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PostPosted: Thu Dec 14, 2006 8:08 pm 
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Searched, but couldn't find the answer...

I'm trying to do some engine RPM calcs based on the XFi's OEM tire size.

But 1) I'm not 100% sure what the OEM tire size is (I think it's 145R12).

And, 2) if that's it, why no aspect ratio in the sizing?? I can't figure out the diameter / circumference without aspect ratio?

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PostPosted: Thu Dec 14, 2006 9:41 pm 
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it is 82 :)

so it could be written as 145-82R12 or however you want to set it up.

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PostPosted: Thu Dec 14, 2006 9:44 pm 
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Thanks, man!

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PostPosted: Fri Dec 15, 2006 11:04 am 
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CoyoteX, do you remember where you got that info?

I just found a page that shows a small difference between EURO-METRIC and P-METRIC sizes:

Euro-metric: 145/82/12 (what you said)
P-metric: p145/80/12
http://www.tirerack.com/tires/tiretech/ ... chart.html

So the Metro used a euro-metric tire size? It doesn't make a big difference in the RPM calcs, but I'm still curious which it is.

(For anyone who cares, the difference between euro- and p-metric is explained here:)
http://www.tirerack.com/tires-techpage-1/24.shtml

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PostPosted: Fri Dec 15, 2006 2:02 pm 
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Yeah, the difference between 80/82 aspect ratio is small: less than 30 RPM at 50 mph on the XFi

using this calculator

@50 mph in 5th (0.757)
145/82/12 XFi
21.362204724409448 tire Outside diameter
FD 3.89
RPM 2315.8

@50 mph
145/80/12 XFi
21.133858267716533 tire OD
FD 3.89
RPM 2340.8

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Last edited by geometro on Fri Dec 15, 2006 8:06 pm, edited 1 time in total.

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PostPosted: Fri Dec 15, 2006 7:44 pm 
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makes me want to put some taller tires on to get my rpms down. I probably would if I knew where to get new gears for the speedo if they were available.

could go to a 30 inch tall tire :) just need some minor sawing of the fender wells.

also isnt the xfi trans a 3.89 final drive with 5th gear being a .75 overdrive or so?

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PostPosted: Fri Dec 15, 2006 8:02 pm 
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Quote:
also isnt the xfi trans a 3.89 final drive with 5th gear being a .75 overdrive or so?


Yeah, you're right about the FD. My bad. (Edited in post above.)

According to this thread...

http://www.teamswift.net/viewtopic.php?t=14845

...the XFi has a 3.89. The 4.105 was the non-XFi FD for hatchbacks with the 145r12 tires. That's what I used by mistake.

Thanks for pointing that out.

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PostPosted: Fri Dec 15, 2006 8:19 pm 
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Coyote X wrote:
makes me want to put some taller tires on to get my rpms down. I probably would if I knew where to get new gears for the speedo if they were available.


I'd do it anyway, if you can't get gears to fix it. Just live with the speedo/odo error.

Since I swapped the 3.52 FD tranny into my car, my speed/odo reads low by about 6%, because the tires that were spec'd on the 1.3 SOHC swift I got the transmission from had a smaller outside diameter (155/70R13).

But I also have the scangauge, and it has a correction factor. So after I adjusted it, the speed, distance & MPG calcs remained accurate. It's just my mechanical speedo/odo that's off.

You could just figure out your correction factor and apply it to your manual MPG calculations. (And your speedometer, so you don't get tickets :D)

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PostPosted: Fri Dec 15, 2006 8:44 pm 
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it looks like around 75 bucks for a ratio adapter for the speedo. I figure if I am going to do it I would want to get it to act like the gears are one spot higher than they are now. The clutch might not like pulling out in a taller gear but it is nothing to replace so no biggie. Only bad thing is I would have to go to 28 inch tires to make 4th turn 2300 at 50. I am pretty sure the car would look really stupid with huge tires like that and have a very bad turning radius.

I will probably go to something like a 185/65/15 tire if I can come up with some rims for the car since there are no more new 145/8?/12 tires left anywhere. That would drop me around 250 rpm. Not much but every bit counts I guess. also a 10% ratio adapter is a common size so it would be cheaper to get.

