Tire Upsizing - Clearance and Pressure Monitors?

[Crazy888888s]

Thought I would report that the speedo readings on my LC200 seem to have ADJUSTED for the tire size change.

By installing tires that are 1.6 inches larger in overall diameter, my tire sizing calculator (see first post in this thread for link) indicates that my indicated speed should be 3.6% lower than actual. So, with the larger tires, when the speedo indicates 60mph the vehicle is actually traveling 62.2mph on the math formula.

Now here is the cool part, using my hand held GPS I just tested the speedo gap and there is none! This means one of three things: (1) the speedo is somehow linked to the GPS or (2) the speedo is linked to a system that compensates for the tire size or (3) the speedo is marking off the tire pressure monitors which are mounted to the wheels which are the same size. If (3) is the answer, then speed would vary with wheel size deviations from standard. I doubt this is the case since non-US LC200s don't have 18 inch wheels as standard.

Either way, pretty cool. I tested speeds ranging from 30-80mph for a 10 mile ride so I am confident my results are accurate.

So Toyota can't install a tire pressure monitoring system that tells you which tire is actually low and they put their towing electrical hook-up in the same spot Homer Simpson would install it, but the speedo is set up somehow to adjust for tire size. Pretty cool.

Yeah, you may be thinking I have too much time on my hands, but any excuse to tinker in the garage during Thanksgiving is a welcome break. I do have a beer fridge in there.

 

[JBHorne]

Thought I would report that the speedo readings on my LC200 seem to have ADJUSTED for the tire size change.

By installing tires that are 1.6 inches larger in overall diameter, my tire sizing calculator (see first post in this thread for link) indicates that my indicated speed should be 3.6% lower than actual. So, with the larger tires, when the speedo indicates 60mph the vehicle is actually traveling 62.2mph on the math formula.

Now here is the cool part, using my hand held GPS I just tested the speedo gap and there is none! This means one of three things: (1) the speedo is somehow linked to the GPS or (2) the speedo is linked to a system that compensates for the tire size or (3) the speedo is marking off the tire pressure monitors which are mounted to the wheels which are the same size. If (3) is the answer, then speed would vary with wheel size deviations from standard. I doubt this is the case since non-US LC200s don't have 18 inch wheels as standard.

Either way, pretty cool. I tested speeds ranging from 30-80mph for a 10 mile ride so I am confident my results are accurate.

So Toyota can't install a tire pressure monitoring system that tells you which tire is actually low and they put their towing electrical hook-up in the same spot Homer Simpson would install it, but the speedo is set up somehow to adjust for tire size. Pretty cool.

Yeah, you may be thinking I have too much time on my hands, but any excuse to tinker in the garage during Thanksgiving is a welcome break. I do have a beer fridge in there.

2.2mph is such a minute difference that I wonder if it's just that on the speedo the distinction between 60 and 62.2 is so minor that you can't tell the difference. I think my speedo runs a bit high with factory tires, so maybe you just compensated it back to where it should be.

 

[mo.africa]

Crazy88888's
I checked my speedo to a gps awhile ago and when my speedo reads +-125 km/h, the Gps reads 120km.I have the standard 285/65/17 tyres on a 4.5 diesal vx 200.I think JBHorne is right when he says its compensated to where it should be.
Your speedo is probably reading your complete tyre rotations,and because your tyre is larger you are covering more distance with the same rotation.

 

[sdtash]

The LC 200 in Australia on 17" tyres operates with the speedo indicating 4 kmh slower than actual. When upsizing to the larger 285/70 17 diameter tyres the speedo is correct by GPS.

 

[Crazy888888s]

$164 to have my new tire pressure monitor properly synched with the LC200s computers!

Can you say Toyota-Enema? Oh what a feeling!

Lessons to be learned:

1. Do all your tire work at Toyota since if they "bust it" they will have to "fix it for free" or

2. Make sure that you warn any tire tech that the tire pressure monitor is connected to the tire valve and that if it breaks it is about a $200 proposition with the cost of the new monitor and the reprogramming charge.

Now I have to decide whether I am going to stick this bill to my restoration shop which did the tire swap for me. They charged me for 1.0 hours of labor for the swap and I paid. They did foot the bill for the monitor part and all. But this $164 bill and the 2 hours of inconvenience schlepping to and from Toyota did not need to happen. On the other hand, the tech who did this does alot of work on my old cars and is a good guy and I would hate to get him in trouble.

Maybe this will be his silent Secret Santa gift. The gift of nothing - no trouble.

 

[chimyz]

$164 to have my new tire pressure monitor properly synched with the LC200s computers!

Can you say Toyota-Enema? Oh what a feeling!

Lessons to be learned:

1. Do all your tire work at Toyota since if they "bust it" they will have to "fix it for free" or

2. Make sure that you warn any tire tech that the tire pressure monitor is connected to the tire valve and that if it breaks it is about a $200 proposition with the cost of the new monitor and the reprogramming charge.

Now I have to decide whether I am going to stick this bill to my restoration shop which did the tire swap for me. They charged me for 1.0 hours of labor for the swap and I paid. They did foot the bill for the monitor part and all. But this $164 bill and the 2 hours of inconvenience schlepping to and from Toyota did not need to happen. On the other hand, the tech who did this does alot of work on my old cars and is a good guy and I would hate to get him in trouble.

Maybe this will be his silent Secret Santa gift. The gift of nothing - no trouble.

I wouldn't stick it to him, but I would let him know what the outcome was and the cost...SH*T happens.

This sounds like more of a PITA than a serious cost issue. If he's a good guy and does good work for you, you wanna keep that. Good mechanics are hard to find.

 

[fcfred]

call your congressman and bitch to him, the law says the truck has to have tire pressure monitoring systems, so now we all get screwed by expensive parts that we seemed to have survived with for years without. unless you were driving a ford and your let your tires get low, flipped over, and blamed ford and firestone.

 

[1loudLX]

164 dollars? WHAT? WOW, thats insane.

Personally I'd take all the TPMS' out of the wheels if the truck didnt actually show me the pressures at each corner. Take em out and put em in a "TPMS bomb", store it away under the dash or behind a panel.