Duetto/105 tire size conversion

[Dan Walker]

I am about to re-shoe my Duetto, and am seeking advice on tire sizes. The car has 14 inch Cromodora rims, and currently has P185 70 R14 Yokohamas mounted- they are directional, and have worked well, but are showing signs of age even though there is some good tread left. My dilemma is whether to go with the same size and profile, or find what size will closely approximate the original 15 inch tire and rim rolling diameter. I believe this will make my speedometer read closer to the actual speed I'm going- probably a good thing! Anyway, I'm open to thoughts or suggestions, and would like to get others' experience with converting from 15 inch to 14 inch rims, problems with rubbing, what would be too wide, etc. I really like the Cromodoras on the car- thanks for any input! Here's a shot of one of the wheels off the car when I was putting the car back together after paint and another of the car as she sits today......

[Peter]

the size you have now is actually pretty close to stock size, and a size commonly used on our Spiders. Check out this tire size calculator to find out what would work best:
Tire size calculator

[Dan Walker]

Quote:

Originally Posted by Peter the size you have now is actually pretty close to stock size, and a size commonly used on our Spiders. Check out this tire size calculator to find out what would work best: Tire size calculator

[Wille R.]

Here is a site that helps determine the tire size: http://www.veloce.se/MECH3.HTM on a Duetto.

Cordially Wille R.

[Dan Walker]

The original tires that came with the Duetto were listed as 155-15- I guess back then they didn't figure in the profile of the tire like they do today. If the profile was about 75 (i.e. 155/75-15), then the current 185/70-R14's would be about the right circumference. I was just wondering because I suspect my speedometer reads incorrectly- I believe it reads higher than my actual speed, but I'll have to confirm this with my wife following me and comparing speeds with her Camry, which I know is correct (verified by an Arizona DPS officer and his radar gun!). Does anyone know if the old tires were 75, 80 or some other profile? Thanks again- the calculators are pretty cool!

[101/105guy]

All of these had speedos that read high right off the showroom !!

[conedriver]

Dan,

I think the old tire sizes were 78 series. The original high performance tires were advertised as 70 series. You don't really need the profile section of your original tires, just use one of the tire calulators to compare the existing diameter to your other tire options. Also, the original Duettos had 15 in. rims so diameter shouldn't be a problem. On the other hand, my square tail Spiders were more critical of rear tire width and wheel offset. The first rubbing I remenber was on the inside of the rear, which is cureable by a wheel spacer. My next experiment in additional width caused rubbing inside of the rear wheel opening which was not as easily fixed (I flattened the inside flange with gentle hammer blows, which I suspect you are not about to do).

Quote:

Originally Posted by Dan Walker The original tires that came with the Duetto were listed as 155-15- I guess back then they didn't figure in the profile of the tire like they do today. If the profile was about 75 (i.e. 155/75-15), then the current 185/70-R14's would be about the right circumference. I was just wondering because I suspect my speedometer reads incorrectly- I believe it reads higher than my actual speed, but I'll have to confirm this with my wife following me and comparing speeds with her Camry, which I know is correct (verified by an Arizona DPS officer and his radar gun!). Does anyone know if the old tires were 75, 80 or some other profile? Thanks again- the calculators are pretty cool!

[Dan Walker]

Quote:

Originally Posted by 101/105guy All of these had speedos that read high right off the showroom !!

[Dan Walker]

Quote:

Originally Posted by conedriver Dan, I think the old tire sizes were 78 series. The original high performance tires were advertised as 70 series. You don't really need the profile section of your original tires, just use one of the tire calulators to compare the existing diameter to your other tire options. Also, the original Duettos had 15 in. rims so diameter shouldn't be a problem. On the other hand, my square tail Spiders were more critical of rear tire width and wheel offset. The first rubbing I remenber was on the inside of the rear, which is cureable by a wheel spacer. My next experiment in additional width caused rubbing inside of the rear wheel opening which was not as easily fixed (I flattened the inside flange with gentle hammer blows, which I suspect you are not about to do).

[101/105guy]

with the combo on my Duetto:
14x6 wheels and Mischelin Harmony tires.
I know others will scoff at the "all season" rating, but they work very well, are affordable and look just right with Centerline red springs.
Randy

[Dan Walker]

Quote:

Originally Posted by 101/105guy with the combo on my Duetto: 14x6 wheels and Mischelin Harmony tires. I know others will scoff at the "all season" rating, but they work very well, are affordable and look just right with Centerline red springs. Randy

[101/105guy]

Thanks Dan !
Yes, they are Campy wheels. Hard to find in the 105 bolt pattern, but I really like them !
I really like the Michelin Harmony tires. I too do not autocross or race, so they are perfect. Very grippy compared to the old style radials and much better than the Dunlops on my Super. In spirited street driving, I haven't got a squeel or slip out of them yet.
Another good thing about them is price. Got them on sale for about $60 each !
Randy