Using "smaller" tires??

I know, bigger is better, but not always...

I just got an 06 PR and I need to crawl up a hill to get to my house. Plus the speedometer seems a bit high for what I'm traveling. The only way this would be possible, minus a flawed speedometer, is if someone changed the rear-end gears... That may be the prob. I have to get that checked but...

I figured I could kill two birds with one stone, or four stones, by buying smaller tires. That would enable me to crawl, and it may adjust the difference I am feeling in the speedometer. Slowest I can go up a mild hill is about 8-10 mph which is way too fast due to the gullies and ruts in the road.

I still need to get someone out in front of me to verify the speedometer is off by about 7-8mph, high. Say I am doing 60 the speedometer reads 52 for example. I am doing 60 in 4th with RPM's to spare. Right around 2500.

Anyone have speedometer probs? I checked the search box and someone said you could "flash" the memory, but then someone else said you couldn't do that??? So IDK. Seems like smaller tires would work for me.

It comes with 245/70-16's I believe, but I was thinking about going with 215/65-16's. I checked the tire chart and it says that would give me what I am looking for as far as speed goes.... But that is IF it doesn't make the truck look stupid with too small of tires on it.

Any advice is appreciated!
Bob

 

Whether or not it looks silly will be a matter of opinion, and yours is the only one that matters. As far as your RPMs go, Toyota has changed the gearing several times on second gens (I think). People complain about gearing being too low frequently, while on my 2012 I think first and reverse are geared too high and (manual trans) 6th is slightly low. 2000 rpm in 6th at 60 mph.

Was this truck heavily modded when you bought it? If it still has 245s on it, I'd guess no. If not, I would guess you are on stock gears and speedo is correct-ish.

Welcome to TW!

 

I am assuming this is a 4 cylinder and does not have 4x4. Get a GPS to check your real speed. The only real fix is a final gear change. Also that tire change would not make any appreciable difference for what you are seeking if you are running the stock tires you mentioned. If you are now going 8 MPH idling that tire change would only drop you to 7.32. If you are going 10MPH idling that tire difference would only drop you to 9.15 MPH. Tire size change for what you are seeking is not the answer. Gearing is however.

 

Going to 215's would impact your stopping distances, and handling. I wouldn't go that narrow.

 

'It comes with 245/70-16's I believe'

Can you verify that is your tire size, and what engine and transmission do you have?

 

If you have a smartphone, a free app called GPS status will take care of knowing how fast you are really going (and be useful for other things)

I'm not sure I understand the concept of why smaller tires would allow you to 'crawl' up the hill any better.

 

Smaller tires will allow truck got go slower at a given rpm than a larger size, but not sure if there would be a significant difference, ie. 'crawling'...

 

I was about 5 miles from home when I realized it has to be the gearing. Someone before me probably saw those $3.75 a gal gas prices and wanted better mileage. That is what I am assuming. There is no reason to put as high of a gear as there is in there.

I calculated by miles, every 5 real miles is 4 on the speedometer. I figure, by that huge 20% difference that they are 2:72's or something high as hell like that. That would account for the speedometer reading 53 at 65mph or there about.

I mean I have to "fly" up the hill, crawl may be the wrong word, that would be maybe 1/2mph, lol? But I have to go 7mph to get up the hill without lugging the motor.

I have called the dealer I bought it from, the Service Mgr actually, to see what the deal is. If they can help me by changing them out to what they are supposed to be. I figure 100,000 miles would be more like 120,000 miles. The truck reads 89k miles, so maybe I can fenagle them to trade the extra miles the truck has on it for the repair. Wish me luck.

I know it is a long shot. Anyone know what it costs to replace the rear gears?? I asked the service people but they haven't gotten back with me yet... ugh

Thanks,
Bob

 

Oh, it is a 3.7L. 2WD, Reg Cab, with the standard 245/70-16's on it. It threw me for a loop because I would never suspect a truck to come with the gearing so dang high!

 

I'm going to assume you meant 2.7 liter. Is it a prerunner (6 lug) or 5 lug? Literally count the lugs on your wheels to figure out which model you have.

Stock tire on a 6 lug is 245/75r16.

Stock tire on a 5 lug is 215/70r15.

245/70r16 is not a stock configuration from toyota, I have a feeling someone put big tires on your truck when it was meant to have small ones, which is why it feels underpowered.

 

Figure about 1000 to 1500 dollars parts and labor if you have it done. A dealer may want even more. If you do it yourself around 200 to 300 dollars for parts. If you have never done it don't try it as it takes proper calibration of the ring and pinion gears.

