Rook, this one is especially for YOU, because of your focus on weight - even to the extent of ounces and fractions of an ounce. This mod is about POUNDS of weight loss and VERY significant drop in rotational moment of inertia, which affects handling, overall weight, and acceleration - a 3-in-1 impact.

I looked up the weight of the OEM Bridgestone tires on my 2017 ZX-14R (HARD to find!), and realized that:
- the front tire = 9.25 lb
- the rear tire = 14.75 lb
- Total = 24.0 lb

I started looking for lighter, high performance replacements for when the OEM tires wear out, and found that a prime contender tire pair is one that I have had great previous experience with on 2 different bikes: Pirelli Diablo.

These are available in the correct same size as OEM, have a "W" speed rating, have the exact same load capacity each as the OEM front and rear, and are relatively inexpensive. Here's the eye opener:
Pirelli Diablo Rear = 12.90 lb
Pirelli Diablo Front = 9.00 lb
Total = 21.90 lb
This is 2.10 lb less than the OEM tires!

The 2.10 lb weight reduction is impressive all by itself, because once we get past installing a Lithium battery and lighter exhaust, we usually struggle to find other mods that are measured in pounds of weight reduction versus ounces.

But the reduction in rotational moment of inertia is even more impressive.

Moment of inertia for a rotating wheel/tire assembly is proportional to the sum of each increment of mass times the SQUARE of that mass's radius from the axle. The tire is usually the heaviest individual component of the wheel assembly - heavier than the chain, the sprocket, the brake rotor, and usually even the wheel. Even more sigficantly, being the outermost component of the wheel assembly, the tire by definition has the largest radius. And that radius gets SQUARED when calculating the rotational moment of inertia.

The rotational moment of inertia (RMOI)is a measure of how HARD it is to tilt the wheel (for turns) and to first accelerate the wheel in order to then accelerate the bike. This means reducing RMOI makes your bike handle more nimbly AND accelerate more quickly.

Notice in this OEM versus Pirelli Diablo weight comparison that the weight difference between the 2 sets of tires is almost entirely concentrated in the REAR tire. You're taking 2 lb off the mass that is concentrated at the outermost radius of the wheel assembly. This is mammoth.

But it gets better. You can supplement this effect with a lightweight rear sprocket, which takes off another full pound from that rear wheel. This has a much smaller impact on RMOI but the one pound pure weight reduction is notable.

Also, the combination of the lighter tires and rear sprocket also moves the center of gravity for the bike as a whole slightly FORWARD. On a high speed bike like the ZX-14R, this is a huge plus, echoning whT kawasaki tried so hard to do in the design of the bike. Ever noticed how far forward the engine, radiator, cockpit, and front fairing are on this bike versus other bikes? Look carefully at a profile shot of a ZX-14R and compare to other sportbikes. You'll see that emphasis on forward weight. (That's why that "gas tank" cover is so looooong, as a result)

I've got the tire on order and already have had the sprocket for may weeks. I just don't want to "waste" the OEM tires by taking them off too prematurely. :)

Jim G

hmmm yes but get the composite wheels and the polar MOI is increased and with less mass the MOI is decreased - a twofer - its only $$

Cruderudy: I did the BST wheels on the Yamaha R3 I am currently preparing to sell (ready to move on to the ZX-14R as the main project bike). The improvement WAS dramatic. But, interestingly, the weight loss was much larger on the R3 than it would be on the ZX-14R, because the ZX-14R comes with pretty light OEM wheels compared to typical OEM wheels.

The bigger deterrent is the cost. Here in Canada, a set of BST wheels for the ZX-14R, after shipping, currency exchange, customs, sales taxes, etc gets pretty close to $5k, which is NOT in the budget.

Furthermore, once you sell a bike withBSTs, you really reduce the size of your potential market unless you want to take a BIG financial bath, because the BST wheels are too high a percentage of the bike's value tacked on to the bike's price. I'm probably going to have to sell the BSTs on the R3 separately from the R3. And even then, I'll get only a portion of what they cost me.

So, no to carbon fiber wheels on my ZX-14R.

