weights of MPSC vs R888
04-29-2009, 06:22 PM
#16
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04-29-2009, 07:07 PM
#17
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First thing: You'd probably be better off looking at 18" wheels/tires for track usage, rather than 19". For reasons of cost, weight and tire choice.
Second: Saving 3-4 lbs per corner in tire weight would be significant, IMHO. It's all at the outer edge of the rotating, unsprung wheel. The latest Excellence Mag/Manthley Racing article says Porsche uses a multiplier of 7:1 when evaluating the benefits of reducing wheel/tire weight. In other words, saving 4 lbs per wheel x 4 wheels = 16 lbs x 7 = same benefit as reducing sprung vehicle mass by 112 lbs.
I run 18" MPSCups.
Second: Saving 3-4 lbs per corner in tire weight would be significant, IMHO. It's all at the outer edge of the rotating, unsprung wheel. The latest Excellence Mag/Manthley Racing article says Porsche uses a multiplier of 7:1 when evaluating the benefits of reducing wheel/tire weight. In other words, saving 4 lbs per wheel x 4 wheels = 16 lbs x 7 = same benefit as reducing sprung vehicle mass by 112 lbs.
I run 18" MPSCups.
04-29-2009, 07:19 PM
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Yeah... I just referrenced what the article stated. I agree 7:1 sounds too good to be true... but we all know the benefit of reducing unsprung rotating mass is better than 1:1 vs sprung mass. So, given the choice between (roughly) similar tires with different weights, why not go lighter?
I think the OP's question was answered long ago.
I think the OP's question was answered long ago.
04-29-2009, 07:20 PM
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For the record, I was responding to:
"(snip)......Second: Saving 3-4 lbs per corner in tire weight would be significant, IMHO."
4lbs a tire, (and usually it is more for the fronts than the fatter rears), is a little bit of weight. Sure, all things equal, I would obviously want the lighter tire. bummed that i cant run the Hoosiers because they were 3-4lbs lighter per tire, but just cant afford buying new tires. So, in the end, I lose the equivilant of 1 to 2hp for acceleration, but thats not the end of the world and is hardly significant.
mk
"(snip)......Second: Saving 3-4 lbs per corner in tire weight would be significant, IMHO."
4lbs a tire, (and usually it is more for the fronts than the fatter rears), is a little bit of weight. Sure, all things equal, I would obviously want the lighter tire. bummed that i cant run the Hoosiers because they were 3-4lbs lighter per tire, but just cant afford buying new tires. So, in the end, I lose the equivilant of 1 to 2hp for acceleration, but thats not the end of the world and is hardly significant.
mk
When you begin ending your grandiose statements with phrases such as "is hardly significant TO ME", I will no longer think of you as such an arrogant A WHOLE (as in complete Markie).
So, are we to understand that the weight savings of the Hoosiers is significant to the point that you are "bummed", but you DECLARE the weight savings as "insignificant" because you can't afford the tires???????
04-29-2009, 07:22 PM
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Yeah... I just referrenced what the article stated. I agree 7:1 sounds too good to be true... but we all know the benefit of reducing unsprung rotating mass is better than 1:1 vs sprung mass. So, given the choice between (roughly) similar tires with different weights, why not go lighter?
I think the OP's question was answered long ago.
I think the OP's question was answered long ago.
04-30-2009, 01:41 AM
#22
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Excuse me. I thought you were correcting my 3lb vs the earlier quoted 4 lbs in my post.
something doesnt have to be significant for me to be bummed I cant take advantage of it. If you knew the work I did to lose the last 15lbs, you would understand. It all adds up, but it is hardly significant individually.
yes, 1.5HP as a net effect on accelerative power loss is not significant to me. is it "significant" to you ?
Never mind.
mk
something doesnt have to be significant for me to be bummed I cant take advantage of it. If you knew the work I did to lose the last 15lbs, you would understand. It all adds up, but it is hardly significant individually.
yes, 1.5HP as a net effect on accelerative power loss is not significant to me. is it "significant" to you ?
Never mind.
mk
I simply answered the man's question. I never made a statement about what someone should consider "significant".
When you begin ending your grandiose statements with phrases such as "is hardly significant TO ME", I will no longer think of you as such an arrogant A WHOLE (as in complete Markie).
So, are we to understand that the weight savings of the Hoosiers is significant to the point that you are "bummed", but you DECLARE the weight savings as "insignificant" because you can't afford the tires???????
