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Unofficial Big-Wheel Thread: 18/18 and 18/19 - the future for NSX tire sizes
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- 18/18 18/19 big wheels
I need to do my 17/18 vs 18/19 NA tire test first. But mathematically:
NA power: 18x8 with 225/40-18 and 19x10 with 275/35-19
Low power FI: 18x8 with 225/40-18 and 19x10.5 with 295/35-19
Higher power: 18x8.5 with 235/40-18 and 19x11 with 305/35-19 (well 305/30-19 since 35's dont exist. Not ideal, but should work)
NA power: 18x8 with 225/40-18 and 19x10 with 275/35-19
Low power FI: 18x8 with 225/40-18 and 19x10.5 with 295/35-19
Higher power: 18x8.5 with 235/40-18 and 19x11 with 305/35-19 (well 305/30-19 since 35's dont exist. Not ideal, but should work)
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I am going to be using the downforce wide front fenders with an 18/19 wheel diameter set up. Billy I will be on the high power range side of the scale so as much rubber as I can squeeze under the stock rear fenders the better If I could get a 295 under it that would be great. This thread has some great info. I can't wait to get the car back and get a wheel so Dave and I can start trying to fit a 225/40/18 up front together.
Post #123 for offsets 
Dave lets get a wheel and a tire and start checking things out!
Billy can you explain the correlation you are making between the cars weight distribution and tire width? These percentages you are listing for various tire combinations like (43/57) is of what? Section width? And if so, is this a common thing to try to correlate that to the car's natural weight distribution?
The thing I'm not getting is section width may be increasing but contact patch is probably increasing a very tiny percentage... So what is the rationale behind comparing weight distribution to section width?
The thing I'm not getting is section width may be increasing but contact patch is probably increasing a very tiny percentage... So what is the rationale behind comparing weight distribution to section width?
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Yes section width from a tire volume standpoint and while the contact patch won't change much at all in size given the same pressure, at a lower pressure the contact patch will be larger. Its not a common correlation but one I'm drawing to modern supercars relative to the nsx, which is under tired by modern standards.
Why is 305-30-19 "on the edge of acceptable diameter?"
Am I miscalculating something? because it seems a better match to the factory ratio than some of the others you have listed as "good". Where am I going wrong?
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I understand the OEM OD difference is 1.3" (and you already posted that pic). However the tires we are looking at is ~1" larger in diameter than OEM. I look at the relationship of the front to rear ratio between all 3 generation of tire sizes, and I pay closer attention to the ratio of the ABS system that i'm going to be using.
(Ex: A 1.3" difference front to rear is a lot bigger on 8" go-kart tires compared to 30" semi-truck tires).
For ABS and TCS, it's important to look at the ratio. 305/30-19 will probably work with no real issues, but its further outside the OEM Honda range, which is why I called it "on the edge of acceptable". Without testing all of the above F-R ratio differences and measuring their effect, we will not know for sure how significant the F-R ratio is or how far we can stray from it before running into issues.
We are going up in size, making that F/R difference less critical. That probably allows more variance because essentially the whole car is "slowier" to the sensors. But I still don't get why two tires with a 1.6" difference are better than two at a 1.2" difference when the goal is 1.3. Whether you go up or down in size, you are simply just exaggerating or reducing the same difference. They aren't going to just cross over each other at some point.
Perhaps I am just looking at this wrong. If I am not annoying you again (which I seem to be by the tone of your last two posts on the other thread), do you have a way of explaining this that will help me understand or can you point me to something that will show me why I am off. I am saying I don't get how you are arriving at what you are calling a good match versus a marginal match, because I see the opposite of what you see.
The other stuff: Yes, I am definitely faster on R comps and by a large margin, but that doesn't matter much... the more important thing to me is if I am designing and paying for a custom wheel, I don't want to design it for a size that then limits my tire options as before. 17/18 isn't all that bad. There are still AD08's, ZII's and NT01's. I am looking at what is available at 305 and it is massive. I am also looking at your own post saying "High power FI 295, 305", and this is a wheel I most likely have to share with Shaylor who has close to 1000 HP. If two separate wheels and sizes must be bought then it must be, but why wouldn't that size work for us both? You suggested 275 for NA, I am not NA. So that is confusing.
For me, the best tire choices as I have said before, exist at 265 and at 305. So if 305 is definitely detrimental, I think I would drop down to 265. I don't know... perhaps I will like a set of super sports so much that I will forget R comps but are they really better than the AD08's or the Star Specs I have used before? Because I saw a huge difference between those and the NT01. Of course the NT01 sizing was larger as well.
If I don't have to go with a 305, then wheel sizing is much easier. One thing you have told me about several times which you think I am ignoring, is sizing at 10 and 10.5. Have we talked about an 11? I felt I needed to calculate out for that hence my other post.
