I've been looking for some rims and have been looking at the Kosei K1 in 15x7 that weigh 12.8lbs. And also the 5zigen FN-01R(cast rim) in 15x7 that weigh 14.0lbs. And I will be running on azenis 205/50/15. My question is if I get the 5zigen will 1.2lbs make that much of a difference on the autocross course. Because the azenis in that size I "think" weigh like 25lbs each. So one more pound wouldn't really hurt that much performance would it. Considering the azenis weigh so much already. I know enertia plays a roll in this also.

 

the Kosei's really weigh about 13.5lbs in 15x7.....at least on my scales

 

It is really very interesting to me that everyone obsesses over rim weight when the tire weight is actually more important. Since the tire is furthest away from the center of the wheel, it has the furthest distance to travel, thus its weight will effect the rotational motion the most. So no, I wouldn't sit and worry over the 1.2 lbs...if you are leaning toward the 5zigen rims (price, styling, whatever.) Now if you consider both rims equal, than hell go ahead and save the 1.2 lbs. Every rotational and unsprung bit saved is

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by siisgood00 &raquo;</TD></TR><TR><TD CLASS="quote">It is really very interesting to me that everyone obsesses over rim weight when the tire weight is actually more important. Since the tire is furthest away from the center of the wheel, it has the furthest distance to travel, thus its weight will effect the rotational motion the most. So no, I wouldn't sit and worry over the 1.2 lbs...if you are leaning toward the 5zigen rims (price, styling, whatever.) Now if you consider both rims equal, than hell go ahead and save the 1.2 lbs. Every rotational and unsprung bit saved is </TD></TR></TABLE>

You have to consider where most of the mass of a wheel is located =&gt; the rim. The rim is also significantly displaced from the wheel rotational axis. If you've ever seen rims without center piece (spokes and hub) then you'll be very surprised how much the rim weighs. Since the tires are identical in both scenarios, I would believe that 1.2lbs 15" away from the wheel axis would definitely require more torque to accelerate and decelerate the wheel. Not to mention the unsprung weight you already mentioned.

Edit: I worked at a Discount Tire and was very surprised at the distribution of mass in wheels. There were a few people who had broken spokes off the wheel sometimes completely off (from doing stupid *** things). The spokes and wheel hub weigh nothing, practically.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by GSpeedR &raquo;</TD></TR><TR><TD CLASS="quote">
Since the tires are identical in both scenarios, I would believe that 1.2lbs 15" away from the wheel axis would definitely require more torque to accelerate and decelerate the wheel. Not to mention the unsprung weight you already mentioned. </TD></TR></TABLE>

I think you can assume that the 1.2 lbs will be distributed evenly across the wheel. In this sense, it is not 1.2 lbs 15 in. away. If it were, than I would have said hell yea go for the lighter rim.

Edit: Well your edit puts a new spin (no pun intented) on things.

 

Yeah, it does depend on the spoke design...

If the hub/spokes weigh 20% of the rest of the wheel (that's what I would assume after picking up destroyed Rota attacks and some 7 spoke Enkei wheel) then the differences in the rim masses is .96 lbs.

Of course, this isn't scientific at all so...

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by GSpeedR &raquo;</TD></TR><TR><TD CLASS="quote">

You have to consider where most of the mass of a wheel is located =&gt; the rim. The rim is also significantly displaced from the wheel rotational axis. If you've ever seen rims without center piece (spokes and hub) then you'll be very surprised how much the rim weighs. Since the tires are identical in both scenarios, I would believe that 1.2lbs 15" away from the wheel axis would definitely require more torque to accelerate and decelerate the wheel. Not to mention the unsprung weight you already mentioned.
</TD></TR></TABLE>

Its ONE pound!!!! Unless you are consistently losing to a National Caliber driver by .01 secs, it does not really make that much difference. And yes I understand that there are 4 wheels, so it is really 4 lbs, but I seriously doubt you will be able to tell the difference.

Buy whatever wheel you like better or is the least expensive!!!!

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by StageOne &raquo;</TD></TR><TR><TD CLASS="quote">

Its ONE pound!!!! Unless you are consistently losing to a National Caliber driver by .01 secs, it does not really make that much difference. And yes I understand that there are 4 wheels, so it is really 4 lbs, but I seriously doubt you will be able to tell the difference.

Buy whatever wheel you like better or is the least expensive!!!!</TD></TR></TABLE>

Agreed...it doesn't make THAT much of a difference. Sure it IS a difference, but I don't think anyone is going to lose a National Championship over it.

 

Well 4 lbs is 4 lbs. People do some pretty crazy things to remove 4 pounds, like drilling holes in the hub (an EP crosser I know of).

fine...buy whichever you like better...

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by GSpeedR &raquo;</TD></TR><TR><TD CLASS="quote">Well 4 lbs is 4 lbs. People do some pretty crazy things to remove 4 pounds, like drilling holes in the hub (an EP crosser I know of).

fine...buy whichever you like better...</TD></TR></TABLE>

Take a poo before your run group...

