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Essays:
A Technical Review of Limpert's
"Brake Design and Safety"


TECHNICAL REVIEW BY WADE BARTLETT
TEXT TITLE: Brake Design and Safety
SECTION REVIEWED: pages 1-100
TEXT AUTHOR: Rudolf Limpert
PUBLISHER: Society of Automotive Engineers
DATE PUBLISHED: 1992
ISBN: 1-56091-261-8
SAE Order No.R-120

INTRODUCTION: In a review of the first 100 pages of Mr. Limpert's book I found what I believe to be many numerical errors, and many more nit-picky editorial things. An e-mail to SAE noting that there were errors in the book drew a response asking for more detailed information. A detailed letter sent in January '97 has gone unanswered as of June 1997. Copies of the book purchased as recently as December '96 were not accompanied by any type of errata sheet. I have included here the numerical and algebraic problems, as their dissemination is the most critical, in my opinion. Locating the nitpicky-editorial stuff is left (more-or-less) as an exercise for the reader. Commentary on my commentary is welcome, and will be incorporated into this document as I deem appropriate. My comments will be identified by the text's numbered section and the page to which they apply. Suggested changes and comments will be listed to the right.

3/98 UPDATE: A second letter to SAE (in March, 1998) drew a response! They are working on the next edition, and "are very concerned with the accuracy of our products". I hope they follow through.

4/98 UPDATE: SAE has forwarded a draft manuscript to me of the second edition for technical review. I am working on it as we speak, and will keep this page updated on the results.

11/98 UPDATE: Several months ago, SAE received from me a complete review of the book. There were numerical problems throughout, as well as my editorial differences with Mr. Limpert. The 30-odd page document is too lengthy to transcribe into HTML at this time, but may happen sometime in the future. As a little thank-you, SAE sent me a coupon good for materials at the SAE bookstore!

3/99 UPDATE: SAE is still selling the old version at its website for the full price. They should be ashamed of themselves.

JAN 2000 UPDATE SAE released the second edition of this book, and sent me a gratis copy late last year. Thanks guys! Some of my suggestions were used word-for-word. It is very odd seeing my writing under someone else's byline. Most (and perhaps all) of the numerical problems and some of the variable-related problems have been resolved. I have not undertaken a comprehensive review of the new edition of the book but I scanned some of the areas I originally flagged as troublesome. There is a bunch of material in the book which just isn't necessary (how many of us civilians need to have info on the design of brakes for 40-ton tracked-vehicles taking up space on our shelves?), some material which is still very manufacturer-specific (omitting references to competing products and design), some material which is unsubstantiated and fairly apocryphal (with regard to problems experienced by particular manufacturers), and some coefficients which were revised dramatically (by factors of 100 or more) without any source reference or explanation (which does NOT give me confidence enough to actually use them). Nonetheless, the second edition is an improvement over the first. That's probably all I will have to say on the matter. If you use the first edition, please be very careful with the numbers it uses!!!

Section and Page ITEM TO CHANGE
Sec. 1.3
pg 6
22 N should be 445 N (100 pounds is correct, and 1 pound equals 4.448 Newtons)
Sec. 1.3
pg 6
42 N should be 823 N (see previous item)
Sec. 1.3.1
pg 6
22 to 25 N should be 445 to 489 N
Sec. 1.3.1
pg 7
13 to 22 N/g should be 267 to 445 N/g
Sec. 1.3.1
pg 7
22 to 34 N/g should be 445 to 667 N/g
Sec. 1.3.2
pg 7
11 to 17 N should be 222 to 334 N
Sec. 1.3.2
pg 7
1 N should be should be 13 to 22 N
Sec. 1.3.3
pg 7
22 N should be 445 N
Sec. 1.3.3
pg 7
22 N should be 445 N
Sec. 1.3.3
pg 7
22 N should be 445 N
Sec. 1.3.4
pg 7
18 N should be 356 N
Sec. 1.3.4
pg 7
22 N should be 445 N
Sec. 1.4.3
Eqn.(1-5)
pg 12
St should be S1 [This is especially problematic, as St is used later, with S1 in Eqn.(1-13).]
Sec. 1.4.3
Eqn.(1-6)
pg 13
amaxt / tb should be amax(t - tr - ta) / tb [Assuming that time is measured from the origin, as indicated in Figure 1-4d. Also, this equation is only valid if (tr + ta) < t < (tr + ta + tb ); The acceleration is zero at all times less than ( tr + ta) , and is constant at all times greater than (tr + ta + tb ).]
Sec. 1.4.3
Eqns.(1-6) to (1-12)
pg 13
The time-equals-zero point moves around for different equations. When carried through the integral, they do clear up, as long as one doesn't misapply things. Be careful!
Sec. 2.2.2
Fig. 2-12
pg 42
[The Released piston should have a gap of 0.006 between it and the disk surface, based on the seal shown in the Applied picture. This is one of the nit-picky ones.]
Sec. 2.7.3
pg 57
There are more sources than just "rotors with nonuniform thickness or out-of-round drums" for front-end vibrations during braking.
Sec. 2.7.3
pg 58
"...backing plates [are] covered by special paint..." [This statement should be accompanied by the note that aftermarket pads are often supplied with a tube of "grease" which firms up after exposure to air which is to be applied to the backing plate and allowed to dry briefly before installation for vibration control.
Sec. 2.8.2.k
Table 2-1
pg 71
In the title, BF should be BF1 (see Tables 2-4 and 2-5 for the accompanying data on BF and BF2)
Sec. 2.9
Fig. 2-31
pg 78
The three curves for the "Rigid Shoe" do not have the same symbol: be careful if mixing / matching curves.
Sec. 3.1.1
Eqn.(3-3)
pg 90
Both V1ís should be capitalized
Sec. 3.1.1
Eqn.(3-14)
pg 93
Pb0 should be Pbav based on Figure 3-2 or Pbav should be Pb0 in Figure 3-2
Sec. 3.1.2
Eqn.(3-20)
pg 95
RR should be RP
Sec. 3.1.3
Eqn.(3-23)
pg 97
The equation incorporates Ld but the definition only lists L. Be careful.


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This page created on 17-APR-1997 and last modified 17-JAN-2000