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Does a light tire help? Some specs inside.

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TippsTheFoo

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Discussion starter · #1 ·
I will be replacing the stock Contis on my SVTF shortly and will be doing an entire wheel swap to reduce the love-handles a little bit. I am planning on shedding at least 4 pounds per corner with the new wheel (stock SVTF = 21.5lbs, new wheel = no more than 17.5lbs). When thinking about which tire to pair with my new wheels, I also thought it might be nice to drop additional weight with a lighter replacement tire. Below is some information I've compiled. I'm looking for a tire that will serve,roughly, 85-90% street and 10-15% track duty.

Bridgestone S-03: 24lbs, 847 rev., 1201 load
Goodyear Eagle F1 GS-D3: 24.6" dia., 1356 load
BF Goodrich g-Force T/A KDW: 844 rev., 1201 load
Yokohama AVS ES100: 843 rev., 1201 load
Kumho Ecsta 712: 23lbs, 838 rev., 1201 load
Kumho Ecsta MX (215/45): 21lbs, 24.7" dia., 1201 load
Kumho Ecsta MX (215/40): 19.8lbs, 23.9" dia., 1074 load, 35psi?!?

The Bridgestone and Kumho weights were provided by the manufacturers online, the others (obviously) not. If anyone has numbers (or where I can find them) on the others, that would also help.

But, the main question is, will a lighter tire help or does it sacrifice anything (if so, what)?

Many seem to like the Kumho MX for what it gives at the price it is offered at. Moving down to a 215/40 (as Slick has suggested in the past) gains a little over 1lb in relation to the same tire in the stock 215/45 size, and over 4lbs compared to the Potenza S-03 (which has received many great reviews). The AVS ES100 also interests me, especially at its price, but I don't (at this time) have a weight value for it.

So,
1. Which tire above would best suit a 85/15 lifestyle?
2. Does a lighter tire help, or does it sacrifice (ie, strength, etc)?

TIA,
-Matt
 
#2 ·
don't know about the track duty, but less rotational weight is better. if you're counting grams it's the most important place to consider. less energy is required to make them spin around, which is naturally better.
 
Discussion starter · #3 ·
The only thing that concerns me is this:

17x7 SVTF rims w/ 215/45 Kuhmo MX's - 39.8 lbs
17x7 SDR's w/ 215/40 Kuhmo MX's - 38.8 lbs
17x7 SVTF rims w/ stock 215/45 Contisports - 38.0 lbs
Click to expand...
SlickShoes posted those weights on the Wheel/Tire board HERE.

From that data I get a bit lost. If the SVTF wheels weigh 21.5lbs and the Kumho MX's weigh in 215/45 weigh 21lbs, we should be seeing a combined total of 42.5lbs not 39.8lbs, right?

But, if we just put that aside and JUST compare tire weight, we can derive the following:

1. Kumho MX in 215/45 weigh 21lbs. If the stock SVTF wheels + the Kumho rubber (215/45) weigh 39.8lbs and the stock SVTF wheels + the stock Conti rubber weigh 38.0lbs then, with all the above data, the Conti rubber should weigh 19.2lbs. Could this be right? That is more than half a pound less than the Kumho MX in 215/40.

What disturbs me even more is the second wheel/tire combo in the above data from Slick. How can that figure be so?

The Rota SDR's weigh 17lbs, 4.5lbs LESS than the stock SVTF wheels. If we assume the Conti's weigh 19.2lbs and the Kumho's (215/40) weigh 19.8lbs, then we are actually seeing a weight GAIN of 0.2lbs!!! Not 4.5lbs less, but 0.2lbs more.

Can anyone explain this?
 
#4 ·
Yeah, statistics, damn statitics and lies.
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Don't forget to factor in the 40-44 lbs of air in each tire.....
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Seriously, unless you factor in extra audio weight, extra stuff in the dashbox, extra weight of the bodacious muffler, uh, that extra bean burrito you had at lunch, 15-16 lbs for tires/ wheels is not gonna make that much difference. Unless you can shave 80-100 lbs you aren't going to notice much change. Get the tires that stick. Drive around the extra couple of pounds.
 
#5 ·
Yeah, statistics, damn statitics and lies.
Image
Don't forget to factor in the 40-44 lbs of air in each tire.....
Image
Seriously, unless you factor in extra audio weight, extra stuff in the dashbox, extra weight of the bodacious muffler, uh, that extra bean burrito you had at lunch, 15-16 lbs for tires/ wheels is not gonna make that much difference. Unless you can shave 80-100 lbs you aren't going to notice much change. Get the tires that stick. Drive around the extra couple of pounds.
Click to expand...
WRONG! There IS an appreciable difference between sprung and unsprung weight. Every pound of UNsprung weight equals "X"(several ?) pounds of sprung weight--someone out there I am sure can fill in the "(x)". You are reducing rotational mass and thus reducing inertia which is a VERY good thing--think of each wheel/tire as a flywheel. A lighter flywheel on your engine makes the motor more responsive to both accelerating and decelerating; lighter wheels and tires do the same for the suspension and for accelerating and braking. All good
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I run some light BBS 14x6" wheels with 195/60 Azenis mainly for the reductuion in unsprung weight as well as the shorter diameter resulting in an effectively lower final drive. Get the best tradeoff between weight/cost/grip that you can afford!
 
