Can PSI in tires affect roadspeed?
 

(The truck I drive is an International 4200 5-speed automatic, 6-wheeler straight truck).

Today for the 2st time I got out onto the interstate to get some road miles on the truck I drive (it's a street sweeper and the majority of its life is spent idling at 2 to 5 mph). The truck I believe is governed at 70. Here's the thing. When I exited, it accelerated fine until it got up to about 45 or 50. After that it started slowing down, and finally wouldn't accelerate anymore past 55. Straight and level road (no uphills and with AN EMPTY LOAD), and with the accelerator pedal to the floor, it wouldn't go any faster than 55 mph until I got to a downhill slope, then it went up to 65 mph pretty easily.

Once it got to 65 after that little down hill, I was able to keep it around that speed fine, even after leveling off again. It's just until I got got to that down hill, the engine pretty much had no power whatsoever to go any faster. :oops:

The air pressure in the tires range from about 70 to 80. I know they're supposed to be at 100 (110 psi max), but someone told me not to worry, as long as I wasn't going anywhere very far away (and as long as the air pressure didn't get TOO low), I'd be alright.

Just wondering will a big truck run a lot better at 100 psi than at 70 to 80 psi? (Yes, I know it's supposed to get better mileage as well).

And keep in mind this was with an empty load, just the gross weight of the truck is all.

Tire Pressure
 

Tire air pressure, at the correct pressure will decrease rolling resistance, road speed may increase due to less resistance, and fuel mileage will increase, and tire life will increase to a point. I'm guessing the person who told you running 30 to 40 pounds low doesn't own the truck.
You didn't say whether the engine is "governed" or what the gear ratios may be. If you normally run 2 - 3 mph, maybe the ratio is such that the truck can pull at that speed and not be lugging. which could cut the top speed.
As far as tire pressures on big trucks, that's why I always carry a pressure gauge and check when going from cold temps to warm and vice versa. And always check pressures when the tires are cold, like before you run for the day. BOL

Hey Douglass!

When I'm not driving a dump truck pulling an Elgin Pelican, I drive an Elgin Eagle (6-wheel cab-over straight truck with a broom sweeper built onto it)

That thing is well, not really governed at 73mph, but the gearing/engine won't let you go over 73 - I usually keep it at about 65 on roads with limits posted higher than that.

Anyhow, yes, Tire pressure can effect your speed - additionally, if your water tank is full, that's LOTS of extra weight there too which could be effecting your speed.

--Dave.

Those street sweepers make alot of dust, make sure that the air filters are cleaned or blown out. Diesel engines need to breathe. I don't know if that's the problem but it can't hurt.

Nice to see there are some other street sweepers on here too. I drive a Tymco 600. I've seen an Elgin Pelican (though it was sitting at the shop ready to be surplused by the time I became a street sweeper operator.

I think my water tank may have been a little less than halfway full. But my tires probably do need to be aired up.

Our Superintendent very recently told us that he wanted us to get those sweepers out on the interstate once a week to help blow the carbon out of the front engines and let them get some 'excercise'. I've heard excess idling is bad on a diesel engine.

We used to have a Schwarze A7000, and the front engine (Sterling cab-over, not sure which model) RAN LIKE CRAP!! It never got out on the open road any, and by the time it was about 5 to 6 years old, you were luck to get it over 45 mph, goind downhill!!! It'd also run hot when you got it up to speed, but strangely cooled back down when idling at sweeping speed... :?

I blow them out once a week, and I also spray the radiators out with a water hose (I've heard it's not good to blow out radiators but I don't know if it's true or not).

There'll be some dust that comes out of the filter when I blow it, but by the time I get done, there's hardly any that comes out at all.

Heres a little refresher course for all you "Air Filter Blowers" out there.

http://www.classadrivers.com/phpBB2/...ght=air+filter

Ahh, the li'l 600's, those regenerative air sweepers are nice - not quite as effective as a broom, but they're nice none the less. The company I work for has a small fleet of them (about 8 I think) Nice little units, and great for monthly spot cleanings.

The tires on those trucks have to hold LOTS of weight, and I mean LOTS* ... those sweeper units are damn heavy, if you start running the tires low, you start adding way too much extra stress on the rims/bolts/studs. I saw one where a guy blew out one rear tire, didn't realize it right away, got out on the highway and it pealed the outside rim right off the truck, wrecked the studs, lugnuts, and even the hub on that side - he was totally empty when it happened.

I've seen strange things happen with those trucks too - one of them had a leak on the intercooler hose between the turbocharger and the intercooler - and that caused the thing to be totally gutless, wouldn't break 50mph no matter what, etc, etc.

Just a couple things to look into there.

And like Splitshifter points out, blowing out the filters is not always the best idea.

--Dave.


**** EDIT ****

I've gotta edit my previous statement, the company I work for has a fleet of the 210's, not the 600's. the 210's are MUCH smaller than the 600's, but same basic idea. whoops, sorry.

--Dave.

**** EDIT ****

If I'm not supposed to blow out the air filters, then what should I do? :?: :?: :?:

Thanks for the info. That might be what happened to that 1999 Sterling we had, because it was gutless too (as I mentioned).

Is an intercooler hose leak hard to fix, replace, etc.? (And if it is fixed, will the engine run much better again??