Are these wheels worth it?

[Improbcat]

I have a chance to buy a set of used rims for my xB for $250 (with tires). They are the same size as the stock steel wheels, but are 13lbs each vs the stock 21lbs.

He says the tires are nearly new, and since I don't have stock or LRR tires on the box I'm not too worried about added resistance there.

However my current tires/rims are in perfectly good shape, and I've seen sets of stock rims w/stock tires in near-new condition going for $200 or less.

Will the 8lb/wheel give me any noticeable mpg improvement over stock? In particular am I likely to see enough to offset the cost?

[UfoTofU]

Are you doing it only for the MPG benefits or also for a visual upgrade?

If I were you and I liked the looks of them AND they are lighter then I would go ahead and buy them. Sell the stock rims and tires you have and then end up with a fresh set of tires and lighter rims for not too much money.

[BEEF]

In my opinion, if you are doing it just for the FE, then the answer is no on all accounts. if the wheels look cool and you like them, then yes.

not too many people on here talk too much about weight reduction. I have seen myself that there is a very minimal difference in FE when I ride alone vs when my friend rides with me (220lbs) there is a difference but you are only talking about 24lbs.

another friend of mine was talking about weight reduction and he said that you have to take 100lbs out of your car to gain 1 tenth of a second on a qtr mile. I am pretty sure that that is a rule of thumb as it depends on the weight of the car when you start weight reduction but you see my point.

I am sure that if you keep your car long enough or if gas prices go stupid then maybe you will recoup your money from that investment but it will be a long time regardless.

on the other hand, if the rims look cool and you like them and you get better FE, then go for it. I am sure it will take me quite a while to recoup the savings enough to pay for my scangauge but it is a cool piece of gadgetry and it was a good excuse for me to buy a toy.

[Improbcat]

thanks, that was what I thought.

They are neat rims, but I am always nervous about bending alloy rims, and super-light ones will probably be even more prone to that.

I'll have to think about it some more, but now at least I know I can remove "useful FE improvement" from the equation.

[civic lover]

I can maybe help answer the question. I am going to be replacing my stock 13 steelies for a set of vx rims. Watch my gas log to see if it improves or not.

[JV-Tuga]

The way I envision it you may reap some rewards if you drive mostly city (stop and go), but you may lose some on the highway because the momentum from the heavier wheels also helps you along.

Those that know more may correct me if I am wrong.

[Powerstroke IN]

You have to remember that each pound of rotating weight you save equals 3 pounds of stationary weight when it comes tostarting and stopping. So 8lb wheels over the stock 21 equals 13lbs on each wheel. Thats 52 lbs total, and a virtual savings of 156 lbs. Your brakes will apreciate that. Follow up with lightweight brake rotors and even pullies for your motor and I would think you would notice some kind of improvement...

[Improbcat]

I may have been unclear. The new rims are 13lbs each, *saving* 8lbs per wheel. For a total of 32lbs and a virtual total of 96lbs, or one skinny kid.

[Powerstroke IN]

Originally Posted by JV-Tuga

The way I envision it you may reap some rewards if you drive mostly city (stop and go), but you may lose some on the highway because the momentum from the heavier wheels also helps you along.

Those that know more may correct me if I am wrong.

You are mostly correct, but the added momentum would really only help if you were coasting. The best thing to do is reduce friction before you worry about the weight. The savings while accellerating more than make up for the lack of momentum. At least thats what I found on a highschool team when we built a one person 'car' that got 6800mpg in a practice run and a solid 2000mpg from a 3.5 hp lawnmower engine.

[theholycow]

Originally Posted by Powerstroke IN

You have to remember that each pound of rotating weight you save equals 3 pounds of stationary weight when it comes tostarting and stopping.

I would like for someone to challenge this piece of folklore. I question whether it's true or not. In bicycling, where such issues are FAR more important because its not only our own speed but indeed our own legs, muscles, and pain on the line, the most scientific and logical arguments I've seen were that it is in fact a myth.

I spent quite a bit of time in rec.bicycles.tech for awhile, where there are some real experts who have the credibility and research to back up their claims and arguments, and I do recall that such people did not buy into the "rotating weight is worth more than other weight" stuff. I also learned about tire pressure, tire width, and rolling resistance; and some of what I learned is counterintuitive but definitely true.

[BEEF]

I have heard that a larger tire can have a significant affect on the brakes. this is part of the reason that the SUVs with the 24" rims seem to go through brake pads like nobodys business.

