is it possible to change the final drive ratio like you can with a differential?
perhaps different pulley sizes on the belt drive?
gearing
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I'm sure you know the easiest route to this is to just change the diameter/circumference of the rear tire, just making sure to change the front tires by about the same amount, as to not set off the ABS/TC alarms. I forget the exact number off the top of my head, but all the way up to about a 4% variance between front and back would be safe. I don't believe there's any getting around the speedometer becoming uncalibrated (other than getting the exact size of an existing model (an SL using base size, for example) and having the dealer update the ECU programming value to that model... but the speedometer calibration difference is typically hardly enough to notice. I've never heard of a different pulley size being available, but I'm sure you'd lose traction control if you tried, and few are brave enough to drive around without TC full-time, unless they're dumping the angle drive and getting an extra rear wheel out of the deal, and even then, watch out.
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I'm sure you know the easiest route to this is to just change the diameter/circumference of the rear tire, just making sure to change the front tires by about the same amount, as to not set off the ABS/TC alarms. I forget the exact number off the top of my head, but all the way up to about a 4% variance between front and back would be safe. I don't believe there's any getting around the speedometer becoming uncalibrated (other than getting the exact size of an existing model (an SL using base size, for example) and having the dealer update the ECU programming value to that model... but the speedometer calibration difference is typically hardly enough to notice. I've never heard of a different pulley size being available, but I'm sure you'd lose traction control if you tried, and few are brave enough to drive around without TC full-time, unless they're dumping the angle drive and getting an extra rear wheel out of the deal, and even then, watch out.
You do not have to change the front tires in the same relationship to the rear. I am running 265 35 18s on the front and a 295 18 45 on the rear without a problem. I put the bigger circumference tire io the rear to run lower pressure and get more grip. A positive is that it has changed the ratio and 1st gear is more usable now. My front tires are 24.5 inches tall and the rear is 28.5 inches tall. The ECU is flashed for the SL.
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I'm not sure we can just yet declare that you just don't have to worry about it at all. Over the years now, the forums are littered with complaints of people who lost their traction control for trying a 9%-10% variance (whereas stock is 3.7%, listed below next to yours). Also notice the calculator is giving your front tires 25.3, instead of 24.5. By under-inflating the rear tire, it would effectively have a lesser rolling diameter, and if was just a half inch lower, that would be a full inch less diameter, which would put you at a 7.4% variance, or just 3.4% more than stock, possibly not a high enough variance to cause a problem. So the question would be, have you run for any great length of time fully aired-up in the back?
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Yes. If my intention is for straight line traction I run 20 psi. If I am playing in the twisties I run 25 psi. I know there are a lot of theories about the ratio. I have been running like this since May and have put on over 3000 miles
With the Base program in the ECU I had lights, with the SL no lights.
I listened to the theories about front to rear ratios for 2 years which all said I would have problems, I don't. The measurements I provided are what is measured on my Sling, not calculations.
My traction is considerably better now. -
With the Base program in the ECU I had lights, with the SL no lights.
Well I'm glad you mentioned this; would be good for future experimenters to know.
