Tire/wheel (basic) question

[Lipton]

Mine is a very basic question. I've been working with Terrance (great guy btw) on wheels and tires.
My '25 BW could be here next month.
I mentioned to Terrance that my goal was to minimize the gap between the top of the title and wheel well (w/o using lowering springs) at this time. So we decided on the following.
295/30ZR/20 (frt) & 315/30ZR/20 (Rear)
Riding on his SC304S (2pc) 20" 10"(frt) &
20" 11" (rear).
Will the above accomplish my goal reducing gap from stock w/o lowering springs with absolutely no drivability issues. Or do you go with 19" aftermarket wheels mentioned above and retain stock tires and use lowering springs to accomplish the narrower gap?
My car will Not be tracked. This is purely aesthetics (I've got a 427 Corvette if I want to track, etc...). Here's the wheel I'm going with.
Thank you for your input.
Steve.

 

[sps4runner]

Short answer:

Will the above accomplish my goal reducing gap from stock w/o lowering springs with absolutely no drivability issues.

Yes & not sure.

Longer answer:
Presuming the larger tires are also Pilot sport 4Ss, then yes it will reduce the gap. The 315/30/20s are 1.2" larger diameter so the gap should be .6" less. Wouldn't expect any issues rear but unsure about any rubbing issues front; prob. depends on offsets of new wheels.
Also understand thar speedometer will be a little off. Prob. indicate 60 mph but you'd be going 62.77 mph.

Actually, fronts are only about .4" difference in dia. so only about 1/4" change in apparent gap. A 295/35/20 front would be a 1.5" diff. so .6" less gap. Again, don't know about rubbing issues (when turning).

Put some trust in Terrance: has that combo been used on other CT5s without issue?

 

[PrimeTime]

@sps4runner has covered some of the important math with profile and fitment consideration. Nice write up.

How much visual difference one can make out in a 30 vs 35 profile front to rear in fender gap may be minimal? IDK?

Terrance certainly can give you some good advice based on what he's already tried and tested on his own 5BW.

My fitment was perfect for me with the fender flares and the flush fitment. No issues or poke....except at the bottom of the front and rear panels.

That's just the design of the car as we know....you can PPF that area or, like some of here search for some flaps that will both function and look good. 4BW has some options out there, 5BW is a little tougher so far. Terrance, you listening?

We spoke at length on a few occasion before I was sure of what I was getting in my setup for my 5BW.

If eating up the fender gap is important to you, then the geometry of the springs may also need to be considered in addition to your wheel and tire profile.

I think what's somewhat forgotten IMO is both Swift and Eibach put some time, money and testing in the design of these springs with the factory dampers specifically for the 5BW. So it's not a "thrown" out there and see if it sticks product for the car by any means.

The fact that there is limited production of these cars certainly supports my thinking. It's not a huge market right? If it goes wrong everyone interested will know....I cut several springs in the driveway with a torch back in the day!

These springs for the BW's are NOT that for sure.

That said, Caddy Engineers designed the best possible for these cars in the boiler room. Enough said there.

I'm not sure if you can get the visual effect of the fender gap with just tire and wheel profile....I'm not an expert by any means.

BTW, those wheels were on my short list! Good eye IMO..... Love those wheels! Not sure if this helps, I can share is my experience with Terrance and Sig Performance .

Terrance gets back with me on questions about my wheels and tires long after that check has cleared. True, important to me.

Good luck, keep us posted on your choices, welcome to the family! You picked a fantastic car!

 

[Lipton]

Thank you for the great responses. Tomorrow I have a call with Terrance. My main question will be is it better to use 19" (the wheels I posted from Terrance) and use Swift springs on stock tires or 20"s w/ new tires to achieve a smaller / tighter gap with (obviously) no drivability issues (i.e. rubbing, etc..). I've already have a standing appt with my local guy for PPF, ceramic, paint correction, window tinting.
Fyi. My 25BW CT5-V is Radiant Red Tintcoat. Wheel I selected is 2 PC, brushed aluminum, w/polished chrome lip and black hardware. My wife calls it the "tree branch" (we both think it looks pretty nice. Car will also have the optional carbon ceramic brake pkg. I think this should look good. Opinions? I'm an old school (62 yr old g-guy) so I'm not a fan of black wheels.

 

[ngoni]

You chose the correct car color. Everything else is gravy.

 

[Lipton]

@sps4runner has covered some of the important math with profile and fitment consideration. Nice write up.

How much visual difference one can make out in a 30 vs 35 profile front to rear in fender gap may be minimal? IDK?

Terrance certainly can give you some good advice based on what he's already tried and tested on his own 5BW.

My fitment was perfect for me with the fender flares and the flush fitment. No issues or poke....except at the bottom of the front and rear panels.

That's just the design of the car as we know....you can PPF that area or, like some of here search for some flaps that will both function and look good. 4BW has some options out there, 5BW is a little tougher so far. Terrance, you listening?

We spoke at length on a few occasion before I was sure of what I was getting in my setup for my 5BW.

If eating up the fender gap is important to you, then the geometry of the springs may also need to be considered in addition to your wheel and tire profile.

I think what's somewhat forgotten IMO is both Swift and Eibach put some time, money and testing in the design of these springs with the factory dampers specifically for the 5BW. So it's not a "thrown" out there and see if it sticks product for the car by any means.

The fact that there is limited production of these cars certainly supports my thinking. It's not a huge market right? If it goes wrong everyone interested will know....I cut several springs in the driveway with a torch back in the day!

These springs for the BW's are NOT that for sure.

