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Wheels | Tires | Spacers | Hub -- Sponsored by The Tire Rack Specific topics relating to wheels and tires.


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Old 07-05-2018, 07:42 PM   #43
SuperTom
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Originally Posted by rvoll View Post
So normally, I wouldn't even slightly mod my new 2018 BRZ, but so many of you have added spacers to get a flush look, I thought the very slight increase in understeer wouldn't be a problem. So yesterday, I received a set of 20mm spacers from ft86speedfactory -- their own brand -- and put them on the rear wheels. So many have said that 20 in front and 25 in back would be perfect. Their spacers are really well built, hub centric, and just good looking. The only other functional mod I made on the car was replacing the OEM Primacies with 225 PS4S.

After taking the car on a test drive, the handling was an absolute disaster. Severe understeer and more difficult cornering. As for looks, to my eyes the poke was about 5mm too much on the rears, which really surprised me. I know the 225's are slightly wider than the stock 215's, so perhaps that is one of the issues. I think the understeer was multiplied by the extra sticky tires I had. I know that also putting spacers on the front will reduce some of the understeer, but I hate the look of poke in the front and if 20's were too big in the rear, then I'm not sure there is a good solution. If I'm only going 10-15's, it just isn't worth the effort in my book. I did have the advantage of taking a test drive just before and then one right after and perhaps that amplified the difference. I owned Porsches for 27 years so I am very sensitive to handling and suspension.

I guess I don't understand why this isn't more of an issue here. But I've learned a lesson that the Subaru/Toyota engineers knew what they were doing when "balancing" this car. No more mods for me except for accessories and perhaps an audio upgrade.

So I'll take them off today and put them up for sale at half price or so plus shipping. They are the nicest spacers I've ever purchased. Years ago, I did use some spacers on a couple of cars but I guess they were not as sensitive as this one....


The reason its not more of an issue here is most of the board are ricers who fit the biggest wheels they can and use 2" spacers to go with their knockoff rocket bunny fenders
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Old 07-05-2018, 07:57 PM   #44
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Originally Posted by rvoll View Post
I know you are trying to make an argument, but instead of trying to find inconsistencies (of which there are none), please actually think about what you are saying. Given the weight and power of a vehicle, there is a point where wider tires do not add more grip because no more grip is needed. Add weight and or power and those things change. Capish? With our car, I can find no evidence that when driving the car on the street under all conditions, including dry and wet, that standard size tires, or close to it, won't give you maximum benefit. And no, I didn't like what I perceived to be added understeer with the rear spacers. Some people may not notice it or even like it, and that is fine. Things are different on the track where things like tire temps and need for more lateral grip may be optimal especially on dry pavement. Even there, people will tell you there are optimal setups that balance grip and handling.
im not sure things like understeer are different on the track vs on the street but if you want to continue to be confused why your car handles different when you make a change to half of the car go ahead. treat each mod like its in a vacuum or look at the car as a whole, realize an alignment will probably get you where you want to be and move on.
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Old 07-05-2018, 09:16 PM   #45
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Checked tire pressures again and they are fine. Perhaps I'm not explaining it properly (that is entirely possible). Let me try again. When the spacers are on, and I'm turning a corner, I have to turn the steering wheel more to accomplish the turn. Could it be a placebo effect? Possibly, as I'm considered partially human. I do understand your theoretical argument, so I'm puzzled as well. Perhaps since the outer driving wheel must make more rotations around a corner that is, in some way, affecting how it corners. The car did feel different enough that I noticed it immediately. I'll put them on again tomorrow and this time pay more attention to whether it's real or in my mind.

