EMIRA Custom wheels Size

[finny76]

I'm planning to order some EMIRA wheels, but want to slightly modify the front wheel size/width for a staggered look.

FACTORY SIZE

Front: 8.5J x 20 ET57

Rear: 10.5J x 20 ET54

Factory Wheels are all 20" Non staggered.

MY CUSTOM SPECS

Front: 9J x 19 ET52

Rear: 10.5J x 20 ET54

All I am doing is changing the front wheel from 20" down to 19" and then making the wheel 0.5" wider for a staggered look.

I used the following calculator to get the offset as close to factory

https://www.willtheyfit.com

 

[Porter]

Why ET 52?

 

[finny76]

Why ET 52?

Per the offset calculator if i increase the width of the front wheel from 8.5 to 9, I would need to adjust the ET from 57 to 52 to make sure there is enough clearance and as close to factory.

 

[Time2Fly]

If I were doing it I would change the rear to a 19 as well for more sidewall, but your way sounds okay. Why 9 instead of 8.5? I assume you checked to make sure the tires you want are available for 9s but not for 11s in the back?

 

[finny76]

If I were doing it I would change the rear to a 19 as well for more sidewall, but your way sounds okay. Why 9 instead of 8.5? I assume you checked to make sure the tires you want are available for 9s but not for 11s in the back?

Since I'm transitioning from 20" to 19", I'll only have to swap out the front tires with the new wheels.

The rear tires have the same specs, so they should fit perfectly without any changes.

 

[Porter]

Per the offset calculator if i increase the width of the front wheel from 8.5 to 9, I would need to adjust the ET from 57 to 52 to make sure there is enough clearance and as close to factory.

That's doing the math for inner clearance (to the suspension) and maintaining the factory gap there.

I think in order to optimize this, you'll need to know how much room you actually have between the rim/tire and the suspension components.

Ideally for a 9" wide wheel l think you'd want to get your scrub radius (center of turning axis) as close to zero as possible, so that the center of the track doesn't change compared to the factory tuning. Increasing the scrub radius (moving the wheel/tire outward) will increase the perceived weight of the steering and change how it feeds back information from the road to the driver's hands.

With a zero scrub radius change and 9" width, I'm calculating a retention of the 57mm offset. That moves the inner wheel/tire surface inward by 6mm toward the suspension, and also 6mm outward toward the fender. If you have the room on both sides, that's a good solution. Here's a zero scrub radius example: https://www.wheel-size.com/calc/?wh...40-19X9ET57&fcl=50mm&wcl=30mm&scl=50mm&sr=0mm

If you don't have the clearance inboard but you do outboard, you'd want a lower offset as your math indicated, something like an ET54 or ET52, depending on how much clearance you really need inboard. Here's a conservative example that would probably be workable on the actual car even if the factory inboard clearance was relatively tight: https://www.wheel-size.com/calc/?wh...40-19X9ET54&fcl=50mm&wcl=30mm&scl=50mm&sr=0mm

If you do have the clearance inboard but you don't outboard, you could go to a higher offset like an ET60 if necessary, but that's not typically encouraged since it tends to make the steering lighter.

 

[wallstbear]

That's doing the math for inner clearance (to the suspension) and maintaining the factory gap there.

I think in order to optimize this, you'll need to know how much room you actually have between the rim/tire and the suspension components.

Ideally for a 9" wide wheel l think you'd want to get your scrub radius (center of turning axis) as close to zero as possible, so that the center of the track doesn't change compared to the factory tuning. Increasing the scrub radius (moving the wheel/tire outward) will increase the perceived weight of the steering and change how it feeds back information from the road to the driver's hands.

With a zero scrub radius change and 9" width, I'm calculating a retention of the 57mm offset. That moves the inner wheel/tire surface inward by 6mm toward the suspension, and also 6mm outward toward the fender. If you have the room on both sides, that's a good solution. Here's a zero scrub radius example: https://www.wheel-size.com/calc/?wh...40-19X9ET57&fcl=50mm&wcl=30mm&scl=50mm&sr=0mm

If you don't have the clearance inboard but you do outboard, you'd want a lower offset as your math indicated, something like an ET54 or ET52, depending on how much clearance you really need inboard. Here's a conservative example that would probably be workable on the actual car even if the factory inboard clearance was relatively tight: https://www.wheel-size.com/calc/?wh...40-19X9ET54&fcl=50mm&wcl=30mm&scl=50mm&sr=0mm

If you do have the clearance inboard but you don't outboard, you could go to a higher offset like an ET60 if necessary, but that's not typically encouraged since it tends to make the steering lighter.

quick question - do you normally worry about rim rubbing or tire rubbing in this situation?

 

[Porter]

quick question - do you normally worry about rim rubbing or tire rubbing in this situation?

It depends entirely on the car and on the design of the suspension and wheel well, including the shape of the liner. Some cars have more clearance than others.

Generally, double wishbone cars like the Emira tend to have more inboard clearance than strut suspension cars because of the angles involved, but that's not universally true, it depends on a bunch of factors including total wheel travel.

 

[Eagle7]

I would highly recommend you wait until you get your car and get through the first 1,000 mile break-in period before making a decision like this.

Don't take this the wrong way because I'm not lecturing you, but the Emira isn't like a Honda. It's not a simple boulevard car you can rice up and it'll be fine. Did you see the Macau Grand Prix where the Emira GT4 in it's debut race destroyed the rest of the field? They swept first and second place, and it wasn't even close. In the pits was the guy who designed the Emira's suspension and chassis setup, Gavan Kershaw. He's literally legendary for his chassis skills. Years ago when GM was having trouble with the Corvette, they hired him as a consultant to come and sort it out. He's that good.

It would cost you a fortune to hire someone like that to setup your car, and you're literally getting a car he himself designed and set up. Obviously it's your car and you can do what you want, but I would hate to see you make an expensive mistake just for a "look" as you put it.

You're getting a special car, with a chassis and suspension designed and tuned by Gavan Kershaw himself. Drive it first and live with it awhile before making a drastic change like you're proposing.

 

[Speedy Emira]

I looked into buying some 18s for track use but have been put off by one of my mates who works a tech in a race team.
He said something that I hadn’t thought of which is really obvious when you think about it. Comparing the FE Emira to the GT4, the GT4 had the suspension designed from scratch to take into account the tyre size changes and uses the higher profile tyres as part of the spring capability, meaning much harder shocks can be used. If we simply used 18 inch wheels with our suspension it would handle badly and be far to soft even for fast road use.
I have now given up on the idea of changing the wheel sizes.
It wouldn’t be the first time I’ve done a mod just to reverse it later but hopefully this time I will make better decisions.