17/19" wheels??

[nsx808]

I got some beautiful Axis Seven wheels for my NSX with the following tires:

225-40-18 in front
275-30-19 in back

Back fits perfectly and looks great... front rubbed so much you couldn't turn the wheel.. and the wheel looked terrible on the nsx. It was way too big for this car.

So, what I think I'm going to do now is get the 17" Sevens for the front. I got the S-03's for tires.. and the fronts would be 215-35-17... would that be a good combo? 215 in front and 275 in back? What about the 2" difference in wheels? Any problems with that? Anyone with experience with that combo?

thanks,
Rob

 

[justin hall]

I'd imagine it would be tough to get a low enough profile tire for the 19" rear tire, or the front will be too tall, one or the other. For TCS, you need to keep your variance from stock front to back close to eachother.

 

[NSX 3.0]

I went with 17x7.5 in the front with 215-40-17s and 18x10 in the rears with 265-35-18s and have no problems at all and thats with Konis and Eibachs.

Steven 91 Blk/Ivory

 

[sjs]

215-35-17 front with 275-30-19 in back is WAY off for TCS. You're talking about going down an inch (from 18 to 17) and narrower (225 to 215) and shorter sidewall (40% of 225 to 30% of 215). So no, this is not a good fit. I also wouldn't suggest 215/275 in any sizes.

You need to do the math to see the smallest practical fronts to match the rears, then see what sizes that gives you. But given the existing rear, you can't significantly reduce the overall diameter of the fronts by any combination unless you disable TCS. Sorry to say, you are probably out of luck.

Have you lowered your car?

 

[nsxtasy]

Actually, TCS wouldn't be a problem with the proposed 17"/19" sizes. Compared with the stock '91-93 sizes, the outer diameter of the proposed sizes is 0.6 percent smaller in front, 2.6 percent bigger in the rear. The 3.2 percent difference should be okay. (Differences of 5 percent or greater are NOT advised and I wouldn't want to get too close to that threshold either).

The TCS problem is with the sizes you have NOW, the 18"/19" sizes. The outer diameter of the 225/40-18 tires in front is 8.7 percent larger than the '91-93 stock size. And that's WAY too big for your TCS to function effectively. (Note that the difference between the front increase and the rear increase is 6.1 percent which is significantly above that 5.0 percent threshold.) When sjs notes that there is a big impact on the TCS when moving from the 18"/19" sizes to the 17"/19" sizes, he's right - but it's the 18"/19" sizes that won't work, not the 17"/19" ones.

I'm not sure the car would perform all that well with the 17"/19" sizes, though. And I'm also not sure the car would look all that great; in fact, this is the first time I've ever heard of someone considering a two-inch difference in wheel size front to back.

[This message has been edited by nsxtasy (edited 30 August 2001).]

 

[justin hall]

Originally posted by sjs:
I also wouldn't suggest 215/275 in any sizes.

215/40-17 and 275/35-18 works quite well for some people.

 

[ak]

17" and 19" ?? Wouldn't that look ridiculous? You might fare better with 225/35ZR18's.

 

[sjs]

Originally posted by justin hall:
215/40-17 and 275/35-18 works quite well for some people.

Sure, but they have different priorities than I, which is why I said I wouldn't recommend it. The car is pretty well balanced with a measure of understeer stock. All else being equal, that combination will likely increase understeer. Since udersteer means you already have less traction in front than in the rear, then the front is the "weak link" and more rear traction won't improve handling overall. Since I, like the designers, see handling as very central to the car as a whole, I would not recommend such a combination because it will likely yield no benefits (as I define them) and will likely decrease performance overall.

 

[sjs]

Originally posted by nsxtasy:
Actually, TCS wouldn't be a problem with the proposed 17"/19" sizes. ... Compared with the stock '91-93 sizes...

Thanks to nsxtasy for checking the numbers. I mistakenly assumed that whoever sold you the wheels and tires had a clue. If they knew what you were putting them on, then they were negligent in not trying to prevent such a discrepancy in the first place.

As for 17/19 (tire widths not withstanding and covered in my prior post) there is no reason why it should be a major problem. The main difference would be that the sidewall height is shorter in the rear relative to the front. Taller means more flex, which may feel a bit different. But since the fronts will be in the normal range and the backs shorter (still speaking about absolute sidewall height only), I'm guessing it would be fine.

