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Faster steering tires?

KevinRT

KevinRT
All other things being equal (yes, I realize this is most likely impossible) will a larger diameter tire be slower or faster steering than a smaller diameter tire?
 
Faster steering tires

Lots of variables involved, but to keep it simple a front airhead tire sized 100/90x18 will turn in faster than a front airhead tire sized 100/90x19. Is that what you were asking?

Friedle
 
What Friedle posted +1

Smaller diameter is usually quicker handling, think mini-bike vs. earthmover.
There is a lot at play. At racing speeds, handling changes as the tire wears.
At cruising speeds, most riders aren't paying attention.
 
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As I understand the geometry, a wider tire makes it "harder" to turn as you have more of a lever to work against. Harder is relative and most people might not notice. There's also clearance issues to consider. In general, one should use the tires that were spec'd for the bike...that provides the optimum geometry that was designed in to the frame.
 
Faster steering tires

As I understand the geometry, a wider tire makes it "harder" to turn as you have more of a lever to work against. Harder is relative and most people might not notice. There's also clearance issues to consider. In general, one should use the tires that were spec'd for the bike...that provides the optimum geometry that was designed in to the frame.

Kurt, you are addressing "width" where the original question specifically addressed "diameter". That is why I asked the OP if my answer was what he was wanting to know. I didn't want to get into width, profile, pressure, tread pattern and a host of other variables and start another "best oil thread". :dunno

Friedle
 
Kurt, you are addressing "width" where the original question specifically addressed "diameter".

:banghead I missed the diameter issue. So, never mind!!! Not sure that the diameter much affects the steering, although it will increase the rake/trail which does have an impact on steering. Not to mention issues with side/center stands. I would personally run the spec'd tires to take full advantage of all the geometry had to offer.
 
:banghead I missed the diameter issue. So, never mind!!! Not sure that the diameter much affects the steering, although it will increase the rake/trail which does have an impact on steering. Not to mention issues with side/center stands. I would personally run the spec'd tires to take full advantage of all the geometry had to offer.

Rotational inertia is the issue. The integral of (radius^2)*(mass). The smaller the value, the lower the force needed to change direction of the spinning wheel or accelerate it. As a result, gyroscopes are used for guidance and race cars/MC's have small diameter wheels and flywheels.
 
Rotational inertia is the issue. The integral of (radius^2)*(mass). The smaller the value, the lower the force needed to change direction of the spinning wheel or accelerate it. As a result, gyroscopes are used for guidance and race cars/MC's have small diameter wheels and flywheels.

That's the answer I was looking for. I am not trying to swap out one diameter for another, or change the handling of my bike in any way. A friend mentioned that larger diameter wheels steer faster but I thought that didn't sound right.

Thanks!
 
Good reading but me thinks "width" should be replaced with"profile" regarding turn in. A "V" shape turns quicker than a "U" shape. As for smaller diameter turning quicker, yes, but ...... anyone remember the 16" tires from the 80's? They were a handling disaster, including street and professional racing. I've always been amazed how different bikes and different tires can handle so differently. And no, I don't have the answers, just many more questions. :dance
 
That's the answer I was looking for. I am not trying to swap out one diameter for another, or change the handling of my bike in any way. A friend mentioned that larger diameter wheels steer faster but I thought that didn't sound right.

Thanks!
Many people confuse an noticed effect as being attributed to something that is not the actual cause because they haven't dug into it enough.

What I mean is that your friend may have experienced a situation where a larger diameter tire did indeed exhibit a quicker turn-in, but, all other things being equal, it would not have been from the diameter being larger. Most often it is from the having a lower aspect ratio number.

There are 3 dimensions to a tire (I'll use car tires as it is easier to illustrate - say a 1998 BMW 328is with OE tires of 205/60/15):
  • Diameter - ie. 21", 19", 18", 17", etc. (in this case 205mm)
  • Aspect Ratio - ratio of sidewall height to sectional width (60%)
  • Sectional Width - distance from sidewall to sidewall for a motorcycle and tread-width for a car (205mm)

The 205/60/15 has a typical overall diameter of 24.6". Many people move up to a 17" wheel on these cars and use a 225/45/17 tire which has an overall diameter of 25.0". The 225/45/17 tire is heavier and carries it's weight farther out from the center (all a negative), but the lower aspect ration 45 vs the OE 60 will generate a a more direct feel and reaction while the sectional width increase of 225 from 205 will generate more grip. All of that will produce a quicker turn-in. However, if one simply went from a 205/60/15 to a 205/60/17 the larger diameter tire would be noticeably less responsive.

With a motorcycle it is more complicated but, as has been said (with all other aspects being unchanged), a larger diameter:
  • turns slower due to increased contact patch - street bikes run 17" fronts while dirt bikes run 19"-21" fronts
  • is heavier and moves the weight out farther from the center - gyroscopic effect means greater resistance to turning
  • increase the actual wheelbase - slower responding
  • changes the suspension geometry - slower responding
 
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