Best "performance" tire for a 70 240z

[Matthew Abate]

Hi everyone,

According to some searches I have done the OEM tires for S30s in the USA were:

Brand	Model	Width	Ratio	Rim	Sidewall	Diameter	Circumference	Revs/Mile	Difference
OEM	240z	175	82	14	5.65	25.30	79.48	797.18	0.00%
OEM	280z	197	70	14	5.43	24.86	78.09	811.32	-1.77%

I see above that Arne recommended around 825-840  revolutions per mile to keep the speedo accurate, but that doesn't match the math I have above, so either those aren't the right OEM tire sizes or those aren't the right RPM figures. I wonder if Arne's numbers come from pairing them with a different or a-typical transmission speedometer gear.

I am putting together a spreadsheet of available tire sizes for 14 and 15" wheels and what to get this correct first. If you know of better threads with more or more accurate information, please reply,y with the link so that we can connect all of this and ensure that people don't go down the wrong path. I know this is a long dead thread, but in an effort to make sure that people are finding the best information possible, I wanted to push on some things said and verify what I have been finding in other places.

[w3wilkes]

2 hours ago, Matthew Abate said:

 

Brand	Model	Width	Ratio	Rim	Sidewall	Diameter	Circumference	Revs/Mile	Difference
OEM	240z	175	82	14	5.65	25.30	79.48	797.18	0.00%
OEM	280z	197	70	14	5.43	24.86	78.09	811.32	-1.77%

 

I thought the 240Z OEM 175 R14's had a ratio of 78, not 82 and I thought the 280Z was 195/70 R14. See post's 13 and 14 in this thread.

Edited September 11, 2018 by w3wilkes

[Matthew Abate]

On 9/11/2018 at 12:02 PM, w3wilkes said:

I thought the 240Z OEM 175 R14's had a ratio of 78, not 82 and I thought the 280Z was 195/70 R14. See post's 13 and 14 in this thread.

That's helpful, thanks. I have found various places online that give 82% as the ratio for a 175sr14, but I guess I've seen 78% just as much, and Arne gives the ratio as 80% in that thread you posted.

That 4% spread makes a huge difference in what options will work, though, so thanks.

The 280Z size I have above came from Arne's post in this thread (#19):

On 12/20/2008 at 9:28 PM, Arne said:

The stock size for a 240Z was 175-14 … 197/70-14 (stock on 280Zs)…

From what I understand is the195/70-14 is a common choice to replace the unavailable sizes, not the original size.

 

However, none of this solves the RPM question I had.

Edited September 13, 2018 by Matthew Abate

[w3wilkes]

Other than that post by @Arne I've only seen 195/70 R14 listed for a 280Z

http://www.automobile-catalog.com/tire/1978/2104790/datsun_280_z.html

Then using the Discount Tire size calculator and comparing the 195/70 R14 to a 175/78 R14 the RPM's are identical

https://www.discounttire.com/learn/tire-size-calculator

I run 205/60 R15 which comes out to a 2 RPM difference from what I believe is stock tire size using the Discount Tire size calculator.

[Matthew Abate]

Right, but several tire retailers list the sidewall ratio of a 175HR14 at 82%, which is 0.55 inches larger in diameter and throws the equation quite significantly.

 

All of these sites have something that supports the 175HR14 sidewall ratio being 82%.

https://www.moderntiredealer.com/article/311243/understanding-tire-dimensions

https://en.wikipedia.org/wiki/Tire_code

https://www.tirerack.com/tires/tiretech/45_conversionchart.jsp (see 1960 to present EURO-METRIC column)

https://www.utires.com/articles/buying-tires-guide-tire-numbers-mean/

https://www.errolstyres.co.za/odcalculator

https://www.denniskirk.com/learn/tire-sizes-explained

 

If it was 82%, then a 195/70-14 is 0.95 inches smaller in diameter and additional RPM.

 

Ultimately, though, I'm not trying to argue whether people should get 195/70-14s or not. I'm more interested in all the other sizes and which ones are good choices, particularly for 15" rims, but also 16s.