 

To add to Juggernaut's post

width (mm) is overall width of the tire. It is not tread width, which will vary depending on tire manufacturer. For instance, I went from oem Dunlops to Michelin LTX MS2, both are P245/75-16, but tread width is .40 inch wider. All other specs the same, except Tire Rack lists rev per mile for both as 683 instead of 662.9 - but the difference may be the effect of "tire bulge" of a mounted tire with vehicle weight on it. Michelin website also lists 683 revolutions per mile.

If you elect to go smaller, be aware a lot of chain/corporate tire dealers WILL NOT mount tires different from stock sizes. Not a problem at some independent dealers. Just be sure you have load capacity rating on whatever tire you choose.

 

Well, they are not stock tires. But likely is stock gearing. While lots of folks here chat about regearing after bigger wheels and lifts, it's to get more gear, not less.

Sorry, I'd not trust manual calculations for the Speedo error. Use a GPS and get it right. You can play with tire calculators to see how a size would affect gearing.

If you do wind up changing gearing (bet you don't) you'll find that a rear end specialist (think race car/hot rod shop) will do a better job for less than a dealer. Odds are high a dealer would farm the job out anyway. Since there's not much call for R&P changes anymore, they may not even staff a tech that has a clue how to do it.

Also keep in mind that your speedo could just plain be wrong. My '13 is off by 2 mph consistently across all speeds, and is totally stock. My '96 sports car that I autoxd had an increasing error, ie it was accurate till about 30 and by 80 was about 5 optimistic. Same with the tach on that car, at 'redline' on the gauge it was about 500 over actual. OTOH, my '04 Highlander is perfect, and the tach in my Tacoma is perfect.

Back to going up hill. What gear do you have the trans in during this venture? And I don't recall seeing what the trans is? You should have no issue going very slow in first gear, either auto or stick.

 

Hey ya'll,

Thank you so much for the replies. I HOPE and PRAYYYYYYYYYYYY it is the tires. I went 5 miles by highway mile sign, it said "X" road is 5 miles away, my odometer read 4 exactly when I got there. IDK, something is fishy. That is 20% if I did my math right. I know it is probably not exactly 5 but rounded off to 5, so it could be just the 13.5% difference I am hoping for it!!!!

I will talk with the tire shop on Monday to see what they say about the difference, but Juggernaut's post suggests a 13.5% difference... A little less than 20%, but still, that is significant.

It has 6 lugs. And on the door it says 245/70-16 So the tires are not stock they are the 75 series. I will have to fix the tire problem before I fool with the gears.

It is a stick, and I am in 1st, barely able to stay under 7, unless the speedometer was bouncing because of the road and gave me a wrong number, lol?? It is very bumpy, ruts, and full of pot holes. It sucks trying to get up it at that speed. But yeah, it is in 1st.

Thanks again for all the replies. I hope it is the tires, I hope it is the tires, and I hope it is the tires!!!

Bob

 

I just checked inside the door frame, and it says 245/75-16's are the original tire size.

I'm gonna have my mechanic check it out Monday. I will report back what they find.

Yes it is the 2.7, I have dyslexia and mix numbers and letters up sometimes. But I checked, rechecked and triple checked the numbers on the tires and inside the door frame, they match.

Thanks,
Bob

 

Bob, there is no tire size change that can lower the speed enough if you are running 8 or 10 mph now at idle and you want to craw. If you change the final gears to get what you want the truck will be useless on the road. You need a transfer case to achieve what you want if you want to also drive the truck on the road.

 

You can get a gear ratio if you have jackstands or a lift.
Link explains how.
http://www.how-to-build-hotrods.com/gear-ratio.html

 

Have used that method before, but the link sums it up very nicely.

Thanks. Now bookmarked!

 

That type of mile sign is not accurate - it might be to the city limit, might be to the center of town. Do it on an interstate or freeway where there is a marker every mile, and do at least 20 miles, 50 is better.

Or use a gps, again for at least 20 miles.

BTW, odometer (and speedometer) accuracy changes as tires wear - well-worn P245's can easily lose a full inch from new to when down to the wear bars.

 

I would double check your speed with a gps as others have said. There are free apps if you have a smart phone. Also you should be in 5th gear at 60. My truck is stock and I have the same engine/trans/gears as your truck when it came off the lot. Let me know what rpm you are at on the highway at 65 in 5th, and I can compare that to mine tomorrow when I go to work. If they match then you have stock rear gears.