Wheel sizes---What Gives???
11-03-2002, 06:05 PM
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Wheel sizes---What Gives???
My 02 C2 has 8J/10J x18 wheels. Tire Rack says an 8.5 x18 will fit the front but it has the same 225/40-18 tire for either wheel!!!! What Gives????
Why would I want a wider wheel and the same size tire???
Would a 9F/11R inch wide wheel work?? I know I may have to change/adjust the offset with spacers or the construction/design of the wheel itself, but shouldn't the addition of rubber width (within reason) allow better cornering?
Also, I know lighter weight means faster times, but would 3 or so pounds a wheel make that much difference?? I mean if one wheel cost $500 but was 2-3 lbs. heavier then an $850 wheel, Would it make that much difference, when I could spend the extra $$$ on the tires I'd most likely have to buy since I'd be whipping around the track (DE) so much faster!!!!! And, these new wheels and wider tires would just be for the track.
I'm scratchin' my head!!! Can someone give me knowledge???? Please!!
Why would I want a wider wheel and the same size tire???
Would a 9F/11R inch wide wheel work?? I know I may have to change/adjust the offset with spacers or the construction/design of the wheel itself, but shouldn't the addition of rubber width (within reason) allow better cornering?
Also, I know lighter weight means faster times, but would 3 or so pounds a wheel make that much difference?? I mean if one wheel cost $500 but was 2-3 lbs. heavier then an $850 wheel, Would it make that much difference, when I could spend the extra $$$ on the tires I'd most likely have to buy since I'd be whipping around the track (DE) so much faster!!!!! And, these new wheels and wider tires would just be for the track.
I'm scratchin' my head!!! Can someone give me knowledge???? Please!!
11-03-2002, 07:56 PM
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A wider wheel will take better advantage of the tire size.
A big tire is not the only thing to consider ya know. You have to think about the width of the wheel as well - to get optimum performance.
The 8.5 rim can give you the optimum use of the tire (or footprint if I may) over the 8 inch rim - assuming everything else is the same.
As for unsprung weight (adding 2-3 pounds per wheel), for giggles just use a simple figure of "TIMES TWO" when you add unsprung weight. I think 2-3 lbs. per wheel is within boundary's. If you were talking 10 per, then I would personally object - if it were my car.
Toss that potential weight gain in with the performance gained via the larger footprint, and you may just figure that "its a wash" and go with it.
A big tire is not the only thing to consider ya know. You have to think about the width of the wheel as well - to get optimum performance.
The 8.5 rim can give you the optimum use of the tire (or footprint if I may) over the 8 inch rim - assuming everything else is the same.
As for unsprung weight (adding 2-3 pounds per wheel), for giggles just use a simple figure of "TIMES TWO" when you add unsprung weight. I think 2-3 lbs. per wheel is within boundary's. If you were talking 10 per, then I would personally object - if it were my car.
Toss that potential weight gain in with the performance gained via the larger footprint, and you may just figure that "its a wash" and go with it.
11-04-2002, 09:51 AM
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OK, so I now find that I eat the outside edge of the driver side tire when I do Watkins Glen. If I put an 8.5 inch wheel on (vs. the 8.0) with the same tire, would the wear decrease? Would performance increase? (Assuming I correctly adjust pressure).
How does the wider wheel help optimize the footprint on the same size tire? Does it help the slip angle?(I thought tire height did that better)
How does the wider wheel help optimize the footprint on the same size tire? Does it help the slip angle?(I thought tire height did that better)
11-04-2002, 11:14 AM
#4
Stem
The easiest way of getting the idea is to think about the opposite extreme. If you put an extemely wide tyre onto a narrow rim, the tyre would 'balloon' actually causing a smaller footprint than if you had a narrower tyre fitted. The opposite applies as well.
Would you be able to tell the diff between an 8inch wheel compared to 8.5 with the same tyre? Probably not. Possibly on the track depending on your driving style.
