I have heard of a lot of people talkin about figuring out there 1/4 mile time based on their 1/8 mile time. What is the formula for converting a 1/8 mile time to a 1/4 mile time? Or is there a website that does that calculation for you?

 

anyone know?

 

A good rule of thumb, multiply your 1/8 time by 1.55

 

I think 1.55 is alittle generous unless you have a stick car. I think 1.57-1.58 is more realistic, especially if the car has a pretty big converter.

Randy

 

Hard to say. My last trip out was 9.0 1/8 and 13.3 1/4. Damn street tires.

 

thanks for the replies.. just for anyone reading this, I also posted on this question on a couple other forums and got these websites (that both seem to give the same result for conversion):
http://www.tciauto.com/tech_info/calculators.htm#2
http://www.wallaceracing.com/eigth-t...conversion.php

 

There is no exact formula but I've always used 1.56 as the conversion number.

I just grabbed one of my old timeslips to see. It was a time trial run so the runs were flat out.

1/8 mile = 6.556
1/4 mile = 10.175

6.556 x 1.56 = 10.227

My opponent ran 5.733 and 8.958

5.733 x 1.56 = 8.994

The only way to know exactly what your 1/4 mile time will be is to actually run on the 1/4 mile. There are too many factors that can change that time.

 

1.56 is a commonly accepted factor for this conversion. The NHRA uses a factor of 1.60 ...I guess because it is a conservative factor for them. NHRA likes the 1/4 mile IMHO.


Vince

 

The basic assumption on this issue and the math used is that most cars make 64 percent of their ET in the first 660ft, or 1/8 mile. Therefore, the number 1.5625 is derived by dividing 0.64 (64 percent) into 1. And, this method (1/8 ET x 1.5625) is a very accurate way to determine possible ¼ ETs using the 1/8 ET as a baseline.

 

Where exactly does the formula:
1/4 mile ET=(1/8 mile ET + .22)/.655 come from then? I've seen that on a few websites for the formula used for the online calculators, seems to end up with really close to the same result..

 

Agreed. Some cars have better top end than others and gearing and aero comes into play as well. Like you said too many variables to be precise with any formula.

 

NHRA also uses the 64 percent theory for their 1/8 mile and 1/4 mile ET class indexes. Again, this formula will provide a "good indication" of your possible 1/4 mile ET, based on the 1/8 mile. And, that was the context of the basic question, how to convert 1/8s to 1/4s (an estimate).

Additionally, I also checked the math using my friend's big-block N/A dragster that runs 7.90 to 8.10 in the 1/4 to see if that type vehicle would be different. The dragster 1/8 mile ET was "very close" to 64 percent of the 1/4.

So, the math does work and you can use it to make a "very close" determination!