Why do we go for the wrong rear wheel/tire combo?

TURBO2GO

TURBO2GO

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Seems like a majority of guys that get a 17/18 combo go for 265/35/18 or 275/35/18. I don't get this. On my 2005 at least, overall diameter on the stock 17" wheel is 25". Overall diameter on a 255/35/18 is exactly the same. 25". As you go to 265 or 275, you start to increase diameter. 25.3 for a 265/35/18. You also increase weight, by approximately 1 pound. Seems like the "right" fit, is a 255/35/18 which is readily available in many high performance versions.

You can argue that a 265 is a better fit on an 18x10 wheel. But I don't get that either. It seems a 10" width is excessive. An 18x9 again is lighter, and fits the more appropriate tire (255/35/18) better.

As for looks, 18x10 actually slightly stretches either the 255 or 265. That gives the rim less protection, and to me looks worse. Lots of people like the concave look. You actually INCREASE that visual effect, when the tires sidewall is straight or slightly bowed in. For the wheel I am considering, the advan RSII, the spokes bow out to create this effect. When I have looked at tires on this wheel, the ones that are less stretched look better.

So then why? Why this 265/35 on an 18x10 combo, and not a 255/35 on a 18x9 combo? You save 2 pounds, get the closer diameter to stock, and the tire looks better. What am I not seeing?
 
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I have 255's on my rears!:biggrin:
 
I notice NSX owners in Japan, almost never run anything bigger than 18x9.5 in the rear. The most common size they use are 18x9 or 17x9. Maybe here in the US, owners care more about running huge rear tires, than actually what makes the car perform best. :confused: Hellaflush yo!
 
I'm of the school that the wider contact patch is better for grip during cornering,thus I use 275 on my track setup,but I'm a 255 street guy:redface: And remember the area of contact patch is rather static but as the tire increases in width the patch changes shape.
 
On a '94-05 NSX, 255/35-18 is indeed the better fit with a 215/40-17 front, because it preserves the ratio of the front-to-rear outer diameters, which is good for the TCS:

'94-01 (stock) 215/45-16 and 245/40-17 - rear is 4.7 percent larger
'02-05 (stock) 215/40-17 and 255/40-17 - rear is 5.3 percent larger
215/40-17 and 255/35-18 - rear is 5.3 percent larger

However, the '91-93 came with a different ratio front to rear, and for those years, the 265/35-18 is actually closer to that ratio:

'91-93 (stock) 205/50-15 and 225/50-16 - rear is 7.8 percent larger
215/40-17 and 265/35-18 - rear is 6.4 percent larger

The 275 is even closer in ratio (7.6 percent) but I generally avoid that size because the NSX handling seems to suffer when the stagger (difference in width, front vs rear) is 60 mm or more.

So the answer to your question is, 255/35-18 is "right" (i.e. closer to the ratio for the TCS) for a '94-05 NSX, but 265/35-18 is "right" for a '91-93 NSX. Oh, and there were slightly more '91-93 NSX's sold than '94-05's.

As for the widths, there really isn't that much variation (typically the range is 1"-1.5" from narrowest approved to widest), and I'm not sure it makes all that much difference, as long as you're staying within the approved range. I suspect people buy widths based on availability, and that some widths just aren't available in the offsets that will fit. Just guessing here.

HTH
 
I put a 265/35/18 Dunlop Starspec on my 18x9.5" wheel. Worked pretty well.

I've always gone by the saying "Go BIG or go home" :biggrin:
 
nsxtasy said:
On a '94-05 NSX, 255/35-18 is indeed the better fit with a 215/40-17 front, because it preserves the ratio of the front-to-rear outer diameters, which is good for the TCS:

'94-01 (stock) 215/45-16 and 245/40-17 - rear is 4.7 percent larger
'02-05 (stock) 215/40-17 and 255/40-17 - rear is 5.3 percent larger
215/40-17 and 255/35-18 - rear is 5.3 percent larger

However, the '91-93 came with a different ratio front to rear, and for those years, the 265/35-18 is actually closer to that ratio:

'91-93 (stock) 205/50-15 and 225/50-16 - rear is 7.8 percent larger
215/40-17 and 265/35-18 - rear is 6.4 percent larger

The 275 is even closer in ratio (7.6 percent) but I generally avoid that size because the NSX handling seems to suffer when the stagger (difference in width, front vs rear) is 60 mm or more.

