HPDE Wheel Decision
01-13-2019, 01:55 PM
#1
Drifting
Thread Starter
HPDE Wheel Decision
Wheels are going on C5 non-Z.
Installing a BBK so front wheels need to go up to 18's. Currently run NT01's (275 / 305) on C5Z 17/18 wheels.
I have an additional four factory 18" C5Z wheels and was planning on 315's on all four corners but do not want to lower the front of the car the required 1/2" that would be required to keep factory rake. That leads me to stay with 275 / 305 but on all 18's. My concern with that change is decreasing the front section height (relative to current) will result in an increase in front roll stiffness and possibly increase understeer.
Then it occurred to me that I could use C6Z rears (12" wide) and go with 315 front and 325 rear with the C5Z / C6Z wheels. This would now have similar decrease in section height so no change in f/b relative stiffness. It will also provide the same OD as the factory setup so no change to suspension height for rake required. NT01's are available in those sizes.
Front to back rotation is not part of my decision. Tire cost is also not part of the decision.
Will the 325 rear on a 12" wide C6Z wheel fit a C5 (without spacers or tubbing)?
Any reason (ignoring tire cost and rotation) not to do it?
Thanks
Rob
Installing a BBK so front wheels need to go up to 18's. Currently run NT01's (275 / 305) on C5Z 17/18 wheels.
I have an additional four factory 18" C5Z wheels and was planning on 315's on all four corners but do not want to lower the front of the car the required 1/2" that would be required to keep factory rake. That leads me to stay with 275 / 305 but on all 18's. My concern with that change is decreasing the front section height (relative to current) will result in an increase in front roll stiffness and possibly increase understeer.
Then it occurred to me that I could use C6Z rears (12" wide) and go with 315 front and 325 rear with the C5Z / C6Z wheels. This would now have similar decrease in section height so no change in f/b relative stiffness. It will also provide the same OD as the factory setup so no change to suspension height for rake required. NT01's are available in those sizes.
Front to back rotation is not part of my decision. Tire cost is also not part of the decision.
Will the 325 rear on a 12" wide C6Z wheel fit a C5 (without spacers or tubbing)?
Any reason (ignoring tire cost and rotation) not to do it?
Thanks
Rob
01-14-2019, 11:41 AM
#2
Burning Brakes
So you are currently on:
(f) 275/40-17 (25.7" total diameter)
(r) 305/35-18 (26.4" total diameter)
You need to increase the front to an 18" tire.
Option 1 - You could use either a C5 Z06 rear wheel on the front or a C5 base model rear wheel on the front.
(f) 275/35-18 (25.6" total diameter)
(r) 305/35-18 (26.4" total diameter)
Option 2 - This changes rear width only and may mess with the grip balance a bit too much for your liking. C6Z front and rear wheels. Also not sure who may make tires to fit these sizes.
(f) 275/35-18 (25.6" total diameter)
(r) 315/35-19 (26.4" total diameter)
Option 3 - Your suggestion. C6 front and rear wheels.
(f) 315/30-18 (25.4" total diameter)
(r) 325/30-19 (26.7" total diameter)
I don't really know an answer to your question, I just kinda went down a tire size rabbit hole.
(f) 275/40-17 (25.7" total diameter)
(r) 305/35-18 (26.4" total diameter)
You need to increase the front to an 18" tire.
Option 1 - You could use either a C5 Z06 rear wheel on the front or a C5 base model rear wheel on the front.
(f) 275/35-18 (25.6" total diameter)
(r) 305/35-18 (26.4" total diameter)
Option 2 - This changes rear width only and may mess with the grip balance a bit too much for your liking. C6Z front and rear wheels. Also not sure who may make tires to fit these sizes.
(f) 275/35-18 (25.6" total diameter)
(r) 315/35-19 (26.4" total diameter)
Option 3 - Your suggestion. C6 front and rear wheels.
(f) 315/30-18 (25.4" total diameter)
(r) 325/30-19 (26.7" total diameter)
I don't really know an answer to your question, I just kinda went down a tire size rabbit hole.
01-15-2019, 05:50 PM
#3
Burning Brakes
I have read many general C5 and C5 Tech posts about the need to maintain the proper rake.
And Ive read almost as many in the tracking sub forum that its ok to run square (4 identical tires and wheels = no rake). I run square, with traction control off, and with active handling disabled. No problems.
Perhaps it it is the TC and/or AH factors that you should investigate, to confirm that such mods are necessary to run square. I recall posts suggesting that, but I don’t recall a clear answer.
And Ive read almost as many in the tracking sub forum that its ok to run square (4 identical tires and wheels = no rake). I run square, with traction control off, and with active handling disabled. No problems.
Perhaps it it is the TC and/or AH factors that you should investigate, to confirm that such mods are necessary to run square. I recall posts suggesting that, but I don’t recall a clear answer.
01-16-2019, 07:46 AM
#4
Race Director
I'd drop the front 1/8" and raise the back 1/2" and forget about it. Also, just because your car frame doesn't physically have any rake, the suspension geometry still does.
Rake is good, but only critical in a car with full aero. I'm not sure if this applies to you.
Rake is good, but only critical in a car with full aero. I'm not sure if this applies to you.
01-16-2019, 05:39 PM
#5
Drifting
Thread Starter
No aero. Its a 2000 so no AH and TC turns completely off.
I've read the rear suspension is more sensitive to height changes. But who knows. Years ago I had suspension analysis software and used that with the Rx7 to see what changes were good / bad.
Originally I was going to split the difference, lower the front 1/4" and raise the rear 1/4". But then went down the path of not changing heights at all. Right now the car is very neutral. It does not push bad like several people seem to experience with their setup.
Any idea how turning the factory height adjusters affects spring pre-load? The car still has stock (Z51) springs.
Bob at House of Wheels has some forged 19 x 11 wheels at a reasonable price. I'll go through the exercise of measuring the clearance of my 18" 305's to see if a 325 NT01 with my current camber will fit w/o rubbing or sticking way out. Hell, its only 10mm wider than the 315!
Thanks
Rob
I've read the rear suspension is more sensitive to height changes. But who knows. Years ago I had suspension analysis software and used that with the Rx7 to see what changes were good / bad.
Originally I was going to split the difference, lower the front 1/4" and raise the rear 1/4". But then went down the path of not changing heights at all. Right now the car is very neutral. It does not push bad like several people seem to experience with their setup.
Any idea how turning the factory height adjusters affects spring pre-load? The car still has stock (Z51) springs.
Bob at House of Wheels has some forged 19 x 11 wheels at a reasonable price. I'll go through the exercise of measuring the clearance of my 18" 305's to see if a 325 NT01 with my current camber will fit w/o rubbing or sticking way out. Hell, its only 10mm wider than the 315!
Thanks
Rob