On the subject of unsprung mass: it is pretty small on a car. If you are adding 15lbs to that mass then it may be a fairly hefty percentage of the total mass. I would buy the lightest wheels I could afford, and if you want to get some new ones then these should not be heavier. Also, bigger wheels=bigger tyres, so even more weight is added. Try to create a balance, but don't compromise on performance if that is your aim. If that was my focus I wouldn't buy cheaper wheels just to save money for tyres. You might as well stick with what you already have.
All IMHO
The easiest way of getting the idea is to think about the opposite extreme. If you put an extemely wide tyre onto a narrow rim, the tyre would 'balloon' actually causing a smaller footprint than if you had a narrower tyre fitted. The opposite applies as well.
Would you be able to tell the diff between an 8inch wheel compared to 8.5 with the same tyre? Probably not. Possibly on the track depending on your driving style.
On the subject of unsprung mass: it is pretty small on a car. If you are adding 15lbs to that mass then it may be a fairly hefty percentage of the total mass. I would buy the lightest wheels I could afford, and if you want to get some new ones then these should not be heavier. Also, bigger wheels=bigger tyres, so even more weight is added. Try to create a balance, but don't compromise on performance if that is your aim. If that was my focus I wouldn't buy cheaper wheels just to save money for tyres. You might as well stick with what you already have.
All IMHO
11-04-2002, 01:56 PM
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When it comes to wheels, lighter is better, as long as strength isn't compromised. Two or three pounds per wheel isn't an enormous difference, especially if you aren't competing with the car. If paying $400 extra per wheel will impact your tire budget so much that you'd have to buy Sears Roadhandlers instead of Kumho Victoracers, then I'd go with the heavier wheels and really good tires.
11-09-2002, 04:12 AM
#6
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"OK, so I now find that I eat the outside edge of the driver side tire when I do Watkins Glen."
Sounds like an alignment problem. You should have around 2.5 degrees of negative camber, maybe a little more in the rear. Then adjust pressure so that the tire temp at the center is the average of the inside & outside edges. The difference between the inside & outside edges will tell you whether you need more or less negative camber.
"If I put an 8.5 inch wheel on (vs. the 8.0) with the same tire, would the wear decrease? Would performance increase?"
It will help the wear and improve the grip a little. You want to look up the manufacturer's rim-width specs for the tires you'll be using and go with the widest width they recommend for that size. This will spread out and 'pre-stretch' the sidewalls into the cornering shape so that there will be minimal lateral squirm of the tread in a corner (also flattens out the contact patch). So now in a corner, your sidewalls will only flex sideways 1" instead of 2" like before, giving you much quicker transient response (turn-in).
If you take a comparison of all the high-performance cars, you'll see that as you go up the food chain from MustangGTs, Firebird/Camaros, Corvettes, Porsches, Viper, Porsche GT2/GT1, Ferrari Testarossa, 288GTO, F40, etc. that the higher-performance the car, the wider the wheels are for the same tire width. The Ferraris are close to 1:1 for section-width vs. rim-width (13" rim for a 335/345mm tire, 10" for 255mm).
Finally, the factor that makes the BIGGEST difference, is tire-compound! You may be able to squeeze out 1sec/lap with wider rims, and maybe another 2-3sec/lap with suspension mods. But the tires alone will give you 4-5sec/lap (more than all suspension & wheels mods combined). The grip available with R-compound DOT-legal street tires is simply AMAZING. Popular tires are the Yokohama A32R, Kumho Victoracers or its new replacement the V700, Hoosiers, etc.
Sounds like an alignment problem. You should have around 2.5 degrees of negative camber, maybe a little more in the rear. Then adjust pressure so that the tire temp at the center is the average of the inside & outside edges. The difference between the inside & outside edges will tell you whether you need more or less negative camber.
"If I put an 8.5 inch wheel on (vs. the 8.0) with the same tire, would the wear decrease? Would performance increase?"
It will help the wear and improve the grip a little. You want to look up the manufacturer's rim-width specs for the tires you'll be using and go with the widest width they recommend for that size. This will spread out and 'pre-stretch' the sidewalls into the cornering shape so that there will be minimal lateral squirm of the tread in a corner (also flattens out the contact patch). So now in a corner, your sidewalls will only flex sideways 1" instead of 2" like before, giving you much quicker transient response (turn-in).
