Wheel Spacers or not?
Thread Starter
Joined: Mar 2020
Posts: 591
Likes: 341
From: Northeast USA
2020 AMG GTC
Wheel Spacers or not?
I am looking for your expert advice about wheel spacer for the following scenario:
For track days I have decided to upgrade my 2020 GTC wheels from the original OEM 265/35-19” offset: 61 front, and 305/30-20” offset 46 rear, to the GTR’s lighter forged wheels with Michelin Pilot Sport CUP 2 Connect 240 tires. The new setup has 275/35-19 offset 56 front and 345/30-20 offset 52 rear.
Without spacers (rear). Both front and rear wheels sit very well within the wheel well and have good fender clearance. The setup creates a +4mm scrub radius in the front in comparison the OEM 61 offset, which is not an issue. However, there is a negative 11mm of scrub radius in comparison to the 305/30 OEM tire and the offset of 46 on the rear.
My question: Is this 11mm negative scrub added to the original scrub radius could be an issue? My understanding is that it does not have major effect when on the rear.
I know that a 15mm spacer (like the SCC 12169RT) in the rear will change the scrub radius from -11 to +4mm, but I am not a big fan of spacers. I may gain a bit of wider rear track, but other then higher load on the rear hubs, and potential balancing issues, it will definitely cause fender clearance issues over bumps.
In addition, the 2020 model has active rear-wheel steering with +/- 1.5 degree of rear axle toe change to keep in mind.
So, before I go for wheel alignment, is it safe to stay with no spacers? or should I use spacers?
Your advice will be much appreciated
For track days I have decided to upgrade my 2020 GTC wheels from the original OEM 265/35-19” offset: 61 front, and 305/30-20” offset 46 rear, to the GTR’s lighter forged wheels with Michelin Pilot Sport CUP 2 Connect 240 tires. The new setup has 275/35-19 offset 56 front and 345/30-20 offset 52 rear.
Without spacers (rear). Both front and rear wheels sit very well within the wheel well and have good fender clearance. The setup creates a +4mm scrub radius in the front in comparison the OEM 61 offset, which is not an issue. However, there is a negative 11mm of scrub radius in comparison to the 305/30 OEM tire and the offset of 46 on the rear.
My question: Is this 11mm negative scrub added to the original scrub radius could be an issue? My understanding is that it does not have major effect when on the rear.
I know that a 15mm spacer (like the SCC 12169RT) in the rear will change the scrub radius from -11 to +4mm, but I am not a big fan of spacers. I may gain a bit of wider rear track, but other then higher load on the rear hubs, and potential balancing issues, it will definitely cause fender clearance issues over bumps.
In addition, the 2020 model has active rear-wheel steering with +/- 1.5 degree of rear axle toe change to keep in mind.
So, before I go for wheel alignment, is it safe to stay with no spacers? or should I use spacers?
Your advice will be much appreciated
Member
Joined: Nov 2021
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AMG GT C Edition 50
I find it interesting that no one replied to you. This is a very active channel so I'm going to guess most commenters either didn't have experience or didn't like your setup. What did you end up doing? Another thread on spacers today. What tires did you go with for street?
MBWorld Fanatic!
Joined: Nov 2016
Posts: 1,291
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From: California
2020 McLaren 720s Spider
I dont think its going to affect your track day,
You have basically converted your parameters to a GTR set up - the cars are identical, including rear wheel steer. They just differ with weight, HP/TQ, and aero - the fenders are wider on the GTR in the front so it gives the impression that the geometry is different but its not. Just the wheel width/offset. The offset and wheels are different in the rear too but only to accommodate the added width of the wheel (11" vs 12").
You have basically converted your parameters to a GTR set up - the cars are identical, including rear wheel steer. They just differ with weight, HP/TQ, and aero - the fenders are wider on the GTR in the front so it gives the impression that the geometry is different but its not. Just the wheel width/offset. The offset and wheels are different in the rear too but only to accommodate the added width of the wheel (11" vs 12").
