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03-27-2002, 02:48 PM
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#1 |
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Registered User
Join Date: Mar 2001
Location: indianapolis,indiana,usa
Posts: 506
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can i change tire size to lower rpm @ highway speed
i have 410 gears with 27 inch tires. i am thinking about going with the bfg 285 70 15s to try and get my rpm @ 50 mph down ( its 2900 now) the 285s are about 30 to 31 inches will this help my highway rpm enough to matter. if so what will the new rpm @ 55 be. thanks
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03-27-2002, 03:12 PM
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#2 |
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Registered User
Join Date: Oct 2000
Location: St. Johns, Arizona
Posts: 2,660
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30" tire w/4.10s @ 55 = 2500 rpm (approx)
31" tire w/4.10s @ 55 = 2440 rpm (approx) ------------------ Bowen '68 K20 fleet '69 K10 swb fleet '72 C10 lwb step
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my 2¢ - t.i.o.l.i. Bowen 1968 K20 fleet 1969 K10 swb fleet 1972 K10 Suburban 1972 C10 lwb step 1992 K1500 'burb 1995 K2500 'burb 1997 C1500 'burb 1999 K1500 2000 K1500 'burb Why do I own so many Suburbans? |
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03-27-2002, 03:14 PM
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#3 |
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I need another Barley Pop
Join Date: Feb 2001
Location: Grants Pass, OR
Posts: 1,629
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Is this one of those funny math questions? lol
Yes it would help! How much, not a clue! I went from 30" tires to 35" tires with 4.10 gears and it definitely made a difference. Couldn't say how much, I'm not currently running a tach. ------------------ 67 SWB 4x4 - 396 BB / SM420 4 spd 8" lift / 15x14 Welds & 35X14.5 SSR's Grants Pass, OR
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67 Short Fleet 4x4 04 Honda CRF450R 89 Toyota 4-Runner 34 Ford 2 door sedan - Long term project ---------------------------------------------- There is a very fine line between "hobby" and "mental illness" 
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03-27-2002, 03:38 PM
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#4 |
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Wiseass secured himself a BAN
Join Date: Nov 2000
Location: MOON!!!
Posts: 2,282
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03-27-2002, 04:28 PM
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#5 |
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Account Suspended
Join Date: May 2000
Location: IL
Posts: 0
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why do you have only 27" tires on a truck anyways ?? hmm...
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03-27-2002, 04:47 PM
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#6 |
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70 Chevy 3/4t
Join Date: Sep 2000
Location: Kokomo,IN USA
Posts: 1,230
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Well, seeing ckhd's post pretty much confirms to me I have 4.56 gears.
 I run about 2950rpms at 60 mph with my inline six. I checked out the link posted also and saw that 4.11 gears would knock it down to 2500 rpms @ 60mph. Guess I'm gonna have to start saving my pennies to get new gears and have them installed. ------------------ 1971 Chevy 1/2t, 350 -- SOLD 1998 Yamaha V-Star 650 1970 Chevy 3/4t, I6(freshly rebuilt), 4 speed Keokuk,IA http://communities.msn.com/SchweringFamily/shoebox.msnw MSN Messenger = boilrman Find a job you love and you'll never have to work a day in your life.
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Find a job you love and you'll never have to work a day in your life. 1998 Yamaha V-Star 650 1970 Chevy 3/4t, I6 (rebuilt), 4 speed Kokomo,IN |
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03-27-2002, 05:14 PM
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#7 |
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Registered User
Join Date: Oct 2000
Location: St. Johns, Arizona
Posts: 2,660
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Oh, that link where you just plug in numbers is cheating! I did mine using algebra & geometry. Bookmarked it, so I could do it the easy way next time!
boilrman, I'll bet you do have 4.57 gears. That was standard in '69 C20s. Don't have the resto manual for '70 3/4 tons, but I'll bet it was the same. ------------------ Bowen '68 K20 fleet '69 K10 swb fleet '72 C10 lwb step
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my 2¢ - t.i.o.l.i. Bowen 1968 K20 fleet 1969 K10 swb fleet 1972 K10 Suburban 1972 C10 lwb step 1992 K1500 'burb 1995 K2500 'burb 1997 C1500 'burb 1999 K1500 2000 K1500 'burb Why do I own so many Suburbans? |
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03-27-2002, 05:34 PM
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#8 |
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Registered User
Join Date: Mar 2001
Location: indianapolis,indiana,usa
Posts: 506
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i got a good deal on some hooser 275 60 15. when i measured them they measured 27 in dia. strange thing is bfgs are 28 in dia. thats why i have 27 in tires
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03-27-2002, 07:37 PM
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#9 |
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Registered User
Join Date: Aug 2001
Location: rock island,il,usa
Posts: 5,382
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Im runnin 275/60s with 4.10 coggs....28" tall,& 3000 rpms @ 59 mph. Lots of fun,but not a hyway gear! ......69 longhorn.
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http://community.webshots.com/user/hotrodhorn |
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03-27-2002, 09:37 PM
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#10 |
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Registered User
Join Date: Mar 2000
Location: Granite Shoals, TX, USA
Posts: 159
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A good calculator including exact tire size is www.randysringandpinion.com
------------------ 67 Stepside 383/420 h.p. Re-Built by me again- 4-speed forsaken in favor of modified 700R4, 12-bolt 3:42 [This message has been edited by Hwy2Hll (edited March 27, 2002).]
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67 Stepside 468 BBC Built by me @ Texas Engine Machine in Llano, TX. Modified 700R4, 12-bolt 3:73 ..Exactly when did I decide that I could spend more than I make?  "The more I think about it, old Billy was right..."
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