A Few Questions & Your Thoughts on 16.5 Rear Wheels

-Which Tire Manufacturers offer a 16.5 Rear? I know Pirelli does, anyone else?
-Do they have em readily available out at Chuckwalla and local club races?
-Are they priced similar to their other race tires?
-Do they generally only come in 190 slicks?
-What are the Pro's & Cons of a 16.5 Rear?
-Is common/ok to run a 16.5 rear and a 17 front?

What are your thoughts on a 16.5 wheel for a racing application?

TIA

 

17 inch rubber has been making advancements to the point that there really isn't much use in going with 16.5. Even World Superbike is switching back to 17in for the 2013 season. I think if you go with 16.5's you'll just be limiting the number of classes you can race in as well as make sourcing tires for each even a little more tricky since you'll have to pre-order what you need more often since most vendors don't carry much 16.5 in the trucks with them. 16.5 only come in slicks and rains.

 

you could run 16.5 in anything but a supersport legal rules class that requires dot tires if not mistaken.. Michelin has line of 16.5 slick tires (and you will only have slicks as spl170db noted above), but you would need to contact your local guy to see if they will continue to be made. They only came in 6" rear wheel widths for the rear (no 5.5" wide ones)

yes, you could run a 16.5" at one end and 17 at another.. Robert jensen ran a 16.5" slick front and 17" DOT rear a bunch .. i did the same till the new cups came out as it was so much better than the DOT fronts we had for the past years. the theory is that a 16.5" slick has more edge grip. I can not tell you what is better, but yes, the technology has moved to 17" stuff not too much 16.5" . Is motoGP still using 16.5" though??

 

^yes, motogp uses 16.5 and in different widths

 

I thought MotoGP was using 16" tires.

Don't know much about them but one thing I found interesting a few years ago, an egghead buddy of mine (UW Physics faculty, writes his own chassis design software, and builds/modifies frames accordingly.. that egghead-y) was tinkering with Dunlop 16.5's and measured the dimensions: The "contact" part of the tire was the same total area and actually had the same diameter, meaning the useful part of the tire wasn't even shaped differently. The extra half-inch was made up completely via sidewall.

 

Rgr..
I got a 16.5 PVM mag wheel spare with a bike I picked up. Guess I'll try to sell it, and if I'm lucky, get $50. lol

 

If this is for sv I would not run it on rear, to big. We still run 16.5 front with 180x17 rear. It works really good. I think front is cheaper than 17.
But as mentioned 17's are so good now, specially Pirelli that there is no point of running 16.5 any more.

 

That's it! Do you realize you just stated the advantage of 16.5 over 17's?
Leaned WAY over the sidewalls are your suspension, absorbing bumps, rolling
over FOD(foreign object debris), conforming to the track surface...the 16.5's
extra sidewall is more pliable than a 17, resulting in better traction, smoother
rolling, larger contact patch - especially when braking or hard on the gas -
the weight transfer loads the tire and the 16.5 flattens out more for
a larger patch - more grip.
However, for most of us, the differences would be negligible.Top riders
may be able to exploit the 16.5's advantages, the rest of us can dream.
I have for several seasons of trackdays. When a racer quits and sells you
16.5 wheels and new slicks cheap, you mount 'em, ride 'em, and grin when
guys say "you got 16 and a half(s) ! "

 

You mean for those of us that do this on a regular basis?

 

I have some photo's of me riding like that, but they always called it "crashing".

 

re. contact patch vis-a-vis rim size:

if two tires have the same air pressure, they have the same contact area (i.e. contact patch).

physics degree not required.

vince

 

i don't think so. All things equal maybe, but tire brands and tire carcass construction are NOT the same. same psi in two differently constructed tires could easily have different size contact patches. sidewall height and other carcass characteristics could easily have a tire flex more than another tire built differently.

I also think motoGP uses 4" front tires, not 3.5"

 

Try running 21psi HOT in your rear Michelin slick, then tell me the contact patch is the same.

Vince - keep working on the degree.

 

moto GP uses 4 inches!!!!

 

As mentioned above, the air pressure is only one component of the tire stiffness, which is what ultimately will determine how much it deforms under stress. Dunlop NTEC slicks @ 18psi will deform considerably less than Pirelli rains @ 18psi. Likewise, the longer sidewall of a 16.5" would enable more deformation than the shorter sidewall of a 17", even given the exact same construction.

 

fwiw. I have two old michelin fronts, 16.5 and 17 and sidewall difference is about 2mm.

 

not nit-picking on you, but i read these two as conflicting.

i'll reiterate that i was only allowing for a difference in rim diameter. of course there are other variables that have an effect.

i'll add that additional stiffness due to specific tire construction can lessen the contact area, but it would seem can be no greater than what the tire pressure allows. regardless of construction differences.

(limit of contact) area = pressure / force.

...not to deviate from the thread topic.

vince

 

nope. air psi is plain and simply not the only thing that will determine a tires contact patch. That is not how things work with tires.
think of a heavy duty inner tube, and a very thin inner tube. put 18psi in both. The thin inner tube will deflect more with a similar weight applied vs. the heavier duty inner tube. Then, add construction differences, and it is very easy to see your logic is a bit flawed on this topic

 

sorry, maybe i was not clear. there is an upper limit to the contact area. it is defined by the pressure. only. the area can be reduced by additional stiffness, e.g. the finite stiffness due to construction, material, etc. etc. however, it can not be greater.

make sense now?

and, i agree with your example; it is inline w/ my comment.

vince