Speed calculation - Honda Motorcycles - FireBlades.org
Tools / Garage / Paddock Discussion of Motorcycle Related Tools, Stands, Lifts, etc.

User Tag List

 
LinkBack Thread Tools
post #1 of 7 Old 05-19-2009, 7:11 PM Thread Starter
 
Join Date: 02-26-2009
Location: essex, uk
Posts: 147
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Reputation Power: 11
 
Speed calculation

Hey All,
It's my first time on tools/garage/paddock, but thought I might get a better response to this question here rather than at the fireblade forum.

I'm calculating gearing and road speed for a YPVS (RZ350 over the pond) project; Would you calculte the rolling diameter of a wheel as the full dimensional diameter (18" wheel=457.2mm 140/60 tyre=60% of 140mm=84mm, so 457.2+(84x2)= 625.2mm diameter) OR do you take into consideration the deflection of the tyre at the contact patch?

It may be too small to be worth considering, or maybe at speed, when the tyre is expanding due to the centrifugal forces, it's at it's full dimensional size. For reference I calcuted the standard bike, with standard tyres to be at 120mph at 9500rpm in top, which seems to me to be pretty much right.

Any input would be appreciated.
shittyarsedmonk is offline  
Sponsored Links
Advertisement
 
post #2 of 7 Old 05-19-2009, 7:31 PM
 
Join Date: 04-24-2007
Location: Sydney, Australia
Age: 54
Posts: 1,003
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Reputation Power: 21
             
Re: Speed calculation

Actually the deflection doesnt affect it!

Why...
the tyre is compressed and forms a contact patch, so yes the "radius" is now smaller. But its also no longer a circle and hence 2pi*r doesnt apply.
The important thing is the circumference - that is the distance the tyre will move in one rotation (ignoring slip)
And the circumference of tyres is relatively fixed by construction (mainly by belts). So you can calc it from 2pi*r when its a circle. But it will keep pretty much the same value even if you push down on it.

Think of it this way - get a rubber band and make it a circle. Measure it. Thats the length of the band. Now flatten one side - still the same length!

I said above "ignoring slip" but at high speeds this can be a big factor. Your tyre speed and actual speed could differ by a couple of percent due to wheel slip. Full throttle, top speed - you are effectively doing a mini-burnout.
dicknose is offline  
post #3 of 7 Old 05-19-2009, 7:50 PM Thread Starter
 
Join Date: 02-26-2009
Location: essex, uk
Posts: 147
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Reputation Power: 11
 
Re: Speed calculation

Yeah, come to think of it i've read about tyre slip before, but more with cornering. Interesting about the tyre circumference, considering it more like a tank track that has to roll it's full length rather than a decreased rolling raduis.
Cheers dicknose (cool name )
shittyarsedmonk is offline  
Sponsored Links
Advertisement
 
post #4 of 7 Old 05-20-2009, 1:41 AM
 
Join Date: 04-24-2007
Location: Sydney, Australia
Age: 54
Posts: 1,003
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Reputation Power: 21
             
Re: Speed calculation

Quote:
Originally Posted by shittyarsedmonk View Post
Yeah, come to think of it i've read about tyre slip before, but more with cornering.
Anytime your tyre is "working" you have slip.
So that includes cornering, braking, accelerating and even applying power to keep a speed (obviously higher speed needs more power = more slip)
If you are applying a force from the tyre in a direction, then you also have slip in that direction.
This is not the same as a lockup and slide. But there is always a small percentage of slide while getting traction!


Quote:
Interesting about the tyre circumference, considering it more like a tank track that has to roll it's full length rather than a decreased rolling raduis.
Yes thats pretty much how to think of it!

Lots of people get hung up on the "radius changes", but that is also the reason you cant use the circle rule.
And more tyres (both car and bike) are designed to keep roughly a constant circumference even when they "contact patch"
There is some change - and some "detect flat" systems use that.
But its a lot smaller change than you would think just looking at the change in radius.

Yeah Im a geek!
Got degrees in engineering and mathematics and done a couple of years of physics.
dicknose is offline  
post #5 of 7 Old 05-20-2009, 1:55 AM
 
Join Date: 04-24-2007
Location: Sydney, Australia
Age: 54
Posts: 1,003
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Reputation Power: 21
             
Re: Speed calculation

Did a quick google and found a discussion on another forum.
Interesting thing is to look at the initial graph
View topic - Must a tire slip to generate force? - F1technical.net
You will see that force(or torque) goes up with slip - ie more traction requires more slip!
But once past a point that depends on tyre+surface and you cant get any more traction. Push harder and you overcome traction and start to get more slip. Worse - you are now getting into a slide/burnout in that you start getting less traction for more slip!

I think most people understand the concept of sliding = less grip.
What is confusing is that the opposite holds true at times, for normal traction, more slip=more grip!
dicknose is offline  
post #6 of 7 Old 05-20-2009, 11:20 AM Thread Starter
 
Join Date: 02-26-2009
Location: essex, uk
Posts: 147
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Reputation Power: 11
 
Re: Speed calculation

Wow! A discussion going from tyre slip to particle physics, I'll keep an eye on that forum.
Isn't the slip that you are talking about pretty small and concerning road tyres, you're average joe would be unaware of it, but racers search for it?

Tyres(track oriented) do seem to hold on to more traction even with a slide these days, or at least thats what it feels like.
shittyarsedmonk is offline  
post #7 of 7 Old 05-20-2009, 9:15 PM
 
Join Date: 04-24-2007
Location: Sydney, Australia
Age: 54
Posts: 1,003
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Reputation Power: 21
             
Re: Speed calculation

You should be completely unaware of the slip while you have "traction"
The slip percentage is very small. Unless you are a computer with sensors and can check say front to rear wheel speed you wouldnt even notice it.

Note - if you are accelerating in a straight line the rear wheel will be going faster than your road speed. The front tyre is slightly resisting your motion and in theory would be going slightly slower (the road is push it around, while the rear tyre is pushing the road past!)
When you brake its the reverse - the front tyre is now the one with the big slip difference.
dicknose is offline  
Reply

  Lower Navigation
Go Back   Honda Motorcycles - FireBlades.org > General Motorcycling > Tools / Garage / Paddock

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Honda Motorcycles - FireBlades.org forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
A valid e-mail address is REQUIRED. You will not have access to any site features until you activate your account using the activation e-mail that is sent to this address.

Email Address:
OR

Log-in










Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page



Similar Threads
Thread Thread Starter Forum Replies Last Post
Speedo Calculation 2001 929rr General Discussion 1 05-04-2006 1:14 PM
Goodwood Festival of Speed (on SPEED Channel) Pete General Discussion 4 10-19-2004 11:37 AM
Verizon High speed to Cable High Speed, WOW SilverBullet Off-Topic 20 08-27-2004 10:25 AM
Uh Oh, speed could be bye bye for AMA deez Road Racing: Professional 2 03-25-2004 5:11 PM
speed tv right now freq Road Racing: Professional 0 07-13-2003 10:06 PM

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

 
For the best viewing experience please update your browser to Google Chrome