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Old 13th April 2006, 10:01   #1
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Default How does an upsize tyre make a steering lighter???

Hey Guyz.....

I own a zen 2000 Mpfi model which came with 145/80-12 MRF ZVTS tyres n 4J steel rims...... After running them for 5 years it was time for new rubbers for my zen...So i decided for an upsize tyre so did some research n took views from experts (Satya)....But being a student i always had a small pocket n dad wasnt too keen for alloys...So finally i got 165/65-13 Bridgestone Donuts with 4J steel rims of Zen carb some 6 months back....After some time i found out the ride quality had gone down but it was very quite while running on good roads as compared to the stock set of tyres...
My main purpose of putting broad tyres were to improve the handling n braking to an extent but all went the other way round.....The steering response became so eratic that i lost all control of the car at speeds above 60kph....braking was scary to say the least....
Then after consulting a few experts including Rehaan found out that the rim size is not within propsed limits for the tyre size which is 4.5J - 6J for 165 tyres.....
So got my rims changed to esteems 4.5J steel rims n now the braking has improved drastically but still the steering feels so light even without power steering at parking speeds.....N at higher speeds the steering becomes even lighter.....
I even test drove my car by swapping the tyres to stock size145/80 12 the steering became harder, precise n lots of understeer ...n back to broader tubeless 165/65-13 the steering became lighter n causing oversteer at high speeds.....

To my knowledge whenever u get a broader tyre the steering should become heavy....Why is it the opposite in my case??????

I've checked up all suspension, steering,brakes and allignment.....

waiting for your valuable suggestions....

regards

KP
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Old 13th April 2006, 10:19   #2
aZa
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maybe the new rims are lighter than the previous ones ! what else could it be ? and isn't it a good thing if ur steering is lighter ?
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Old 13th April 2006, 11:39   #3
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Quote:
Originally Posted by aZa
maybe the new rims are lighter than the previous ones ! what else could it be ? and isn't it a good thing if ur steering is lighter ?
Its good to have light steering at parking speeds but as speed increases it become lighter n u have less control...
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Old 13th April 2006, 15:38   #4
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what is the air pressure you are at...at high pressure the tyre will become convex and the contact oact become much smaller...thereby making this "lighter steering" effect make its presence felt.
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Old 13th April 2006, 16:47   #5
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Quote:
Originally Posted by Buffetfan
what is the air pressure you are at...at high pressure the tyre will become convex and the contact oact become much smaller...thereby making this "lighter steering" effect make its presence felt.
Exactly kpzen check your air pressure and try running the car once on about 2-3 psi lower than the recommended air pressure on stock tyres. This could help especially the steering and ride.
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Old 13th April 2006, 22:45   #6
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I have tried all pressure from 24 - 32psi....all in vain...
currently running with 28psi...

Last edited by kpzen : 13th April 2006 at 22:47.
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Old 14th April 2006, 09:33   #7
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the wider tyre with same height of sidewalls of a smaller width will make turning the tyre a more difficult job.

say, if you would have opted for 165/80R12 (if any!) in place of your original 145/80R12, then your steering wud have became much harder too steer.

but since the proflie ratio (i.e., the proportionate height of tyre wall in relation to its footprint's width) of your new tyres is much lower than that of your older tyres, there has been an improvement in steering effort.

low-profile tyres tends to turn quicker than those with high-profile sizes of their sidewalls.

smaller sidewalls offers a lower "slip angle" due to the lower flex in the sidewall of the wheel as a whole, this improves steering response.
and, due to this less height of sidewalls, and lower "slip angle" , and bettter steering response, low profile tyres are a much better option for enthusiasts.

but they do gives a very poor ride in comparison to high profile (higher sidewall) tyres.
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Old 25th August 2006, 01:42   #8
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Light steering can mean 2 things, either you're running a higher tyre pressure or you've got negative wheel offset.

Every suspension is setup for a certain degree of wheel offset. Offset is basically the position of the hub wrt to the center of the rim.

Positive offset is when the hub is more towards the outside of the rim.

Zero offset is when the hub is in the middle of the rim

Negative offset is when the hub is behind the center of the rim (towards the suspension).

Nagetive offset is said to make the steering light and finicky.

You don't feel this with the stock rims bcoz the company would have calculated the offset before fitting it.

Another thing, even if the offset reading on your new rims read the same as the old ones, it maynot help. When you upsize to bigger and broader rims, offset requirments change as well.

This will help you understand offset.


Shan2nu

Last edited by Shan2nu : 25th August 2006 at 01:47.
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Old 25th August 2006, 12:29   #9
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Offset fundas are all ok but is there any how i can find out offset of my steel rims(esteem 4.5J) n adjust them to have proper steering response...

I doubt that something's wrong in caster or camber angles.......

The braking is also vulnerable n inconsistent after i cross speed of 80kmph...but there is no vibration n all....In case of slammin the brakes at 80+ speeds the steering almost goes anyside as if no tyres are there...

KP
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Old 25th August 2006, 12:40   #10
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Quote:
Offset fundas are all ok but is there any how i can find out offset of my steel rims(esteem 4.5J) n adjust them to have proper steering response...
Ask the company, they'l be able to tell you. You could measure it yourself but i'd reccomend the first option (for accurate readings).

You get aftermarket spacers that can compensate for wrong offset but it has it's limits.

Quote:
I doubt that something's wrong in caster or camber angles.......
If that was the case then it should have shown similar behaviour with stock rims. But you say the car is stable with stock ones.

Get the offset readings clarified.

Shan2nu
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Old 30th May 2007, 22:38   #11
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After 10 months i'm still unable to find the offset of Esteem steel rims..If anyone knows it pls do lemme know..

shan2nu
How can i calculate the offset myself ?

For making the steering heavier i've been running my tyres with 26psi in front n 28psi for the rear. The result is after 25K kms my front tyres have only 40% thread left n rear still has 80% thread left.

Last edited by kpzen : 30th May 2007 at 22:42.
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Old 31st May 2007, 12:25   #12
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I thought when you get you allignment done, you choose your car model and year of mfs. They have a database and mesure it to your actule reading and adjust to the base data.
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