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Old 11-27-2012, 09:45 PM
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Weight of OEM 20's and other combos

Does anyone know the weight of the OEM 20" rims with tires? I weighed my Helos 20" with 285's (34.8" tall) on them this weekend and they came in at 96.7 lbs with about 5-6/32nds tread left.

If you have another wheel combo that you have weighed, feel free to list it.

A lot can be learned from this. Reducing unsprung and rotational mass can improve fuel economy, ride comfort, suspension reaction, power to the ground, and wear/tear on your truck. Thanks for participating if you do.
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Old 11-28-2012, 04:55 AM
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i just sold a rig with three sets of wheels/tires..

set one was stage five 17"x9" w/ 285/75/17 dura grapplers which weighed in at 72#'s.. highway tread, with a silly hard compound and some deep arse treads that lacked decent sipes and was pretty much void of tread blocks.. it was a great highway tire, though, and mileage was easily +4 from the third set, and a solid 2+ from the second.. rolling resistance on these things was minimal..

set two was factory 20"x9" 'flower pedals' w/ goodyear AT/S 275/60/20's on them.. they weighed in @ 90# almost even, (w/the balancing weights), and were horrible tires that cupped, wore unevenly, and absolutely sucked on anything but pavement..

set three was motometal 951 20"x10" w/ Dick Cepek 35"x12.5"x20" FCII Radials.. these were flogging awesome looking, had great traction in the conditions I used them, wore evenly, held up while trailing w/o issues- and weighed a ton.. these things were 170# each..

rotational weight is (easiest to figure) a factor of four.. 100# wheel/tire combos feel like 400# to the engine- and the overall height alters leverage and overall drive ratio.. there is always that balancing act we play though, right? I don't mind shorter height tires if I'm not running long distances- but they are nice when you are running distances and holding a decently steady highway speed- unless those tall tires are also wide tires, or have uber-aggressive tread- then you throw any of those benefits out the window, no?

this is a subject that interests me greatly, if you can't tell..

right now I have terra grappler 275/70/20's on board.. they will be swapped for 285/75/20 dura grapplers when they've finished serving me.. those are the best tires (for my purposes) I've ever owned.. light, ridiculous tread life and good bite, strong E rating 10 ply tread w/ 3ply sidewall, and has the rolling resistance characteristics of a floggin' trailer tire..
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Old 11-28-2012, 06:57 AM
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Awesome info man. I was trying to stay out of the physics of what it actually means to the engine for a while. Some people have enough trouble processing linear accelerations and inertia... angular equations and calculations are out of the question if you don't want people to fall asleep. I'll try to keep it simple once I get a list of wheels up.

For example. I'm going to do a simple equation where half the mass of a rim is at its radius while the other half is contained a r/2 (the midpoint of the spokes).

For tires, I'll do roughly the same thing where 1/2 the weight is at the radius and the other half is at ((radius(tire)-radius(rim))/2)+radius(rim).

That should give some decent rough numbers that are easy to understand without having to do a lot of tedious calculus-based calculations.

I'm surprised not a lot of people think about how much their tire and rim choices affect their MPG, ride, handling, and acceleration. On my Audi I had a set of 18x9 rims that weighed 16.7 lbs each and a set of 19x8.5's that weighed 21 lbs each (minus tires). The stockers were 17x8 and weighed 23 lbs each. The difference in performance and ride varied because of the tire weight and size (which cut sidewall height do to +1 and +2 type configurations to maintain equal height to stock tire combo). Right now I'm evaluation which rims/tires I want on my Cobra. I want light but I also want big. I'm willing to sacrifice on weight though since the car will probably be making slightly excessive power (looking at maybe 750-900 HP).
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Old 11-28-2012, 08:03 AM
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is your cobra a strip car or a course car?

if strip, I'd personally go with a smaller diameter tire looks be damned.. get you rolling and the engine at stall speeds quicker.. I'd get as much contact patch as possible on the rear because the grip overwhelms the concern of weight IF you drop diameter.

if course, I'd go with a reasonably narrow, like, in the 285~305 range (less weight) on a lowish profile (no more than 40%, no less than 30%) for less lateral wiggle, and on no more than 18" diameter.. that seems to be the perfect diameter for negotiating the weight/torque loss to usable RPM range/distance covered by circumference ratio.. if the course was wet, though, I'd not hesitate to NARROW the tires width, soften the compound, and select a tire with outstanding sipes or tread designed to displace water..

and yup, in any case, keep the majority of the weight in the center as much as possible..


anything from this point forward is just me ranting about a subject that interests me, reader beware..


I first started paying close attention to size/diameter/weight when I began competitive mountain biking.. several broken bones and many many cases of beer later, I'm not so competitive anymore... but, the same holds true for any wheel/tire set-up on anything that applies power to them..