Two questions not asked:

What year is your car? The late 16/17s on the late model were a significantly different ratio, although they can (just) be used on the early cars.

What width are the front wheels? 215s shouldn't go on a wheel of over about 8 inches. You might get away with wider, but it's not recommended and you also increase risk to the wheels

 

[nsxtasy]

What year is your car? The late 16/17s on the late model were a significantly different ratio, although they can (just) be used on the early cars.

Oh shoot, good point. If your car is a 1994 or later, your current tires are fine, but the proposed ones don't work.

Front
215/45ZR16 stock
215/35ZR17 2.9 percent decrease
225/40ZR18 6.2 percent increase

Rear
245/40ZR17 stock
275/30ZR19 3.2 percent increase

Thus if your car is a 1994 or later, the difference in the rate of change between front and rear is 3.0 percent with the 18" tires, and that's acceptable. But the difference in the rate of change is 6.1 percent with the proposed 17" tires, and that's a problem for the TCS. So don't get this size if you have a 1994 or later NSX.

[This message has been edited by nsxtasy (edited 30 August 2001).]

 

[sjs]

nsxtasy, I'm not getting quite the same numbers. I always use the manufacturer's revolutions per mile as a starting point figuring it's the highest resolution value available, although diameter is probably close enough. Here are some of the numbers: (Larger value = smaller diameter)

Pre '94
Front: 896
Rear: 807

'94 on
Front: 879
Rear: 840

nsx-808 tires on average rim widths:
(According to http://www.tirerack.com/tires/Spec.jsp?make=Bridgestone&model=Potenza+S-03+Pole+Posit ion)

___________Early Late
Front: 833 +7.56% +5.5%
Rear: 814 -0.9% +3.2%

I don't see a 215-35-17 for the SO-3.

Given the rears, you would want roughly 905 revs/mile for pre '94 and 850 revs/mile for a '94+ car.

Looking at the same chart, that makes a 205-40-17 the closest for a pre '94, with 215-40-17 still OK. For a 94+ it gets easier. 235-40-17 is perfect, and reduces overall diameter by 1.1 inches. Is that enough for clearance? To keep your 18's, the 225-35-18 would work, but it has the RF notation, but I don't see what the stands for.

Note: All numbers assuming wheel widths as listed in the chart. The difference from other widths is small, but if you are already marginal than it is worth noting.

Also, looking back now, the chanrt at Tire Rack is suspect for the SO-3. I see tires with the same diameter but significantly different revs/mile. Can't trust anyone!

Well, try the Bridgestone site if you want to be sure.


Darn, I had work to do tonight!

[This message has been edited by sjs (edited 30 August 2001).]

 

[nsx808]

I have a 93.
The wheel in question is 7.5" wide.
I'm also considering going with newer stock wheels or another set...

The only thing is... I bought the tires from Tirerack and the wheels from Rod Millen Motorsports. I was going to get them all from RMM but they didn't have the tires in stock at the time. I told the wheel place to put on the wheels first to see if they would fit... he said the fronts were close but with such a low profile tire it should work. So they mounted them, put them on the car.. I pulled out and couldn't even turn the wheel.

How do you think I should handle this? Could Tire Rack tell if the tires were unmounted if I returned them?

Maybe going 235-40-17 would be best?


[This message has been edited by nsx-808 (edited 30 August 2001).]

 

[justin hall]

http://www.nsxsc.com/tirecalc.html

I use bills calculator, it has been helpful to me.

 

[sjs]

Originally posted by justin hall:
I use bills calculator, it has been helpful to me.

A good first look, but perhaps not close enough if you are already on the edge, and doesn't give rim width assumption. In fact, I see that there is a note at the bottom to the same effect.


[This message has been edited by sjs (edited 30 August 2001).]

 

[nsx808]

Damn, maybe I should just go with 225-35-18's?

You'd think Tirerack wouldn't give me a problem on returning them... after all, I did tell them what kind of car they were going on before I ordered them.



[This message has been edited by nsx-808 (edited 30 August 2001).]

 

[nsxtasy]

nsxtasy, I'm not getting quite the same numbers.

Sure, let's take a look.

I always use the manufacturer's revolutions per mile as a starting point figuring it's the highest resolution value available, although diameter is probably close enough.

Either one should work, except for rounding differences.

