Question for suspension Gurus re Scrub Radius and Offset for CTR

Dave B

Senior Member
First Name
Dave
Joined
Oct 19, 2019
Messages
148
Reaction score
68
Location
Whitby On Canada
Car(s)
Corvette Z06 (sold) 2020 CW
Country flag
I gather that the scrub radius on CTRs is a very small number, something like 1-2 mm negative and that this is an issue with buying wheels with lower than a 60 mm offset. Wondering about 2 possible cures when buying 18" rims.

If the replacement tire is shorter than the OEM tire, does this not add more negative scrub radius to allow a more positive offset wheel?

Also if negative camber is added at the top of the strut, doesn't this do the same thing i.e add negative scrub radius?



Advertisement


 

.grimace

Senior Member
First Name
Byron
Joined
Nov 9, 2017
Messages
1,352
Reaction score
896
Location
Reno, NV
Car(s)
2017 CTR, 2014 911 4S, 2019 Range Rover, 2018 F-JuanFitty
Country flag
You’re over thinking this. Let me guess you read the article saying changing to 18s or more specifically a lower offset will induce torque steer? It doesn’t just throw on some 18x9.5” +45 wheels and enjoy. Literally nothing to worry about
 

LURK-R

Senior Member
Joined
Oct 24, 2019
Messages
195
Reaction score
181
Location
PHX
Car(s)
Civic Hatch
Country flag
OP

Dave B

Senior Member
First Name
Dave
Joined
Oct 19, 2019
Messages
148
Reaction score
68
Location
Whitby On Canada
Car(s)
Corvette Z06 (sold) 2020 CW
Country flag
  • Thread starter
  • Thread Starter
  • #4
Thanks for the quick reply guys. Yes, I had read the Road and Track article and some of it makes sense. OTOH, they didn't discuss any other factors such as camber or tire diameter which also should, in my opinion, have a role to play. (Shorter tire should shift the scrub radius to the negative I think). I am really glad to hear you guys were ok with 45 mm offset. These would be for track use only and I would hate to damage the CTRs stability under braking.
 

.grimace

Senior Member
First Name
Byron
Joined
Nov 9, 2017
Messages
1,352
Reaction score
896
Location
Reno, NV
Car(s)
2017 CTR, 2014 911 4S, 2019 Range Rover, 2018 F-JuanFitty
Country flag
There are thousands of us tracking these on 18s even people with +35 or +38 you will feel zero change. In fact the 18s offer stickier tire choices so on a nice RE71r or such you’ll brake better, turn better and accelerate better never noticing a thing.
 

LURK-R

Senior Member
Joined
Oct 24, 2019
Messages
195
Reaction score
181
Location
PHX
Car(s)
Civic Hatch
Country flag
If you have a dedicated track wheel/tire package, then you're really setting yourself up well. You can drive it in stock form, on the streets and not mess with the handling as Honda engineering intended it to be. When you want to "mess up the handling" and go faster than the way Honda engineering intended it to be, you can get some 18s with a "bad" offset and some sticky tires. In my opinion, the Road & Track article reads from the perspective of say an engineer who in theory/on paper is correct. However, it's no accident that those who are actually testing said theory are faster on 18s. Still an interesting discussion to have.
 
OP

Dave B

Senior Member
First Name
Dave
Joined
Oct 19, 2019
Messages
148
Reaction score
68
Location
Whitby On Canada
Car(s)
Corvette Z06 (sold) 2020 CW
Country flag
  • Thread starter
  • Thread Starter
  • #7
Agree that what sometimes doesn't look so good on paper can work really well in reality. Personally, I think having 20" rims with all the extra wgt entailed is just stupid. My only concern with 18" rims is does this allow for enough air to escape the rotor to keep the brake temps down and do I need to come up with some functioning brake ducts.

As for tire choices, there are a bunch but the tire/wheel combo in 18" size is going to be way lighter than any 20" combo so it is a no brainer to use the 18s.

BTW, how much neg camber can you get from just after market strut tower mounts? I would have thought that the actual spring rate for the CTR must be relatively soft given that the effective suspension travel from the OEM 20" tire must be pretty small and the tire itself must be pretty stiff. To me this implies the need for a fair bit of negative camber.
 

tinyman392

Senior Member
First Name
Marcus
Joined
May 21, 2018
Messages
2,324
Reaction score
1,354
Location
Illinois
Car(s)
'18 Civic Type R (RR)
Country flag
I gather that the scrub radius on CTRs is a very small number, something like 1-2 mm negative and that this is an issue with buying wheels with lower than a 60 mm offset. Wondering about 2 possible cures when buying 18" rims.

