225/45/17

[moots]

Just wondering if anyone have used this size tire 225/45/17 and if there is any difference in handling/performance between the norm size of 235/45/17 for the e34.

[Mas (UK)]

a metric tyre size and for some reason a couple garages I've asked only seem to stock 2 brands to choose from here in the UK: Dunlop TD Sport 2000 or Avon Technics. I will shortly be looking to replace my tyres and would like to know my options for the standard TD rims, as I don't like the Dunlops which are really bad in the rain with very little grip and are also prone to aqua-planing at higher speeds on our motorways. As for the Avon, I'm told this is a remould tyre and cheaper at about half the price of the Dunlops. The guys at the garages tell me some people always use them and others just don't want to know and don't touch them. What are your views to improving the road-handling in the wet? Are remoulds worth a try?

What other brand tyres and sizes can you guys recommend I check out which would fit the standard TD rims?

Cheers,

Mas

[mholbrook]

I assume since you have metric tires on metric wheels, you will be buying new tires and wheels.

The 225/45-17 is too short for an E34. It will give you an effective lower gear ratio and throw your speedometer way off. BMW's are already about 5 mph optimistic. If you ran a 245/45-17, that would make the speedo almost perfect and there is clearance with most 17" wheels. If you are going to buy new wheels and tires, why not look for some E39 wheels and tires to swap onto your 5er. The size you are looking at is more of a 3er size, no?

[Unregistered]

Speedometer way off? Sure about that? There's no way you could tell the difference in 0.2" side wall difference. If you drive 800 miles, you would be off by only 8 miles! That's it... If you check the diameter of 255/40/17 (which is recommended by BMW for 5 series for rear) is the same size in diameter of a 225/45/17. 225/45/17 is recommended for 3 series and slighty shorter but it is O.K. to use on E34. The difference between 225 to 235 is so slight that you will not notice the change.

I assume since you have metric tires on metric wheels, you will be buying new tires and wheels.

The 225/45-17 is too short for an E34. It will give you an effective lower gear ratio and throw your speedometer way off. BMW's are already about 5 mph optimistic. If you ran a 245/45-17, that would make the speedo almost perfect and there is clearance with most 17" wheels. If you are going to buy new wheels and tires, why not look for some E39 wheels and tires to swap onto your 5er. The size you are looking at is more of a 3er size, no?

[Robert K]

Holbrook was right, BMW speedometers are optimistic by 2-5% from the factory. That means you are never going as fast as your speedometer says you are. So, if you put a smaller diameter tire on your car than what is specified, you will make the problem worse. I suppose my question is, "Why would you want to do that?"

Tirerack shows the Michelin Pilot A/S 235/45-17 tire at 25.6" in diameter, which results in 811 tire revolutions per mile. The 225/45-17 is 25.1" in diameter which results in 829 revolutions per mile. That means you are inducing an additional error of approx. 2.2% in your already optimistic speedometer reading. If you assume that the speedometer is 3% optimistic from the factory (which seems about right from my testing), then at an indicated 70 mph with the 235/45-17 tire, you'd actually be doing 68 mph. If you put the 225/45-17 tire on the car, then you'd actually be doing 67 mph. You're right, not much difference. But again, why not try to correct the problem instead of make it worse?

I will also tell you this. I've thought about putting something like a 225/50-17 tire on my 1991 535i, which would just about correct the speedometer error. However, there is not much room left between the strut housing and the inside edge of the tire to be putting much larger a tire on the car than it calls for. Whether you go for a larger diameter tire or a wider tire, you run a serious risk of the inner sidewall contacting the strut tower. Don't believe me? Go to your car and reach in the front wheelwell and try to put your finger between the inner tire sidewall and the strut tower. I don't even think I can fit my pinky in there. It is CLOSE!.

My suggestion...stick with the size the factory calls for. They went to a lot of trouble to design the suspension and other components around a certain size tire. Anytime you go for something different, you run the risk of having problems.

Grace and peace,

Robert K
1991 535i

[Unregistered]

I don't know the reason why Moots wants 225/45/17 instead of recommended size of 235/45/17 on his car but I'm sure there is a reason. Maybe he has a chance to pick them up cheap or free... Tires aren't cheap. One of my friends pickup a used set of 225/45/17 for his 5 series from another friend who decided the get different set. He put them on and works perfect. When you say that little difference in diameter makes a big difference is not true. Please check the BMW recommended size 255/40/17 for the 5 series. Check the diameter. It is the same size diameter as 225/45/17. Another thing, depends on manufacture and model, the same size tires DO VERY. 235/45/17 can very from 25.2" to 25.6" difference in size! Check tirerack again and you will see the difference in size from same size tires. They very. Also, think about the loss in tread as they wear. It also very. That small difference is not going to throw off the speedo. Of course, the recommended size is preferred but slight difference is NOT going to hurt it either.