Edited September 13, 2018 by Matthew Abate

[Matthew Abate]

I found 175 HR 14s for sale: https://www.longstonetyres.co.uk/175hr14-michelin-xas.html

These are 634mm, which makes the ratio for the sidewall 79.542857142%

So Arne was right according to this tire.

Edited September 13, 2018 by Matthew Abate

[Matthew Abate]

I put together a spreadsheet for 14 to 16" wheels that I hope does a better job of illustrating why I think this question of 175HR14 sidewall-ratio accuracy is important if you want speedometer accuracy.

Width	Ratio	Rim	Side	Diam.	Circ.	R/Mi	Δ	Width Range
175		14	5.51	25.02	78.61	805.96	N/A	4.5 - 5
197	70	14	5.43	24.86	78.09	811.32	-0.67%	6
175	50	14	3.44	20.89	65.63	965.45	-19.79%	5 - 5.5
175	55	14	3.79	21.58	67.79	934.63	-15.96%	5 - 5.5
175	60	14	4.13	22.27	69.96	905.71	-12.38%	5 - 5.5
175	65	14	4.48	22.96	72.12	878.53	-9.00%	5 - 5.5
175	70	14	4.82	23.65	74.29	852.93	-5.83%	5 - 5.5
175	75	14	5.17	24.33	76.45	828.78	-2.83%	5 - 5.5
175	80	14	5.51	25.02	78.61	805.96	0.00%	5 - 5.5
185	50	14	3.64	21.28	66.86	947.60	-17.57%	5.5 - 6
185	55	14	4.01	22.01	69.15	916.24	-13.68%	5.5 - 6
185	60	14	4.37	22.74	71.44	886.89	-10.04%	5.5 - 6
185	65	14	4.73	23.47	73.73	859.37	-6.63%	5.5 - 6
185	70	14	5.10	24.20	76.02	833.50	-3.42%	5.5 - 6
185	75	14	5.46	24.93	78.30	809.15	-0.39%	5.5 - 6
185	80	14	5.83	25.65	80.59	786.17	2.46%	5.5 - 6
195	50	14	3.84	21.68	68.10	930.39	-15.44%	6 - 6.5
195	55	14	4.22	22.44	70.51	898.56	-11.49%	6 - 6.5
195	60	14	4.61	23.21	72.92	868.84	-7.80%	6 - 6.5
195	65	14	4.99	23.98	75.34	841.03	-4.35%	6 - 6.5
195	70	14	5.37	24.75	77.75	814.94	-1.11%	6 - 6.5
195	75	14	5.76	25.52	80.16	790.42	1.93%	6 - 6.5
195	80	14	6.14	26.28	82.57	767.33	4.79%	6 - 6.5
205	50	14	4.04	22.07	69.34	913.79	-13.38%	6.5 - 7
205	55	14	4.44	22.88	71.87	881.55	-9.38%	6.5 - 7
205	60	14	4.84	23.69	74.41	851.51	-5.65%	6.5 - 7
205	65	14	5.25	24.49	76.94	823.45	-2.17%	6.5 - 7
205	70	14	5.65	25.30	79.48	797.18	1.09%	6.5 - 7
205	75	14	6.05	26.11	82.02	772.54	4.15%	6.5 - 7
205	80	14	6.46	26.91	84.55	749.37	7.02%	6.5 - 7
215	50	14	4.23	22.46	70.57	897.77	-11.39%	7 - 7.5
215	55	14	4.66	23.31	73.23	865.17	-7.35%	7 - 7.5
215	60	14	5.08	24.16	75.89	834.86	-3.59%	7 - 7.5
215	65	14	5.50	25.00	78.55	806.60	-0.08%	7 - 7.5
215	70	14	5.93	25.85	81.21	780.19	3.20%	7 - 7.5
215	75	14	6.35	26.70	83.87	755.45	6.27%	7 - 7.5
215	80	14	6.77	27.54	86.53	732.23	9.15%	7 - 7.5
225	50	14	4.43	22.86	71.81	882.31	-9.47%	7.5 - 8
225	55	14	4.87	23.74	74.59	849.39	-5.39%	7.5 - 8
225	60	14	5.31	24.63	77.38	818.85	-1.60%	7.5 - 8
225	65	14	5.76	25.52	80.16	790.42	1.93%	7.5 - 8
