Atroz Posted February 11, 2007 Share Posted February 11, 2007 Hi, I've seen it said a few times, including on Tire/wheel seller's sites something along the lines of: When changing tire sizes, we recommend staying within 3% of the diameter/height of the original tire. Any more than this and you face the risk of brake failure.Why is this? I can see a heavier wheel/tire causing stress on the brake. I can see that the farther the weight is away from the hub the more impact it will have. However, it's not necessarily true that a larger wheel is heavier. Is the warning just an over simplification that says "extra weight is bad", or is truly the size? Thanks. Link to comment Share on other sites More sharing options...
Xenonk Posted February 11, 2007 Share Posted February 11, 2007 that's actually rubbish, where did you find that info??? Keefe Link to comment Share on other sites More sharing options...
robinlsb Posted February 11, 2007 Share Posted February 11, 2007 that's actually rubbish, where did you find that info??? Sounds to me like a legal CYA type of thing. Probably brought on by the guy that added huge oversize AT tires on his pick-up and found out the hard way that adding 50 pounds per wheel caused a slight problem! "Belief does not make truth. Evidence makes truth. And belief does not make evidence." Link to comment Share on other sites More sharing options...
Atroz Posted February 11, 2007 Author Share Posted February 11, 2007 that's actually rubbish, where did you find that info??? That particular quote came from http://www.1010tires.com/TireSizeCalculator.asp However, I'm sure I've seen similar in other places. Doing a quick search on google shows it comes up on a number of sites, but as far as I can tell the info can always be traced back to 1010tires. I just found another statement in 1010Tire's glossary where they blame it on confusing the braking system computer: http://www.1010tires.com/glossary.asp There may be something in that if the system is relying upon knowledge of circumference? I would think that if it's monitoring anything though it would be rotations. Link to comment Share on other sites More sharing options...
Xenonk Posted February 11, 2007 Share Posted February 11, 2007 Sounds to me like a legal CYA type of thing. Probably brought on by the guy that added huge oversize AT tires on his pick-up and found out the hard way that adding 50 pounds per wheel caused a slight problem! even off-road jeep guys running 36" tall tires dont have this issue.. some people are just plain stupid when it comes to overdriving the car and dont know what mods they did that would cause such failures. Keefe Link to comment Share on other sites More sharing options...
Vimy101 Posted February 11, 2007 Share Posted February 11, 2007 Two things come to mind for me: 1. Extra rotational mass/inertia 2. Additional wheel torque upon braking due to larger circumference. Link to comment Share on other sites More sharing options...
Xenonk Posted February 11, 2007 Share Posted February 11, 2007 That particular quote came from http://www.1010tires.com/TireSizeCalculator.asp However, I'm sure I've seen similar in other places. Doing a quick search on google shows it comes up on a number of sites, but as far as I can tell the info can always be traced back to 1010tires. I just found another statement in 1010Tire's glossary where they blame it on confusing the braking system computer: http://www.1010tires.com/glossary.asp There may be something in that if the system is relying upon knowledge of circumference? I would think that if it's monitoring anything though it would be rotations. it only holds true if you are totally changing the tire diameters from stock dramatically.. like running staggered sizing on purpose on a non-staggered setup.. if the car ran on 25" tall tires and you go and change the fronts to 23" and the rears to 27", of course the ABS will freak out, in fact, the AWD system wouldn't like you either as it keeps thinking the fronts are spinning way too fast. I know a few racers that have done such a set up before to get more bias out of the AWD setup (not as dramatic) but it works. You, as an owner and driver, must assume all responsibility when making changes to the car. That's all there is to it. If it works or not is just dependent on how well you did your homework. I can safely say that I ran tires that were well over the 3% mark on the GT. It's not a big deal on the brakes.. my assumption is that this quote applies to people putting reall outrageous tire sizes on their cars for the looks and totally forgot that their brakes are still stock and can't handle such momentum calculations and thus the brakes get beat up more from the heavy 26" dubs. Keefe Link to comment Share on other sites More sharing options...
