- December 3, 2005
- Reaction score
- City, State
- New Britian, CT
- Year, Model & Trim Level
- 1991 Explorer XLT
Assuming you really have 275/35r15 tires.. Which are actually 22.6" tall... 2900 rpms may be correct..
assuming .78:1 for top gear (.75 for a4ld, .78 for 5 speed manual)...
3000 rpms with a Rear Diff of 4.10 with a trans gear ratio of .78 and transfer case in high range (1:1) would be 63mph...
3000 rpms with a rear diff ratio of 3.73 and all else above being the same would be 69mph...
Now, if you really have 235x75r15 which is a 28" tall tire.....
3000 rpms with a rear diff of 4.10, trans gear ratio of .78 and transfer case in high range (1:1) would be 78.2mph...
the same with 3.73 would be 85.9mph..
the same with 4.56 woudl be 70.3mph
BUT, if your not going into OD (assuming an auto tranny).. you would have the following..
3000 rpms, 4.10 gears 28" tire-->61mph
3000 rpms, 3.73 gears 28" tire --> 67mph
3000 rpms 3.27 gears 28" tire --> 76.5mph
I did not figure it for 22" tires since I doubt thats what you really have (and the speed would be mucher lower than for the 28" tire)..
Soo, in short.. It looks like your are either not going into OD, or lockup is not working (with an auto tranny).. If your a manual tranny, You would have to have 4.56 gears (which is not an available stock gear ratio)
BTW.. to help figure the numbers I used http://www.4lo.com/calc/gearratio.htm I filled in the tire diameter, diff ratio, rpms, and set the transmission ratio to either .78 (for od) for 1 (for no od and the transfercase ratio to 1 (high range).
Sorry, yeah, Im sick with some flu type cold right now and not thinkin straight.
Let me turn my brain on..
yes, 235/75 R15, 5 Speed... I checked a few diff speeds on the highway this eve, at 65mph, it's around 2894rpm. But there seems to be very little difference between 60-65 when it comes to engine rpm (only about 150 -200 rpm or so.)
The reason I ask, is I'm *terrible* with numbers and ratios and such.
I guess Im looking for someone to say "thats normal, or your gears are spanked"
Im assuming when you say "no od" you mean the 5 speed?
When I put that all into the calc...
I get 67mph
Thats about what my truck is doing.. 2900 rpm or so, at around 65mph.
One time I had to do about 85 for short period, and it sounded like the thing was about to blow up on me. Is there any way to regear for a better rpm range at highway speeds?