Effect of weight on FF lap times

[billtebbutt]

All,

I've looked a bit on the web, not really finding anything as concrete as I would like. I'm wondering about extra weight vs lap times, trying to figure out how much I am giving up by being a little heavy. Here are the numbers:

- Minimum weight in our Toyo F1600 series post qually and post race is 1125 lbs WITH driver
- I currently carry 60 lbs of ballast in the RF 90
- With the tank filled pre race, post race the car will weigh 1143 on the series' scales, give or take a pound
- My best lap around Mosport this season was in the 1:31s

Given the inputs, how do I calculate the estimated lap time benefit of taking out say 10 or 15lbs? There are lots of rules of thumb out there, but is there anything a little more precise?

Thanks in advance

bt

[Steve Davis]

I would say there are WAY too many variables in play to make a "good estimate" of what you might be giving up with your 20 lb overage. IMHO, you probably shouldn't worry about it unless you are milliseconds back from first in several races. It's just not worth the effort. I don't know how your 1:31 compares to 'top dog times', but removing 15 lbs from your car is not likely to gain you more than a couple of tenths. That said, no one really WANTS to weigh more than they need to so.. if it's repeatable (weight wise) and you are carrying THAT much ballast, it's worth considering removing 10 lbs. The other issue is WHERE is your ballast now and HOW can you remove 'some amount' without affecting the balance of the car. For my money, I leave the weight running about 5 to 10 lbs over, but keep an eye on it. I also made sure that I have weight at/near the center of MY weight that I can easily change if I gain, say 10 lbs (PERISH that thought!!!). Anyway .. if YOU are part of the weight problem, that would come into play.

Just some of my rambling thoughts and I'm NOT in FF. Maybe someone else can give you better numbers :-).
Steve

[Bob Wright]

FWIW- a few years ago a couple of accomplished (read Natl championship level driver) F2000 guys did a test at Summit Pt with weight. Summit is a 2 mile track and a really good F2000 goes around it in 1:09 and change. F1600 current top times are 1:16s or a little better (track record is 1:13.9 on a freshly repaved track). F2000 min weight is 1210.

25lbs was worth about 3/10 second/lap.

[TimH]

Lap time would depend on the track. The rule of thumb I've heard is that 10# is worth 2-3 HP. Maybe.

[problemchild]

Why do you have 60 lbs of ballast if you are 20+ lbs overweight? Coming in at 1030-2 after a full green session is a reasonable target. With yellows, blacks, and shortened sessions, you will rarely come in that light.

Seems like an easy fix without knowing how much it will help.

[Rick Iverson]

Why do you have 60 lbs of ballast if you are 20+ lbs overweight? Coming in and 1030-2 after a full green session is a reasonable target. With yellows, blacks, and shortened sessions, you will rarely come in that light.

Seems like an easy fix without knowing how much it will help.

Yep, law of momentum: m1v1=m2v2.

More weight requires more energy to get it going. More weight requires more energy to stop it.

[problemchild]

Throwing in some anecdotal commentary ..... in my 35 years of mostly competitive race driving (5 championships, winning a race most years), I was heavy and low budget, meaning I was often 35-40 lbs over minimum weight. None of my best seasons were when I was in that range. I am not sure 20 lbs is a big deal, but 40 sure is!

[S Lathrop]

Another consideration of excess weight is the degradation of the tires over a race distance. You might not see a measurable loss of time on any particular lap but over a race distance it might be several seconds. This can be the difference in several positions at the end of the race.

Bottom line, why carry the extra weight? 5 pounds as an insurance policy should be sufficient.

Also, don't wait until the end of a race to check the accuracy of the "official scales". If they are off by 5 pounds, take advantage of the discrepancy. It may result in a position in your favor.

[Steve Davis]

...
Also, don't wait until the end of a race to check the accuracy of the "official scales". If they are off by 5 pounds, take advantage of the discrepancy. It may result in a position in your favor.

I have to disagree with Steve on this one. I can't count the number of times I have gone to the scales before the race, only to find a quite measurable difference after the race from what I expected. It wouldn't be the first time that the "scales" ... which are ALWAYS THE SCALES got 'modified' JUST before the first group impound. It's hard enough to 'stay in range' without 'taking advantage' of a weight you just got pre-race (that you might suspect is less than it should be). I say, use the pre-race weight as a 'guide'.. certainly NOT a chance to take advantage of a 'light weight scale reading'. Of course, if you don't expect to go to impound you can be a little more free with such decisions .. but the risk is still there.
Just sayin'...
Steve

[billtebbutt]

Why do you have 60 lbs of ballast if you are 20+ lbs overweight? Coming in at 1030-2 after a full green session is a reasonable target. With yellows, blacks, and shortened sessions, you will rarely come in that light.

Seems like an easy fix without knowing how much it will help.

Well, Greg, you're calling out my laziness! In the car's previous state (before the huge shunt at the start of 2021), I needed the 60 to get to weight. Then, the body work got "heavier" with the repairs, and there was a little "weight creep" . All of this would be fine, except I had previously melted and poured a SINGLE lead plate for the 60 lbs (it sits under the battery, under my knees). I just never got around to it this season, to be honest, and loathe having to re fab the lead.

But I will!

cheers,
BT

cheers,
BT

[Steve Davis]

Since I was adding weight anyway, I fabbed a steel box from 1/4 plate to hold ~5lb lead weights. I made them in 2x4x4 size to match the size of my lead weights. Now I can change the ballast fairly easily by swapping lead for wood and still have a 'tight pack'. SO.. if you're going to change your 'big block' of lead, you might consider doing something like what I've done for at least part of the total weight needed.
Steve

[EYERACE]

Oh no!! You need to do a test day and play with the weight that day.....then back and forth off & on scales....then you'll know. Oh no!! What a terrible idea........having to take the car out on track that is.

Grin grin

[Terry Hanushek]

Cautionary note: Consider fuel load

The ballast you need you need with half a tank is less than the ballast you need on a nearly empty tank. Seems simple ... but I've seen cars DQ'ed as under weight because of an extra pace lap. Car weights are absolute, one pound under is non compliant.

[Purple Frog]

50 years ago in a F1 article of the era, I read that 5 lb was equal to 1 HP. Not that that factoid is worth anything.