Finally got the '98 C4S Home
#17
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If it is truely a pinhole leak with no structural damage to the tire, there is no danger driving hard or any other way IMO. The worst thing that can happen is the patch comes off, and you loose a few psi of pressure over the next week or so. I'm talking about a pinhole leak, not a nail in the sidewall where the tire could quicly loose pressure. I get mesquite thorns in my truck tires (including sidewalls) and shops just will not patch them on the sidewalls. They leak so slow that I just make sure I check the pressure every week and they are never more than a couple psi short. I had a co-worker almost killed in one of the explorer roll-overs because of low tire pressure, and a weekly tire check on all my vehicles has been a Sat. morning ritual since then (even the one with tps).
#18
Burning Brakes
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I picked up my new to me '98 C4S (forest green.....I am told the only forest green C4S imported to the US in '98 but haven't verified)! Yes, yes, I will post pictures as soon as I detail the car this weekend (weather permitting). It was pretty much as advertised (bought it in Florida sight unseen but Zotz Garage did a PPI). A couple of minor disappointments but overall I am very happy with the car.
I have two questions:
1. I have a slow pin hole leak in the right rear sidewall tire. They are Bridgestone Potenza S02A with lots of tread left (60%). Since the hole is in the sidewall, should I just replace the tire or can it be repaired? If I have to replace it, should I replace both rear tires?
2. All compressions and leak down from PPI came back strong and no issues. However, When I picked up the car, it had been sitting in a garage for 2 months without being driven and it ended up being one quart low. I have now driven the car about 300 miles and the oil is low again. Just had a Mobile 1 change in January, probably no more than 500 miles ago. Garage floor is dry after the car being in there a week. Any thoughts?
Cheers!
I have two questions:
1. I have a slow pin hole leak in the right rear sidewall tire. They are Bridgestone Potenza S02A with lots of tread left (60%). Since the hole is in the sidewall, should I just replace the tire or can it be repaired? If I have to replace it, should I replace both rear tires?
2. All compressions and leak down from PPI came back strong and no issues. However, When I picked up the car, it had been sitting in a garage for 2 months without being driven and it ended up being one quart low. I have now driven the car about 300 miles and the oil is low again. Just had a Mobile 1 change in January, probably no more than 500 miles ago. Garage floor is dry after the car being in there a week. Any thoughts?
Cheers!
#19
Instructor
Thread Starter
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Thanks for all the advice....it's dipstick for oil checks and a new set of rear tires.
grwoolf.....its a pin hole but not a two or three day leak more like one day and pressure is down to 15 psi or less. Doesn't go completely flat but its low. I will just get it behind me and buy a new set. The fronts are almost new so I will only replace the rears. All four are some brand/model.
Cheers!
grwoolf.....its a pin hole but not a two or three day leak more like one day and pressure is down to 15 psi or less. Doesn't go completely flat but its low. I will just get it behind me and buy a new set. The fronts are almost new so I will only replace the rears. All four are some brand/model.
Cheers!
#21
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Congrats on the purchase. You will never go wrong with a 993... I still have my C4S and will never let it go!
#22
Three Wheelin'
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I seem to recall reading in Adrian Streather's book that when replacing tires on a C4 that it is best to replace all four at the same time. Since rear tire wear occurs faster than front tire wear, many of us just purchase new tires of the same brand for the rear tires, especially on a C2. If the rears are worn the fronts may still have decent tread but the rolling circumference on the fronts may not be the same as the two new rears. The rolling circumference front to rear should be within, if my memory serves me correctly, about 3% of each other or it can affect the AWD system. For the price of a new set of four tires these days (Sumitomos in particular) I would personally replace all four.
#23
Drifting
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I seem to recall reading in Adrian Streather's book that when replacing tires on a C4 that it is best to replace all four at the same time. Since rear tire wear occurs faster than front tire wear, many of us just purchase new tires of the same brand for the rear tires, especially on a C2. If the rears are worn the fronts may still have decent tread but the rolling circumference on the fronts may not be the same as the two new rears. The rolling circumference front to rear should be within, if my memory serves me correctly, about 3% of each other or it can affect the AWD system. For the price of a new set of four tires these days (Sumitomos in particular) I would personally replace all four.
Replacing 2 sets of rears to 1 set front tires is a Porsche 911 standard (same on my '86 and '96). Yes the front/rear rolling circumfrence has to be close (I thought I saw 5%, but not sure on that).
As a sanity check, I did the math:
[geekOn]
What is the difference in rolling circumference after a tire is worn down ~0.25" (a extremely pessimistic guesstimate of tread depth) in its radius compared to a new tire?
Reference on tire size calcs: http://www.tirerack.com/tires/tirete...e.jsp?techid=7
My rears are 285/30R18, so tire height is: 285mm*0.30 / (25.4mm/in) = 3.37"
D=Dwheel+2*tireHeight, so D=24.74"
C= 2*pi*R = pi*D with C=circumfrence, R=radius, D=diameter
The % change in C:
deltaC% = 100 * (C1-C2) / C1 with C1 new circumference, C2 worn circumference.
deltaC% = 10 0* (pi*D1-pi*D2) / (pi*D1) with D1 new diameter, D2 worn diameter.
deltaC% = 100 * (D1-D2) / D1
deltaC% = 100 * 2*treadDepthChange/D1
deltaC% = 100*(24.74-24.24)/24.74
deltaC% = 2.0%
Not too much change really. And I've made a very pessimistic assumption on tread depth difference. Doing the math again with 1/8" tread wear gives 1.0%.
[/geekOn]
So just change the rears if the fronts are ok.
my 2c, YMMV...
kjr
Last edited by kjr914; 04-29-2009 at 04:48 PM. Reason: Improved math with real numbers instead of guesstimates. End result similar 2% instead of orig 1.2% estimate.
#28
Addict
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Congrats on your purchase. Can't wait to see the pics. You have a unique car. As others have said, there aren't many Forest Green 993s around. Even less '98 C4S's.
Last fall, when I saw this car advertised (I think it was in Pano), I tried to interest of friend of mine (in Ft. Lauderdale) in this car. He is a fan of 993s and of Forest Green paint. He passed on it for some reason or other. It might have been a purely cosmetic reason. I believe this car has a black leather interior, right?
It really seemed like a great car for someone.
I hope you are able to get in some miles soon and can post your driving impressions.
Best regards,
rj777
RickJ