rnoll98

Hey guys,
I drilled an extra hole in both our stock and Mazdaspeed bars. 15 mins of labor and now they're adjustable. There's plenty of room on the flat spot. Not sure if our RB bar has room, I think it might. Just a thought. I'm gonna run calcs on them one of these days, and I'll post the numbers. I'm guessing between the three bars and the extra holes we'll have small enough steps to find the right setup.

Randy Noll

tuj

Hassan: how are you preventing understeer during corner entry?

tuj

What is the best way to tune the car to have more oversteer with air pressures? Assuming the fronts are set at optium pressure, does it make sense to go higher with the rears, or maybe lower? I would think higher in the rear would make the car rotate easier as the contact patch is smaller, but it would also decrease traction out of the corners. Likewise, lower in the rear should let the tire deform and give up grip before the front. Any tips? I'd much rather control oversteer with the throttle than control understeer by reducing entry speed.

PedalFaster

Either adding or reducing pressures relative to the optimal setting will decrease traction. I prefer adding pressure; reducing pressure can make that end of the car feel mushy.

Jason (ULLLOSE) and Ron and I were all running artificially high rear pressures at Atwater in order to loosen up our cars. But the preferred approach is always to fix the problem end of the car rather than reducing the non-problem end's grip.

Hassan

How high? I am just curious to get some input from drivers that have been running these cars for a little while now

TeamRX8

iTrader: (25)

Randy

I think you'll find that extra hole is at best just a fine tuning, it won't impact rate significantly

rnoll98

Using the formula on p.150 of Fred Puhn's book "How to Make Your Car Handle" and some rough measurements with my handy Stanley tape measure, I got the following:

Stock 1-1/16": 100%
Stock hole 2: 122%
Mazdaspeed 1-5/32": 140%
Mazdaspeed hole 2: 171%
Racing Beat 1-9/32": 211%

I only measured the stock bar and assumed the dimensions were the same for the others. The thicknesses are also from memory, so someone please correct me if I'm wrong. On a bar with longer arms, another hole might not have as much impact. But I measured center of bar to center of hole as 7-3/8". That's very short.

Even if I'm off (my 211% vs 231% for the RB bar stated above--which could also be in the different bushing material), it's not gonna change the relative values much. Also remember, if you drill an extra set of holes the bar is now 3-way adjustable--stiff, soft, and staggered. It helps to have adjustable endlinks for the last one.

Randy Noll

TeamRX8

iTrader: (25)

well I was going by memory myself, these were quadruple checked, there may be some slight variance due to rounding off decimals, this is the info I have:


stock bar is 1.05" OD x 0.134" wall/0.79" ID (26.7mm x 3.4mm/20.2mm)

assuming same material coefficients and same geometry/dimensions

Mazdaspeed bar is 1.07"OD x 0.157" wall/0.76" ID (27.2mm x 4.0mm/19.2mm) + 18.2%

Racing Beat bar is 1.25" x 0.188" wall/0.88" ID (31.8mm x 4.8mm/22.2mm) + 123%

what is the new hole location measurement, I'm coming up with quite a long distance to get that percentage change

TeamRX8

iTrader: (25)

well I was going by memory myself, these were quadruple checked, there may be some slight variance due to rounding off decimals, this is the info I have:


stock bar is 1.05" OD x 0.134" wall/0.79" ID (26.7mm x 3.4mm/20.2mm)

assuming same material coefficients and same geometry/dimensions

Mazdaspeed bar is 1.07"OD x 0.157" wall/0.76" ID (27.2mm x 4.0mm/19.2mm) + 18.2%

Racing Beat bar is 1.25" x 0.188" wall/0.88" ID (31.8mm x 4.8mm/22.2mm) + 223%

what is the new hole location measurement, I'm coming up with quite a long distance to get that percentage change

John V

iTrader: (1)

I agree. This is has been one of my big obstacles to going fast in this car. If I trail brake at all, I overload the front tires and have corner entry push. I'm striving to do all my braking in a straight line and just get on the gas right after turn-in.

We're running different tires than you, so pressure comparisons would be useless.

rnoll98

I didn't take into account the different wall thicknesses. Just went by OD. So that's definitely a variable I'm missing. My stock hole is 7-3/8" from bar pivot center. The new hole is 6-3/4", a 5/8" difference or so. Like I said, they're all kinda rough measurements. I also measured the true arm length (including curves) to be 9-5/8" and 9" respectively. Looks like my formula is for a solid bar (these guys are heavy enough to be). Do you have a formula for a hollow bar?

TeamRX8

iTrader: (25)

same formula just calculate it for both the OD and ID (ID = OD - 2xwall), then subtract the ID number from the OD number

you have to use the straightline dimension, 7.375 is correct, that is the perpendicular torque arm length, the factory type bend will add a small amount of flexure, these calcs are simply rough estimates, you'd literally have to do finite element analysis to get accurate representations and even then there are variables that are hard to account for

the difference in hole position is strictly a proportional ratio, I come up with a 9.3% change (7.375/6.75) or approx. half that if you stagger

which adjustable endlinks are you using?

rnoll98

Yeah, i got 9.3% from that calc too, but using the other formula it ended up being much more.

Don't have adjustable endlinks yet. I'll probably end up building some custom ones like I did for my SM2 car.

Randy

TeamRX8

iTrader: (25)

what formula are you using?

and let me know if you can readily find a LH/RH-threaded turnbuckle that's the right length, I'm still looking for one that's short enough, may have to be custom made/ordered

StrokerAce

Check out Aircraft Spruce. They have all the various heim joint hardware you could ever need.

TeamRX8

iTrader: (25)

thanks, I found what I wanted elsewhere, just had to reverse my thinking a bit

clyde

well, we sorta measured yesterday (vertically from the top of the wheel rim to the bodywork; all cars on OEM 18" wheels)...

Car 1 - base, sport, nav, prototype Konis
Car 2 - base, hitch from hitch-web
Car 3 - base, sport
Car 4 - GT plus ???

Front:
Car 1 9/16" lower than Car 4
Car 1 7/16" lower than Cars 2 & 3

Rear:
Car 1 9/16" lower than Cars 3 & 4
Car 1 5/16" lower than Car 2

rnoll98

Just found an error in my numbers, I'll recalc today. I left out B. Here's the formula from the book.

K=stiffness
D=diameter
A=effective arm length (center of bar to center of hole)
C=true arm length
B=length of center of bar

K=(500,000 x D^4)/((0.4244 x A^2) x B + (0.2264 x C^3))

TeamRX8

iTrader: (25)

yes, but the only thing you're changing when you move from one hole position to the other is the arm length, so the simple ratio I provided you earlier is good enough for government work.

You only use that formula if you are attempting to theoretically compare bars of alternate configurations

bmc

contract job paid off, so my konis are on the way. Weeee!

TeamRX8

iTrader: (25)

alright!

clyde

WTG Brian!

edj

If anybody else needs shocks, I just put an ad in the For Sale section...