That said, Caddy Engineers designed the best possible for these cars in the boiler room. Enough said there.

I'm not sure if you can get the visual effect of the fender gap with just tire and wheel profile....I'm not an expert by any means.

BTW, those wheels were on my short list! Good eye IMO..... Love those wheels! Not sure if this helps, I can share is my experience with Terrance and Sig Performance .

Terrance gets back with me on questions about my wheels and tires long after that check has cleared. True, important to me.

Good luck, keep us posted on your choices, welcome to the family! You picked a fantastic car!

So to keep it simple. Would keeping the new wheels (from Terrance i.e. SV304S) at 19" and then lower with Swift springs accomplish tightening up the gap. Actually less expensive to buy lowering springs then 4 new Michelin Pilot 4S. Correct?

 

[PrimeTime]

So to keep it simple. Would keeping the new wheels (from Terrance i.e. SV304S) at 19" and then lower with Swift springs accomplish tightening up the gap. Actually less expensive to buy lowering springs then 4 new Michelin Pilot 4S. Correct?

Short answer, yes.

I put a 30/ZR20 profile tire all the way around and went wider on the front and back tires 295 & 315. I was spending the extra cash on the PS4's to get the look I wanted.

Keep in mind the OEM front tires are 35 profile so there may be a slight visual difference in the fender gap there.

Id ask Terrance to see if he has pictures of a lowered 5BW with 19" wheels so you can get an idea of what it may look like. Its gonna be pretty low.

I always considered 20" from the start for show and I left my 19" in storage for track days.

Good luck. Post pics if you would when you set her up.

 

[1Evil55]

So to keep it simple. Would keeping the new wheels (from Terrance i.e. SV304S) at 19" and then lower with Swift springs accomplish tightening up the gap. Actually less expensive to buy lowering springs then 4 new Michelin Pilot 4S. Correct?

Less expensive to buy the springs. You still need to either install or have them installed($$$) and then an alignment for another couple hundy. Without doing the math, springs is still probably less. I'll let others talk about the changes in handling characteristics.

 

[Lipton]

Less expensive to buy the springs. You still need to either install or have them installed($$$) and then an alignment for another couple hundy. Without doing the math, springs is still probably less. I'll let others talk about the changes in handling characteristics.

I read where 20" wheel are on option on the 2025 CT5-V Blackwing. By this "logic" then putting 20"s on should pose no problems, correct?

 

[Lipton]

I read where 20" wheel are on option on the 2025 CT5-V Blackwing. By this "logic" then putting 20"s on should pose no problems, correct?

 

[MDM]

View attachment 29630

The 20's shown in the above pic are for the regular CT5, non Blackwing model. The Blackwing is only available with 19's from the factory.

 

[FLYARMY]

Here is an old school question. Back in the day if you changed the diameter of the wheel and tire, it would throw off the speedometer. Do modern cars have electronic computers for the speedometer that the diameter of wheel/tire does not have an effect ?

 

[brewski]

Here is an old school question. Back in the day if you changed the diameter of the wheel and tire, it would throw off the speedometer. Do modern cars have electronic computers for the speedometer that the diameter of wheel/tire does not have an effect ?

Most cars you can reprogram the diameter. But you'll find that a minor size change isn't needed (like if you went from a 305 to 315 width on a 30 profile tire). If you go larger wheel, then you reduce your aspect ratio to have the sidewalls of the tire reduce in line with the wheel increase.

I've also found most modern cars are programmed slightly before actual OD from real world testing I've done using a 10mile measured mark. My assumption is that they don't mind being below the speed the speedo reads, but if you were to be going faster than speedo says on factory tires then it might leave them vulnerable for lawsuit.

 

[Lipton]

The 20's shown in the above pic are for the regular CT5, non Blackwing model. The Blackwing is only available with 19's from the factory.

Are you sure? This is the Cadillac website. See pic

 

[brewski]

Are you sure? This is the Cadillac website. See pic

you're looking at an AI overview, not the actual website.

the CT5-V has a 20in option, but the Blackwing only has 19in option from factory

Edit
Went to the website to find where the AI was erroneously grabbing info. Here you go.

 

[PrimeTime]

Caddy.com

Try the build and buy configurator for 5BW, with 20". Not an option, not sure where this^^^^ is from? AI strikes again!

 

[brewski]

Caddy.com

Try the build and buy configurator for 5BW, with 20". Not an option, not sure where this^^^^ is from? AI strikes again!

On Cadillacs website the Blackwing and regular CT5-V are discussed on the same page since they are both CT5Vs. They do not have separate webpages for info on them. And AI sees it’s the website for Blackwing but can distinguish that the 20in wheel option is only for CT5V and not the CT5V BW.

This all comes back to a confusing naming concept. The V used to be the top performing trim, now it is the V Blackwing trim… which I personally love the name Blackwing but it’s a mouth full to say CT4V Blackwing or CT5V Blackwing.

 

[beamon]

Personally, I would get the 20” wheels and tires to get the look you desire plus the wheels will look killer on the car. The problem with lowering springs at older age is getting in and out of a lower vehicle as well as increased potential to scrape carbon fiber splitter. Just my $0.02.

 

[MDM]

Yes, very sure. This is out of the actual dealer order system.

 

[hawk02]

Going with a 20-inch wheel is going to add unsprung mass just for aesthetics. For better performance and handling you should be going in the opposite direction and reducing as much unsprung mass as possible.

I would stick with 19-inch wheels and lowering springs if it were my car to keep weight in the same ballpark.

If it were my car, I'd skip the lowering springs and just get lighter 19-inch wheels.