Corner Balance, Idiot check of percentages... Options

[yeahmag]

I'm getting very close to aligning and corner weighting the car. What sort of percentages should i be looking for in cross and front to rear? I would guess 50% cross with me in it and closer to 45% front/55% rear.

[Woody]

I'm getting very close to aligning and corner weighting the car. What sort of percentages should i be looking for in cross and front to rear? I would guess 50% cross with me in it and closer to 45% front/55% rear.

Yes that's about right. These are mine with me in the car.

[brant]

Woody you need to take those numbers and use the corner balance formula to calculate ideal balance

[Woody]

What do you mean ideal balance?

[brant]

there is a formula to calculate Ideal balance using your actual corner weights...


it will tell you how far off you are... what each corner should ideally weigh given the weight distribution of the actual car.

your pretty close woody... within 3 lbs on each corner
good enough really
I usually quit trying in the 1 to 1.5lb range.

brant

[Seabird]

Having a cross weight of 50.04% (second pic) is darn good.

[Woody]

Having a cross weight of 50.04% (second pic) is darn good.

Thanks. It wasn't too hard to get it there.

[stimpyvan]

Hi everybody. We are getting ready to start building a 914 track car. Is the ideal weight distribution on a 914 45%F/55%R and not 50/50?

Thanks in advance.

Van

[Woody]

50/50 would be optimal on any car. 45/55 is where I see most mid engine cars end up. Anywhere from 40/60 to 43/57 on a rear engine car.

[stimpyvan]

50/50 would be optimal on any car. 45/55 is where I see most mid engine cars end up. Anywhere from 40/60 to 43/57 on a rear engine car.

Okay, thank you. 914s are new for us so I didn't know if the chassis preferred a slightly rear weight bias.

Van

[Randal]

there is a formula to calculate Ideal balance using your actual corner weights...


it will tell you how far off you are... what each corner should ideally weigh given the weight distribution of the actual car.

your pretty close woody... within 3 lbs on each corner
good enough really
I usually quit trying in the 1 to 1.5lb range.

brant

Oh yes, the magic calculator. Probably does more for handling than anything, IMHO.

[stimpyvan]

Just out of curiosity, why not 50/50? Is everybody dead set against adding ballast?

Van

[J P Stein]

Just out of curiosity, why not 50/50? Is everybody dead set against adding ballast?

Van

After busting my chops REDUCING weight, it pained me to add ballast to make class minimum.
Adding weight for any reason beyond class requirements is an anathema.
Shifting weight to get ( let's say ) side to side balance is SOP.

Personally, I like a rearward weight bias percentage in the mid to high 50s.
spending a lot of time fooling around with corner weights becomes moot under most non-static activities...makes ya feel good, tho. Note tires contact.
Care to guess the percentage of car weigh on that left rear?

[Woody]

Just out of curiosity, why not 50/50? Is everybody dead set against adding ballast?

Van

I would only add ballast to meet a class minimum weight. Moving stuff around in the car such as the battery is how you would optimize your F-R and L-R weight. Like JP, I also prefer a slight rear weight bias.

[stimpyvan]

Just out of curiosity, why not 50/50? Is everybody dead set against adding ballast?

Van

After busting my chops REDUCING weight, it pained me to add ballast to make class minimum.
Adding weight for any reason beyond class requirements is an anathema.
Shifting weight to get ( let's say ) side to side balance is SOP.

Personally, I like a rearward weight bias percentage in the mid to high 50s.
spending a lot of time fooling around with corner weights becomes moot under most non-static activities...makes ya feel good, tho. Note tires contact.
Care to guess the percentage of car weigh on that left rear?

We had to add about 80 Lbs of ballast to our RX7 to get to 25/25/25/25. I wasn't wild about adding the weight, but without it the car felt as though it was trying to kill you in every corner (the transition from understeer to oversteer was very abrupt) and 90 minutes of that was very fatiguing. We had already done everything we could to eliminate/transfer weight.

I haven't driven a 914 in about 25 years and I can't remember what the handling was like. Is the preference for a slightly rear weight bias because of the open diff?

What wheels are on the back of that car?

Thanks!