Perhaps I am just looking at this wrong. If I am not annoying you again (which I seem to be by the tone of your last two posts on the other thread), do you have a way of explaining this that will help me understand or can you point me to something that will show me why I am off. I am saying I don't get how you are arriving at what you are calling a good match versus a marginal match, because I see the opposite of what you see.
The other stuff: Yes, I am definitely faster on R comps and by a large margin, but that doesn't matter much... the more important thing to me is if I am designing and paying for a custom wheel, I don't want to design it for a size that then limits my tire options as before. 17/18 isn't all that bad. There are still AD08's, ZII's and NT01's. I am looking at what is available at 305 and it is massive. I am also looking at your own post saying "High power FI 295, 305", and this is a wheel I most likely have to share with Shaylor who has close to 1000 HP. If two separate wheels and sizes must be bought then it must be, but why wouldn't that size work for us both? You suggested 275 for NA, I am not NA. So that is confusing.
For me, the best tire choices as I have said before, exist at 265 and at 305. So if 305 is definitely detrimental, I think I would drop down to 265. I don't know... perhaps I will like a set of super sports so much that I will forget R comps but are they really better than the AD08's or the Star Specs I have used before? Because I saw a huge difference between those and the NT01. Of course the NT01 sizing was larger as well.
If I don't have to go with a 305, then wheel sizing is much easier. One thing you have told me about several times which you think I am ignoring, is sizing at 10 and 10.5. Have we talked about an 11? I felt I needed to calculate out for that hence my other post.
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I honestly don't know how to say it any clearer than I did in my previous post. But I will try.
What matters is the front to rear RATIO, not the front to rear difference in diameter. Just like the example in my previous post. If you take the 1.3" diameter difference on a 8" front gokart tire, the rear would be 9.3" (1.3" larger). That makes the rear ratio 1.1625 times larger than the front. Now take a 30" semi truck tire. A 31.3" rear semi truck tire (1.3" larger) has a rear tire 1.04333 times larger than the front. A much smaller difference. While that's an extreme example, there is a 11.917% variance between these two examples despite the same 1.3" larger rear tire than front in both examples. Yes the tires will be rotating slightly slower with a larger tire, but it's more accurate to look at the ratio and not the diameter difference.
The question becomes is how sensitive is the first and second gen ABS systems to F-R tire size changes.
91-93 cars have a rear 1.079 X larger than front
94-01 cars have a rear 1.046 X larger than front
02-05 (new Gen ABS have a rear 1.054 X larger than front.
1.046-1.079 is the max and min RATIOS of the first gen ABS and what was used on the NSX. If you have a 2nd gen ABS 1.054 is the ratio the ABS was designed for.
Again, without testing, we do not know how much this 3.3% spread in ratio is or how far we could stray outside of that (keeping in mind the 2nd gen ABS is in the middle of that range) without negatively affecting the ABS. At the end of the day, you can probably go outside this range and be fine, but without testing and spending a lot of time and money, it's probably safer to stay to the numbers above and the analysis of the various sizes that I already listed.
AD08R's are suppose to be 1-2 seconds faster on the sub 1:00 Tskuba circuit (so a 2-4 second improvement on a typical 2 minute track) -which should really close the gap to the NT01.
You seem to contradict yourself a bunch, wanting an all purpose good track tire that will be good on the street and rain, but then you 'need' R-comps. You can use a 295/30 or 295/35 Hoosier A6/R6 or R888.
It's possible a 275-295 PSS, RS3, or AD08R is as fast or faster than a 265 NT01. Again, you need to decide on what tire you want first, then go from there.
The problem with 11's under the factory fender is you have to be in a very tight window (11.25 was the max, so with a 11" wide wheel, you have 3mm of wiggle room on each side. If I were you, i'd go with a 19x11+47 to give you 1 more mm of clearance to the shock, and 5 more mm on the outer side. But you're pushing the envelope here and there's a good chance you'll run into an issue. Or you can just go with a wider fender and life would be a lot easier.
How is he making 1,000hp? How much power are you making? Does he drag race his car or track his car?
Keep in mind, just by going to the larger diameter tire, the contact patch can increase (by lowering the pressures) and having a longer contact patch is good for straight line acceleration. It's not all about width.
The PSS has won the One Lap of America event for the last 5 years or so (I think most of the cars in the top 10 use them ranging from 600-1000HP Vipers, GTRs, GT2s, R8s, SLRs, etc...) its a very capable tire.
What matters is the front to rear RATIO, not the front to rear difference in diameter. Just like the example in my previous post. If you take the 1.3" diameter difference on a 8" front gokart tire, the rear would be 9.3" (1.3" larger). That makes the rear ratio 1.1625 times larger than the front. Now take a 30" semi truck tire. A 31.3" rear semi truck tire (1.3" larger) has a rear tire 1.04333 times larger than the front. A much smaller difference. While that's an extreme example, there is a 11.917% variance between these two examples despite the same 1.3" larger rear tire than front in both examples. Yes the tires will be rotating slightly slower with a larger tire, but it's more accurate to look at the ratio and not the diameter difference.
