Tires and dimensions:

[McRat]

Are larger diameters are more likely to sustain higher speeds?

What about aspect ratio?  Is a short sidewall better or worse than a taller profile?  I know taller profiles will support more weight in general, but I don't know about speeds.

[Dean Los Angeles]

Centrifugal force calculator:
http://calctool.org/CALC/phys/newtonian/centrifugal

If you could find two tires that were exactly the same weight but different diameters the larger tire would have a higher force. Smaller and lighter is the key.

The size and aspect ratio are only part of the equation that involves the tire construction, inflation pressure, and the quality of the build. It also involves the frame,  suspension geometry, and load that the tire maker doesn't have control over.

What you want is someone else to do the math and testing.

[McRat]

Centrifugal force calculator:
http://calctool.org/CALC/phys/newtonian/centrifugal

If you could find two tires that were exactly the same weight but different diameters the larger tire would have a higher force. Smaller and lighter is the key.

The size and aspect ratio are only part of the equation that involves the tire construction, inflation pressure, and the quality of the build. It also involves the frame,  suspension geometry, and load that the tire maker doesn't have control over.

What you want is someone else to do the math and testing.

Thanks for link!

Yes, I'm working with a professional testing lab.  But experience trumps everything IMO, what sometimes makes sense on paper doesn't always translate the same on the racetrack.

[Dynoroom]

Centrifugal force calculator:
http://calctool.org/CALC/phys/newtonian/centrifugal

If you could find two tires that were exactly the same weight but different diameters the larger tire would have a higher force. Smaller and lighter is the key.

The size and aspect ratio are only part of the equation that involves the tire construction, inflation pressure, and the quality of the build. It also involves the frame,  suspension geometry, and load that the tire maker doesn't have control over.

What you want is someone else to do the math and testing.

But Dean, didn't they make tires huge (36" +) in the olden days to reduce serface speed and keep them together?

[wolcottjl]

What about the larger contact patch with the taller tire?   Depending on HP and speeds you add another factor into the equation.

[fredvance]

What about the same height and larger contact patch? The tire I ran last year had about 60% wear, so it had a much larger contact patch. Does more traction override the additional rolling resistance?

[McRat]

I would think for El Mirage or the short course at Bonneville, traction would more important than rolling resistance, at least in my case.

[Gwillard]

Centrifugal force calculator:
http://calctool.org/CALC/phys/newtonian/centrifugal

If you could find two tires that were exactly the same weight but different diameters the larger tire would have a higher force. Smaller and lighter is the key.

The size and aspect ratio are only part of the equation that involves the tire construction, inflation pressure, and the quality of the build. It also involves the frame,  suspension geometry, and load that the tire maker doesn't have control over.

What you want is someone else to do the math and testing.

You have it backwards. The larger tire will have less force on it then a smaller one. Centripital acceleration (in g) is given by the v^2/(32.174*r), where v is velocity in feet/sec, and r is the radius in feet. Changing r will cause an inverse change in g, where changing v will have an exponential change in g.
To get the force needed to hold agianst that centripital acceleration, just multiply g-force by the mass of the object that is being spun.

[wolcottjl]

Man I wished I had payed more attention in math classes.     Learning this stuff over 40 sucks!

[Racerboy]

You are correct!!! Number and the ABC is a bit*h when your over 50. But thanks for homework now I got work to try and figure out

[wolcottjl]

Here is my question since I can't find my gearsplit software backup.  I have a final gear ratio of 3.67 and a 4th gear of 1.13 and a 5th gear of .91

In choosing a speed that I think I can hit should I match a tire to fit the speed with peak horsepower in 4th or 5th gear? 

[Sumner]

Here is my question since I can't find my gearsplit software backup.  I have a final gear ratio of 3.67 and a 4th gear of 1.13 and a 5th gear of .91

In choosing a speed that I think I can hit should I match a tire to fit the speed with peak horsepower in 4th or 5th gear? 

What is your 3rd ratio.  Personally if it was mine I would pick the gear where there was less rpm drop between it and the one before it.

The spread sheet on my site at......

http://purplesagetradingpost.com/sumner/bvillecar/bville-spreadsheet-index.html

..... will give you the rpm drop between any two gears at any rpm shift point.

c ya,

Sum

[wolcottjl]

3rd is a 1.44 - doing some math it looks like shifting at redline the RPM drops a couple hundred RPM (give or take) above peak torque.  With speed loss during the shift, RPM probably drops to either peak torque in the 3/4 shift to a touch below in the 4/5 shift. 

[Sumner]

3rd is a 1.44 - doing some math it looks like shifting at redline the RPM drops a couple hundred RPM (give or take) above peak torque.  With speed loss during the shift, RPM probably drops to either peak torque in the 3/4 shift to a touch below in the 4/5 shift. 

If you can't change the rear gear ratio and/or find the right tire dia. then you are going to have to go with which ever one is going to get you the right overall ratio for the speed you think you can run.  If you can make either work with tires and/or rear get I would go with the 4/5 final shift since it has the least amount of rpm drop.  With Hooley's Stude we have a 7% drop going from our 1:1 third to our .93 overdrive and that is great.  I like the "touch below in the 4/5 shift", but will be interested to see what others think.

c ya,

Sum

[wolcottjl]

What I do not have enough knowledge about is the torque properties with gear ratios versus tire diameter.  Dad always mentioned a 1:1 final gear ratio out the trans as being ideal.  Don't know if that is a myth or not.