Tire question(s)

[Gluefactory]

So car came to me with about 16k on it, and what I'm assuming is the entire FRPP track handling kit on it (1" drop?), after some googling.

It also came on these wheels, with 275/30r20s on the front and 295/30r20s on the back end.

The questions are: Can I fit some more sidewall on these things? Like 305/35s or something? I feel like I'm going to lose em to a pothole in the near future.

I'd also like to keep the speedometer accurate, as right now it's pretty spot on.

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[Rael]

I don't know the answer to your tire-size question, but the data from a change in tire-size can be input so that your speedometer will remain accurate.

 

[m3incorp]

What are your wheel widths and offsets? That will be a big determining factor. Many of us are running 275/35R20 up front and 305/35R20 out back.

 

[shadowx]

What are your wheel widths and offsets? That will be a big determining factor. Many of us are running 275/35R20 up front and 305/35R20 out back.

got the same question. For me i have 20×10 with +40 and 20×11 with +48
275/35 front. and buying between 305/30 or 305/35 rear.

if 30, the rear will be shorter than the front. if 35, the rear will be around 0.9 inch taller. so is there any problem in both cases?

I have a tuner device and can change the tire size for the speedometer, so i won't have problem with the reading.

 

[m3incorp]

Both will fit, it is just a matter of how much poke there will be. The fronts should be good to go. The rears may have a very slight poke. If you are not lowered too much, the 35 rear will work. You could go 30 on both front and rear if you are wanting to run the shorter profiles.

Are you using ForScan as your tuner to correct the speedometer for the tire sizes, or some other device?

 

[m3incorp]

Very true. I had my car in for Roush software download and the tech decided to change the value for my tire sizes. Before the speedometer was reading 2 mph slower than GPS; now it reads 6 mph slower than GPS.......good for showing less mileage lol but very bad for avoiding speeding tickets. If the dealer wasn't two hours away, I would have him change it but looks like I will have to do it myself.

I don't know the answer to your tire-size question, but the data from a change in tire-size can be input so that your speedometer will remain accurate.

 

[shadowx]

Both will fit, it is just a matter of how much poke there will be. The fronts should be good to go. The rears may have a very slight poke. If you are not lowered too much, the 35 rear will work. You could go 30 on both front and rear if you are wanting to run the shorter profiles.

Are you using ForScan as your tuner to correct the speedometer for the tire sizes, or some other device?

I have SCT BDX and I think I can adjust the tire size.

I'm not lowered yet but I'm going to lower it after I get the tires. didn’t decide yet for which lower I'm getting. which do u recommend overall 30 or 35 with 305?

 

[The Demon]

I just changed the tires on mine from 255/40/19 up front to 275/40/19 and 275/40/19 on the back to 305/30/20. I used this website to get an idea of what the speedometer will do with these changes.

https://tiresize.com/speedometer-calibration/

These were the results. I don't have Forscan or plan on getting it. Driving in California you are going 80 MPH anyways just to keep up so 1 MPH isn't going to hurt.

 

[shadowx]

I just changed the tires on mine from 255/40/19 up front to 275/40/19 and 275/40/19 on the back to 305/30/20. I used this website to get an idea of what the speedometer will do with these changes.

https://tiresize.com/speedometer-calibration/

These were the results. I don't have Forscan or plan on getting it. Driving in California you are going 80 MPH anyways just to keep up so 1 MPH isn't going to hurt.

I think the speedometer is only from the rear tires. If I'm wrong please correct me.

 

[The Demon]

I think the speedometer is only from the rear tires. If I'm wrong please correct me.

You would think so. The website only does one calculation at a time so it doesn't know if it's back or front. Coud be RWD or FWD.

 

[rxryanm]

I think the speedometer is only from the rear tires. If I'm wrong please correct me.

You would think so. The website only does one calculation at a time so it doesn't know if it's back or front. Coud be RWD or FWD.

Calculated by the drive axle. That's why Forscan asks for the tire size of the rear wheels so it can calculate speed.

 

[shadowx]

You would think so. The website only does one calculation at a time so it doesn't know if it's back or front. Coud be RWD or FWD.

I meant the error would be only on the tires

Calculated by the drive axle. That's why Forscan asks for the tire size of the rear wheels so it can calculate speed.

That what I thought about the drive axle

 

[BLUE DEVIL]

I think the front tire size & rotation rate is pertinent to the stability system. It can cause the system to engage when it should not, which can be dangerous.

 

[m3incorp]

You need to plug in 305/30/20, as the speedometer reads from the rear tires on a Mustang.

I just changed the tires on mine from 255/40/19 up front to 275/40/19 and 275/40/19 on the back to 305/30/20. I used this website to get an idea of what the speedometer will do with these changes.

https://tiresize.com/speedometer-calibration/

These were the results. I don't have Forscan or plan on getting it. Driving in California you are going 80 MPH anyways just to keep up so 1 MPH isn't going to hurt.

 

[The Demon]

You need to plug in 305/30/20, as the speedometer reads from the rear tires on a Mustang.

I don’t get what you are saying? I really don’t care about the speedometer as I go as fast as I care. What is the question?

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