Tom
I never liked working with rolling radius or tire diameter. They are
vague terms, IMO, due to tire wear, the tire manufacturer and other factors.
I prefer to measure the circumference and work from that number. The
radius or diameter of a tire can be difficult to measure but the
circumference is not.
Getting an accurate speedometer reading depends on the tire size, the
gearing, the speedometer you have and the gear ratio on the speedometer
cable.
Ron Fraser
-----Original Message-----
From: Tom Parker [mailto:tkparker1941@gmail.com]
Sent: Sunday, July 04, 2010 6:00 PM
To: rfraser@bluefrog.com
Cc: wsamouce; tigers@autox.team.net
Subject: Re: [Tigers] Gas milage with different tires?
I went scurrying to the workshop manual. The original Tiger tires were
listed as 5-90x 13 with a rolling radius of 11.5 inches (Diameter 23
inches). I'm not interested in mileage necessarily, more interested in a bit
more ground clearance, so I was shooting for a diameter @ 24". I could
probably get some of that with new springs, but I need the tires anyway;
mine are thirty years old.
Either way if you go to a larger tire the speedometer will be off by a bit ,
but I'm sure there are shops that can calibrate it for me (Nisonger does
it). Anyhow, a 22 or so inch diameter tire will run at a somewhat higher
engine speed than a 24" tire. Wiki tells me C = Pi x D, so a tire with a 22
inch diameter rolls a bit more than 69 inches per revolution, a 23 inch
diameter tire rolls @ 72 1/4 inches per revolution,a 24 inch diameter tire
rolls a bit less than 75 1/2 inches per revolution.
I'll leave it to the engineers to complete the calculations, but it would
appear at first glance that going from a 23 inch diameter tire to a 24 inch
diameter tire isn't going to save you a lot of gas.
Tom
' 67 Mark 2
_______________________________________________
Tigers@autox.team.net
Donate: http://www.team.net/donate.html
Archive: http://www.team.net/archive
Forums: http://www.team.net/forums
|