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#6 ·
I don't know about that. When I changed to my MX's, I had no idea they were going to be heavier than the stock Conti's, and just driving away from Discount Tire I instantly knew things got slower. And now with my lighter weight track-only wheels, I dropped 4+ lbs per corner and again I can definitely feel it. Could be an overactive imagination I guess, but I'm usually pretty level headed with this stuff.
 
#8 ·
Yeah, statistics, damn statitics and lies.
Image
Don't forget to factor in the 40-44 lbs of air in each tire.....
Image
Seriously, unless you factor in extra audio weight, extra stuff in the dashbox, extra weight of the bodacious muffler, uh, that extra bean burrito you had at lunch, 15-16 lbs for tires/ wheels is not gonna make that much difference. Unless you can shave 80-100 lbs you aren't going to notice much change. Get the tires that stick. Drive around the extra couple of pounds.
Click to expand...
WRONG! There IS an appreciable difference between sprung and unsprung weight. Every pound of UNsprung weight equals "X"(several ?) pounds of sprung weight--someone out there I am sure can fill in the "(x)". You are reducing rotational mass and thus reducing inertia which is a VERY good thing--think of each wheel/tire as a flywheel. A lighter flywheel on your engine makes the motor more responsive to both accelerating and decelerating; lighter wheels and tires do the same for the suspension and for accelerating and braking. All good
Image


I run some light BBS 14x6" wheels with 195/60 Azenis mainly for the reductuion in unsprung weight as well as the shorter diameter resulting in an effectively lower final drive. Get the best tradeoff between weight/cost/grip that you can afford!
Click to expand...
Hey now.......easy on the rheacerman there
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, while he will WHOLEHEARTEDLY agree with you about the significant difference between sprung and unsprung weight....I think his point was simple - quit splitting hairs about a few pounds of tire weight and get out and spend more time going like hell on a road course or Solo II venue to get better going fast no matter what combo is under you.

Anyhoo.....I think the disparities among Slick's weight totals and the other observations are simple variance in construction + variances in scales.

So as rheacer almost said "pick some sound tires and get out and drive the piss out of them"
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not that I didn't try to have my current wheel/tire combo weigh in at lean 34.5lb or anything
Image
 
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#9 ·
Um, on paper, of course, there is an advantage with lower mass, yes. Can't argue with physics. I agree, smaller wheels DO make a difference, but it is as important (as you pointed out, indirectly) WHERE the weight is as how much. A 19 lb 17 inch rim is going to be harder to stop/spin than a 19 lb 15 inch rim. (It's a lever thing) Hence 15 inch rims on a IRL car instead of 17 in.- Why make wheels any bigger than needed to clear calipers?? Sure look at weights, but don't get caught up over 4 oz per corner. What about forged vs cast wheel? How often can you afford to replace them? My point was (is) most, if not all of the folks on this list (my self included) would be hard pressed to notice a difference in 4 oz between 2 17in combos. How many 20 oz speaker magnets offset 4 ounce savings on wheel/tire combo?
unless you factor in extra audio weight, extra stuff in the dashbox, extra weight of the bodacious muffler, uh, that extra bean burrito you had at lunch, 15-16 lbs for tires/ wheels {total} is not gonna make that much difference {to going faster}.
Click to expand...
I would certainly argue sticky tires are more important than saving, what was it?- 0.8 lbs a set. Got a friend that pushes 250-260 lbs, but can out drive 150 lb drivers (2 of them) in the same car, as he did this past weekend.
 
#12 ·
Didn't mean to come across so harshly--please accept my apologies.

While one may not notice an oz. or 4, a couple of pounds will be something that you can feel.
 
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#14 ·
Then we must also return to another part of the Initial Q....
While Wheel/Tire Combo X MAY Well be 4lbs Lighter than Combo Z, What Sacrifice, if any, is there with regard to sidewall stiffness and durability?
It May make little Difference for Straight-Line, but for cornering, the Response of a Nice Firm Sidewall is undeniable. Is it worth the weight savings to do without stiffness, or are the two not necessarily related?
Image

I Fully appreciate the advantage of less rotating mass, but I'd rather have more "Stick" and Response and push a LITTLE more weight.... IF that's a compromise that must be made....
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#15 ·
This is just speculation, but a lighter tire would obviously heat up more then a heavy tire under the same load and driving conditions. So to compensate for that extra heat, tire makers may have to use a harder compound to keep consistent performance. Or they might have to stiffen up the tire, resulting in better steering, but worse ride.
There are so many factors in tire design, I would think that stiffness is not directly related to weight. I would think there would be plenty of ways to make a stiff, light tire.
 
