Correct Body Ride Height

[ron69912t]

I am about to replace the rear suspension bushings in my 69. I have 185x15's all around.

I have already replace the front suspension bushings.

My top of the fender wheel openings are all at 25-1/4 to 25-3/8". The body angle measured at the door sills ar zero degrees slant on both sides.

What should the body ride height be for street use. The manuals are no help. Should there be a nose down attitude?

Thanks for your help...again!

Ron D

[craign]

Ron,

this should help!

http://www.hillmanimages.com/912/height.html#hdr1

Craig

[ron69912t]

My 185 x 15 tires are 24" in diameter (approx.). The tops of the wheel opening measure 25-1/4" to 25-3/8" at all four wheels so there is 1-1/4" to 1-3/8" clearance over the tires to the fender lip.

Does this sound right?

Thanks,
Ron

[craign]

Ron,

That sounds a bit on the tight side and might cause some rubbing. Here is what Dave has to say on tire sizes and it sounds like they should be OK as 185 x 15 were offered starting in 69.

http://www.hillmanimages.com/912/tires.html

I have a tire size calculator at home where you plug in the 185HR15 and it gives you exact tire dimensions. Let me know if you want it and I can send to you. It is in MS Excel format.

Craig

[ron69912t]

Craig:
Thanks for the offer of tire size calculator. Can you e-mail it to me? If so send it to me at powernail@powernail.com

I also think my car is sitting too low at 25-1/4". From various pictures I have examined I'd say another inch or so would be more common. Although there are no signs of my 4 tires rubbing anywhere.

What are the wheel opening heights on your car?? Anybody else willing to measure theirs?? Floor to inside top of the wheel openings at all four wheels.

Thanks,
Ron

[craign]

Ron

I won't have time to measure until next week, I am leaving Friday morning to hook up with 50-60 other 912's in Solvang.

You should plan to join us next year, we have others talked in to it from east of the mississippi.

I'll send you the tire size thing tonight though. I run 195/65HR15's all the way around and have no rubbing problems.

Craig

[ron69912t]

Craig:
Great..take your ruler with to Solvang.

Ron

[Duke]

Here are my measurements after lowering my car:
Rear: 24 7/8
Front: 25 3/8

Tire size is 195/65/15 and no rubbing. Takes corners like it is on rails! I installed the Sway-away adjustable rear swing arms. Sure makes the job a lot easier.

[ron69912t]

Duke:
Have you measured your body angle with a protractor level off the door sills?

I wonder what the angle is since your front dimension measurement is more than the rear but that does not mean the car is nose-up in attitude. The wheel openings are not the same front to back so I have read.

I bought a very nice and reasonably accurate to 1/2 degree protractor/level from Sears for $10.00.

Thanks for your help again.

Ron

[Duke]

The front wheel arches are cut different than the rear-that is why the measurements are 1/2 inch more in the front. This gives you about a one degree nose down attitude. I confirmed this with a magnetic protractor on the door sill per factory recommendation. There are many articles on lowering especially in the 911 web site.
Duke
69 912

[ron69912t]

Duke:
I am more interested in finding out what the factory ride height dimensions are supposed to be for a 69 with 185 x 15 tires.

I don't want to lower the car just set it up stock. It just looks too low, especially at the rear wheels. Yet the body angle is zero.

What size tires do you have on your car?

I have three shop manuals none of which mention specific body angles. They just tell you how to measure the angle. Where can I get this info?


Thanks,
Ron

[Duke]

I have 195/65/15 tires. The factory stock ride height is covered in "Porsche 912-Handbook & Service Manual" which is available from Performance Products as well as Pelican I believe. It is several paragraphs in length & more than I could cover in this message but for the rear the measurements are taken from the ground to the wheel center & from the ground to the torsion bar center. The difference should be 12mm +or- 5mm. The height difference from right to left side should not be more than + or - 8mm. For the front you measure from the ground to the center of the wheel and from the ground to the center of the torsion bar. The difference between these two measurements should be 41/4 in. and should not be more than 5mm from left to right side. Hope this helps. Your car may have been lowered by a PO-maybe a little too much.