[J P Stein]

We had to add about 80 Lbs of ballast to our RX7 to get to 25/25/25/25. I wasn't wild about adding the weight, but without it the car felt as though it was trying to kill you in every corner (the transition from understeer to oversteer was very abrupt) and 90 minutes of that was very fatiguing. We had already done everything we could to eliminate/transfer weight.

I haven't driven a 914 in about 25 years and I can't remember what the handling was like. Is the preference for a slightly rear weight bias because of the open diff?

What wheels are on the back of that car?

Thanks!

Just my.02 based on what you've written.
Suspension set up is the place to cure an unwanted transision. Consistent handling be it slight understeer or oversteer with no transitions is ideal.I've not heard of any design flaw in the RX7 that would cause this (such as is the case in the 911).
Class rules may preclude taking the steps necessary,( limits on allowable suspension mods, tires, whatever.) however. I have heard of guys building in a transision using progessive springs tho.

Anything to avoid adding weight.

The only dishonest feature of the 914's handlingis the snap oversteer that comes when messing with the absolute limit.....there is no warning, it just goes and there is no catching it unless one is readyfor it, It takes a lot of butt time in the car to know when you're on that edge.....even then it will "gotcha" occasionally.

The rear wheels were made by Monocoque....now defunct. 10 X 16 and 11 lbs each.
22,5 X 10 Hoosier R35 slicks.
I was fooln' with rear tire pressures & got em' a bit low. They were OK at 20 psi...but not at 18. (IMG:style_emoticons/default/biggrin.gif) Damn near ran the tire off the rim (IMG:style_emoticons/default/blink.gif) .....didn't go there no mo.

The rear bias helps with traction. TB diff in place. Helps the car rotate controlably in the tight suff at AX.

[stimpyvan]

Just my.02 based on what you've written.
Suspension set up is the place to cure an unwanted transision. Consistent handling be it slight understeer or oversteer with no transitions is ideal.I've not heard of any design flaw in the RX7 that would cause this (such as is the case in the 911).
Class rules may preclude taking the steps necessary,( limits on allowable suspension mods, tires, whatever.) however. I have heard of guys building in a transision using progessive springs tho.

I don't know if you would call it a design flaw, but the suspension on a 1980 RX7 is nothing to get excited about. Mac struts in the front with no adjustment for caster or camber and a live axle with a Watts linkage in the back. And we are very limited in the amount of suspension modifications that can be made.

We didn't weigh the car until after our first race and the corner numbers were:

Total weight: 2100# (with driver)
LF = 37%
RF = 30%
LR = 18%
RR = 15%

Thus, the demonic handling. There simply wasn't enough weight that could be removed or moved to get anywhere close to a better balance, thus the ballast. Not surprisingly, the handling was vastly improved with equal weight at all corners (& we simply added about 30% more HP to overcome the additional 5% weight).

The rear bias helps with traction. TB diff in place. Helps the car rotate controlably in the tight suff at AX.

Sorry to go OT here and pardon my ignorance, but what is a "TB Differential"? I Googled it and ended up reading about tuberculosis. Is TB a manufacturer? Pretty sure that neither of the transaxles we have are factory LSD but the 914 is still in the trailer and we haven't looked.

Thanks for all the great info.

Van

[J P Stein]

Sorry, TB is Torque Biasing. na LSD with an extea rweak.
It acts like an open diff till you put the power to it.

[Randal]

We had to add about 80 Lbs of ballast to our RX7 to get to 25/25/25/25. I wasn't wild about adding the weight, but without it the car felt as though it was trying to kill you in every corner (the transition from understeer to oversteer was very abrupt) and 90 minutes of that was very fatiguing. We had already done everything we could to eliminate/transfer weight.

I haven't driven a 914 in about 25 years and I can't remember what the handling was like. Is the preference for a slightly rear weight bias because of the open diff?

What wheels are on the back of that car?

Thanks!

Just my.02 based on what you've written.
Suspension set up is the place to cure an unwanted transision. Consistent handling be it slight understeer or oversteer with no transitions is ideal.I've not heard of any design flaw in the RX7 that would cause this (such as is the case in the 911).
Class rules may preclude taking the steps necessary,( limits on allowable suspension mods, tires, whatever.) however. I have heard of guys building in a transision using progessive springs tho.

