FAQ is Wrong re MP5 Stabilizer Bars

[mp5user]

I measured the stabilizer bars on my U.S. MP5 last night. I used a digital caliper for the measurements. The front bar measured 23 mm diameter and the rear bar measured 17 mm diameter. I repeated these simple measurements several times.

The FAQ is not alone in giving bad data. I had misinformation given to me by Mazda online customer support. The lesson here is to be question the integrity of information given.

PS - the roll stiffness ratio of the MP5 23-17 mm bars is almost identical to the roll stiffness ratio of the Mazdaspeed stabilizer bars.

Fred

 

[PhatTrax]

i know this is an old thread but I'm looking for suspension parts for my car. So, because of this, what would you recommend as upgrades? should i just get the struts/springs and keep the stabilizer bars?

 

[MarkSpark]

I measured the stabilizer bars on my U.S. MP5 last night. I used a digital caliper for the measurements. The front bar measured 23 mm diameter and the rear bar measured 17 mm diameter. I repeated these simple measurements several times.

The FAQ is not alone in giving bad data. I had misinformation given to me by Mazda online customer support. The lesson here is to be question the integrity of information given.

PS - the roll stiffness ratio of the MP5 23-17 mm bars is almost identical to the roll stiffness ratio of the Mazdaspeed stabilizer bars.

Fred

okay fine, the rear sway bar is 17mm stock..but the MSP/MP3 sway bar is 20mm...so the stiffness ratio is not the same no?

 

[mp5user]

i know this is an old thread but I'm looking for suspension parts for my car. So, because of this, what would you recommend as upgrades? should i just get the struts/springs and keep the stabilizer bars?

Modification priorities should reflect your goals, e.g. looks, handling, balance, control. Going to a higher load-rated tire was my first choice. The tires are the "transducers" and, arguably, the single most important suspension component. A correspondingly wider wheel will help make the most of the new tire choice.

A damper upgrade is, almost always, beneficial. The OEM dampers, while not horrible, are inadequate for my preferences. The high velocity valving is simply inadequate and the low velocity valving doesn't supply the control I desire. I'm waiting for some quality dampers to become available, i.e. Koni or Bilstein.

If different springs are on the wish list, consider concurrent damper and spring replacement. Try for an engineered match of springs and dampers - adjustable dampers might be the ticket. My concern for the OEM springs is not ride-height, but rather the rate - I bottom the front occasionally and would prefer higher rate springs.

The stock steering characteristic is understeer. A more neutral cornering car can be had by either increasing the rear stabilizer bar diameter or decreasing the front stabilizer bar diameter.

If you plan to compete with the car, check the rules before making any changes.

 

[mp5user]

okay fine, the rear sway bar is 17mm stock..but the MSP/MP3 sway bar is 20mm...so the stiffness ratio is not the same no?

You need two variables for a ratio; you've only mentioned one when suggesting the rear stabilizer bar diameters. I'll be a little more explicit.

Given the MazdaSpeed OEM stabilizer bar diameters are 27 mm and 20 mm for the front an rear respectively; and the MP5 OEM stabilizer bar diameters are 23 mm and 17 mm for front and rear respectively; and the stabilizer roll stiffness varies as a factor of X^4 for diameter (diameter to the fourth power) . . .

27^4 / 20^4 = 3.322:1 front to rear for MazdaSpeed
23^4 / 17^4 = 3.352:1 front to rear for MP5

So, you see, the front to rear stabilizer bar roll stiffness ratio, as a function of diameter, of the MazdaSpeed and MP5 are closely matched.

 

[mp5user]

I measured the stabilizer bars on my U.S. MP5 last night. I used a digital caliper for the measurements. The front bar measured 23 mm diameter and the rear bar measured 17 mm diameter. I repeated these simple measurements several times.

BTW - the FAQ has been updated to indicate the correct stabilizer bar diameters for the MP5