So the answer to your question is, 255/35-18 is "right" (i.e. closer to the ratio for the TCS) for a '94-05 NSX, but 265/35-18 is "right" for a '91-93 NSX. Oh, and there were slightly more '91-93 NSX's sold than '94-05's.

As for the widths, there really isn't that much variation (typically the range is 1"-1.5" from narrowest approved to widest), and I'm not sure it makes all that much difference, as long as you're staying within the approved range. I suspect people buy widths based on availability, and that some widths just aren't available in the offsets that will fit. Just guessing here.

HTH
Click to expand...

Very interesting Ken, thanks for the detailed input. So basically you really should consider the year of your NSX, and that what is true for one model year is not "best" for anothet model year. For my 2005, my assumptions hold true. I am better off with a 255/35/18 on an 18x9 wheel.
 
Ken nailed it, and also since our 1992's speedos both read over 6% high (freeway speeds as compared to our GPS) on it's stock tires the 275/35/18 rears zero'ed that out.

We run 215/40/17 fronts and 275/35/18 rears on both cars, the balance is great on the street and track.

Brian
 
docjohn said:
I'm of the school that the wider contact patch is better for grip during cornering,thus I use 275 on my track setup,but I'm a 255 street guy:redface: And remember the area of contact patch is rather static but as the tire increases in width the patch changes shape.
Click to expand...

Are you running a 275 street tire? Or an R comp?
 
Also worth considering most tires differ in actual width/height per equal sizing, some 255's are taller/wider than others. It's best to check the actual tire spec, and take in consideration the mounted wheel width can also slightly modify the tire.
 
F0oBot said:
Also worth considering most tires differ in actual width/height per equal sizing, some 255's are taller/wider than others. It's best to check the actual tire spec, and take in consideration the mounted wheel width can also slightly modify the tire.
Click to expand...

Yes, and another thing I have noticed is some decent variation in weight. You work so hard to reduce wheel weight then the tire throws it back on at the worst spot, the outermost edge of the rotating mass. Same size tires vary by as much as 2 pounds in just a 17"!!

For example I noticed Michelins in general are a bit lighter. But there is also a 1 pound differrence between say a 215/40/17 Dunlop Star Spec and a Yokohama AD08 (yoko being lighter). As you go to larger sizes the variations increase. Everyone always talks about wheel weight but hardly anyone ever asks about tire weight. We check traction, skidpad numbers, wet performance, etc... but even magazine tests don't pay enough attention to this.
 
F0oBot said:
Also worth considering most tires differ in actual width/height per equal sizing, some 255's are taller/wider than others.
Click to expand...
This is true. However, ...

F0oBot said:
It's best to check the actual tire spec
Click to expand...
Tire manufacturers differ in how they come up with the specs they publish. Some of them take actual measurements and state the "measuring rim width" (as you note, rim width can change specs); others simply publish specs that are calculated based on the tire's labeled size, which doesn't take into account actual variations between one tire of that size and another.
 
Good thread. I run a 255/35/18 tire on an 18x9 and I think it's perfect. Usually when people go for wider, it is because it's perceived that the extra width looks better or it's for "wow" factor. There is also the perception that just using wider tires makes the contact patch larger, which it doesn't (but it does change the shape of it as pointed out here).
 
255 on an 18x10. It looks a little stretched (certainly not "hella flush"), but that was not premeditated. I got a good deal on the wheels. They look great (imo), correct offsets, etc. but I wanted to keep a known-good width stagger and keep the speedo at least reasonably accurate.

If I get another set of wheels for track tires, I'll go with a 17/17 combo with a 9 or 9.5 wide wheel in the rear, but probably maintain the 255 width depending on tire availability.
 
