need a math guy

Reply Subscribe

Thread Tools

Search this Thread

Apr 29, 2012 | 01:22 PM

#31

Texas Fat Boy

Extreme HDF Member

Joined: Dec 2006

Posts: 10,045

Likes: 36

From: ST. Louis

http://www.youtube.com/watch?v=Qhm7-LEBznk

Apr 29, 2012 | 01:32 PM

#32

sgdiesel

Road Warrior

Joined: Nov 2008

Posts: 1,296

Likes: 3

From: Cheltenham, UK

Quote:

Originally Posted by Texas Fat Boy

http://www.youtube.com/watch?v=Qhm7-LEBznk

I challenge anyone to watch that and not be drawn to making a blonde comment!! Very funny

Apr 29, 2012 | 01:51 PM

#33

Expat1

Road Master

Joined: Jun 2010

Posts: 1,221

Likes: 4

From: Annemasse (border of Geneva-Switzerland) facing Mt-Blanc.

Quote:

Originally Posted by grbrown

hoggy05 asked for a math guy to give him the speed his bike is doing at 3,000rpm. As an engineer I use applied math and it was too tempting to give him the answer as a math equation! Iron Butt has correctly identified the tyre diameter and gear ratio.

It's the weekend after all, time for a little fun!

Hey guys, nobody mentions the loss by friction between asphalt and rubber

A normal value is 3% depending on grade of incline and wind. 3,000 RPM is 129 KM/H on my GPS

Apr 29, 2012 | 01:58 PM

#34

bluffalobob

Road Warrior

Joined: May 2007

Posts: 1,277

Likes: 4

From: Austin, TX - Some call it heaven.

My nephew is mathematically challenged. I told him to try logic instead of math. He asked me what I meant. Well, supposed the problem is "What's 80% of 375?" You could do it by multiplication, or you could say: "10% of 375 is 37.5, so 20% is 75. 375 - 75 = 300. See, you're using logic to break it down to the easiest way to solve it.

In this case you could use math to figure how how fast the wheel is turning for a given RPM and gear size, then factor in things like tire pressure, temperature of the road surface, aerodynamics, etc.

Or you could use logic and look down at the speedometer.

Last edited by bluffalobob; Apr 29, 2012 at 06:46 PM.

Apr 29, 2012 | 02:11 PM

#35

Gearhead3

Road Captain

Joined: Jan 2009

Posts: 739

Likes: 2

From: St. Louis

Here's a link to one of my favorite websites, you could 'play' for hours on here.

http://www.wallaceracing.com/Calculators.htm

Apr 29, 2012 | 02:43 PM

#36

X Iron Butt

Road Master

Joined: Jun 2011

Posts: 974

Likes: 13

From: Chesapeake Virginia

Quote:

Originally Posted by Expat1

Hey guys, nobody mentions the loss by friction between asphalt and rubber

A normal value is 3% depending on grade of incline and wind. 3,000 RPM is 129 KM/H on my GPS

Considering your post location it looks like incline and altitude has a little to do with this answer.

Apr 29, 2012 | 04:12 PM

#37

grbrown

Club Member

Joined: Jun 2007

Posts: 45,429

Likes: 2,898

From: Bedford UK

Quote:

Originally Posted by sgdiesel

Now, as an engineer I was always trained to show my workings clearly and documented.....

But it's the weekend!

Quote:

Originally Posted by X Iron Butt

If I come to the UK and Dunlop spells it tyre I will spell it tyre. Over here Dunlop spells it tire so I will follow. Try looking up a tyre shop in our yellow pages and you won't find it. I didn't do it it happened before my time I still spell it colour sometimes.

Dunlop was originally a British company old chap, so of course they spell it correctly. However they also have a translation service for overseas markets......

Interestingly Avon spell it correctly on their US website!

Apr 29, 2012 | 04:25 PM

#38

Retrop

Outstanding HDF Member

Joined: Nov 2008

Posts: 2,034

Likes: 128

Quote:

Originally Posted by sgdiesel

Saw that, but only saw a row of numbers, not confirmation of what each was, apart from the pi constant which is clear. Silly me :-)

Whoa! Somebody say something about pie? I admit, I got lost at the bakery when all that math was being bantered about. But pie, that is something I can really get my hands on. Are we talkin apple, cherry, peach or whatever? There is no such thing as bad pie.