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‘24 BMW iX M60
As someone who’s done a fair bit of HPDE road course running I personally would never use spacers; I’d just get a set of track wheels made in the offset that gave me the results I wanted. Just something else vital that could fail.
Thread Starter
Joined: Mar 2020
Posts: 591
Likes: 341
From: Northeast USA
2020 AMG GTC
I find it interesting that no one replied to you. This is a very active channel so I'm going to guess most commenters either didn't have experience or didn't like your setup. What did you end up doing? Another thread on spacers today. What tires did you go with for street?
I had 2 separate track days and the performance was superb.
Btw, I tried the 15mm spacers at the rear: the fact that the car has rear wheel steer and 345/30-20” tire, I did get some fender rubbing while cornering over bumps.
For street, I go back to the OEM wheels and tires, 265/35-19” offset: 61 front, and 305/30-20” offset 46 rear, no spacers, still on my original Michelin Pilot Super Sport. At the end of their life, I am planning to switch to the PS4S.
Thread Starter
Joined: Mar 2020
Posts: 591
Likes: 341
From: Northeast USA
2020 AMG GTC
MBWorld Fanatic!
Joined: Nov 2016
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From: California
2020 McLaren 720s Spider
For this wheel/tire setup, I just added 5mm spacer to the rear wheels. Although I don’t like to use spacers (I care about safely and performance and no so much about aesthetics), I felt that adding a 5mm rear spacer will get the rear scrub radius to -6mm (better then the -11mm without spacer) and keep the rear track to the same width as the OEM wheel. My impression from Skilly’s comment is that there is no real performance effect with rear wheel scrub radius change. It is usually concern front wheels only. I also left the camber setups at the default setting (-2.15 front and -1.55 rear).
I had 2 separate track days and the performance was superb.
Btw, I tried the 15mm spacers at the rear: the fact that the car has rear wheel steer and 345/30-20” tire, I did get some fender rubbing while cornering over bumps.
For street, I go back to the OEM wheels and tires, 265/35-19” offset: 61 front, and 305/30-20” offset 46 rear, no spacers, still on my original Michelin Pilot Super Sport. At the end of their life, I am planning to switch to the PS4S.
I had 2 separate track days and the performance was superb.
Btw, I tried the 15mm spacers at the rear: the fact that the car has rear wheel steer and 345/30-20” tire, I did get some fender rubbing while cornering over bumps.
For street, I go back to the OEM wheels and tires, 265/35-19” offset: 61 front, and 305/30-20” offset 46 rear, no spacers, still on my original Michelin Pilot Super Sport. At the end of their life, I am planning to switch to the PS4S.
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Thread Starter
Joined: Mar 2020
Posts: 591
Likes: 341
From: Northeast USA
2020 AMG GTC
The 11mm is a scrub radius. The offset of the rear GTR wheel is 52 while the GTC OEM wheel is 46. Adding 5mm to the GTR, put the GTR wheel to offset of 47 (just 1mm off), which you are correctly stated that it's on the same plane.
Last edited by G. P; Aug 21, 2022 at 10:07 PM.
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MBWorld Fanatic!
Joined: Nov 2016
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From: California
2020 McLaren 720s Spider
That doesn't appear to be accounting for the different wheel width. The GTR wheel is a 12j ET 52 with a 325mm tire and the GTC is 11j ET46 with a 305mm tire. I agree that adding the spacer brings it to an ET47 but that seems to move it away from the OEM scrub radius geometry rather than closer to it.
Thread Starter
Joined: Mar 2020
Posts: 591
Likes: 341
From: Northeast USA
2020 AMG GTC
That doesn't appear to be accounting for the different wheel width. The GTR wheel is a 12j ET 52 with a 325mm tire and the GTC is 11j ET46 with a 305mm tire. I agree that adding the spacer brings it to an ET47 but that seems to move it away from the OEM scrub radius geometry rather than closer to it.
MBWorld Fanatic!
Joined: Nov 2016
Posts: 1,291
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From: California
2020 McLaren 720s Spider
Thread Starter
Joined: Mar 2020
Posts: 591
Likes: 341
From: Northeast USA
2020 AMG GTC