Holbrook was right, BMW speedometers are optimistic by 2-5% from the factory. That means you are never going as fast as your speedometer says you are. So, if you put a smaller diameter tire on your car than what is specified, you will make the problem worse. I suppose my question is, "Why would you want to do that?"

Tirerack shows the Michelin Pilot A/S 235/45-17 tire at 25.6" in diameter, which results in 811 tire revolutions per mile. The 225/45-17 is 25.1" in diameter which results in 829 revolutions per mile. That means you are inducing an additional error of approx. 2.2% in your already optimistic speedometer reading. If you assume that the speedometer is 3% optimistic from the factory (which seems about right from my testing), then at an indicated 70 mph with the 235/45-17 tire, you'd actually be doing 68 mph. If you put the 225/45-17 tire on the car, then you'd actually be doing 67 mph. You're right, not much difference. But again, why not try to correct the problem instead of make it worse?

I will also tell you this. I've thought about putting something like a 225/50-17 tire on my 1991 535i, which would just about correct the speedometer error. However, there is not much room left between the strut housing and the inside edge of the tire to be putting much larger a tire on the car than it calls for. Whether you go for a larger diameter tire or a wider tire, you run a serious risk of the inner sidewall contacting the strut tower. Don't believe me? Go to your car and reach in the front wheelwell and try to put your finger between the inner tire sidewall and the strut tower. I don't even think I can fit my pinky in there. It is CLOSE!.

My suggestion...stick with the size the factory calls for. They went to a lot of trouble to design the suspension and other components around a certain size tire. Anytime you go for something different, you run the risk of having problems.

Grace and peace,

Robert K
1991 535i

[Mas (UK)]

to have them replaced just yet. As for the rubber, do I have to stick metric tyres on these metric rims? Because it then comes down to a choice for me of Dunlops with pi** poor grip in the rain or Avon remoulds with questionable quality. Is there an imperial equivalent for TD230/55ZR/390's? If not I may like you say go ahead and look for some new alloys to give me more choices with tyres to improve the cars grip in the wet.

Cheers

Mas

I assume since you have metric tires on metric wheels, you will be buying new tires and wheels.

The 225/45-17 is too short for an E34. It will give you an effective lower gear ratio and throw your speedometer way off. BMW's are already about 5 mph optimistic. If you ran a 245/45-17, that would make the speedo almost perfect and there is clearance with most 17" wheels. If you are going to buy new wheels and tires, why not look for some E39 wheels and tires to swap onto your 5er. The size you are looking at is more of a 3er size, no?

[Craig]

BMW's are already about 5 mph optimistic.

I think that's an internet myth. I just got a ticket for 75 in a 60, and had the cruise set at 75.

[mholbrook]

The metric wheels require metric tires (390). No getting around that. The main reason people toss the metric wheels is the tires are so expensive because only a couple companies manufacture them. Thus, if you are going to get new tires, you have two choices or buy new wheels and tires. If you are going to buy new wheels and tires, the recommended size for BMW E34 5 series is 235/45/17 if it is 17" wheels you are going to be running. It is correct that 255/40/17 is correct for the staggered size and only in the back. My style 32 wheels have a 26mm offset in the rear to allow for this size tire. My front wheels are 20mm offset.

[Robert K]

The article was about speedometer error. Sure enough, almost every manufacturer makes their speedometers read a bit higher than the car is actually moving. I would expect they do it so that someone doesn't come back and try to sue them for the speeding ticket they got because of a low mph reading. In the article, they actually stated that BMW's almost always were the most optimistic. I've actually timed my car for ten mile stretches on the interstate using the mile marker posts and found that at an indicated 70 mph, I was actually traveling about 67 mph. That was using the correct 235/45-17 size tires. I repeated the test two or three times for ten miles each and always got the same answer. So I tend to believe the C & D article. Personally, I'd love to put a little larger tire on the car and make the speedometer correct. But as I mentioned before, there is not a lot of room between the inside of the tire and the strut housing.

Grace and peace,

Robert K
1991 535i