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Steering feel from change in scrub radius/offset

8.9K views 7 replies 5 participants last post by  Thejoyofdriving  
#1 ·
I am looking into new rim for my 09 STI, I currently have the heavy 5 spoke stockers (they are now my winter boots). My goal is to improve the quality the driving experience first and looks second. I am currently interested in Enkei PF01's or OZ Alleggerita HLT's and I was wondering will the 45 ET on the PF01's increase the steering effort and feedback relative to the 55ET (stock ET) on the OZ's? It is my understanding that the 10mm drop in ET will result in an increase in the negative scrub radius, is this true? Final question, how much change in ET can I put in before the feedback / steering effort becomes too much?

As a reference point my previous car was a 06 GTI on 18" factory summer high performance tires. I really enjoyed the car and loved the steering but it was just to slow. My other car is a 1994 Mustang Cobra w/ supercharger, goes like hell but drives like a box of rocks. The STI is to replace both cars. I live up in New England and do frequent trips to the mountains via the frost heaved back roads.

Sorry if I have missed this info in another post, I looked but did not find it.

PROSUM
 
#3 ·
The change in offset will slightly affect handling as the wheels move further out away from the hub. I can't say it is good or bad... just different.

That being said, if you are going to replace your wheels, GO WIDER! Wider wheels, and subsequently wider tires provide more surface area in which to grip the road.

I just put on a set of Advan 18 x 9.5" 38 wrapped in DZ101. They are freaking awesome! I love the extra contact area when whipping the car around turns. It is significantly harder to get my car to lose traction while applying throttle around the turns = higher speed turning.

The fact that the Advans are sub 18lbs at that size is also incredible... Just like the PF01 in a similar size.

Get the PF01 in either 9" or 9.5" and I guarantee that you'll be pleased with your purchase!
 
#8 ·
GO WIDER! Wider wheels, and subsequently wider tires provide more surface area in which to grip the road.

Thats not necessarily true. Wider tires doesnt equal more surface area ie more contact patch. Getting a wider tire changes the shape of the contact patch, thats it, if pressure remains constant. The patch will get wider and narrower creating a more favorable shape under load. You will only get more contact patch if you lower the PSI in the tire. Its a tricky concept of physics im just beginning to understand, someone please correct me if im wrong

A=F/P

Where A is area
F is normal force, force applied on the tire
and P is pressure.

You cant get more area without changing the right side of the equation ie lowering your PSI or applying more force on the tire via aerodynamics or more weight.
 
#5 ·
Well I got a set of TR Motorsports MT1's with 275/35 rubber and the steering effort has increased nicely. It feels much more European. I am not sure that the feel has improved much, however the steering does tug harder over ridges and grooves. Turn in is much sharper and the car does seem a little less settled over bumps but also more lively. The car still has the factory alignment so who know where it is actual set. The ride over bumps is noticeable improved which I credit to the large drop in un-weight at each corner. The MT1's weigh in a 19 lbs while the factory 5 spokes are about 28 lbs. The 275 tires weigh 27 lbs vs. the factory tires at 26 lbs, and the aluminum lugs nuts drop a little weight too. All totaled I should be down by slightly more than 8 lbs a corner.

For the folks that are concerned with fit, yes I did have the rear fenders rolled by the fine brothers Salb at Synaptic 3 in Candia NH (No cracks in the paint :)). The wheels have a 45mm offset and it is still a tight fit. No rubbing yet, however I have yet to whip in thru the turns with anyone in the back seats.

As "Sub a ru" had for told the grip is great!
 
#7 ·
The more outside you move the wheel center the more you increase your rolling resistance (like increasing your spring rate during rolling of the car). Hence, it will impact your handling (usually positively since it is higher) but will also impact your ackerman. The change in ackerman means it will change your steering (feel, response etc.). Not sure if it is good or bad depending on the baseline.