26" mountain bike wheel w/ 2.2" front and 2.1" rear, inflated to 22psi on soft track for traction (conforming to obstacles and in effect biting on at least two sides instead of one where the small contact patch touches) is a helluva lot harder to pedal than inflating them to 40psi on hard track- and the harder tire maintains speed hella easier..

29" wheel/tire- hard to accelerate (you REALLY notice when it's YOU providing power), but easier to maintain speed- the angle of approach obstacles such as protruding rocks or limbs, ect, is much smaller, so they sap much less inertia.. getting them up to speed can't be understated though- but neither can the engines (me) ability to maintain that speed once achieved..

in terms of vehicles:

the larger diameter 'trail' tires require less work load from the engine (in terms of torque) to roll over obstacles, because of the drastically reduced angle of approach.. in simple terms, I would have to accelerate the engine to 2kRPM to clear a 7" stump with 32" tires, but I can easily clear it @ 1200RPM with 35" tires.. yup.. that much difference..

on the road, smaller diameter tires allow for hella lower driving ratio's.. it takes MUCH less energy to get them rolling.. great for towing or hauling.. larger diameter tires are really tough on the engine to get rolling, but once there and maintaining speed, don't work near as hard on the engine... unless those tires also weigh a LOT more.. which, they often do..

contact patch- the more narrow, the less traction- but the less drag.. no good for offroad, but very good for economy..

tread pattern- the less tread blocks (treads that impact perpendicular to road) the less rolling resistance, the less noise, and the less ability to shuck debris and water..

sipes- the little cut looking things on treads- the less sipes, the less venting and the more hydroplaning.. the longer lasting tread, though..

compound- the softer the better traction, the more heat, the quicker wear, and the heavier; the harder the less traction, the longer wear, and the lighter..

for a DD, and a working DD on our rigs, I can't understand using less than a E load rated tire with a harder compound, and pretty much devoid of sipes and blocks (like that dura grappler, or most commercial rated tires)..

for a truck that sees a lot of offroad, I can't see anything useful less than a 12.5" width tire.. the bigger footprint the better, so we don't sink in at the drop of a hat- wanna spread that weight over as much ground as possible- also, we produce enough torque down low to not worry much about drive ratio- so at least a 34~35" tire.. WITH A TALL SIDEWALL- so, 20" rims are out.. 17's are the way to go, so you can lower pressure and conform to the terra without rolling the tire off the rim..

if you play in your work truck, terra grapplers, cooper at3's, BF' AT's are good choices.. around 275~285/60~75 range... kinda hardish compound to get some life out of them, yet plenty of blocks to get decent traction in most undemanding conditions..

just my $2.. (i think i blew my .02 around the second sentence)..
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Old 11-28-2012, 08:53 AM
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As far as contact patch area, tire size does play a role, but that is in conjunction with air pressure, tire construction, and load. For example, choosing a tire that is twice as wide does not give you twice as much contact patch area. What you gain is essentially a wider contact patch of essentially the same area (helps with lateral grip). It's (contact patch area) a funny calculation to do and no single equation can truly assess the measurements of all tires.

Little more off topic, but the Cobra sees more course/track work than strip. It racks up about 500 miles a year now.

I don't care about absolute performance on the track. I want a good looking street cruiser. It's a convertible after all. If performance were a concern, I'd stick with ultra-lightweight 17's. But, for this, it'll be running a 255-275 up front and 295 or 305 in the rear in a reasonably sticky compound with a "streetable" tread pattern.
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Old 11-28-2012, 10:51 AM
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I agree with you about attempting to explain the contact patch thing.. it's even used in several different contexts that make it even more confusing..

I used to teach a motorcycle safety course, and though it wasn't part of the class, I USED to try to explain traction in relationship to contact patch.. I never could explain it easily, and I don't think I was ever successful.. the only way I could approximate it was by saying: "you may be in a total loss of traction with your current contact patch, but the very next contact patch may have perfect traction if you allow the tire to simply roll to it"..

anyway, sorry for ruining your thread- back on point..

I, for one, am willing to sacrifice traction/noise/looks/diversity for longevity/less rolling resistance/and less diversity, and comfort/appearances for function/dependability.. that is just me, though.. I'm NOT willing, however, to sacrifice ALL of the before mentioned for ALL of the after mentioned..

fortunately for us, there are a helluva lotta tires to choose from out there..
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Old 11-28-2012, 11:24 AM
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When I swapped out the stock Contitrac TR's to studded Winterforce's (same exact tire size on the same wheels) I lost almost 2mgp! I expect some drop but holy crap!
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rims, rotational, tires, unsprung, wheel weight

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