If the replacement tire is shorter than the OEM tire, does this not add more negative scrub radius to allow a more positive offset wheel?

Also if negative camber is added at the top of the strut, doesn't this do the same thing i.e add negative scrub radius?
If you want absolutely 0 torque steer, then you could go about and buy a set of rims that are 18x8.5 +60 5x120 rims and it should not have much of an adverse affect on the torque steer of the car. You'll get all the benefits of an 18" rim (possibly lighter, mass more centered, etc.) which can lead to faster lap times (as people have seen) due to more responsive acceleration (brake, gas, turn) and less parasitic power loss (there was a test on a V8 Camaro that showed +1HP per pound lost on the rims, for an FF drivetrain this number might be higher).

However, if you decide not to keep that +60 offset, then you will get a little torque steer in the car. It's definitely there and something I do feel with my 18x8+42 rims. The thing is, the amount of torque steer is so minor it barely makes any difference unless you're doing a very strong launch on the vehicle. I do feel the weight of the wheels impacting the vehicle (positively, since my rims are 20lbs per corner vs 30lbs stock) as well. Note I do not track the car myself, so I can't tell you the impact it has there. But in everyday driving you get the slightest hint of torque steer, but it's nothing crazy.
 

tinyman392

Senior Member
First Name
Marcus
Joined
May 21, 2018
Messages
2,324
Reaction score
1,354
Location
Illinois
Car(s)
'18 Civic Type R (RR)
Country flag
Agree that what sometimes doesn't look so good on paper can work really well in reality. Personally, I think having 20" rims with all the extra wgt entailed is just stupid. My only concern with 18" rims is does this allow for enough air to escape the rotor to keep the brake temps down and do I need to come up with some functioning brake ducts.

As for tire choices, there are a bunch but the tire/wheel combo in 18" size is going to be way lighter than any 20" combo so it is a no brainer to use the 18s.

BTW, how much neg camber can you get from just after market strut tower mounts? I would have thought that the actual spring rate for the CTR must be relatively soft given that the effective suspension travel from the OEM 20" tire must be pretty small and the tire itself must be pretty stiff. To me this implies the need for a fair bit of negative camber.
The CTR has an air curtain that flows outside the front wheels anyways so air would have trouble escaping through the wheel opening. The air that would be cooling the brakes actually travels from an opening between the bottom of the bumper and front splitter. It is sent behind the brakes using an air deflector then out through the side vents in front of front doors.

Edit: the offset for the Mugen CTR rims are +45 or +53 (they're 20x8.5 though).
 
Last edited:

various cheeses

Senior Member
Joined
Dec 31, 2018
Messages
74
Reaction score
23
Location
NC
Car(s)
2016 Porsche Cayman
Country flag
I’ve been wondering about something - does the previously mentioned air curtain get blocked by pushing the wheels further out?
 

.grimace

Senior Member
First Name
Byron
Joined
Nov 9, 2017
Messages
1,352
Reaction score
896
Location
Reno, NV
Car(s)
2017 CTR, 2014 911 4S, 2019 Range Rover, 2018 F-JuanFitty
Country flag
If you want absolutely 0 torque steer, then you could go about and buy a set of rims that are 18x8.5 +60 5x120 rims and it should not have much of an adverse affect on the torque steer of the car. You'll get all the benefits of an 18" rim (possibly lighter, mass more centered, etc.) which can lead to faster lap times (as people have seen) due to more responsive acceleration (brake, gas, turn) and less parasitic power loss (there was a test on a V8 Camaro that showed +1HP per pound lost on the rims, for an FF drivetrain this number might be higher).

