wheel weight and performance

[black180sx]

there are 2 wheels I like, one weighs 15.7lb each and the other 17.5lb each. I know rolling mass weight is important to keep low. If I like the looks of the heavier ones am i sacrificing acceleration?

[sr20power]

gee...it seem like you answered your own question?Quote »I know rolling mass weight is important to keep low.[/quote]if its that much of a concern, then remove the spare tire and buy a can of fix a flat. That should make up the difference...

[black180sx]

true, another issue is the 205/40 tires that come with the wheels, i have heard problems with these?

[sr20power]

like what?

[Grant@tirerack]

A complete make, model, and year for the car and a complete tire size would help all of us if you want an answer that means anything. Just a thought....

[PalmerWMD]

If I like the looks of the heavier ones am i sacrificing acceleration?

An extra pound on a wheel is like 4 extra pounds elsewhere.

So:

17.5-15.7=1.8

1.8 x4= a bit over 7 pounds.So its like driving with an extra 7 pounds in the trunk.

Fred..

[PalmerWMD]

More extreme examples involve all those fools putting 30lbs, 19 inch chrome wheels when their stock wheels weight 18 lbs.

30-18= 12

12x4= 48 lbs!

Almost extra 50 lbs equivalent.

Fred...

[Grant@tirerack]

If we're not careful, we'll all start sounding like the Miata guys Fred is right. You'd have more of a change in handling by running with half a tank of gas in the car.

[black180sx]

thanks for the help, I have a 1990 240sx with the stock se alloys and sorry tires (205-60 in front and 225-50 in the rear) and i need new tires. I found a tire wheel package, the adr concept pro with 205-40 tires. I guess they will be ok. How much do stock alloys weigh?

[Grant@tirerack]

A 205/40-16 or 205/40-17 is going to be way too short in either size. Too short in O.D. and way under on load rating for the car.

[TurboKA37]

grant or fred, what size tire would u suggest on a 17x7 and 17x7.5 wheel for a S14? i think i may be getting some new wheels and tires soon and need to kno what size tires to order.

[Ceptos]

how much of a difference would 2 pounds make in unsprung weight?

[Nismo_Freak]

17.5 - 15.7 = 1.8 lbs.

1.8 lbs. x 4 = 7.2 lbs. of unsprung weight

7.2 x 4 = 28.8 lbs. <--- equivalent weight to sprung vs. unsprung

So while that minor amount of difference per wheel seems small... it is in fact a large difference, not to mention that the multiplication factor in the final equation grows the more intensive you get with handling, so if this were a strong auto-x car you could get a better answer by multiplying by 6.

This is why the Miata owners absolutely go ape-**** over wheel weight, even down to lugnuts. It's also why most racing wheels in the Formula classes are magnesium.

[Grant@tirerack]

True, in autocross or road racing it makes a much bigger difference. For daily driving, most folks are not going to notice that much of a difference. 28.8 lbs is not going to have that dramatic of an effect on handling for the street. 99.9% of the drivers out there are not going to notice that much difference. Gasoline weighs around 6 lbs per gallon. For autocross or hard driving, I'm thinking 30 lbs of weight (at 6 lbs per gallon with a half tank full) will make a difference, but on the daily driver? I'ts all very relative to how you are using the car.

225/45-17 or 215/45-17 would be the best two sizes. The 225/45-17 would be about 4/10" taller but will still work well with a 7.5" rim.

[black180sx]

with these wheels it will just be a daily driver and they are 17x7 and weigh 16 lbs each

[Grant@tirerack]

For most folks, if you are at or under 1 lb per 1" in diameter on the wheel you are doing good.

[black180sx]

ok i ordered these wheels and yes they have 205-40s on them. I am rather poor. i know this is not an excuse but how serious is it, will these wheels function at least the same as my stock wheels?

[PalmerWMD]

Check this link:http://www.miata.net/garage/tirecalc.html

Your speedo might be off just a tad and your load rating lowered a bit but you drive a very light car so probably not such a big deal.

Hope fully the tires are decent brand/make?

Fred...

[Grant@tirerack]

The load rating for your stock tire size at 29psi was 1091 lbs per tire. These would max out at 882 lbs if it's a 76 load index tire and 992 lbs per tire if it's an 80 load index tire. That's if you run them at the maximum air pressure they are rated for. You've just reduced your tires' ability to handle the stress and weight of your vehicle in motion by over at least 400 lbs:eek: and that's if you you run the tires at maximum pressure. At the best you can expect faster tire wear and poor handling since the tires are overloaded. They will also be more prone to damage from overheating and impact. The sidewalls are not going to be able to handle the added stress and will break down faster internally. Not a good thing in my book. This is where we start hearing folks saying BRAND X is a lousy tire because the sidewalls bubble. I don't want to be harsh but it's a safety issue folks. Chet is working on getting a load range chart up in the FAQ's for us. One of our board members set up a file so we can post it. I'll give a detailed how-to on how to figure load ratings once it's posted.

[black180sx]

yes i understand, i know over 100 lbs weight reduction but i would need 400 lbs to make it ok i guess.

[black180sx]

oh yeah the offset is +43 which will fit but but is crappy i guess since its a fwd offset

[PROJECTRB240SX]

GAS IS 6.8 POUNDS PER GALLON AND WATER IS ABOUT 7.3 POUNDS PER GALLON.

[PROJECTRB240SX]

OK WHAT ABOUT 205/40-17'S WITH A LOAD RATING OF 87? WILL THAT MEET STOCK WEIGHT REQUIREMENTS WITH TIRES INFALATED TO 44PSI?

[black180sx]

well as far as me ignoring his advice, i dont have alot of money and i am trying to gauge exactly how severe the problem will be, of course with cars everything is a risk, but i guess some more than others. I already ordered wheels with a +43 offset and 205/40 tires and they will fit and whereas the tires will have a small sidewall i will just have to be careful. In the future i will plan my purchases better, but this was rushed due to certain reasons so ill make the best of it.

[Ceptos]

this doesnt really help anything, but i was wondering...say the tires are now rated 400lbs less than stock, if he reduced the weight of his vehicle by 400lbs, this still wouldnt make up the difference, right? im thinking that the load rating is most significant in a turn, where considerable weight is being transferred to the outside tires. or am i wrong?

[Exar-Kun]

you'll have to run the tires at higher inflation that normal. Yeah, keep in mind, I run a 225-45-17 Pzero thats got a load index of 98(i think..maybe 96), and run 35 psi in THOSE.

load index/sidewall sturdiness is most important in towing and/or cornering...so you're right...

-chet

[Grant@tirerack]

It it's an 87 you would be at 1201 lbs at 36 psi. That would be okay. Just don't run them lower than 35.

[black180sx]

so if i run 40 psi and check it often i will be ok?

[PROJECTRB240SX]

WELL I HAVE FOUR 205/40R17 AT 87 RUNNING AT 44PSI PLUS THE CAR HAS BEEN LIGHTEN BY 200 POUNDS AND COUNTING.

[Grant@tirerack]

As long at it's an 87 you'll be fine. Most tires are only an 80 in this size.