Alignment for different tire sizes
04-05-2015, 11:42 AM
#1
Racer
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Member Since: Oct 2010
Location: Huntington Massachusetts
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Alignment for different tire sizes
The car is an 02 C5Z gutted (~2900lbs empty), fully caged, LG GT2 coilovers with JOC sways, poly bushings, about stock power. The car has 2 main activities: hillclimbs and track days (and some occasional autoX).
Last year I was running Conti slicks in 285/305 fr/rr and I was struggling for grip in the hillclimbs mostly because we always start with cold tires and the Conti have pretty hard compound similar to the Hoosier R6.
For this year, I have a set of R6s in 285/315 (scrubs) for the track. For the hillclimbs, I picked up a set of barely used Hankook with the C51 compound in 275s all around.
The idea is that the 275s will get faster to temp without sacrificing too much grip in the rear. Now the questions are about alignment:
- will switching between 275 & 315 at the rear affect the rake significantly enough that I should re-adjust the height?
- I still need to weigh my wheels, but will the corner balancing be completely off between the 2 sets of wheels?
- I can't imagine toe or camber being significantly affected by the tire change (assuming rake remains close enough) but maybe I'm missing something?
- should I just forget about running 275s in the rear and get some 305s/315s in softer compound?
Last year I was running Conti slicks in 285/305 fr/rr and I was struggling for grip in the hillclimbs mostly because we always start with cold tires and the Conti have pretty hard compound similar to the Hoosier R6.
For this year, I have a set of R6s in 285/315 (scrubs) for the track. For the hillclimbs, I picked up a set of barely used Hankook with the C51 compound in 275s all around.
The idea is that the 275s will get faster to temp without sacrificing too much grip in the rear. Now the questions are about alignment:
- will switching between 275 & 315 at the rear affect the rake significantly enough that I should re-adjust the height?
- I still need to weigh my wheels, but will the corner balancing be completely off between the 2 sets of wheels?
- I can't imagine toe or camber being significantly affected by the tire change (assuming rake remains close enough) but maybe I'm missing something?
- should I just forget about running 275s in the rear and get some 305s/315s in softer compound?
04-05-2015, 12:21 PM
#2
Melting Slicks
The car is an 02 C5Z gutted (~2900lbs empty), fully caged, LG GT2 coilovers with JOC sways, poly bushings, about stock power. The car has 2 main activities: hillclimbs and track days (and some occasional autoX).
Last year I was running Conti slicks in 285/305 fr/rr and I was struggling for grip in the hillclimbs mostly because we always start with cold tires and the Conti have pretty hard compound similar to the Hoosier R6.
For this year, I have a set of R6s in 285/315 (scrubs) for the track. For the hillclimbs, I picked up a set of barely used Hankook with the C51 compound in 275s all around.
The idea is that the 275s will get faster to temp without sacrificing too much grip in the rear. Now the questions are about alignment:
- will switching between 275 & 315 at the rear affect the rake significantly enough that I should re-adjust the height?
- I still need to weigh my wheels, but will the corner balancing be completely off between the 2 sets of wheels?
- I can't imagine toe or camber being significantly affected by the tire change (assuming rake remains close enough) but maybe I'm missing something?
- should I just forget about running 275s in the rear and get some 305s/315s in softer compound?
Last year I was running Conti slicks in 285/305 fr/rr and I was struggling for grip in the hillclimbs mostly because we always start with cold tires and the Conti have pretty hard compound similar to the Hoosier R6.
For this year, I have a set of R6s in 285/315 (scrubs) for the track. For the hillclimbs, I picked up a set of barely used Hankook with the C51 compound in 275s all around.
The idea is that the 275s will get faster to temp without sacrificing too much grip in the rear. Now the questions are about alignment:
- will switching between 275 & 315 at the rear affect the rake significantly enough that I should re-adjust the height?
- I still need to weigh my wheels, but will the corner balancing be completely off between the 2 sets of wheels?
- I can't imagine toe or camber being significantly affected by the tire change (assuming rake remains close enough) but maybe I'm missing something?
- should I just forget about running 275s in the rear and get some 305s/315s in softer compound?
Perhaps those who have changed to a square setup can chime in, but typically a tire change that significant is going to require a setup change to keep the car neutral.
04-08-2015, 12:01 PM
#3
Racer
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Member Since: Oct 2010
Location: Huntington Massachusetts
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The rake isn't that significant. But going to 275's from 315's is going to cause the car to oversteer a good bit more since you just have a lot less tire in the back. I suspect that along with the tire change you're going to have to soften the rear bar or stiffen the front bar a bit when you go to the smaller rear tire.
Perhaps those who have changed to a square setup can chime in, but typically a tire change that significant is going to require a setup change to keep the car neutral.
Perhaps those who have changed to a square setup can chime in, but typically a tire change that significant is going to require a setup change to keep the car neutral.
I'll try the setup at AutoX to see how it handles with 275 on all 4 corners. I wonder what the setup/experience is with people who have been running square 275s.
