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[Richard230]

I am a little mystified about the tire pressure recommendations for the 2014 Zero S (I don't know what was recommended for the 2013 bikes).  My 2012 Zero recommends 32 psi in front and 35 psi in the rear tire and that seems to work well.  Since there is no other recommendation for different loads, I assume that this pressure will accommodate the bike's 641 gross vehicle weight.

The 2014 S has a gross vehicle weight of 765 pounds and it uses the same tire in the front as the 2012 bike, with a 10mm wider tire in the rear.  But the recommended tire pressures are 30 psi in both the front and rear tires.  As someone who typically uses 36 pounds in the front tire and 40 pounds in the rear tire of all of my other motorcycles, Zero's recommendation seems kind of low to me.   

My gut feeling, based upon owning a lot of different motorcycles over the years would be to put 34 pounds in the front tire and 36 to 38 pounds in the rear tire.  This would approximate what I used in my Suzuki SV650, which uses wider front and rear radial tires on wider rims.  Perhaps because the tires are a bias-ply construction that accounts for the lower pressure?  It just seems too low to me, though.

Does anyone else have any thoughts?  Has this pressure worked OK in the 2013 models?  Does anyone else care besides me?   

(The attached photo was taken from an unsold 11.4 S on my dealer's showroom floor.)

[spelunker]

I use the pressure that is stamped onto the side of the tire.

[BrianTRice@gmail.com]

The usual recommendation under load is to increase by a few pounds the pressure of the tire that will mainly take it (the rear for passengers and luggage). Also, pressure recommendations are typically minimums to avoid tire stress and wear. I find that it works fine to add a few pounds pressure to the tire and let it gradually decrease to the minimum before I re-pressurize it. Higher pressure can help with mileage by reducing the footprint / rolling resistance of the tire, at some expense to traction.

So, honestly, I pressurize both tires on my 2013 DS to 38 and 40psi, respectively.

[LiveandLetDrive]

I use the pressure that is stamped onto the side of the tire.

Aren't those maximum values?  Seems not ideal, if you want to stay attached to the road at least.

[spelunker]

Hasn't been a problem. In fact, I get better mileage.

[Burton]

I use the pressure that is stamped onto the side of the tire.

Aren't those maximum values?  Seems not ideal, if you want to stay attached to the road at least.

You should always use max sidewall cold pressure if you want to stay glued to the road. The more air pressure the smaller the contact patch and the greater the weight per square inch on that contact patch. Expert witnesses for motorcycles will tell you this is accurate and it is a sure way to avoid hydroplaning as more uplift is required to cause it. If I recall correctly too the channels in your tire work better at the max cold psi stamped on the sidewall and your tire wear should reduce when this number is maintained.

My current bke, pregen ninja 250, has two bt45's on them rated at 41 and 42 psi ... guess what they are currently set at
I ride year round and have never had an issue with the tire slipping out in sporty conditions and in heavy rain. My rears last about 9k before I replace them and the front about 16 to 19k.

If you want a lot more detail on this I would suggest reading motorcycle safety and dynamics vol1, I dont think vol 2 has anything on tire pressure.

[NoiseBoy]

If you are setting your pressures to the max when cold, they will be well over when on the highway.

I find experimentation is the best option.  On my KTM the supermoto tyres were rated up to 38psi or something but i ran them at 24/25 for best results.  They felt awful above 28.

Can you post a section of that book on running higher pressures? It doesnt sound right to me.  If you walked down a wet slope in stilettos you would be much more likely to slip than if you were wearing trainers despite having more pressure on the heel.  The hydroplaning thing makes sense but i have never experienced it on a bike regardless of pressure.

[Burton]

If you are setting your pressures to the max when cold, they will be well over when on the highway.

The tire sidewall indicates the MAX PSI number when COLD, just ran down stares to check my spare tires in my garage to confirm. This to me indicates the designers are aware the tires are going to warm up.

I find experimentation is the best option.  On my KTM the supermoto tyres were rated up to 38psi or something but i ran them at 24/25 for best results.  They felt awful above 28.

I simply go by the manufactures tested guidelines when setting my pressure. If anything the bike feels better with higher pressure as the aspect allows for the bike to flick more.

Can you post a section of that book on running higher pressures? It doesnt sound right to me.  If you walked down a wet slope in stilettos you would be much more likely to slip than if you were wearing trainers despite having more pressure on the heel.  The hydroplaning thing makes sense but i have never experienced it on a bike regardless of pressure.

