Performance Comparing 16", 17" Rims.
02-18-2001, 07:11 AM
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Is handling significantly improved with 17" rims over that of 16"?
Weight wise I would think it difficult to get a lightweight 17" down to weight of a purpose built lightweight 16".
Thoughts?
Thanks.
Weight wise I would think it difficult to get a lightweight 17" down to weight of a purpose built lightweight 16".
Thoughts?
Thanks.
02-18-2001, 08:13 AM
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Hey dude-
I kind of touched upon the subject on your other thread...
Anyhow-
Wheel weights are important- but don't forget tire weight since the tires represent the most mass on the farthest point from the center of rotation and therefor affect the acceleration the most. Although most lightweight 16" wheels are lighter than their 17" counterparts, you also have to include the fact that you will use a shorter tire sidewall, which means less rubber and steel belt. If you go with a plus 1 sizing, the tire weights are very close. Going with a shorter sidewall with the proper wheel width on a plus 1 sizing will give you more responsive handling (assuming same tire brand/type) but on the negative side you have to deal with poorer ride quality (rougher ride). The positive is the shorter sidewalls are stiffer, but they also allow the wheels to ride closer to the ground- a bad thing in pothole infested cities like Chicago.
Of course, the best of both worlds (lighter wheels AND tires) would be ideal which is why you see ultralightweight wheels that aren't necessarily very durable used with lightweight tires using nylon casings (Hoosiers) on race cars. The only real negative to such a setup is that it's easier to flatspot the tires when braking than if you were using a heavier setup- momentum takes care of the heavy stuff in that regard... And, the wheels in this case have limited lifespans, which negate their use on the streets.
[Edited by GTRPower on 02-18-2001 at 09:20 AM]
I kind of touched upon the subject on your other thread...
Anyhow-
Wheel weights are important- but don't forget tire weight since the tires represent the most mass on the farthest point from the center of rotation and therefor affect the acceleration the most. Although most lightweight 16" wheels are lighter than their 17" counterparts, you also have to include the fact that you will use a shorter tire sidewall, which means less rubber and steel belt. If you go with a plus 1 sizing, the tire weights are very close. Going with a shorter sidewall with the proper wheel width on a plus 1 sizing will give you more responsive handling (assuming same tire brand/type) but on the negative side you have to deal with poorer ride quality (rougher ride). The positive is the shorter sidewalls are stiffer, but they also allow the wheels to ride closer to the ground- a bad thing in pothole infested cities like Chicago.
Of course, the best of both worlds (lighter wheels AND tires) would be ideal which is why you see ultralightweight wheels that aren't necessarily very durable used with lightweight tires using nylon casings (Hoosiers) on race cars. The only real negative to such a setup is that it's easier to flatspot the tires when braking than if you were using a heavier setup- momentum takes care of the heavy stuff in that regard... And, the wheels in this case have limited lifespans, which negate their use on the streets.
[Edited by GTRPower on 02-18-2001 at 09:20 AM]
02-18-2001, 09:42 AM
#3
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Al, Nick has got it right. You can actually do some rough estimate calculations of the effects of wheels vs. tires. What you're really concerned with is Moment of Inertia. This has to do with mass and mass distribution around the axis of rotation.
For a typical wheel/tire combo, I think you'll find that the tire, even though it may mass about the same as the wheel, possesses a Moment of Inertia that is easily 3-4 times as large as that of the wheel. In essence, this means that the tire takes 3-4 times as much torque to accelerate at a given rate. Thus, every pound you take off the tire is worth taking 3-4 off the wheel (these are rough estimates as it depends on where you take the mass off). Another way to look at it is that by reducing wheel weight by 25% (assuming no change in mass distribution) will only reduce your overall MOI by 5%.
This doesn't mean that lighter wheels aren't worth it. Any weight reduction helps in acceleration, suspension performance, etc. And since we're really more concerned about lots of other factors besides weight when it comes to tires(as Nick pointed out), it's easier to take weight out of the wheels as long as we make sure they're still strong enough.