BTW, I took my numbers from the Powerdog tire calculator website. They do a straight calculation based on wheel size and tire size. Those measurements SHOULD be the same as the Bridgestone specs on the Tire Rack website (but they aren't; more on that in a moment).

Here are some of the numbers: (Larger value = smaller diameter)

Pre '94
Front: 896

I'm not sure where you get that number. When I look at the Tire Rack's specs for the Bridgestone S-03 in 205/50-15, it says 902 revolutions.

Rear: 807

I'm not sure where you get that one, either. Tire Rack says 837 for 225/50-16.

'94 on
Front: 879

I'm not sure where that one comes from. I can't even find the 215/45-16 size on the Tire Rack website for that tire.

Rear: 840

THAT one I see.

nsx-808 tires on average rim widths:
___________Early Late
Front: 833 +7.56% +5.5%
Rear: 814 -0.9% +3.2%

833 and 814 are the same revolutions stats I see on the Tire Rack website.

Recalculating using the revolutions numbers that I found on the Tire Rack website for the stock tire sizes, it looks to me like the changes would be:

___________Early Late
Front: 833 +8.3% N/A
Rear: 814 +2.8% +3.2%

Those numbers are pretty close to what the powerdog calculator had provided, per my previous post:

___________Early Late
Front: 833 +8.7% +6.2%
Rear: 814 +2.6% +3.2%

So unless I'm mistaken, I think most of the difference may have occurred because you might have pulled the wrong numbers off the Tire Rack website.

-------------------------

What's interesting to me, though, is how Bridgestone calculates its numbers, and how the revolutions per mile differ from the powerdog site. Let's take the 225/50ZR16 size as an example. Bridgestone and Powerdog both calculate the outer diameter of this tire as 24.9 inches. I'm sure Powerdog calculates revolutions per mile by simply multiplying this number by pi (3.1415926536) to get the outer circumference, and then dividing that result into 63360 (number of inches in a mile). If you do that, 63360 / (24.9 x 3.1415926536) = 810 revolutions. Powerdog shows the revolutions as 811 (the difference due to rounding, since it was probably not EXACTLY 24.9 inches in their calculations). However, the Bridgestone website shows this figure as 837 revolutions per mile - a substantial difference. I am guessing that Bridgestone somehow calculates a figure for "rolling" circumference rather than the calculated outer circumference, to take into account the amount of deflection caused at the contact patch. Clever, and undoubtedly more accurate. However, as we can see, it has little effect on the percentage differences, since this adjustment is performed on the before AND after measurements.

Darn, I had work to do tonight!

Yeah, me too. But this seemed like one of those "Stump Ken" puzzle distractions...

 

[sjs]

Originally posted by nsx-808:
Damn, maybe I should just go with 225-35-18's?...

Sorry, that was before you said it was a '92. They would be closer than your current tires, but still outside recommended limits for TCS. They are the shortest 18, but still probably too tall. And, the only save you 0.7 inch for clearance, or about 0.35 from center to top. Is that enough?

 

[nsxtasy]

Damn, maybe I should just go with 225-35-18's?

You could... but keep in mind that your 225/40-18 tires were rubbing a lot - no doubt because the outer diameter is 8.7 percent or so larger than stock. I would say that you still risk rubbing with the 225/35-18, which are still 4.9 percent larger in outer diameter than stock - it's close enough to your rear increase that it shouldn't upset the TCS, but they may still rub.

If you DO decide to change to 17" wheels up front, while using the 19" tire sizes you have in the rear, I would suggest the 215/40ZR17 size. It's 3.0 percent larger than stock, almost the same increase that you have in the rear. Second choice might be the 215/35ZR17, which is 0.6 percent smaller than stock, which should still permit the TCS to operate okay. I doubt that either of these sizes would rub.

You'd think Tirerack wouldn't give me a problem on returning them... after all, I did tell them what kind of car they were going on before I ordered them.

I don't know what to tell you on that. Feel free to discuss it with them. They have VERY good technical advisers and VERY good customer service.

[This message has been edited by nsxtasy (edited 31 August 2001).]

 

[nsx4jlp]

I don't see why you would have a problem. My friend here in Miami has a 93 with 18x7.5 and 20x9.5 an he doesnt rub at all. All yu need to worry about is the rapid inner wear of the tires.

