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View Full Version : Tire pressure vs ride smoothness


TimJuhl
04-24-2009, 04:41 PM
I've posted before that my 3500 Sprinter has a bit of a hard ride in the back. I wonder if one approach to "softening" the ride might be to reduce the tire pressure somewhat. The manual calls for 65 PSI which I assume is related to the van's published max vehicle weight. My van is only lightly loaded so wouldn't say 50-55 psi be safe and appropriate under the circumstances?

I know that proper inflation is related to tire wear and fuel mileage but I wonder if there isn't a range of safe working pressures?


What got me thinking about this is my background in aircraft maintenance. For example, I own a classic Aeronca Champ with a max weight of 1220 lbs. Proper tire inflation is 15 psi. The pressure in the same sized tires on the 3000 lb Cessna I used to own was 38 psi. If I were to pump the tires much more than 15 psi in the lightweight airplane the result would be hard, bouncy landings. The "give" in the tires aids in the overall shock absorption capability of the landing gear.

Your thoughts?
Tim

mean_in_green
04-24-2009, 06:20 PM
See how you get on, I run my dually in commercial use at bit lower - 55psi. Apart from the shoulders scrubbing on the fronts the ride is acceptable (for a three spring cargo...) and the tyres wear evenly.

I rotate the wheels to get best mileage out of the tyres, I think you might find they first start to wear in the centre of the tread at 65psi.

sikwan
04-24-2009, 06:22 PM
I forget where I saw it, either the sticker on the van or the owner's manual, that the front tires have a 55psi recommendation. I can't see a reason why you couldn't do 55psi in the back if you're lightly loaded or loaded to the same weight as if the engine was in the back.

For grins (and if it worked, for fuel mileage), I pumped up all 4 tires to the maximum pressure of 80psi and took a short drive. It was terrible for the front because it was all over the place. The lightly loaded rear was bouncy, but it didn't bother me as much.

I decreased it to 60psi and it was much more bearable. In fact, I now know why the MB spec's the front at 55psi. When we're loaded for a trip (never loaded like some of you contractors or expeditors), I pump the rear to 80psi and keep the front at 55psi.

david_42
04-24-2009, 09:04 PM
My 2500 has recommended soft-ride pressures for low load levels, I'm surprised the 3500 doesn't. I've tried the lower pressures though, and haven't noticed any difference. It's a hard ride regardless.

TimJuhl
04-25-2009, 02:11 AM
Thanks for the input guys. My 3500 calls for 65 psi all around. It is also approved for up to 4752 lbs of combined passenger and cargo weight. I suspect that when fully loaded I'm carrying about 3000 lbs less than capacity. I measured the rear bumper height empty and after conversion and it changed less than 1/8th inch so the springs aren't loaded much.

I think I'll give lower pressures in the rear tires a try and see what happens.

Tim

Douglas Hicks
04-28-2009, 03:09 AM
I find my 2005 158 2500 SHC handles best at 65 front and 70 rear. I know it is time to have the pressures adjusted by the lousy handling. the 158 seems to be less forgiving than the 144.

rlent
04-28-2009, 06:10 AM
Running 80 psi all the way around, although my fronts are currently down to 78 psi (gotta keep that rolling resistance down :eek:)

mean_in_green
04-28-2009, 08:51 AM
May I ask if you know how durable your tyres are at 80psi? I found mine started to wear in the centres over 60 / 65psi.

With 55psi-ish I can get around 80,000 miles life out of a Uniroyal Rainmax, which are a little on the soft side but I quite like that. I have had over 120,000 miles out of a nasty commercial tyre, but the feel of them was awful (very skittish).

rlent
04-28-2009, 11:49 PM
May I ask if you know how durable your tyres are at 80psi?
You certainly may.

I found mine started to wear in the centres over 60 / 65psi.
Mine are actually wearing on the outsides, not in the center - with over 185K miles on the clock, and about 60K on the tires, I suspect that my lower ball-joints need replaced. This is based on a friend's Sprinter, which had similar wear patterns on his tires. He replaced his lower ball-joints at around 200K miles and found there was significant slop/play in the joint (over 1/4")

With 55psi-ish I can get around 80,000 miles life out of a Uniroyal Rainmax, which are a little on the soft side but I quite like that. I have had over 120,000 miles out of a nasty commercial tyre, but the feel of them was awful (very skittish).
I got over 123K out of the original Michelin LTX A/S tires on the vehicle - and they were still plenty good enough to run on the rear (around 4/32nds) - but I swapped them out as the rubber in the sidewalls was cracking (dry rot)

The current tires (Michelin LTX M+S), which have around 62K miles on them, are at no point less than 8/32nds thread depth - which is more than 1/2 the original tread value (15/32nds) At the deepest point (in the centers) they are >12/32nds.