If your wearing stilettos your balance isn't on your heal it is on your toes. However I will assume you have observed someone fall over more in heels when the heel strikes the ground first. Even if you do this there are other variables to consider when trying to determine the likely causal relationships.
What was the surface like, what material was found on the end of the heal, were there any obstructions (even small) which caused the fall, how fast was the person moving, was the person distracted in any way from the task of waking in heals, etc. Also I might note when walking down a slope you walk on the balls of your feet as well (near your toes) to keep balance even in sneakers.

The only time I have seen someone fall in heals was because they tried to walk like they normally do and fast without practicing first or when the heal breaks.

Moving on to tire pressure.

The tire pressure in your manual only refers to the tires that come with the bike. The moment you buy new or different tires the recommendations change. Max Cold sidewall pressures set by tire manufactures are given to indicate the highest PSI to obtain the longest life of the tire.

The trick in proper tire inflation is to pump in as much air as is safely possible without reducing the traction necessary for acceleration, braking, and handling. Too little air causes your tire to flatten out under load, and the resulting distortion means increased "rolling resistance" (drag) and decreased gas mileage. Too little air also means your tires will be getting an uneven grip on the road, which will cause some portions (typically the outside edges) to wear more quickly than usual, shortening tire life.

A typical tire with a maximum recommended pressure of 32 pound per square inch has a safe pressure range of 24-32 PSI. Variations within that range won't affect traction that much, but they will affect your gas mileage, ride quality, and tire life. At 24 PSI you'll get a softer ride but lower mileage and faster tread wear, while at 32 PSI you'll get a rougher ride but higher mileage and longer tire life. Not surprisingly, in pre-energy crisis days auto makers recommended 24 PSI, but nowadays a lot of them recommend 30 or 32.

The relation between air pressure and mileage goes something like this: 10 percent underinflation (with 24 PSI being the norm), 5 percent mileage loss; 20 percent under, 15 percent loss; 25 percent under, 20 percent loss. As for pressure/tread life, 15 percent underinflation mean 10 percent loss of tread life; 25 percent under, 20 percent loss; 50 percent under, 40 percent loss. These figures are meant to give you the basic idea and are subject to considerable fluctuation depending on individual conditions.

By the same token, if you increase pressure from 24 to 30 PSI, you'll increase your gas mileage about 3-4 percent (more in some cases) and your tire life maybe 3-6 percent. As a general rule, the best thing to do is check the maximum safe pressure printed on the side of the tire and maintain inflation at or slightly below that level. (Caution is advised with older tires. For accuracy's sake, make sure you check pressure when the tire is cold, using your own gauge if possible.) The ride may be a tad on the rocky side, but think how patriotic you'll feel.

As for the section in the book that will have to await. I searched all my HD's I currently have plugged up and only found my volume 2 copy -_- I suspect since I first ordered vol 1 back in 2011 it is on another HD so I will have to hunt it down as I don't feel like paying 3x more than what I paid in 2011 for the same product

[Richard230]

I know very little about auto tire pressure (not being very interested in vehicles with four wheels), so I just follow the pressure recommendations shown on the sticker (in US vehicles) on the driver's side door panel.

But, I do know a fair amount about motorcycle tires, both from reading many articles in motorcycle magazines, as well as reading all of the motorcycle tire informational brochures and manuals published by the major brands.  I have also attended several seminars given by motorcycle tire engineers and developers.

They all recommend not using the maximum pressure molded into the tire sidewall, unless you are carrying the maximum load recommended by the motorcycle manufacturer.  This information is there to advise you not to exceed that pressure when carrying a very heavy load in order to keep the tire from being damaged.  All of the motorcycle tire manufacturers publish charts showing the recommended tire pressures and tire models for almost every motorcycle sold in the U.S that their various tires will fit.  Unfortunately, Brammo and Zero motorcycles are not yet represented in these manuals.

I have the Metzeler "Dealer Full Line Tire Guide" brochure in front of me right now.  Looking at their "Fitment Guide" section, I picked out the tire recommendation for the Kawasaki Ninja 250R, which recommends their 110/70-17 54H Tl Lasertec and 130/70-17 62H Lasertec tires for this bike (similar to the tires used on the 2012 Zero S).  They recommend using a minimum front tire pressure of 32 psi and a minimum rear tire pressure of 36 psi for this bike that weighs about 360 pounds and is rated to carry two passengers.  Maximum permitted tire pressures for both tires is listed as 42 pounds, but in my experience, using 42 pounds in a bike like this would make the ride very harsh and slippery when cornering or when stopping unless you were carrying a heavy passenger and lots of luggage.  And even then you would not want to put 42 psi into the front tire as all of the weight would be on the rear tire, which would only lightly load the front tire unless you were braking hard.

My thought is that using 32 psi in the front tire of the Zero and 36 psi in the rear tire of the Zero when not carrying a passenger is more in line with what I would expect would be optimum.

