| Focus Guy |
| When you change your tires to a differant size, if its smaller than the stock was your ride should move throughout the gears faster and if it was larger it should be the oposite. So how do you know what your best tire size would be for a "light to light" race. This is why I ask. The Focus had 215/45/17's on it and I had a hard time keeping up with my friends 2002 SiR but now with 205/40/17's the tables have turnned. There was a noticable improment in exceleration through out first and second gear from there no differance was noticed. What is the gear ratio change to tire size change? Or is there one? |
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| Genki |
| could also be the tire weight playing a factor too, now that you have less rubber. |
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| schlong8 |
Midasguy: in one word yes. By changing the size of ur tire by decreasing the sidewall depth, u have shortened your gearing and thus increased ur acceleration, BUT limited your top speed.
What were are talking about is called rolling diameter. If you were to get a larger rolling diameter, you in effect lengthen your gears and can gain a higher top speed. A smaller rolling diameter will do the opposite, decrease top speed but increase acceleration. |
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| Focus Guy |
quote:
Originally posted by schlong8@Jan 19 2003, 09:18 PM
What were are talking about is called rolling diameter. If you were to get a larger rolling diameter, you in effect lengthen your gears and can gain a higher top speed. A smaller rolling diameter will do the opposite, decrease top speed but increase acceleration.
This we know but what is the ratio change to rolling diamater. Or are we mearly changing "groung speed" by generation revs sooner? |
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| schlong8 |
| I don't know what the gear ratio change is. That's an engineering question, and i'm not an engineer. |
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| dogstar |
there are formulas floating around for figuring out how much your gearing changes, but i cant find any right now.
also, id wager your wheel and tire weight has gone down, and from physics class, i recall that rotating mass needs to be multiplied by pi, then by rpms to get its true weight at speed. (i think)
if you change wheel weight by a few pounds and do the formula, youll notice the change is pretty signifigant.
you probably already know, but unsprung, rotating mass is the best kind of mass to remove from a car. |
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| bigpappa |
| i think it depends if you have slicks''tire chioces''i run a 4.88 with a 31.13.15 my tires expand inward on the top end and the burnout,if i run this combination on a less horse power engine i would need a 5.14 to run the same time hope this helps you :rolleyes: |
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