UL
For a typical wheel/tire combo, I think you'll find that the tire, even though it may mass about the same as the wheel, possesses a Moment of Inertia that is easily 3-4 times as large as that of the wheel. In essence, this means that the tire takes 3-4 times as much torque to accelerate at a given rate. Thus, every pound you take off the tire is worth taking 3-4 off the wheel (these are rough estimates as it depends on where you take the mass off). Another way to look at it is that by reducing wheel weight by 25% (assuming no change in mass distribution) will only reduce your overall MOI by 5%.
This doesn't mean that lighter wheels aren't worth it. Any weight reduction helps in acceleration, suspension performance, etc. And since we're really more concerned about lots of other factors besides weight when it comes to tires(as Nick pointed out), it's easier to take weight out of the wheels as long as we make sure they're still strong enough.
UL
02-18-2001, 12:00 PM
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Hmmmm...I remember reading recently that a pound ( or 2)added to wheel weight, was like adding 100 pounds to the car (dead weight) in terms of acceleration. I know i'm not explaining this very well ...although it seems a simple calculation its pretty far from it....! I will try to find the article and post it.The general consesus however is that given the option between 16, 17 , and 18 inch wheels the best compomise and track numbers came from the 17 inch combo.
I recently got 17 inch mf-10's and realized that tire weight is also a significant diff for 17, 18s , )I had avs intermediates) Side by side same width but I'd hazzard 3 or 4 pounds difference at least. I have'nt weighed every tire out there, but believe this is true for most 17 to 18 differences. (but not between 16 and 17 where some 17's are less)
I know that I lost a half second after selling my volks, and thought this was a screw up in my g-tech until I got the mf-10's and am back up there. thats my 2 cents
I recently got 17 inch mf-10's and realized that tire weight is also a significant diff for 17, 18s , )I had avs intermediates) Side by side same width but I'd hazzard 3 or 4 pounds difference at least. I have'nt weighed every tire out there, but believe this is true for most 17 to 18 differences. (but not between 16 and 17 where some 17's are less)
I know that I lost a half second after selling my volks, and thought this was a screw up in my g-tech until I got the mf-10's and am back up there. thats my 2 cents
02-18-2001, 01:29 PM
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Thanks for all the replies; I'm learning lots.
And Viscreal2000, your Volks were 16"? It's nice to hear about the 17"s being a good compromise between sizes.
And Viscreal2000, your Volks were 16"? It's nice to hear about the 17"s being a good compromise between sizes.
02-18-2001, 04:18 PM
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Viscreal2000,
There is a short thread on this over at vtec.net in the technical forum that actually goes through the calcs with formulas if you're _really_ interested (it can get kinda heavy).
But, to put it as succinctly as possible, the effect of wheel/tire mass on performance depends on a lot of factors. One is the moment of inertia (as discussed), another is the acceleration rate (lower moment of inertia helps more when accelerating hard in low gears).
If I were going to try and generalize an "effective weight" to simplify MoI effects on acceleration, I'd say that in lower gears you're looking at a maximum effective weight of about 2x the actual (maybe 3x in 1st gear with a very fast car), with that multiplier diminishing rapidly as speeds climb and acceleration diminishes.
For Prolene, if you're concerned primarily with handling, then you're almost definitely better off with some larger wheels to gain the sidewall stiffness and contact patch stability. The effect on acceleration of additional weight is measurable, but will be small compared to the handling gains if you're measuring lap times.
UL
There is a short thread on this over at vtec.net in the technical forum that actually goes through the calcs with formulas if you're _really_ interested (it can get kinda heavy).
But, to put it as succinctly as possible, the effect of wheel/tire mass on performance depends on a lot of factors. One is the moment of inertia (as discussed), another is the acceleration rate (lower moment of inertia helps more when accelerating hard in low gears).
If I were going to try and generalize an "effective weight" to simplify MoI effects on acceleration, I'd say that in lower gears you're looking at a maximum effective weight of about 2x the actual (maybe 3x in 1st gear with a very fast car), with that multiplier diminishing rapidly as speeds climb and acceleration diminishes.