Jim G

* Last updated by: JimGnitecki on 4/20/2019 @ 9:46 PM *

wow that price is insane ... I never considered it but I think the cost here is like $3500 think Rook may have BST though

I started looking for lighter, high performance replacements for when the OEM tires wear out, and found that a prime contender tire pair is one that I have had great previous experience with on 2 different bikes: Pirelli Diablo.

As for the effect of tire weight on handling, I can't say if I notice it or not. It's true the Pirellis handle better than other tires I have used but I also have only used the Pirellis with a 190/60 and 200/55 aspect for the rear. The larger diameter must add weight but it also makes turn in and a lot quicker and I believe it also improves corner grip. SO light weight isn't everything when it comes to handling, far as I can tell. Ideally, I guess you'd shim the rear or lift it by some other means and go with as light of a 200 width tire as you could find. The 200 tire has a sharper profile and tips in better. I even noticed a difference going from 190/50 to 190/55. 200/55 is even better.

I never considered it but I think the cost here is like $3500 think Rook may have BST though

Rook: The Diablo and the Diablo Super Corsa and other Diablo variants are all different weights. Deniis Kirk is the only website that shows the weight for each tire they sell, with very few exceptions for which they themselves were not given a weight by the factory. The differences from model to model are very interesting and patternless. The plain "Diablo" is the lightest. It is also less costly.

Jim G

If you're buying tires by weight rather than performance, I think you're on the wrong machine. ZX-14s are hard on tires in any case, and the bargain skins like Pirelli Diablos and Conti Motions won't last OR perform worth a crap on a bike with this much power and weight. The power will waste any back tire with enough miles and abuse and the front suffers from the weight. Stick with the better tires and forget about tires as a weight factor.

"kawasaki tried so hard to do in the design of the bike"..lol.It's a drag bike first and foremost.That's how it was designed;)They didn't 'try so hard'...they built it the way they wanted.Gotta have weight over the frontend for those killer launches.I think sometimes people get the impressions that 'they could have..'such and such.That's not who they are.Yeah,'they' could do a lot of things different.They don't want to.

Diablos are really good tires.Used to be that's all I put on there.

* Last updated by: Grn14 on 4/23/2019 @ 5:50 AM *

Danno: For tires, light weight IS performance. For the reasons I mentioned in the first posting in this thread, a lighter weight tire provides huge advantages. Yes, you can ALSO specify tires that have specific profiles and specific single or multiple rubber compounds, and differing degrees of tread (depending on how much wet weather riding you do), but in the final analysis, a lighter tire is always going to be a more nimble tire, and for sportbikes (unlike tourers), nimbleness is key. Bicycle riders will tell you the same thing, which is why sew-up tires are so strongly preferred over clinchers.

It is true that a lighter tire will often have a shorter mileage life, because in general it will have less rubber, and rubber that is optimized for traction versus long life. But I value nimbleness and safety WAY above the number of miles I get from a set of tires.

Here's a simple analogy to help clarify what is going on with a light weight tire versus a heavy tire:

Imagine you are running a foot race over a winding (not straight)course. Imagine running it in the best lightweight racing running shoes. Now imagine running it in a pair of heavy shoes, or to really make the point vividly, boots. BIG difference in your performance and your pleasure.

Jim G

It is true that a lighter tire will often have a shorter mileage life, because in general it will have less rubber, and rubber that is optimized for traction versus long life.

How about buying a Super Corsa and wearing it out some? Then it would be as light as the Diablo. You get longer wear plus you eventually get a lighter tire if you keep it on long enough.

OK now you got me thinking. I am now going to need to weigh my old tires after they are removed from the rim to find the lightest weight worn out tire. That's the winner!

Which is lighter, a worn out Diablo or a worn out Super Corsa??

I had BST's on my 14.Honestly couldn't tell very much difference in handling.Sorry to say.However...when leaned in at over 110 mph,the chassis waddled.I tried tightning up the suspension to no avail.The bike was way to firm to feel good on.Didn't stop the wallowing either.Probably very good at the drags or something like that.But fast cornering...kinda scary.Tires were Pirelli Angels.In decent shape.Once I returned to the stock wheels,it stopped all that.They did have 2 types for the 14.I got the cheaper ones(not as thick I think).Still VERY expensive and they didn't inspire confidence at all.Over 4K and then some.