The question becomes is how sensitive is the first and second gen ABS systems to F-R tire size changes.
91-93 cars have a rear 1.079 X larger than front
94-01 cars have a rear 1.046 X larger than front
02-05 (new Gen ABS have a rear 1.054 X larger than front.
1.046-1.079 is the max and min RATIOS of the first gen ABS and what was used on the NSX. If you have a 2nd gen ABS 1.054 is the ratio the ABS was designed for.
Again, without testing, we do not know how much this 3.3% spread in ratio is or how far we could stray outside of that (keeping in mind the 2nd gen ABS is in the middle of that range) without negatively affecting the ABS. At the end of the day, you can probably go outside this range and be fine, but without testing and spending a lot of time and money, it's probably safer to stay to the numbers above and the analysis of the various sizes that I already listed.
AD08R's are suppose to be 1-2 seconds faster on the sub 1:00 Tskuba circuit (so a 2-4 second improvement on a typical 2 minute track) -which should really close the gap to the NT01.
You seem to contradict yourself a bunch, wanting an all purpose good track tire that will be good on the street and rain, but then you 'need' R-comps. You can use a 295/30 or 295/35 Hoosier A6/R6 or R888.
It's possible a 275-295 PSS, RS3, or AD08R is as fast or faster than a 265 NT01. Again, you need to decide on what tire you want first, then go from there.
The problem with 11's under the factory fender is you have to be in a very tight window (11.25 was the max, so with a 11" wide wheel, you have 3mm of wiggle room on each side. If I were you, i'd go with a 19x11+47 to give you 1 more mm of clearance to the shock, and 5 more mm on the outer side. But you're pushing the envelope here and there's a good chance you'll run into an issue. Or you can just go with a wider fender and life would be a lot easier.
How is he making 1,000hp? How much power are you making? Does he drag race his car or track his car?
Keep in mind, just by going to the larger diameter tire, the contact patch can increase (by lowering the pressures) and having a longer contact patch is good for straight line acceleration. It's not all about width.
The PSS has won the One Lap of America event for the last 5 years or so (I think most of the cars in the top 10 use them ranging from 600-1000HP Vipers, GTRs, GT2s, R8s, SLRs, etc...) its a very capable tire.
I get the ratio thing. I always have. But can you tell me specifically with numbers how the ratio on a 225/40/18 and 305/30/19 is WORSE than a 225/40/18 and 275/35/19? These two specifically with numbers. It may just be that I am doing the math wrong and I'd like to see how you are arriving at the 275 being closer to the ideal 1.054. That would help me see it.
How is he making that power? He has a built and stroked twin turbo car that runs E85 at SOS. He will be dragging and tracking the car. I currently have a CTSC but I am switching to a twin turbo. I will be closer to the 450 HP range as I have no plans right now to build the bottom end.
How is he making that power? He has a built and stroked twin turbo car that runs E85 at SOS. He will be dragging and tracking the car. I currently have a CTSC but I am switching to a twin turbo. I will be closer to the 450 HP range as I have no plans right now to build the bottom end.
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275/35-19 = 26.6" Diameter = 1.060 ratio (26.6/25.1 for the 225/40-18 diameter)
305/30-19 = 26.2" Diameter = 1.044 ratio (26.2/25.1 for the 225/40-18 diameter)
For the 2nd Gen ABS' 1.054, the 275/35-19 has a 0.006 (or 0.6% difference) while the 305/30-19 has a 0.01 (1% difference)
The 1st Gen ABS (91-93 cars) have a 1.079 ratio while the 94-01 cars have a 1.046. The 305/30-19 is outside even the 94-01 ratio while the 275/35-19 is in between the 02-05 and 91-93 ratios, while being closer to the 02-05. That is why the 305/30-19 is 'worse'.
Take the above information for what its worth, most likely the 305/30-19 will be fine but without testing, there is no way to be certain, while the 275/35-19 will have a high probability that the ABS/TCS will work very well. I think at this point you should have more than enough information to make your own decision and run with it. You probably wont get any significant piece of information beyond all of this so it's probably time to just make a decision.
Link to his build?
Honestly, if he's serious about drag racing, he should be using a 15-17" rear tire and proper drag radial like a ET Street. Unless he really knows what he's doing and experienced, 1,000hp isn't going to be trackable for 99% of the people out there, especially using tires under stock fenders. Most likely he will lower that power level for the track, and from there, should pick a good balance of tire size, stickyness, and performance. If he's serious about tracking, he should be using a Hoosier A6/R6 type of tire, a 275/40-18 NT01, or just pick a PSS/AD08R/RS3 in a size he wants and learn how to drive.
