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Topic: Slight wander wen tires warm up (Read 611 times) previous topic - next topic

Slight wander wen tires warm up

I stalled new Bridgestone steer tires recently. See my post on Bridgestone tires and larger size. Because of the 295 size compared to the 275 size of the original Michelin tires  I run more pressure in them ( 105 vs 100). The dealer said 120 is listed on the tires sides.  On my recent trip I am on I notice that at cold temperatures the tires track well, but a t warmer tire temperatures the coach seems to wander abit requiring some correction (oversteer).  Is this related to tire pressure being that I should run higher pressure or would this be steering box issues? There are no leaks from the steering box. The oversteer is not radical but does require slightly mor concentration.  Suggestions?
Peter    Alberta Canada
'98 U320 40'  Build 5359 M11 450 HP, Aqua hot, Blu Ox

Re: Slight wander wen tires warm up

Reply #1 –
More informed will chime in but you need to get your axle weights and the Bridgestone chart for air pressures and set your pressure by the chart,if all else is in good working order is sounds like you are running too much air pressure.
96 U270 BUILD 4810
85 380SL
Drummonds TN.

Re: Slight wander wen tires warm up

Reply #2 –
Quote from: dicksop –
I stalled new Bridgestone steer tires recently. See my post on Bridgestone tires and larger size. Because of the 295 size compared to the 275 size of the original Michelin tires  I run more pressure in them ( 105 vs 100). The dealer said 120 is listed on the tires sides.  On my recent trip I am on I notice that at cold temperatures the tires track well, but a t warmer tire temperatures the coach seems to wander abit requiring some correction (oversteer).  Is this related to tire pressure being that I should run higher pressure or would this be steering box issues? There are no leaks from the steering box. The oversteer is not radical but does require slightly mor concentration.  Suggestions?
With 120 psi listed on the side of the tire, you must have H rated tires. We also  have H rated 295s (different brand) and run 105 rather than the 120 listed on the side of the tire. The dealer said we can safely do so as we only are approx 25,000 lbs so way under the tire capacity at 120 psi. We get zero wander at 105 psi

You have a higher capacity front axle and are quite a bit heavier than our coach so I would be careful reducing the pressure any more than you have. Heat is the enemy of any tire and the hot, hot weather we have been having plus lower tire pressure for the weight means a tire that could approach the danger zone for impact resistance, etc.

Perhaps you need a little more toe in as neutral or toe out means wandering, especially on roads with uneven surfaces. A bad shock on once side can also cause wandering. Check tie rods for wear also with someone moving the steering wheel while you observe. Make sure the rear tires are even pressures.

Pierce

Pierce and Gaylie Stewart
'93 U300/36 WTBI
Detroit 6V-92TA Jake
1140 watts on the roof
SBFD (ret)

Re: Slight wander wen tires warm up

Reply #3 –
What is the weight of your heavier side in front (best)? Add 5 PSI safety factor to that minimum. Both tires to that same PSI.

OR

What does the front axle weight when fully loaded (full fuel, etc)?

What does the Bridgestone Inflation Table say is the minimum PSI for that weight? Add 10 PSI safety factor to that minimum.

What is the answer??
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: Slight wander wen tires warm up

Reply #4 –
The pressures are coming up with temp and you may be over pressured, dropping the contact patch size.  Try lowering to the lower pressure  on the charts.  10# should make a difference .
I went back to a smaller tire, so that more pressure could be run and keep the contact patch size correct.  Works much better for me . 

 Toe in does not change with temp , only pressure.

Re: Slight wander wen tires warm up

Reply #5 –
I run 90 lbs in the front and have no tire heating problems with that. I put my
hands on the tires after a drive to see how they are doing heat wise. This is something
I learnt a long time ago.
Peter and Frieda Morin
1999 36ft. U320 Foretravel
Build # 5436
1998 Suzuki Sidekick Sport

Re: Slight wander wen tires warm up

Reply #6 –
Well I know the front axle is near capacity...about 400 lbs under.  That is why I don't think they are over filled. I may be wrong
And yes they are H tires. Old guy. Are yours H rated as well?
When I had the new fronts put on the tire shop did an alignment
I am wondered if if raising the pressure 5 lbs to 110 would help
Unfortunately Bridgestone do not even have the chart available for THIS tire.  That is how new they are....I have phone several dealers and the tech side of Bridgestone who forwarded me the chart for the earlier series h tire
Peter    Alberta Canada
'98 U320 40'  Build 5359 M11 450 HP, Aqua hot, Blu Ox

Re: Slight wander wen tires warm up

Reply #7 –
Most tire charts will be within 5#, regardless of manufacturer .  Look around .
  Also, if the tires that are coming off drove well and wore well, dont touch the alignment .  Dont mess with success.