Anything to avoid adding weight.

The only dishonest feature of the 914's handlingis the snap oversteer that comes when messing with the absolute limit.....there is no warning, it just goes and there is no catching it unless one is readyfor it, It takes a lot of butt time in the car to know when you're on that edge.....even then it will "gotcha" occasionally.


The rear wheels were made by Monocoque....now defunct. 10 X 16 and 11 lbs each.
22,5 X 10 Hoosier R35 slicks.
I was fooln' with rear tire pressures & got em' a bit low. They were OK at 20 psi...but not at 18. (IMG:style_emoticons/default/biggrin.gif) Damn near ran the tire off the rim (IMG:style_emoticons/default/blink.gif) .....didn't go there no mo.

The rear bias helps with traction. TB diff in place. Helps the car rotate controlably in the tight suff at AX.


JP said:
The only dishonest feature of the 914's handlingis the snap oversteer that comes when messing with the absolute limit.....there is no warning, it just goes and there is no catching it unless one is readyfor it, It takes a lot of butt time in the car to know when you're on that edge.....even then it will "gotcha" occasionally.

I believe you can dial this out with balance and wheel and tire combination. (IMG:style_emoticons/default/biggrin.gif)

Right, and TB diffs make a huge difference as well.

[Woody]

We had to add about 80 Lbs of ballast to our RX7 to get to 25/25/25/25. I wasn't wild about adding the weight, but without it the car felt as though it was trying to kill you in every corner (the transition from understeer to oversteer was very abrupt) and 90 minutes of that was very fatiguing. We had already done everything we could to eliminate/transfer weight.

I haven't driven a 914 in about 25 years and I can't remember what the handling was like. Is the preference for a slightly rear weight bias because of the open diff?

What wheels are on the back of that car?

Thanks!

Just my.02 based on what you've written.
Suspension set up is the place to cure an unwanted transision. Consistent handling be it slight understeer or oversteer with no transitions is ideal.I've not heard of any design flaw in the RX7 that would cause this (such as is the case in the 911).
Class rules may preclude taking the steps necessary,( limits on allowable suspension mods, tires, whatever.) however. I have heard of guys building in a transision using progessive springs tho.

Anything to avoid adding weight.

The only dishonest feature of the 914's handlingis the snap oversteer that comes when messing with the absolute limit.....there is no warning, it just goes and there is no catching it unless one is readyfor it, It takes a lot of butt time in the car to know when you're on that edge.....even then it will "gotcha" occasionally.


The rear wheels were made by Monocoque....now defunct. 10 X 16 and 11 lbs each.
22,5 X 10 Hoosier R35 slicks.
I was fooln' with rear tire pressures & got em' a bit low. They were OK at 20 psi...but not at 18. (IMG:style_emoticons/default/biggrin.gif) Damn near ran the tire off the rim (IMG:style_emoticons/default/blink.gif) .....didn't go there no mo.

The rear bias helps with traction. TB diff in place. Helps the car rotate controlably in the tight suff at AX.


JP said:
The only dishonest feature of the 914's handlingis the snap oversteer that comes when messing with the absolute limit.....there is no warning, it just goes and there is no catching it unless one is readyfor it, It takes a lot of butt time in the car to know when you're on that edge.....even then it will "gotcha" occasionally.

I believe you can dial this out with balance and wheel and tire combination. (IMG:style_emoticons/default/biggrin.gif)

Right, and TB diffs make a huge difference as well.

I used to have a very unpredictable snap oversteer problem with my car when I was running a square setup. When I went to the 205/225 Hankooks the problem lessened. With my current setup of 225/275 A6s the problem is non existant. I have the car set up just a tad loose in the rear because thats how I like it. If you go to hot into a corner the car will let you know and the back end will start to come around but it is easily caught. Same with corner exit, the backend will start to come around and is easily caught with a quick jab of the wheel. Mid corner is neutral. I am not running a LSD yet either. I need to because it will spin up the inside tire on corner exit.