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Old 5th June 2007, 02:15   #1
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Default Alloys - Speedometer difference

I recently bought a Swift D and changed the stock 165/70 R 14 to the 185/70 R 14 alloys. I am certainly happy with the handling characteristics and am fiddling with the tyre pressures to arrive at the best pressure for my driving style.

While using one of the resources on this forum, I came across the tyre size calculator and on doing a comparison between the stock rims and my new tyres, found that there would exist a 4.8% difference in the speedometer reading between the stock and new. If I am to believe the calculation, I am running about 2.8 kmph slower than the speedometer reading. This will naturally affect the odo reading as well.

My question is whether this is accurate and if yes, is it ok to run this difference? Is there some way the speedometer can be recalibrated for the new tyres? And how accurate are the FE readings if this difference exists?

Cheers!
K
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Old 5th June 2007, 10:14   #2
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http://www.team-bhp.com/forum/techni...libration.html (Odometer recalibration)

This might help
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Old 5th June 2007, 10:26   #3
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I hope there is not much error after your upgrade as there is no much differnece in rolling radius(i.e. around 10mm) which can compensated by pressure adjustment.

Here is some info:

Plus One Concept -
The plus one concept describes the proper sizing up of a wheel and tire combo. Basically, each time you add 1 inch to the wheel diameter, add 20mm to the tire width and subtract 10% from the aspect ratio. This compensates nicely for the increases in rim width that generally accompany increases in diameter too. By using a larger diameter wheel with a lower profile tire it's possible to properly maintain the overall rolling radius, keeping odometer and speedometer changes negligible. By using a tire with a shorter sidewall, you gain quickness in steering response and better lateral stability. The visual appeal is obvious, most wheels look better than the sidewall of the tire, so the more wheel and less sidewall there is, the better it looks. However, be prepared for a stiffer ride as there will be less sidewall to cushion undulations in the road.

Source: TalonTire.com - tire glossary
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Old 5th June 2007, 11:46   #4
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Hey Kartik..!!!
U have calculated using a wrong size.
Stock size of Swift is 165/80-14 for which the upsize 185/70-14 is perfect....This upsize will create -0.8% difference in speedo reading which is quite acceptable..
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Old 5th June 2007, 11:59   #5
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Actually VDi stock rims are 165/80/R-14. Thus 185/70/R-14 is the perfect upsize. By using the calculator @ tyre bible, your speed difference is less than 0.5 km/h and hence is accepted very well.
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Old 5th June 2007, 13:33   #6
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Quote:
Originally Posted by kpzen View Post
Hey Kartik..!!!
U have calculated using a wrong size.
Stock size of Swift is 165/80-14 for which the upsize 185/70-14 is perfect....This upsize will create -0.8% difference in speedo reading which is quite acceptable..
I can't believe I made that rookie mistake. This is what comes from doing these things at 4.30 in the early hours of the morning, when taking a break from work!!!

Thanks guys.
Kartik
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Old 5th June 2007, 23:15   #7
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The best upsize for the Swift is 195/60/15 virtually no error with same OD.
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Old 6th June 2007, 00:13   #8
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Quote:
Originally Posted by BUSA View Post
The best upsize for the Swift is 195/60/15 virtually no error with same OD.
for that one have to change rims also. 0.8% is not much difference.
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Old 6th June 2007, 00:22   #9
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I think BUSA meant that 195/60-15 is the best upsize for Swift....
Mugen u are right katik's doubt was related to his 14" tyre upgrade only...
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Old 6th June 2007, 01:38   #10
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Quote:
Originally Posted by BUSA View Post
The best upsize for the Swift is 195/60/15 virtually no error with same OD.
BUSA you are probably correct on the best upsize. But I quite like the alloys on the ZXi and have got that fitted on the VDi, so my query wasn't on upsize but whether I need odo reclibration, which I don't, as has been pointed out to me. I mean a 0.8% difference on the speedo is really negligible. Translates to almost nothing in real terms. Thanks for the advice though.

Cheers!
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