If you take a comparison of all the high-performance cars, you'll see that as you go up the food chain from MustangGTs, Firebird/Camaros, Corvettes, Porsches, Viper, Porsche GT2/GT1, Ferrari Testarossa, 288GTO, F40, etc. that the higher-performance the car, the wider the wheels are for the same tire width. The Ferraris are close to 1:1 for section-width vs. rim-width (13" rim for a 335/345mm tire, 10" for 255mm).
Finally, the factor that makes the BIGGEST difference, is tire-compound! You may be able to squeeze out 1sec/lap with wider rims, and maybe another 2-3sec/lap with suspension mods. But the tires alone will give you 4-5sec/lap (more than all suspension & wheels mods combined). The grip available with R-compound DOT-legal street tires is simply AMAZING. Popular tires are the Yokohama A32R, Kumho Victoracers or its new replacement the V700, Hoosiers, etc.
11-09-2002, 08:38 PM
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Stem, I have used both 8.5 and 9 inch wheels at the track on the front of my 996 and both 10.5 and 11 inch on the back. For front tires I use either 245/35 or 265/30s. 245s are an easy fit. 265s are very tight and requires rolling your fenders and just the right offset and camber.
On the outer tire wear, I can confirm what others have said, it is most likely a camber problem. If you have the stock alignment settings then you have almost no negative camber in front. With stock suspension you might be able to get up to -1 degree which would be better. If you lower your car a bunch you can get up to -2 degrees which is great on the track and ok on the street as long as you have a big tire budget. With -2 in front I use -2.5 in back.
Hope this helps,
Jim
On the outer tire wear, I can confirm what others have said, it is most likely a camber problem. If you have the stock alignment settings then you have almost no negative camber in front. With stock suspension you might be able to get up to -1 degree which would be better. If you lower your car a bunch you can get up to -2 degrees which is great on the track and ok on the street as long as you have a big tire budget. With -2 in front I use -2.5 in back.
Hope this helps,
Jim
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11-10-2002, 10:24 PM
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Danno (and others)
Thanks for this thread. I really liked the point about tire sizes and rim widths and the 1:1 ratio for sports cars.
I just bought a custom set-up with room for future changes and I thought I'd submit it for comment.
This is purely a street application, although I definitely enjoy spirited driving (don't we all)
I put flares on my (previously) narrow 964 and was able to increase widths. I checked some things myself, then took it to a professional shop where a highly respected specialist took some measurements.
We decided to order 8.5" rims in front and 11" wide in the rear. To be cautious, I decided to go conservative on the first set of tires and go with the minimum widths for these rims: 225/40/18 in front and 285/30/18 in the rear.
I'd like to go to 255/35 in the front and 315/30 in the rear, if they'll fit. We will check it out once this first set is mounted. The PZero Rosso's that I ordered are available in these sizes and I figure I can change one axle at a time, as they wear out.
Here are the issues, from what I can gather:
The wider tires will be more expensive, will me more susceptible to hydroplaning and tramlining, and they will be further from the 1:1 ratio that Danno mentions (so not so sporty, not so stiff, not such a hard ride?). The will also look meaner, will facilitate more testosterone bragging, and maybe provide more grip in the turns.
The narrower tires will be less expensive, less susceptible to hydroplaning and tramlining, and closer to the 1:1 Danno ratio.
I have adjustable sway bars so I'm not to concerned about understeer/oversteer issues, figuring I can dial it out.
Any comments would be appreciated!
Thanks for this thread. I really liked the point about tire sizes and rim widths and the 1:1 ratio for sports cars.
I just bought a custom set-up with room for future changes and I thought I'd submit it for comment.
This is purely a street application, although I definitely enjoy spirited driving (don't we all)
I put flares on my (previously) narrow 964 and was able to increase widths. I checked some things myself, then took it to a professional shop where a highly respected specialist took some measurements.
We decided to order 8.5" rims in front and 11" wide in the rear. To be cautious, I decided to go conservative on the first set of tires and go with the minimum widths for these rims: 225/40/18 in front and 285/30/18 in the rear.
