Speedometer change w/ 38's
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From: Roswell USA
Speedometer change w/ 38's
I have a 5-speed manual V10. I just put on some 38" tires. Haven't had a chance to put on the Truespeed and have a 2,000 mile trip ahead of me next week. Can somebody please tell me about how fast I'm really going w/ 38" tires and 3.73 gears at 2250 RPM's and it's reading 56mph on the speedometer? I took a test drive on the highway last night. These were the readings w/ the cruise control on while in 4th gear. Any input is greatly appreciated! If you have a link to a calculator that would be fine too, but I haven't seen any the give the true MPH w/ the above variables. Thanks!
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From: Back in the TX Coast
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From: Allen, Tx
Ok, the original tires were 265/75R16E's and they are 31.9" tires.
(31.9" x 100)/38"=83.95
100-83.95=16.05%
You now have a +16.05% difference in speedometer reading. So your new speed would be:
56mph+16.05%=64.988mph
3.73 with 38" tires? Does it still drive ok? You'd need 4.30's to bring it back close to factory specs. (3.73+16.05%=4.328)
Now, this is very simplified math but it worked very well for my 94 F150 with an I6-300. (Checked by a police radar no less.)
(31.9" x 100)/38"=83.95
100-83.95=16.05%
You now have a +16.05% difference in speedometer reading. So your new speed would be:
56mph+16.05%=64.988mph
3.73 with 38" tires? Does it still drive ok? You'd need 4.30's to bring it back close to factory specs. (3.73+16.05%=4.328)
Now, this is very simplified math but it worked very well for my 94 F150 with an I6-300. (Checked by a police radar no less.)
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From: Oxnard, CA
4.56 would bring it closer to the actual factory gear ratio. the truck has to drive like **** right now (i.e. gutless). tankhead... wait til you try a hill.
this is why i always say..... if you can't afford a gear change, you can't afford a lift.
this is why i always say..... if you can't afford a gear change, you can't afford a lift.
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From: Roswell USA
Not too bad in 4th @ 2250 RPM's. I could run it that way all day. Got lots of Guts at that RPM! But not from a standstill. I could regear right now IF i wanted. But I'm waiting a little longer to do it right w/ ARB's! Won't be but 3 to 4 months. Sometimes you have to wait for things you really want.
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From: IN FRONT OF YOU
Originally posted by abendx
this is why i always say..... if you can't afford a gear change, you can't afford a lift.
this is why i always say..... if you can't afford a gear change, you can't afford a lift.
I have been running the stock 3.73's with my 38's for the last year, it is a bit guttles of the line, but makes a hell of a highway cruiser.
I have a set of brand new gears sitting on the shelf, that Im to lazy to stick in, so for me it's not the problem of affordability, just a problem with motivation!!!!
But anyhow, the Truespeed is the way to go, and you can have a "stock" tire setting, so if you put the small ones back on, you just hit the switch.
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If you go to Interco's site they have a link to a speedo calc that you enter the orig. tire size(31") and the new tire size. The you enter the speedo reading and it will tell you the real reading.I like gps.Works in real time and I always know the truth. One day i'll break down and get a tru-speed.
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From: Dallas
i switch out my 38's and 35's quite often, depending on whether i will be towin much or not. This is where my truspeed has shined. Like Yeti said, you merely switch to the tire size and boom, 100% accurate speedo. It didn't take too long to install... and with a gps you can tune the thing to dead on.
I like my setup with the 3.73's just fine. When i run either my 35's or 38's it has plenty of power for whatever i am doing. No- i don't peel out with that setup.. biut then again tires cost too much to do that anyways.
If someone gave me a set of 4.30's or 4.56's i would swap it out, but until then the 3.73's with the stroker are just fine.
hmm.. that sparked an idea.. yeti you wanna sell your 4.30's?
I like my setup with the 3.73's just fine. When i run either my 35's or 38's it has plenty of power for whatever i am doing. No- i don't peel out with that setup.. biut then again tires cost too much to do that anyways.
If someone gave me a set of 4.30's or 4.56's i would swap it out, but until then the 3.73's with the stroker are just fine. hmm.. that sparked an idea.. yeti you wanna sell your 4.30's?
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From: IN FRONT OF YOU
Originally posted by 02superstroker
hmm.. that sparked an idea.. yeti you wanna sell your 4.30's?
hmm.. that sparked an idea.. yeti you wanna sell your 4.30's?
Not yet, Spring, I'll make up my mind what I'm doing with the truck, and if I get rid of it, then yes, I'll get rid of them.
Remind me in a few months
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From: Roswell USA
Thanks for all the help guys. Like I said "Any input..." It was really runnin great in 4th. I like it. I doubt I'll be using 5th too much but I'm in no hurry this trip. Somebody else had highly recommended 4.3's instead of 4.56 when I do change gears. I thought 4.56 too. But I'm reconsidering it. And using smaller tires for towing when I get the TT is another good idea. I will definately get the Truspeed when I get back though.
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From: Oxnard, CA
i run 4.56s and kind of wish i had gone to 5.38s.... not only would it have saved me some cash when i get bigger tires, but i think it'd have been better (5.38s would be slightly lower than a stocker with 4.30s).