Quote:
Originally Posted by serialk11r
Er, smaller tires better fuel economy? I think it's the other way around...
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Often it is, but when driving on hilly ground it can be working against you as rpm goes too low, so you need to shift down. With smaller wheels my car manages to climb hills much better, engine stays on powerband and with diesel less load is always better than less rpm, when you just keep it off the boost, which means there is limit to how much rpm you can have. Boost means lot of enrichment.
On level ground bigger wheels are really helping my economy, but not when there is hills.
As was posted previously, one can see that 250 area, with bigger wheels it is not possible stay in there at all on hilly area. (We have warning signs of 7% hills here for example).
With diesels at least higher load increases fuel usage a lot, you will start to get black smoke from end of tailpipe telling there is lot of unburnt fuel, efficiency is not optimal, better to stay at maximum torque with smaller wheels, better speed on 5th than with bigger wheels and 4th at maximum torque rpm so economy is better too.
Below 1800rpm for me is where there is nothing happening in motor, even I push pedal to floor there is very little happening except that black cloud and above 2200 boost enrichment adds lot of fuel, so that is also causing issue in my case, speed with bigger wheels 5th gear and max torque (around 2000) would be illegal by expensive amount, so that is also why bigger wheels will cause more fuel consumption.
Perfectly possible, such has happened many times, there is certain maximum that is going to be optimal, go above and there is impact to economy, go smaller and again there is impact to economy, finding that optimal is not always easy.