Correlation between lap times and weight loss

[JimLill]

Here's an quick/dirty IT version of something I did years ago.......

http://www.vectorbd.com/am-rennsport/vwsim.xls

fill in the green blocks, it calcs the rest. You can see the effects on HP req'd

[mbuskuhl]

It makes sense one of the million variables is also where the weight is removed from, could be all over or more front/rear. The weight I am removing is lead in the passenger floorboard, 150lbs of it. I'm curious as to what impact it will have on lap times. I guess if I had time on a test day, run with and without the ballast but that will throw off the setup, so again more factors. Unfortunately my setups are done by a shop and not by myself at the track (no scales).

[Gary L]

Here's an quick/dirty IT version of something I did years ago

Hmmm.... may have been 'quick', but it certainly doesn't appear to be very 'dirty'. I made adjustments to a couple of formulae to closer fit my car (frontal area & driveline loss), filled in the necessary blanks to include some 75-90 mph accel data I was comfortable with and... Voila! Calculated flyweel HP was very close; I'd say within 3 percent or so.

[JimLill]

Hmmm.... may have been 'quick', but it certainly doesn't appear to be very 'dirty'. I made adjustments to a couple of formulae to closer fit my car (frontal area & driveline loss), filled in the necessary blanks to include some 75-90 mph accel data I was comfortable with and... Voila! Calculated flyweel HP was very close; I'd say within 3 percent or so.

Thanks for that feedback...........

[JimLill]

Now knowing someone actually used that.......... I improved it a bit

and here's a better version yet.........

http://www.vectorbd.com/am-rennsport/hpcalc.xls

Enter the data in the green boxes...

[23racer]

I couple of years ago I spent an incredible amount of time comparing the effects of weight versus horsepower on my car at Mosport. I was very lucky to be using the Bosch LapSim software which had Mosport as one of the modeled tracks. I input all the data requested in the software, including the tire grip levels, aero effects, spring rates, horsepower, torque, rear end and gearbox gearing, etc.... and asked it to spit out an expected laptime. I also have a full data logging system in my car, so i was able to quantify actual criteria closer than some people.

The number that came out was 2/10ths faster than my fastest ever race lap. It was stunning, especially when I ran the simulation as a model around the track. The gears selected were the same, the little touch of oversteer in Turn 2 was calculated and the same (in the same place). It was mind blowing. The MPH going into the turns was the same, even the braking points and duration was very very close to what I do. As the class that I was moving into allowed open engine mods and weight reduced by over 500 lbs, I worked those calculations into the simulation.

Therefore, based at Mosport in a Second Gen RX7, each 20 hp increase in engine hp was worth a second (assuming an 18% driveline loss). Each 100 lb (45kg) weight reduction was worth 1 second. Surprisingly, switching from my stock 4:10 diff to a 4:88 diff made no difference as the new requirement to use 5th in 2 places per lap negated the acceleration advantage out of turn 5 and 3. All my messing about with bars and spring rates only changed the laptimes by 2/10ths.

In using the other tracks in the simuation I noticed that the effects weren't the same. The tighter the track the less HP made a difference versus reducing weight and adding gearing.

So I guess my response to the initial question is, "it depends".

Eric Nummelin

[Flyin' MacLean]

I couple of years ago I spent an incredible amount of time comparing the effects of weight versus horsepower on my car at Mosport. I was very lucky to be using the Bosch LapSim software which had Mosport as one of the modeled tracks. I input all the data requested in the software, including the tire grip levels, aero effects, spring rates, horsepower, torque, rear end and gearbox gearing, etc.... and asked it to spit out an expected laptime. I also have a full data logging system in my car, so i was able to quantify actual criteria closer than some people.

The number that came out was 2/10ths faster than my fastest ever race lap. It was stunning, especially when I ran the simulation as a model around the track. The gears selected were the same, the little touch of oversteer in Turn 2 was calculated and the same (in the same place). It was mind blowing. The MPH going into the turns was the same, even the braking points and duration was very very close to what I do. As the class that I was moving into allowed open engine mods and weight reduced by over 500 lbs, I worked those calculations into the simulation.

Therefore, based at Mosport in a Second Gen RX7, each 20 hp increase in engine hp was worth a second (assuming an 18% driveline loss). Each 100 lb (45kg) weight reduction was worth 1 second. Surprisingly, switching from my stock 4:10 diff to a 4:88 diff made no difference as the new requirement to use 5th in 2 places per lap negated the acceleration advantage out of turn 5 and 3. All my messing about with bars and spring rates only changed the laptimes by 2/10ths.

In using the other tracks in the simuation I noticed that the effects weren't the same. The tighter the track the less HP made a difference versus reducing weight and adding gearing.

So I guess my response to the initial question is, "it depends".

Eric Nummelin

This is the first time I've ever seen reliable empirical data on this. THANKS!

[Z3_GoCar]

I'm downloading the free-ware version of Lap-Sim, but having looked at the manual it looks like the engine version will allow the holy grail of prediction a-priori how any motor will react to an IT build. The lap-times is more complicated as it requires lap data to make predictions. Check it out http://www.bosch-motorsport.com/cont.../html/3589.htm

James