However, if you decide not to keep that +60 offset, then you will get a little torque steer in the car. It's definitely there and something I do feel with my 18x8+42 rims. The thing is, the amount of torque steer is so minor it barely makes any difference unless you're doing a very strong launch on the vehicle. I do feel the weight of the wheels impacting the vehicle (positively, since my rims are 20lbs per corner vs 30lbs stock) as well. Note I do not track the car myself, so I can't tell you the impact it has there. But in everyday driving you get the slightest hint of torque steer, but it's nothing crazy.
what tires are you running? People who say they feel torque steer and switched to 500tw POS tires always confuse me.

edit: now I feel like a dick. I see you switched to 500tw ps as3+ tires. I was just guessing but that seems to be common. Your oem tires were far more sticky than the all season tire you switched to. Commenting on torque steer with a not grippy tire is part of the issue I think. Try a sticky tire or even something close to as good as your oem and you’d change your mind
 

tinyman392

Senior Member
First Name
Marcus
Joined
May 21, 2018
Messages
2,324
Reaction score
1,354
Location
Illinois
Car(s)
'18 Civic Type R (RR)
Country flag
what tires are you running? People who say they feel torque steer and switched to 500tw POS tires always confuse me.

edit: now I feel like a dick. I see you switched to 500tw ps as3+ tires. I was just guessing but that seems to be common. Your oem tires were far more sticky than the all season tire you switched to. Commenting on torque steer with a not grippy tire is part of the issue I think. Try a sticky tire or even something close to as good as your oem and you’d change your mind
Long post ahead, a lot to deal with tread wear and why I don't trust the number normally (though Conti's numbers may actually be true, other tire setups that I've had are far from what they should be). I have a TL;DR at the end.

It's funny you mention tread wear ratings since they are part of the Uniform Tire Quality Grade (UTQG) aren't completely standardized and can't be compared against different manufacturers since each manufacturer will perform their own tests to determine the grade for each of their tires. Specifically TireRack talks about the tread wear grading stating that:

UTQG Treadwear Grades is that they are open to some interpretation on the part of the tire manufacturer because they are assigned after the tire has only experienced a little treadwear as it runs the 7,200 miles. This means that the tire manufacturers need to extrapolate their raw wear data when they are assigning Treadwear Grades, and that their grades can to some extent reflect how conservative or optimistic their marketing department is. Typically, comparing the Treadwear Grades of tire lines within a single brand is somewhat helpful, while attempting to compare the grades between different brands is not as helpful.
Basically it's up to the manufacturer to extrapolate how long they expect their tires to last. But that rating can really only be compared within a given manufacturer vs across all manufacturers since the NTSB doesn't conduct their own tests (but are free to do their own tests and fine manufacturers if tires fall below what they are stated; this setup can allow manufacturers to underrate tires).

Keep in mind that I've only used the following wheel/tire combinations with my car:
  • Continental SportContact 6 (stock) 245/30/20 (20x8.5 +60): 240 tread wear, AA traction, A temp.
  • Nitto NeoGen 245/30/20 (20x8.5 +60): 280 tread wear, AA traction, A temp.
  • Michelin PS AS3+ 245/40/18 (18x8 + 42): 500 tread wear, AA traction, A temp.
In terms of traction in the dry (70 degree day), I felt like the Conti > Michi > Nitto which kind of makes sense since the Nitto and Michi are both all-season tires. If you look at wet traction I had Conti >= Michi >> Nitto. Looking at cold traction Michi >> Nitto > Conti. If you look at cold wet/snow I felt that Michi > Nitto.

Basically to sum it up, the Michelin PS AS3+ hooked up far better than the Nittos in just about every scenario while in dry they seemed to be about equal with the Michi taking a slight edge. However, if you create an inverse relationship between tread wear and stickiness, tread wear doesn't reflect this as the Nitto would be assumed to be quite sticky in comparison having a 280 tread wear.

That being said, while I might believe Continental's rating, I definitely don't believe Nitto and Michelin's as both probably underrated the value to make their tire look more "sticky" than it actually is; Nitto underrating it more than Michelin. Also, according to the tread wear ratings the Nitto NeoGen should last 16% longer than the Conti, the Michelin 5x longer than the Conti. The official test is to last 7200 miles, so we can extrapolate from this as say that on average the Conti should last about 17k miles on average, the Nitto 20k miles on average, and the Michi lasting 36k miles on average. But, my Nitto tires came with a 30k warranty when I purchased them (looks like Nitto no longer warranties their NeoGen tires, I checked today) which would give it a "true" tread rating of about 420 and Michelin warranties out for 45k or a "true" tread ratings about 620 if the tire warranties are to be believed. Continental, unsurprisingly doesn't offer a mileage warranty on the SportContacts. Manufacturers are allowed to underrate on their ratings, so there isn't foul play here. For reference a 10k warranty on the tires might equate to a 140 tread wear rating while a 20k would equate to 280.

