Omega Owners Forum
Omega Help Area => Omega General Help => Topic started by: Rockhampton on 10 October 2009, 19:17:25
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Hi all,
I posted a while ago that my Omega had the wrong tyres fitted on the front - 205/50x16 versus the standard 225/55x16 on the rear. I've finally got around to changing them (cambelt & service took priority!) to the correct size, and lots of things suddenly seem to have gotten better. Obviously, the new tyres and 4-wheel balance have made the vibration through the steering wheel a thing of the past, and the ride is much better - but in addition, the autobox seems to be working much better - it has started changing down more on hills, and seems much smoother. Similarly, the MPG reading on the computer is better, and the braking feels better too. Now, as there would have been a size difference of several centimeters in the sidewall size of the tyres, I can understand how having non-matching sizes between front and rear could affect the ABS computer - but I guess my question is, does the engine or gearbox ECU take any speed measurement from the front wheels, hence causing the improvements I am experiencing, or am I way off, and it is something else?
Any ideas gratefully received! :D
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I will never forget the first time I put 4 brand new tyres on a car, after years of using secondhand tyres and maybe the odd new remould here and there, the difference in the car (a Sierra) was unbelievable it handled and peformed like a new car! so maybe its just this sort of effect your experiencing?
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The ABS computer measures the speed of each individual wheel. If one is deamed to be decelerating too fast relative to the others, the pump is activated and the pressure to that wheel is pumped back into the master cylinder untill the rotation speed is normal again.
The traction control is a similar system, but works in reverse to that.
The improvement in the ride quality will be partly down to your car now having the correct amount of sidewall between the wheel and the road that the suspension settings were tuned for. I would expect handling and grip to also be better as there is now the correct amout of rubber in contact with the road.
As for the MPG, it probably didn't make any real difference but having all 4 wheels the same will make the computer readings more accurate :y
Baffled by the gearbox though :D Maybe the car is just happy with all the attention it has received recently! ;D
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The ABS computer measures the speed of each individual wheel. If one is deamed to be decelerating too fast relative to the others, the pump is activated and the pressure to that wheel is pumped back into the master cylinder untill the rotation speed is normal again.
The traction control is a similar system, but works in reverse to that.
The improvement in the ride quality will be partly down to your car now having the correct amount of sidewall between the wheel and the road that the suspension settings were tuned for. I would expect handling and grip to also be better as there is now the correct amout of rubber in contact with the road.
As for the MPG, it probably didn't make any real difference but having all 4 wheels the same will make the computer readings more accurate :y
Baffled by the gearbox though :D Maybe the car is just happy with all the attention it has received recently! ;D
Yes, he's cheered his car up ::) ;D ;D :y
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Thanks Guys - it certainly is a lot happier ;D. But it is different - as an example, on my way home from work, there is a steep descent on a dual carriageway. Driving a long, as I started going down, the car would always pick up speed really quickly, and would have increased by over 20mph by the bottom (foot off accelerator) - like there was no engine braking. Today, same place, car hardly increased in speed at all, again with foot off the accelerator. It seems like I've suddenly got engine braking. I always thought that the gearbox did not seem as great slowing down as the one on my Commodore, but I put that down to the AR35 being an older design. Now, it feels more like the Commodore gearbox. All the gears change, I've checked them, and kick down works etc. I don't know if the torque convertor lockup had stopped working & has just started again, or indeed the change in rotational size of the front wheels with the correct tyres has affected some sensor somewhere. It beats the hell out of me, but as I say, I am well happy :y :y :y
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The ABS computer measures the speed of each individual wheel. If one is deamed to be decelerating too fast relative to the others, the pump is activated and the pressure to that wheel is pumped back into the master cylinder untill the rotation speed is normal again.
The traction control is a similar system, but works in reverse to that.
The improvement in the ride quality will be partly down to your car now having the correct amount of sidewall between the wheel and the road that the suspension settings were tuned for. I would expect handling and grip to also be better as there is now the correct amout of rubber in contact with the road.
As for the MPG, it probably didn't make any real difference but having all 4 wheels the same will make the computer readings more accurate :yBaffled by the gearbox though :D Maybe the car is just happy with all the attention it has received recently! ;D
Sadly not, the speed reading comes from the rear ABS sensors (and the fuel computer uses this speed reading to calculate the fuel consumption)
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As I understand it ... the MID is "programmed" with the "correct" tyre size for your car. The ABS sensor gives a rotational speed input and the system then calculates your speed and fuel consumption.
If you have the "wrong" size tyres then both speed and consumption figures will be wrong (small tyres cover less distance per revolution, large ones .. more)
The torque required to turn different size wheels, under the same conditions, also changes .. so this must have an effect on the autobox behaviour IMHO.
Probably wrong but ........ :)
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As I understand it ... the MID is "programmed" with the "correct" tyre size for your car. The ABS sensor gives a rotational speed input and the system then calculates your speed and fuel consumption.
If you have the "wrong" size tyres then both speed and consumption figures will be wrong (small tyres cover less distance per revolution, large ones .. more)
The torque required to turn different size wheels, under the same conditions, also changes .. so this must have an effect on the autobox behaviour IMHO.
Probably wrong but ........ :)
Correct but, only the front ones were wrong :y :y
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As I understand it ... the MID is "programmed" with the "correct" tyre size for your car. The ABS sensor gives a rotational speed input and the system then calculates your speed and fuel consumption.
If you have the "wrong" size tyres then both speed and consumption figures will be wrong (small tyres cover less distance per revolution, large ones .. more)
The torque required to turn different size wheels, under the same conditions, also changes .. so this must have an effect on the autobox behaviour IMHO.
Probably wrong but ........ :)
I guess those were the lines I was thinking along as well :) It's a strange one!