M-920 1600 r20

[Karl kostman]

Hey guys I have recently mounted 1600 R20 tires on HEMTT rims on my M-920, the first time I drove the truck on the road I got a very rough jumpy ride and I just figured the tires were as round as a horses head because the truck had been in my shop for a few months, and it was cold outside. Yesterday I drove the truck because it was almost 85 degrees outside and the sun was shining. I pulled the truck ouside into the sun to make sure the tires were good and warm (about ans hour) then started the truck and let it warm up for about another 20 minutes then I took off on the highway. I am going to say that for now about 35 to 40 mph is top speed because the tires are very out of balance, I am going to load the tires with Equal this coming Thursday, a tire dealer told me I should plan on 2 pounds of Equal per tire? then he asked me if I had tried changing the air pressure in the tires to see if that made any difference? My questions to those with more knowledge in the LARGE TIRE ARENA, is the dealer telling me the correct amount of Equal per tire? and will reducing the tire pressure possibly help and out of balance situation? (and how does pressure make a difference) I am currently running 90 PSI in the tires on the front axle and 85 PSI on the 2 active rear axles. Any advice in this area would sure help and I have read virtually every post on this subject, I dont want to use tennis balls, BBs, used motor oil or antifreeze, is what I got out of that!
Thanks very much for any assistance you folks have to offer!
Karl

 

[theanimal]

Man I have the same problem on my truck with the same tires. It feels like there are huge flat spots but they never round out. I hope someone here has some experience with this problem cause I could sure use the help with mine too.

 

[dmetalmiki]

WOW (and crikey old bean!) I run my my 1600 x20 tires at 40 psi. and yes sometimes a bit bouncy on rough British roads, but smooth on motorway and other good road surfaces. Remember these tires are running like no load with our trucks. I never have put gunk in my tires, I would experiment with tire pressures first. Just my 1/2 penn'eth.

 

[turnkey]

Check out the different air PSI first ...As stated worked for me...I bet lots of folks on this site have good infor for you to use....

 

[RobertoGatos]

How did you mount up the wheels? Did you use lug nuts with a threaded snout on them, or spacers and thimbles in the rear? Just running regular hemet valve stems?Pictures would be great. In the middle of this swap now.

If balancing doesn't work, you can try shaving the tires.

 

[Coffey1]

My M923A2 super singles runs 55 psi front and rear.
That's what Ctis keeps it at in hwy mode.

 

[todds112]

My M923A2 super singles runs 55 psi front and rear.
That's what Ctis keeps it at in hwy mode.

Wish my CTIS was set at 55 PSI. Mine go to 70PSI at "Hwy". It's a pretty brutal ride with an empty truck. I do get the bucking bronco ride every now and then. Feels like flat spots that sync up to cause it. Other times it's as smooth as any other vehicle. I haven't tried rotating the wheels/tires yet to see if it helps.

Can't use the dyna beads or powder with the CTIS, unless you get the larger size beads that you have to dissassemble the rim to install. FYI Dynabeads recommends 16 oz. per tire for this size.

 

[sweetk30]

my old first mud truck with super swampers was bad . till I had a old guy tell me do the tire chalk test on the tread . I went from 35-40 psi down to 25 psi .


man what a difference this made in ride and handling .


I think playing with your air pressure will get you dialed in a lot .

 

[Karl kostman]

Guys Thanks VERY much for giving me a few things to try BEFORE I go the Equal route, tomorrow I will drop the air pressure down in the tires into the 60 PSI range and give that a try, one question I feel that I can for sure safely drop the rear axles down to 60 PSI but because of all the additional weight on the front axle can I safely run tire pressure at 60 PSI on that axle? Also to answer Roberto Gatos question, On the front axle everything is pretty straight forward, shave the hub to the needed dimensions and install the wheel and tire assembly. On the rears I wanted to keep it as stock as possible to retain as much strength in the system as possible so I cut the centers out of 6 of my stock wheels and mounted these centers to the hubs using the standard nuts etc. then again using the standard hardware I then mounted the HEMTT wheels with the 1600 R20 tires to the cutout centers on the hubs. Essentially doing it this way gives me the most strength possible because it is essentially the exact way the stock tires and wheels are mounted on the truck.
Please give me your thoughts on running 60 PSI on the front axle, again I have no worries on the rear axles just unsure of that pressure on the front axles?
Thanks much folks
Karl

 

[Coffey1]

Karl I believe you will be fine at 60 try it and see if the ride improves.

 

[98G]

I'm suspicious of the cutouts...

 

[RobertoGatos]

Thanks Karl, think I'll be doing the same.

 

[Karl kostman]

Well to anybody who is/was sharing the same troubles I was having with their M920 with HEMTT rims and 1600R20 tires on the truck it looks like I have the solution, in my case any how! In the beginning of this thread I explained that on my truck the tires were so out of balance that it was virtually impossible to get over 38 mph with my truck setup in this configuration without it feeling like there was going to be some damage done (and yes I am pretty conservative). After reading all your responses concerning tire pressure and adding equal to the tires to balance them on the road I started changing things. First I dropped the front steer axle tire pressures down to 65 PSI (was at 90 PSI) then I dropped the 2 rear drive axles tire pressure down to 60 PSI (they were at 85 PSI) and drove the truck on the highway and it was better but still not where I wanted it to be, my goal was to be able to drive the truck 55 MPH since that is the posted tire limit, my next step was to add 35 ounces of Equal to all of the tires NOT including the pusher axle. I had a local tire shop do this for me and I picked up the truck this morning. When I got out of town I was thinking that it was better but when I got out on the highway and the equal had a chance to go where it was needed inside the tires I GPS ed the truck at 55 mph with not so much as a jump or shake anywhere, needless to say I was beyond pleased! Also wanted to thanks you all for your input on this problem, your ideas and suggestions gave me the needed knowledge to actually get this issue fixed!
Thanks very much for you help.
Karl

 

[Artisan]

Must see pictures of the most Awsome of 10 Wheelers, the
M920 w/ 16's. !

Remember, your headlights are now above Federal specs
(54" ground to center of light ) Behind the headlight bulbs
are electrical junction blocks, remember this if you consider lowering
the lights to a "you can't sue me anymore" height. Or kill
those lights and add DOT approved on the bumper.

One of my clients is a HUGE insurance company. Inside one
of there chief attorneys office sits and easel showing where
someone did something similar. I have no doubt they won
the case...

Be forewarned sir...

 

[Andrmorr]

Karl,
Just saw this thread so I feel like I'm late in answering, but CBRMETALWORKS has a M920 w/ 16s that he drives to meets and tractor pulls...He might be able to give you some pointers...at least for next time...