Thanks Grn. I better keep doing my homework. I was considering the narrowest rim without the interior reinforcement. I'm going for lightest. Still building an LSR bike outta the busa. Perhaps I will learn an expensive lesson. The 14 is a heavy bike and that might be the reason for the handling characteristics you experienced with BSTs.

Carbon Fiber wheels tend to expose flaws that are masked on a bike by the dampening effect of heavy wheels.

On my Yamaha R3 I notice an immediate notble improvement in nimbleness, but also "uncovered" some things that had been hidden by the weight of the OEM wheels. Within the very first 1/2 mile of riding after installation of the BST wheels, I realized just how much the heavy OEM wheels (11.4 lb heavier than the BST wheels!) had been dampening the ACTUAL surface of the highway pavement by the motorcycle shop that did the mounting of the wheels for me.

At first, I seriously thought that maybe they had not done the wheel balancing correctly, but then realized that I was now feeling what the pavement ACTUALLY felt like.

Other motorcycle owners with Carbon Fiber wheels, and even some magazine test reports, have reported how the installation of BST wheels has exposed warped brake rotors, marginal wheel bearings, and slight chain alignment shortfalls.

This should not surprise us. We all know that on cars with stylish but overweight wheels that are too heavy, the drivers lose road feel, and that big heavy cars are more "comfortable" for people who are NOT performance drivers.

Weight is an effective dampener, but sportcars, and sportbikes, reject weight for that very reason.

Grn's "waddle" was exposed by the BST wheels. It was there all along, but was sufficiently dampened by the weight of the OEM wheels spinning at 110 mph (VERY high moment of inertia at that speed).

Jim G

* Last updated by: JimGnitecki on 4/24/2019 @ 7:26 AM *

(VERY high moment of inertia at that speed).

Nope- MOI is a physical property of the structure, the angular momentum was very high. Sorry can't not be a smart ass here

Yes Cruderudy, you are correct. :) The point is that with a heavy wheel doing 110 MPH, there's a LOT of resistance to change and thus a lot of dampening of any disturbances that would have otherwise manifested, and DID once the wheels were lightened significantly,

Did you guys know that on the "performance package" version of the Mustang GT350, Carbon Fiber wheels were included? And the car magazines loved them.

Jim G

Good thread and discussion Jim

To me the light wheel is only really beneficial for racing where acceleration and 1/4 or lap times in races are won or lost by msec's. The rotating wheel mass is a critical component of the suspension dynamic architecture. One of the reasons we all love the zx14s is the over powered over damped over-weighted design of the beast. (sorta like boats and airplanes too - always get the biggest motor possible)

For the price of the light metal or composite wheels I can buy a used 10R and really reduce my lap times. I dont even have the all the rage composite wheels/rims on my fancy Colnago C50 road bike because I want the durability of the AL rims not the uber light wheels and the roads around here are actually in relatively good shape pothole wise.

Crude!LOL.So Jim,you're suggesting my 14 had suspension issues then,just hidden with the stock wheels?Well,I had an Ohlins shock for the 14 on there(a TTX or something).Dialed it in virtually as firm as it would get.Wallow.I still believe it was the BSTs flexing.No road's perfect.But with stock wheels,I actually was moving faster through that one particular curve with zero chassis movement and right at the factory shock 'mid' setting.On the ohlins( it had to be dialed all the way down to match).So it was actually slightly firmer.I will say that curve is a very smooth surfaced curve.So it wasn't like the chassis was bouncing or anything.I was solidly planted.Like I said...that particular set of BST's I got were the 'lighter' version.They did have a heavier(meaning composition design,not weight wise) version for drag racing(I assume).Perhaps those would be fine?IDK.