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PostPosted: Fri Dec 15, 2006 8:53 pm 
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Coyote X wrote:
if I am going to do it I would want to get it to act like the gears are one spot higher than they are now.


That's effectively what I did. My "new" 4th gear is about 75 RPM lower than my original 5th gear @ 50 mph. So my "new" 5th gear is gravy.

Quote:
The clutch might not like pulling out in a taller gear but it is nothing to replace so no biggie.


I haven't had much trouble in normal driving (by myself mostly on the flat). My new 1st is almost exactly half way between my original 1 and 2. A car full of people on a hill is a different story though. :shock:

One thing to consider is how much would your new tire size lift your car off the ground?

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Last edited by geometro on Fri Dec 15, 2006 9:17 pm, edited 1 time in total.

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PostPosted: Fri Dec 15, 2006 9:08 pm 
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guess I cant lower it any more since I only have about an inch left till the bump stops. I would have to just live with it I figure unless I do some serious welding on the suspension to relocate stuff. Might do that if I go to a tube chassis though.

Maybe if I could find the 3.52 trans and go to the taller tires I would be able to get it down to a nice low highway rpm. I will be getting another metro in about 3 weeks but I don't think any of the metros came with 3.52 I will have to find a swift somewhere. The extra metro I have here has the 4.10 I figure it is a stock 91 3cyl 5spd.

Either way new tires are something I will have to get since I only have 2 145/12 tires left other than what is on the car now. They are getting pretty hard to find.

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PostPosted: Sat Dec 16, 2006 9:26 pm 
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This is what I was working on. I never posted a thread at my site about the tranny swap this summer. But I'm putting one together now, and thought this would illustrate it nicely.

Noticed you've got a site up for your car. Good stuff. It's worthy - you've done a lot more FE mods than the average Metro owner. I'll link to it from metrompg.com when I get caught up.

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Last edited by geometro on Sun Dec 17, 2006 9:13 pm, edited 1 time in total.

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PostPosted: Sun Dec 17, 2006 12:00 am 
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geometro wrote:
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Thank you!

Are A and D the same car just with the different trannies?

What kind of mileage gain did you measure from the rpm drop?


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PostPosted: Sun Dec 17, 2006 9:28 am 
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Yep. (A & D are the same car)

A bit more than 5%. See the last post in this thread: http://www.teamswift.net/viewtopic.php?t=25447

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PostPosted: Sun Dec 17, 2006 8:24 pm 
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I've seen references to both 3.89 and 3.79 for the XFi final drive throughout teamswift, eg:

google

I just got from a good source that it's 3.79

Quote:
My info came from the 1994 Factory Service Manual (published 6/93) page 0a-5. Love when I can back my statements...not often though.

XFi standard axle ratio 3.79:1


So I'm going back through this thread to change my calcs & references to 3.89...

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PostPosted: Thu Mar 20, 2008 3:52 pm 
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Geometro-i believe i asked you if you knew already, but the rest of you....I have a 91 Metro, so i have no scanner capabilities to accomodate the speedo problem. If i put the trans from an Xfi in my car, and the xfi tires, will i have to change the speedo gear to have my speedo accurate?

I too would love to drop my RPM's, but i DEFINITELY want the speedo to be correct.


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PostPosted: Sat Mar 22, 2008 6:51 am 
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If you put an XFI trans in, everything will be cool, all Metros came with the same tires until the 95 body change. If you put in a 3.79 from a 95 and up four cylinder you'll end up with the exact same result except the speedo will be off.

