CRG Discussion Forum
Camaro Research Group Discussion => Originality => Topic started by: Fred Mertz on April 24, 2019, 10:49:18 PM
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Or were they part of the X33 trim package?
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Z/28 equipment included the taller V32 rear bumper guards, presumably to comply with federal bumper height requirements.
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Z/28 equipment included the taller V32 rear bumper guards, presumably to comply with federal bumper height requirements.
Wouldn't all Camaro's need to have then if they had to comply with the federal standards? I always thought they were just part of the appearance package? But I am no expert. :)
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I do not know the exact reason. But they were part of the Z28 package.
I always listen to william.
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I recall reading somewhere years ago now, that the rear ride height of the Z/28 model put the rear bumper height about 1" lower than on other Camaro models, thus requiring the large rear bumper guards.
However, the chart in 'Trim Heights' in the 1969 AIM (UPC0/A10) shows that other models (notably those with E78 x 14 and F70 x 14 tires) shared almost identical 'shipped' and 'curb' ride heights at the rockers (locations J and K) as the Z/28. Those models did not come with the V32 bumper guards, yet would have had comparable or even slightly lower rear bumper height to a Z/28.
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My Z sets beside my BB SS in my shop and the Z is lower but not enough to need the "tall" bumper guard in my opinion. Is there any evidence of the federal regulation?
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Z/28s had the lowest 'D' measurement; cars with G31 special rear springs had the highest. G31 also included V32 rear guards.
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I started off looking at the 'D' measurement but since that's taken between the top of the axle tube and the rear frame rail, the overall tire diameter affects the distance to the top of the axle tube above ground. The height of the rear bumper above ground will be determined by the ride heights at 'J' and 'K' and if those measurements give an upwards or downwards rake towards the rear.
The ride height specs at those locations are also each subject to a tolerance of +/-0.38" which suggests that the rear bumper height can't have been that critically close to not meeting federal requirements, if no other model than the Z/28 had V32 bumper guards standard.
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15" wheels & its effect on bumper heights?
just a random thought.
JIM
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The E70-15 tires that all 69 Z's came with are very close to 27" tall. Some give a spec of 26.9 inches.
The typical factory F70-14's hovered right around 26 inches. Some specs show 26.2 inches.
So at most you might be looking at roughly an inch difference in circumference which would equate to about a 1/2" in effected ride height.
As William stated, Z's did in fact have a lower ride height than other Camaros when measured at "D" Pretty sure the assembly manual also showed differences at the rocker measurements "J" and "K" and that includes the minor tire height differences as far as I can interpret.
I don't know if all this means that's why all Z's got bumper guards, but they did.
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Remember, that extended back to '68 Z's, too. One of the first indicators you should look for when scoping out a potential '68, as the holes in the tail panel are overlooked occasionally when someone "recreates" a '68 -
Regards,
Steve
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Sometimes I use too many words and people don't read them.
So here are the specs from the '69 AIM to explain my point.
Compare curb height at J and K; if a Z's bumper was too low, so was every car's with E78x14 and F70x14 tires.
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Typo in AIM I believe. I remember this from an older discussion.
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Typo in AIM I believe. I remember this from an older discussion.
Typo on which dimensions? The trim height tables in the '67 and '68 AIMs are far more complicated, but look very comparable figures to the '69.
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I've read that too Stinger and it would seem to make sense when you look at J and K and D and pay particular attention to the tire sizes.
The only other lowest ride height are with the E78-14 tire which doesn't make sense, because the 78 series tire is 26.7" tall, nearly the same height as the E70-15's on the Z/28. Yet it's giving a lower height measurement on the E78 car at K but a lower height measurement at D on the Z/28. The measurement at D is more than 2 tenths difference. So how can the Z clearly have a lower suspension measurement but the E78 car has a lower rocker measurement when they both have nearly identical tire height? Clearly anyone good at math can see there is a discrepancy given the known tire heights.
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Minor difference at D is probably due to difference between mono and multi leaf spring arrangement and arch profile, and tolerance on manufacturer's tire dimensions. That's why the dimensions that are comparable across all models relating to bumper height are J and K.
I wouldn't be too quick to say the AIM is incorrect.
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Sure looks that way to me. Been discussed in the past. It's pretty obvious when you look at the numbers.
How can you have 2 cars with virtually the same tire height, yet one is lower at K while the other is lower at D. D being the actually suspension measurement. Just not possible.
Lets make it easier. 2 identical cars in every way. When both are measured at D, example 1 is lower than example 2, yet example 1 measures higher at the rocker??? Someone must have had a few beers when they hung the sheet metal on example 1. ;D
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D is a relative measurement between two parts on the vehicle, sprung and unsprung. The measurements from the ground are what count.
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Actually, the D measurement is the important one. The measurements from the ground have other variances (like tires) that affect the measurement, and even air pressures come into play. So like I said earlier, when you have 2 cars and example 1 is lower at D than Example 2, yet example 2 is lower at K than example one, yet both have the same height tire, the math doesn't add up. That's why people question the numbers in the AIM.
Frankly, If I were looking to set a 1st gen properly, I would be using the D measurement to base my cars from, then put the proper tires on it.
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We don't have to agree, but I'd rather see a discussion on what factors influence the height of a rear bumper.
