RPM reduction with taller tire

[monkeyy337]

I'm trying to figure out how much RPM (engine) reduction I can expect in the 1/4 mile when going from a 23.9" tall rear tire to a 26.1" tall tire. Is there a formula for figuring this or if you know the answer give it up. The rearend gear is a 3:73.

[DaWildcat]

http://www.offroaders.com/info/tech-corner/reading/mph-rpm.htm

Devon

[monkeyy337]

http://www.offroaders.com/info/tech-corner/reading/mph-rpm.htm

DevonThanks DaWildcat, if I figured it correctly the RPM will drop 415 RPM. The car in question is my little TR7 (Buick V6 powered) bracket car that don't like going through the 1/4 mile traps at 4927 RPM.

[Steiner99]

I made this a while back and it's fun to play with. Mouse over the file "speed calculator" and select download.

http://cid-85e579bdb0954510.office.live.com/browse.aspx/.Documents



Screen shot:


http://farm6.static.flickr.com/5209/5222964796_a324cc2760_z.jpg

[LARRY70GS]

336/tire diameter X gear X MPH = RPM

[monkeyy337]

Ran the Buick powered TR7 tonight at Beech Bend in the street car shootout and it crossed the 1/4 mile finish line at 5000 RPM. I think it used to cross at about 5400 RPM so the bigger tires did help although they did slow the car down but its only bracket racing so doesn't matter. I ended up beating a Chevy in the finals so that is three weeks in a row that I have won the shootout with a Buick powered car even though they are V6 motors. The best pass for the little car was a 14.35 ET @ 92 mph.