[Burton]

while I have a pregen, that is before 2008, I will go with the 2008 example in this case. The owners manual says 2 bar for front and 2.25 bar for rear. http://www.kawasaki-techinfo.net/showOM.php?view_lang=EN&spec=US&book_no=99987-1445&lang_code=EN

I found the Metzeler online fitment guild here and looked up the same bike in question http://www.metzeler.com/site/uk/mediaObject/MetzelerSite/DE/grafik-30-05/TDB_2013low/original/TDB_2013low.pdf

It recommends the same tires you gave but the Front is 2bar and 2.25bar which is identical to the owners manual.

I then tracked down on Metzelers page a snippet about PSI found here http://www.metzeler.com/site/us/tech-and-safety/safety-maintenance.html

You will find the correct pressure in the operating manual of the motorcycle.

It should be noted the stock tires on a ninja 250 newgen are not Metzeler or lasertecs. And since your recommended tire pressure changes with the tire you buy I cannot trust Metzelers guild.

Now on the other hand I can trust someone who has worked for several tire companies and is an expert in his field, Ron Bowen, who states "For ALL bikes except track day sportbikes should run MAX PSI at all times, front AND rear." If you are on the track then you use whatever you want or manufactures suggested PSI's

On that note when I start getting less MPG I always check tire pressure first. If you like, after I get my bike set up and running I will do some MPGe experiments for you with the 32 / 36 vs the max sidewall to see which give better results. But that might be a month or two from now -_-

[Richard230]

It looks like the Kawasaki 250 Ninja uses the same size IRC tires as the 2012 Zero S.  Also, I have read that the new Kawasaki 300 Ninja uses the same size IRC tires as the 2014 Zero S.

[LiveandLetDrive]

I don't think anyone's doubting you get best mileage at the highest possible pressure.  That's simple physics.  If that's the most important thing for you, and I suspect for some early electric vehicle adopters that's certainly true, that may be best for you.  Personally, mpg on an ICE is simply a metric of powertrain health and Wh/mi on the Zero is a number I actively try to drive UP!

Maximum grip and response is rather complex physics.  For those seeking it (like, say, sportbike riders who are unsurprisingly an exception to Bowen's max pressure rule), it's going to depend on more than just the tires themselves (GVW, suspension, road surface, ambient temp), and max pressure is going to give you minimal tire temp (excessive is bad for life but grip is best in an optimal range) and minimal absorption of road defects (which can cause skipping across the road as Richard mentioned).  I've been to that kind of talk before and at that level what they're telling you is conservative and safe, for mass consumption.  Few people ever "need" that extra bit of performance and most would likely not recognize it if they had it but those of us who push our limits on a regular basis (having the Sierra Nevadas literally in your backyard helps) are often willing to make the sacrifice of hypermiling.

Aquaplaning on rounded motorcycle tires is a bit of a mystery for me so I will remain mum.

[Burton]

LiveandLetDie, the author of the book I linked goes into detail about what is required for a motorcycle to hydroplane and if I recall it isn't too much.
You are correct in saying Bowen's 'rule' doesn't apply to racing, and he states this in his talks. If I ever make it to a track I will ask people who race what tires and PSI I should be running and how to set up my suspension to handle the differences from both.

Richard230, my ninja 250 (a pregen aka pre 2008) uses 100/90-16 and my rear is 130/90-16. The newgen, post 2008, uses 17" tires so you are correct in that regard. I used the 08+ numbers because Metzeler didn't have the pregen on their list -_- People with pregens are often jealous of those with newgens because they don't have as many tire options to choose from.

[dkw12002]

Just to cover all my bases, I plan to keep my tires at 41 psi (stated max cold) AND wear high heals while riding. You can't be too safe. Actually, I go with 32/32 which is just a little more than the 30 lbs./30 lbs. recommended for the 2013 S Road Winner tires. I've never hydroplaned, but I have slid a bit on wet pavement due to loss of traction.

[Richard230]

Speaking of older 250 Ninjas, my daughter just sold my 2004 model that I gave her some years ago last night.  It had 30K miles on the clock and she sold it for $1,400 USD.  I bought the bike new in 2004 for $2,800, so I would say that it held its value pretty well.  I performed all of the servicing on the bike and I really hated to do the valve adjustments.  It was an all day project.  Frankly, I am happy to see it go and she will be getting my 2012 S for a birthday present later this month.     No more valve adjustments!   

Getting back to tire pressures, I have read many times that the best way to set your tire pressure on a motorcycle is to check its pressure cold, go for a typical ride for at least ten miles and then check the tire pressure while it is warm.  The increase in pressure should be about 10%.  So if you set your pressure at 30 psi before riding off and your gauge reads 33 psi after your ride, then that would be the best pressure for your riding style and tire choice.