Will tire size change affect towing?

[turnipgreen]

I have a 2004 Tundra double cab. I tow a boat in the summer, it weighs about 4K lbs. I currently have the stock 265/65/17 tires, but will have to replace them soon. If I move to a 265/70/17 which is slightly larger, will it noticably affect my towing? I know it would slightly affect my speedometer, and my odometer, but sometimes the difference in cost on those two sizes is significant.

Thanks for any help.

Ron

[sknaus]

I did the same thing on mine and did not notice any difference in towing and my speedo was still showing the correct number per the stationar radars the police use. I wouldn't hesitate for a moment going to the new size tire. I put Revos on mine and absolutely love them.

[RockyMtnRay]

Originally Posted by turnipgreen

I have a 2004 Tundra double cab. I tow a boat in the summer, it weighs about 4K lbs. I currently have the stock 265/65/17 tires, but will have to replace them soon. If I move to a 265/70/17 which is slightly larger, will it noticably affect my towing? I know it would slightly affect my speedometer, and my odometer, but sometimes the difference in cost on those two sizes is significant.

Thanks for any help.

Ron

Define "noticeably" affect. A 265/65-17 tire has a 30.6 inch diameter; a 265/70-17 has a 31.6 inch diameter...that 1 inch increase is about 3% of the total tire diameter. Which is the equivalent of a 3% drop in rear wheel torque. Also the equivalent of a 1.8 mph change in indicated versus actual speed at 60 mph.

Generally...repeat generally...most people won't notice a 3% torque change...the effects are pretty subtle. In towing, it'll mean the truck will be just a bit more likely to downshift on hills to 2nd (if you tow with OD off), or downshift from 4th to 3rd (if you tow with OD on). And it'll be just a tiny bit more sluggish during on-ramp acceleration.

I went the other way with a 3% torque increase (by installing a Gibson muffler along with my JBA headers). The 3% effect of the muffler was indeed subtle...the truck became a bit less likely to downshift on hills and acceleration on an on-ramp was just a tiny bit quicker so merging in heavy traffic was less nerve racking while towing.

[turnipgreen]

So would one option if I noticed a diff in torque be to change to a Gibson muffler? I thought at one point you mentioned the Gibson wouldn't have gained anything without the headers, and I'm not up for switching that out yet.

Thanks for the replies.

Ron

[RockyMtnRay]

Originally Posted by turnipgreen

So would one option if I noticed a diff in torque be to change to a Gibson muffler? I thought at one point you mentioned the Gibson wouldn't have gained anything without the headers, and I'm not up for switching that out yet.

Thanks for the replies.

Ron

Not 100% sure but have a strong hunch the headers have to be part of the deal. I can't recall if anyone did the Gibson swap before headers...I think most did it the same way I did: headers first or headers/muffler at the same time.

From a engineering standpoint, the exhaust manifold is apparently the primary restrictor in the stock exhaust, especially at low-mid RPM on the '04 and earlier engine. Until that's replaced with headers, it's pretty unlikely you'll see much if any effect at the low to mid RPM that are important for towing by swapping mufflers. Once the restriction caused by the manifolds is taken out of the equation, then...and really only then...is it likely that a muffler swap will help the low end.

(I should mention that swapping mufflers to a traditional (but rather noisy) "performance" design can make a difference in top end HP even with the stock manifolds).

So, to directly answer your question, I'm of the view that headers have to be part of the situation before a Gibson would counteract the slight loss of low end torque from changing tires. That's why I noted "by installing a Gibson muffler along with my JBA headers".