* Last updated by: Grn14 on 4/24/2019 @ 9:15 PM *

It's hard to believe that anyone could get a motorcycle Carbon Fiber wheel to flex, especially when CF wheels don't even flex under the MUCH higher loadings of supercars where both weight and speed are higher. I really do think that the CF wheels on your 14 just exposed something that heavier wheels hide.

That something could have been the Angel tires. Angels are NOT hi-perf tires. Pirelli itself describes them as "Sport Touring tyre built to last". The words "touring" and "built to last" in that official description are serious clues.

Or it could have been just a hair too little psi in the tires for the conditions at the time.

Or it could have been slightly loose wheel bearings.

Many possibilities.

Jim G

* Last updated by: JimGnitecki on 4/24/2019 @ 10:46 PM *

lol.Could have been a lot of things I suppose.Comparing motorcycle wheels to car wheels isn't exactly accurate.I don't think so anyway.3.5 width front compared to...what's a car wheel width?6" back wheel.Oh yeah.They'll flex.They're not solid.They're supposed to flex some.Especially at higher speeds with a 570 something lb motorcycle on em.In a corner.Now for a lighter bike...like your R3...yeah.I can see they'd stay flex free mostly.If the stock solid wheels aren't allowing chassis movement like described,and then putting on these CF wheels in the circumstances...and the bike moving around,that tells me the wheels are moving.If the stockers don't allow this,but these do.I gotta say...I've ridden Angels several times over the years.They stay secure at higher speeds on a big bike like the 14.If they didn't,I would have ditched em in a heartbeat.That's one thing I don't minimize.Tire performance.Not with the riding I do.Don't let 'high mileage' monikers put ideas in yer head about performance(and I don't mean mileage).At least with the Pirelli lines.

* Last updated by: Grn14 on 4/24/2019 @ 11:18 PM *

I got lucky!

As most of you guys undoubtedly know, because of the way motorcycle tires are manufactured, their weight varies from tire to tire even for supposedly "identical" tires.

My Pirelli Diablo tires arrived yesterday and the COMBINED weight is a bit better than the statistical average to be expected based on tire manufacturer specs:

The rear Diablo actually weighs in at 12.31 lb (versus 12.90 expected for the Diablo, and versus 14.75 for the OEM Bridgestone).

The front Diablo tire weighs in at 9.40 lb (versus 9.0 expected for the Diablo, and versus 9.25 for the OEM Bridgestone.

So the COMBINED actual weight for the pair of Diablos is 21.71 lb versus 21.90 expected, and versus 24.0 for the OEM Bridgestones.

So an actual reduction of 2.29 lb (9.5%) versus the Bridgestones.

Yes, I could keep the Bridgestone on the front and lose another 0.15 lb versus the Diablo front, but I don't like to mix brands and models of tires without a more compelling reason. When I DID mix brands on another bike I owned, a 2014 Harley Breakout, the result WAS a giant performance improvement (beyond the weight reduction) over OEM. BUT that motorcycle came from Harley with a radial tire on the rear and a bias ply tire on the front - no kidding - proving that even usual rules sometimes need to be broken - even by manufacturers. :)

Note that by going to the Diablo,I am taking a full 2.44 lb off the rear tire. Plus I am taking off another 1.01 lb off the sprocket, for a total rear wheel weight reduction of 3.45 lb, which is pretty significant in terms of moment of inertia reduction.

Jim G

* Last updated by: JimGnitecki on 5/1/2019 @ 12:59 PM *

Cool. Watch out or you'll have people ordering tires by the dozen, selling the ones that are heavier and keeping the lightest for their bike!

Hey, when I lived in Austin, and had local access to a friend's motorcycle shop where he actually STOCKED, not merely custom ordered, performance tires, I used to bring my digital weigh scale with me when shopping for new tires, and he let me weigh multiple tires and select the lightest one. He said that since NO ONE else seemed to care about tire weight, he figured why stop me. :)

Jim G

I would do the same thing. I wonder if the lighter ones wear out quicker though?

No idea if the lighter ones wear out faster, as I don't know in which components of the tire the manufacturing weight variations occur.

But, I do know they vary significantly for motorcycle tires of the same model from the testing I did back in Austin.

Jim G