When you begin ending your grandiose statements with phrases such as "is hardly significant TO ME", I will no longer think of you as such an arrogant A WHOLE (as in complete Markie).
So, are we to understand that the weight savings of the Hoosiers is significant to the point that you are "bummed", but you DECLARE the weight savings as "insignificant" because you can't afford the tires???????
04-30-2009, 01:47 AM
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04-30-2009, 09:32 AM
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Can we get back to the OP's original question and discussion? He was thinking that he was considering some pretty expensive wheels that would save weight, so should he be concerned about tires that weigh between 4 and 6 lbs more each. I think we can all agree that less weight is better and that unsprung rotational mass weight on wheels / tires / rotors is much more significant than sprung weight (ie: rip out parts of your interior).
04-30-2009, 11:39 AM
#26
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Again, we have to define "significant". If a 1.5 or 2hp acceleration savings is significant, then yes, it is.
The formula for calculating this is:
1/2Iw^2 ( KE rotational) = 1/2M(w x R) ^2 (KE Linear) This compares the mass if it is in the car vs spinning on the wheel or tire.
Every pound you add to a tire roughly comes out to about 2x that if it was in the car.
As far as unsprung weight, it depends on the track. gyroscopic forces as well need to be considered, to quanitify this is a little more difficult.
mk
The formula for calculating this is:
1/2Iw^2 ( KE rotational) = 1/2M(w x R) ^2 (KE Linear) This compares the mass if it is in the car vs spinning on the wheel or tire.
Every pound you add to a tire roughly comes out to about 2x that if it was in the car.
As far as unsprung weight, it depends on the track. gyroscopic forces as well need to be considered, to quanitify this is a little more difficult.
mk
Can we get back to the OP's original question and discussion? He was thinking that he was considering some pretty expensive wheels that would save weight, so should he be concerned about tires that weigh between 4 and 6 lbs more each. I think we can all agree that less weight is better and that unsprung rotational mass weight on wheels / tires / rotors is much more significant than sprung weight (ie: rip out parts of your interior).
04-30-2009, 12:14 PM
#27
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Thanks guys. Lots of good discussion and in true rennlist fashion a few raging debates. One thing I have noted as a result of my research is the tire choices for 11.5 rears and 8.5 fronts on 18s are pretty slim. I would have thought they would have been better. I could go with the 18" cups but the rotation is a bit different than spec for the 997S. It would change my gearing and speedo. Not an issue for the track, but an incovenience for the road. The other item I noticed is that the Champion 18" wheels I was looking at are not available right now as the demand isn't high enough for an 80 set run. And....there is no ETA. The 19"s are just about as light though and would save 20lbs off my lobsters total while giving me a half inch of width over the lobsters all around (8.5 & 11.5 vs 8 & 11). The tire choices are all there too (MPSCs, Toyos, Hoosiers & super expensive Corsas).
04-30-2009, 01:07 PM
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Thanks guys. Lots of good discussion and in true rennlist fashion a few raging debates. One thing I have noted as a result of my research is the tire choices for 11.5 rears and 8.5 fronts on 18s are pretty slim. I would have thought they would have been better. I could go with the 18" cups but the rotation is a bit different than spec for the 997S. It would change my gearing and speedo. Not an issue for the track, but an incovenience for the road. The other item I noticed is that the Champion 18" wheels I was looking at are not available right now as the demand isn't high enough for an 80 set run. And....there is no ETA. The 19"s are just about as light though and would save 20lbs off my lobsters total while giving me a half inch of width over the lobsters all around (8.5 & 11.5 vs 8 & 11). The tire choices are all there too (MPSCs, Toyos, Hoosiers & super expensive Corsas).
04-30-2009, 01:12 PM
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Can we get back to the OP's original question and discussion? He was thinking that he was considering some pretty expensive wheels that would save weight, so should he be concerned about tires that weigh between 4 and 6 lbs more each. I think we can all agree that less weight is better and that unsprung rotational mass weight on wheels / tires / rotors is much more significant than sprung weight (ie: rip out parts of your interior).
I certainly agree with your last sentence Ron..."less weight is better", "unsprung...weight is much more significant than sprung weight".
04-30-2009, 02:20 PM
#30
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This spread sheet might help with choices but it's slanted towards the 6GT3 sizes. I've asked Nitto for the weights for the NT01s but no reply yet. Hoosiers are definitely lighter...
I heard a similar multiple before for rotating un-sprung mass...net effect is X6.
I heard a similar multiple before for rotating un-sprung mass...net effect is X6.