225	70	14	6.20	26.40	82.94	763.90	5.22%	7.5 - 8
225	75	14	6.64	27.29	85.73	739.10	8.30%	7.5 - 8
225	80	14	7.09	28.17	88.51	715.86	11.18%	7.5 - 8
235	50	14	4.63	23.25	73.05	867.37	-7.62%	8 - 8.5
235	55	14	5.09	24.18	75.95	834.18	-3.50%	8 - 8.5
235	60	14	5.55	25.10	78.86	803.43	0.31%	8 - 8.5
235	65	14	6.01	26.03	81.77	774.88	3.86%	8 - 8.5
235	70	14	6.48	26.95	84.67	748.28	7.16%	8 - 8.5
235	75	14	6.94	27.88	87.58	723.44	10.24%	8 - 8.5
235	80	14	7.40	28.80	90.49	700.21	13.12%	8 - 8.5
245	50	14	4.82	23.65	74.29	852.93	-5.83%	8.5 - 9
245	55	14	5.31	24.61	77.32	819.50	-1.68%	8.5 - 9
245	60	14	5.79	25.57	80.35	788.59	2.16%	8.5 - 9
245	65	14	6.27	26.54	83.38	759.93	5.71%	8.5 - 9
245	70	14	6.75	27.50	86.41	733.28	9.02%	8.5 - 9
245	75	14	7.23	28.47	89.44	708.44	12.10%	8.5 - 9
245	80	14	7.72	29.43	92.47	685.22	14.98%	8.5 - 9
185	50	15	3.64	22.28	70.01	905.07	-12.30%	5.5 - 6
185	55	15	4.01	23.01	72.29	876.42	-8.74%	5.5 - 6
185	60	15	4.37	23.74	74.58	849.54	-5.41%	5.5 - 6
185	65	15	4.73	24.47	76.87	824.25	-2.27%	5.5 - 6
185	70	15	5.10	25.20	79.16	800.42	0.69%	5.5 - 6
185	75	15	5.46	25.93	81.45	777.93	3.48%	5.5 - 6
185	80	15	5.83	26.65	83.73	756.68	6.12%	5.5 - 6
195	50	15	3.84	22.68	71.24	889.36	-10.35%	6 - 6.5
195	55	15	4.22	23.44	73.65	860.24	-6.73%	6 - 6.5
195	60	15	4.61	24.21	76.07	832.96	-3.35%	6 - 6.5
195	65	15	4.99	24.98	78.48	807.36	-0.17%	6 - 6.5
195	70	15	5.37	25.75	80.89	783.29	2.81%	6 - 6.5
195	75	15	5.76	26.52	83.30	760.61	5.63%	6 - 6.5
195	80	15	6.14	27.28	85.71	739.21	8.28%	6 - 6.5
205	50	15	4.04	23.07	72.48	874.18	-8.46%	6.5 - 7
205	55	15	4.44	23.88	75.01	844.63	-4.80%	6.5 - 7
205	60	15	4.84	24.69	77.55	817.02	-1.37%	6.5 - 7
205	65	15	5.25	25.49	80.09	791.15	1.84%	6.5 - 7
205	70	15	5.65	26.30	82.62	766.87	4.85%	6.5 - 7
205	75	15	6.05	27.11	85.16	744.04	7.68%	6.5 - 7
205	80	15	6.46	27.91	87.69	722.52	10.35%	6.5 - 7
215	50	15	4.23	23.46	73.72	859.51	-6.64%	7 - 7.5
215	55	15	4.66	24.31	76.38	829.59	-2.93%	7 - 7.5
215	60	15	5.08	25.16	79.03	801.67	0.53%	7 - 7.5
215	65	15	5.50	26.00	81.69	775.58	3.77%	7 - 7.5
215	70	15	5.93	26.85	84.35	751.13	6.80%	7 - 7.5
215	75	15	6.35	27.70	87.01	728.17	9.65%	7 - 7.5
215	80	15	6.77	28.54	89.67	706.58	12.33%	7 - 7.5
225	50	15	4.43	23.86	74.95	845.33	-4.88%	7.5 - 8
225	55	15	4.87	24.74	77.74	815.07	-1.13%	7.5 - 8
225	60	15	5.31	25.63	80.52	786.90	2.37%	7.5 - 8
225	65	15	5.76	26.52	83.30	760.61	5.63%	7.5 - 8
225	70	15	6.20	27.40	86.08	736.02	8.68%	7.5 - 8
225	75	15	6.64	28.29	88.87	712.97	11.54%	7.5 - 8
225	80	15	7.09	29.17	91.65	691.32	14.22%	7.5 - 8