After some of you raised this issue, I did a Google search and here is what was posted:

https://rennlist.com/forums/964-foru...ndersteer.html

http://www.mycarforum.com/topic/2691...he-real-truth/

https://www.6speedonline.com/forums/...teristics.html

https://www.evolutionm.net/forums/ev...ndersteer.html

https://forums.vwvortex.com/showthre...-or-understeer

http://www.maseratilife.com/forums/g...nly-wheel.html

I admit I don't know as much about the BRZ suspension as you guys, but it seems the general consensus is that adding rear spacers very slightly increases understeer. What I've found over the years is that a car's geometry is quite complex and what seems to be simple answers aren't quite that. I'll report back and try to take real measurements this time.

I'm not disputing that widening the rear track alone will cause more understeer, my point was that if you're nowhere near the limit you won't feel that at all. Understeer by definition is the front wheels losing grip before the rears in a corner, if no wheels are losing grip you're not under or over steering, the car is just turning.


IMO, take the spacers out and go for a drive and record it. Take a bunch of 90* corners and make sure the video can see your hands and the steering wheel. Put the spacers back in and do it again, same corners and same speed. I still bet it's in your head.


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Originally Posted by JimmyMac View Post
Widening the rear will cause more push and less rotation in the corner.

See above, and the original comment from the OP about the car not being anywhere near the limits of grip.
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Old 07-05-2018, 10:13 PM   #46
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I’m talking general setup theory. Not sure if you understand that or not. I’m not saying if you widen the rear of an FRS/BRZ/86 by 20mm per side that you will feel understeer/less steering. We really don’t know all the details and some people are more sensitive than others. How about you try to widen the rear of your car and give us your feedback? I can’t because my engine is out of the car. Heheh
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Old 07-06-2018, 12:32 AM   #47
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Originally Posted by wparsons View Post
I'm not disputing that widening the rear track alone will cause more understeer, my point was that if you're nowhere near the limit you won't feel that at all. Understeer by definition is the front wheels losing grip before the rears in a corner, if no wheels are losing grip you're not under or over steering, the car is just turning.

IMO, take the spacers out and go for a drive and record it. Take a bunch of 90* corners and make sure the video can see your hands and the steering wheel. Put the spacers back in and do it again, same corners and same speed. I still bet it's in your head.

See above, and the original comment from the OP about the car not being anywhere near the limits of grip.
I did install the spacers again and the steering wheel, even at low speeds, had to be turned slightly more with the spacers. Is it technically "understeer". It felt that way, but it may not be. When I first put on the spacers, I was not expecting a noticeable difference, so when it happened, it was probably amplified in my mind. This second time, my perception of it was much less, but it was still there. I'm a bit OCD and do things like close open cabinets, turn off lights, and am uncomfortable when things aren't spaced properly. I also lost an eye in the military so my brain has compensated for things like balance and distance. It could be a combination of the two. So, perhaps I'm a bit more sensitive to this type of change than most people. I've confirmed it is real, but not nearly "severe" as I perceived the first time. I guess most people wouldn't notice it. But it is confirmed that a wider track in back causes a slight increase in understeer.

But you are wrong about not feeling it at all. Perhaps YOU don't sense it, but I certainly do and now with measurements have confirmed that it is true.
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Old 07-06-2018, 12:34 AM   #48
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The reason its not more of an issue here is most of the board are ricers who fit the biggest wheels they can and use 2" spacers to go with their knockoff rocket bunny fenders
And headers and loud exhausts and intakes and lowering it more than an inch?
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Old 07-06-2018, 01:30 AM   #49
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I did install the spacers again and the steering wheel, even at low speeds, had to be turned slightly more with the spacers. Is it technically "understeer".
That is not even "technically" understeer.
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Old 07-06-2018, 01:47 AM   #50
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That is not even "technically" understeer.
I really don't care if it is "technically" understeer or not. That's why I put it in quotes. The effect is still there no matter what it is.

However, if you want definitions, here they are:

un∑der∑steer (Google)
verb
1. (of a motor vehicle) have a tendency to turn less sharply than is intended.
"the car understeers on very fast bends" noun ˈəndərˌstir/Submit
1. the tendency of a vehicle to understeer.