For Prolene, if you're concerned primarily with handling, then you're almost definitely better off with some larger wheels to gain the sidewall stiffness and contact patch stability. The effect on acceleration of additional weight is measurable, but will be small compared to the handling gains if you're measuring lap times.
UL
02-18-2001, 06:10 PM
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Originally posted by ultimate lurker
For Prolene, if you're concerned primarily with handling, then you're almost definitely better off with some larger wheels to gain the sidewall stiffness and contact patch stability.
For Prolene, if you're concerned primarily with handling, then you're almost definitely better off with some larger wheels to gain the sidewall stiffness and contact patch stability.
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02-18-2001, 06:49 PM
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Hi,
My volks were 17 inchers. As for the calculations....I know it's too many factors to make a general statements. But the interesting thing about this particular test was the real world performance figures were almost a perfect match. i.e. 1 plus pound equaled 100 pounds ballast. And it was a match through the entire setup. Even more interesting was that lighter cars without a lot of torque i.e civics.....were the most affected by this. My suggestion is go for the lightest rim in whatever size you want. But once again, weight in 18 inch tires is not a good tradeoff. Go for 17's ismy opinion....cheers
My volks were 17 inchers. As for the calculations....I know it's too many factors to make a general statements. But the interesting thing about this particular test was the real world performance figures were almost a perfect match. i.e. 1 plus pound equaled 100 pounds ballast. And it was a match through the entire setup. Even more interesting was that lighter cars without a lot of torque i.e civics.....were the most affected by this. My suggestion is go for the lightest rim in whatever size you want. But once again, weight in 18 inch tires is not a good tradeoff. Go for 17's ismy opinion....cheers
02-18-2001, 08:29 PM
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Originally posted by ultimate lurker
...if you're concerned primarily with handling, then you're almost definitely better off with some larger wheels to gain the sidewall stiffness and contact patch stability...
UL
...if you're concerned primarily with handling, then you're almost definitely better off with some larger wheels to gain the sidewall stiffness and contact patch stability...
UL
Can you say more about this "contact patch stability"?
02-18-2001, 09:33 PM
#10
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Well, I don't know how much I can offer as I am no expert, but...
With a bigger wheel and lower profile tire (to retain the same overall tire height) you get a shorter sidewall (of course). This has several implications. But I think the easiest way to think about it is that in almost any imaginable case, the wheel has less flex than the tire Exchanging tire sidewall for extra wheel is a good tradeoff from that standpoint. The sidewall also behaves as a spring. The shorter the spring, the stiffer it is (for a given construction technique).
Because the sidewall has less flexibility, cornering forces are less likely to deform the tire to the point where the contact patch is compromised.
Now, this is a _very_ rough interpretation. Sometimes, lower profile tires can actually run softer sidewall materials because they are shorter in the sidewall region. Construction techniques in tires are also highly varied, so like most other things in life, execution is at least as important as theory. Finally, the tire and suspension must be engineered to work together. A suspension that doesn't have good camber control may see no gains with a plus size tire setup, or even a decrease, because the taller tire may tolerate suspension inadequacies better (the flex allowing it to "ignore" poor camber control, etc.).
UL
With a bigger wheel and lower profile tire (to retain the same overall tire height) you get a shorter sidewall (of course). This has several implications. But I think the easiest way to think about it is that in almost any imaginable case, the wheel has less flex than the tire Exchanging tire sidewall for extra wheel is a good tradeoff from that standpoint. The sidewall also behaves as a spring. The shorter the spring, the stiffer it is (for a given construction technique).
Because the sidewall has less flexibility, cornering forces are less likely to deform the tire to the point where the contact patch is compromised.
Now, this is a _very_ rough interpretation. Sometimes, lower profile tires can actually run softer sidewall materials because they are shorter in the sidewall region. Construction techniques in tires are also highly varied, so like most other things in life, execution is at least as important as theory. Finally, the tire and suspension must be engineered to work together. A suspension that doesn't have good camber control may see no gains with a plus size tire setup, or even a decrease, because the taller tire may tolerate suspension inadequacies better (the flex allowing it to "ignore" poor camber control, etc.).
UL