235	50	15	4.63	24.25	76.19	831.61	-3.18%	8 - 8.5
235	55	15	5.09	25.18	79.10	801.05	0.61%	8 - 8.5
235	60	15	5.55	26.10	82.00	772.65	4.13%	8 - 8.5
235	65	15	6.01	27.03	84.91	746.21	7.41%	8 - 8.5
235	70	15	6.48	27.95	87.82	721.51	10.48%	8 - 8.5
235	75	15	6.94	28.88	90.72	698.39	13.35%	8 - 8.5
235	80	15	7.40	29.80	93.63	676.71	16.04%	8 - 8.5
245	50	15	4.82	24.65	77.43	818.32	-1.53%	8.5 - 9
245	55	15	5.31	25.61	80.46	787.50	2.29%	8.5 - 9
245	60	15	5.79	26.57	83.49	758.92	5.84%	8.5 - 9
245	65	15	6.27	27.54	86.52	732.34	9.14%	8.5 - 9
245	70	15	6.75	28.50	89.55	707.56	12.21%	8.5 - 9
245	75	15	7.23	29.47	92.58	684.40	15.08%	8.5 - 9
245	80	15	7.72	30.43	95.61	662.70	17.77%	8.5 - 9
255	40	15	4.02	23.03	72.36	875.68	-8.65%	9 - 9.5
255	45	15	4.52	24.04	75.51	839.10	-4.11%	9 - 9.5
255	50	15	5.02	25.04	78.66	805.46	0.06%	9 - 9.5
255	55	15	5.52	26.04	81.82	774.41	3.92%	9 - 9.5
255	60	15	6.02	27.05	84.97	745.66	7.48%	9 - 9.5
255	65	15	6.53	28.05	88.13	718.98	10.79%	9 - 9.5
255	70	15	7.03	29.06	91.28	694.13	13.88%	9 - 9.5
265	40	15	4.17	23.35	73.35	863.86	-7.18%	9.5 - 10
265	45	15	4.69	24.39	76.62	826.91	-2.60%	9.5 - 10
265	50	15	5.22	25.43	79.90	792.99	1.61%	9.5 - 10
265	55	15	5.74	26.48	83.18	761.74	5.49%	9.5 - 10
265	60	15	6.26	27.52	86.46	732.86	9.07%	9.5 - 10
265	65	15	6.78	28.56	89.73	706.09	12.39%	9.5 - 10
265	70	15	7.30	29.61	93.01	681.21	15.48%	9.5 - 10
275	40	15	4.33	23.66	74.33	852.36	-5.76%	10 - 10.5
275	45	15	4.87	24.74	77.74	815.07	-1.13%	10 - 10.5
275	50	15	5.41	25.83	81.14	780.90	3.11%	10 - 10.5
275	55	15	5.95	26.91	84.54	749.48	7.01%	10 - 10.5
275	60	15	6.50	27.99	87.94	720.49	10.60%	10 - 10.5
275	65	15	7.04	29.07	91.34	693.66	13.93%	10 - 10.5
275	70	15	7.58	30.16	94.74	668.76	17.02%	10 - 10.5
185	40	16	2.91	21.83	68.57	924.01	-14.65%	5.5 - 6
185	45	16	3.28	22.56	70.86	894.17	-10.94%	5.5 - 6
185	50	16	3.64	23.28	73.15	866.20	-7.47%	5.5 - 6
185	55	16	4.01	24.01	75.44	839.92	-4.21%	5.5 - 6
185	60	16	4.37	24.74	77.72	815.20	-1.15%	5.5 - 6
185	65	16	4.73	25.47	80.01	791.88	1.75%	5.5 - 6
185	70	16	5.10	26.20	82.30	769.87	4.48%	5.5 - 6
195	40	16	3.07	22.14	69.56	910.86	-13.02%	6 - 6.5
195	45	16	3.45	22.91	71.97	880.34	-9.23%	6 - 6.5
195	50	16	3.84	23.68	74.38	851.80	-5.69%	6 - 6.5
195	55	16	4.22	24.44	76.80	825.04	-2.37%	6 - 6.5
195	60	16	4.61	25.21	79.21	799.92	0.75%	6 - 6.5
195	65	16	4.99	25.98	81.62	776.28	3.68%	6 - 6.5
195	70	16	5.37	26.75	84.03	754.00	6.45%	6 - 6.5
205	40	16	3.23	22.46	70.55	898.09	-11.43%	6.5 - 7
205	45	16	3.63	23.26	73.09	866.93	-7.56%	6.5 - 7
205	50	16	4.04	24.07	75.62	837.86	-3.96%	6.5 - 7
205	55	16	4.44	24.88	78.16	810.68	-0.59%	6.5 - 7
