Typ85
Typ85 New Reader
10/6/19 10:25 p.m.

Howdy folks, 

Running an '84 4000 quattro, race prepped about 2,350lbs. w/o driver.

I recently bought a set of Proform scales, I'm entering the weights in a spreadsheet (see pic below, specs on left are actual #'s with me in the car, specs on the right are the "target" numbers), I noticed the spreadsheet recommends I run my cross weights a little offset 49.6% instead of 50%

Can anybody tell me why I should run slightly offset like this? I also noticed this would reduce my "bite" below 50 (%?)?

ClemSparks
ClemSparks UltimaDork
10/6/19 10:32 p.m.

I'll be curious to find out why, myself.  I'm wondering if it has to do with the AWD-ness of your car.

My experience with RWD stuff is that you want pretty much perfect cross weight if you can get it.

Typ85
Typ85 New Reader
10/6/19 11:00 p.m.

In reply to ClemSparks :

4wd isn't a variable I can plug into this spreadsheet. I assume the target is set like that because there's alot more wieght on the lft. side of the car fromthe driver.......

frenchyd
frenchyd UberDork
10/7/19 6:52 a.m.

In reply to Typ85 :

A 50/50 spilt isn’t ideal on a toadrace track.  Exactly what you want depends on the corners and their position on the track.  

Let’s start with circle track racing.  There you pretty much want as much weight on the inside as possible . 

On a road race track that essentially goes in a circle that’s how you’ll want to set your car up.  But what if the turn leading to the main straight instead of being to the right is to the left?  

TurnerX19
TurnerX19 Dork
10/7/19 7:18 a.m.

In reply to frenchyd :

Frenchy makes a good and valid point here. As an example, when I ran at Lime Rock I always set up for a right hand circle, because only one slowish left turn on the whole track. You gain more from the rights, especially entering the main straight, than you loose from the left. Each track needs to be considered individually.

Driven5
Driven5 UltraDork
10/7/19 9:55 a.m.

Note #2 on the spreadsheet specifically states that the target corner weights are calculated to give a 50/50 diagonal weight distribution. Seems to me that one or more of the formulas in your version of the spreadsheet may be incorrect or have been tampered with.

dps214
dps214 Reader
10/7/19 10:12 a.m.

Looks like it's wants the situation where the f/r ratio equal on both sides. (ie LF/LR = RF/RR). That's actually the "correct" setup for consistent handling in both directions, In a roughly 50/50 f/r setup that's the same as 50% cross weight, but as you diverge from there (like your 60/40 setup) that ratio can get thrown off which is why it wants you do do something that isn't quite 50% cross. That being said, given that you're currently within 5lbs of what it wants at each corner I wouldn't bother changing anything.

Slippery
Slippery GRM+ Memberand UltraDork
10/7/19 10:15 a.m.

I am just posting to say that you have the coolest race prepped Audi I have seen in a long time. 

Slippery
Slippery GRM+ Memberand UltraDork
10/7/19 10:16 a.m.

Where did you get that spreadsheet from?

frenchyd
frenchyd UberDork
10/7/19 10:48 a.m.
dps214 said:

Looks like it's wants the situation where the f/r ratio equal on both sides. (ie LF/LR = RF/RR). That's actually the "correct" setup for consistent handling in both directions, In a roughly 50/50 f/r setup that's the same as 50% cross weight, but as you diverge from there (like your 60/40 setup) that ratio can get thrown off which is why it wants you do do something that isn't quite 50% cross. That being said, given that you're currently within 5lbs of what it wants at each corner I wouldn't bother changing anything.

Then play with tire pressures. A pound or two changes things without getting all squirrelly on you.  

I assume you taped  the tires? Since there is so much hand labor in tires, No two tires will be exactly the same diameter.  Depending on brand there can be a really significant difference.  

When checking diameter  it’s best to grind a point  at the tip and using the thinnest tape you can find  measure all the way around.  Those 16ths of an inch add up quickly. 

Move the tallest to where you are light and the shortest to where you are heavy. Whatever you do mark the tire.  +3/8ths -1/16th etc. 

MrFancypants
MrFancypants New Reader
10/7/19 10:54 a.m.
Slippery said:

I am just posting to say that you have the coolest race prepped Audi I have seen in a long time. 

+1 to this. Beautiful car!

Driven5
Driven5 UltraDork
10/7/19 3:15 p.m.

In reply to dps214 :

Whether that's the original creators intent or a later modification to the spreadsheet, that appears to be exactly what it's doing.  Well spotted.

Typ85
Typ85 New Reader
10/7/19 6:06 p.m.

In reply to dps214 :

Thanks!! makes sense!

Typ85
Typ85 New Reader
10/7/19 6:08 p.m.

In reply to Slippery :

Honestly don't remember, I can say it looks like there's a Corvette in background wallpaper....

Typ85
Typ85 New Reader
10/7/19 6:11 p.m.

In reply to Slippery :

L5wolvesf
L5wolvesf New Reader
10/7/19 7:35 p.m.
Slippery said:

Where did you get that spreadsheet from?

https://robrobinette.com/corner_weight.htm 

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