sebpv Posted August 2, 2015 Report Share Posted August 2, 2015 Hi everybody, Im purposely fitting smaller wheels onto my 620. The overall wheel diameter goes from 648mm(stock spec) to 594mm. So now I need to change the pinion. I read that switching to the next size is rougly 5% in speed output. 648/594 is 1.09; meaning about 10% error in the speedometer? Should I then purchase a pinion with 22T or 18T? Thanks! EDIT: I forgot to mention I changed the transmission from the stock XX63 4 spd to a 200sx? short 5 pd. I dunno if this needs to be taken into account... Quote Link to comment
Sealik Posted August 2, 2015 Report Share Posted August 2, 2015 http://www.graytechsoftware.com/garage/cogcalc.asp Quote Link to comment
datzenmike Posted August 2, 2015 Report Share Posted August 2, 2015 You are reducing the tire size so the speedometer will be turning faster at the same speed and reading higher that you are really going. To correct this you would need to slow the speedometer cable down to read the true speed. A larger number of teeth on the speedometer pinion gear will take longer to turn once so it will be slower. Your '73 (assuming a stock 4 speed) will have a 16 tooth gear in it that is compatible with the original 6:00 X 14 tires and 4.375 rear end ratio to correctly show the speed. The 600 X 14 tire is roughly equivalent to a 185/70R 14 which is 24.2" tall. (617mm) So you are not really changing as much as you think as your tires now are already oversize from stock and the speedometer incorrect. The difference between the stock 617mm and going down to your 594mm is only 3% and that is 1.5 MPH fast driving at 50 MPH. I say this in MPH because your speedometer is a '73 and will be marked in MPH. In KPH it's fast by 1.5 KPH when driving at 100KPH .... not worth worrying about. Math wasn't my thing in school so if you or anyone see fault in this, say so. :lol: Quote Link to comment
sebpv Posted August 2, 2015 Author Report Share Posted August 2, 2015 According to the link, it recommends 22T... I read that the stock spec was 195/75/14... PO had installed 195 and 215/75/14 Mike, does that change a thing knowimn I put a 200sx tranny? Quote Link to comment
sebpv Posted August 2, 2015 Author Report Share Posted August 2, 2015 My 4spd pinion is no good so Ill order a new one to fit on the 5spd. Thx guys for the fast replies Quote Link to comment
datzenmike Posted August 2, 2015 Report Share Posted August 2, 2015 EDIT: I forgot to mention I changed the transmission from the stock XX63 4 spd to a 200sx? short 5 pd. I dunno if this needs to be taken into account... Missed this. The FS5W63A in the '77-'79 200sx used a 17 tooth gear so you will be 6.25% slower on top of the calculated 1.5% faster that you are really going. Roughly 6.25 - 1.5 = 4.75 KPH at 100KPH. To reduce this error by 5.8% you need a 18 tooth gear bringing the error to about 1% (I think) You are in luck if Nissan still has them. The A10 (HL510) through '79 in US and '80 in Canada used the FS5W63A dogleg with an 18 tooth pinion gear. The part number is 32703-N9018 Again have this info verified. Quote Link to comment
datzenmike Posted August 2, 2015 Report Share Posted August 2, 2015 According to the link, it recommends 22T... I read that the stock spec was 195/75/14... PO had installed 195 and 215/75/14 Mike, does that change a thing knowimn I put a 200sx tranny? The stock tire was a 600 X 14" so if anyone knows exactly what the metric equivalent of this old tire is today post it up. Not what you're running and getting away with, but what the stock size is. I had to take an educated guess at 185/70 14 Quote Link to comment
sebpv Posted August 2, 2015 Author Report Share Posted August 2, 2015 http://www.turbinecar.com/tires.htm im currently looking through it Quote Link to comment
Rjawm Posted August 2, 2015 Report Share Posted August 2, 2015 http://chevellestuff.net/tech/tires.htm 6.00-14 works out to 175/70-14 according to the chart in the link above. That works out to 23.65 inches or 600.7 mm It also says 6.00-14 is the equivalent to 185/65-14 in the same chart. That works out to 23.47 inches or 596.1 mm FWIW I found 2 other charts that listed the same equivalents as the chart I provided a link for http://www.tirerack.com/tires/tiretech/45_conversionchart.jsp http://www.tpocr.com/tiresize.html 1 Quote Link to comment
datzenmike Posted August 2, 2015 Report Share Posted August 2, 2015 That's so close 600mm to the new tire size 594mm I would just leave it as is then. Quote Link to comment
sebpv Posted August 2, 2015 Author Report Share Posted August 2, 2015 Well after further research, the stock '80 200sx tire size according to FSM is 185/70/14 or 615mm. I will go measure my tires to account for the stretch. Could sit between 594 and 564mm... Quote Link to comment
datzenmike Posted August 2, 2015 Report Share Posted August 2, 2015 The stock 200sx tires do not matter as it had a different differential ratio (3.889) to your truck's. (4.375) Quote Link to comment
DanielC Posted August 3, 2015 Report Share Posted August 3, 2015 I have a 1970 521, 4.375 rear axle. The rear tires are P205/70 R14. I got a chance to check the odometer against a measured 5 mile section on the freeway a few months ago. In five actual miles, the odometer clocked 5.1, rolling into 5.2 as I passed the last milepost. Quote Link to comment
datzenmike Posted August 3, 2015 Report Share Posted August 3, 2015 So 0.4 mile per 10 miles and 4 miles per 100 miles. 4% fast reading? At 50MPH that's only 2 MPH. That's so close 600mm to the new tire size 594mm I would just leave it as is then. sebpv..... drive it and see first. Check it out on the highway over at least 5 miles like Daniel did. Quote Link to comment
sebpv Posted August 3, 2015 Author Report Share Posted August 3, 2015 will do. Too early to tell yet. Just doing my homework :) Quote Link to comment
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