Topic: power loss - weight vs diameter

[huntingbuck101]

what effects power loss the most? the taller tire that brings the final ratio higher or the heaver rational weight?
let's say if you had a 33 At tire that weighted 50# and Mt in a 32 that was 60# which one would be the more power robing of two?

[Jeffy]

what effects power loss the most? the taller tire that brings the final ratio higher or the heaver rational weight?
let's say if you had a 33 At tire that weighted 50# and Mt in a 32 that was 60# which one would be the more power robing of two?

Without running it on a dyno, you won't get hard numbers.

BUT a AT's are shorter then MT's of the same height.  So there is probably less then .5" between a 32MT and a 33 AT.  So there is very minimal difference between the two.  (If you're talking about a Radial vs. bias ply, then the a 32" bias ply tire could infact be taller then a 33" radial AT.)  10lbs difference is a lot of weight though.  When rotating, 10lbs is equivalent to 40lbs of unsprung weight.  That's an additional 200lbs for 5 tires.  You'll probably notice it when accelerating or decelerating.  Cruising, probably won't make much of a difference.

On area you didn't give any info, was if the 32's are the same width as the 33's or not.  A narrower tire will have less rolling resistance.

[chrisfranklin]

Here's a couple of articles that look at tire diameter, wheel weight (but, whether tire or wheel, weight is the main issue).  Of course its on BMW 3 series and a miata and we are talking track tests.

http://www.tirerack.com/wheels-techpage-1/108.shtml
http://www.grmotorsports.com/backissues/heavy-vs-light-wheels.php

Width is a third dimension to the calculation.

The miata piece seemed to suggest that the light wheel weight was beneficial on the track by allowing more rapid suspension articulation that would allow greater traction (wheel contact with road) and faster lap times (course, we are talking .2 seconds, but that's all you need in a race)

The bmw piece showed the same 3 series with 205 tires and 16" wheels versus 245 tires on 17 inch wheels (17 inch wheels were alloys of two different weight, one 10lbs heavier than the other per wheel; with the 245s versus 205 you are talking a 1.5-2 (?) inch diameter increase which, in tests, cost you 1.3mpg).   The 10lb-each heavier wheels seemed to cause a .4mpg decline (wouldn't be surprised if you find that a 1 inch tire diameter increase affects milage/performance roughly the same as a 10lb weight increase on a 1 inch smaller tire, maybe a little more, so long as tire width remained constant)

You might have a point bringing up the 33AT versus 32MT.  The 10lb weight difference of the second  may balance out the 1 inch diameter size increase of the first.  Course, that's maybe if the widths are constant with both.

[huntingbuck101]

I'm just talking hypothetically with the hight and weight.  would a taller but lighter tire have less power loss then a heaver shorter one?
after looking at some tire weights it looks like only about 1# savings from most 33 AT over a 32" MT which 1# lighter is not going to make up for 1/2 taller.
I'm having troubles deciding on 32x11.5 or 33x12.5. I want the look of a 33 but I don't know if I will have the power for them with out gearing down. i have been told that 32's will slow me down much less.

[might4banger]

Here is my take... your results may vary:

When I was on 30x9.5x15 Mud rovers (a light tire) and my buddy had his Rubicon stock... we ran 'em down a 2 lane on the way to the trail... He had his winch mounted and I was carrying the tools ~ equal trade off... I got the launch and he never did take me. The stock MTRs on the Rubicon are heavy. (Seems like +10 lbs tire vs. tire.)

Fastforward - he has blown up 2 motors and now has a 4.6L stroker and running 33's... I need to install my 4.88s and I am running 35's. I'm not up for a rematch ~ someone will break something... and I don't want to wrench on his Jeep! hehehe... Yes, there are a few more stories to back that up... but not now.

Back to it... I was told how bad 33's would be with a 4banger and stock (4.10s) gears. I have about the same results with alum. rims and 35's again Mud Rovers. I had zero complaints with 30's and 4.10s... By comparison the 35's with AR Baja rims weigh in ~ 80lbs. each in contrast the 30's on stock alum. 5 spokes were ~ 56lbs.

In short, my take is weight is the biggest factor.

[Jeffy]

I'm just talking hypothetically with the hight and weight.  would a taller but lighter tire have less power loss then a heaver shorter one?
after looking at some tire weights it looks like only about 1# savings from most 33 AT over a 32" MT which 1# lighter is not going to make up for 1/2 taller.
I'm having troubles deciding on 32x11.5 or 33x12.5. I want the look of a 33 but I don't know if I will have the power for them with out gearing down. i have been told that 32's will slow me down much less.

I'd just go with 33's.  Consider this; if you ever have more then one flat, it will be easier to find someone with a spare that's 33".  This is important if you run lockers.  The 1lbs difference isn't going to be noticeable.   The 1" between 32's and 33's isn't going to be a big difference even if you're currently running 32's and move to 33's.  Going from stock to either is a HUGE jump though.  If you want to keep some performance then stick with 31's and go with MT's.  Otherwise, make the jump to 33's and regear eventually.

Another thing that wasn't mentioned was if you had a manual or auto.  Auto's have higher gearing which isn't as good as the manual when it comes to larger tires.  Although, it does give you the option of cheaper gear changes since you can go to lower gears by swapping axles instead of gears.

[Tall Boy]

whether you have aluminum rims vs. steel wheels makes a difference too. The aluminum rims will get you faster off the line and sorts because they are lighter by far, but the steel wheels keep momentum, but also take more braking to stop and more gas to get started. Of course rock rash is worse on aluminum, and a steel rim will bend as opposed to aluminum rims just breaking. But steel will only bend soo far and a repair will only go so far before it breaks too. You can't bend steel too many times or it tears.