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strokercutlass
Joined: 09 Jun 2003
Posts: 379
Location: Wis
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| Posted: Wed Dec 10, 2003 11:29 pm Post subject: |
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i think a better way to compare tires is to look at the revolutions per mile
revolutions per mile are a direct byproduct of tire diameter, so if you have a tire with a nearly identical diameter, then your speedo and shift points will remain close if not the same |
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88delta88
Joined: 09 Jun 2003
Posts: 2401
Location: Canada
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| Posted: Thu Dec 11, 2003 10:57 am Post subject: |
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Ok. Shift points. How much of a difference will a person notice by changing to a tire that is roughly 2 inches smaller diameter than stock? I dont think I noticed anything when I first got the tires on, but how much difference would there be?
Theoretically, you would get more power with smaller tires on, wouldnt you? |
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86Delta
Joined: 06 Nov 2003
Posts: 281
Location: NJ, USA
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| Posted: Thu Dec 11, 2003 2:19 pm Post subject: |
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| it would make it feel like it had more power. a smaller diameter tire is like switching to a lower gear ratio. a shorter tire would make the trans shift sooner than it would on stock size tires. will 2 inches do it? not sure. all i know is that i had to drive with a donut on the front for a day and my shifts were very noticably different. |
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speedy266
Joined: 25 Jun 2003
Posts: 347
Location: Ontario, Canada
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| Posted: Sat Dec 13, 2003 2:04 pm Post subject: |
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| i dunno about that theory, it might feel like ur going faster. But doesnt it make more sense that a bigger tire gives u more power. Because one revolution of the tire covers more distance, and the computer senses the number of revolutions then shifts to the next gear correct me if im wrong. With a smaller tire, ur car would rev a little higher but ur actual covered distance (speed if u wanna say) would be less. I got the 185/75/R14 stock on mine right now, and if i went to 215/70/R14 i found this calculator online that calculates speed difference, and with the upgrade id be going 4km/h faster than wat the speedo says. I dunno thats wat makes sense to me, but this smaller tire thing might work to i just need a good explaination on how it works please? |
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Cutlass95Ciera
Joined: 27 Jun 2003
Posts: 433
Location: Portage, Michigan
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| Posted: Sat Dec 13, 2003 2:22 pm Post subject: |
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| I'm not sure quite hot to explain it but I do recall seing it on junkyard wars alot! |
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strokercutlass
Joined: 09 Jun 2003
Posts: 379
Location: Wis
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| Posted: Sat Dec 13, 2003 4:56 pm Post subject: |
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"Theoretically, you would get more power with smaller tires on, wouldnt you?"
With a smaller diameter tire, you'll accellerate faster, but limit your top end and RPM, as the smaller tire will make the gear ratio steeper geared. Heres a good example....
On my race car, I generally run a 30" radial slick. With the 3.73 gears, this makes an effective gear ratio of around 3.42. If I put a shorter tire on the back, for example, a 27" tire, it will make the gear ratio move up, for example, to a 3.60 or better. The car will accellerate and may in fact cross the 1000 ft mark faster with the 27" tire than the 30" tire,because the effective gearing is higher, but at the end of the track may actually be slower, because the gearing with the 27" tire has caused the car to hit the RPM limit, while the gearing with the 30" tire will still allow the car to accellerate without hitting the RPM limit.
heres another way to look at it....
at 55 mph, with a 30" tall tire, in 3rd gear, which would make for a 1: 1 gear ratio, and a 3.73 gear, we can find the cruise RPM would be 2,298 RPM
with the same combination, but with a 27" tall tire, the cruise RPM will be 2553 RPM, and will increase exponentially as the RPMs increase.
