were developed this might be possible. Michelin (and Continental and Bridgestone) claim to have developed an improved way of using silica compounds that does exactly this. But does it work??????

It is also relevant if the OEM B391 tyres are not identical to the RE92 OEM tyres. I have emailed Bridgestone in Australia and asked them how much the B391 165/65 R14 tyre weighs (following Guillermo's comment). This might tell me if the B391's are also lightweight. I have asked Michelin the same question about the XM1 tyres.

If I do change from the B391's I would prefer to go for the 175/60 size so as to retain as much fuel efficiency as possible. I assume though that the 175/60 size will cause the engine to be running slightly faster for the same ground speed and this may cause some increase in fuel use. Any thoughts on this or is the difference too small to have any measurable effect.

I guess I'm also interested in trying the XM1 tyres just to give something different a go - and reporting the results here. :D
 

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Oops! The comments about weight were from Dougie not Guillermo... sorry guys. :oops:
 

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I also want to minimize the "tramlining" effect.
 

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ghillie said:
I want to use the Michelins to improve handling (especially in wet weather) without sacrificing fuel economy.
I would suggest to abandon the all season tire and all it's compromises and try this high peformance summer only tire with low rolling resistance and the same aerodynamic size of the OEM tires.

165/65R14 Nokian i3
http://www.nokiantyres.com/passengercars_product_en?product=1170571&name=NOKIAN+i3

The tyre features three prominent main grooves, and lateral grooves open to the side, giving the tyre excellent hydroplaning properties.
The ecological nature of the Nokian i3 is particularly evident in two features. Similar to other Nokian tyres, no high aromatic oils are used in the manufacturing process. The tyre is also economical: it rolls easily and consumes little fuel.
I love this part:
The tyre maintains its grip properties in cold spring mornings and in the cool early autumn, even when temperatures drop below 10 degrees centigrade.
A summer tire that brags that is still provides grip at temperatures below 50 F. Imagine how much more grip it has at 80F :lol:

This is the tire i'm going to buy when my current summer tires wear out.
I'm very curious to find out what the mileage difference would be between the OEM Bridgestone RE92 and the Nokian i3 in the same size.
 

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A tyre that works below 10 degrees C is pretty much all season where I live. Unfortunately I don't think Nokians for cars are available in Australia but I will do some more searching.
 

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ghillie said:
A tyre that works below 10 degrees C is pretty much all season where I live. Unfortunately I don't think Nokians for cars are available in Australia but I will do some more searching.
Yes but in warmer weather this Nokian summer tire would be significantly better then any all season tire, rain or shine.
 

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Guillermo - what I meant was that the Nokian summer tyre you refer to would do me all year round as it rarely gets below 5 degrees C as a minimum here in Melbourne - so I am interested in them. However, I don't think they are readily available in Australia (from my brief search so far) but I am going to check.

If I can find them I will certainly consider them - price may be a factor.
 
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