Originally Posted by TDIwyse
hotrod, I would appreciate any feedback from your extensive drag racing experience regarding my tire question from post #16.
"Question regarding tire size from a dragsrip newbie for those more experienced:
Used 245/45R17 Hoosiers which have a 26.2 in diameter (correction, it's 26.0 based on the manufacturers website). This is significantly larger than stock wheel size and pushes the 4th-5th shift up to ~111mph. Thought this would be high enough that the car wouldn't waste time shifting into 5th during the pull, and more than make up for the slower acceleration at the beginning from the larger tires. However, looking at the recording of the pull (used the Track Recorder option the Android Torque app, and overlaid rpm data on the display) it shows the car was going a bit faster than anticipated and did the 4th-5th shift just before crossing the finish line. So the car was just getting into 5th gear as it went through the trap and finish line.
Would it be better to move to a lower diameter tire and have the 4-5 shift occur before the trap, so the car isn't coasting through the line, and also get better starting acceleration? Or is the larger diameter tire a better option?"
Any insight for a 1/4 mile newbie would be appreciated.
Good info on that meth injection! Diesels are such a different animal.
I just used the same tires from my 335i on the 335d. Nitto NT555Rs on, 275/40/17's. They are a little taller. So on the gas car, I actually got better times with the taller tires. It allowed me to hit 60mph easily in 2nd gear, and finish the 60-130 times before the shift into 5th gear. Not how this comes into play with the diesel. With its taller gearing, I would imagine smaller diameter "could" be better. I would have to see the gear shift point, and how it relates to the qtr mile. I was just doing some preliminary testing this morning on the Stock RFTs still. They are very slippery, yielding 2.3 sec 60' times, and not allowing me to launch with any boost at all. Still mid 13's. A 1.9 sec 60' times should be solid high 12 second runs. Not sure if this is with the JBD set at 75% or 100%. It has been so long since I ran this car, I don't remember the setting. Perhaps I will do a video next time showing the shift points. Actually, you can probably tell the shift points by my you tube video. I'm pretty sure today the car was shifting at 4500rpm. Is that what yours does. I assume no need to go to 5000rpm. But i'm surprised the car shits so early from the factory. 2nd gear launch, and just letting it shift by itself afterwards.
looks like it might be shifting right before the end of the qtr mile. And that is with the taller DRs in this video.