Lets try another one....a 185/75R14 ( stock baseline) compared to a 215/70R14 compared to a tire 2" shorter than a 185/75R14....1:1 transmission ratio in 3rd gear, and a constant of 3.23 for a final drive ratio....
at 55 mph, in 3rd gear (NOT overdrive)
2" shorter 23" tall 2595 RPM 207 RPM over stock
185/75R14 25" tall 2388 RPM
215/70R14 25.9" tall 2305 RPM 83 RPM under stock
at 75 mph, in 3rd gear
2" shorter 23" tall 3539 RPM 283 RPM over stock
185/75R14 25" tall 3256 RPM
215/70R14 25.9" tall 3143 RPM 113 RPM under stock
We can see by this that the RPM will increase or decrease exponentially with increases or decreases in speed.
So, by varying tire height, we can change final drive gearing without changing the gears themselves, and either gain low end response, or top end speed.
Will it make a huge difference on a FWD Olds? I imagine there will be a "seat of the pants" difference, but it will all depend on how much of a tire diameter change is made....
Oh, and for those wondering, switching from a 185/75R14 to a 215/70R14 will net the following results....
the speedometer will be 3.7% slower...at 60 mph you'll actually be going 62.2 mph..
Hope this helps clear some things up :wink: |
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88delta88
Joined: 09 Jun 2003
Posts: 2401
Location: Canada
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| Posted: Wed Dec 17, 2003 11:22 am Post subject: |
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| stroker saves the day again! very good explination, I'm quite content! |
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strokercutlass
Joined: 09 Jun 2003
Posts: 379
Location: Wis
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| Posted: Wed Dec 17, 2003 9:24 pm Post subject: |
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| :notworthy: Machismo!!!!!!!!! ROTFLMFAO!!!!!! |
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88delta88
Joined: 09 Jun 2003
Posts: 2401
Location: Canada
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| Posted: Thu Dec 18, 2003 11:18 am Post subject: |
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| all hail to the oldsmobile god! |
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No53Alero
Joined: 09 Jun 2003
Posts: 157
Location: CINCINNATI, OH
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| Posted: Fri Dec 19, 2003 9:27 pm Post subject: |
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| smaller do make a big difference, they put way more miles on car then actually travelled. When I had the 13x7 knock-off's on w/ the 155/80/13 tires my tenth's went by really fast at what my speedo said was 80. I guess it was realy like 70 in real life though. Maybe that's what thrashed my tranny back then. probalby that coupled w/ the fact that they vibrated real bad at highway speeds, they actually vibrated less at higher speeds. actually it was also driving slammed while going that fast and vibrating, those axles are at a wierd angle that low!! it was too much for the th 125C. |
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No53Alero
Joined: 09 Jun 2003
Posts: 157
Location: CINCINNATI, OH
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| Posted: Fri Dec 19, 2003 9:29 pm Post subject: |
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| where would 19" rims put my speedo. they would have 235/35/19 tires. |
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strokercutlass
Joined: 09 Jun 2003
Posts: 379
Location: Wis
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| Posted: Fri Dec 19, 2003 10:09 pm Post subject: |
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actually airbagged, you're only off by a small bit...
on your speedo, 60 mph is actually 61.3 mph, IF the original size was a 185/75R14...
heres the link of anyone wants to play around with tire sizing...
http://www.miata.net/garage/tirecalc.html |
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88delta88
Joined: 09 Jun 2003
Posts: 2401
Location: Canada
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| Posted: Mon Dec 22, 2003 11:36 am Post subject: |
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| Hey, I used that same calculator when I was trying to choose a tire size for my car! Thats a neat calculator, gives you an idea of the size of your tire and everything! |
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No53Alero
Joined: 09 Jun 2003
Posts: 157
Location: CINCINNATI, OH
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| Posted: Tue Dec 23, 2003 9:27 am Post subject: |
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| wow looks like i'm a pretty lucky guy b/c I've been driving it like it was 5 off for some time now so that would mean that I was doing 9 over going by cops shooting radar! |
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73Delta88
Joined: 08 Jun 2003
Posts: 973
Location: Western Massachusetts
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| Posted: Tue Dec 23, 2003 9:52 am Post subject: |
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| Screw all that number crunching.... just drive around till you find one of those stand alone speed traps that shows your current speed in beg red numbers, and check your speedo against that! :D |
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