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18s and 20s combo ?

NSXAU

Registered Member
Joined
15 March 2005
Messages
92
Location
Australia
can/ would 18x8s on the front with 20x8.5s [they don't come wider] on the back work on a 93... :confused:
the wheels I'm thinking of dont come in 19s :frown: ..running rim tyre combos thru Powerdog the following measures come thru..
Std
Tire size results
Specification Sidewall Radius Diameter Circumference Revolutions Speedometer Odometer Difference
225/50-15 4.4" 11.9" 23.9" 75.0" 845/mi 60MPH 10000mi N/A
225/50-16 4.4" 12.4" 24.9" 78.1" 811/mi 58MPH 9598mi 4.2%
so 4.2% variance front to back as std, then
Possible ?
Tire size results
Specification Sidewall Radius Diameter Circumference Revolutions Speedometer Odometer Difference
225/40-18 3.5" 12.5" 25.1" 78.8" 804/mi 60MPH 10000mi N/A
275/30-20 3.2" 13.2" 26.5" 83.2" 761/mi 57MPH 9468mi 5.6%

Going up/down to 215/40x18s takes difference out to 7.0% based on 20s as above .... thoughts pls

David
 
The stock front size on a '93 is 205/50-15, not 225/50-15.

Here's how the outer diameter of those sizes compare with stock:

225/40-18 +8.7 percent
275/30-20 +6.6 percent

That front size is going to rub BIG TIME on the fender well liners. Folks with 18" front tires generally use 215/35-18 (+3.7). Any bigger - such as 225/35-18 (+4.9 percent) - and you risk rubbing; some folks with 225/35-18 have rubbing, others don't. I'm sure that 225/40-18 almost guarantees rubbing.

You are also going to have poorer acceleration. Using that rear tire size (275/30-20) is like using taller gears, and is the equivalent of changing from a 4.062 stock R&P gear to a 3.81 R&P gear. :eek: And, of course, the speedometer and odometer will read low by approximately the same 6.6 percent.

And, of course, the very short sidewalls will mean that those wheels will be VERY susceptible to damage from potholes.

It's your decision, of course, but these are some things to consider...
 
Hey thanks ..muffed the fronts size..I was wondering why it looked like it could possibly work, but @ 215/35x18 to the 20s is 15% difference ..which is huge when the std difference fr to back is only 7.7%.

..another question..the fact is I have a set of 18s that I have off another car that i only put about 3000Ks before I sold the car; they are currently

fronts - 18x8s 35offset, tyres [are too big] at 235/40s
rears - 18x9s 40 offset, tyres are 265/35
...if I change the front tyre to 215/35 then the calc fr to back is ..

215/35-18 3.0" 12.0" 23.9" 75.2" 843/mi 60MPH 10000mi N/A
265/30-18 3.1" 12.1" 24.3" 76.2" 831/mi 59MPH 9862mi 1.4%

So is 1.4% too low compared to the 7.7% difference the 93 were designed with....FYI the wheels are by Koya INOX2 [multi spoke with s/s lips] tyres are non directional Falkens...based on offset and size of the rears what size spacer would I need to achieve a nice wheel arch fit ...

Thanks for your help
David
 
David,

Try a 265/35 18" in your calcs for the rear. It will still have a lower F/R ratio than stock though.

I still think 18" is too big for the front in an NSX even if you run a 19" rear.

Wheels this big on the NSX make the car slower to accelerate and effect braking as well because of the larger rotating mass even if the overall diameter is the same.

The biggest wheels I would use on an NSX are:
215/40 17 (7.5 +35 or 8.0 +40)Front and
265/35 18 (9.5 +40 or 10.0 +45) Rear.

30 series rubber is just not enough to absorb the bumbs in our roads in Australia... You will buckle or bend the rims!

Remember as well the the hub diameter is different front to rear on the NSXas well....

NSXAU said:
Hey thanks ..muffed the fronts size..I was wondering why it looked like it could possibly work, but @ 215/35x18 to the 20s is 15% difference ..which is huge when the std difference fr to back is only 7.7%.

..another question..the fact is I have a set of 18s that I have off another car that i only put about 3000Ks before I sold the car; they are currently

fronts - 18x8s 35offset, tyres [are too big] at 235/40s
rears - 18x9s 40 offset, tyres are 265/35
...if I change the front tyre to 215/35 then the calc fr to back is ..

