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Discussion Starter · #1 ·
What is the largest diameter tire size that can be fitted on the Cruze CTD?

Consider if you get a tune installed, such as a +40hp Fleece or Trifecta tune. The tune is interesting since the power comes in about 20% sooner in the rev range or about 20% stronger at the same revs compared to the standard tune. Could you get a larger diameter tire to give you a higher effective final drive ratio?

For instance could you go from 215/55r17 to a 225/65r18 this would give you an engine speed difference of 8.5%, right?
Even though the car is riding slightly higher dropping the revs by this much should give even better fuel economy.
Sure you would not as fast accelerate from stop, and you would likely force the car to down shift more compared to the smaller tire.

So what is the largest tire you can fit in the space given?
Have I missed something important when playing with tire sizes?
 

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Have I missed something important when playing with tire sizes?
In a word: Yes.

You, and the collective knowledge of cruzetalk, know exponentially less than the boatload of engineers at GM who decided on the CTD's tire size.
 
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In a word: Yes.

You, and the collective knowledge of cruzetalk, know exponentially less than the boatload of engineers at GM who decided on the CTD's tire size.
It's not like they were thinking the best tires goes on an economy car. Way more into this that just engineering.
 

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It's not like they were thinking the best tires goes on an economy car. Way more into this that just engineering.
1) A CTD is not an economy car.

2) Any tire decision made by GM, regardless of vehicle cost, is subject to countless regulations and legal liabilities in the courts.

3) Any decision made by a private individual on their vehicle is at their own liability. Until, that is, it leads to an injury or death that then gets litigated. Read the fine print: Your auto insurance doesn't cover you for claims based on modifications you've made to your vehicle.
 

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1) A CTD is not an economy car.

2) Any tire decision made by GM, regardless of vehicle cost, is subject to countless regulations and legal liabilities in the courts.

3) Any decision made by a private individual on their vehicle is at their own liability. Until, that is, it leads to an injury or death that then gets litigated. Read the fine print: Your auto insurance doesn't cover you for claims based on modifications you've made to your vehicle.
1) What is the Cruze, and more specifically the CTD, then if it is not an economy car?

2) Proved my point that your first reply had almost nothing to do with engineering and everything to do with money

3) That's not up for debate here.


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I'm willing to bet that you will lose mileage putting bigger tires on there. The added weight/rotating mass and drag from extra width will offset any potential mileage increase from just barely dropping the rpms. Especially if the new tires arent LRR tires. Lower rpm doesn't always equal better mileage especially when you're adding weight and drag.

As far as opening yourself up to lawsuits by going with a tire that's a size up from stock, I've never heard of that and quite frankly that sounds ridiculous. Im sure there is no law out there that says that you HAVE to stay with the exact same size tire that your car came with from the factory. Most vehicles have packages that have completely different size wheels and tires yet mounted on the same car. **** you can get a Silverado with steelies and 30" tires from the factory or you can get the same Silverado with a lift, 20s and 35s from the factory. So what's the difference between the Silverado with 35s from the factory, and the one that came with steelies and then were swapped to 35s?
 

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In a word: Yes.

You, and the collective knowledge of cruzetalk, know exponentially less than the boatload of engineers at GM who decided on the CTD's tire size.
I agree that the engineers spend a lot of time/money on every aspect of vehicle design. Most of their designs are a compromise between a wide ranges of operating conditions.

An engineer could definitely do a far better job at optimizing performance than "us". However, the engineers don't get to design a 60+ mpg model for me and a 250 horsepower CTD for someone else. They only get to design one CTD for all of us, hence the compromises.

Almost every vehicle modification has a known benefit, i.e, better fuel economy, lower ride height, darker windows, better airflow, etc. These same mods have known adverse effects, i.e., less power, reduced vision, harsher ride, more noise, etc.

It is up to the individual to determine how they will utilize their particular vehicle and what they expect from it. This is where "we" know more than the engineers and can tweak our cars for our needs.




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Discussion Starter · #8 ·
My father before he died, was a well known mechanical engineer.
His statement to me was that engineering is a study in compromise.

Tomko while giving a factual answer you didn't actually answer the question. It is obvious you had nothing pertinent to say.

I only explained why someone would want larger tires to get the question of "why" out of the way. Having changed the tune of the engine the current tires may no longer be the "ideal" size for the car to get best fuel economy possible. My assumption is that since diesels get the best fuel economy at the top of the torque curve that getting lower RPM at speed should give MPG gains all other things being equal. (they NEVER are)

I could not find a tire that was 215/75R17...
 

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In a word: Yes.

You, and the collective knowledge of cruzetalk, know exponentially less than the boatload of engineers at GM who decided on the CTD's tire size.
The "Engineers" should have spent less time on the tires and more time on the emission system.
 

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The "engineers" should have started with a lighter wheel. Stock CTD wheels are beasts!!!
 

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Discussion Starter · #11 ·
I checked on the drive home and the car is actually doing 2200rpm at 75/76mph.
(Its the vue that does 2600 rpm at the same speed.)

I guess the size of tire actually fine.
Danny5 your point of the tires being heavy is a good point.

I guess if I ever get a windfall I might look into getting a much lighter set of rims.
 

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You folks jumped right into liabilities and engineering pretty quick. I was thinking that a 225-65r18 would probably rub somewhere. Like the front strut.
 

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I put some 215 65-R16 winter tires on custom alloys. Tires look a bit larger than stock in diameter, but close for sure. Not sure if it's a softer compound or taller sidewall but i instantly lost a couple mpg and car is noticeably more sluggish. I don't think a larger tire would fit without mods. I too believe you will lose more mpg with a bigger tire before the lower rpm will give you gains.
 

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I put some 215 65-R16 winter tires on custom alloys. Tires look a bit larger than stock in diameter, but close for sure. Not sure if it's a softer compound or taller sidewall but i instantly lost a couple mpg and car is noticeably more sluggish. I don't think a larger tire would fit without mods. I too believe you will lose more mpg with a bigger tire before the lower rpm will give you gains.
This is on a diesel?
 

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