Topic: Power To Weight Revisited

[chrisfranklin]

Posted on this in the past, but can't seem to find it now.  Basically its about reducing weight on your Jeep and does it bring any performance improvements...

Right now I am not running with the back seat in, the top is off and doors are off.  So probably 100-some pounds lighter and, perhaps, slightly less air resistance, too.  And, I gotta admit, the 4 Banger power to weight actually feels fairly good now, at least  on puny Revo 29"s.   General quickness and throttle response is ok in the city, too

May just get one of those long Bikini tops and just run like this, w/doors off/back seat out/full soft top off, year round in So Cal.  4Banger definitely seems to drive better this way. :D

[Jeffy]

You're still running small stock sized tires though.  The problem with removing weight is when you move to highway speeds.  This is when aerodynamics come into play.  When that starts, it won't matter how much weight you remove, you're still dealing with a box and it's not going to cut through the wind easily.

If you're just doing intown sort of stuff then a reduction of weight would help. 100 lbs is supposed to give you the equilivant to 1hp.  When I remove my hard top and full doors, it makes a big difference in city driving.  That's around 300lbs.  The seat isn't really large enough to make much of a difference.  As for aerodynamics, it's moot.  Air will travel over the Jeep and start to cause a jetty.  Try spitting out of the Jeep.  If you don't spit it hard enough, it will come back around and end up on the back of your seat.

There's actually an interesting article in Popular Mechanics on what you'd need to do to get 100MPG.  Things like tire weight when rolling increases 50%.  When you're looking at almost 200lbs a wheel and tire, it makes a big difference.

But then if you want to go all the way then removing their rollbars, seats, doors, windshield, spares...  Swap out the front axle for a spindle from a 2wd XJ.  Loose the transfer case and the front driveshaft.  Lower the body and put some skinny tires on it.  Might as well remove the windshield to cut down on even more drag.  Then you've got to close the front fender since they act like parachutes.  Might as well buy a Miata at that point.

[chrisfranklin]

Well, I don't really need the doors, top, back seat in there most of the time.  But, low speed it drives better.  Highway speed acceleration is improved as well -- ie. climbing the 405N near UCLA in 5th gear and accelerating slightly versus having to run it in 4th to make the climb.  

As for aerodynamics, sure a brick is a brick.  But, no top means you're not getting dragged on as much by crosswinds and by air currents generated by other vehicles.  No doors may help in that department as well.  So, for what little its worth, it would seem that you're aerodynamic battle is mostly with the front only when you are not running top and doors  

[Jeffy]

As for aerodynamics, sure a brick is a brick.  But, no top means you're not getting dragged on as much by crosswinds and by air currents generated by other vehicles.  No doors may help in that department as well.  So, for what little its worth, it would seem that you're aerodynamic battle is mostly with the front only when you are not running top and doors  

Well, not really.  The top will cause the air to flow over the Jeep cleanly.  Remove the top and doors and that starts to let air into the vehicle where it causes drag.  Think of it this way;  a square boat is still better then a boat with holes in it.

ALso, if you ever drive with a hardtop on then switch to a soft top and then no top, you'll quickly notice that even with the extra weight, the hardtop will cut through the wind better then with the soft top.  With no top, you have less weight but it's like putting up a sail.

[chrisfranklin]

About the only formal test I have seen on this type of matter involved the old tail-gate open or closed on a pickup -- as in, "which affords better aerodynamics?"  

Are there formal scientific tests regarding Jeep tops?  Probably not.  

Not a scientific test, of course,  but I did detect improved performance with no top, doors at highway speeds today and previously.   So, give it try all yee warm-weather 4 bangers -- it don't cost nothin' and you might detect better drivability city/highway.  Then again, you might think Jeffy's right and I'm  full of sh#$