I have ball-joints, tie-rod ends, and all bushings (stabilizer bar, stabilizer links, and lower control arm) currently on order, along with new lower control arm bolts & nuts. A set of new front Koni struts are waiting at the house. Once I get back home I'll probably take the vehicle down to the alignment shop and have them inspect everything and let me know what needs to be replaced, then once that's done, I'll have it aligned.

I am running nitrogen in these tires and I have seen no significant pressure drop or variation on any tire in the last 4 to 5 months (meaning I have not had to have them inflated in that time)

Hope to get 150K+ out of these tires.

sikwan
04-28-2009, 11:58 PM
I am running nitrogen in these tires and I have seen no significant pressure drop or variation on any tire in the last 4 to 5 months.

Rlent...where are you getting your nitrogen fill?

I need a nitrogen fill unrelated to tires (suspension shock), but it still has a shrader valve. Just wondering if a tire supplier that uses nitrogen would do it, for a fee, not for tires up to 140psi.

Also, how are you or they purging the air out of the tires? I know nitrogen makes up over 78% of air, but still how do you get close to the 99%.

Just wondering if you have your own tanks. :D: An option I'm looking at if the regular shock places charge an arm and a leg and the tire places don't purge the system right.

Ciprian
04-29-2009, 04:05 AM
I am running 80 psi all the time. No wear in the middle either. I have always had a little wear on the outside of the front tires (looks like toe in condition), but I rotate them every time I change my oil, every 12k or so. I notice now a little more outside wear than usual, need to check them ball joints. The first set of tires lasted me 170k or so. I have 100k on the second set of tires, with a little less than half life left in them. It might ride a little rough, but the tires don't seem to mind, and I don't either. :)

rlent
04-30-2009, 08:26 AM
Rlent...where are you getting your nitrogen fill?
Terry's Tire Town ... small local tire chain, near where I live.

I need a nitrogen fill unrelated to tires (suspension shock), but it still has a shrader valve. Just wondering if a tire supplier that uses nitrogen would do it, for a fee, not for tires up to 140psi.
Dunno ... I do know that all Terry's uses to fill tires with is nitrogen - they have it plumbed throughout all their shops (about 6 or 8 locations IIRC)

Also, how are you or they purging the air out of the tires? I know nitrogen makes up over 78% of air, but still how do you get close to the 99%.
I dunno - I just took it in and they did it - as matter of fact, I don't think they charged me the first time I had it done on the original tires ..... and when I put on new rubber, I had them do the mount and balance (I got the tires from Tire Rack) - and they only charged me for mounting and balancing one pair (the fronts, the rears were gratis) ... the nitrogen was n/c that time too. They earned my business on my next set of rubber. :clapping:

Just wondering if you have your own tanks. :D:
I do have my own tanks - but not for nitrogen (the big one with 80%/20% Argon, CO2 for steel, and the little one with 100% Argon for aluminum :D:)

An option I'm looking at if the regular shock places charge an arm and a leg and the tire places don't purge the system right.
Right.

You TIG dontcha ? .... might check your gas house and see if they have nitrogen available .... they might be able to fill it for ya :idunno:

miki
07-01-2009, 02:26 PM
Hey Rlent, I know what you mean about the harsh ride. My wife and I bought a used 3500, and are surprised with the harsh ride. I guess we blew it on our test drive, we only drove on perfect so cal roads. We've tried lowering the tire pressure to 55psi all the way round - I havent seen mileage suffer - probably because if the 3500 is underloaded it has way too much pressure in the back imo. We haven't noticed fasted wear on the tires. Unfortunately the van doesn't ride very well still. I know we are most pleased with the 3500 when we load up the van - we just moved about 4.5 hours away and with a full load the van handled like a dream. Decent gas mileage at 22 as well. Maybe the solution is to keep it loaded.

surlyoldbill
07-01-2009, 05:22 PM
Unscientific observation: I filled all 4 tires to 75psi prior to a 2500 mile trip. Acheived 25mpg from CA to CO going 55-60mph with about one ton of cargo. Acheived 22mpg (normal for me driving in combo traffic in SF Bay Area) coming back at 70-75mph with 200lbs of cargo. No problems with handling, but I did almost get stuck in the sand streets of Landers CA.