If you put a jack under the front and raised the front wheels a foot off the ground, the lever effect pivoting around the rear axle would drop the rear bumper height significantly.
D would not change as it is vertically over the pivot point, the rear axle (ignoring any change of the frame rail frofile and assuming the effect of jacking did not transfer more weight to the rear) but would J and K measurements change? You bet.
My point being that other models besides the Z/28 had a very comparable rear bumper height, yet did not have mandatory V32 guards. To those who suggest the AIM trim height table must be wrong for at least several tire sizes needs more thought.
The V31 front bumper guards are very similar to the V32 guards, yet nobody has put forward a theory that these were required to make the front end bumper height meet safety standards, presumably because they weren't mandatory on any model.
I'm not sure how one could 'set' a car to those AIM dimensions anyway. I would think the table shows the tolerance on ride height, with the car built with the correct components. No doubt the line workers could spot an anomaly in ride height, and that would trigger checking the car, but the table shows where a car should sit if all was well.
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Springs got complicated in 1969 due to federal bumper height regulations; the primary impact point of the bumpers (both front and rear) had to be within a height "window" relative to the ground, regardless of style or options, so the springs were selected by an Engineering computer program that determined front and rear weights based on each car's specs and selected the appropriate springs for those weights. That's why Z/28's all got the "tall" V32 rear bumper guards due to their reduced rear ride height dimensions.
Post by John Hinckley. Good enough for me. :)
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John's credibility was never in question. That statement has been repeated many times since. However it doesn't address the fact that other models appear to have shared the same 'reduced' ride height, yet had no V32 bumper guards mandatory. Just saying the AIM must be wrong in this regard because it doesn't fit the statement seems strange. This site is about research and discussion after all.
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So perhaps another consideration should be:
What were the 'Federal bumper height regulations' in place for the 1969 model year (and even earlier, since previous 1967 and 1968 MY Z/28's also had mandatory rear guards), and what were the dimensional requirements of those?
From what I can determine, the first Federal Standards for passenger vehicle bumpers came into force in late 1972 for the 1973 MY.
NHTSA CFR 49 (Transportation) Part 581 (Bumper Standard) and FMVSS 215 (Exterior Protection) specify performance and testing requirements related to impacts in the height range of 16"-20" above the road surface. FMVSS 215 became effective in September 1972 and led to the demise of chromed bumpers in favour of resilient rubber versions.
So what national bumper height standards applied to passenger cars in the late 1960's? Were there any, or did manufacturers position bumpers to suit aesthetics and functional protection areas?
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1967 Z-28s did not have mandatory rear bumper guards. That started with the '68 Zs.
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Thanks for clarifying that Jon, that was based on http://www.camaros.org/diffs67.shtml which says the '67 Z/28 had them.
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A couple of things to note...
For what is it worth...
From the 1969 Camaro AMA specs, the distance listed in the GROUND CLEARANCE section for these cars in general for the height from Bumper to ground - rear is 21.2 inches for coupe and 20.8 inches for convertible. There are also AMA specs listed for the Z28 as well, and the height from Bumper to ground - rear is listed as 21.2 inches.
Also for what it is worth, opinions will vary on ideal tire size and "look". Well here is a 1968 big block Camaro - with rear bumper guards - with rear tires and wheels that are not stock. The look is about ideal in my opinion.
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Looks like Bryon,s type car. 468 or 496?
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Also for what it is worth, opinions will vary on ideal tire size and "look". Well here is a 1968 big block Camaro - with rear bumper guards - with rear tires and wheels that are not stock. The look is about ideal in my opinion.
You're kidding??? with tires sticking outside the body by 2" or so??
They should have radiused the wheelwells a little higher and put even larger / wider wheels on it ... and they could protrude even farther!
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cmon Gary, Are you too young to remember Day 2?
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Tire/wheel combination is legal. It’s a Bill Thomas Camaro with a 396 and “two fours”. Has original block, otherwise 496 would have been preferred. Search for it if you are bored, currently at SMT.
Sorry for the Day 2 distraction. Now back on topic. ;)
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Yep... I'm TOO young.. :) When I remember the big huge protruding tires and jacked up rear was more like mid-60's... or maybe a bit later on older cars... Not on Camaros! Seems pretty 'red-necky' to me 'Bill Thomas or not'... Bill made his name on the drag strip not the street... :)
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the Z had E70x15's so yes it is a typo
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What is the typo?
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Thanks for clarifying that Jon, that was based on http://www.camaros.org/diffs67.shtml which says the '67 Z/28 had them.
Tim, I don't see where full (large,tall, etc) rear bumper guards are mentioned in that link you've provided ? Small rear guards, AKA "bumperettes" however were included on all all 67's. No bumperettes factory installed in 68.
Sorry for the late reply as I don't frequent this site as much as I should...
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Garth, that's because it was edited after my post, according to the version date near the top of that page:
Version: Friday, 03-May-2019 21:18:56 EDT
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Thanks, I should've known... :-[ Good catch.
After studying the 68 AIM trim heights, I can't come to any conclusions one way or the other as there's just not enough difference that I can see. My feeling is the guards were added simply to go along with the race theme of a Z/28. They actually provide a little more protection down low for the gas tank and filler neck