mileage meter and larger tires

Hi Jim,

I know that fully loaded I was at 14000 pounds.

I was running 225 @ 80 psi rear 9880 and 65 psi front 4670

The 235 @ 80 psi are 10111 (derated 9% for dual) and @ 65 psi are 4762

The door sticker won't be right any more (never was really but now it is more off). If you look up the weight table for your old tires and check what PSIs equate to what weights, you could input the assumed weights from the door sticker PSIs to the weight tables for your new tires to find the door sticker equivalents.

But really you would be the first heavy C I have ever seen to run max on the front axle. On longer C's, the more loaded they get, the *less* weight is typically on the front axle. Excessive tire pressure up front for the weight being carried gives a small contact patch, and a light feeling front end with floaty steering.

I ran 55 lbs for the weight my old C carried up front and it ran much better than at 65. Rode better too.

With new more capable tires you really could benefit by taking a look at the inflation pressures per weight tables, compared to the tables for the stock tires that come on your unit, if you have a few minutes.

Jim

Hi Jim,

Those are the figures on the driver's door.

I should mention that shifting seems "smoother" somehow, with less of a "bump"

I've driven 375 k on the clock (actual is probably around 410 kilometers) The first 80 k were at city speeds.

I'm glad I did the taller tires rather than the 245's They would have been darn near the wheel wells at the rear of the vehicle, and had the exact same increase in load capacity as the 235.

The front wheels have been torqued twice--and the rear wheels three times.

I suspect I'm going to love having real brass valve stems. I'll know that later this morning.

The alignment person thought that the tie rod ends and bushings had been replaced when the tires/wheels were done. They are OEM and have 104,000 k on them. I'm well pleased by that news, as it is a "weak point".

A camber sleeve had to be added, so the alignment, I guess, was essentially done twice. Cost was $396 including tax.

Tires were $1700 for Toyo
Wheels were $1600 from southwest wheel--which including ground shipping by Fedex. There was no brokerage fee, and no Canadian tax.

The engine and and transmission computers learn characteristics of the vehicle. Tire size change can alter how the system goes about up and down shifting, timing advance and several other operating parameters as well as your driving style.

No worries as it does this on it's own, but a reset forces the systems to start learning fresh.

Is 65 based on your estimated or measured weight up there? Sounds a little high?

Jim

Hi Jim,

How do you mean 'relearn'?

65 in front 80 in rear--but I should check today when the tires are cold.

HiTech wrote:
The system will relearn faster it you reset the ECU by disconnecting the battery then pressing the brake for good measure, then reconnect and let it idle a bit.

But by now it has probably relearned anyway.

Good report! What tire pressures are you running?

Jim

The system will relearn faster it you reset the ECU by disconnecting the battery then pressing the brake for good measure, then reconnect and let it idle a bit.

But by now it has probably relearned anyway.

Good report! What tire pressures are you running?

Class C's frequently blow out or delaminate the inner rear tires first. My theory has always been they get less cooling, heat up more, then take on extra weight due to the higher running pressure.

My answer that seems to have worked is to find the OEM spec for how close in pressure the dually tires are supposed to be to the same pressure, and run the outters a bit higher and the inners a bit lower, staying within the OEM spec.

I still delaminated the inners first so I did not mitigate the effect entirely, but I had great handling and wind stability, and the inexpensive commercial tires I had, ran 7+ years including 3 on hot hot Texas roads before delaminating.

Jim

Hi,

The first results and impressions:

speedometer error is 8% so at 80 kph reading I am going 85 kph

I found the biggest hill in the area and was able to maintain my usual cruising speed of 80 kph. The tranny downshifted twice. It did the same with the "stock" tires.

1800 rpm = 80 kph (according to gps device) on the OEM tires that was 76 kph.

scan gauge reads 46 mph @ 1800 rpm--confirming the 8% error

Initial trip was with a head wind/side wind. Mileage appears to be measurably improved--but that won't be known for sure until I have a few thousand kilometers "on the clock"

No difference in engine temperature with the larger wheels/tires

It did take about 30 minutes of driving for me to get "used to" the new configuration.

I was on a four lane highway and had no opportunity to see how trucks going the other direction might affect the ride.

At one point there was a gusting wind situation. No extra sway seemed to be evident.

Road noise is reduced--but there is a low pitched rumble that was not there before. It got better (or perhaps I became desensitized to it) as the trip progressed (Regina to Saskatoon, destination Pike Lake, SK)

There was fairly vicious thunderstorm at the Black Strap Valley. I would normally have dropped out of cruise--but decided to risk leaving it on. There was no issue of hydroplaning nor loss of stability.

Ride is somewhat smoother.

I can tell the difference in height--which surprised me a bit.

I hope to find a washboard road tomorrow.

I did "take it up" to 110 kph to pass a slightly slower moving vehicle. I found I was over correcting on the steering at the higher speed.

So far I'm pleased with the results.

I can hardly wait to confirm the increase in miles per gallon. I should know for sure by about July 6th.

Pianotuna,

The user manual can be downloaded at
In my manual, the speed calibration is on page 17.

Steve

pianotuna wrote:
Hi Pauljdav,

How do you calibrate the scangauge? I have a gps and would find that cheaper than paying Ford $60.00

There is an ability to adjust the % error rate for speed in the scan gauge. I do not have the instructions in front of me right not. I believe it is in set up.

I will have time tomorrow to look at mine and walk you through the steps if you have not found the answer by then.

Paul

I did the same but used same wheels unloaded looked fine but when loaded 15,000 lb 5th wheel had a rub the way we found was I had a sway when on interstate went back to dealer they thought the tech had not put 85lb air lucky for me they could not find air tool to check outer tire with so had to take tire off that's when we saw rub so had to go back to 225