 

[Veleno]

What about a 215/35/18? I'm not sure if they(Bridgestone) make it in that size, but other manufacturers do. I'm not however, recommending using different brand tires front to rear.


------------------
Richard
NSXTASY

[This message has been edited by Veleno (edited 31 August 2001).]

 

[apeltier]

I would not recommend going to 17/19. Its going to look very bad, not to mention how it will affect handling having such a difference front/rear.

I also recommend trying to return the tires to the Rack. They of all places should know that the tire they sold you is too tall for the front of an NSX.

I recommend the 225/35ZR18.

My calcs:

225/35ZR18
225 x .35 x 2 / 25.4 + 18 = 24.2" Overall Dia. vs. 23.6 for Stock '94 = 2.5% change

275/30ZR19
275 x .30 x 2 / 25.4 + 19 = 25.5" Overall Dia. vs. 24.7 for Stock '94 = 3.2 % change

These are overall diameters, not rolling diameters, but if you're comparing apples to apples it shouldn't matter.

The 18/19 setup with these tires are both tall front/rear. There really isn't another option for the NSX in 18/19. We have never heard that it upsets the TCS with any of our customers running 18/19. Its more of the difference in rotation from front/rear that matters, not so much the difference from original, as long as the difference is a similar % from stock front/rear.

For the '94 above cars this setup should be fine. I can't remember stock tires for the '93 and older cars, but the % change for the '94 seems about the same so it might be okay for the '93 and older cars too, but do the same calc's to check.

You may still rub with 225/35s but that depends on the offset. If the offset is correct for the NSX, I know 225/35s work without rubbing.

Alan

------------------
Alan Peltier
Operations Manager
HRE Performance Wheels
[email protected]

'94 black/black NSX
HID only so far. Needs wheels!
Performance upgrades coming as soon as I can scrape up the cash! Donations much appreciated!!

Check out our website at http://www.hrewheels.com

 

[nsxtasy]

I recommend the 225/35ZR18.

For the '94 above cars this setup should be fine. I can't remember stock tires for the '93 and older cars, but the % change for the '94 seems about the same so it might be okay for the '93 and older cars too, but do the same calc's to check.

As I previously noted, this size would be 4.9 percent greater than the '91-93 stock front size of 205/50ZR15. As I also previously noted, this size shouldn't be a problem for TCS when used with the current rear 19" size, which is 2.6 percent greater than the '91-93 stock 225/50ZR16. As Alan points out, TCS will work if you increase front and rear by close to the same percentages - and the 2.3 percent difference here is pretty close. (If the difference is 5 percent or more, you'll have problems.)

You may still rub with 225/35s but that depends on the offset. If the offset is correct for the NSX, I know 225/35s work without rubbing.

Thanks - that was the only thing I was not sure of.

[This message has been edited by nsxtasy (edited 31 August 2001).]

 

[sjs]

nsxtasy, your numbers for stock sizes are different than mine because you are looking at SO-3s and I am looking at the OEM tires. The differences are usually small, but for an accurate comparison I use measurements for each specific tire.

Originally posted by apeltier:
I would not recommend going to 17/19. Its going to look very bad, not to mention how it will affect handling having such a difference front/rear.

My calcs: ...

Likewise here, calculations are fine for ballpark numbers, but you are better of using tire specific values before plunking down the $.

And, I still don't see why handling should be as big of an issue as you suggest. The whole point of seeking out the right combination for TCS ratios means that overall diameter up front is correct relative to the rear regardless of base wheel diameter. So what's the problem?

 

[nsxtasy]

nsxtasy, your numbers for stock sizes are different than mine because you are looking at SO-3s and I am looking at the OEM tires. The differences are usually small, but for an accurate comparison I use measurements for each specific tire.

That makes sense. I thought you were using the measurements for S03 tires because that's what you indicated in your previous post.

Where did you find the specs for the OEM tires? I couldn't find them on Tire Rack's website (for either brand), on Bridgestone's, or on Yokohama's.

 

[sjs]

Originally posted by nsxtasy:
... Where did you find the specs for the OEM tires? I couldn't find them on Tire Rack's website (for either brand), on Bridgestone's, or on Yokohama's.

At Tire Rack, but you can't get there by brand. (dumb) Since the NSX OEM tires are so specialized they quit listing them most places on the site. Go in by Car Make/Model/Year and there is a Specs link along with the price etc.