Are tall skinny tires the future?

[TexasCotton]

Originally Posted by CapriRacer

You have to be really careful here. "Skinny" can mean different things.

If you start with a 185/65R15 and go to a 175/65R15 (which is your question), you are not only getting a smaller diameter, you are also getting a lower load carrying capacity, which has safety implications (that is, a more intense loading is directionally towards more frequent tire failures.)

PLUS, that is the wrong direction for RR. Tires don't like being more intensely loaded and one of the ways they exhibit that is in the amount energy they consume - ie, Rolling Resistance.

But "skinny" could also mean "narrower, but taller" - like going from 185/65R15 to 175/70R15. The problem here is that load carrying capacity plays more of a role in RR than width.

If you want to improve RR by changing tire size, get the largest tire that will fit under the fenders - without rubbing, of course. There is a couple of percentage points to be gained here.



Barry's Tire Tech

You have stated several issues and now am lost and concern
Your terms quoted "skinny, tall, and large" just confuse and jade my perspective and not my understanding

Clearly going from 15 inch to a large rim 17 inch only reduce mpg and there is a thread already that is active to that accounts for that very experience

[TexasCotton]

Originally Posted by TexasCotton

Hello all
I have not posted in this forum long long time.However have follow some of the regular and impressive posters.
I have the following question ,concern , issue, etc

I have a 2004 Toyota Prius (Gen 2) OEM tire size is 185/65R15
so I have 15 inch alum oem rims.
I have witness others go with michelin energy X, brigdestone ecopia LRR tires and kept the oem tire size rating and above 44 psi inflation with minor mpg gains of 1-2 at best. The issue question is would a "skinny" tire make any improvement.
Specifically would a tire size of 175/65R15 make any postive mpg improvement

I listed oem spec above for the fact that I want to stay with the oem rims and maybe consider a mountable tire like 175 size .... I do not want to spend more money on different rims that reduce mileage seen that, read that , do not want to go that misdirection

[RedDevil]

Originally Posted by TexasCotton

You have stated several issues and now am lost and concern
Your terms quoted "skinny, tall, and large" just confuse and jade my perspective and not my understanding

Clearly going from 15 inch to a large rim 17 inch only reduce mpg and there is a thread already that is active to that accounts for that very experience

Ah, you mean this thread.
That's all about changing the rims but not the outer diameter of the tires, as to not offset the speedo and gearing.
To have bigger rims with the same thread diameter you have to decrease the sidewall height, which means those lower sidewalls will bend (relatively) deeper and cause more friction.
Those tires are not taller, they just have a bigger hole on the middle.
(gotta coin #bigholetires to demean them GTI boys' rubber strips on halved oil barrels)

This thread is about tires with a bigger outer diameter. So the rims have to grow in diameter too, or the sidewalls would get too high.
A bigger size (circumference, largeness, tallness) means also a larger contact area with the ground, so the tire can be made narrower (skinny) to compensate.

[euromodder]

Originally Posted by NachtRitter

Psssh... figures. Not even sure why they bother doing a press release if nobody in the "real world" can buy them... well, I suppose I know why, but it doesn't help them IMHO...

PR ...

Just like Nokia e.a. claiming they have A-A rated tyres (on the new-ish EU tyre labelling system) while they are simply not available, or only available in limited numbers, in limited sizes (limited as in 1 size ... ) .

[euromodder]

Originally Posted by TexasCotton

You have stated several issues and now am lost and concern
Your terms quoted "skinny, tall, and large" just confuse and jade my perspective and not my understanding

If you go for narrower tyres, the profile height needs to be increased to keep the same (or similar) tyre diameter.

185/65R15 stock :

You get the sidewall height by multiplying the width (which is in mm),
185,
by the profile height ,
65,
and divide by 100

This value should stay about the same on the alternative tyre.
So you'd need 175/70R15 to keep the diameter constant.

If you increase this value, the tyre will be bigger, do less revs, and so your engine will do less revs - good for fuel efficiency, but ... not always.
If you overdo it, it can actually hurt your FE.
Quite a few people here are running slightly taller tyres than specified by the car manufacturer - I'm one of them.



You can compare alternative tyre sizes here :

Tire Size Calculator - Tire & Wheel Plus Sizing

It'll also give you an idea wether there are any tires available in that size.


You must keep an eye on the tyre's load index.
Smaller tyres may have a lower load capacity than what's required for your car.
Make sure you stick with at least the same (or higher) load rating !

[mcrews]

There are several threDS on the ADVANTAGEs of taller tire. Need to be AT LEAST 5% larger diameter to see noticeable mpg improvements

[TexasCotton]

Originally Posted by euromodder

If you go for narrower tyres, the profile height needs to be increased to keep the same (or similar) tyre diameter.

185/65R15 stock :

You get the sidewall height by multiplying the width (which is in mm),
185,
by the profile height ,
65,
and divide by 100

This value should stay about the same on the alternative tyre.
So you'd need 175/70R15 to keep the diameter constant.

If you increase this value, the tyre will be bigger, do less revs, and so your engine will do less revs - good for fuel efficiency, but ... not always.
If you overdo it, it can actually hurt your FE.
Quite a few people here are running slightly taller tyres than specified by the car manufacturer - I'm one of them.



You can compare alternative tyre sizes here :

Tire Size Calculator - Tire & Wheel Plus Sizing

It'll also give you an idea wether there are any tires available in that size.


You must keep an eye on the tyre's load index.
Smaller tyres may have a lower load capacity than what's required for your car.
Make sure you stick with at least the same (or higher) load rating !

Okay I somewhat understand your statement and is in line with my personal perspective and thinking. Going from 185/65R15 OEM spec to 175/65R 15 and/or 175/55R 15 may be inline with that mindset. Not that I want to single other thread posters out however many make the comments of taller, larger, skinny and other relative terms that detract from the clarity to my specific application.................
fyi there are other tire calcs out there that do not require security codes......

[RedDevil]

Originally Posted by TexasCotton

Okay I somewhat understand your statement and is in line with my personal perspective and thinking. Going from 185/65R15 OEM spec to 175/65R 15 and/or 175/55R 15 may be inline with that mindset. Not that I want to single other thread posters out however many make the comments of taller, larger, skinny and other relative terms that detract from the clarity to my specific application.................
fyi there are other tire calcs out there that do not require security codes......

For your specific application, if you mean 175 wide tires by that, you clearly need a higher sidewall/threadwidth (the 2nd number in the size code), not lower.
If your OEM tires are 185/65R15 you'd need 175/70R15 or maybe 175/75R15. The first is a tiny bit less tall, the latter is slightly bigger and should yield the best FE of both.

The gains are marginal though, and 185 is a good width for a Prius. I bet OEM size comes cheaper and gives you more choice of make and type. It may not be worth it to go narrower than that on this relatively heavy car.

[euromodder]

Originally Posted by TexasCotton

Okay I somewhat understand your statement and is in line with my personal perspective and thinking. Going from 185/65R15 OEM spec to 175/65R 15 and/or 175/55R 15 may be inline with that mindset.

If you go to the same or lower profile heights, the tire diameter will be smaller, and your engine will rev higher - that's not the way you'd want to go for fuel efficiency.

The Prius' CVT complicates matters a bit, as it'd try to lengthen the gearing to get the rpm low again.

[cRiPpLe_rOoStEr]

Originally Posted by euromodder

The Prius' CVT complicates matters a bit, as it'd try to lengthen the gearing to get the rpm low again.

In a modern electronically-controlled CVT it's possible to overcome that issue.