Tires

[CKOT]

Thinking about putting some new tires on my 63 GT Hawk. I like the look of the raised white letters, specifically BF Goodrich radial TAs, and the wider track/lower profile they can offer. I currently have non-stock rims on my GT, with 215-75-15s, I was thinking 215-70-15 or even 215-60-15s. Outside of changing the reading of my speedo a bit, any other major things I should look out for? The tire shop checked out my current rear clearance and said neither size would pose a problem. Any info appreciated.

[ROADRACELARK]

Depending on your rear axle gear ratio, if you go to the 205-60, your highway crusing RPM will certainly change... meaning higher RPM at say 70 MPH. Fuel consumption will also increase. Get lots of tire outside circumfrence measurements to compare to your original size tires.
Dan Miller

[N8N]

How wide are your rims and what's the offset? Personally I think 215/70s look good, but I currently have 245/60s on the back and they fit fine. How big do you want to go?

nate

--
55 Commander Starlight
62 Daytona hardtop

http://home.comcast.net/~njnagel

[blackhawk]

Chris - you asked what size tires I have on my Hawk. They are P215/65R15. Dale

[CKOT]

I believe the rims are 15x7. They are Appliance rims, chrome, with wire baskets that mount from the center caps...kind of a cheap mans version of true spoke wheels. They came with the car, I have never seen any like this before, but it gives it a realy nice look (in my opinion of course). Not sure what the offset is. I'll probably go up to 60's, currently got the datasheets from BF goodrich to compare sizes overall. Just looking for others experience going to lower profile ones.

[studegary]

On my modified '54 Starliner, the Crager S/S rims are, I believe, 8"X15". The tires are P235/60R15. The tires fit and look good. Keep in mind that my car does not have Studebaker front suspension. If your car has the original suspension, you may have interference problems. You are more likely to have a clearance problem in the front than in the rear (suspension/steering vs. sheet metal).

Gary L.
1954 Commander Starliner (restomod)
1959 DeLuxe pickup (restomod)

[hank63]

To understand how much your engine revs and speedo accuracy are affected, you need to compare the "rolling radius" of the different tyre sizes you are contemplating.
It's not difficult, the tyre shop should have the data.
The calculations are not difficult either. Work out the circumference for each rolling radius. The tyre with the smaller rolling radius will have the smaller circumference.
The circumference is the distance your tyre will travel for one complete revolution.
To travel one mile, the smaller tyre will have to rotate a few more times, which means the motor will have to do the same.
Hence, smaller tyre = higher engine revs for same distance travelled (which means more fuel).

Now, most speedo's tend to be a bit optimistic (showing higher speed than actual). With a smaller tyre you will increase this "optimism".
If you move away too far from the original rolling radius, it's probably a good idea to re-calibrate the speedo.
/H