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| | | | Joined: Dec 2010 Posts: 62 Wrench Fetcher | | Wrench Fetcher Joined: Dec 2010 Posts: 62 | I now have 215/70/15 if i increased my rear tire size to 255/70/15,with 3.55 Ring Pinion on my 1948 1/2 ton, at normal high way RPM i now go about 50 MPH.I do not have tac or working speedomiter. If increase my tire size to the 255/70/15 how much will my MPH. increase? And will the tires fit my wheelwell ? I saw that tire size on truck like mine, but i never talked to the ouner.Thanks
Last edited by oldchevyguy; 10/05/2013 3:54 PM.
| | | | | Joined: Jul 2005 Posts: 640 Shop Shark | | Shop Shark Joined: Jul 2005 Posts: 640 | It depends on the brand of tire. They're both 70 ratio tires, while the 255's are wider than the 215's. The diameter (height) doesn't necessarily change with the change in width. As for whether the 255's will fit the wheel well, I couldn't say. I have 235's on my '48 and they're fine. You haven't said what truck you have... | | | | | Joined: Sep 2001 Posts: 29,270 Bubba - Curmudgeon | | Bubba - Curmudgeon Joined: Sep 2001 Posts: 29,270 |
What is the difference in the rolling/loaded diameter of the two tires?
That % difference is the % difference to be expected in your speed/RPM.
| | | | | Joined: May 2006 Posts: 8,351 'Bolter | | 'Bolter Joined: May 2006 Posts: 8,351 | A 255/70/15 will be taller than the 215/70/15, in addition to being wider. The 215/70/15 will be approximately 26.9" tall, the 255/70/15 comes in at around 29.1". Those diameters will vary depending on brand and inflation pressure. You may also need to get wider wheels, depending on what you currently have. The 255 will work best on a 7-8 inch wide wheel.
Bill Burmeister
| | | | | Joined: Jun 2009 Posts: 1,596 'Bolter | | 'Bolter Joined: Jun 2009 Posts: 1,596 | It depends on the brand of tire. They're both 70 ratio tires, while the 255's are wider than the 215's. The diameter (height) doesn't necessarily change with the change in width. As for whether the 255's will fit the wheel well, I couldn't say. I have 235's on my '48 and they're fine. You haven't said what truck you have... 255/70/15 is a size measurement. Every tire of that size will be the same height and width, regardless of brand. Same with 215/70/15, etc. There may be slight differences depending on tread design, but that's it. | | | | | Joined: Feb 2007 Posts: 434 Shop Shark | | Shop Shark Joined: Feb 2007 Posts: 434 | There are various calculators on the world wide web around this subject, FYI. For example: http://www.currieenterprises.com/cestore/calculators.aspx#?
R-Bo
1959 Apache 1/2 ton Big Window, Short bed Fleetside (under reconstruction)
1966 GMC 305V6 in the family
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