Wondering re 40psi on 09 Ultra

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Wondering re 40psi on 09 Ultra

Post  Vahoagie on Tue Sep 27, 2011 8:58 am

Ok I have read a lot of posts regarding tire pressure and have a longish question. First the facts-I have a CT a Hankook optimo 426 OE size 195/60 16, my cycle weighs 850 lb and I weigh 280 lb(I'm like 2up in one seat), my owners manual says rear tire pressure 40psi (mc tire)- so I put 40 in the CT and have 350 mi. so far so should I be reducing pressure below the owners manual suggestion when I reach the end of the break-in. I have seen where some are at a range of 29-32 for their pressure and don't know if going below recommended pressure is bad for the tires carrying capacity. Thanks for any thoughts, facts and recommendations!
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Re: Wondering re 40psi on 09 Ultra

Post  Doc on Tue Sep 27, 2011 3:12 pm

A lot of people run that size tire on their Goldwings. Your bike is only about 50lbs lighter than a Wing.
With the non run flat tire like your Hankook, they use pressures in the 38-40psi range and that
seems to work well.

I'm thinking that you are pretty close with where you want to be with what your are running now.

You might try going down 2psi and see if you like the feel of it there.

Just to clarify about what you are asking in your question.
The manufactures recommended pressures go out the window when you change to a Car Tire.
I bet your Hankook has an 84 load rating which is about 1100 lbs, so you have a large margin on
carrying capacity, remember a lot of cars use pressures in the sub 30psi range...

Hope this helps. thumbup

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Re: Wondering re 40psi on 09 Ultra

Post  Vahoagie on Tue Sep 27, 2011 10:21 pm

Thanks for the Reply Doc,
I checked the capacity of the tire i'm running and it is 1279 lb with a max air rating of 44 psi. What i'm not sure about is how low will it be safe to go with that max number? Is 33lb out of a max of 44 lb mean that my load rating would be 33/44 of 1279? and of course does that mean half of the weight on front tire and half on the back. thanks for any further input.
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Re: Wondering re 40psi on 09 Ultra

Post  Doc on Wed Sep 28, 2011 9:41 am

A tire's load carrying capacity rating doesn't have anything to do with the tire's maximum inflation pressure.
Maximum load is tested at a "standard" of 35psi.

This is from Tire Rack's website...
A tire's "maximum inflation pressure" may be different that the assigned tire pressure used to rate the tire's "maximum load." For example, while a P-metric sized standard load tire's maximum load is rated at 35 psi, many P-metric sized standard load performance and touring tires are designed to contain up to 44 psi (and are branded on their sidewalls accordingly). This additional range of inflation pressure (in this case, between 36 and 44 psi) has been provided to accommodate any unique handling, high speed and/or rolling resistance requirements determined by the tire and vehicle manufacturers.

Recommended pressures are determined by the manufacturers who take things like suspension, vehicle weight, tire size, handling, and tire temperatures into consideration.
Forget about the max pressure and load ratings as relevant to your tire pressure needs, it just isn't. My Corvette had a recommended tire pressure of 29psi, and the tire has a max pressure of 44psi with corner weights in the 800 lb range.
You are doing what a lot of noobies do... You are trying to overthink this. Wink
You want to use a pressure which gives you a good contact patch and enough sidewall support. The original recommendation by Harley of 40psi is based on the stock size tire. You have gone to a bigger tire with different characteristics. You could safely run 29psi in your tire, but you probably would not like the ride. It would most likely wallow (feel like it squirms side to side) and would wear quickly on the edges but it would be very soft and comfortable on the straights.
Based on what a lot of others have done with bikes of similar size with that size tire and what they report in terms of handling and wear I'm going to stick with a recommendation of 38-40psi, but play with those pressures and drop them down to 32-36psi and see what feels best to you. Stop worrying about if it will be safe. The car tire in my opinion is the safest tire you can put on your bike.
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Re: Wondering re 40psi on 09 Ultra

Post  Vahoagie on Wed Sep 28, 2011 9:49 am

Ok I'm feeling better about lowering it and looking for a sweet spot
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Re: Wondering re 40psi on 09 Ultra

Post  quadancer on Wed Sep 28, 2011 7:38 pm

You won't know where it is until you've been above and below it with some riding at each setting for a while. Once hit, the tire sort of "disappears"
and feels more like a bike tire. Part of that is that you've become accustomed to the countersteering pressure. I don't even notice any of it anymore.

When I dive into a turn (looking far ahead of course) I just apply and hold the bars while putting my head inside of the center of balance. I don't scootch
off the seat unless I'm coming in too fast and don't want to hit the crash bars. The bike should feel like it's on rails in a hard curve and shouldn't do anything
else.
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