[snik]

Hi

I have a set of brand new 195/50/15 high perf summer tires.

My car (88 300CE) currently has stock 195/65/15 Toyo Observe winter tires

I was thinking since I have a set of new 15" summer tires, to just put those on the car (all 4)

granted speedo will be off by about 10 km/h, and the wheel gap will incrase a bit. Stock tire dia is 24.98" & the new setup will be 22.67" (2.31" difference)

will this cause any issues (other than speedo reading 10km/h faster than I am actually going)

 

[Yal]

You may have ABS issues.

 

[Nagchampa]

Yal - 2/18/2005 12:48 PM

You may have ABS issues.

Shouldn't have ABS problems if the tires are the same height (diameter) all around. The computer will not know the difference.

 

[snik]

ok,.. so if you were me, and had a brand new set of 195/50/15s laying around, would you install them on your 124 or get another set of new 195/65/15s?

 

[Jackd]

I'd stick with the 195/65/15.
the 195/50/15 will give you an harsher ride, will look funny leaving a wide open wheel well, will result in higher RPM for the same speed, less mpg,

 

[Nagchampa]

I would sell them and get a bigger set of tires. I am running 215/40-16 on my W124 but I am going to go to 50 series in a month or so for the new wheels I have.

The ride doesn't bother me at all even though my car is lowered, and my car has a manual transmission so I am not overly concerned about the fuel economy. Maybe it would be different if I had to drive on the highway all the time.

 

[Yal]

Nagchampa - 2/18/2005 5:38 PM

Yal - 2/18/2005 12:48 PM

You may have ABS issues.

Shouldn't have ABS problems if the tires are the same height (diameter) all around. The computer will not know the difference.

You're kidding me right? If the rolling diameter increases or decreases by a certain maximum it will cause ABS problems because your ABS sensor is calibrated just like your speedometer for specific revolution ratios. So even though the difference between the wheels are non existent because you have the same tires all round you STILL have the problem of the sensors thinking the car is going faster or slower than it really is. Wouldn't your ABS engage later or sooner depending on this factor?

 

[Nagchampa]

Yal - 2/18/2005 12:48 PM



You're kidding me right? If the rolling diameter increases or decreases by a certain maximum it will cause ABS problems because your ABS sensor is calibrated just like your speedometer for specific revolution ratios. So even though the difference between the wheels are non existent because you have the same tires all round you STILL have the problem of the sensors thinking the car is going faster or slower than it really is. Wouldn't your ABS engage later or sooner depending on this factor?

Have you ever tried it in practice or are you just talking about what you have heard from some backyard mechanic? My car is rolling on 215/40 16 tires which are roughly the same diameter as 195/50 15 tires. I guess if what you were saying was correct, then I would have all kinds of problems with my ABS. The way ABS sensors work is they basically compare the rate at which the 4 wheels are turning to make sure they are within a very close percentage of each other. When the car senses a different speed between the wheels, then it reacts to correct the difference by engaging and disengaging the wheel that is locked up. As long as the wheels are the same diameter, there will be no problems. The ABS sensors are located in fixed location on the front spindle or wheel bearing assembly, rear ones are either on the axle shaft or differential(depending on the manufacturer) and these sensors have no way of determining the difference in rolling diameter as long as the 4 tires are the same diameter.

There are plenty of resources to check this information since you obviously think I am making this up.

 

[Pringles]

This is definitely all about rolling diameter . My car runs on 225/45 x 17 Goodyear F1 tyres on an Amg wheel . This size wheel did not fit in the spare wheel well and so Mercedes supplied a 215/55 x 16 wheel( standard 8 hole alloy ) and tyre as the spare . This has a very similar diameter.

Mercedes did put in the handbook that it was best not to drive at high speeds with one wheel slightly smaller though !

195/65x15 has a very similar diameter to 225/45x17 and 215/55 x 16.

 

[Yal]

Nagchampa - 2/22/2005 7:14 PM

Yal - 2/18/2005 12:48 PM



You're kidding me right? If the rolling diameter increases or decreases by a certain maximum it will cause ABS problems because your ABS sensor is calibrated just like your speedometer for specific revolution ratios. So even though the difference between the wheels are non existent because you have the same tires all round you STILL have the problem of the sensors thinking the car is going faster or slower than it really is. Wouldn't your ABS engage later or sooner depending on this factor?

Have you ever tried it in practice or are you just talking about what you have heard from some backyard mechanic? My car is rolling on 215/40 16 tires which are roughly the same diameter as 195/50 15 tires. I guess if what you were saying was correct, then I would have all kinds of problems with my ABS. The way ABS sensors work is they basically compare the rate at which the 4 wheels are turning to make sure they are within a very close percentage of each other. When the car senses a different speed between the wheels, then it reacts to correct the difference by engaging and disengaging the wheel that is locked up. As long as the wheels are the same diameter, there will be no problems. The ABS sensors are located in fixed location on the front spindle or wheel bearing assembly, rear ones are either on the axle shaft or differential(depending on the manufacturer) and these sensors have no way of determining the difference in rolling diameter as long as the 4 tires are the same diameter.

There are plenty of resources to check this information since you obviously think I am making this up.

Ok go ahead and give him the advice and if he has the problems its on you. I personally would not do it.
"..backyard mechanic" LOL thats funny and childish.

 

[ebock]

ABS works on a comparative, not a constant index. As a result, the tire diameter is only an issue if the four tires differ from each other, not if they differ from "stock" dimension.