I'd like to go to 255/35 in the front and 315/30 in the rear, if they'll fit. We will check it out once this first set is mounted. The PZero Rosso's that I ordered are available in these sizes and I figure I can change one axle at a time, as they wear out.
Here are the issues, from what I can gather:
The wider tires will be more expensive, will me more susceptible to hydroplaning and tramlining, and they will be further from the 1:1 ratio that Danno mentions (so not so sporty, not so stiff, not such a hard ride?). The will also look meaner, will facilitate more testosterone bragging, and maybe provide more grip in the turns.
The narrower tires will be less expensive, less susceptible to hydroplaning and tramlining, and closer to the 1:1 Danno ratio.
I have adjustable sway bars so I'm not to concerned about understeer/oversteer issues, figuring I can dial it out.
Any comments would be appreciated!
11-12-2002, 10:36 AM
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OK, I have already talked to the tech at the dealership and he says I can get to about -1 on the front and a little more then that on the back( I don't remember the exact setting). I already have the Factory 030 Sport Suspension. While that camber won't be optimum for the track, I'm hoping it will be a better compromise since I'll still drive on the street. It may wear more on the street, but I can accept that in exchange for better wear on the track tires at the track!
2. I'm not gonna roll the fender so I'll be sticking with, I guess, an 8.5 on the front and an 11 on the rear. This with the 225-40-18 should give me the more vertical sidewall on both the front and rear. Should I consider anything different?????
3. Now...... I'm getting these new wheels and tires just for the track. I'll be trailering the car (long way from home) so I have no problem with getting a tire that will never see the street. Does that mean Hoosier, or Kuhmo or any other brand racing tires? Or should I get the DOT R rated? Are these almost the same or worlds apart?? I'll not be racing at all. Just DEs, but I would like to optimize the rubber on the road, or in this case... track.
I've got plenty of time to choose since this is for next season. I know there is a lot involved in choices like this, but what do you think?????
2. I'm not gonna roll the fender so I'll be sticking with, I guess, an 8.5 on the front and an 11 on the rear. This with the 225-40-18 should give me the more vertical sidewall on both the front and rear. Should I consider anything different?????
3. Now...... I'm getting these new wheels and tires just for the track. I'll be trailering the car (long way from home) so I have no problem with getting a tire that will never see the street. Does that mean Hoosier, or Kuhmo or any other brand racing tires? Or should I get the DOT R rated? Are these almost the same or worlds apart?? I'll not be racing at all. Just DEs, but I would like to optimize the rubber on the road, or in this case... track.
I've got plenty of time to choose since this is for next season. I know there is a lot involved in choices like this, but what do you think?????
11-12-2002, 10:37 AM
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OK, I have already talked to the tech at the dealership and he says I can get to about -1 on the front and a little more then that on the back( I don't remember the exact setting). I already have the Factory 030 Sport Suspension. While that camber won't be optimum for the track, I'm hoping it will be a better compromise since I'll still drive on the street. It may wear more on the street, but I can accept that in exchange for better wear on the track tires at the track!
2. I'm not gonna roll the fender so I'll be sticking with, I guess, an 8.5 on the front and an 11 on the rear. This with the 225-40-18 should give me the more vertical sidewall on both the front and rear. Should I consider anything different?????
3. Now...... I'm getting these new wheels and tires just for the track. I'll be trailering the car (long way from home) so I have no problem with getting a tire that will never see the street. Does that mean Hoosier, or Kuhmo or any other brand racing tires? Or should I get the DOT R rated? Are these almost the same or worlds apart?? I'll not be racing at all. Just DEs, but I would like to optimize the rubber on the road, or in this case... track.
I've got plenty of time to choose since this is for next season. I know there is a lot involved in choices like this, but what do you think?????
2. I'm not gonna roll the fender so I'll be sticking with, I guess, an 8.5 on the front and an 11 on the rear. This with the 225-40-18 should give me the more vertical sidewall on both the front and rear. Should I consider anything different?????