205	60	16	4.84	25.69	80.69	785.21	2.58%	6.5 - 7
205	65	16	5.25	26.49	83.23	761.29	5.54%	6.5 - 7
205	70	16	5.65	27.30	85.76	738.78	8.34%	6.5 - 7
215	40	16	3.39	22.77	71.54	885.67	-9.89%	7 - 7.5
215	45	16	3.81	23.62	74.20	853.93	-5.95%	7 - 7.5
215	50	16	4.23	24.46	76.86	824.38	-2.29%	7 - 7.5
215	55	16	4.66	25.31	79.52	796.81	1.14%	7 - 7.5
215	60	16	5.08	26.16	82.18	771.03	4.33%	7 - 7.5
215	65	16	5.50	27.00	84.84	746.86	7.33%	7 - 7.5
215	70	16	5.93	27.85	87.49	724.16	10.15%	7 - 7.5
225	40	16	3.54	23.09	72.53	873.58	-8.39%	7.5 - 8
225	45	16	3.99	23.97	75.31	841.30	-4.38%	7.5 - 8
225	50	16	4.43	24.86	78.09	811.32	-0.67%	7.5 - 8
225	55	16	4.87	25.74	80.88	783.41	2.80%	7.5 - 8
225	60	16	5.31	26.63	83.66	757.35	6.03%	7.5 - 8
225	65	16	5.76	27.52	86.44	732.97	9.06%	7.5 - 8
225	70	16	6.20	28.40	89.23	710.11	11.89%	7.5 - 8
235	40	16	3.70	23.40	73.52	861.83	-6.93%	8 - 8.5
235	45	16	4.16	24.33	76.42	829.05	-2.86%	8 - 8.5
235	50	16	4.63	25.25	79.33	798.67	0.90%	8 - 8.5
235	55	16	5.09	26.18	82.24	770.45	4.41%	8 - 8.5
235	60	16	5.55	27.10	85.14	744.15	7.67%	8 - 8.5
235	65	16	6.01	28.03	88.05	719.58	10.72%	8 - 8.5
235	70	16	6.48	28.95	90.96	696.59	13.57%	8 - 8.5
245	40	16	3.86	23.72	74.51	850.38	-5.51%	8.5 - 9
245	45	16	4.34	24.68	77.54	817.15	-1.39%	8.5 - 9
245	50	16	4.82	25.65	80.57	786.41	2.43%	8.5 - 9
245	55	16	5.31	26.61	83.60	757.91	5.96%	8.5 - 9
245	60	16	5.79	27.57	86.63	731.40	9.25%	8.5 - 9
245	65	16	6.27	28.54	89.66	706.68	12.32%	8.5 - 9
245	70	16	6.75	29.50	92.69	683.57	15.19%	8.5 - 9
255	40	16	4.02	24.03	75.50	839.24	-4.13%	9 - 9.5
255	45	16	4.52	25.04	78.65	805.58	0.05%	9 - 9.5
255	50	16	5.02	26.04	81.81	774.52	3.90%	9 - 9.5
255	55	16	5.52	27.04	84.96	745.77	7.47%	9 - 9.5
255	60	16	6.02	28.05	88.11	719.08	10.78%	9 - 9.5
255	65	16	6.53	29.05	91.27	694.23	13.86%	9 - 9.5
255	70	16	7.03	30.06	94.42	671.04	16.74%	9 - 9.5
265	40	16	4.17	24.35	76.49	828.38	-2.78%	9.5 - 10
265	45	16	4.69	25.39	79.76	794.34	1.44%	9.5 - 10
265	50	16	5.22	26.43	83.04	762.99	5.33%	9.5 - 10
265	55	16	5.74	27.48	86.32	734.02	8.93%	9.5 - 10
265	60	16	6.26	28.52	89.60	707.16	12.26%	9.5 - 10
265	65	16	6.78	29.56	92.87	682.21	15.35%	9.5 - 10
265	70	16	7.30	30.61	96.15	658.95	18.24%	9.5 - 10
275	40	16	4.33	24.66	77.48	817.80	-1.47%	10 - 10.5
275	45	16	4.87	25.74	80.88	783.41	2.80%	10 - 10.5
275	50	16	5.41	26.83	84.28	751.79	6.72%	10 - 10.5
275	55	16	5.95	27.91	87.68	722.63	10.34%	10 - 10.5
275	60	16	6.50	28.99	91.08	695.64	13.69%	10 - 10.5
275	65	16	7.04	30.07	94.48	670.60	16.80%	10 - 10.5
275	70	16	7.58	31.16	97.88	647.30	19.69%	10 - 10.5