These observations probably don't help because of the variation of speed and load. I intend to run 60 front and 65-70 rear depending on load.

si.
07-01-2009, 10:55 PM
I used to work as a elivery driver for a small family business which had 4 lwb sprinters and we all were told to check to vans pressures,oil & water etc.One guy always had a bigger load so he always insisted in going 80psi all round so it didnt look over weight. In mine i used to follow the manual 41psi front and 65psi rear as i thought if any body should know what psi should be in the tyres mercedes should as they've probily spent on design/roadtest etc. My round involved a few steep hills etc and i had done the same round for 4+ years but i had to use a work mates van while mine was being serviced and on a wet day(not unusual for the UK) is was driving down a 10' hill when i noticed a tractor pull out, i went to brake and the road just felt like ice and ended up driving side ways past the tractor. I done a 360 degree spin some how and it left me quite shaken to say the least. I just about managed to miss the tractor and the traffic that had seen me side ways and dived in to a layby before finishing on the right side of the road:bow: After getting back to work i told the guy that usualy drives the van what had happened and he said that it does slide in the wet quite easy and thought it was funny:smirk: :lol:D**K ED:bash:. Im not saying that pumping the tryes is stupid if uve got a full load but if your only carrying 100-200 kg average 41 & 65psi is ampel.Now in my own van I carry about 400kg 24/7 and i go 45psi front and 65psi rear and its comfy and the tyres last too.
If you pump the tyres up to 80-90Psi like some folks do (when cold) on a hot summers day driving at 60 mph the tyres will have well over 100 psi :crazy:in them and i know that the modority of van tyres are only rated up to 65 psi (cold):hmmm:

Gray
07-07-2009, 11:22 AM
I have 2005 3500 Sprinter. 45 psi - rear tires, 55 psi - front tires. No excessive wear in rear, little bit on the sides on front tire ( maybe this is because the front tires in Mercedeses lean in the direction of turn :thinking: ), plus I stil had to carry 4 bags with sand ( 50-60kg each ) above tire wells in the rear to make the ride smoother.
And I don't carry any loads now, just myself and passengers sometimes. But even this way the rear door is squiling, but it's the :censored: roads , I guess .
By the way ,you can find recommended comfort tire preassure in the manual.

Gray
07-22-2009, 10:35 AM
Correction : not 45 psi , but 35 psi rear tires.

TimJuhl
07-23-2009, 06:23 PM
Gray,
How many miles have you put on running 55 front and 35 rear in your 3500? My manual says to look at the placard inside the driver's door frame, which simply says to pump all tires to 65 psi. My van is equipped with Continental 15 inch tires.

Tim

maxextz
07-23-2009, 11:56 PM
mine say the same tim, ive 15s but keep them at 60 i think 65 in too high and hard.

max.....:thinking:

Gray
07-24-2009, 01:46 PM
Gray,
How many miles have you put on running 55 front and 35 rear in your 3500? My manual says to look at the placard inside the driver's door frame, which simply says to pump all tires to 65 psi. My van is equipped with Continental 15 inch tires.

Tim

I have around 45000 miles on odometer. Original Continental tires are still on my van, the thread depth is 6 mm.
Last time I checked I spent 60 liters of fuel and drove 350 miles (A/C was on, highway mostly, 65 mph ), it's like 10.5 liters per 100 kilometers or 22 mpg (US) or 26.5 mpg (UK).

glasseye
07-24-2009, 03:47 PM
I believe the owner's manual for my 04 says 33psi all around for "comfort" setting. With no cargo weight at all, I lowered mine from the as-delivered 60+ psi to 40 psi on all four corners and was delighted with the result. The ride and quietness were much improved. I get 23+ mpusg at 70 mph and AC on max.

TimJuhl
07-24-2009, 07:27 PM
Glasseye,

Is that a 2500 or 3500?

Thanks!

Tim

glasseye
07-25-2009, 12:19 AM
2500.

http://sprinter-source.com/forum/showthread.php?t=7135

TimJuhl
08-07-2009, 04:44 PM
I thought I'd provide an update. I reduced the pressure in my front tires to 55 and in the dualies to 45 just prior to making my annual trip to Oshkosh, WI. I put on around 1200 miles and noted the following:
Handling - no noticeable change
Mileage - the same as last year when I made the same trip
Ride smoothness - my wife and I both believe the ride is smoother - one of us could take a nap in the back without complaining about the "square wheels." There is no doubt that it is a cargo van but the ride is less jarring.
Tire wear - nothing noticeable but that isn't surprising

If there is anything to add after our trip to the left coast I'll post another update.

Tim

mendonsy
08-07-2009, 09:58 PM
Our '06 2500 has 80 in the fronts and 90 in the rears. It is still wearing the outside more than the center, but I don't want to chance going any higher.:wtf: