View Full Version : Not all tires are created equal

John Kirchhoff
10-26-2006, 10:45 PM
Several times here of late the issue of what wheel width, offset and tire size best fits a certain Stude. I agree the wheel width and such is important, but what may be more so is the actual size of a tire. Not what the numbers on the side of the tire say, but the true width and height. This is nothing new to me, but as an example, the other evening I compared two tires, both 205-70X15, a Goodyear and a General. The Goodyear was slightly taller but the actual mounted and inflated widths vary considerably. At the widest part of the tires, the sidewalls, the General was 7.5" or 190mm wide and the Goodyear 8.0 inches, or 203mm. The actual tread width where the rubber meets the road was General 5.75 or 146mm, Goodyear, 6.25" or 159mm. Both tires were mounted on 5 1/2" rims with comparable air pressure. At both points the Goodyear was 13mm wider than the General. I would expect a General 215-70 of the same model tire to be closer to the 205 Goodyear in aactual width. I'm not saying all Generals are smaller than Goodyears, but one sure needs to compare the true width of economy tires of any make against the higher priced tires. This alone could be why some folks can run supposedly wider tires than others.

10-27-2006, 07:28 AM
Yeah, but how are you going to know all of this before you buy tires? I doubt the tire dealer is going to mount up several different brands on your rims so you can decide which one is the better fit.

Mark Anderson
1965 Cruiser


10-27-2006, 09:57 AM
That could be a chapter activity. Why not?

John Kirchhoff
10-27-2006, 11:08 AM
As far as knowing the size before you buy, I do know that Dunlop and Continental do or at least did publish actual cross section dimensions of different tire sizes as well as recommended rim width ranges, rolling radius, load range and so on. One of them (I forget which)even had the contact patch width based on a particular rim width. I'll have to check and see if either of them or other companies still publish such data. On the two tires I measured, the widest width of both tires was 13mm wider than the tread. Before mounting, measuring the width at the sidewalls is impractical because the rim width after mounting can change that somewhat. In addition, if the tires are stacked on top of each other, the bottom one is going to be flat as a pancake. However, the actual tread width is going to be consistant and easily measured even if a bulldozer has been parked on it. I've yet to see a tire where the actual tread is wider than the cross section width, so you can pretty well be assured that regardless of tire size or brand, the cross section will be wider than the tread. Oh oh, I need to correct myself, I actually have seen a tire with the tread wider than the cross section, a knobby tire on a dirt bike. Somehow I don't think knobbies on a R3 Studie is going to be an effecient manner of transfering horsepower to the pavement. I also bet the handling would be less than stellar.