Edited September 13, 2018 by Matthew Abate

[jfa.series1]

Seriously nice work!  I  thinks lots of folks will appreciate this.  Perhaps it should be added to the technical library.

[pontiacguy]

Matthew many thanks for thr research thats one of the best charts ive seen concerning side dia. FWIW I have 185/70'S on shelby cal 500's i dont like them sidewall too short but came on the car when i bought it an are still like new so once they wear ill go to a different size  i like the look of the 70's tires tall side walls

[Stanley]

Using a set of Falken / Ziex a size smaller than stock.  Car sits a little lower due to the tires. 130 MPH speed rating, good in the rain. Tires with a high speed rating wear out a little faster, seems like a bad gamble to go with lower speed rating though. I went smaller to get a faster time at the strip, although I haven't raced it since installing them. Feels a lot faster off the line and 40 to 90 MPH for freeway on ramps. Speedo optimistic per table, but I don't care. 

Bigger motor now so maybe I'd get a quicker ET and/or faster top speed in 1/4 mile by going back to stock diameter, don't know though, lots of variables. Guess that's a question for a different thread.  Main thing is get good tires. H rating or above. Bought some Enterprise cheapies when  was broke. Scary in the rain, also one blew out on the freeway. It was fairly new.

[Zup]

Great info in that table!

Edited September 14, 2018 by Zup

[CanTechZ]

Matthew, thanks for producing that awesome chart, it is very useful.  For reference I just measured the lightly used original spare from my 7'70 car, its a Bridgestone 175SR14.  Using a Pi tape I measured the existing outside diameter at 25.17" and a tread depth of 7/32".  Calculates to just over an 81% aspect ratio, right in the middle of that 80 - 82 range.

Cheers

Mike