Considering torque steer, the Conti and Nitto both had no observable torque steer. That is, if I went max send (no slipping of the front tires) with no hands on the wheel on a flat-is road from 0-55 (nearly maxing out 2nd gear) the car tracks straight. If I go on my Michi and repeat the process the car won't track straight. The traction from my Michi and Nitto are about even when it comes to dry performance with the Michi taking a slight edge. Since the wheel setup is lighter on the Michi (about 10lbs per corner) there is more power going to the ground with the Michi setup as well.

So what have I learned from all this? Tread wear means jack when it comes to how sticky the compound is going to be and isn't a good determination of how long a tire should last (even though that's what the test is set up to do!). Using two tires that feel equally as sticky, with the differences being 20x8.5 +60 (30lb) rims and 18x8 +42 (20lb) rims, the +60 setup has no torque steer while the +42 has a marginal amount of torque steer. I'll add that if a lower offset were to make no difference in torque steer, then the stickiness of the tire shouldn't affect the torque steer to begin with.

TL;DR: tread wear ratings are either accurate or they aren't, in many of my experiences they aren't. But using two wheel setups which I felt were equally as sticky (Nitto NeoGen 245/30/20 +60 offset and Michelin PS AS3+ 245/40/18 +42 offset), the +42 setup had a slight torque steer over stock while the +60 setup had no torque steer and matched that of stock. I'll add that if a lower offset were to make no difference in torque steer, then the stickiness of the tire shouldn't affect the torque steer to begin with.

Edit: if I were to put Nitto NeoGens on my current rim setup, even with its 280 tread wear rating (No clue where the 300 cutoff came from), it'll torque steer, I'm sure of it. Unfortunately I don't have the money nor time to go about testing this.

Edit 2: I do believe there was another user on here that was running Falkens with a RPF1 (+40 offset I believe) and still experienced a little bit of torque steer. The Falkens they were running were quite sticky. The amount of torque steer experienced was slight and not an issue, but it was there. It kind of mirrors what I found with my setup.
 
Last edited:
OP

Dave B

Senior Member
First Name
Dave
Joined
Oct 19, 2019
Messages
148
Reaction score
68
Location
Whitby On Canada
Car(s)
Corvette Z06 (sold) 2020 CW
Country flag
  • Thread starter
  • Thread Starter
  • #14
Th
The CTR has an air curtain that flows outside the front wheels anyways so air would have trouble escaping through the wheel opening. The air that would be cooling the brakes actually travels from an opening between the bottom of the bumper and front splitter. It is sent behind the brakes using an air deflector then out through the side vents in front of front doors.

Edit: the offset for the Mugen CTR rims are +45 or +53 (they're 20x8.5 though).
The issue I was referring to is the gap between the outside edge of the rotor and the inside edge of the wheel. If there is limited space there, there will be limited air flow and decreased rotor cooling. Just don't know if that is significant going from a 20" wheel to an 18" wheel.

As for the tires, with 18s I would likely be using either Nitto NT01s, Yokohama A052s or possibly Bridgestone RE71Rs, all of which are much stickier than the tires mentioned here. I would have thought that might lead to more torque steer but not really sure.

In many ways, I am more concerned about the braking stability as I don't drag race the car
 

tinyman392

Senior Member
First Name
Marcus
Joined
May 21, 2018
Messages
2,324
Reaction score
1,354
Location
Illinois
Car(s)
'18 Civic Type R (RR)
Country flag
Th


The issue I was referring to is the gap between the outside edge of the rotor and the inside edge of the wheel. If there is limited space there, there will be limited air flow and decreased rotor cooling. Just don't know if that is significant going from a 20" wheel to an 18" wheel.

As for the tires, with 18s I would likely be using either Nitto NT01s, Yokohama A052s or possibly Bridgestone RE71Rs, all of which are much stickier than the tires mentioned here. I would have thought that might lead to more torque steer but not really sure.
That's something for you to find out. I would have thought the same thinking that if there is torque steer, there is a difference in torque between L-R which a stickier tire would amplify vs subdue. You'll find out if you do the setup I guess.

I'm not sure if the airflow goes into that region on the stock car, and how much of it does that. That being said, when I first saw this thread something that came to my mind was whether or not the wheels could actually act more like a heat sink now that they are closer to the heat source (brakes) and offset the issues with the airflow (if any). Though there is no real proof behind this, it's more of a thought.
 

Advertisement












Advertisement


Top