tire width's affects on speedo?
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tire width's affects on speedo?
ok i am having a hard time understanding how the different measurements affect the cars sensors. i understand how tire diameter affects speed, basically the bigger the tire diameter from stock the faster you will actually be goin compared to the speedo, and you have the opposite effect with smaller wheel diameter from stock. but how does the width of the tire affect the sensors? or does it affect it at all? in my mind i feel like the faster you go the more grip is needed to maintain your speed so a wider contact patch will will yield better acceleration or a higher speed compared to the stock tire, right? this is really bugging me and if anyone is able to help please do so. the thing that brought this to my attention was the tire calculators, which i figured out that they are not necessarily accurate, but the tire width seemed to affect the resulting speed.
#2
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Section width doesn't have a direct impact on the speedo.
If you increase your section width but keep the same ratio of sidewall height to section width then you'll get taller tire and a greater outer diameter.
The sensors have no way of knowing about the tires' width except how it affects the diameter based on the ratio of the sidewall height to section width.
Tire sizing is done with a ratio.
Stock size
225/45/18 means:
Tire width: 225mm
Sidewall height: 45% of 225mm (101.25mm)
Inner diameter: 18"
Total height: 18" + 7.96" (101.25 mm in inches x 2 since you have the sidewall on either side of the wheel) = 25.96"
Wider than stock but maintaining stock ratio
265/45/18 means:
Tire width: 265mm
Sidewall height: 45% of 265mm (119mm)
Inner diameter: 18"
Total height: 18" + 9.36" (98mm in inches x 2 since you have the sidewall on either side of the wheel) = 27.36"
Wider than stock with shorter ratio than stock
265/35/18 means:
Tire width: 265mm
Sidewall height: 35% of 265mm (92.75mm)
Inner diameter: 18"
Total height: 18" + 7.3" (98mm in inches x 2 since you have the sidewall on either side of the wheel) = 25.3"
If you increase your section width but keep the same ratio of sidewall height to section width then you'll get taller tire and a greater outer diameter.
The sensors have no way of knowing about the tires' width except how it affects the diameter based on the ratio of the sidewall height to section width.
Tire sizing is done with a ratio.
Stock size
225/45/18 means:
Tire width: 225mm
Sidewall height: 45% of 225mm (101.25mm)
Inner diameter: 18"
Total height: 18" + 7.96" (101.25 mm in inches x 2 since you have the sidewall on either side of the wheel) = 25.96"
Wider than stock but maintaining stock ratio
265/45/18 means:
Tire width: 265mm
Sidewall height: 45% of 265mm (119mm)
Inner diameter: 18"
Total height: 18" + 9.36" (98mm in inches x 2 since you have the sidewall on either side of the wheel) = 27.36"
Wider than stock with shorter ratio than stock
265/35/18 means:
Tire width: 265mm
Sidewall height: 35% of 265mm (92.75mm)
Inner diameter: 18"
Total height: 18" + 7.3" (98mm in inches x 2 since you have the sidewall on either side of the wheel) = 25.3"
Last edited by NotAPreppie; 02-14-2011 at 06:44 PM.
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ok, so i shouldnt really care about the width as long as the diameter is the same, or close to. see thats what i originally thought but then i came across some tire calculators and i messed with the width and on every single one of them it changed the speed, which didnt make any sense to me, and i guess i looked to far into it. i know what all the numbers mean its just like i said i think i may have looked to far into it.
#9
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It's funny that I see this thread today. I actually just put stock wheels and tires back on my car since I sold my Volks and I am awaiting my new wheels and tires.
Anyway, i did a test on teh way back into town on Sunday.
With my staggered Volks and 245/40-18 tires I was about 3MPH faster per my Magellan GPS and my phone. With my stock wheels and 225/45-18 tires I was still 2MPH faster.
Anyway, i did a test on teh way back into town on Sunday.
With my staggered Volks and 245/40-18 tires I was about 3MPH faster per my Magellan GPS and my phone. With my stock wheels and 225/45-18 tires I was still 2MPH faster.
#11
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Going back to stock only affected it 1MPH which basically means it affected nothing at all.
#12
Blue Bullet?
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Well when I was running 245/40-18's on stock wheels I was still 3MPH faster, nothing changed when I installed the Volks (18x8 Front and 18 x 9 rears with same tires all the way around).
Going back to stock only affected it 1MPH which basically means it affected nothing at all.
Going back to stock only affected it 1MPH which basically means it affected nothing at all.
#23
Those tire calculators are for a theoretical size since all manufacturers sizes vary some.
Best way to compare is to look up tire your running on Tirerack.com, and under specs see how many revs the tire makes per mile, then, look up the revs for the tire you want to run.
My stock 225/45r18 SPT's were 803 revs per mile, and I put on 225/40r18 Hankook Ventus V12 with 828 revs per mile.
803 plus 3.1% (approx) = 828 revs on new tire.
So, I set my Scan gauge for 3% lower on speed to account for speedo being off. This can be verified by using interstate mile markers for several miles with distance calculator on the Scan gauge.
One more thing, I think we've seen drag radials get larger circumference when spinning, but street tire have firm belts inside to prevent that, so the belt would keep revs per mile very close unless you're spinning on purpose.
Best way to compare is to look up tire your running on Tirerack.com, and under specs see how many revs the tire makes per mile, then, look up the revs for the tire you want to run.
My stock 225/45r18 SPT's were 803 revs per mile, and I put on 225/40r18 Hankook Ventus V12 with 828 revs per mile.
803 plus 3.1% (approx) = 828 revs on new tire.
So, I set my Scan gauge for 3% lower on speed to account for speedo being off. This can be verified by using interstate mile markers for several miles with distance calculator on the Scan gauge.
One more thing, I think we've seen drag radials get larger circumference when spinning, but street tire have firm belts inside to prevent that, so the belt would keep revs per mile very close unless you're spinning on purpose.
Last edited by REDRX3RX8; 02-16-2011 at 05:00 AM.
#24
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Just curious, what are the exact tire size measurements on your 18 x 7.5 wheels? I'm getting ready to buy some XXR wheels and they will be 18 x 7.5 and I want to make sure the tires I get will work without any issues.
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