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Old 09-30-2001, 07:27 PM   #1
Sean
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Unhappy How are RE730s supposed to feel? 215/45-ZR17 on Prodrive P7 feels very mushy...Luke?

OK, I've had a set of 215/45-ZR17 RE730 tires on my Prodrive P7 wheels for about two weeks now and I love them! I have two concerns, however. The tires seem to catch and grab every little rut in the pavement and make the car a bit nervous. I came from hard Pirelli P8000s, so I know that the RE730s are a much stickier tire...but is it normal for the car to be so twitchy?

Second, at the S&W autocross today, the car felt extremely mushy! I had front and rear at 44 PSI and then 42 PSI, and the car felt really weird. I pulled the fastest runs ever, but it felt like the tires were sloshing from side to side, almost like they were rolling over. After inspecting the chalk marks, however, I was nowhere near rolling over...I was smack dab in between the two sets of raised nipples on the sidewall and nowhere near the danger arrow (whatever it's called).

It felt almost like driving a fast speedboat, the way it carves through water. Except the tires weren't sliding on the pavement, it's like the sidewall was very soft and flexing back and forth on the footprint.

If this is how RE730s are supposed to feel, great! I can get used to it...I've never driven on kickass tires before. If this sounds terribly wrong, what's next? Experiment with tire pressures? Alignment?

Tirerack.com recommends the 205/50-ZR17 but I went with 215/45-ZR17 because the size was much closer to my 205/60-HR15 Pirellis and many people recommended the 215/45 instead of the 205/50. Did I just make a horrible mistake by choosing the slightly wider tire?

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Old 09-30-2001, 08:02 PM   #2
RidinLow
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Sounds like by upgrading your tires, you're now uncovering weaknesses in the rest of your suspension. Could the feeling be caused by springs and shocks not up to the task of taking on the grip?
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Old 09-30-2001, 08:09 PM   #3
jmott
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have you had an alignment?
add a little toe-in and/or caster and you wont track on ruts so much.

as for the mushy feeling, it might just be cuz the tires are new and the tread blocks are tall and mushy?

dunno.
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Old 09-30-2001, 08:36 PM   #4
Ethan
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Sounds to me like its time to upgrade your suspension. I think with the higher gripping tires you can know see exactly the limits of the suspension. This is assuming your still running stock suspension...
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Old 09-30-2001, 08:42 PM   #5
jmott
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the stock springs and shocks take the grip of race tires just fine.

[EDIT]

oops! different car! nevermind

Last edited by jmott; 09-30-2001 at 09:02 PM.
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Old 09-30-2001, 08:48 PM   #6
Sean
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It's the stock Impreza Outback Sport suspension, which is essentially 2.5 RS struts and slightly taller springs. The car was aligned about six months ago to completely neutral specifications per Subaru spec. The treads are still new and not worn at all yet...the tires feel very similar to my mushy Bridgestone Blizzak WS50 snow tires.

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Old 10-01-2001, 03:05 AM   #7
Kostamojen
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Its your suspension
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Old 10-01-2001, 07:08 AM   #8
paultg
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Sean, I have the same tires and rims as you, but with 205/50R17 size on my RS. I just took the Eibach Springs off the car, and have not really "pushed it" yet, but I would tend to agree it is some of your suspenion, and just takes gettting use too. The OBS have lots of body movement, and flex quiet a bit with the open rear strut bar area (I would think). Do you have a rear sway bar? Right now I have a 20mm and stock RS springs, which I bet help more than your OBS springs. A nice combo on the OBS is the KYB/AGX setup with stock springs and a rear sway bar. You might want to e-mail Wayne (wac) for some suggestions, since he actually drives an OBS. I know he has KYB/AGX's on stock springs. Not sure if he has tried it with good tires yet though. I would also think a front sway bar would help too. I plan on upgrading mine in the future, and adding KYB/AGX tomy stock springs.

Paul G.
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Old 10-01-2001, 11:13 AM   #9
skidplatez
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Sean-

I know you have a lot of autocross experience and your car is at least mildly modified so although suspension was my first instinct I think I know what it is. I also had RE730s that I wore out completely, as they wore they got better and better. Until they had too many heat cycles. What you are feeling is tread squirm because they are new tires give em about a month of hard driving and you will be really happy. the tread needs to wear down a little. If you had had them shaved you wouldn't have had the problem. Obviously shaving tires that you use on your daily driver is a bit insane so just let them break in.

Also the tracking thing is a product of the stiff sidewall. and is pretty normal for a good high porformance tire. Your Pirelli's weren't even playing the same game as the RE730 I've had these tires next to each other and the RE is so much stiffer it's really incredible.

I would also recomend running a little lower pressure at autocross, these tires are very different from the RE92 and don't require that much pressure. A little lower pressure might actually help the surface of the tread conform to the road better.
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Old 10-01-2001, 12:35 PM   #10
paultg
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Yeah, what he said!

It took a good 600 miles for me before the tires wore down enough. I had a horrible time at the first autocross. The car was just plain weird. I just thought it was because I never had a "real" set of tires before.

I also run about 38/36 PSi or 36/34 Psi at the autocross. At NHIS I bump it up, because the course is pretty tight.

Paul G.
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Old 10-01-2001, 01:36 PM   #11
Sean
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Talking Great...thanks!

Yeah, I have a 19-21mm rear bar set to 19mm with stock droplinks. I'll set it to 21mm once I receive my replacement solid droplinks from SPO Motorsports (long story, not to be told here).

Anyway, I figured it was the tall tread not being worn yet. I had about 700 miles of very light driving on them before the autocross...so light, the tread looked new and smooth. After the autocross, my tread looks more like the pimplescarred surface of R compounds. I like it!

After seeing the comments, I can see where the odd feeling could have been body roll and soft suspension. I'll definitely play with pressures...I'm not a tire geek and basically followed the "add 10 PSI" rule, so I was obviously running pressures too high.

Thanks again, all!

Fear the Trunkmonkey. There is no cone.
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