Similarly, you would be fine with a 265/275 rear tire for your power level. I think you could mess the balance up of your car if you choose a crazy wide rear width and offset that compromises your alignment. A 305 rear tire with too much rear camber could effectively have a much smaller amount of that tire touching the ground than a 265 with a proper amount of camber. It's more important you have your alignment correct for your tire width, and the wider you go tire wise, typically the less camber you need to run. If you're trying to stuff a 19x11 with a 305 on the rear, sure you could probably make it fit under a stock fender but the camber needed to make it work could be too much for ideal handling.
At the end of the day, and for the last time, for your power levels and experience levels, Pick a tire (in a 265-295) and a 19x10 or 19x10.5 in the offsets I already mentioned, and go from there.
If you want to have a 305 to have a 305, and if your camber is compromised to make it work and you won't buy new rear tires to make your setup work, or wont go to a widebody (or like the FXMD wide fender kit), then you really have your priorities screwed up and probably need to stop putting money in your car and buy a spec miata if you really want to improve your driving skills.
Very good explanations. I understand now and see where my math went wrong. Thank you.
Do you think I am doing too much trying to have a wheel that fits both our needs? There is a definite cost difference.
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Shaylor's build:
http://www.nsxprime.com/forum/showthread.php/174269-92-street-track-02-conv-NA2-type-r-Have-questions
Do you think I am doing too much trying to have a wheel that fits both our needs? There is a definite cost difference.
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Shaylor's build:
http://www.nsxprime.com/forum/showthread.php/174269-92-street-track-02-conv-NA2-type-r-Have-questions
With a 305/30-19 you are pushing the limits as much as Bolidogodo did. Be prepared to runin to issues. Who knows, by then the FX wide fenders might be done and that could give you more flexibility with spacers. So that could be a backup option.
Either way. Get your priorities in order, then decide.
Either way. Get your priorities in order, then decide.
That 1000hp is what we are hoping to hit for crank horsepower. It won't be kept up there. It will have two pressures and map settings. Somewhere between 575 and 625 rwhp and another one around 775 to 825 rwhp. But it's all speculation right now. I've done thing totally the wrong way around and I know it. Built the car before I really learned to drive. It was more of a hobby that I wanted to build the car and a project to see what the platform could really do completely maxed put. Then Dave talked me into actually learning how to properly drive and tracking it. I am trying to read through all do this and make sense of it there's a lot of into here. And truthfully tire sizes and offsets have always confused me. I don't know who thought of the way we size tires but seems like to me would be so much easier if it was width and outside diameter/circumference and what diameter wheel instead of the whole ratio to width thing but anyways thank you both for all the info in this thread now I just need to make sense of it and do some measuring with Dave.
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I think both Dave are and I are against the idea of wider rear fenders. I have just personally never liked any of the wide rear fenders. We just want to squeeze as much under the stock as possible
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I think both Dave are and I are against the idea of wider rear fenders. I have just personally never liked any of the wide rear fenders. We just want to squeeze as much under the stock as possible
The FX fenders would be similar to the DF fenders, where you wouldn't even know it was wider unless you really knew what you were looking at. OEM styling but giving you more room. Would that interest you?
No. Use spacers. Or it'll fix your stupid wide wheel/tires when they don't fit.
You mean space out 275's? What's the point of that? Isn't the point of the fender to allow more tire?
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I don't think there is an easy way. Either we decide the whole fender thing now and get proper wheels and tires for it now, or we sell/buy again later... Or just be satisfied with what there is and forget trying get more in there. What the fender will give for sure though is more freedom to go with various wheels available on the market not something custom.
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I don't think there is an easy way. Either we decide the whole fender thing now and get proper wheels and tires for it now, or we sell/buy again later... Or just be satisfied with what there is and forget trying get more in there. What the fender will give for sure though is more freedom to go with various wheels available on the market not something custom.
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Billy is there any more info on this wide body kit? How much wider is the rear?
You keep missing a lot of important pieces of information. Increasing the diameter of a tire has benefits like increasing the width. So just a 275/35-19 will have advantages over a 275/35-18. A wider stance also improves the cornering ability of the car, even if the tire width is the same. So a wider track width 275/35-19 has a lot of benefits over a narrower track width 275/35-18.
The whole point of 18/19 sizes was to open the options for awesome tire options. So pick a fricken tire and decide. If you want a 305 and it does not work, then the FX fender might be done by then and could save your tire decision if you goof up the offsets and widths.
The FX fenders have not been started yet because I'm waiting on tires for my 18/19s and the fenders will be built around the tires. Ideally ~15mm wider than stock just like the fronts (vs 7mm for the DF).
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NT05s. They will be competitively priced. Should be good amt less than most widebodies.
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