Wikipedia
"Understeer and oversteer are vehicle dynamics terms used to describe the sensitivity of a vehicle to steering. Oversteer is what occurs when a car turns (steers) by more than the amount commanded by the driver. Conversely, understeer is what occurs when a car steers less than the amount commanded by the driver.

Automotive engineers define understeer and oversteer based on changes in steering angle associated with changes in lateral acceleration over a sequence of steady-state circular turning tests. Car and motorsport enthusiasts often use the terminology more generally in magazines and blogs to describe vehicle response to steering in all kinds of maneuvers."

I don't know where you are getting your definitions. Do you really understand the term? Specifically, my car steers less than the amount commanded by me when compared to stock.
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Old 07-06-2018, 02:53 AM   #51
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If you don't care to be technically correct in your posts, how do you expect any sort of help to your own discussion? Understeer is absolutely universally used to describe a condition where while cornering, the front tires begin to slip first. By using the term understeer you are describing the performance of the tyre as it is sliding, it really is that simple. If you want to use it to describe extra steering effort or some weird feeling that you canít describe thatís fine (this is the internet after all), just be aware that people might perceive you as just inexperienced, in whom an investment in a comprehensive reply will not be accepted or even understood. Most who are technically competent (there are plenty on this forum) simply wonít bother to reply.

On top of that, may I say that just casually dropping that you have driven a Porsche for 27 years somehow gives you some sort of sixth sense on how cars handle, or maybe that youíve lost an eye gives you some sort of superhuman abilities. It all is just a bit too weird. In many forums, when someone starts waxing on about how many years heíd driven a Porsche, heíd be politely asked to take his hand off it, if you catch my drift.

Good luck with your spacer problem.
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Old 07-06-2018, 09:46 AM   #52
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And headers and loud exhausts and intakes and lowering it more than an inch?
well no headers are proven performance mods, small gains with catback & intake.

I'm talking about the stance crowd with wide tires or spacers and basically running on stock HP.
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Old 07-06-2018, 11:22 AM   #53
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I was running 20mm spacers on 225/45-17 Bridgestone S-04's with wheels that had 4mm more positive offset than stock, (so the wheels were out 16mm at all 4 corners.)

I had a spacer snap a stud when I took it off one day, so I took both fronts off and drove around for a couple days while I waited on studs. I noticed oversteer reduced at the limit of the rear tires grip, and I noticed the car pushed a bit more, (I was running -2.5 degrees of front camber, and -1.5 degrees of rear camber on ST coilovers through this whole 'event'.)

Put the fronts on and see if it's better. Also try the 20's in the rear with no fronts to see if you can feel the dynamics change front to back, which can help you get the right balance. (Maybe you need some 15mm slip on spacers at all 4 corners with extended studs...)
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Old 07-06-2018, 11:54 AM   #54
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Gosh!! 4 pages in and this thread has taken a turn for the worse...
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Old 07-06-2018, 01:24 PM   #55
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Originally Posted by Subsonic View Post
If you don't care to be technically correct in your posts, how do you expect any sort of help to your own discussion? Understeer is absolutely universally used to describe a condition where while cornering, the front tires begin to slip first. By using the term understeer you are describing the performance of the tyre as it is sliding, it really is that simple. If you want to use it to describe extra steering effort or some weird feeling that you canít describe thatís fine (this is the internet after all), just be aware that people might perceive you as just inexperienced, in whom an investment in a comprehensive reply will not be accepted or even understood. Most who are technically competent (there are plenty on this forum) simply wonít bother to reply.
Noted. Whatever it is that is causing this difference, whether it is understeer or something else, I do appreciate the comments. I can definitely feel the difference, however, so I'm getting rid of the spacers. And I can see how others might not notice this slight difference.
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Old 07-06-2018, 01:41 PM   #56
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I agree that putting spacers ONLY on the rear will increase understeer slightly. I read it wrong, I thought there was only a 5mm difference between the rear and front
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