Re: Slight wander wen tires warm up

Reply #8 –
Yes mine are H and when I bought the coach I think the fronts were 80 and the rears were
75 and drove it from Michigan to Burnaby BC with the coach handling great and the tires
weren't heating up but it was late fall when we did the trip. 
Peter and Frieda Morin
1999 36ft. U320 Foretravel
Build # 5436
1998 Suzuki Sidekick Sport

Re: Slight wander wen tires warm up

Reply #9 –
At lower pressures, your speed rating (probably L (75 mph) won't be as high either. Pressures don't make much difference in contact patch. Our FD always maxed the pressures on recommendation from the manufacture and would not have done so if the best handling and stopping qualities would have been compromised.

Owners don't like to think they are in denial by running less pressure to give a softer ride. Brett has good suggestions in his post.

I chose an H rated tire (regional/highway) with a M speed rating as just an extra margin for our light U300. At 105 psi, I still have the M speed rating but would not hesitate to raise it to 120 for hot weather, poor roads.

Pierce
Pierce and Gaylie Stewart
'93 U300/36 WTBI
Detroit 6V-92TA Jake
1140 watts on the roof
SBFD (ret)

Re: Slight wander wen tires warm up

Reply #10 –
Lots of opinions. Which one is correct? Get it weighed and use the chart number. Then you are using the tire manufacturers opinion 😁
John Duld
1995 U320C SE 40'

Re: Slight wander wen tires warm up

Reply #11 –
Quote from: dicksop –
I am wondered if if raising the pressure 5 lbs to 110 would help
Why do you wonder?  Why don't you just try it and see how it feels?  YOU are the best judge of ride, steering and handling.

Your tires have a range of pressures within which you should feel free to experiment.  Minimum allowable pressure (cold) is found in the manufacturer pressure chart for your coach axle weights.  Maximum allowable pressure (cold) is 120.  Anything between those two pressures should be safe, so why not play around with different pressures until you find the sweet spot?

JMHO

1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Nature abhors a vacuum"

Re: Slight wander wen tires warm up

Reply #12 –
Quote from: John Duld –
Lots of opinions. Which one is correct? Get it weighed and use the chart number. Then you are using the tire manufacturers opinion 😁
The molded information in the side of tires is not an opinion but a DOT standard that the tire is manufactured to meet. Many will also have the European standard also molded into the tire sidewall.  The information will have the size, load rating for dual and single application, speed rating and pressure that is needed to meet these standards. If the load rating is exceeded, it won't meet the speed or weight DOT standard. And with reduced pressure below the maximum pressure, it also will not meet the DOT standard for the placarded weight and speed.

No, you are not the best judge of handling. The weight of your coach along with the axle rating are the criteria the DOT uses to make the required pressures and load rating for the tires the coach must have to be safe for occupants and those who you share the road with. Any deviation from these numbers must be done carefully while accurately knowing your weight, etc. and never done for comfort's sake alone.

Pierce


Pierce and Gaylie Stewart
'93 U300/36 WTBI
Detroit 6V-92TA Jake
1140 watts on the roof
SBFD (ret)

Re: Slight wander wen tires warm up

Reply #13 –
Try plus 10 for 30 min , try minus 10  at that point. Checking  the chart and comparing to others with that bus , you are a little over.
 If you run the 295 on narrow rims , you will never fix it. 

Re: Slight wander wen tires warm up

Reply #14 –
Mike makes a good point about the narrow rims. Look at the part number on your Alcoa wheels and then go to their website to get the specs. Also good to have your part number in case you need to buy another wheel. I bought a used wheel with the exact number but ending in a different letter as I remember. When I looked it up, it was for the matte finish on the wheel but everything else was the same. The tire manufacture will have the recommended wheel width for your tire at their site.

Tire manufacture pressures are the number to look at, not the coach recommended pressures. As the coach ages, it's recommendations will age with it while tire companies are constantly changing tire construction, load capacity and speed rating for our tire sizes.

You can always jack one front wheel off the ground, wet a portion of the tire, rotate the tire so the wet spot is facing down and then let the jack down so the tire footprint makes it's pattern on a piece of white board. Repeat at different pressures to see if there is any difference. Narrow wheels will put a slightly smaller footprint on the ground on the width dimension as the pressure goes up.

The tire acts like a shock absorber and the pressure determines how much flex the sidewall has. Going over bumps with uneven pressure will cause a side to side movement of the coach. OTR tires may have a thinner sidewall with more flex compared to a regional tire with a thicker and less flexible sidewall. RV manufactures tend to recommend the regional tire as it takes more sidewall abuse and the tread pattern may go down in the valley with more of a V shape so they chuck rocks better. Good if spending time going to campsites off of gravel/dirt roads.

Another factor to consider is that no RV manufacturer wants to have a reputation for a hard riding vehicle so they recommend the lowest pressure that will satisfy load requirements in relation to the weight of the coach while being safe. Ford recommended 26 psi for the Firestone tires on the early Ford Explorers. Look at all the accidents and deaths that it caused. All because Ford wanted a nice passenger car ride on the Explorer.

Good article from 2000 on Ford vs Bridgestone/Firestone tire pressure recommendations: https://abcnews.go.com/US/story?id=95667&page=1

Pierce
Pierce and Gaylie Stewart
'93 U300/36 WTBI
Detroit 6V-92TA Jake
1140 watts on the roof
SBFD (ret)