#16 ·
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No problem, Auto. I knew what you meant,
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and yes 16 extra lbs of ROTATING mass might be felt. The thing is, most of us drive around little things like that. My point was don't let a few ounces in wheel/ tire be the deciding factor in going fast on track or autoX course. Like Murph said, the biggest factor is going to be practice, practice, practice. Conti vs MX The Conti's aren't bad tires at all. I autocrossed on them many times when I discovered a crack in the spoke of my "lightweight" ROH wheels/ Kumho's and was having trouble finding a replacement- they are yellow chrome I bought from a World Challenge racer. I guess bottom line, racing is as much mental as realworld. If you think you have an edge, sometimes it helps. I always go in thinking I can beat 2/3's of ANYone that shows up at an event. Sometimes it works, sometimes it doesn't..right, Michael
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(I've beat him and he has beaten me)Great fun!
 
#17 ·
:the biggest factor is going to be practice, practice, practice.
Click to expand...
That is certainly a fact--especially for someone who does not have that much seat time. Us more "seasoned" guys will notice those changes, however. I can think of at least 4 examples in my racing "career" where I've made changes to reduce unsprung weight--all for the better:
1984 RX7 CS switched from 205/60-13 on OE alloys to 185/60-13 on Revolutions--BIG difference even with smaller contact patch...my first "insight" into the importance of unsprung weight.
1984 RX7 GSL-SE CS switched from OE alloys to Panasports--eliminated high speed rear axle hop under braking (which was common for SSA cars...) Went from beeing spooky to being a real joy to drive. I miss this car every day!
1996 Cobra ESP--switched from BFG R1 to Hoosiers at mid-season; made the feel like it lost hundreds of pounds.
1984 ITA/Spec7--switched from Diamond Racing Steelies to Revolutions--again made the car "feel" like it lost significant weight; lap times came down measureably at RA.

If someone is willing to spend the cash to lighten up wheels/tires, IMHO, it is one of the best places on the whole car to appropriate those funds; there is no downside (other than perhaps the durability of the wheel) to doing this. In all of my instances noted above the cars instantly "felt" better which in turn gave me more confidence--especially doing roadracing and high speed track events. So, yes, there is a mental aspect too--but that was all tied in to the physics involved by taking those pounds off. Call it waht you like--attribute it to what you like-- but all things being the same , taking unsprung weight off will make the car faster.
 
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#18 ·
Absolutely, didn't mean to imply otherwise. But if we are really interested in spinning/stopping those rotating masses, would it not be more prudent to go to a smaller wheel(16 or even 15 in rim- if it would clear the calipers) ? When I was serious, instead of just having fun, I used the Revolutions/Hoosiers- great setup. To answer original question, yes, sure it helps, but is it going to sigificant on a car that sees mostly street use, on street tires? Should 4 oz be the limiting factor in making a buying decision? I don't think so. IMHO. 4 pounds, sure!
Question. When buying race tires, knowing both are important, do you think weight or stickie?
 
#19 ·
Absolutely, didn't mean to imply otherwise. But if we are really interested in spinning/stopping those rotating masses, would it not be more prudent to go to a smaller wheel(16 or even 15 in rim- if it would clear the calipers) ? When I was serious, instead of just having fun, I used the Revolutions/Hoosiers- great setup. To answer original question, yes, sure it helps, but is it going to sigificant on a car that sees mostly street use, on street tires? Should 4 oz be the limiting factor in making a buying decision? I don't think so. IMHO. 4 pounds, sure!
Question. When buying race tires, knowing both are important, do you think weight or stickie?
Click to expand...

In a race tire, I would lean towards weight--but from what I can tell now, thie lightest tire IS ALSO the stickiest tire--Hoosier. I also happen to run in STS, so with street tires, I opted for what you mentioned and did the 14" wheel thing...whereas most do 15's and 16's or even 17's...which are strictly for show, IMO. I give up 10mm of width to the (205) 15" and 20mm to the (215) 16" Azenis, but I know that my weight per corner is WAY less. It also works out as a bonus that the 195/60-14 is about 4/5" shorter in diameter, so I end up with a bit lower final drive to boot. Once I get my damper and swaybar setups figured out (just ordered S/T 7/8" rear bar), I am pretty certain that the car will be very competetive.
 
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#20 ·
W/o the Money to A/B a bunch of tires, I'm tempted to Speculate that I'd rather have a Slightly Heavier, STICKY Azenis than a Lighter, Less Sticky Kumho....
Unless the Weight Savings is Drastic, I'd want to opt for Grip.
The Idea of a Smaller, Lighter wheel is VERY Attractive however.
I just wonder what the weight is on the S2 16's, and what else is out there that's REMOTELY Affordable that has the right offset, width, and a noteworthy weight reduction...
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rheacer
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