215/35-18 3.0" 12.0" 23.9" 75.2" 843/mi 60MPH 10000mi N/A
265/30-18 3.1" 12.1" 24.3" 76.2" 831/mi 59MPH 9862mi 1.4%

So is 1.4% too low compared to the 7.7% difference the 93 were designed with....FYI the wheels are by Koya INOX2 [multi spoke with s/s lips] tyres are non directional Falkens...based on offset and size of the rears what size spacer would I need to achieve a nice wheel arch fit ...

Thanks for your help
David
Click to expand...
 
thanks Mike..I just found out that this wheel now does come in 19s but its only 8in wide not 9in wide like the 18s that I could use on the rear..so I'll check to see if they now have a 17x7.5 for the front and then I can use the existing 18x9 that I have on the rear and then add spacers to fill the rear wheel arches..here's a pic of the wheel - low res[sorry]

David
 

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AU_NSX said:
Try a 265/35 18" in your calcs for the rear. It will still have a lower F/R ratio than stock though.
Click to expand...
Mike is correct. 265/30-18 will cause problems for the TCS. 265/35-18 will be fine.
 
Hey malibu et al
thanks for the link, [the wheels look monstrous !! wow] but, I read right thru the thread ..and its a shame that it ended the way it did ...so...did 'nsxpr' ever do the 19s, or did he continue with 18/20 ...and how is it that he could run the 18/20 combo without TCS problems..powerdog shows 15% diff front to back for that combo over the std [on 93s] 7.7% ...according to all FAQs and threads I've looked into the fr to rear difference, to avoid TCS issues, must be within the 5%..

Regards
david
 
I'm not sure anyone has the exact formula for when TCS starts to have problems. I have 19/18s on my car and I do think the 19 in the back just looks a tad on the small side. A 20 fills it up just right but too bad a 19 doesn't fit in the front.
 
Malibu Rapper said:
I'm not sure anyone has the exact formula for when TCS starts to have problems.
Click to expand...
Actually, we do. The TCS is programmed for its own model year of car (the stock tires were different sizes in '91-93 from '94-01 from '02-05). If the ratio of front-to-rear outer tire diameters differs from stock by more than 5 percent, it will cause problems for the TCS. That's the formula. However, there are variables that add some "noise" to the formula; for example, tire sizes are not always exact, and tire wear can create a difference in outer diameter of up to 2 percent.

You can calculate using that 5 percent figure in two different ways that are mathematically equivalent:

1) You can calculate the stock front-to-rear outer diameter and the proposed front-to-rear outer diameter, and make sure the difference is within 5 percent. For example, the stock '91-93 rear is 7.7 percent larger than the front. That means TCS should work as long as the proposed rear is 2.7-12.7 percent larger than the front. (Although the "noise" factor may mean that you might not want to be at the very end of that range.)

2) You can calculate the percentage difference from stock at one end, and make sure the other end is within 5 percent. For example, if the front tire is 3.0 percent larger than stock, then TCS should work as long as the rear tire is anywhere from 2.0 percent smaller to 8.0 percent larger than stock. (Ditto with the "noise" factor.)
 
nsxtasy said:
Actually, we do. The TCS is programmed for its own model year of car (the stock tires were different sizes in '91-93 from '94-01 from '02-05). If the ratio of front-to-rear outer tire diameters differs from stock by more than 5 percent
Click to expand...

Then why did nsx_pr not have an issue with his TCS when he ran his 20/18 configuration? The ratio is way off.
 
Malibu Rapper said:
Then why did nsx_pr not have an issue with his TCS when he ran his 20/18 configuration?
Click to expand...
Who is nsx_pr? If you're referring to NSXAU, he apparently has not yet driven with those sizes.
 
Malibu Rapper said:
Then why did nsx_pr not have an issue with his TCS when he ran his 20/18 configuration? The ratio is way off.
Click to expand...
His ratio is off by 5.9 percent (front 1.3 percent larger than stock, rear 7.2 percent larger) - enough that it should have created problems with the TCS. I can only guess that those other variables that constitute "noise" - tire sizes slightly different from their nominal specs, treadwear, etc - had an effect. Perhaps his rear tires were more worn than the front?
 
AU_NSX said:
David,


Remember as well the the hub diameter is different front to rear on the NSXas well....
Click to expand...

Does anyone know what the rear hub diameter is? I know the front is 70.3mm but I can't find the info for the rear.
 
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