I don't know that for fact but figured I would add to the conversation. (it may just be because SUV drivers seem to drive fast and stop hard)

[theholycow]

That's true. A taller tire requires the brakes to work harder, just as it requires the engine to work harder. At least with the engine, you can change the gearing between the tires and the engine. With the brakes you can't.

[Powerstroke IN]

Originally Posted by theholycow

I would like for someone to challenge this piece of folklore. I question whether it's true or not. In bicycling, where such issues are FAR more important because its not only our own speed but indeed our own legs, muscles, and pain on the line, the most scientific and logical arguments I've seen were that it is in fact a myth.

I spent quite a bit of time in rec.bicycles.tech for awhile, where there are some real experts who have the credibility and research to back up their claims and arguments, and I do recall that such people did not buy into the "rotating weight is worth more than other weight" stuff. I also learned about tire pressure, tire width, and rolling resistance; and some of what I learned is counterintuitive but definitely true.

When our highschool team was designing the car, we appraoched it from the angle of a recumbent bike with two wheel in front. Our first year (my junior year), we tried driving at a constant speed of 25 mph (the required average speed) on one run, and accellerating to 35 mph and cruising down to 15mph after killing the engine. We only got 800mpg from burning and cruising. Our second year, we tweaked the body (which was constructed from aluminum J-channel and covered in heat-shrink plastic) and our only other changes were a smaller wheel made from carbon fiber that weighed half as much, special Michelin tires ordered from france to reduce rolling resistance, and ceramic bearings in the front hubs. That year we got 1500mpg with the same driver on the same track in mostly the same conditions (I think the humidity was 2% higher). Every time we reduced sprung (rotating) weight, we saw proportional increases in mpg. This past year in a national competition in California, the exact same body we built in 2005 got 6800 mpg in a test run. The only changes were yet lighter wheels and tires, lighter rear axle, lighter spokes than provided with the wheels, and a milled flywheel. That alone speakes volumes to me. Either the driver that they recruites this year somehow mastered the techniques, or reducing sprung weight is the key.

[theholycow]

I think you mean unsprung weight, not sprung. Anyway, your experiments certainly proved that your actions increased efficiency, but not 100% surely that saving rotating weight is any better than non-rotating weight. Don't forget that there are environmental factors to consider, too.

An experiment specifically to determine if rotating weight really means that much more than non-rotating weight would be to add some wheel weights, do some test runs, then move the wheel weights to the seat.

I'm not trying to be argumentative, it's just that one learns a lot challenging generally accepted but not thoroughly explored concepts like this.

[1cheap1]

I think that a little here, a little there all adds up to maximum FE. Each little thing ( weight reduction, technique, aero mods, friction reduction, etc.) are not much by themselves but add up to max mpg when done together. Just my 2cents.

[VetteOwner]

if you live where the dump salt, keep the stock rims+ tires as winter rims/tires...

[Powerstroke IN]

Originally Posted by theholycow

I think you mean unsprung weight, not sprung. Anyway, your experiments certainly proved that your actions increased efficiency, but not 100% surely that saving rotating weight is any better than non-rotating weight. Don't forget that there are environmental factors to consider, too.

An experiment specifically to determine if rotating weight really means that much more than non-rotating weight would be to add some wheel weights, do some test runs, then move the wheel weights to the seat.

I'm not trying to be argumentative, it's just that one learns a lot challenging generally accepted but not thoroughly explored concepts like this.

I believe you are correct, and 1cheap1 is as well. I'm interested, but there would have to be a way to add the wheel weights in such a way that the wheels were balanced. Adding a weight to the wheel must be done carefully. I think we can all agree that an unbalanced wheel is a FE nightmare... I think the weights would have to be pretty significant to have any significant change show up in any tests us, the laymen, could do. Seeing how much fuel you put in the tank and reading the odometer isn't the most scientific thing ever...

[theholycow]

Originally Posted by Powerstroke IN

there would have to be a way to add the wheel weights in such a way that the wheels were balanced. [...] I think the weights would have to be pretty significant to have any significant change show up in any tests us, the laymen, could do.

For the 6800mpg car, the weights probably wouldn't need to be huge. The adhesive-backed wheel weights used to balance normal automotive wheels ought to do fine.

For a normal car, the OP could keep both sets of wheels, the 13lb ones and the 21lb ones. Carry one set in the vehicle and mount the other set, then switch. I suspect that, for this experiment, it will not be possible to measure accurately enough, and that the wheel switch will not produce any measurable gain even without carrying the old wheels in the vehicle.

If I were the OP, I might still get the new wheels anyway, under the following conditions: I'd have to be confident that I could sell the old set for nearly what I paid for the new set, and I'd have to be confident that the new wheels aren't going to be too weak and get damaged easily.