I'm probably 60 lbs heavier than some of my competitors...I'll save my cash on the 4 lbs.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by PseudoRealityX &raquo;</TD></TR><TR><TD CLASS="quote">

Take a poo before your run group...

I'm probably 60 lbs heavier than some of my competitors...I'll save my cash on the 4 lbs.</TD></TR></TABLE>

Nooo, rotational weight my friend, rotational weight!
I would opt to drop 1 lbs of rotional weight for every 25-50 lbs of sprung weight

 

Mgineering.net
check under 4sale

 

thanks for all the information fellows. I really didn't think a total of 4lbs was going to make that much of a difference. I know it does but I probably won't feel it. And even if I get the lighter rims I probably won't be able to take advantage of the less weight considering I"m still kind of a novice driver still. But yeah thanks for all the info.

 

So does that mean you like the 5zigen rims better? Are they less expensive/look better?

 

mmm...rotas.....

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by siisgood00 &raquo;</TD></TR><TR><TD CLASS="quote">

Nooo, rotational weight my friend, rotational weight!
I would opt to drop 1 lbs of rotional weight for every 25-50 lbs of sprung weight</TD></TR></TABLE>

Depends on the change in the polar moment of inertia that this weight reduction will cause, and the angular acceleration said part will experience.

There are very few things in a car that would benefit from 1lb less rotating weight versus 25-50lbs of sprung weight.

I'll take the 50lbs off the body of the car thank you very much.

 

Yes 50 lbs is quite drastic, I agree. Now if we were talking about 1 lb of rotational weight inside the engine....
I was reading in Road & Track that Porsche managed to cut 7.7 lbs of roational weight from the engine of the new GT2!!! Amazing.

 

Sorry to interrupt this thread but i had a q. that seems like you guys could be able to answer. I have 17x7" Nippon V5 rims on my Si that weigh 22.5lbs. I weighed them on a scale with the tires and they came out to 44lbs.

Of course, i plan on getting some smaller wheels -- 15x6.5" rotas most likely. They weigh about 12lbs. But with Falken Azenis 205/50/15 tires, how much will the rota 12lb. wheel weigh? TIA


Modified by MikeBSI at 2:12 AM 5/25/2003


Modified by MikeBSI at 2:15 AM 5/25/2003

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by MikeBSI &raquo;</TD></TR><TR><TD CLASS="quote">how much will the rota 12lb. wheel weigh? TIA
</TD></TR></TABLE>

12 lbs

Falkens in that size will run 22 or 24 lbs or so - dont remember the exact number, but they're heavy.

I ran this combo at the track last year and they worked fantastic.

 

This topic is funny.

Even the pros don't obsess over one or two pounds when they have BBS or Fikse or whomever handing them wheels. I doubt any driver in any major race series could tell a one pound difference in wheel weights, let alone any of us.

-Adam

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by mityVR6 &raquo;</TD></TR><TR><TD CLASS="quote">This topic is funny.

Even the pros don't obsess over one or two pounds when they have BBS or Fikse or whomever handing them wheels. I doubt any driver in any major race series could tell a one pound difference in wheel weights, let alone any of us.

-Adam</TD></TR></TABLE>

Exactly. Use whats cheap, reliable and available. Falkens + Rotas cant be beat for their price/wear/performance.

 

I'm going to get the 5zigen rims they are like $20 more per rim compared to the kosei k1. They are the only rim I could find that came in 15x7 and 42mm offset and didn't break the bank to much. I know their are alot of 15x6.5 rims out their but I want to utilize every bite of the tire, don't want to get the mushey feeling with narrow rim.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by goforbroke &raquo;</TD></TR><TR><TD CLASS="quote">I'm going to get the 5zigen rims they are like $20 more per rim compared to the kosei k1. They are the only rim I could find that came in 15x7 and 42mm offset and didn't break the bank to much. I know their are alot of 15x6.5 rims out their but I want to utilize every bite of the tire, don't want to get the mushey feeling with narrow rim.</TD></TR></TABLE>

How do you know there will be a mushy feeling?

What do you have to compare with? The kosei's are 15x7 also, and if they are cheaper and lighter go with that. If you want mush turn in, use 225/45's on a 6" wheel. 205/50 azenis on a 6.5" wheel wont cause you any hassles at all.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by .RJ &raquo;</TD></TR><TR><TD CLASS="quote">
if they are cheaper and lighter go with that. </TD></TR></TABLE>


Dont pay more for a heavier wheel.

 

I've heard some recent discussion on a track mailing list about how SSR Competitions are easily bent on tall, firm berms, like those now in the Esses at Buttonwillow (I used one, I know. They aren't fun.) You might not want to spend a bunch of money on lightweight, somewhat fragile wheels. If you're new to the whole track thing you might want to set your priorities such that you get wheels that are 1. strong enough to handle some abuse, 2. inexpensive enough to replace when you bend one on a berm and 3. reasonably wide/lightweight/painted the right color/whatever.

Of course, you mentioned autocrossing. I offer this advice only because you'll probably end up trying track days (and why shouldn't you, with a good set of wheels and tires?) and it might become an issue.

-Adam