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Why do motorcycles have a larger diameter wheel in the front & a smaller in back? Is there some sort of physics behind it?

This never dawned on me until the UPS guy stopped by my garage today to see my project triumph which has an 18" rear & a 19" front. He said "why is the front wheel bigger than the back?" i said "you know what man? i really couldnt tell ya. its just the way its always been with bikes."

if i were to take a wild guess, id say its because the taller front wheel gives a smoother ride & easier handling? the smaller rear transfers power better?

does anyone know?
 

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sojerscraper said:
Why do motorcycles have a larger diameter wheel in the front & a smaller in back? Is there some sort of physics behind it?

This never dawned on me until the UPS guy stopped by my garage today to see my project triumph which has an 18" rear & a 19" front. He said "why is the front wheel bigger than the back?" i said "you know what man? i really couldnt tell ya. its just the way its always been with bikes."

if i were to take a wild guess, id say its because the taller front wheel gives a smoother ride & easier handling? the smaller rear transfers power better?

does anyone know?
The bikes that have a larger diameter front wheel from the original manufacturer that was not installed for looks (i.e., V-MAX) are:

1) Ground clearance for front of engine area without longer forks or decreased rake.

2) To slow the steering rate response.

Most custom bikes and many oem are done for style.
 

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measure from the bottom of the tire to the top on the front and back wheels. the overall diameter is just about even with a 16 or 18 rear and a 21 front (im guessing on a 19 also)
 

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Kyle your right. But the larger diameter is also skinner and lighter the therefore better handling. Most older bikes Indians, HD's, etc had the same size. My Chief came with two 18" wheels. I'm currently running and 18 in the rear and a19 up front but am in the process of lacing up two new 18 inchers so I'll be testing my handleing theory. My UPS guy just throw the package over the fence or leaves it with the neighbors.
 

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That lighter thing really comes into play on the rear, in my experience. I used to run a shop back in the '70's, lots of guys wanted 16" on the back "to lower it", I'd show them it wasn't lower, just fatter. I told 'em that they would notice a little bit less handling quality and a notable decrease in acceleration. They wouldn't believe me, style came before function. I'm building a semi-recreation of my old '71 Honda 750 Amen chopper, but this time it'll keep the 18" on the back, and skip the 21" front so I can keep the 19". I have wondered about putting an 18 on the front too, but I'm not sure it would make much difference on this bike. I'm not sure when different diameter wheels came about, I once had a couple of late '30's Rudge bikes, seems like one of 'em had different diameter wheels and one was the same. Like Creepinogie, I like 18" on Indians, had a '37 Chief once with 16" wheels, laced up a set of '18"ers, and had a wonderful new bike!
 

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The first bikes I saw with a smaller front wheel than rear were the early 80's Honda Intercepters. I think almost all the modern sport bikes run equal heights front and rear. Performance vs. looks.
Jakemon
 
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