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Message started by cheapnewb24 on 01/03/16 at 06:45:07

Title: Wheel physics?
Post by cheapnewb24 on 01/03/16 at 06:45:07

I'd like to start a discussion on the effects of different wheel/tire sizes, not specifically tire width, but also rim size. How does the behavior of a 21 inch rim differ from a 15, 17, or 19 inch rim? Front or rear?

Title: Re: Wheel physics?
Post by MMRanch on 01/03/16 at 07:23:11

In Tractors , The bigger the tire Diameter - The smother the ride .

Title: Re: Wheel physics?
Post by Steve H on 01/03/16 at 08:30:58

The larger diameter will smooth the ride a little. Larger will also increase the gyroscopic forces exerted by the tire.
https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=9&cad=rja&uact=8&ved=0ahUKEwiG59imho7KAhUW32MKHdW8A8QQFghGMAg&url=http%3A%2F%2Fwww.renj.com%2Fcontent%2FMotorcycleSpeedAndSteering.pdf&usg=AFQjCNG94Ymsxk7a3k3F3c_VC_R1LUJ65A Check this out. It goes into gyroscopic forces related to motorcycle steering.

This one actually gets into the math with diagrams.
http://www.dinamoto.it/dinamoto/8_on-line_papers/effetto%20giroscopico/Effettigiroscopici_eng.html

Generally, the bigger tire will make it easier to cruise down the road nice and straight, it will also require more effort to turn.

Title: Re: Wheel physics?
Post by cheapnewb24 on 01/03/16 at 13:08:21

Quote:

Tire Size: Stay clear of spoke wheels, but go with cast wheels with those big 16" tires front and rear. They absorb road bumps, will not grab cracks in the road making for a nice straight-line smooth ride even on old roads in need of repair. Stay clear of those skinny 21" wheels as they will make for a horrendous arm-workout. The bike squiggles down the road with those skinny tires constantly tiring you out just like the old dreaded Sportster's used to do. Get the upgraded wide 16" tires as they run cooler and last longer too! It is not unusual to get over 10,000 miles on a set of 16" tires as they run cooler and shed heat to the fat rim like a heat-sink keeping tires at optimum temperature.

http://www.jamesrussellpublishing.biz/sportster1200.html

That James Russell dude doesn't seem to like big rims. Perhaps it's just the narrow tires he's complaining about. :-?

One thing that makes me think of wheel size is offroading. Do you really need a 21 inch front for a scrambler? I notice that dirt bikes and dual sports like this. What is the smallest front wheel for off-roading? Has anyone here done a Savage scrambler? Did you use the original rim/tire size?

Now that I look at the above quote, I can't say he knows what he's talking about. :P I doubt a Sportster would have 16 inch front AND rear!

Title: Re: Wheel physics?
Post by cheapnewb24 on 01/03/16 at 13:13:11

Then again, I looked at the quote again and thought some more. I had a doubt. Upon Googling it-- Lo, and behold-- Sportster 16 inch front!? :o
https://www.google.com/search?q=16+inch+front+sportster&ie=utf-8&oe=utf-8

Title: Re: Wheel physics?
Post by gizzo on 01/03/16 at 13:38:29

63686561706E6577623234000 wrote:

One thing that makes me think of wheel size is offroading. Do you really need a 21 inch front for a scrambler? I notice that dirt bikes and dual sports like this. What is the smallest front wheel for off-roading? Has anyone here done a Savage scrambler? Did you use the original rim/tire size?

My daughters PeeWee 50 has I think a 12" rim and she off roads like a demon so I guess you could go with that. Us grownups use 21" for a reason- stability in loose stuff, larger diamerter rolls over obstructions easier. Really, do you think the manufacturers just eyball it or might there be some actual knowledge behind their choices (excepting HD who would just do what looked cool). In the 80's there was a fashion for 16" front wheels on sportsbikes. the one that havent been crashed have mostly been upgraded to 17" rims. Better choice of tyres in 17, too.