Bridgestone Announces Large Diameter Narrow Tires

[sheepdog 44]

The benefits:
Taller gearing when converting from a smaller diameter tire without the common issue of the larger diameter tire having higher rolling resistance and more mass.

Tall skinny tires have a contact patch that is longer than it wide. Giving it better traction than a smaller tire of the same width.

Taller tires have less deflection due their larger diameter. lowering rolling resistance.

Higher tire pressure designed for a tire with a smaller sidewall.

That is the concept. Will there be more weight? The specs i know of are only for the wheel, which is 15lbs vs the lightweight 11lbs Insight wheel. Will the extra weight negate the benefits of a large corporation engineering a tire specifically for low rolling resistance with millions of dollars in R&D budget? Absolutely NOT! what a baseless thought!

[NeilBlanchard]

The geometry of a larger diameter tire means that the "wedge" formed by the tire at the road surface has a mechanical advantage to lift the tire over the bumps in the surface.

All else being equal, it will roll better - which is the whole point.

[niky]

Originally Posted by P-hack

Then why is it here?

Because Neil posted it. But honestly, good PR copy has to be understandable to a wider audience. Even though this is PR copy, it answers some of the questions you've been asking.

Perhaps the "higher pressure" part should be further explained, as that part is definitely written poorly. I believe it is meant to suggest the tires can accomodate higher pressures than regular tires safely.

Originally Posted by P-hack

Again, baseless. Crappy writing if that is the case (already too much of that on the web). The only thing this article is good for is wild speculation.

It's a Bridgestone press release. If they quote numbers, then those numbers will have come from internal testing. Whether they're completely BS numbers, fudged cherry-picked statistics or an honest-to-goodness comparison between the large and narrow tire and a control tire with the same compound and tread pattern, only Bridgestone know.

[P-hack]

FWIW, there is a lot of conflicting info on the web about this stuff, and this article is no exception and doesn't clarify anything.

i.e.:
Barry's Tire Tech
says larger and wider is better RR.

Originally Posted by sheepdog 44

The benefits:
Taller gearing when converting from a smaller diameter tire

in a properly geared system this would be wasteful since the gearing from the engine is always reduction, you would have to reduce it even more to compensate for the final increase.

Originally Posted by NeilBlanchard

The geometry of a larger diameter tire means that the "wedge" formed by the tire at the road surface has a mechanical advantage to lift the tire over the bumps in the surface.

I don't think that is it, they aren't testing on a washboard, and higher psi means you have to lift the entire wheel with every bump instead of deforming around it.

Like I said, lots of conflicting info, starting to think that tire/road dynamics are a lot like aerodynamics, you HAVE TO TEST to know if changes are good or bad (and you have to share the results IN A MEANINGFUL WAY).

Even the impetus for this very tire, the deltawing racer, is not a fan of larger diameter:
"“The front also has 15-inch rims for brake discs,” says Marshall. “Rim size is all about getting brake discs in. Clearly with race cars, it’s not like road cars, where the bigger the rim, the better for some people. It carries a lot of inertia with it. Big rims aren’t necessarily good for performance. You get the rim big enough to fit your brake package.”"
Tall, thin, FAST tires - Article - Modern Tire Dealer

Case and point, the tires are not 20" tall, if bigger=better.

[P-hack]

Originally Posted by niky

Perhaps the "higher pressure" part should be further explained, as that part is definitely written poorly. I believe it is meant to suggest the tires can accomodate higher pressures than regular tires safely.

Tires are tested for Coefficient of Rolling Resistance, and they have moment of inertia, without that it is marketing bile. EVERY company says their crap is the best, no point in regurgitating it. And even then it depends on the application.

[NeilBlanchard]

Small bumps count, too.

Why does the VW XL1 use similar tires? And every solar racer ever made?

[P-hack]

Originally Posted by NeilBlanchard

Small bumps count, too.

Why does the VW XL1 use similar tires? And every solar racer ever made?

you reach a point of negative returns when considering inertia vs diameter. I would be more inclined to think that increased bearing drag is more of factor in RR of smaller tires.

The xl1 uses 15" tires, the bridgestone ecopia solar racer tire is 14" (and meant for lighter vehicles). There isn't a simplified "bigger diameter" is better generalization here. Application (such as vehicle weight) are an engineering consideration and tires are full of engineering compromises. If we try to oversimplify it, it is like selling vacuum cleaners by the number of wall amps they consume.

Like I said, tire width/diameter/etc depends on the application:


We don't know anything about how these tires will perform on a random vehicle.

[sheepdog 44]

The only way we will know for sure is by experimental data. I would love to buy either the BMWi3 or XL1 tires. I suspect i'll only be able to get my hands on the I3 tire when it comes out in the US. But that is IF i can find a wheel with the right bolt pattern that isn't exspensive.

Now the XL1 tires are a perfect replacement as they actually have the same outside tire diameter as the ones that go on my stock 14inch wheels. No gearing benefit, but they are super skinny, and the XL1 is in the same weight category as the Insight! These would be the first modern LRR tires with such a skinny width. Sadly i suspect the XL1 tires will be unobtanium even when it is shipped to customers in Europe.

[NeilBlanchard]

The VW XL1 has 115/80 R15 front, 145/55 R16 rear - narrow and tall tires. The Bridgestones in question are similar OD to standard 16" diameter tires.

Deflection is essentially like rolling uphill all the time, and even the small surface bumps in the paving add a little to that. A larger diameter wheel "bridges" across more of those bumps, and all else being equal, a larger diameter tire will have lower rolling resistance than a smaller diameter tire.

Consider bicycles.

[sheepdog 44]

You can buy compact spare wheels that'll fit the tires on the XL1 and BMW i3. It's not too much trouble, i could cover the cost by selling my stock alloys. For me i'd need to get a pair of 4x100 to 5 x 114.3 wheel adapters. Any spare 16 inches and up will have a 5 bolt pattern.

The 115 80 r15 on the front wheels of the XL1 can be got from a Mini cooper in my 4x100 stock bolt pattern. Which would be great, but 115 is for the non driven front wheels, not the 145 rear drive wheels. Could be sketchy, but i wonder how much mpg i could get.

A few of the stock spare tires have a highway speed rating. But all spare tires have an F or worse rating in rolling resistance!