[WFBowen]

Ron:
I'm going from memory here, but I don't think the factory ever offered 185x15. All had 165x15, then the 185/70x15 tire was a 911 option (maybe 912 also.) Since the 185/70 and 165 share close diameters, the factory settings would apply to both. If you're using a straight 185 series tire, you car will look "different" even if it's sitting at factory specs (ground to torsion bar measurements,) since this tire is noticeably taller in profile.
Good luck,
Bill.
p.s. If you're in fact running 185/70, disgregard all above.

[ron69912t]

Bill:
I am sure the tires on my 69 are not the original ones. I know they are 185's but don't recall the profile number, I will have to look at them tonight.

The gold decal on tire size calls out both tires. The 185 was an option I believe.

Thanks for your help.

Ron

[Duke]

Ron: the 185/70/15 tires were an option for the 69 912-they were standard on the 69 911S. My car came with these tires & I changed to the 195/65 size because the 185's were hard if not impossible to find. The 195's have very little affect on your speedo-maybe one mile slower at 70mph.

[ron69912t]

Duke:
I have that shop manual but like all the others I have read they focus on the ride height as it relates to the center of the torsion bars NOT the body. The shop manual measurements just did not make any sense to me as I tried to make the adjustments.

For example:
For the front torsion bars the dimension from the center of the torsion bar to the floor I calculated at 7-11/16"(195 mm). Based on a tire diameter of 23-7/8" (606mm). The wheel radius is 11-15/16" (303 mm) less the 4-1/4" (108 mm) from the wheel center line to the center of the torsion bar which leaves 7-11/16" (195 mm) for the TB center to the floor.

The final TB center measurement to the floor was actually 5-7/16" (138 mm) which gave me a wheel opening to floor dimension of 25-3/8". If I rased the car another 2 plus inches to meet the manual specs I think the car would be way too high.


Thanks,
Ron

[Duke]

Sounds like your front height is the same as mine, 25 3/8 to fender lip. If you raised it 2in you would probably be 1in above the original factory specs and the car would look like it was ready for some off road adventure. If it is not rubbing & is handling ok I would not change the height. These cars can be very interesting to work on, best of luck.

[ron69912t]

Bill & Duke:

Checked my tires, they are Michlen MX L 185/65 R15 (87T).

The tire decal in the engine bay calls out 165R15 as stock and 185R15 or 185R14 as options.

Also checked my rear wheel toe-in which is 1/8" shouldn't it be zero?

Took her for a ride today..how sweet it was!

Thanks,
Ron

[Duke]

Have you had a 4 wheel alignment done recently? The factory specs call for 0 toe-in for the rear wheels. For track purposes I have read settings of -15 toe-in should be used. I assume this could also be used for street if you want better handling. Just depends on the way you drive & how you want your car to handle. By the way, my original ride height at the fender lip before lowering was as follows: Front: 26 1/2
Rear: 26

[ron69912t]

Duke:
I have not had the car aligned yet. I just bought it last July. Waiting until I get all the suspension bushings replaced then Ii will get it done. I think I can correct the rear toe-in after I change the rear bushings and make the adjustments via the eccentric bolts on the stabelizer bars.

Yesterday I set up a test for body various body angle measurements as they impact the front & rear fender wheel openings..

1. Theoretical: The wheel base for a 69 is 89.29 inches, the tangent for 1 degree is 0.01745 inches. So a one degree nose down angle would produce a 1.56 inch difference (89.29" x 0.01745"= 1.56) between the front and rear wheel base (wheel openings). This is a lot more than I have read anyone doing.

2. Actual: I measured my door sill angle to be zero degrees then I jacked up the engine (and body) with a padded floor jack to a 1 degree nose down inclination. The rear wheel openings were 26-1/16" high, the fronts were 25-3/16" high.

3. Actual: I increased the angle to 2 degrees and the rear wheel openings were 26-7/16" high, the fronts were 26-3/16" high.

So there is something other that simple trigonometry occuring here.

Overall body length for a 69 is 163.9 inches so a 1 degree nose down attitude would be 0.01745 x 163.9 = 2.86 inched difference between the front and rear. If the body was flat across the bottom which it isn't. So trying to determine where the body starts and ends is beyond me.

I have decided to keep the car neutral axis, zero degrees inclination and zero rear wheel toe-in so I can sleep at night.

Good night & thanks.

thanks,
Ron