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Old 7th October 2007, 14:23   #1
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Default Tyre Comfort - unexpected result from calculator

I saw in the Innova thread someone was recommending that the tyres should be changed from 205/65 R15 to 225/60 R15. I would have expected this to reduce body roll but create a slightly harsher ride as the aspect ratio has come down. However the tyre calculator at the site below shows that the ride comfort parameter increases when you go from 205/65 to 225/60. Is this right ? Could be because of larger air volume ???

TRC Calculator

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Old 7th October 2007, 17:16   #2
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Aspect ratio has reduced, not the 'profile'. In fact overall radius is larger with the 225/60 R15.
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Old 7th October 2007, 17:35   #3
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The correct upsizes for 205/65 R15 are 215/60 R15 or 225/55 R15. Both of these bring down the comfort, and more so for 225/55. You can also consider an upsize 215/55 R16. Although the rolling radius is almost exactly the same as for 205/65 R15, the comfort level comes down by a couple of points (from 9.7 to 7.4); in fact this is less comfortable than even 225/55 R15 (8.2).
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Old 7th October 2007, 17:43   #4
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I guess because the sidewall height is greater in case of 225/60 than in case of 205/65. Anyhow the correct upsize will be 215/60.
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Old 7th October 2007, 20:18   #5
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Quote:
Originally Posted by rks View Post
The correct upsizes for 205/65 R15 are 215/60 R15 or 225/55 R15. Both of these bring down the comfort, and more so for 225/55. You can also consider an upsize 215/55 R16. Although the rolling radius is almost exactly the same as for 205/65 R15, the comfort level comes down by a couple of points (from 9.7 to 7.4); in fact this is less comfortable than even 225/55 R15 (8.2).
nope 225/60 is fine. infact its smaller by 0.5% or so.
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Old 7th October 2007, 20:34   #6
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225/60-15 is a fine upsize for Innova which will have 2mm more of sidewall rubber but it isn't gonna create substantial difference in comfort.
Yes, there would be noticeable difference in comfort level if u get good comfort based 225/60 tyres for eg Michelin MXV8.
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Old 7th October 2007, 21:02   #7
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Originally Posted by akshay1234 View Post
nope 225/60 is fine. infact its smaller by 0.5% or so.
You are right. I had applied the rule of increasing width by 10 mm and decreasing profile by 5%, to arrive at 215/60, but apparently in this range 225/60 is a better fit than 215/60.
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Old 7th October 2007, 22:36   #8
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thanks guys, I'm going in for the 225/60 upsize with Michelin MXV8
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Old 26th October 2007, 13:33   #9
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I upgraded from 205/65 R15 Bridgestone to 225/60 MXV8. The tyres look fatter and IMO nicer, but the difference in ride is not that great. On decent road surface the michelin tyres feel very smooth almost velvety, but on bumpy tarmac with tar lumps it is much more 'jumpier' than the earlier set. In fact I feel i made a mistake and wasted money. The tyre dealer said fatter tyres take more time for the sidewalls to start flexing so I should wait, but I do have this bad feeling that i should have kept the standard size and not upgraded to 225/60.

Any thoughts ?
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Old 26th October 2007, 17:12   #10
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What are ur current tyre pressures?
Try decreasing it by a single psi and let us know the difference.
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Old 29th October 2007, 22:50   #11
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The tyre pressure is 33 PSI in all tyres. Most of the time the load is just the driver and 1 or 2 passengers. Changing the pressure by 1 PSI didn't make any difference at all. Do you think reducing the tyre pressure to 30 or 28 would help while the vehicle is lightly loaded ?
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