3. Now...... I'm getting these new wheels and tires just for the track. I'll be trailering the car (long way from home) so I have no problem with getting a tire that will never see the street. Does that mean Hoosier, or Kuhmo or any other brand racing tires? Or should I get the DOT R rated? Are these almost the same or worlds apart?? I'll not be racing at all. Just DEs, but I would like to optimize the rubber on the road, or in this case... track.
I've got plenty of time to choose since this is for next season. I know there is a lot involved in choices like this, but what do you think?????
11-14-2002, 08:03 PM
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Stem,
I'll give my 2 cents worth on your questions.
3) The Hoosiers and Kuhmo track tires people are generally refering to are "R" compound, DOT approved tires. Others in this catagory are Michelin Pilot Sport Cups and Pirelli PZero Corsacas (sp?). I prefer the Sport Cups for their stick and long life and the Hoosiers for stick but there are many other valid opinions.
2) The battle you are going to fight with your car is getting rid of understeer. I'm pretty sure they will tell you the minimum camber you want in the back is around -1.6 and obviously the most you can put in front in -1 so you start the game a bit behind on understeer. The 996 works much better on the track with a -2/-2 or -2/-2.5 combo.
Next you have the wheels. The 8.5 width will spread out your 225 tires and improve grip a little but an 11 inch wheel will do the same to the rear so you're getting no help there. You might want to consider an 8.5/10.5 combo. If you are set on 225s in front rather than 245s which I think are optimal, I would definitely stick with 265s in back.
Hope this helps,
Jim
I'll give my 2 cents worth on your questions.
3) The Hoosiers and Kuhmo track tires people are generally refering to are "R" compound, DOT approved tires. Others in this catagory are Michelin Pilot Sport Cups and Pirelli PZero Corsacas (sp?). I prefer the Sport Cups for their stick and long life and the Hoosiers for stick but there are many other valid opinions.
2) The battle you are going to fight with your car is getting rid of understeer. I'm pretty sure they will tell you the minimum camber you want in the back is around -1.6 and obviously the most you can put in front in -1 so you start the game a bit behind on understeer. The 996 works much better on the track with a -2/-2 or -2/-2.5 combo.
Next you have the wheels. The 8.5 width will spread out your 225 tires and improve grip a little but an 11 inch wheel will do the same to the rear so you're getting no help there. You might want to consider an 8.5/10.5 combo. If you are set on 225s in front rather than 245s which I think are optimal, I would definitely stick with 265s in back.
Hope this helps,
Jim
11-24-2002, 09:51 AM
#12
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I just bought a new set-up for the street, that seems similar to what is being discussed. 8.5" front with 225/40/18, and 11" rear with 285/30/18. PZero Rosso tires and Kinesis Supercup wheels. Should be installed on Tuesday. I'll post a note with some comments when I have a chance.
11-27-2002, 12:34 PM
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So if I get a -1 on the front (max factory w/o mod to suspension) and go with a 245 vs a 225 on an 8.5 inch wheel on front, with a 265 tire on a 10.5 inch wheel on the back.... will that start to solve my understeer and optimize my grip???
I'm leaning toward the Michilin Pilot Sport Cup for a tire and as yet, have no preference for wheels. I'll be looking for something light weight and low $$$$. Isn't everyone???
I'm leaning toward the Michilin Pilot Sport Cup for a tire and as yet, have no preference for wheels. I'll be looking for something light weight and low $$$$. Isn't everyone???
11-29-2002, 11:26 AM
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Stem,
Unless something has changed recently, Sport Cups don't come in 245x18 so you are stuck with either 225s or 265s up front. I use 265s but I don't think they will work with your set up so you are looking at 225s. With 225s in front I would stick with 265s in back. If you decide to go with Hoosiers then a 245/285 combo works well. Either combination will really help with understeer although you might want to consider some adjustable swaybars.
Jim
Unless something has changed recently, Sport Cups don't come in 245x18 so you are stuck with either 225s or 265s up front. I use 265s but I don't think they will work with your set up so you are looking at 225s. With 225s in front I would stick with 265s in back. If you decide to go with Hoosiers then a 245/285 combo works well. Either combination will really help with understeer although you might want to consider some adjustable swaybars.
Jim