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PostPosted: Sat Mar 22, 2008 6:40 pm 
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Thanks Woodie! Now i just wish i could find a 13 or 14" tire around here that would be the same diameter as the 145r12's and not mess with my speedo......
If i lived in another country i could get them!!! =(


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PostPosted: Sun Mar 23, 2008 9:41 am 
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Here is information on the speedometer gears so when you do a transmission swap or tire change you can swap to the correct # of teeth on the speedometer gear in the trans

Quote:
speedometer ratio (faster) 18 x 16(brown) for wheels 14" (GT,GTi)
speedometer ratio (slow) 18 x 17(white)for wheels 13" (GA,GL,GLX,GS)
speedometer ratio (slower)18 x 18 (yellow/beige) for wheels 12"

The speedometer drive plastic gear with 18 teeth is the same on all(fixed on diff.).The differents are only on speedometer driven plastic gear (smaller on which is speedo cable) 16 teeth for 14"wheels and 17 teeth for 13" wheels.If you put on car 14" wheels you must have speedometer driven gear with 16 teeth so the cord can spin faster for speedometer because with bigger wheels for one turn car cross larger way.


Hope this is useful info, a Suzuki dealership should be able to get the gears easily if you can't find one in a junkyard. They are typically pretty cheap so it isn't worth hunting around for days in a junkyard for them.

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PostPosted: Wed Mar 26, 2008 11:27 pm 
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btw-maybe i'm recalling this wrong, but doesnt the xfi have a 3.52, not a 3.89...?

Now that i know i can chang e the trans, tires, and speedo gear; i wish i had some equations to use to determine how accurate my speedo would be with different options. Then, maybe i could find a 14" that would make my speedo off a bit, but the gear would bring it back in....


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PostPosted: Wed Aug 27, 2008 5:38 pm 
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I may have made a little boo boo. I bought and finished the rims I wanted, but they are roughly the same diameter as the 13" tires, not the 12". That said-which speedo gear would i go with if i put the xfi trans in(with 145R12...?) with new 175/65R14?

I'm pretty sure if i put the 92 Swift trans in that i found(it has the SOHC 4cyl and 13" tires, so i think it's a 3.52...is that right?) and put on the 14" tires, it will read very close--correct?

Anyone have a nice gear ratio calculator that includes the tire sizes in the formula? I like to use the 1010tires.com calculator, but that's just for tire sizing.


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PostPosted: Thu Aug 28, 2008 6:48 am 
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By going from 12" to 13" you have effectively done the same thing as installing an XFI transmission. If you now install an XFI (3.79) transmission, you're doubling the effect. An 8V transmission (3.52) is getting really drastic, don't know if that three cylinder is going to be able to get the car going. Very tough on clutches anyway. The speedo should be right as the 8V car came with 13's.

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PostPosted: Thu Aug 28, 2008 6:59 am 
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Woodie wrote:
By going from 12" to 13" you have effectively done the same thing as installing an XFI transmission. If you now install an XFI (3.79) transmission, you're doubling the effect. An 8V transmission (3.52) is getting really drastic, don't know if that three cylinder is going to be able to get the car going. Very tough on clutches anyway. The speedo should be right as the 8V car came with 13's.


The 3.52 is not drastic, the g10 is a very torquey motor considering it's size and the 3.52 isn't really that tall, it just makes the car feel laid back and relaxed.
If you are going to use the whole 4cyl tranny you will need to make an adapter to get the gear lever stabiliser rod to attach as the mounting point is quite different than on the 3 cyl box.


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PostPosted: Thu Aug 28, 2008 5:35 pm 
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Yeah, definitely think I'll go extreme and go all out on the gearing. Now, that I say that, the trans won't be in the yard anymore.....
I can do that clutch work myself, easy, but how bad are we talking that it kills the clutch? A new disc once a year is a bit ridiculous.
It's been quite some time since I've read up on the swap, but the axles and all are the same, just the shift mechanism mounting has to be modified, right? THought there was a post on here with pics, but i can't find it....any help please?

Guess I'll have to talk my cousin into finally getting a metro again and using the Xfi trans if I don't.


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PostPosted: Thu Aug 28, 2008 10:00 pm 
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I absolutely guarantee you that you won't wear out your clutch any quicker unless you have a habit of riding the clutch all day, if you are concerned then find a 4 cyl flywheel and clutch.
The 3.52 is not that much taller, it's not like taking off in 2nd gear or anything stupid, the difference in 1st gear at 5000rpm between a 3.52 and a 4.1 is about 4mph :roll: the diff ratio has much more effect in 5th than it does in 1st.

Check my album as there is a photo of both mk2 3cyl and 4cyl boxes.


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