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Discussion Starter #1
Hey guys, does anyone know if there's a way to adjust the speedometer/odometer if you increase wheel size? The wheel arch gap on the Classica is rather big and I'm thinking of fitting some bigger wheels to fill it up.

On older cars it seems the only thing you can do is to change the axle ratio or make some other complicated modifications... I'm hoping the Spider, being a newer car and all, can have its speedo adjusted through ECU adjustments... anyone know if this is the case?
 

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I'm not too sure how to re-calibrate it, but there are online calculators that can help you determine how much it's off by. I would expect the changes to be extremely minimal though.
 

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For legal reasons, they would never allow you to recalibrate the speedometer. Larger wheels and tires would also add more weight and cause clearance issues. Your best bet would be to simply lower the car with new springs and struts.
 

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For legal reasons, they would never allow you to recalibrate the speedometer. Larger wheels and tires would also add more weight and cause clearance issues. Your best bet would be to simply lower the car with new springs and struts.
He could install 17" wheels with lower profile tires, just like the Lusso, without affecting the calibration of the speedo, and without adding weight.
 

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For legal reasons, they would never allow you to recalibrate the speedometer. Larger wheels and tires would also add more weight and cause clearance issues. Your best bet would be to simply lower the car with new springs and struts.
Not true, several programmers for other vehicles allow for calibration, and for those that don't have programmers the dealerships can calibrate for you with a minimal fee, whether or not they will allow/do this at Fiat dealers, I do not know. I had asked about this in another thread and never got a response.
 

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For legal reasons, they would never allow you to recalibrate the speedometer. Larger wheels and tires would also add more weight and cause clearance issues. Your best bet would be to simply lower the car with new springs and struts.
Unless maybe there's a chance we can get that done at an independent shop, some which I doubt would have a problem with doing it. Worth the try.
 

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Discussion Starter #7
Not true, several programmers for other vehicles allow for calibration, and for those that don't have programmers the dealerships can calibrate for you with a minimal fee, whether or not they will allow/do this at Fiat dealers, I do not know. I had asked about this in another thread and never got a response.
I contacted my dealership today and they weren't willing to do it. Maybe they'd do it if I told them the speedo is off without mentioning about the bigger wheels. >:)

He could install 17" wheels with lower profile tires, just like the Lusso, without affecting the calibration of the speedo, and without adding weight.
Yeah, Lusso-sized tires are what I'm actually thinking of getting, though they actually would throw off the calibration by a little since they're 2.5% larger than Classica tires in OD. It's not that big of a deal really... in practice at least... it's just that exasperating feeling that your car is not perfect anymore! :mad:

I don't suppose there's such a thing as a universal programmer that can work with any ECU, is there? So for independent shops to do the calibration they would actually have to order the programmer for the 124 Spider first, right?
 

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He could install 17" wheels with lower profile tires, just like the Lusso, without affecting the calibration of the speedo, and without adding weight.
I took that he wanted larger wheels and tires to fill the wheel arch gap as he stated;

"The wheel arch gap on the Classica is rather big and I'm thinking of fitting some bigger wheels to fill it up."

That would necessitate more weight.
 

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I'm finding that the Classica's speedometer is running a little high from reality so if the OP wanted to get 17" wheels and whatever tires the Lusso is running, his speedometer might actually be closer to realty if the Lusso tires are a little larger in diameter.
 

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Discussion Starter #15
I'm finding that the Classica's speedometer is running a little high from reality so if the OP wanted to get 17" wheels and whatever tires the Lusso is running, his speedometer might actually be closer to realty if the Lusso tires are a little larger in diameter.
I've measured the speedometer against the GPS before and the speed reading is around 1.3% above GPS speed. With 2.5% larger tire OD on 17" wheels, the speedo would under-report the speed.

The bigger issue is the odometer. If I'm not mistaken, manufacturers intentionally make speedos over-report the speed, but keep odometers accurate. With larger tires, the odometer would be off, and that would in turn throw off fuel economy calculations and maintenance scheduler reminders. It would be good if you want to sell the car though since the odo would under-report mileage. Kinda dishonest though.
 

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little different from original issue.
but I'm considering to change wheels from 16 to 17.
What should be the offset on the wheels and tire width?
 

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I've measured the speedometer against the GPS before and the speed reading is around 1.3% above GPS speed. With 2.5% larger tire OD on 17" wheels, the speedo would under-report the speed.

The bigger issue is the odometer. If I'm not mistaken, manufacturers intentionally make speedos over-report the speed, but keep odometers accurate. With larger tires, the odometer would be off, and that would in turn throw off fuel economy calculations and maintenance scheduler reminders. It would be good if you want to sell the car though since the odo would under-report mileage. Kinda dishonest though.
I'm willing to bet that the two cars don't have different calibrations between the Classica and Lusso wheels and tires. You're looking at a 1.3% or smaller error to either side of accurate. As the Classica's tires wear, the error grows and as the Lusso's tires wear, it becomes more accurate. It's trivial in the end. I had motorcycles that over-report speed by more than 7%.
 

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There is no easy way to re-calibrate the speedo. Vehicle speed is calculated from the wheel sensors, not the transmission. It may be possible to manipulate the signal driving the speedo, but there could be unexpected side effects.
 

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I took that he wanted larger wheels and tires to fill the wheel arch gap as he stated;

"The wheel arch gap on the Classica is rather big and I'm thinking of fitting some bigger wheels to fill it up."

That would necessitate more weight.
Not necessarily more weight. There are 18" wheels that weight less than 17 pounds and tires to fit that would be in the 19 to 20 pound range. I'm not sure what the wheel and tire combination on the Classica weigh, but I'm betting it's more than 37 pounds.
 
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