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Old 1st July 2005, 11:33   #1
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Default Upsize confusion (Phiat Siena)!

Dear Gurus,

I am pondering on upsizing the stock tyres (175/70 R13) on a three year old Siena (old model).

I found out the following :

# 185/60 R 14 (Increase in rolling radius is +.42%) – (Section Height decreases by 11mm)
# 195/60 R 14 (Increase in rolling radius is +2.5%) – (Section Height decreases by 5mm)

Is a 2.5 % increase in rolling radius too high? I would not mind a 20mm increase in width as I will have to shell out 30-35000/- on alloys and tubeless tyres anyway? Also, if Section Height plays a role in ride quality – 117mm (122mm in stock tyres) will be useful as the roads in my town are really 3rd class.

What sort of deterioration can I expect if I increase circumference by 2.5%?

Sorry for opening a new thread for this ghissa-pitta question? I found out that new Palios come with stock 165/80 R13s (that is +3.3% compared to the stock Siena). This is confusing me as the old Siena was an old Palio with a boot. In that case, perhaps they did not use the optimum circumference for the stock tyres, leaving me some room to upgrade to 195/60 R14s?

Please help me out on this one.

Thank you very much!

Phatichar
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Old 1st July 2005, 12:48   #2
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195/60 R14 looks like a better option. You'll have better grip and decent ride. Others can confirm, but I believe variation upto 3% is permissible. Your top speed should marginally increase due to higher rolling radius, but it would get compensated due to more traction (broad tyres).
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Old 1st July 2005, 19:51   #3
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Hi Phatichar,

Quote:
Is a 2.5 % increase in rolling radius too high?
Not a problem at all. It is well within the tolerances.
Infact its probably better to go with the slightly higher sidewalls in your driving conditions. (however i would have prefered a width of 185 but thats a moot point)

Another thing i was going to suggest was the possibility of finding 14" steel wheels, which would save you some $$$, however, thinking about that further i realise that its not the best idea given the fact that you will be driving on bad roads and steel wheels do deform a lot easier (not fun with tubeless tires).

cya
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Old 1st July 2005, 20:12   #4
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No problem with 195/60 R14, as long as the diff is below 3%, you're absolutely safe.

If you don't mind 185s then you can give Viper's tyres a try. he's also selling his wheels with it. Viper's wheels/tyres

Shan2nu
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Old 1st July 2005, 20:41   #5
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Quote:
Originally Posted by phatichar
Dear Gurus,
I found out that new Palios come with stock 165/80 R13s (that is +3.3% compared to the stock Siena). This is confusing me as the old Siena was an old Palio with a boot. :

hey phatichar ,
the palios always had their speedos calibrated for 165/80r13.but since the pre-NV palios had different tires,they used to show wrong readings due to which everyone said that palio's have lesser FE.


the reason for the 1.2 having the better ride over the 1.6 is because of its higher profile tires.
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Old 4th July 2005, 11:32   #6
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Dear Gurus,

Many thanks for your enlightening responses.

I have a couple of questions,

# With regards to ride quality; what is more important – Aspect Ratio or Section Height?

(aspect ratio in 185/60 and 195/60 is same but section height varies)

# What will be the estimated hit to fuel efficiency if rolling radius is increased by 2.5%?

Again, much thanks!

Yours,

phatichar

Last edited by phatichar : 4th July 2005 at 11:34.
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Old 4th July 2005, 11:37   #7
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Quote:
what is more important – Aspect Ratio or Section Height?
Aspect ratio. Be it for handling or comfort, the aspect ratio should always be taken into consideration.

Lets take these 2 tyres for instance.

1. 175/60 R14 - section height - 105mm
2. 205/50 R15 - section height - 102.5mm

Even though their section height is almost identical, the 205/50s won't be able to match the ride comfort provided by the 175/60s but, at the same time, the 175/60s would experience a lot more sidewall flex while cornering, compared to the 205/50s.

This can only be true if the 2 tyres are tested on the same car/suspension.

Shan2nu

Last edited by Shan2nu : 4th July 2005 at 11:51.
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Old 5th July 2005, 15:39   #8
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Quote:
Originally Posted by Shan2nu
Aspect ratio. Be it for handling or comfort, the aspect ratio should always be taken into consideration.

Lets take these 2 tyres for instance.

1. 175/60 R14 - section height - 105mm
2. 205/50 R15 - section height - 102.5mm

Even though their section height is almost identical, the 205/50s won't be able to match the ride comfort provided by the 175/60s but, at the same time, the 175/60s would experience a lot more sidewall flex while cornering, compared to the 205/50s.

This can only be true if the 2 tyres are tested on the same car/suspension.

Shan2nu

Thanks for the illustration; I get it now.

Thank you!
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