New rear tires - back end handles squishy! - Rennlist Discussion Forums



New rear tires - back end handles squishy!

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Old 07-08-2016, 11:32 PM   #1
CFM928
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Default New rear tires - back end handles squishy!

I replaced my bald rear tires with Kumho ECSTA AST (Same size 225-50-15) and the rear feels totally unstable. A minute turn of the steering wheel makes the back end feel like it wants to come around. Fronts are old Yokahama 008s - so very little tread (even when new) compared to the rear Kumhos.

I want to get my old bald tires back!

The car is lowered and stiffened, was fine before the new tires.

Ideas?
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Old 07-14-2016, 05:46 AM   #2
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Have you checked the tyre pressures?
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Old 07-14-2016, 07:49 AM   #3
LexVan
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Never mix & match tires. Never use tires that are more than 5 years old.

Buy new matching fronts. Your Yoko AD08 are completely different tires from the new rear Kumho.

Need about 500 miles in new tires to scrub off mold release agents.
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Old 07-15-2016, 12:32 PM   #4
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Default Thanks for the replies!

One rear tire was 32 PSI, the other 26 (Even though mounted and balanced by a 'trusted tire shop'?!)

A neighbor that was a mechanic at a Porsche dealership when 914s were new test drove it and also mentioned getting a few miles on the tires... We'll see...

With multiple vehicles and 2 sets of tires for 'daily drivers' (Snows and summer) it's pretty cost prohibitive to have all tires less than 5 years old....
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Old 07-18-2016, 06:15 PM   #5
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Quote:
Originally Posted by LexVan View Post
Never mix & match tires. Never use tires that are more than 5 years old.

Buy new matching fronts. Your Yoko AD08 are completely different tires from the new rear Kumho.

Need about 500 miles in new tires to scrub off mold release agents.
+1

your new tires are all season tires, with a lot of tread on them, so yes in a way the car may be a little squirley compared to 'bald' tires since you are riding on blocks of tread. Pressures matter a lot - only a few lbs low make our GT3 difficult to drive, and ESPECIALLY if they are uneven. "Cheaper" tires take some time to wear off the mold release - we had the same issue with Kuhmo and Hankooks...car felt downright scary for a few hundred miles. Michelins not as all, but they are 5x the cost...

But also, as LexVan said, you should never mix & match tire models. The tread patterns are different and will make the car track wrong. Get new fronts!!!
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Old 07-28-2016, 04:43 PM   #6
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if you have 225 50 tires on a stock wheel you will have the jello affect as the tires will move on their bulging sidewall. 225 has to go on a seven inch wheel at least, and for the other I totally agree with everyone else who has commented about the mismatch and the passenger vs Yok 008 virtual racing tire!
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Old 08-02-2016, 11:57 AM   #7
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How about fitting the right thing from Pirelli and homologated by Porsche. they just turned up with us today

http://www.longstonetyres.co.uk/page...ato-p7-n4.html
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Old 08-07-2016, 09:59 PM   #8
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I always check pressures after having new tires installed. They are almost always over inflated.
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Old 08-14-2016, 10:35 AM   #9
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I agree with The Brewmeister 100% - tire shops always screw up the tire pressure and typically do not torque lug nuts/bolts correctly. As soon as I get home from a tire shop I always check both. The last time I was at America's Tire in San Ramon they not only did not torque the lugs correctly, they lost one lug nut and said nothing to me. I discovered it upon arriving home and they ordered me a new lug nut....never did apologize for the inconvenience or how they managed to lose a lug and still "check all the lugs with a torque wrench". Typical kids working there who know very little about cars and care even less.
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Old 08-20-2016, 11:29 PM   #10
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Quote:
Originally Posted by CFM928 View Post
With multiple vehicles and 2 sets of tires for 'daily drivers' (Snows and summer) it's pretty cost prohibitive to have all tires less than 5 years old....
.
We're talking about safety here, and your life. Scrimping on tires is a risk that you shouldn't be taking. And a blowout wouldn't only endanger your life, but the lives of others, as well.

In addition, Porsche says this about tires for its cars:

"...eventually all tires will either wear out or age out. Chemical additives make rubber elastic lose its effectiveness in the course of time and the rubber becomes brittle and cracks. Considering the performance capabilities of a Porsche, under no circumstances should tires older than 6 years be used."

Source: TIRES, Porsche Approved Original Equipment Tires - Spring/Summer 2016
.

Last edited by VGM911; 08-21-2016 at 02:17 PM.
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Old 08-23-2016, 10:43 AM   #11
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Yeah - totally agree. These cars have really only got two safety features built into them - brakes and tires. Don't cut corners on either please.
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Old 08-23-2016, 10:49 AM   #12
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Out of interest this is Porsches current fitment guide for their classic cars http://www.longstonetyres.co.uk/page...-porsche-tyres
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Old 09-17-2016, 07:54 PM   #13
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I agree with the statements above on tire pressures and matching tires front to back. From the book of I Can't Believe I Did That - I believe these are directional tires. By any chance do you have them mounted on the wrong sides of the car? That would cause very strange handling. Don't ask how i know ....
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Old 09-29-2016, 12:19 PM   #14
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Quote:
Originally Posted by CFM928 View Post
I replaced my bald rear tires with Kumho ECSTA AST (Same size 225-50-15) and the rear feels totally unstable. A minute turn of the steering wheel makes the back end feel like it wants to come around. Fronts are old Yokahama 008s - so very little tread (even when new) compared to the rear Kumhos.

I want to get my old bald tires back!

The car is lowered and stiffened, was fine before the new tires.

Ideas?
Throw all those tyres away and put something decent on unless you are on a perfectly smooth race track fitting fitting 225/50R15 on a 914 will be like having sex while wearing 4 condoms.
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