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Ken would you mind answering some questions on offset then:

I have seen people be all over the place with offset, and there's a lot of talk about what fits "better", but "better" in many cases is more flush for the look. While that is fine, I want to know how offset affects performance.

In general, is it a good idea to try to keep the offset close to OEM spec? Or at least keep the difference between front and rear similar to OEM spec? Seems like if you widen the front, or widen the rear, you are definitely making the car handle differently. If I have room on both sides, and I get a wheel an inch wider, with the same offset, that should theoretically split the differnce between where the wheel is wider. Right? It would stick out 1/2" more on the outside, and be "in" 1/2 an inch more on the inside. Right? So in 2 wheels that have 50mm offset, one being 18x9, one being 18x10, with the same design, I would get a more concave effect on the 18x10. The spokes have to extend that extra (roughly) 1/2".

Right now on my OEM 2002 wheels, the specs are 55mm front, 56 mm rear. I am running a 15mm spacer up front to clear my stoptechs, and 20mm rear. So essentially, my offsets are now 40mm front, and 36mm rear. Is this correct? I have changed the front/rear ratio by 5mm. The rear used to be higher by 1mm, now it is lower by 4.

If I could CHOOSE my ideal offset, in other words, I was making a wheel from scratch, how would I come up with the right number? I've read that as you increase track, theoretically handling becomes better. I had this question on spacers before, whether they were just for looks and what their affects on performance were. Seems there was some consensus that widening the track was a benefit, to a certain extent and beyond that the suspension geometry changed too much and you lost grip.

This whole thing really seems like a maze. Because you have to consider track ratio, clearance inside, clearance outside, clearance for the caliper, and of course suspension geometry during compression. I guess you also reduce turning radius as you increase track. I swear I can almost feel that with the 30mm added to the fronts after my spacers. It was shitty before but now I really need to make a 3 point turn out of everything. Is this my imagination?

I know I brought up a lot here but am just looking to get some clarity. A lot of people pick these wheel sizes then when I ask them why that offset or why that width, they aren't really sure!
 
For the third and last set of wheels I've choosen the smallest and reasonable (for CTSC) combo, 7.5/17 and 9/18 with 215/40 and 255/35 and about 50 mm offset. Light wheels (Rays) and tires (Hankook) made a big step forward against the elefant-like cornering of heavy 8/17, 9.5/18 with 265/35 Bridgestones with about 40 mm offset. But the 02+ OEM 17/17 are even a tad responsier than all of them.

I agree with you that
- more than 7.5'' in the front is not needed, you still can go for 225/35/17
- more than 9.0'' in the rear is not needed, you still can mount 265/35/18
- less than ET 45 is not what the handling really likes

I had the most astonishing observation when I switched from heavy and wide 17/18 to OEM 16/17 and Yoko tires years ago. That's where I've recognised those three points above.

People (me too) tend to buy a bigger wheel combo as their first set because bigger is said-to be better until they recognise that smaller would have been better.

This is the latest and lightest 17/18-combo or my third and actual set: http://www.nsxprime.com/forum/showpost.php?p=1462633&postcount=35
Some people may like it wider but this combo is near to OEM and bloody-fast.
 
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goldNSX said:
- less than ET 45 is not what the handling really likes
.
Click to expand...

I am trying to get why... I am not doubting your experience but why would less than 45 be worse and not better. technically you have a wider track with 25 for example than 45. I understand there is more pressure on the suspension arms, and especially on the bearings.

I am already at 40 with my 15 mm front spacer. I need that to clear the stoptechs.

The RSII in 17x7.5, the preferable size, is an ET of 48. In 17x8, the choices are 50, 48, 37.
 
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Bigger is Better :D

Lmao...

All depends on tire brand. I run Falken FK452 they last very well are actually sized smaller than others.
 
Larger diameter will fill gap in the wheel wells that you don't take out by lowering the car without actually lowering the car even closer to the ground i imagine.I run larger diameter wheels then stock.. it may change the gear ratio and what not but i dont mine
 

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