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Old 05-28-2020, 10:42 PM   #1
Flannel-On-A-Camel
 
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Understeer in Relation to Tire Size

Alright, y'all. I'm calling upon the collective expertise and experience of everyone here once more. I've been tearing this forum apart for an answer, but I haven't quite got one that I'm totally satisfied with.

So, most of us know that a staggered set of tires, say 305's in the front and 325's in the rear, will cause understeer. However, just "understeer" is difficult to quantify. Those with experience with this set up, especially if you track your rig, what are your thoughts? If you drive your Z at 8/10th's, is is noticeable? How about around town?

Thanks in advance! Also, pictures are more than welcome. Square 325 set up pictures are also cool!
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Old 05-29-2020, 12:29 AM   #2
'10CamaroDude
 
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Fatter tires in the rear can produce noticeable under-steer. The more rear-biased the
more under-steer. The front tires lose traction first with wider ones on the back,
which causes under-steer.

However alignment, spring rate, sway-bars and very importantly, driving technique
also play a big role. So, if you want the larger tires in back, then modify the
suspension to compensate.
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Old 05-29-2020, 09:41 AM   #3
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Quote:
Originally Posted by Flannel-On-A-Camel View Post
Alright, y'all. I'm calling upon the collective expertise and experience of everyone here once more. I've been tearing this forum apart for an answer, but I haven't quite got one that I'm totally satisfied with.

So, most of us know that a staggered set of tires, say 305's in the front and 325's in the rear, will cause understeer. However, just "understeer" is difficult to quantify. Those with experience with this set up, especially if you track your rig, what are your thoughts? If you drive your Z at 8/10th's, is is noticeable? How about around town?

Thanks in advance! Also, pictures are more than welcome. Square 325 set up pictures are also cool!

Most folks wouldn't notice the difference , certainly at civilized speed. At 8/10ths it would be, to some,but you can dial it out with the pedal on the right The gen 6 1LE's and ZL1LE's all come with a smaller contact patch up front, and they are well balanced cars right out of the box. YMMV
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Old 05-29-2020, 11:10 AM   #4
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I didn't notice much with a staggered set-up. The rims are different widths anyway which will change the specs of the tire anyway. The difference between a 305/325 GY 3R is not much as say a 305/325 Trofeo.
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Old 05-29-2020, 12:28 PM   #5
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Going from a staggered setup to a square setup makes a huge difference, definitely felt the difference in the canyons.
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Old 05-29-2020, 07:13 PM   #6
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I think you would need to be a professional driver to notice any measurable difference. If you notice understeer from a 305 to 325 on the street you probably shouldn’t be on the street.

Also a Trofeo to something like an RE11 street tire can’t be compared, staggered or not.

From what I read they did a square setup with Trofeos because it tweaked a little bit more out on the N’Ring.
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Old 05-29-2020, 09:00 PM   #7
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Quote:
Originally Posted by Flannel-On-A-Camel View Post
Alright, y'all. I'm calling upon the collective expertise and experience of everyone here once more. I've been tearing this forum apart for an answer, but I haven't quite got one that I'm totally satisfied with.

So, most of us know that a staggered set of tires, say 305's in the front and 325's in the rear, will cause understeer. However, just "understeer" is difficult to quantify. Those with experience with this set up, especially if you track your rig, what are your thoughts? If you drive your Z at 8/10th's, is is noticeable? How about around town?

Thanks in advance! Also, pictures are more than welcome. Square 325 set up pictures are also cool!
There really isn't a lot of "expertise" on this forum with regards to racing and REALLY pushing these cars. There's a lot of great guys in here but most of them don't use the car as intended, and there's nothing wrong with that, I'm just saying......

Any "street" evaluation will be flawed because streets aren't prepped, the tires aren't up to temp, pressures could be wrong, etc, etc.

I can give you lots of feedback on real world testing of 305's square when pushing hard from 20mph-60mph. But that's with a Potenza RE-71R, not a Trofeo. Not sure if other tires will behave different. My car has substantially more front end grip than it does in the rear, period. Granted a lot of times when I'm turning the wheel, I'm standing on the brakes, which drives them down, but even in a fast-ish slalom, the tail will step out before the front will push. I can get it to push in certain situations, but mostly the rear is the end that misbehaves.
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Old 06-09-2020, 10:27 AM   #8
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I have tried to remove the small amount of under-steer my 1le had built in. I have changed many things, it's pretty much a Z28 lite now. Just like Joelster says, my car has more grip in the front than the rear. It will push the front tires on the street, it is on colder tires, a tight very slow turn with moderate acceleration, like a u turn or something similar. If I am pushing the car hard around 90deg corners I will get a nice neutral slide as the front will break the same as the rear and with a little more throttle the rear will step out rotating the car a little more. If I went with a 305 in the rear I think I would lose the ability of rotating the car with the throttle.
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Old 06-10-2020, 02:40 PM   #9
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I have run many tire setups on this car, although not staggered, I still adjusted alignment for each tire setup. My RE11 rain track tires need the rear loosened slightly, while the trofeo's handled the stock track alignment well (needed slightly more camber than suggested), and I just got some 315 R888Rs that will need some refinement at the track too. Tire pressure, suspension setup (specifically stiffness of sway bar), alignment, driving technique all play a factor as most people have stated. I had Randy Pobst in my endurance car in January that was tail happy, he completely disconnected the rear sway bar for his driving technique. We were within half a second of each other at Laguna Seca, the sway bar gave him an extra .2 seconds.
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Old 07-06-2020, 09:22 PM   #10
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Why donít you just run four 325s? They fit with enough room to spare front and back. The Michelin Pilot Cup2s allow the car to corner just like the older trofeo-rís .... they corner like a scalded dog...
And at 12 to -12.5Ē wide I get comments at every cruise in
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Old 07-06-2020, 09:59 PM   #11
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Quote:
Originally Posted by The_Raging_Bull View Post
Why donít you just run four 325s? They fit with enough room to spare front and back. The Michelin Pilot Cup2s allow the car to corner just like the older trofeo-rís .... they corner like a scalded dog...
And at 12 to -12.5Ē wide I get comments at every cruise in
I thought about it. I was worried the fronts might bulge over the rim too much. Do you have a few pictures of your set up that you can share?
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Old 07-06-2020, 10:36 PM   #12
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so why do i experience more oversteer in my car vs understeer
I have a 2010 V6 2lt Auto with 275 45 20"s on Front and 315 35 20's on back
if i push it hard the back breaks loose first, which of course then i steer with the throttle
I have driven it hard and the front does not brake loose first.
I been driving the car for ten years
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