Is this true for us 315 guys?

[XcumminsX]

Originally posted by CRoth - BD-Power





As for rotating mass, as soon as you loose that 100+ lb crank and those 35" tires we'll begin to talk.

I was just looking at a thread in the competition forum and i saw this ... Is this accurate... Im gonna be pretty mad and there will be some 315's for sale if this is true.....





Nick:--)

 

[SRadke]

Uh... . what thread? What are we talking about?



-Scott

 

[StephenThomas]

xcx... . if your question is whether or not 315's will slow you down a bit, the answer is affirmative. If you sell your 315's, let me know

 

[XcumminsX]

I am very confused here... doing the math i get that with 4. 10 gears and 35" tires my final ratio is in the 3. 7's



here is a graph showing each tire compared to each other



315/70-17 8. 7 in 17. 2 in 34. 4 in 108. 0 in 587 / mile N/A

265/70-17 7. 3 in 15. 8 in 31. 6 in 99. 3 in 638 / mile -8. 0%

245/70-17 6. 8 in 15. 3 in 30. 5 in 95. 8 in 661 / mile -11. 2%





As some of you know i am going for around 550 rwhp... . With my 4. 10 gears what would be the tire that will get me down the track the fastest ( i mean what size) I am really confused with this tire math... . can anyone help me out here?



Nick

 

[FDavid]

You want a tire size that will allow you to be close to or at redline by the end of the 1/4. You dont want to be having to upshift right before you cross the line. And although your plus size tire gives you a theoretical 3. 7? gear ratio, its not the same as the guy who has factory 3. 73's because you need a bigger (heavier) tire to do this. Rotaing mass is the worst kind.

 

[bighammer]

When they are talking rotational mass, their concern is the large weight and diameter and rotaional inertia. A large, heavy tire/wheel combo takes more power to get and keep rolling.



Back in my bicycling days, the word was that to save an ounce on the wheel is like a pound on the frame.



BTW, I just got my 2nd set of 315s about 20 minutes ago, and according to FedEx, they weigh 64lbs each.

 

[XcumminsX]

So does this mean i should get aluminum wheels are tires with a 28" diameter with 4. 10's ?? how can i determine the right tire what would have me at 3200 rpm at the end of the 1/4 mile??



Nick

 

[DF5152]

my guess is its going to be pretty close to the factory size. with the factory 265 and ur transmission out of OD you will about 75 MPH @3200 then need to shift to OD. my next choice would be something smaller it will give u better acceleration of the line which will help to reduce your ET but you may run out of motor on the top end. A larger tire will slow down you acceleration hurting ur ET but if your making big HP you may be able to make it up on the top end



here is the formula RPM's=MPH*AXLE RATIO*336/Tire Diameter

 

[SRadke]

The first thing you need to know is approximately how fast you'll be going at the end of the 1/4. Then choose gear ratios (tire sizes) accordingly.



-Scott

 

[Duck]

FWIW- I didn't get any exact weights before I sold the stock tires, but from my grunt-o-meter while deinstalling/installing my 315's and MT wheels weigh CONSIDERABLY less than the stock wheels and Michelins.

So, I'd be more concerned with the wheel than the rubber tires when trying to trim weight.

 

[Peter Campbell]

The tire has to not only be accelerated with the vehicle, but brought up to speed. The rotational moment of inertial deals with where the weight is. A drag slick on a steel rim ( heavy center thin and ight tread may weight the same as a 315 on a MT racing rim but the weight location make it an excellent flywheel. To quote some wisdom- "The most boring part of a racecar are the tires. The most important part of the racecar are the tires. " If I remembered I would attribute it to the right guy. I have 19. 5's and I did know this when I got them. HEAVY. But I am not racing- I wanted long tread life- and around 2000 RPM at 70 MPH. The extra rubber that 315 give you is longer tread life. If you want to race with them just shave them to 3/32" to lighten them up and get better dry traction. Of course they are no good after that

 

[BMccollough]

It's not the over all mass of the wheel that's important, but were that mass is located in relation to the axis of rotation. The farther the mass is from the axis of rotation the greater the torque requirement to rotate the wheel. Most of the mass of a tire is located near the outside diameter and with regards to truck tires has the most influence on the mass moment of inertia of the wheel (rim and tire). Going to a lighter rim will help alittle, but not nearly as much as going to a lighter smaller diameter tire. Maybe this will help you understand, mass moment of inertia of a solid body is a measurement of that solids ability to resist rotational acceleration about a specific axis. This means the greater the mass moment of inertia the harder it will be to accelerate the wheel. I know very technical answer, but I got on a roll.

 

[DFrank]

Remember those manual carousels on the playground? Remember how much they accelerate when you bring your mass towards the center? Also how how quickly they slow down if you lean to the outside? same principle.

 

[SRadke]

LOL! So now we've got "the mass moment of inertia of the wheel" and "those manual carousels on the playground". This about covers the text book and the real world doesn't it.



-Scott

 

[Greg Boardman-RIP]

Originally posted by XcumminsX

I am very confused here...

As some of you know i am going for around 550 rwhp... . With my 4. 10 gears what would be the tire that will get me down the track the fastest Nick

First you have to Bomb your truck, Then worry about what power you make will affect. In that thread, They are talking about 800 HP monsters breaking everything. 550 HP is pretty easy, but spendy, to make. The truck will handle it fine with a DTT transmission or a South bend clutch.....



As for the track, Larger tire might be fastest, smaller tire will be quickest.