robinlsb Posted February 11, 2007 Share Posted February 11, 2007 it only holds true if you are totally changing the tire diameters from stock dramatically.. like running staggered sizing on purpose on a non-staggered setup.. if the car ran on 25" tall tires and you go and change the fronts to 23" and the rears to 27", of course the ABS will freak out, in fact, the AWD system wouldn't like you either as it keeps thinking the fronts are spinning way too fast. I know a few racers that have done such a set up before to get more bias out of the AWD setup (not as dramatic) but it works. You, as an owner and driver, must assume all responsibility when making changes to the car. That's all there is to it. If it works or not is just dependent on how well you did your homework. I can safely say that I ran tires that were well over the 3% mark on the GT. It's not a big deal on the brakes.. my assumption is that this quote applies to people putting reall outrageous tire sizes on their cars for the looks and totally forgot that their brakes are still stock and can't handle such momentum calculations and thus the brakes get beat up more from the heavy 26" dubs. Try 36" tires on a truck, you know, like BIGFOOT! "Belief does not make truth. Evidence makes truth. And belief does not make evidence." Link to comment Share on other sites More sharing options...
Xenonk Posted February 12, 2007 Share Posted February 12, 2007 ^ my coworker does a lot of 4-wheelin (he runs 33"s on his Charokee, it's lifted with fender flares).. he has his braking under control just fine on his Jeep (that weighs in at close to 3800 lbs). It's a matter of people needing to understanding how they have to drive differently with different equipment on the car, and not expect the equipment to do the driving for them. Keefe Link to comment Share on other sites More sharing options...
Vimy101 Posted February 12, 2007 Share Posted February 12, 2007 ^ What is his braking distance 70-0? I think what we're talking about here is that OEMs design a vehicle to certain specifications to achieve given performance characteristics. So do track racers and hill climbers, etc. Exceeding design tolerances invites failure. I frankly think that passenger cars are wonderful feats of engineering. Link to comment Share on other sites More sharing options...
Xenonk Posted February 12, 2007 Share Posted February 12, 2007 ^ What is his braking distance 70-0? I think what we're talking about here is that OEMs design a vehicle to certain specifications to achieve given performance characteristics. So do track racers and hill climbers, etc. Exceeding design tolerances invites failure. I frankly think that passenger cars are wonderful feats of engineering. and that's why we are also inclined to increase safety margins of the parts that have become the 'weakest link'. You can certainly get bigger, better brakes and way better tires to match the new sized rims.. let's not get started on people that have a lot of horsepower and still end up running bald-skinny tires with no brake upgrades and think their car can last the next 25 miles through a mountain pass Keefe Link to comment Share on other sites More sharing options...
Vimy101 Posted February 12, 2007 Share Posted February 12, 2007 and that's why we are also inclined to increase safety margins of the parts that have become the 'weakest link'. You can certainly get bigger, better brakes and way better tires to match the new sized rims.. let's not get started on people that have a lot of horsepower and still end up running bald-skinny tires with no brake upgrades and think their car can last the next 25 miles through a mountain pass When you think of it, improving on OEM performance by just 10% requires a fair amount of aftermarket modding. Link to comment Share on other sites More sharing options...
Xenonk Posted February 13, 2007 Share Posted February 13, 2007 that's why I dont mod my car's power all that much.. it's harder to get the rest of the mods to equate to 10% increase in performance, power is easy to do, the rest becomes a limiting factor.. Keefe Link to comment Share on other sites More sharing options...
Noel Posted February 15, 2007 Share Posted February 15, 2007 If they were talking about changing to a softer compound then this would make sense. Many of my fellow Porsche Club track buddies are fine on the track with street tires, but upon switching to race/R compounds, this will overheat the brakes due to the better a Coefficient of friction that enables the car to brake better and build more heat in the brakes. This is sometimes too much for cars stock brake systems without running cooling. It's the old adage..."Better brakes won't stop a car faster as long as your old setup can lock the brakes...but better tires will." Link to comment Share on other sites More sharing options...
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